Dexamethasone and ergonovine effects on cerebrospinal fluid pressure in conscious rats

Prior work showed that intracerebroventricular (i.c.v.) infusions of artificial cerebrospinal fluid (aCSF), at a rate of 8 microliters/min x 10 min, elevated CSF pressure (CSFp) of conscious rats after a 2-hour delay. The rise was associated with an increased resistance to outflow and decreased intracranial compliance. When maintained by a continuous infusion of 0.25 microliter/min into each lateral ventricle, CSFp recordings can be made for 24 h and a higher CSFp occurs. Here, we pretreated rats with ergonovine or dexamethasone to determine their effects on the delayed CSFp rise. Ergonovine (0.5 mg/kg i.p.) pretreatment, in a 6-hour protocol 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 unchanged (p > 0.05). Ergonovine increased intracranial compliance (p < 0.05) 20 min after infusion when CSFp was normal, but not when CSFp was elevated at 4 h (p > 0.05). Dexamethasone (40 micrograms i.m.) pretreatment was tested in the 24-hour protocol. It reduced (p < 0.05) normal CSFp 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 steroidal anti-inflammatory drug have partial efficacy in reducing CSFp, but do not prevent the unknown events that precede the delayed CSFp rise after i.c.v. infusions.