Anatomy & Physiology: Current Research
Open Access

Abstract

The Influence of Gravitational Gradients on the American Alligator (Alligator mississippiensis)

Lucas Knoche, Bruce A. Young* and Tatyana Kondrashova

The cardiovascular systems of terrestrial and aquatic snakes cannot accommodate gravitational gradients, while blood flow in arboreal snakes is not disrupted by tilting. Alligators have a very dynamic cardiovascular system, with multiple means of active regulation; however, the response of alligators to gravitational gradients has never been documented. Gravitational gradients were induced by rotating sub-adult specimens of the American alligator (Alligator mississippiensis) between 45° head-up to 45° head-down in 15° increments. Intracranial pressure was assayed by quantifying the diameter of the optic nerve sheath using ocular ultrasonography; each increment of head-up rotation produced a significant decrease in nerve sheath diameter, while head-down rotations resulted in corresponding significant increases in nerve sheath diameter. Vascular ultrasonography revealed a consistent pattern. Head-down rotation resulted in vasodilation of the carotid artery and jugular vein, and head-up rotation resulted in a decrease in the luminal area of these vessels. In contrast to these manifestations of orthostatic pressure gradients, instantaneous heart rate (determined by EKG) revealed no evidence for a barostatic reflex in A. mississippiensis. This is the first report from a non-mammalian vertebrate of how intracranial pressure varies under gravitational gradients. The alligator has a unique response to gravitational gradients, characterized by the lack of a barostatic reflex.

Published Date: 2019-10-23; Received Date: 2019-10-07