The Influence of Gravitational Gradients on American Alligators (Alligator Mississippiensis)

Abstract

BackgroundCranial fluids of vertebrae mammals are composed of arterial blood, venous blood, and cerebrospinal fluid that can be altered by orthostatic pressures; head‐down postures can elevate intracranial pressure and carotid/jugular luminal area while head up postures produce opposite effects. Previous studies on aquatic and terrestrial snakes showed cardiovascular variation while arboreal snakes showed little cardiovascular variation during orthostatic transitions. Little experimental work regarding orthostatic transitions has been done on alligators. Alligators are known to have unique blood flow patterns due to active regulation of blood flow. The purpose of this study is to investigate the effects of gravitational tilt on vessel luminal diameter and ICP in alligators.MethodsLive adult alligators (n = 5, 165 – 183 cm total length) were subjected to gravitational tilts between 45° head‐up to 45° head‐down in 15° increments. Short (30 s) and long (120 s) duration tilts were performed to assess barostatic reflex and ICP using ocular ultrasonography, respectively. Vascular ultrasonography was also used to assess luminal diameter of the carotid artery and jugular vein. Instantaneous heart rate was inferred from EKG recordings throughout tilts.ResultsThroughout orthostatic transitions, ocular ultrasonography revealed an increase in optic nerve sheath diameter (head down tilts) and a decrease in optic nerve sheath diameter (head up tilts). Head down tilts resulted in jugular and carotid dilation while head up tilts resulted in various jugular luminal diameters and minimal change in carotid diameter. Heart rate increased at the onset of all orthostatic transitions. There was no evidence for a barostatic response.ConclusionsOcular ultrasonography was used to non‐invasively assess intracranial pressure of reptiles. There was a linear relationship between orthostatic transitions and intracranial pressure due to redistribution of CSF. Compared to previous studies, orthostatic transitions produced similar results on vessel flow and diameter. Variations of vessel flow and diameter may be attributed to unusual patters of heart rate or blood shunts in the cephalic venous system. Increases in heart rate in all rotations may be due to a fear response. Additional studies are needed to further understand the underlying regulatory mechanisms that give rise to the alligator's heart rate and blood flow patterns.Support or Funding InformationFunding: The Influence of Gravitational Gradients on American Alligators (Alligator Mississippiensis) project has been funded by A.T. Still University's Masters in Biomedical Sciences program.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.