DEXAMETHASONE AND ERGONOVINE EFFECTS ON CEREBROSPINAL-FLUID PRESSURE IN CONSCIOUS RATS

Prior work showed that intracerebroventricular (ICV) infusions of arti ficial cerebrospinal fluid (aCSF), at a rate of 8 mu l/ min x 10 min, elevated CSF pressure (CSFp) of conscious rats after a 2-hour delay. T he rise was associated with an increased resistance to outflow and dec reased intracranial compliance. When maintained by a continuous infusi on of 0.25 mu l/min into each lateral ventricle, CSFp recordings can b e made for 24 h and a higher CSFp occurs. Here, we pretreated rats wit h ergonovine or dexamethasone to determine their effects on the delaye d CSFp rise. Ergonovine (0.5 mg/kg i.p.) pretreatment, in a 6-hour pro tocol using only the 10-min infusion, slightly reduced CSFp (p < 0.05, one-tail test) but the time course of the delayed rise in CSFp was un changed (p > 0.05). Ergonovine increased intracranial compliance (p < 0.05) 20 min after infusion when CSFp was normal, but not when CSFp wa s elevated at 4 h (p > 0.05). Dexamethasone (40 mu g i.m.) pretreatmen t was tested in the 24-hour protocol. It reduced (p < 0.05) normal CSF p during the 2-hour lag after infusion and the CSFp rise was reduced ( p < 0.05) for about 8 h. However, the time course and ending CSFp were unchanged (p > 0.05). Thus, prior cerebral vasoconstriction or a ster oidal anti-inflammatory drug have partial efficacy in reducing CSFp, b ut do not prevent the unknown events that precede the delayed CSFp ris e after ICV infusions.