PENTOBARBITAL ALTERS THE RESPONSE OF CEREBROSPINAL-FLUID PRESSURE EVOKED BY 2 PROVOCATIVE TESTS IN RATS

The intracerebroventricular (ICV) route of administration is a commonl y used pharmacologic procedure in rats. However, little attention is g iven to changes in cerebrospinal fluid pressure (CSFp) when the ventri cular system is perturbed, especially in conscious animals. This commu nication examined CSFp in pentobarbital-anesthetized rats subjected to two pertubations where CSFp had been previously measured in conscious rats. Pentobarbital treatment resulted in marked, qualitative differe nces after both protocols. Whereas conscious rats responded to a 10-mi n ICV infusion (8 mu l/min) by a delayed, secondary increase in CSFp, this effect was completely eliminated (p < 0.001) by pentobarbital. Al so, whereas conscious rats could maintain CSFp at normal values during an hour of 45 degrees head-down tilt, pentobarbital-treated rats coul d not. Anesthetized rats displayed an immediate fall in CSFp to near z ero values (p < 0.001), followed by a rapid recovery (p < 0.001) after tilting. Such differences in CSF dynamics raise important issues. For example, what mechanism(s) underlie the changes in CSF dynamics? Also , are these differences in conscious and anesthetized rats potential v ariables for drug distribution when the ICV route is used?