The Influence of Movement on the Cerebrospinal Fluid Pressure of the American Alligator (Alligator mississippiensis)

SIMPLE SUMMARY: The cerebrospinal fluid (CSF) supports, nourishes, and cleans the brain and spinal cord. Fulfilling these functions requires a certain dynamic of the CSF, it is constantly being produced (primarily via arterial fluid loss), circulates around and through the brain and spinal cord, then is constantly being lost (primarily to the venous and lymphatic systems). The dynamics of the CSF are greatly influenced, if not driven, by the fluid pressure of the CSF, but the origins and magnitude of the CSF fluid pressure are poorly understood. Earlier experimental and clinical studies documented how arterial pressure and the ventilatory cycle influence CSF pressure; recent studies, mainly using telemetric recordings, have shown that movement increases the magnitude and variation of CSF pressure. The present study was designed to explore the relative contributions of specific body movements to CSF fluid pressure; these movements include physiological (as occurs during ventilation), postural, or physical displacements (bending or locomotion). The study was performed by taking direct CSF pressure recordings from anesthetized and freely moving American alligators (Alligator mississippiensis). The results demonstrate that body movements have a significant influence on CSF pressure, often orders of magnitude beyond the influence of arterial pressure. ABSTRACT: This study was undertaken to document how the cerebrospinal fluid (CSF) pressure varied during movements and physiological activities. Using surgically implanted pressure catheters; the CSF pressure was recorded from sub-adult American alligators (Alligator mississippiensis) under anesthesia and post-recovery. Pressures were recorded during physiological activities (the cardiac cycle; passive and active ventilation); manual manipulation of the anesthetized animals (foot sweeps; tail oscillations; and body bends); as well as voluntary movements post-recovery (changes in body tone; defensive strikes; and locomotion). The CSF pulsations associated with the cardiac cycle had the lowest mean amplitude (3.7 mm Hg); during active ventilation and defensive strikes; the alligators routinely generated CSF pressure spikes in excess of 100 mm Hg. The recorded CSF pressures appear to be caused by a variety of mechanisms including vascular pressure; fluid inertia; and possible physical displacement of the spinal cord. The results of the study suggest that any model of CSF dynamics or perfusion should incorporate the episodic high-pressure CSF pulsations associated with movement