Academic literature on the topic 'Dorsal longitudinal ascending'

In both invertebrate and lower vertebrate species, decussated commissural axons travel away from the midline and assume positions within distinct longitudinal tracts. We demonstrate that in the developing chick and mouse spinal cord, most dorsally situated commissural neuron populations extend axons across the ventral midline and through the ventral white matter along an arcuate trajectory on the contralateral side of the floor plate. Within the dorsal (chick) and intermediate (mouse) marginal zone, commissural axons turn at a conserved boundary of transmembrane ephrin expression, adjacent to which they form a discrete ascending fiber tract. In vitro perturbation of endogenous EphB-ephrinB interactions results in the failure of commissural axons to turn at the appropriate dorsoventral position on the contralateral side of the spinal cord; consequently, axons inappropriately invade more dorsal regions of B-class ephrin expression in the dorsal spinal cord. Taken together, these observations suggest that B-class ephrins act locally during a late phase of commissural axon pathfinding to specify the dorsoventral position at which decussated commissural axons turn into the longitudinal axis.

The aim of this study was to assess the usefulness of ultrasonographic examination of the large intestine in 10 clinically healthy Jersey/Red Sindhi crossbred cows. The area extending from the tuber coxae to the 6^th intercostal space (ICS) and from the lumbar transverse processes to the linea alba on the right side was shaved. An imaginary line was drawn from the distal third of the femur up to the 8^th ICS parallel to the longitudinal axis of the cow. The large intestine was scanned dorsal to this imaginary line. Only the near wall of the large intestine adjacent to the abdominal wall could be imaged ultrasonographically. Based on the topographical anatomy, the ultrasonographic images of the caecum and the proximal loop of the ascending colon (PLAC), resembling the ‘arc of a circle’, were observed in the mid to dorsal right paralumbar fossa and the 12^th ICS; however, the caecum and the PLAC could not be differentiated with certainty using ultrasonography. Similarly, the ultrasonographic images of the spiral loop of the ascending colon (SLAC), resembling a ‘cycloid’, could be imaged through the 12^th to 11^th ICSs and in the dorsal right paralumbar fossa; yet, ultrasonographically, it was difficult to differentiate the SLAC from the descending loop of the ascending colon, transverse colon, and descending colon, respectively. The differences (qualitative and quantitative) in the degrees of curvatures of various ultrasonographic images of parts of the large intestine were also not helpful. In conclusion, ultrasonographic imaging of various parts of the bovine large intestine should be interpreted with caution.  

We describe the new basal abelisauroid dinosaur Austrocheirus isasii gen. et sp. nov. from the Late Cretaceous Pari Aike Formation of southwestern Patagonia, Argentina. The preserved remains include manual bones, a distal tibia, and some pedal and axial elements. Austrocheirus is differentiated from other basal theropods by the presence of metacarpal III with a dorsoventrally compressed shaft and posteriorly displaced collateral tendon fossae located at the same level of the proximal end of distal condyles, and pedal phalanges with a conspicuous longitudinal crest delimitating the dorsal margin of the distal collateral tendon fossae. A cladistic analysis recovered the new species as more derived than Ceratosaurus and Berberosaurus, but within a polytomy at the base of Abelisauroidea, an assignment supported by two abelisauroid synapomorphies: distal end of tibia with a planar vertical scar for the reception of the ascending process of the astragalus that occupies most of its anterior surface and is medially bounded by the longitudinally oriented facet; and scar for the reception of the ascending process with a median vertical ridge, which imbeds into a crescentic vertical groove on the posterior surface of the ascending process of the astragalus forming an interlocking tibiotarsal articulation. Furthermore, Austrocheirus represents the first known medium-sized Late Cretaceous abelisauroid bearing nonatrophied hands. The evidence provided here suggests that the strong reduction of the forelimb recorded in derived abelisaurids is not directly correlated with their increased body-size, but it seems to be an evolutionary event exclusive to this lineage within Ceratosauria.

Using intracellular recording techniques in stationary walking crickets (Gryllus bimaculatus), we have investigated the relationship between locomotion and the activity of interneurones ascending from the terminal ganglion. Nine different types of giant interneurones (GI) were characterized during walking and standing. One third of them reduced their activity, while the others enhanced their spike rate, during walking. These physiological properties were strictly correlated with morphological characteristics such as axon position in the longitudinal tracts of the terminal ganglion. In general, ventral GIs reduced and dorsal GIs increased their spike frequency during walking. In some of them, there was a weak but significant correlation between the spike rate and translational speed, but no correlation with rotational speed. In all GIs except 10-3a, the changes in activity occurred at the start of walking. In GI 10-3a, an increase in membrane potential and spike rate was observed before the start of locomotion. Therefore, an intrinsic mechanism within the central nervous system operating on GI 10-3a is suggested. Additionally, the activities of filiform hair receptors and of previously undescribed small ascending interneurones (SAI) have been studied during walking. About 80 % of the receptors slightly increased their spike rate during walking, while one SAI became more active during walking and another one was hardly affected. The physiological properties of ascending interneurones are discussed with respect to their modulation and particular function during walking.

In vivo measurements of pectoralis muscle force during different modes of free flight (takeoff, level flapping, landing, vertical ascending and near vertical descending flight) were obtained using a strain gauge attached to the dorsal surface of the delto-pectoral crest (DPC) of the humerus in four trained pigeons (Columba livia). In one bird, a rosette strain gauge was attached to the DPC to determine the principal axis of strain produced by tension of the pectoralis. Strain signals recorded during flight were calibrated to force based on in situ measurements of tetanic force and on direct tension applied to the muscle's insertion at the DPC. Rosette strain recordings showed that at maximal force the orientation of tensile principal strain was −15° (proximo-anterior) to the perpendicular axis of the DPC (or +75° to the longitudinal axis of the humerus), ranging from +15 to −25° to the DPC axis during the downstroke. The consistency of tensile principal strain orientation in the DPC confirms the more general use of single-element strain gauges as being a reliable method for determining in vivo pectoralis force generation. Our strain recordings show that the pectoralis begins to develop force as it is being lengthened, during the final one-third of the upstroke, and attains maximum force output while shortening during the first one-third of the downstroke. Force is sustained throughout the entire downstroke, even after the onset of the upstroke for certain flight conditions. Mean peak forces developed by the pectoralis based on measurements from 40 wingbeats for each bird (160 total) were: 24.9+/−3.1 N during takeoff, 19.7+/−2.0 N during level flight (at speeds of about 6–9 m s-1 and a wingbeat frequency of 8.6+/−0.3 Hz), 18.7+/−2.5 N during landing, 23.7+/−2.7 N during near-vertical descent, and 26.0+/−1.8 N during vertical ascending flight. These forces are considerably lower than the maximum isometric force (67 N, P0) of the muscle, ranging from 28 % (landing) to 39 % (vertical ascending) of P0. Based on estimates of muscle fiber length change determined from high- speed (200 frames s-1) light cine films taken of the animals, we calculate the mass-specific power output of the pigeon pectoralis to be 51 W kg-1 during level flight (approximately 8 m s-1), and 119 W kg-1 during takeoff from the ground. When the birds were harnessed with weighted backpacks (50 % and 100 % of body weight), the forces generated by the pectoralis did not significantly exceed those observed in unloaded birds executing vertical ascending flight. These data suggest that the range of force production by the pectoralis under these differing conditions is constrained by the force- velocity properties of the muscle operating at fairly rapid rates of shortening (4.4 fiber lengths s-1 during level flight and 6.7 fiber lengths s-1 during takeoff).

Electrical stimulation with high-frequency (2–10 kHz) sinusoidal currents has previously been shown to produce a transient and complete nerve block in the peripheral nervous system. Modeling and in vitro studies suggest that this is due to a prolonged local depolarization across a broad section of membrane underlying the blocking electrode. Previous work has used cuff electrodes wrapped around the peripheral nerve to deliver the blocking stimulus. We extended this technique to central motor pathways, using a single metal microelectrode to deliver focal sinusoidal currents to the corticospinal tract at the cervical spinal cord in anesthetized adult baboons. The extent of conduction block was assessed by stimulating a second electrode caudal to the blocking site and recording the antidromic field potential over contralateral primary motor cortex. The maximal block achieved was 99.6%, similar to findings of previous work in peripheral fibers, and the optimal frequency for blocking was 2 kHz. Block had a rapid onset, being complete as soon as the transient activation associated with the start of the sinusoidal current was over. High-frequency block was also successfully applied to the pyramidal tract at the medulla, ascending sensory pathways in the dorsal columns, and the descending systems of the medial longitudinal fasciculus. High-frequency sinusoidal stimulation produces transient, reversible lesions in specific target locations and therefore could be a useful alternative to permanent tissue transection in some experimental paradigms. It also could help to control or prevent some of the hyperactivity associated with chronic neurological disorders.

Wing upstroke in birds capable of powered flight is kinematically the most complicated phase of the wingbeat cycle. The M. supracoracoideus (SC), generally considered to be the primary elevator of the wing, is a muscle with a highly derived but stereotyped morphology in modern flying birds. The contractile portion of the SC arises from a ventral sternum, but its tendon of insertion courses above the glenohumeral joint to insert on the dorsal surface of the humerus. To clarify the role of the SC during wing upstroke, we studied its contractile and mechanical properties in European starlings (Sturnus vulgaris) and pigeons (Columba livia), two birds with contrasting flight styles. We made in situ measurements of isometric forces of humeral elevation and humeral rotation and, in addition, measured the extent of unrestrained humeral excursion during stimulation of the muscle nerve. We also generated passive and active length-force curves for the SC of each species. Stimulation of the SC at humeral joint angles of elevation/depression and protraction/retraction coincident with the downstroke-upstroke transition and mid-upstroke produced substantially higher forces of long-axis rotation than elevation. When the humerus was allowed to move (rotate/elevate) during stimulation, we observed rotation about its longitudinal axis of up to 70-80 degrees , but humeral elevations of only 40-60 degrees above the horizontal (as measured in lateral view). In the active length-force experiments, we measured mean (+/-s.d.) maximal tetanic forces of 6.5+/-1.2 N for starlings (N=4) and 39.4+/-6.2 N for pigeons (N=6), unexpectedly high forces approximately 10 times body weight. The working range of the SC in both species corresponds to the ascending limb (but not the plateau) of the active length-force curve. The potential for greatest active force is high on the ascending limb at joint angles coincident with the downstroke-upstroke transition, a time when the humerus is depressed below the horizontal and rotated forward maximally. As the SC shortens to counterrotate and elevate the humerus during early upstroke, the potential for active force at shorter lengths declines at a relatively rapid rate. These findings reveal that the primary role of the SC is to impart a high-velocity rotation of the humerus about its longitudinal axis, which rapidly elevates the distal wing. This rapid twisting of the humerus is responsible for positioning the forearm and hand so that their subsequent extension orients the outstretched wing in the parasagittal plane appropriate for the subsequent downstroke. We propose that, at the downstroke-upstroke transition, variable levels of co-contraction of the M. pectoralis and SC interact to provide a level of kinematic control at the shoulder that would not be possible were the two antagonists to work independently. The lack of a morphologically derived SC in Late Jurassic and Early Cretaceous birds precluded a high-velocity recovery stroke which undoubtedly limited powered flight in these forms. Subsequent evolution of the derived SC capable of imparting a large rotational force to the humerus about its longitudinal axis was an important step in the evolution of the wing upstroke and in the ability to supinate (circumflex) the manus in early upstroke, a movement fundamental to reducing air resistance during the recovery stroke.

The so called anterior meningeal artery (AMA) is a branch of the vertebral artery (VA), which had been interpreted as a supplying vessel of the dura in the foramen magnum and upper cervical level. In this study, we examined the anatomy of this artery and relationships to its surrounding structures for treatment modalities. With the aid of magnification, five adult cadaveric head and neck complex and five cervical spines were examined after perfusion of the vessels with colored silicone. The AMA arose from the VA between the C2 and C3 level, and passed medially through the intrervertebral foramen anterior to the dural sheath of the third cervical nerve root. It ran upwards dorsal to the deep layer of the posterior longitudinal ligament (PLL) with anterior internal vertebral venous plexus. Rostrally, it formed an arcade above the apex of the odontoid process with its contralateral mate. The AMA gave off several tiny branches to the deep layer of the PLL, ligaments and soft tissues above the apex of the odontoid process, and vertebral bodies of the axis. At the level of the foramen magnum, it ended in several small twigs to the dura. Anastomoses between the AMA system and adjacent vessels were observed. One was directed through the hypoglossal canal to the ascending pharyngeal artery and the other was with the V3 segment of the VA. The origin and course of the two AMA, and anastomoses were symmetric. Although the AMA feeds the ventral dura of the foramen magnum, the perfusion area is larger than its name suggests, including the bony and ligamentous structures in the craniovertebral junction. Anatomical knowledge of the AMA, including its anastomoses and layer relationships to the surrounding structures, may help to perform treatment modalities in this region rationally.

Extracellular unit spikes were recorded in and around the Y-group nucleus in the anesthetized cat. Target (T) neurons of floccular caudal zone inhibition were identified by observing cessation of their spontaneous discharges following stimulation of the floccular caudal zone. The axonal trajectories of the T neurons to the rostral brain stem were studied by observing the antidromic responses of single neurons during systematic tracking with a stimulating microelectrode in the brain stem. The axons of the T neurons pass through a region closely ventral to the lateral part of the brachium conjunctivum (BC), continue rostrally in a region between the BC and the lateral lemniscus, arch medially around the rostral part of the nucleus reticularis tegmenti pontis, cross the midline, continue to the contralateral side by about 1.5 mm lateral from the midline, arch rostrally, run in the central tegmental field on the contralateral side, arch dorsomedially around the caudal pole of the red nucleus, and enter the contralateral oculomotor nucleus (OMN) from the ventrolateral side. In the caudal half of the contralateral OMN, the axons of the T neurons branch out and terminate. The T neurons were exclusively located in the dorsal subdivision of the Y-group nucleus (DY), whereas some were in the medial part of the subnucleus lateralis parvocellularis (SLP, Ref. 12) of the lateral cerebellar nucleus. T neurons were not found in the ventral subdivision of the Y-group nucleus (VY). Differences in neuronal connections between the DY and VY neurons were investigated by observing responses of single neurons to stimulation of the contralateral OMN, the ipsilateral floccular caudal zone, the ipsilateral eighth nerve (i8N), and the contralateral eighth nerve (c8N). Most neurons in the DY and the adjacent medial part of the SLP, receiving inhibitory inputs from the ipsilateral flocculus (exclusively from the caudal zone), project to the contralateral OMN, and about one-half of these neurons receive polysynaptic inputs from the i8N and the c8N. On the other hand, most neurons in the VY receive monosynaptic inputs from the i8N, and some of these neurons project to the ipsilateral flocculus. The neuronal tract via the ventral part of the pontine tegmentum demonstrated in the present experiments is distinct from the classically established vestibulooculomotor tracts via the BC, the medial longitudinal fasciculus, or the ascending tract of Deiters. We call this tract the 'crossing ventral tegmental tract'. Previously, we reported that electrical stimulation of the caudal zone elicited conjugate downward eye movement.(ABSTRACT TRUNCATED AT 400 WORDS)

Spinal cord neurons were investigated in embryos of Triturus vulgaris , the smooth newt, just prior to hatching. These embryos can swim if freed from their egg membranes. Horseradish peroxidase (HRP) labelling, together with GABA and glycine immunocytochemistry (ICC), revealed nine distinct anatomical classes of neuron. 1. Ventrolateral motorneurons with mainly dorsal dendrites, sometimes a descending central axon and peripheral axon innervating the trunk muscles. 2. Dorsal primary sensory Rohon-Beard neurons innervating skin and with dorsal ascending and descending axons in spinal cord. 3. Commissural interneurons with mid-cord unipolar soma, glycine-like immunoreactivity, dendrites on initial segment of ventral axon which crosses cord to ascend or branch. 4. Dorsolateral commissural interneurons with multipolar soma in dorsolateral position with dorsal dendrites and ventral axon which crosses and ascends or branches. 5. Giant dorsolateral commissural interneurons with large dorsolateral somata widely spaced (130- 250 µm spacing) with process projecting dorsally to other side, dorsolateral dendrites and ventral axon which crosses to ascend and branch. 6. Dorsolateral ascending interneurons in dorsolateral position with multipolar soma and ascending axon on same side. 7. Ascending interneurons with unipolar soma, GABA-like immunoreactivity and ascending axon on same side. 8. Descending interneurons with bi- or multi-polar soma, extensive dorsal and ventral dendrites, and descending axon on same side. They may also have ascending axons. 9. Kolmer-Agduhr cerebrospinal fluid contacting neurons with cilia and microvilli in lateral corners of neural canal, GABA-like immunoreactivity, no dendrites and ascending axon. Eight of the nine cell classes were found to bear a marked resemblance to neurons previously described in zebrafish and Xenopus embryos in terms of their anatomy, distribution and immunoreactivity to GABA and glycine. Homologies and possible functions are discussed. Giant dorsolateral commissural neurons, were not found in Xenopus or teleosts but were present in Ambystoma mexicanum and Neoceratodus . The regular, possibly segmental longitudinal distribution pattern of these cells within the cord is unusual amoung amphibian spinal neurons.

The dorsal longitudinal ascending (DoLA) interneurons are an uncommon, seemingly irregularly distributed interneuron type of the developing embryonic zebrafish spinal cord. For reasons not yet understood DoLA interneurons express tbx16, a T-box transcription factor originally recognised for its important role in mesodermal development. This is the only cell type expressing tbx16 in the developing spinal cord, making DoLA neurons one of the few neuronal types that can be identified by expression of a unique molecular marker. Throughout the natural world regularity in pattern formation is frequent; mechanisms that direct the production of regular patterns have been studied and many are well understood. The creation of irregular "patterns", especially in embryo development has been subjected to far less analysis. This is largely because studies in developmental biology frequently involve methods that disrupt regular patterning while the disruption of an irregular pattern is likely to result in similarly irregular pattern. The DoLA interneurons with their unique genetic marker offer a rare opportunity to investigate the mechanisms behind irregular patterns in development. This is of particular importance in the development of the spinal cord, as most of the known vertebrate spinal interneurons appear to have irregular distributions. The main focus of the research presented in this thesis has been to try to understand how the distribution pattern of DoLA interneurons is generated. This knowledge may then be extended to other spinal neurons and possibly to other irregular developmental patterns. In the work described in this thesis the distribution of DoLA interneurons has been extensively examined statistically. It was found that there is an underlying cryptic organisation to their peculiar distribution. This led to the surprising discovery that these neurons migrate rostrally a significant distance along the spinal cord. These neurons were also found in larval zebrafish at much older times than has previously been described, suggesting that they may play a role in post-embryonic stages. Notch signalling appears to have an influence on DoLA interneuron distribution since perturbing Presenilin (Psen) function affects the number of these cells. Interestingly, DoLA cell number is not affected when Psen1 function is inhibited but increases when Psen2 function is inhibited. Furthermore the wild type level of DoLA interneuron number can be partially rescued by inhibiting Psen1 function in combination with inhibition of Psen2 function. The creation of transgenic zebrafish lines where GFP is transcribed from tbx16 promoter sequence is described. These animals were produced to attempt to discover more about the patterning of DoLA interneurons and the function of tbx16 during development. Serendipitously, one of these transgenic lines expresses GFP in the commissural primary ascending (CoPA) interneurons. This led to the discovery that the CoPA interneurons are marked by mafba/valentino, revealing a new unique spinal neuron molecular marker.
Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2011