Academic literature on the topic 'Mammalian diving reflex'

The mammalian diving response is a remarkable behavior that overrides basic homeostatic reflexes. It is most studied in large aquatic mammals but is seen in all vertebrates. Pelagic mammals have developed several physiological adaptations to conserve intrinsic oxygen stores, but the apnea, bradycardia, and vasoconstriction is shared with those terrestrial and is neurally mediated. The adaptations of aquatic mammals are reviewed here as well as the neural control of cardiorespiratory physiology during diving in rodents.

Underwater submersion in mammals induces apnea, parasympathetically mediated bradycardia, and sympathetically mediated peripheral vasoconstriction. These effects are collectively termed the diving response, potentially the most powerful autonomic reflex known. Although these physiological responses are directed by neurons in the brain, study of neural control of the diving response has been hampered since 1) it is difficult to study the brains of animals while they are underwater, 2) feral marine mammals are usually large and have brains of variable size, and 3) there are but few references on the brains of naturally diving species. Similar responses are elicited in anesthetized rodents after stimulation of their nasal mucosa, but this nasopharyngeal reflex has not been compared directly with natural diving behavior in the rat. In the present study, we compared hemodynamic responses elicited in awake rats during volitional underwater submersion with those of rats swimming on the water's surface, rats involuntarily submerged, and rats either anesthetized or decerebrate and stimulated nasally with ammonia vapors. We show that the hemodynamic changes to voluntary diving in the rat are similar to those of naturally diving marine mammals. We also show that the responses of voluntary diving rats are 1) significantly different from those seen during swimming, 2) generally similar to those elicited in trained rats involuntarily “dunked” underwater, and 3) generally different from those seen from dunking naive rats underwater. Nasal stimulation of anesthetized rats differed most from the hemodynamic variables of rats trained to dive voluntarily. We propose that the rat trained to dive underwater is an excellent laboratory model to study neural control of the mammalian diving response, and also suggest that some investigations may be done with nasal stimulation of decerebrate preparations to decipher such control.

The mammalian diving response is a dramatic autonomic adjustment to underwater submersion affecting heart rate, arterial blood pressure, and ventilation. The bradycardia is known to be modulated by the parasympathetic nervous system, arterial blood pressure is modulated via the sympathetic system, and still other circuits modulate the respiratory changes. In the present study, we investigate the submergence of rats brought past their aerobic dive limit, defined as the diving duration beyond which blood lactate concentration increases above resting levels. Hemodynamic measurements were made during underwater submergence with biotelemetric transmitters, and blood was drawn from cannulas previously implanted in the rats' carotid arteries. Such prolonged submersion induces radical changes in blood chemistry; mean arterial Pco2 rose to 62.4 Torr, while mean arterial Po2 and pH reached nadirs of 21.8 Torr and 7.18, respectively. Despite these radical changes in blood chemistry, the rats neither attempted to gasp nor breathe while underwater. Immunohistochemistry for Fos protein done on their brains revealed numerous Fos-positive profiles. Especially noteworthy were the large number of immunopositive profiles in loci where presumptive chemoreceptors are found. Despite the activation of these presumptive chemoreceptors, the rats did not attempt to breathe. Injections of biotinylated dextran amine were made into ventral parts of the medullary dorsal horn, where central fibers of the anterior ethmoidal nerve terminate. Labeled fibers coursed caudal, ventral, and medial from the injection to neurons on the ventral surface of the medulla, where numerous Fos-labeled profiles were seen in the rats brought past their aerobic dive limit. We propose that this projection inhibits the homeostatic chemoreceptor reflex, despite the gross activation of chemoreceptors.

In neurophysiological terms, divergence describes the transmission of impulse traffic from a single afferent line, through an integrating nervous system, and out into multiple efferent lines. This feature has been ascribed to the vertebrate central nervous system and invertebrate ganglionic systems but has not yet been associated with the autonomic nervous system in mammals. Therefore, this study investigated the degree of divergence of afferent impulse traffic through a mammalian autonomic ganglion, the inferior mesenteric ganglion (IMG) in guinea pig. Multiunit discharges were recorded extracellularly from the peripheral nerves, which emerge from the IMG, to determine the lines of efferent outflow (i.e., divergence) of impulse traffic generated by stimulating central efferent and peripheral afferent nerves. Pathways interrupted by a cholinergic ganglion synapse were identified by using hexamethonium. Pathways running directly through the IMG were identified by studying the effects of dividing nerves surgically. A complex arrangement of ascending and descending pathways was revealed, showing a neural network that interconnects the upper gastrointestinal tract, distal colon, and pelvic viscera via prevertebral ganglia.

Darren O’Donnell (b. 1965) is a writer, director, actor, playwright, and designer, and the artistic director of the highly decorated Mammalian Diving Reflex. My study is focused on his work in social acupuncture, outlined in his Social Acupuncture: A guide to suicide, performance, and utopia (2006). Social acupuncture is a style of theatre/performance art that “blurs the line between art and life,”impelling people to come together in unusual ways and tap into the power of the social sphere. With social acupuncture, O’Donnell and Mammalian Diving Reflex are striving to create an aesthetic of civic engagement: an avenue through which social edifices like public space, schools, and the media can be used as the armature for the mounting of work that “takes modest glances at simple power dynamics and, for a moment, provides a glimpse of other possibilities.” Mammalian Diving Reflex began their exploration of the form in the summer of 2003 with The Talking Creature, and since then have devised and performed almost two‐ dozen similar “needles” worldwide.Social acupuncture warrants examination not only from a socio‐ political perspective, but through a theatrical lens, as well. It probes the relationship between audience and performer, raises questions about theatre’s ability to keep up with other media in the digital age, and offers tremendous insight into the potential for positive, fruitful intersections between art and civil society. My project will include theoretical examination of O’Donnell’s work, as well as practical exploration of the form’s potential.