Abstract
The mammalian diving response (DR) is a remarkable behavior that was first formally studied by Laurence Irving and Per Scholander in the late 1930s. The DR is called such because it is most prominent in marine mammals such as seals, whales, and dolphins, but nevertheless is found in all mammals studied. It consists generally of breathing cessation (apnea), a dramatic slowing of heart rate (bradycardia), and an increase in peripheral vasoconstriction. The DR is thought to conserve vital oxygen stores and thus maintain life by directing perfusion to the two organs most essential for life—the heart and the brain. The DR is important, not only for its dramatic power over autonomic function, but also because it alters normal homeostatic reflexes such as the baroreceptor reflex and respiratory chemoreceptor reflex. The neurons driving the reflex circuits for the DR are contained within the medulla and spinal cord since the response remains after the brainstem transection at the pontomedullary junction. Neuroanatomical and physiological data suggesting brainstem areas important for the apnea, bradycardia, and peripheral vasoconstriction induced by underwater submersion are reviewed. Defining the brainstem circuit for the DR may open broad avenues for understanding the mechanisms of suprabulbar control of autonomic function in general, as well as implicate its role in some clinical states. Knowledge of the proposed diving circuit should facilitate studies on elite human divers performing breath-holding dives as well as investigations on sudden infant death syndrome (SIDS), stroke, migraine headache, and arrhythmias. We have speculated that the DR is the most powerful autonomic reflex known.
Highlights
The complexity of an animal’s behavior is paralleled by the complexity of the neural systems driving that behavior
The diving response (DR) is a dramatic perturbation of normal function, altering basic homeostatic mechanisms to fit physiological needs. This review emphasizes both the reflex nature of the DR and its neuronal circuitry maintained in the medulla and spinal cord, like numerous other reflexes
Many stimuli affecting paranasal areas initiate the DR, and nerves innervating these areas serve as its afferent limb
Summary
The complexity of an animal’s behavior is paralleled by the complexity of the neural systems driving that behavior. The mammalian DR is usually considered to consist of three independent reflex behaviors: an apnea, a parasympathetically mediated bradycardia and a sympathetically mediated peripheral vasoconstriction (Irving, 1938, 1939; Irving et al, 1942); splenic contraction is sometimes considered a fourth behavior by some (Cabanac et al, 1997, 1998; Cabanac, 2000) These autonomic adjustments are marked mostly in marine mammals such as seals, dolphins, or whales, which spend considerable time submerged underwater. This review focuses on the neural control of the DR only in terrestrial mammals, rodents, and differs from most previous reviews which emphasize the adaptations and physiological consequences of aquatic mammals to underwater submersion with little or no discussion on central neural integration This differs from a previous review (Panneton, 2013) by emphasizing a brainstem reflex circuit driving the DR and a more detailed exploration on its suprabulbar control as well as how this response may help humans clinically. The vasoconstriction seen with diving is mediated via the sympathetic NS (Yavari et al, 1996; McCulloch et al, 1999b), maintaining internal oxygen stores for the brain and the heart (Ollenberger and West, 1998b)
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