Cerebrospinal fluid formation and bulk absorption in the freshwater turtle

Abstract

Turtle brains were perfused from the lateral cerebral to the fourth ventricle with an artificial cerebrospinal fluid (CSF) containing a trace amount of radioiodinated human serum albumin (RIHSA); both inflow and outflow rates and RIHSA concentrations were measured. Steady-state clearances of RIHSA (C RIHSA) from the perfusate were measured at different intraventricular hydrostatic pressures. Both C RIHSA increased and outflow rate decreased linearly with increasing hydrostatic pressure. The CSF formation ( V ̇ f ) was 1.4 μl/min and was independent of hydrostatic pressure. Resistance to bulk absorption of CSF was 1790 cm·min/ml. The large resistance to bulk absorption in the turtle may be due to lack of an arachnoid membrane with associated valves.