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1
Becker, T. S., G. Bothe, A. J. Berliner, and E. R. Macagno. "Identified central neurons convey a mitogenic signal from a peripheral target to the CNS." Development 122, no. 8 (August 1, 1996): 2331–37. http://dx.doi.org/10.1242/dev.122.8.2331.
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Regulation of central neurogenesis by a peripheral target has been previously demonstrated in the ventral nerve cord of the leech Hirudo medicinalis (Baptista, C. A., Gershon, T. R. and Macagno, E. R. (1990). Nature 346, 855–858) Specifically, innervation of the male genitalia by the fifth and sixth segmental ganglia (the sex ganglia) was shown to trigger the birth of several hundred central neurons (PIC neurons) in these ganglia. As reported here, removal of the target early during induction shows that PIC neurons can be independently induced in each side of a ganglion, indicating that the inductive signal is both highly localized and conveyed to each hemiganglion independently. Further, since recent observations (Becker, T., Berliner, A. J., Nitabach, M. N., Gan, W.-B. and Macagno, E. R. (1995). Development, 121, 359–369) had indicated that efferent projections are probably involved in this phenomenon, we individually ablated all possible candidates, which led to the identification of two central neurons that appear to play significant roles in conveying the inductive signal to the CNS. Ablation of a single ML neuron reduced cell proliferation in its own hemiganglion by nearly 50%, on the average. In contrast, proliferation on the opposite side of the ganglion increased by about 25%, suggesting the possibility of a compensatory response by the remaining contralateral ML neuron. Simultaneous ablation of both ML neurons in a sex ganglion caused similar reductions in cell proliferation in each hemiganglion. Deletion of a single AL neuron produced a weaker (7%) but nonetheless reproducible reduction. Ablation of the other nine central neurons that might have been involved in PIC neuron induction had no detectable effect. Both ML and AL neurons exhibit ipsilateral peripheral projections, and both arborize mostly in the hemiganglion where they reside. Thus, we conclude that peripheral regulation of central neurogenesis is mediated in the leech by inductive signals conveyed retrogradely to each hemiganglion by specific central neurons that innervate this target and the hemiganglion they affect.
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Kazakova, T. A., A. I. Yusipovich, and G. V. Maksimov. "Investigation of Changes in Membrane Potential and Rhythmic Activity of the Retzius Neuron upon Stimulation of the Sensory P-Neuron." Herald of the Bauman Moscow State Technical University. Series Natural Sciences, no. 6 (93) (December 2020): 137–44. http://dx.doi.org/10.18698/1812-3368-2020-6-137-144.
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It was found that in "natural neural networks", ganglia of the nervous system of a leech, the frequency of rhythmic excitation (a series of nerve impulses, RE) of one neuron is modulated upon activation of other neurons. Changes in the electrophysiological characteristics of the leech Retzius cell in response to electrical stimulation of one of the sensory neurons (P-cells) were revealed. Registration of changes in the membrane potential of neurons, as well as electrical stimulation of the P-cell was carried out using microelectrodes introduced into the cells. It was found that during electrical stimulation, P-cells increase the frequency of spontaneous RE of Retzius cells, the membrane potential of P-cells increases, but Retzius cells do not change. With an increase in the duration of stimulation, the RE frequency increases in both the P-cell and the Retzius cell. It has been found that RE Retzius cells, upon stimulation of P-cells, arise against the background of RE of the Retzius cell. Thus, during RE of sensory neurons and synaptic transmission to the Retzius cell, RE frequency modulation occurs. According to the authors, changes in the frequency of spontaneous RE of the Retzius neuron in the "natural neural network" are associated not only with a change in the RE frequency during excitation along nerve fibers from skin receptors, but also with the transformation of RE both between cells of one ganglion and between cells in different ganglia leech nerve chain
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Szczupak, L., and W. B. Kristan. "Widespread mechanosensory activation of the serotonergic system of the medicinal leech." Journal of Neurophysiology 74, no. 6 (December 1, 1995): 2614–24. http://dx.doi.org/10.1152/jn.1995.74.6.2614.
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The serotonergic system of the medicinal leech comprises a small number of iterated, identified neurons, of which the Retzius (Rz) neurons are major components. Activity in pressure mechanosensory (P) cells sufficient to elicit locomotory and defensive behaviors also excites Rz neurons. We characterized the interactions between P and Rz neurons within the ganglion and at different distances along the nerve cord. 2. Within a ganglion 1) P cells excited both Rz neurons, electrically close to the site of electrical coupling between the Rz neurons; 2) each of the four P cells had similar effects on the Rz neurons; and 3) homologous contralateral P cells shared interneuronal pathways. These data show that P cells provide nearly identical bilateral information onto Rz neurons. 3. Along the nerve cord 1) every P cell excited Rz neurons in ganglia anterior and posterior to the site of stimulation; 2) the signal was carried the entire length of the nerve cord along interneuronal pathways with similar overall (but regionally different) conduction velocities in the two directions; 3) the amplitude of the Rz responses was smaller as the distance to the activated P cell increased; 4) the rate of change of the amplitude along the cord was larger when the signal traveled from front-to-back than in the opposite direction. 4. These data shows that mechanosensory input from any segment could excite Rz neurons along the cord, in proportion to the intensity of the stimulus.
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Pastor, J., B. Soria, and C. Belmonte. "Properties of the nociceptive neurons of the leech segmental ganglion." Journal of Neurophysiology 75, no. 6 (June 1, 1996): 2268–79. http://dx.doi.org/10.1152/jn.1996.75.6.2268.
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1. The electrical responses of nociceptive (N) lateral and N medial neurons of the leech segmental ganglion to mechanical, chemical, and thermal stimulation of the skin were studied in a superfused ganglion-body wall preparation. 2. Mechanical indentation of the skin > 10 mN evoked in both types of cells a sustained discharge of impulses; afterdischarge was often observed with suprathreshold stimulations. 3. Application to the cutaneous receptive area of 10-100 mM acetic acid or of NaCI crystals and solutions also elicited a firing response in N medial and N lateral cells. In contrast, capsaicin applied to the skin (3.3 x 10(-5) to 3.3 x 10(-2) M) excited N lateral but not N medial neurons. Likewise, impulse discharges were obtained when capsaicin was applied to the cell bodies of N lateral but not of N medial neurons. 4. In both types of N neurons, heating of the skin above 39 degrees C evoked a discharge of impulses whose frequency was roughly proportional to temperature values. 5. Application of repeated suprathreshold heating cycles at 10-min intervals enhanced the impulse frequency of the response (sensitization). Shorter time intervals between heating cycles depressed the response to heat. Sensitization could not be obtained by equivalent soma depolarizations obtained by intracellular current injection. 6. Impulse discharges evoked by irritant agents were also augmented by previous application of noxious heat. 7. N lateral neurons fired in response to low-pH solutions and capsaicin directly applied onto the ganglion. N medial neurons responded inconsistently to acid and were insensitive to capsaicin. Action potentials evoked in N lateral cells by capsaicin had a slow rise, a prominent hump, and a prolonged afterhyperpolarization. 8. It is concluded that N neurons of the leech segmental ganglion respond to different modalities of noxious stimuli applied to their peripheral receptive fields and develop sensitization after repeated noxious stimulation. These properties are typical of mammalian polymodal nociceptors; thus N neurons may be a simple model for analysis of membrane mechanisms associated with polymodality of nociceptive neurons.
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Burgin, AM, and L. Szczupak. "Basal acetylcholine release in leech ganglia depolarizes neurons through receptors with a nicotinic binding site." Journal of Experimental Biology 201, no. 12 (June 15, 1998): 1907–15. http://dx.doi.org/10.1242/jeb.201.12.1907.
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The response of Retzius neurons, the main neuronal source of serotonin in the leech nervous system, to cholinergic agonists has been extensively investigated. In this study, we analyzed the effects of inhibiting the acetylcholinesterase (AChE) activity in the leech midbody ganglion on the electrophysiological activity of the Retzius neurons. Bath application of neostigmine and physostigmine (0.1-100 &mgr;mol l-1) produced, after a delay, a strong depolarization of the Retzius neurons with a dose-dependent amplitude and latency. The amplitude of this depolarization increased as the extracellular level of Ca2+ increased and decreased as the extracellular level of Ca2+ decreased. The response to neostigmine and physostigmine was inhibited by curare (100 &mgr;mol l-1), nicotine (10 &mgr;mol l-1), atropine (100 &mgr;mol l-1) and strychnine (100 &mgr;mol l-1), but was not affected by mecamylamine (100 &mgr;mol l-1) or hexamethonium (100 &mgr;mol l-1). Superfusion with solutions containing 100 &mgr;mol l-1 strychnine or atropine produced a progressive hyperpolarization of the Retzius neurons, while superfusion with 100 &mgr;mol l-1 curare did not. The hyperpolarization induced by atropine was inhibited in the presence of curare. Other neurons in the ganglion showed distinctive responses to the AChE inhibitors that were coincident with their responses to cholinergic agonists. The results suggest the existence of a basal level of acetylcholine (ACh) release in the leech ganglion that is powerfully counteracted by endogenous AChE activity. Under control conditions, this basal release appears to be sufficient to generate an ACh tonus that regulates the membrane potential of Retzius neurons. Since these neurons can support a sustained firing rate, which is dependent on the membrane potential, the results presented in this report suggest that the basal ACh tonus regulates the output of these neuromodulatory serotonergic neurons.
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Opdyke, C. A., and R. L. Calabrese. "Outward currents in heart motor neurons of the medicinal leech." Journal of Neurophysiology 74, no. 6 (December 1, 1995): 2524–37. http://dx.doi.org/10.1152/jn.1995.74.6.2524.
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1. Outward currents were studied in isolation in heart motor neurons in the medicinal leech, using the single-electrode voltage-clamp technique. The currents were divided into four distinct types on the basis of their time and voltage characteristics and sensitivity to external Ca2+ concentration. 2. The four types were a fast transient current, IKA; a slow transient current. IK1; a noninactivating current, IK2, all measured in a bathing solution in which Co2+ was substituted for Ca2+; and a calcium-sensitive current. IK1Cal which was revealed in a bathing solution containing normal levels of Ca2+. 3. The outward currents in heart motor neurons studied in different ganglia possessed differences of quality. For example, heart motor neurons from ganglia 3 or 4 had significantly less IK2 and IK1 than neurons recorded from more posterior ganglia. Heart motor neurons from ganglion 3 often had little or no IK1. Soma input resistance, electrotonic length, and soma capacitance measured in heart motor neurons from both anterior and posterior ganglia exhibited no significant differences. 4. IKA started to activate near -45 mV with half-maximal activation at about -20 mV and was fully inactivated by 0 mV: IK1 started to activate near -45 mV with half-maximal activation at about -10 mV and was not fully inactivated by 0 mV; IK2 started to activate near -50 mV; IK1Cal started to activate near -35 mV. The time constant of removal of inactivation for IKA was 25 ms, measured at -80 mV, and that for IK1 was 380 ms, measured at -40 mV. 5. Tetraethylammonium acetate (TEA) allowed to diffuse from the inside of the recording microelectrode effectively blocked IKA, IK1, and IK2. Bath-applied TEA (25 mM) acted similarly but was less effective, particularly at blocking Ik2. Bath-applied 4-aminopyridine effectively blocked the transient currents IKA and IK1. A reversal potential of -65 mV was found for the outward currents, corresponding to a mix of IK1 and IK2.
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Szczupak, L., J. Edgar, ML Peralta, and WB Kristan. "Long-lasting depolarization of leech neurons mediated by receptors with a nicotinic binding site." Journal of Experimental Biology 201, no. 12 (June 15, 1998): 1895–906. http://dx.doi.org/10.1242/jeb.201.12.1895.
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The serotonergic Retzius neurons of the leech midbody ganglia respond in a complex manner to pressure pulses of acetylcholine (ACh) applied onto their soma with a fast depolarization followed by a slower hyperpolarization and an additional delayed long-lasting depolarization. The delayed depolarization is the subject of the present study. The delayed depolarization could be elicited by long (>1 s) ACh pressure pulses or by short pulses (10 ms) of carbachol, nicotine and DMPP, but not by muscarinic agonists. It was inhibited by bath application of nicotine (10-100 micromol l-1), strychnine (100 micromol l-1) and atropine (10-100 micromol l-1). Nicotinic antagonists that blocked the fast depolarization and the slow hyperpolarization (100 micromol l-1 mecamylamine and d-tubocurarine) did not affect the delayed depolarization induced by carbachol. Partial replacement of the extracellular Na+ by glucamine caused a decrease in the amplitude of the response and a shift of its reversal potential to more negative values. Carbachol pulses applied to Retzius neurons of the ganglia innervating the reproductive segments elicited delayed depolarizations of much smaller amplitude than the ones recorded in Retzius neurons from standard segments. The delayed depolarization could be elicited by the application of short agonist pulses onto different loci over the surface of the ganglion, at a distance from the soma. Isolated cultured Retzius neurons did not exhibit the delayed depolarization although they readily expressed the earlier phases of the complex cholinergic response. Carbachol pulses applied to the soma of other neurons in the leech ganglion produced a variety of specific responses.The results suggest that the delayed depolarization was produced by the activation of a cationic conductance mediated by receptors with a pharmacological profile similar to that of the <IMG src="/images/symbols/&agr ;.gif" WIDTH="9" HEIGHT= "12" ALIGN="BOTTOM" NATURALSIZEFLAG="3">9 nicotinic receptors and was not a byproduct of the early phases of the cholinergic response. The response seemed to be initiated in the extensive neuropilar processes of the Retzius cell, enabling a persistent excitatory signal.
8
Kuwada, John Y. "Pioneering and pathfinding by an identified neuron in the embryonic leech." Development 86, no. 1 (April 1, 1985): 155–67. http://dx.doi.org/10.1242/dev.86.1.155.
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Numerous investigations of pathfinding by embryonic neurons, including many leech neurons, have demonstrated that pathfinding is precise. Neurons project the correct number of growth cones which grow to their target areas by making specific choices along the way. However, one leech mechanosensory neuron, the dorsal P (PD) neuron, is unusual in the sense that it initially projects an excessive number of growth cones. One of the growth cones will form the peripheral axon while the others are eliminated. This suggests that PD is one of the earliest neurons to project a peripheral axon, i.e., it may pioneer a peripheral nerve, and that it searches with its multiple growth cones for an external cue which can guide it to its target area. Examination of the early PD axon with light and electon microscopy reveals that it indeed is the first growth cone in its nerve and that it grows in contact with a large non-neuronal (DV) cell until it reaches its target area. The DV cell has a unique morphology and location: a large cell body with thin fiat processes extending from the edge of the ganglion to the target area of the PD. It is also present with its unique morphology prior to axonal outgrowth by the PD neuron. These features suggest that the DV cell may be an attractive substrate and/or axonal guidance cue for the PD peripheral axon and therefore for the entire peripheral nerve.
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Becker, T., A. J. Berliner, M. N. Nitabach, W. B. Gan, and E. R. Macagno. "Target-induced neurogenesis in the leech CNS involves efferent projections to the target." Development 121, no. 2 (February 1, 1995): 359–69. http://dx.doi.org/10.1242/dev.121.2.359.
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During a critical period in leech embryogenesis, the sex nerves that connect the 5th and 6th midbody ganglia (MG5 and MG6) to the primordium of the male sexual organ carry a spatially localized signal that induces the birth of several hundred neurons specific to these ganglia. We examined particular cellular elements (afferents, efferents, non-neuronal components) within these nerves as potential conveyors of the inductive signal. We show that axons of peripheral sensory neurons in the male genitalia travel along the sex nerves and into MG5 and MG6, but reach the CNS after the critical period has elapsed and cannot, therefore, be involved in the induction. Of the six sex nerves, four contain non-neuronal cells that span the entire distance between the male genitalia and the sex ganglia. However, when male genitalia were transplanted to ectopic locations close to MG6, induction occurred frequently but only in MG6, mediated by ectopic nerves that do not contain these cells. Thus, non-neuronal cells specific to the normal sex nerves are not necessary for induction. In addition, dye injections into the target during the critical period failed to reveal migrating cells in the sex nerves that could convey the inductive signal to the CNS. Finally, we show that 11 pairs of central neurons in each ganglion project to the male organ early during the critical period. In the adult, at least 3 additional pairs of neurons in MG6 also innervate this target. We conclude that the only components of the sex nerves that connect the sex ganglia to the target during the critical period that could be associated with induced central mitogenesis are the axons of central neurons that innervate the male genitalia.
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Schmidt, J., and J. W. Deitmer. "Photoinactivation of the giant neuropil glial cells in the leech Hirudo medicinalis: effects on neuronal activity and synaptic transmission." Journal of Neurophysiology 76, no. 5 (November 1, 1996): 2861–71. http://dx.doi.org/10.1152/jn.1996.76.5.2861.
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1. We studied the effects of photoinactivation of neuropil glial (NG) cells of the leech Hirudo medicinalis on neuronal activity and synaptic transmission. Each segmental ganglion contains two of these giant glial cells, which are electrically and dye coupled. 2. One of the two NG cells in an isolated segmental ganglion was filled with the dye Lucifer yellow (LY). Subsequent irradiation of the ganglion with laser light (440 nm) to photolyze LY caused irreversible depolarization of both NG cells. The NG cells that were filled with LY depolarized from -73 +/- 1.1 (SE) mV to -22 +/- 2.4 mV within 25 +/- 2.8 min of continuous irradiation (n = 22). The other NG cell, which was not directly filled with LY, depolarized with some delay. 3. Photoinactivation of the NG cells caused an irreversible depolarization of Retzius neurons and noxious (N) sensory cells by a mean of 14 mV (n = 36) and 9 mV (n = 24), respectively. In addition, the input resistance was reduced by 54% in Retzius cells and by 34% in N cells. Spikes could not be evoked in Retzius cells after the inactivation of the NG cells, either by intracellular current injection or by electrical nerve stimulation. Similarly, anterior pagoda neurons, annulus erector neurons, and the excitor neurons of the ventrolateral circular muscles became inexcitable. However, N cells, heart interneurons, and most of the heart motor neurons, touch cells, and pressure cells could still generate spontaneous or evoked action potentials. 4. Photoinactivation of the NG cells impaired the electrical connection between the two Retzius neurons. The electrical coupling was completely eliminated in six of eight cell pairs and reduced by 66% in two others. 5. Photoinactivation of the NG cells in the 3rd and 4th segmental ganglion caused a complete block of the chemical synapse between reciprocal inhibitory heart interneurons in these ganglia; the bursting rhythm either stopped or changed to a tonic activity, whereas inhibitory postsynaptic potentials could not be recorded in either heart interneuron anymore. 6. Laser irradiation alone had no effect on neuronal activity and synaptic transmission. Addition of glutathione (10 mM) and ascorbic acid (10 mM) to the saline to bind extracellular radicals that might be produced by the irradiation did not suppress the effects caused by photoinactivation of NG cells. 7. Elevation of bath K+ concentration to 12 mM, acidification of the saline to pH 5.5, and alkalinization to pH 8.5 for 6 min each did not mimick the effects on membrane properties of Retzius cells as produced by inactivation of NG cells. The results suggest some role of glial cells in the maintenance of neuronal activity and electrical and chemical synaptic transmission.
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Brodfuehrer, Peter D., and W. Otto Friesen. "Initiation of swimming activity by trigger neurons in the leech subesophageal ganglion." Journal of Comparative Physiology A 159, no. 4 (1986): 489–502. http://dx.doi.org/10.1007/bf00604169.
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Brodfuehrer, Peter D., and W. Otto Friesen. "Initiation of swimming activity by trigger neurons in the leech subesophageal ganglion." Journal of Comparative Physiology A 159, no. 4 (1986): 503–10. http://dx.doi.org/10.1007/bf00604170.
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Brodfuehrer, Peter D., and W. Otto Friesen. "Initiation of swimming activity by trigger neurons in the leech subesophageal ganglion." Journal of Comparative Physiology A 159, no. 4 (1986): 511–19. http://dx.doi.org/10.1007/bf00604171.
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Romanenko, Sergii, Peter H. Siegel, Daniel A. Wagenaar, and Victor Pikov. "Effects of millimeter wave irradiation and equivalent thermal heating on the activity of individual neurons in the leech ganglion." Journal of Neurophysiology 112, no. 10 (November 15, 2014): 2423–31. http://dx.doi.org/10.1152/jn.00357.2014.
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Many of today's radiofrequency-emitting devices in telecommunication, telemedicine, transportation safety, and security/military applications use the millimeter wave (MMW) band (30–300 GHz). To evaluate the biological safety and possible applications of this radiofrequency band for neuroscience and neurology, we have investigated the physiological effects of low-intensity 60-GHz electromagnetic irradiation on individual neurons in the leech midbody ganglia. We applied incident power densities of 1, 2, and 4 mW/cm2 to the whole ganglion for a period of 1 min while recording the action potential with a standard sharp electrode electrophysiology setup. For comparison, the recognized U.S. safe exposure limit is 1 mW/cm2 for 6 min. During the exposure to MMWs and gradual bath heating at a rate of 0.04°C/s (2.4°C/min), the ganglionic neurons exhibited similar dose-dependent hyperpolarization of the plasma membrane and decrease in the action potential amplitude. However, narrowing of the action potential half-width during MMW irradiation at 4 mW/cm2 was 5 times more pronounced compared with that during equivalent bath heating of 0.6°C. Even more dramatic difference in the effects of MMW irradiation and bath heating was noted in the firing rate, which was suppressed at all applied MMW power densities and increased in a dose-dependent manner during gradual bath heating. The mechanism of enhanced narrowing of action potentials and suppressed firing by MMW irradiation, compared with that by gradual bath heating, is hypothesized to involve specific coupling of MMW energy with the neuronal plasma membrane.
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Verger-Bocquet, M., C. Wattez, M. Salzet, and J. Malecha. "Immunocytochemical identification of peptidergic neurons in compartment 4 of the supraesophageal ganglion of the leech Theromyzon tessulatum (O.F.M.)." Canadian Journal of Zoology 70, no. 5 (May 1, 1992): 856–65. http://dx.doi.org/10.1139/z92-122.
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The use of polyclonal antibodies directed against mammalian peptide hormones and of monoclonal antibodies raised against molecules of supraesophageal ganglion neurons of the leech Theromyzon tessulatum has led to the identification of more than half of the 30 neurons present in compartment 4 of the supraesophageal ganglion. Six cellular types were characterized at stage 3B of the life cycle: (1) a group of four or five large angiotensin II and γ-melanocyte stimulating hormone (γ-MSH) immunopositive cells also immunoreactive with monoclonal antibodies Tt-7 and Tt-159 (cells of class I), (2) a group of five small growth hormone releasing factor (GRF) positive cells, (3) three motilin-positive cells, (4) one met-enkephalin-positive cell, (5) one oxytocin-positive cell that also immunoreacts with monoclonal antibody Tt-1, and (6) one vasopressin-positive cell immunoreactive with monoclonal antibody Tt-9. This study shows the heterogeneity of the neurons constituting compartment 4 and demonstrates that most of them have secretions of a peptidergic nature. The co-localization of epitopes recognized by anti-γ-MSH and anti-angiotensin II is demonstrated in cells of class I. The number of immunoreactive cells found in compartment 4 is not always constant and can vary for the following reasons: (i) changes in the physiological status of the leech, as is the case with anti-GRF and anti-motilin, (ii) individual variations for some cellular types (cells of class I), (iii) variability in the situation of the connective-tissue septum separating compartments 4 and 5.
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Moss, Brenda L., Abby D. Fuller, Christie L. Sahley, and Brian D. Burrell. "Serotonin Modulates Axo-Axonal Coupling Between Neurons Critical for Learning in the Leech." Journal of Neurophysiology 94, no. 4 (October 2005): 2575–89. http://dx.doi.org/10.1152/jn.00322.2005.
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S cells form a chain of electrically coupled neurons that extends the length of the leech CNS and plays a critical role in sensitization during whole-body shortening. This process requires serotonin, which acts in part by altering the pattern of activity in the S-cell network. Serotonin-containing axons and varicosities were observed in Faivre's nerve where the S-to-S-cell electrical synapses are located. To determine whether serotonin modulates these synapses, S-cell action-potential (AP) propagation was studied in a two-ganglion chain containing one electrical synapse. Suction electrodes were placed on the cut ends of the connectives to stimulate one S cell while recording the other, coupled S cell's APs. A third electrode, placed en passant, recorded the APs near the electrical synapse before they propagated through it. Low concentrations of the gap junction inhibitor octanol increased AP latency across the two-ganglion chain, and this effect was localized to the region of axon containing the electrical synapse. At higher concentrations, APs failed to propagate across the synapse. Serotonin also increased AP latency across the electrical synapse, suggesting that serotonin reduced coupling between S cells. This effect was independent of the direction of propagation and increased with the number of electrical synapses in progressively longer chains. Furthermore, serotonin modulated instantaneous AP frequency when APs were initiated in separate S cells and in a computational model of S-cell activity after mechanosensory input. Thus serotonergic modulation of S-cell electrical synapses may contribute to changes in the pattern of activity in the S-cell network.
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Malecha, J., M. Verger-Bocquet, and G. Tramu. "Mise en évidence et évolution, au cours du cycle biologique, de neurones producteurs d'une substance apparentée à la motiline porcine dans le ganglion supraoesophagien de la sangsue Theromyzon tessulatum." Canadian Journal of Zoology 67, no. 3 (March 1, 1989): 636–40. http://dx.doi.org/10.1139/z89-091.
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The life cycle of Theromyzon tessulatum has been divided into stages defined on the basis of feeding pattern and reproductive activity. The use of an antiserum raised against porcine motilin demonstrated the presence of immunoreactive cells and fibers in the supraesophageal ganglion throughout the life of the leech. Immunopositive fibers are present in the neurohemal area of the dorsal commissure. The highest number of immunopositive neurons is found during stages 3B, 3C, and 3D, which precede egg-laying. The control of oogenesis by a substance related to porcine motilin is postulated.
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Brodfuehrer, P. D., H. J. Parker, A. Burns, and M. Berg. "Regulation of the segmental swim-generating system by a pair of identified interneurons in the leech head ganglion." Journal of Neurophysiology 73, no. 3 (March 1, 1995): 983–92. http://dx.doi.org/10.1152/jn.1995.73.3.983.
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1. The aim of this study was to identify neurons that modulate activity of segmental swim gating interneurons. We found a pair of bilaterally symmetrical interneurons, cells SE1, whose activity level directly influences three groups of segmental neurons associated with generating swimming in the medicinal leech. 2. The somata of cells SE1 are located on the dorsal surface of the subesophageal ganglion. Their axons extend most, if not the entire, length of the ventral nerve cord and appear to make identical connections with the same group of swim-generating neurons in all segmental ganglia. 3. Cells SE1 excite monosynaptically all segmental swim gating interneurons, cells 204, examined. The level of excitation in cell 204 is directly correlated with the firing frequency of cell SE1. In most quiescent preparations (when the preparation is not swimming) hyperpolarization of a single cell SE1 eliminates all excitatory synaptic input to cells 204. 4. Cells SE1 excite monosynaptically three swim oscillatory interneurons, cells 115, 28, and 208. The strength of the connection from cell SE1 to cell 115 is stronger than the connection from cell SE1 to either cells 28 or 208. The level of excitation in cell 115 is directly correlated with the firing frequency of cell SE1. In most quiescent preparations, hyperpolarization of a single cell SE1 eliminates all excitatory synaptic input to cell 115 but has only a minor effect on the level of activity in cells 208 and 28. 5. Due most likely to the strong and direct connections cells SE1 have with swim gating and oscillatory interneurons, brief stimulation of cell SE1 can elicit swimming. Swimming generally occurs within 1 s after stimulation of cell SE1. During swimming, the membrane potential of cell SE1 depolarizes by 2-5 mV, and its firing frequency increases. Brief depolarization of cell SE1 during swimming reliably shifts the phase of the swimming rhythm, whereas longer periods of depolarization increase both swim period and burst duration. 6. Excitatory motor neurons to the dorsal longitudinal muscles, cells 3, 5, and 7, are strongly excited by stimulation of cell SE1. The firing frequency of cell 3 is positively correlated with the firing frequency of cell SE1. 7. The results of this study indicate that cells SE1 can modulate the level of excitation in three groups of neurons associated with generating leech swimming.(ABSTRACT TRUNCATED AT 400 WORDS)
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Nardelli-Haefliger, D., and M. Shankland. "Lox10, a member of the NK-2 homeobox gene class, is expressed in a segmental pattern in the endoderm and in the cephalic nervous system of the leech Helobdella." Development 118, no. 3 (July 1, 1993): 877–92. http://dx.doi.org/10.1242/dev.118.3.877.
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A novel leech homeobox gene, Lox10, is shown to encode a homeodomain sequence characteristic of a phyletically widespread NK-2 homeobox gene class. Lox10 expression was examined in leech embryos of various ages by in situ hybridization. In the unsegmented cephalic region, Lox10 RNA is expressed in a subset of the cells descended from the a' and b' micromeres, including a small cluster of cells, believed to be postmitotic neurons, within the supraesophageal ganglion of the central nervous system. Hybridization signal was not detected in either the mesoderm or ectoderm of the trunk segments, and the apparent restriction of Lox10 ectodermal expression to the nonsegmented cephalic domain resembles the restricted forebrain expression pattern of its mammalian homologues. Lox10 is also expressed within the endodermal tissues of the leech midgut, which arises by cellularization from a polynucleate syncytium. Endodermal expression is organized into a pattern of transverse stripes and spots which are aligned with the intersegmental septa, and which prefigure the pattern of gut wall constrictions observed at later stages of development. Lox10 is the first molecular marker of segmentally periodic endoderm differentiation reported for any animal species.
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Nardelli-Haefliger, D., A. E. Bruce, and M. Shankland. "An axial domain of HOM/Hox gene expression is formed by morphogenetic alignment of independently specified cell lineages in the leech Helobdella." Development 120, no. 7 (July 1, 1994): 1839–49. http://dx.doi.org/10.1242/dev.120.7.1839.
Full textAbstract:
The homeobox gene Lox2, a member of the HOM/Hox gene class, is expressed in a restricted domain along the anteroposterior (A-P) body axis of the leech Helobdella. The segmental tissues of the leech embryo arise from the parallel merger of five distinct and bilaterally paired cell lineages generated by embryonic stem cells or teloblasts. Injection of cell lineage tracers coupled with anti-LOX2 immunochemistry reveals that all five teloblast lineages generate central nervous system neurons that express the LOX2 protein, and that each lineage expresses LOX2 within a similar domain of body segments. Some lineally identified neurons display anti-LOX2 immunoreactivity over the entire expression domain, but the OM7 neuron has a distinctively high level of LOX2 expression, which is restricted to the seventh midbody ganglion. To ascertain the role of positional information in the axial patterning of LOX2 expression, we performed focal cell ablations that displaced one or another of the teloblast lineages out of segmental register with the other axial tissues. Such displacements brought about a corresponding shift in the LOX2 expression of the perturbed lineage, and had little or no effect on the LOX2 expression of the other, unperturbed lineages. This result indicates that the axial domain of LOX2 expression is not specified by positional cues acting coordinately across the various teloblast lineages, nor would it seem that the expression domain is imprinted from one lineage to the others. Rather, the different teloblast lineages acquire their axial patterns independently, and secondarily bring these patterns into alignment along the A-P axis through a process of morphogenetic assembly.
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Rela, L., and L. Szczupak. "In Situ Characterization of a Rectifying Electrical Junction." Journal of Neurophysiology 97, no. 2 (February 2007): 1405–12. http://dx.doi.org/10.1152/jn.00973.2006.
Full textAbstract:
Electrical synapses play significant roles in neural processing in invertebrate and vertebrate nervous systems. The view of electrical synapses as plain bidirectional intercellular channels represents a partial picture because rectifying electrical synapses expand the complexity in the communication capabilities of neurons. Rectification derives, mostly, from the sensitivity of electrical junctions to the transjunctional potential ( Vj) across the coupled cells. We analyzed the characteristics of this sensitivity and their effect on neuronal signaling, studying rectifying junctions present in the leech nervous system. The NS neurons, a pair of premotor nonspiking neurons present in each midbody ganglion, are electrically coupled to virtually every excitatory motor neuron. Studied at rest, only hyperpolarizing signals can be transmitted from NS to the motoneurons, and only depolarizing signals are conducted in the opposite direction. Our results show that small changes in the NS membrane potential ( Vm) exerted an effective control of the firing frequency of the CV motoneurons (excitor of circular muscles). This effect revealed the existence of a threshold Vj across which the electrical synapse shifts from a nonconducting to a conducting state. The junction can operate as a relatively symmetrical bidirectional bridge provided that the transmitted signals do not cross this threshold transjunctional potential.
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Harley, Cynthia M., Melissa G. Reilly, Christopher Stewart, Chantel Schlegel, Emma Morley, Joshua G. Puhl, Christian Nagel, Kevin M. Crisp, and Karen A. Mesce. "Compensatory plasticity restores locomotion after chronic removal of descending projections." Journal of Neurophysiology 113, no. 10 (June 2015): 3610–22. http://dx.doi.org/10.1152/jn.00135.2015.
Full textAbstract:
Homeostatic plasticity is an important attribute of neurons and their networks, enabling functional recovery after perturbation. Furthermore, the directed nature of this plasticity may hold a key to the restoration of locomotion after spinal cord injury. Here we studied the recovery of crawling in the leech Hirudo verbana after descending cephalic fibers were surgically separated from crawl central pattern generators shown previously to be regulated by dopamine. We observed that immediately after nerve cord transection leeches were unable to crawl, but remarkably, after a day to weeks, animals began to show elements of crawling and intersegmental coordination. Over a similar time course, excessive swimming due to the loss of descending inhibition returned to control levels. Additionally, removal of the brain did not prevent crawl recovery, indicating that connectivity of severed descending neurons was not essential. After crawl recovery, a subset of animals received a second transection immediately below the anterior-most ganglion remaining. Similar to their initial transection, a loss of crawling with subsequent recovery was observed. These data, in recovered individuals, support the idea that compensatory plasticity directly below the site of injury is essential for the initiation and coordination of crawling. We maintain that the leech provides a valuable model to understand the neural mechanisms underlying locomotor recovery after injury because of its experimental accessibility, segmental organization, and dependence on higher-order control involved in the initiation, modulation, and coordination of locomotor behavior.
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De-Miguel, Francisco F., Mariana Vargas-Caballero, and Elizabeth García-Pérez. "Spread of synaptic potentials through electrical synapses in Retzius neurones of the leech." Journal of Experimental Biology 204, no. 19 (October 1, 2001): 3241–50. http://dx.doi.org/10.1242/jeb.204.19.3241.
Full textAbstract:
SUMMARYWe studied the spread of excitatory postsynaptic potentials (EPSPs) through electrical synapses in Retzius neurones of the leech Haementeria officinalis. The pair of Retzius neurones in each ganglion is coupled by a non-rectifying electrical synapse. Both neurones displayed synchronous EPSPs of varying amplitudes and rise times. The kinetics of synchronous EPSPs was similar in 79 % of the EPSP pairs. In the remaining 21 %, one EPSP was smaller and slower than the other, suggesting its passive spread from the other neurone. The proportion of these events increased to 75 % in the presence of Mg2+ in the bathing fluid. This spread of EPSPs from one neurone to another was tested by producing artificial EPSPs by current injection into the soma of one Retzius neurone. The artificial EPSPs were smaller and arrived more slowly at the soma of the coupled neurone. The coupling ratios for the EPSPs were proportional to the coupling ratio for long steady-state pulses in different neuronal pairs. Our results showed that EPSPs spread from one Retzius neurone to the other and support the idea that EPSP spread between electrically coupled neurones may contribute to the integration processes of neurones.
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Wadepuhl, M. "Depression of excitatory motoneurones by a single neurone in the leech central nervous system." Journal of Experimental Biology 143, no. 1 (May 1, 1989): 509–27. http://dx.doi.org/10.1242/jeb.143.1.509.
Full textAbstract:
Intracellular staining techniques have been used to characterize the morphology of a newly identified neurone, cell 151, in the segmental ganglia of the leech. This neurone ramifies extensively within the neuropile and sends multiple extensions into roots and connectives. Strong dye coupling and non-rectifying electrical coupling were observed between the contralateral homologues. No action potentials were recorded from the cell body, but postsynaptic potentials and slow potential changes (greater than 1 s, greater than 15 mV) were observed. Upon injection of hyperpolarizing currents, the efferent spike activity, recorded extracellularly, was depressed in both the ipsi- and the contralateral roots of the ganglion. The depression was gradual and non-adapting and occurred reliably only within the ganglion where cell 151 is situated. Depolarization of cell 151 was without consequence for the tonic firing of isolated ganglia. Many identified excitatory motoneurones follow the hyperpolarization of cell 151. Currents can be exchanged between cell 151 and motoneurones via rectifying electrical synapses. Spontaneous hyperpolarizations of cell 151 were correlated with depression of spike frequencies, recorded in whole nerves as well as in identified motoneurones. The membrane potential of cell 151 was drastically altered by bursts from mechanosensory cells. The ability of cell 151 to distribute inhibition onto a great number of motoneurones and to curtail excessive neuronal activity is discussed.
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Chiquet, M., and J. G. Nicholls. "Neurite outgrowth and synapse formation by identified leech neurones in culture." Journal of Experimental Biology 132, no. 1 (September 1, 1987): 191–206. http://dx.doi.org/10.1242/jeb.132.1.191.
Full textAbstract:
After injury, neurones in the central nervous system (CNS) of the leech regenerate with a high degree of specificity. The aim of our experiments has been to study the sequential steps involved in neurite growth and synapse formation using isolated identified neurones in culture. An important requirement for sprouting of leech neurones is the substrate. Neurites grow only slowly and sparsely on polylysine or vertebrate laminin. The extracellular matrix of leech ganglion capsules contains a protease-sensitive factor which can be extracted with urea. With this material as substrate, growth proceeds rapidly in defined medium. Another neurite-promoting substrate is provided by the plant lectin concanavalin A (Con A). The activity of Con A, but not of the capsule matrix factor, is blocked by the Con A-specific hapten methyl alpha-D-mannoside. The morphology and branching pattern of the neurites in culture depend on the specific substrate and on the type of neurone. During stimulation, less Ca2+ uptake occurs into growth cones than in cell bodies. The mechanism of neurite growth seems not to depend on activity-mediated Ca2+ influx or on interactions between neuronal cell surfaces. However, even without profuse outgrowth, electrical and chemical synapses develop between neighbouring neurones. The type of synapse depends predictably on the types of neurones within the cell pair. Since the development of a synapse can be followed with time in culture, the sequential events can each be studied separately for this multi-step process.
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Bannatyne, B. A., S. E. Blackshaw, and M. McGregor. "New growth elicited in adult leech mechanosensory neurones by peripheral axon damage." Journal of Experimental Biology 143, no. 1 (May 1, 1989): 419–34. http://dx.doi.org/10.1242/jeb.143.1.419.
Full textAbstract:
1. New growth in cutaneous mechanosensory neurones elicited by axotomy or axon crush was studied using intracellular injection of horseradish peroxidase at different times after the lesion, ranging from a few days to over a year. 2. Cutting or crushing major, large-calibre axon branches of mechanosensory neurones elicits sprouting of new processes, either centrally within the ganglion neuropile or at the site of the lesion in the peripheral nerve. In contrast, cutting or crushing fine-calibre axon branches supplying accessory parts of the receptive field does not elicit sprouting of the main arbor or main axon branches. 3. Different modalities of mechanosensory neurone respond differently to lesions of their axons. Cutting the axons of high-threshold units responding to noxious stimulation of the skin elicits sprouting of additional processes from the axon hillock region within the central nervous system (CNS), whereas cutting or crushing the axons of low-threshold cells responding to light touch of the skin elicits sprouting at the site of the lesion only, and not within the CNS. 4. In addition to the new growth directed into the peripheral nerve, damaged nociceptive neurones also form new processes that wrap the somata of particular cells within the ganglion. 5. Sprouted processes of axotomized neurones are retained for long periods after the lesion (up to 425 days). 6. The electrical properties of touch and nociceptive cells were studied between 1 and 60 days after axotomy, by intracellular recording from the centrally located cell bodies. The amplitude, width and maximum dV/dt of the action potential and after-hyperpolarization, as well as the resting potential and input resistance, did not change significantly after axotomy, despite the considerable process sprouting known to occur during this time.
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Baader, A. P. "Interneuronal and motor patterns during crawling behavior of semi-intact leeches." Journal of Experimental Biology 200, no. 9 (May 1, 1997): 1369–81. http://dx.doi.org/10.1242/jeb.200.9.1369.
Full textAbstract:
Semi-intact tethered preparations were used to characterize neuronal activity patterns in midbody ganglia of the medicinal leech during crawling. Extra- and intracellular recordings were obtained from identified interneurons and from motor neurons of the longitudinal and circular muscles during crawling episodes. Coordinated activities of nine excitatory and inhibitory motor neurons of the longitudinal and circular muscles were recorded during the appropriate phases of crawling. Thus, during crawling, the leech uses motor output components known to contribute to other types of behavior, such as swimming or the shortening/local bending reflex. Interneurons with identified functions in these other types of behavior exhibit membrane potential oscillations that are in phase with the behavior pattern. Therefore, the recruitment of neuronal network elements during several types of behavior occurs not only at the motor neuron level but also involves interneurons. This applies even to some interneurons that were previously thought to have dedicated functions (such as cells 204 and 208 and the S cell). The function of neuronal circuitries in producing different types of behavior with a limited number of neurons is discussed.
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Calabrese, B., and M. Pellegrino. "Remodelling of an intact neurone in the central nervous system of the leech." Journal of Experimental Biology 198, no. 9 (September 1, 1995): 1989–94. http://dx.doi.org/10.1242/jeb.198.9.1989.
Full textAbstract:
The regeneration pattern of two identified central neurones was studied in the leech Hirudo medicinalis. Anterior pagoda (AP) and mechanosensory touch-sensitive (T) neurones were stained in adult segmental ganglia, maintained in culture for 6-10 days. AP neurones, which normally project only to the contralateral nerve roots, sprouted extensively in all the available nerve paths during regeneration. Mechanosensory T cells, in the same experimental conditions, showed only a moderate growth and did not change their normal pattern of axonal projections. The observed differences in the growth pattern might account for the different electrophysiological responses to axotomy exhibited by the two types of neurone. Interruption of interganglionic connectives induced a moderate and stereotyped remodelling of the morphology of intact AP neurones, which was reminiscent of that transiently exhibited during embryonic development. This response was observed in 25% of the AP neurones we examined.
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Chiquet, M., L. Masuda-Nakagawa, and K. Beck. "Attachment to an endogenous laminin-like protein initiates sprouting by leech neurons." Journal of Cell Biology 107, no. 3 (September 1, 1988): 1189–98. http://dx.doi.org/10.1083/jcb.107.3.1189.
Full textAbstract:
Leech neurons in culture sprout rapidly when attached to extracts from connective tissue surrounding the nervous system. Laminin-like molecules that promote sprouting have now been isolated from this extracellular matrix. Two mAbs have been prepared that react on immunoblots with a approximately equal to 220- and a approximately equal to 340-kD polypeptide, respectively. These antibodies have been used to purify molecules with cross-shaped structures in the electron microscope. The molecules, of approximately equal to 10(3) kD on nonreducing SDS gels, have subunits of approximately equal to 340, 220, and 160-180 kD. Attachment to the laminin-like molecules was sufficient to initiate sprouting by single isolated leech neurons in defined medium. This demonstrates directly a function for a laminin-related invertebrate protein. The mAbs directed against the approximately equal to 220-kD chains of the laminin-like leech molecule labeled basement membrane extracellular matrix in leech ganglia and nerves. A polyclonal antiserum against the approximately equal to 220-kD polypeptide inhibited neurite outgrowth. Vertebrate laminin did not mediate the sprouting of leech neurons; similarly, the leech molecule was an inert substrate for vertebrate neurons. Although some traits of structure, function, and distribution are conserved between vertebrate laminin and the invertebrate molecule, our results suggest that the functional domains differ.
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ZHANG, REN-JI, LIXIA ZHU, DAN-BING WANG, and FAN ZHANG. "Positional Discrimination and re-development of Synapses in the Leech Whitmania Pigra." Journal of Experimental Biology 153, no. 1 (October 1, 1990): 47–60. http://dx.doi.org/10.1242/jeb.153.1.47.
Full textAbstract:
Identified neurones in the leech Whitmania pigra have a stable morphology with bilaterally symmetrical branching arborizations, and with axons on both sides arranged symmetrically in the connectives. Each anterior pagoda cell (AP) receives electrical and/or chemical synaptic input from mechanoreceptive cells on both sides of the body. The position in the body can be discriminated by the postsynaptic responses of the APs: as a rule, the responses to input from contralateral receptive neurones are stronger than those to input from ipsilateral ones, and the neurone with its receptive field on the dorsal side produces a stronger response than the neurone with a ventrally sited receptive field. APs integrate postsynaptic potentials and spikes. There are no connections between the two AP cells and so it is possible that positional discrimination depends upon a circuit comparing the inputs. After the body wall has been cut round and rotated by 180°, the mechanoreceptive cells and annular erector motoneurones reinnervate the body wall strictly according to their original orientation, and repair is bilaterally synchronous. This eliminates a role for target cell guidance, particularly in the adult leech. When an extra Retzius cell is implanted into cultured ganglia, synapses develop between the host and the implanted neurone. Such synapses generally show lower coupling ratios or PSP fluctuations. However, the specific electrical connection between the Retzius cells shows a normal coupling ratio.
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Yang, Sung Min, María Eugenia Vilarchao, Lorena Rela, and Lidia Szczupak. "Wide propagation of graded signals in nonspiking neurons." Journal of Neurophysiology 109, no. 3 (February 1, 2013): 711–20. http://dx.doi.org/10.1152/jn.00934.2012.
Full textAbstract:
Signal processing in neuritic trees is ruled by the concerted action of passive and active membrane properties that, together, determine the degree of electrical compartmentalization of these trees. We analyzed how active properties modulate spatial propagation of graded signals in a pair of nonspiking (NS) neurons of the leech. NS neurons present a very extensive neuritic tree that mediates the interaction with all the excitatory motoneurons in leech ganglia. NS cells express voltage-activated Ca2+ conductances (VACCs) that, under certain experimental conditions, evoke low-threshold spikes. We studied the distribution of calcium transients in NS neurons loaded with fluorescent calcium probes in response to low-threshold spikes, electrical depolarizing pulses, and synaptic inputs. The three types of stimuli evoked calcium transients of similar characteristics in the four main branches of the neuron. The magnitude of the calcium transients evoked by electrical pulses was a graded function of the change in NS membrane potential and depended on the baseline potential level. The underlying VACCs were partially inactivated at rest and strongly inactivated at −20 mV. Stimulation of mechanosensory pressure cells evoked calcium transients in NS neurons whose amplitude was a linear function of the amplitude of the postsynaptic response. The results evidenced that VACCs aid an efficient propagation of graded signals, turning the vast neuritic tree of NS cells into an electrically compact structure.
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Borst, Alexander. "Periodic Current Injection (PCI) -A New Method to Image Steady-State Membrane Potential of Single Neurons in situ Using Extracellular Voltage-Sensitive Dyes." Zeitschrift für Naturforschung C 50, no. 5-6 (June 1, 1995): 435–38. http://dx.doi.org/10.1515/znc-1995-5-615.
Full textAbstract:
Abstract A new method is described which allows to image the steady-state distribution of m em brane potential of single neurons in situ. The method consists of staining the tissue with an extracellular voltage-sensitive dye (Di-4-ANEPPS) and impaling a single neuron with a microelectrode. After focusing the imaging system onto the cell a large series of images are taken with a CCD camera at the appropriate excitation wavelength of the voltage-sensitive dye while the neuron’s membrane potential is shifted by a periodic current injection (PCI). Afterwards two groups of images are averaged separately: those images while the cell was at rest and those images while the cell was hyperpolarized. After subtraction of these averaged images, the resulting difference image shows only the membrane potential of the cell which was altered periodically. The success of the method is demonstrated on leech cells in intact ganglia. If applied to cells with a basically two-dimensional arborization pattern, the decrease of activity in the difference image in areas further away from the injection site should relate to a decrease in membrane potential according to the passive electrotonic properties of the cell under study.
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Sardar, S., N. Saha, and A. Ghosh. "Microglia, the Sentinel of Brain in the Evolution of Nervous System from Invertebrate to Vertebrate: A Short Review." Journal of Scientific Research 14, no. 2 (May 1, 2022): 685–97. http://dx.doi.org/10.3329/jsr.v14i2.56222.
Full textAbstract:
The presence of microglial cells as resident macrophage population in the Central Nervous System (CNS) is well documented from the study of repairing of lesions in CNS that varies widely throughout the animal kingdom. The existence of neuroglia cells similar to vertebrate microglia and small mobile phagocytes and hemocytes were documented from ganglia of some invertebrate animal models like leech (H. medicinalis), insects (P. americana and D. melanogaster) and mollusca (M. edulis). Neuronal replacement and migration of immunocompetent cells (macrophage, microglia, ependymal cells etc.) after surgical lesions in CNS of non-mammals (fishes, reptiles and aves) are much restricted to specific neurogenic niches associated to the neural regeneration and migration of cells in invertebrates. Microglial presence is largely restricted in the optic tract of fish and amphibian ganglionic cells because they have a surprising capacity to regenerate their neurons after lesions. Hence the CNS of both invertebrates and vertebrates contain microglia like mononuclear phagocytes, ensheathing glia and reticular glia, which indicate about the evolutionary conserved innate immune response to maintain CNS development and health. But the presence and gradual changes in the structure and function of microglia and neuron-microglia relationship in the CNS along the phylogeny need to be focused thoroughly.
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Angstadt, J. D., and W. O. Friesen. "Synchronized oscillatory activity in leech neurons induced by calcium channel blockers." Journal of Neurophysiology 66, no. 6 (December 1, 1991): 1858–73. http://dx.doi.org/10.1152/jn.1991.66.6.1858.
Full textAbstract:
1. Leech ganglia were superfused with salines in which Ca2+ was replaced with equimolar concentrations of Co2+, Ni2+, or Mn2+. These salines elicited rhythmic membrane potential oscillations with cycle periods ranging from 8 to 25 s in all neurons examined within the ventral nerve cord. 2. Rhythmic activity consisted of a rapid depolarization to a prolonged (3-6 s) plateau level, followed by a rapid repolarization. Each depolarization elicited a burst of action potentials. Peak-to-trough amplitudes of the plateau depolarizations were up to 40 mV in some cells. The plateau depolarizations were separated by slowly depolarizing ramp potentials. 3. Oscillations in all neurons were synchronized (in phase) both within individual ganglia and between ganglia linked by connective nerves. Rhythmic activity in isolated ganglia persisted after the interposed connective nerves were cut. 4. The occurrence of oscillatory activity was strongly correlated with the block of chemical synaptic transmission. 5. Electrotonic interactions persisted during oscillatory activity and may be one mechanism by which oscillations are synchronized. 6. The phase of rhythmic impulse bursts monitored with extracellular electrodes could be reset by electrical stimulation of connective nerves but not by injection of current pulses into individual neurons. Phase reset appeared to occur within one cycle and to a fixed phase point (plateau termination). 7. Oscillatory activity was eliminated by 75-100% reductions of [Na+]o (Na+ replaced with N-methyl-D-glucamine). Smaller reductions of Na+ (by 25-50%) increased the cycle period of oscillations. 8. The Na(+)-K+ pump inhibitors ouabain and strophanthidin disrupted oscillations. Cells were depolarized by approximately 20 mV and fired tonically. After the initial washout of the inhibitors, cells repolarized and became quiescent. After several minutes of continued washing, oscillatory activity resumed. 9. A conceptual model is proposed to explain the mechanisms underlying oscillatory activity induced by Ca2+ channel blockers. According to this model, depolarizing plateaus are generated by a noninactivating Na+ conductance. Na+ influx during the plateau leads to an increase in [Na+]i, which activates an electrogenic Na(+)-K+ pump that contributes to plateau termination. 10. A quantitative computer simulation incorporating six types of currents (capacity, outward rectifying potassium, inward rectifying potassium, sodium, leakage, and an electrogenic sodium pump) demonstrates the plausibility of the conceptual model. 11. These data suggest that a novel Na(+)-based mechanism for membrane potential oscillation is revealed by blockade of Ca2+ channels in leech ganglia.
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Becker, T., and E. R. Macagno. "CNS control of a critical period for peripheral induction of central neurons in the leech." Development 116, no. 2 (October 1, 1992): 427–34. http://dx.doi.org/10.1242/dev.116.2.427.
Full textAbstract:
Most midbody ganglia in the central nervous system (CNS) of the leech Hirudo medicinalis contain about 400 neurons. However, those in the fifth and sixth midbody segments (ganglia M5 and M6) are specialized for reproductive functions, and each contain several hundred additional small neurons. These neurons arise late in embryogenesis as a result of an innervation-dependent inductive interaction between the male genitalia and M5 and M6 and are therefore known as peripherally induced central (PIC) neurons. The results of a series of ablation and transplantation experiments show that the PIC neurons are induced during a 1 to 2 day period about midway in embryogenesis (E15). The male genitalia are not necessary for induction before or after this period, and their presence for only one day may be sufficient for the induction to take place. Heterochronic transplantation of male genitalia shows that the critical period of interaction is independent of the age of the inducing tissues. Since the inductive signal is available from E10 to postembryonic stages, both the beginning and the end of the inductive period are determined by the CNS, not the periphery.
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Merz, D. C. "Segmental specialization of calcium-activated potassium conductances in an identified leech neuron." Journal of Neurophysiology 73, no. 3 (March 1, 1995): 957–63. http://dx.doi.org/10.1152/jn.1995.73.3.957.
Full textAbstract:
1. Retzius (R) neurons of the fifth and sixth segmental ganglia of the leech, called R(5,6) neurons are specialized to innervate the adjacent reproductive organs and are morphologically and functionally distinct from R neurons of standard ganglia [R(x) cells]. In this study the electrical properties of the R(x) and R(5,6) neurons were compared under current-clamp and voltage-clamp conditions. 2. The action-potential waveforms of R(x) and R(5,6) cells were similar except for the presence in the R(5,6) cells of a long afterhyperpolarization (AHP) following action potentials arising from the resting membrane potential but not from more depolarized potentials. Its role may thus be to inhibit firing of the R(5,6) neurons at rest or in response to weak depolarizing stimuli. 3. In the presence of the Ca2+ channel blocker Cd2+, the long AHP of the R(5,6) was abolished, and the action potentials of all R cells were identical. 4. Under voltage clamp, current kinetics and densities were similar between R(x) and R(5,6) cells for Ca2+ currents, delayed and inward rectifier K+ currents, and a rapid Ca(2+)-activated K+ current (IKc) that is common to the two cell types. The R(5,6) cells, however, expressed a second Ca(2+)-activated K+ current that was not observed in the R(x) cells. This current, called IKAHP, activated and inactivated more slowly than IKC, with a time course similar to that of the AHP observed under physiological conditions. 5. Neither IKC nor IKAHP was blocked by high concentrations of charybdotoxin or apamin, which block vertebrate Ca(2+)-activated K+ channels.(ABSTRACT TRUNCATED AT 250 WORDS)
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Lockery, Shawn R., Yan Fang, and Terrence J. Sejnowski. "A Dynamic Neural Network Model of Sensorimotor Transformations in the Leech." Neural Computation 2, no. 3 (September 1990): 274–82. http://dx.doi.org/10.1162/neco.1990.2.3.274.
Full textAbstract:
Interneurons in leech ganglia receive multiple sensory inputs and make synaptic contacts with many motor neurons. These “hidden” units coordinate several different behaviors. We used physiological and anatomical constraints to construct a model of the local bending reflex. Dynamic networks were trained on experimentally derived input-output patterns using recurrent backpropagation. Units in the model were modified to include electrical synapses and multiple synaptic time constants. The properties of the hidden units that emerged in the simulations matched those in the leech. The model and data support distributed rather than localist representations in the local bending reflex. These results also explain counterintuitive aspects of the local bending circuitry.
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Angstadt, J. D., and J. J. Choo. "Sodium-dependent plateau potentials in cultured Retzius cells of the medicinal leech." Journal of Neurophysiology 76, no. 3 (September 1, 1996): 1491–502. http://dx.doi.org/10.1152/jn.1996.76.3.1491.
Full textAbstract:
1. Individual leech Retzius (Rz) cells were removed from mid-body ganglia and plated in cell culture on concanavalin A or polylysine. Experiments on the majority of cells were performed after 6-11 days in culture. Isolated Rz cells were superfused with normal leech saline (NS), cobalt saline (Ca2+ replaced with Co2+), or one of a variety of other modified salines. 2. Prolonged plateau potentials (PPs) with durations ranging from several seconds to nearly 2 min were evoked in isolated Rz cells in response to 1-s depolarizing current pulses delivered under discontinuous current clamp. Some PPs terminated spontaneously while others were terminated with hyperpolarizing current pulses. PPs were associated with a dramatic increase in the input conductance of the neuron. The PP decayed slightly over time, and this decay was accompanied by a small decrease in the input conductance. 3. PP duration was enhanced by penetrating cells with electrodes containing tetraethylammonium (TEA) and by bathing cells in Co2+ saline, but PPs were evoked also in NS and using electrodes without TEA. The effects of TEA and Co2+ saline suggest that voltage-dependent and especially calcium-dependent outward currents normally suppress plateau formation. 4. PPs occurred most reliably in neurons with extensive neurite sprouting. Isolated somata with few or no neurites usually failed to express PP, although there were several exceptions to this trend. 5. PPs persisted when Ca2+ was replaced with either of the calcium channel blockers Co2+, Ni2+, or Mn2+, when 200 microM Cd2+ was added to normal saline, or when Na+ was replaced with Li+. In contrast, PPs were eliminated rapidly when Na+ was replaced with N-methyl-D-glucamine. 6. Isolated Rz cells also expressed repetitive PPs either spontaneously or in response to injection of sustained depolarizing current. Spontaneous repetitive PPs were suppressed by hyperpolarizing current. Repetitive PPs in isolated Rz cells are similar in many respects to the bursting electrical activity induced by Co2+ saline in Rz and other neurons in intact ganglia. 7. The ionic dependence and prolonged duration of PPs suggest that these responses are generated by a persistent voltage-dependent Na+ current. A quantitative computer simulation of PPs was achieved using a depolarization-activated Na+ conductance with very slow inactivation. Repetitive PPs were simulated by addition of a slow outward current in the form of an electrogenic pump.
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Nusbaum, M. P. "Synaptic basis of swim initiation in the leech. III. Synaptic effects of serotonin-containing interneurones (cells 21 and 61) on swim CPG neurones (cells 18 and 208)." Journal of Experimental Biology 122, no. 1 (May 1, 1986): 303–21. http://dx.doi.org/10.1242/jeb.122.1.303.
Full textAbstract:
Serotonin-containing cells 21 and 61 strongly excite a swim central pattern generator (CPG) neurone, cell 208, in nearby segmental ganglia in the leech Macrobdella decora. This excitatory effect is apparently independent of activity in the swim-initiating neurone cell 204, which monosynaptically excites cell 208 (Weeks, 1982b). Cell 208 excites cell 21, apparently directly. This is the first identified direct pathway for feedback from the swim central pattern generator to a swim initiator neurone. Focally applied serotonin has no effect on the soma of cell 208, but causes both excitatory and inhibitory responses in cell 208 when applied to different places within the neuropile. Cell 61 polysynaptically excites distant, posterior cells 208. This excitation is mediated at least in part by the activation of nearby cells 208, which polysynaptically excite posterior cells 208. Cell 208 is dye-coupled intraganglionically to a newly identified pair of neurones, designated cells 18. Cell 208 also excites posterior cells 18, apparently directly. This interaction may be the pathway whereby cell 61 polysynaptically excites posterior cells 208. During swimming, cell 18's membrane potential oscillates in phase with cell 208. Intracellular current injection into cell 18 during swimming perturbs the swim motor pattern. Therefore, cell 18 qualifies as a candidate swim CPG neurone.
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Grey, Kathryn B., and Brian D. Burrell. "Forskolin Induces NMDA Receptor-Dependent Potentiation at a Central Synapse in the Leech." Journal of Neurophysiology 99, no. 5 (May 2008): 2719–24. http://dx.doi.org/10.1152/jn.00010.2008.
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In vertebrate hippocampal neurons, application of forskolin (an adenylyl cyclase activator) and rolipram (a phosphodiesterase inhibitor) is an effective technique for inducing chemical long-term potentiation (cLTP) that is N-methyl-d-aspartate (NMDA) receptor (NMDAR)-dependent. However, it is not known whether forskolin induces a similar potentiation in invertebrate synapses. Therefore, we examined whether forskolin plus rolipram treatment could induce potentiation at a known glutamatergic synapse in the leech ( Hirudo sp.), specifically between the pressure (P) mechanosensory and anterior pagoda (AP) neurons. Perfusion of isolated ganglia with forskolin (50 μM) in conjunction with rolipram (0.1 μM) in Mg2+-free saline significantly potentiated the P-to-AP excitatory postsynaptic potential. Application of 2-amino-5-phosphonovaleric acid (APV, 100 μM), a competitive NMDAR antagonist, blocked the potentiation, indicating P-to-AP potentiation is NMDAR-dependent. Potentiation was blocked by injection of bis-( o-aminophenoxy)- N,N,N′, N′-tetraacetic acid (BAPTA, 1 mM) into the postsynaptic cell, but not by BAPTA injection into the presynaptic neuron, indicating a requirement for postsynaptic elevation of intracellular Ca2+. Application of db-cAMP mimicked the potentiating effects of forskolin, and Rp-cAMP, an inhibitor of protein kinase A, blocked forskolin-induced potentiation. Potentiation was also blocked by autocamtide-2-related inhibitory peptide (AIP), indicating a requirement for activation of Ca2+/calmodulin-dependent kinase II (CaMKII). Finally, potentiation was blocked by botulinum toxin, suggesting that trafficking of glutamate receptors also plays a role in this form of synaptic plasticity. These experiments demonstrate that techniques used to induce cLTP in vertebrate synapses also induce NMDAR-dependent potentiation in the leech CNS and that many of the cellular processes that mediate LTP are conserved between vertebrate and invertebrate phyla.
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ARECHIGA, H., M. CHIQUET, D. P. KUFFLER, and J. G. NICHOLLS. "Formation of Specific Connections in Culture by Identified Leech Neurones Containing Serotonin, Acetylcholine and Peptide Transmitters." Journal of Experimental Biology 126, no. 1 (November 1, 1986): 15–31. http://dx.doi.org/10.1242/jeb.126.1.15.
Full textAbstract:
Connections made in culture by identified leech neurones have been studied using pairs of cells that contain various transmitters. These cells were: motoneurones innervating the heart; the anterior pagoda neurones (which contain both acetylcholine and an FMRFamide-like peptide); the Retzius cells (which contain serotonin); and the pressure sensory neurones, which contain an unidentified transmitter. Heart motoneurones (HE) and anterior pagoda (AP) cells in culture reacted with antiserum against the peptide FMRFamide. The immunoreactive peptide was found in dense-core vesicles at presumptive sites of transmitter release. In culture the HE, AP and Retzius cells formed non-rectifying electrical synapses with one another within 2 days. Some pairs of cells made connections resembling those seen in normal leech ganglia; others formed novel connections seen only in culture. Electrical connections made by sensory P cells with HE and AP cells showed rectification. Confirming earlier results, P cells never established electrical connections with Retzius cells. In certain pairs of neurones, chemically mediated synaptic interactions developed. Thus, stimulation of AP cells evoked hyperpolarizing synaptic potentials that arose after a delay in Retzius cells and in P cells. Similarly, stimulation of HE cells gave rise to delayed, slow synaptic potentials in AP cells and in isolated heart muscle fibres in culture. P cells, which in culture are never presynaptic to Retzius cells, made chemical connections with AP cells. These results support the conclusion that identified leech neurones in culture make synaptic connections with certain specific target cells while ignoring others.
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Dierkes, P. W., P. Hochstrate, and W. R. Schlue. "Distribution and functional properties of glutamate receptors in the leech central nervous system." Journal of Neurophysiology 75, no. 6 (June 1, 1996): 2312–21. http://dx.doi.org/10.1152/jn.1996.75.6.2312.
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1. The effect of kainate and other glutamatergic agonists on the membrane potential (Em), the intracellular Na+ activity (aNai), and the intracellular free Ca2+ concentration ([Ca2+]i) of identified leech neurons and neuropile glial cells was measured with conventional and ion-sensitive microelectrodes, as well as with the use of the iontophoretically injected fluorescent indicators sodium-binding benzofuran isophthalate and Fura-2. 2. In Retzius neurons, AE, L, 8, and 101 motoneurons, and in the unclassified 50 neurons (Leydig cells) and AP neurons, as well as in neuropile glial cells, bath application of 100 microM kainate evoked a marked membrane depolarization and an increase in aNai and [Ca2+]i. The kainate-induced aNai increase persisted in solutions with high Mg2+ concentration in which synaptic transmission is blocked. 3. A membrane depolarization as well as an increase in aNai and [Ca2+]i was also evoked by L-glutamate, quisqualate, and L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA). The agonist-induced [Ca2+]i increase was inhibited by 6,7-dinitroquinoxaline-2,3-dione (DNQX). 4. In Ca(2+)-free solution, the kainate-induced [Ca2+]i increase was abolished in the neurons and in neuropile glial cells, whereas membrane depolarization and aNai increase were unchanged. In Na(+)-free solution, kainate had no effect on Em, aNai, or [Ca2+]i in the neurons. 5. In the mechanosensory T, P, and N neurons, kainate induced considerably smaller membrane depolarizations than in the other neurons or in neuropile glial cells, and it had no significant effect on aNai or [Ca2+]i. 6. It is concluded that in leech segmental ganglia the majority of the neurons and the neuropile glial cells, but probably not the mechanosensory neurons, possess glutamate receptors of the AMPA-kainate type. In the neurons, the [Ca2+]i increase caused by glutamatergic agonists is due to Ca2+ influx through voltage-dependent Ca2+ channels that are activated by the agonist-induced membrane depolarization.
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Lent, C. M., and M. H. Dickinson. "On the termination of ingestive behaviour by the medicinal leech." Journal of Experimental Biology 131, no. 1 (September 1, 1987): 1–15. http://dx.doi.org/10.1242/jeb.131.1.1.
Full textAbstract:
Hungry leeches, Hirudo medicinalis, ingest blood meals averaging 890% of their mass in 29 min. Ingestion is terminated as a result of distension of the body: experimentally distending leeches as they feed causes an immediate cessation of ingestion and inhibits any subsequent biting behaviour; if distension is circumvented by various experimental procedures, leech ingestive periods are prolonged significantly. Ingestion is not terminated as a result of fatigue, chemical cues or mass change. Distension also underlies satiation, for removing blood from the crops of recently fed leeches qualitatively alters their satiated behaviour to biting. Biting is not a defensive reaction to injury. In rostral ganglia, impulses of the serotonergic Retzius (RZ) and LL neurones evoke the physiological components of ingestion. Localized warming of the prostomial lip induces impulses in these large effector neurones. Distending the body wall tonically hyperpolarizes the RZ and LL cells. This inhibitory response to distension is conducted from the mid-body to the anterior neurones via the ventral nerve cord. Distensive inhibition antagonizes the synaptic excitation evoked in RZ and LL neurones by thermal stimulation. Thus, a stimulus which evokes feeding synaptically excites 5-HT neurones and a stimulus which terminates ingestion inhibits them. The integration of these inputs controls the expression of leech feeding behaviour and these connections match precisely a model proposed to regulate the ingestive behaviour of blowflies.
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Groome, J. R., D. K. Vaughan, and C. M. Lent. "Ingestive sensory inputs excite serotonin effector neurones and promote serotonin depletion from the leech central nervous system and periphery." Journal of Experimental Biology 198, no. 6 (June 1, 1995): 1233–42. http://dx.doi.org/10.1242/jeb.198.6.1233.
Full textAbstract:
Thermal and chemical stimuli known to promote ingestive behaviours in the medicinal leech Hirudo medicinalis were tested for their physiological effects on Retzius neurones and for their biochemical effects on serotonin levels in the central nervous system, pharynx and body wall. Retzius neurones throughout the leech nerve cord receive excitatory synaptic input during thermal or chemical stimulation of the prostomial lip. These neurones respond to the rate of change of temperature as well as to absolute temperature at the lip. Exposure of the lip to sodium chloride excites Retzius neurones, whereas exposure to arginine has little effect. Thermal stimulation of the lip elicits a more rapid but less prolonged excitation of Retzius neurones than does chemical stimulation. Stimulation of the prostomial lip is associated with afferent activities in the cephalic nerves D1, D2 and V1-2. Thermal stimulation of the prostomial lip results in depletion of serotonin from midbody ganglia, whereas chemical stimulation has no effect. Conversely, chemical stimulation of the lip results in depletion of serotonin from the body wall, whereas thermal stimulation does not. Pharyngeal serotonin content is decreased with either modality. These data distinguish two important feeding-related sensory input pathways to central serotonergic effector neurones in Hirudo medicinalis.
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Johansen, Jørgen, and Anna L. Kleinhaus. "The effects of procaine, strychnine and penicillin on nociceptive neurons in leech segmental ganglia." Comparative Biochemistry and Physiology Part C: Comparative Pharmacology 86, no. 2 (January 1987): 405–9. http://dx.doi.org/10.1016/0742-8413(87)90104-6.
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Weisblat, David A., David J. Price, and Cathy J. Wedeen. "Segmentation in leech development." Development 104, Supplement (October 1, 1988): 161–68. http://dx.doi.org/10.1242/dev.104.supplement.161.
Full textAbstract:
Segments in glossiphoniid leeches, such as Helobdella triserialis, are the products of stereotyped cell lineages that yield identifiable cells from first cleavage. Cell lines generating segmental tissues are separated from those generating prostomial tissues early in development. Segments arise from five bilateral pairs of longitudinal columns of primary blast cells that are generated by five bilateral pairs of embryonic stem cells called teloblasts. There are four ectodermal cell lines (N, O, P and Q) and one mesodermal cell line (M) on each side of the embryo. In normal development, each cell line generates a segmentally iterated set of identified definitive progeny comprising a mixture of cell types. In the M, O and P cell lines, each blast cell generates one segment's worth of definitive progeny (segmental complement). But the clones of blast cells in each of these three cell lines interdigitate longitudinally with cells of the adjacent clones from the same line, so that the clone of an individual m, o and p blast cell is distributed across more than one segment. Thus, there is no simple clonal basis for morphologically defined segments. In the N and Q cell lines, two blast cells are required to produce one segmental complement of definitive progeny; in each of these two cell lines, two classes of blast cells (nf and ns, qf and qs) are produced in exact alternation. Primary n and q blast cells are about the same size and are produced at the same rate as blast cells for the o and p bandlets, but the longitudinal extent of their clones is roughly half that of the o and p blast cells' clones. During division of the blast cells, the n and q bandlets become compressed relative to the o and p bandlets, so that the segmental complements of the different cell lines can come into register. This compression movement is manifest as a movement of n and q bandlets relative to o and p bandlets in the posterior portion of the germinal band. The number of true segments in leech is fixed at 32; the counting mechanism is not known, but several hypotheses have been disproved. Segmentation in annelids and arthropods differs extensively at the cellular level, yet these phyla are presumed to share a common segmented ancestor. One strategy to identify homologous processes in annelid and arthropod segmentation is to compare the patterns of expression of evolutionarily conserved, developmentally important genes. Preliminary observations using a cross-reacting antibody that is thought to recognize a highly conserved region of a Drosophila segmentation gene, engrailed, labels nuclei of some blast cells early in development and, later, some neurones in the differentiating suboesophageal ganglion.
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Saubermann, Albert J., Carolyn M. Castiglia, and Margaret C. Foster. "Preferential uptake of rubidium from extracellular space by glial cells compared to neurons in leech ganglia." Brain Research 577, no. 1 (April 1992): 64–72. http://dx.doi.org/10.1016/0006-8993(92)90538-k.
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Catarsi, S., and M. Brunelli. "Serotonin depresses the after-hyperpolarization through the inhibition of the Na+/K+ electrogenic pump in T sensory neurones of the leech." Journal of Experimental Biology 155, no. 1 (January 1, 1991): 261–73. http://dx.doi.org/10.1242/jeb.155.1.261.
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In T sensory neurones of the leech, a train of impulses elicited by intracellular electrical stimulation leads to an after-hyperpolarization of up to 30 mV, mainly due to the activation of the electrogenic Na+/K(+)-ATPase but partly to a Ca2(+)-activated K+ conductance. It was found that serotonin reversibly reduced the amplitude of this after-hyperpolarization. We investigated the mechanism of action of serotonin and found: (1) after inhibition of the Ca2(+)-activated K+ conductance with BaCl2 or CdCl2, serotonin was still able to reduce the after-hyperpolarization; (2) when penetration of T cells with microelectrodes leaking sodium was preceded by serotonin perfusion of the ganglia, the normal hyperpolarization due to the activation of the electrogenic pump was converted to a depolarization; (3) after long-lasting perfusion with K(+)-free saline solution (which inhibits the Na+/K+ pump), the application of CsCl caused repolarization by reactivating the electrogenic ATPase; serotonin slowed and reduced this repolarization; (4) serotonin potentiated the depolarization of T neurones caused by the inhibition of the Na+/K+ pump following cooling of ganglia and depressed the hyperpolarization after rewarming to room temperature. These data taken together suggest that serotonin directly inhibits the Na+/K+ electrogenic pump.
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Shaw, Brian K., and William B. Kristan. "Relative Roles of the S Cell Network and Parallel Interneuronal Pathways in the Whole-Body Shortening Reflex of the Medicinal Leech." Journal of Neurophysiology 82, no. 3 (September 1, 1999): 1114–23. http://dx.doi.org/10.1152/jn.1999.82.3.1114.
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The whole-body shortening reflex of the medicinal leech Hirudo medicinalis is a withdrawal response produced by anterior mechanical stimuli. The interneuronal pathways underlying this reflex consist of the S cell network (a chain of electrically coupled interneurons) and a set of other, parallel pathways. We used a variety of techniques to characterize these interneuronal pathways further, including intracellular stimulation of the S cell network, photoablation of the S cell axon, and selective lesions of particular connectives (the axon bundles that link adjacent ganglia in the leech nerve cord). These experiments demonstrated that the S cell network is neither sufficient nor necessary for the production of the shortening reflex. The axons of the parallel pathways were localized to the lateral connectives (whereas the S cell axon runs through the medial connective). We used physiological techniques to show that the axons of the parallel pathways have a larger diameter in the anterior connective and to demonstrate that the parallel pathways are activated selectively by anterior mechanosensory stimuli. We also presented correlative evidence that the parallel pathways, along with activating motor neurons during shortening, are responsible for inhibiting a higher-order “command-like” interneuron in the neuronal circuit for swimming, thus playing a role in the behavioral choice between swimming and shortening.
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Wilson, R. J., W. B. Kristan, and A. L. Kleinhaus. "An increase in activity of serotonergic Retzius neurones may not be necessary for the consummatory phase of feeding in the leech Hirudo medicinalis." Journal of Experimental Biology 199, no. 6 (June 1, 1996): 1405–14. http://dx.doi.org/10.1242/jeb.199.6.1405.
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During the consummatory phase of feeding, in which blood is ingested, medicinal leeches display a characteristic set of behaviours: they extend their jaws, are less responsive to sensory input, produce mucus, relax the body wall and exhibit waves of peristalsis that can run the length of the body. Earlier reports suggested that this pattern of behaviour is orchestrated by serotonin released from Retzius cells in response to the appropriate sensory stimulation of the lip. We have developed a semi-intact preparation in which only the nervous system in the posterior half of the leech was exposed. The front half of the leech was free to explore, bite through and feed until satiated from a blood-filled sausage casing while continuous intracellular and extracellular recordings were made from identified cells and the nerve roots of the exposed segments. Prior to attachment of the animal to the feeding device, the firing frequency of the Retzius cell increased transiently during spontaneous movements or tactile stimuli to its front or posterior end. In contrast, Retzius cell activity decreased after the anterior sucker attached to the membrane of the feeding device at about the time when ingestion was initiated. Increased activity of Leydig cells, which are known to modulate several circuits in the leech, was also associated with exploration. However, unlike that of Retzius cells, the activity of Leydig cells increased significantly following the onset of consumption. These results suggest that increased activity of Retzius cells in midbody ganglia is not a prerequisite for the consummatory phase of feeding and raises questions regarding the role of serotonin in regulating this behaviour.