Sustained Effects of Pilocarpine-Induced Convulsions on Brain Inositol and Inositol Monophosphate Levels and Brain Morphology in Young and Old Male Rats

Abstract

Cerebral inositol and inositol monophosphates, products of phosphoinositide (PI) turnover, and neuronal injury were studied in young (10 weeks) and old (24 months) male Wistar rats after pilocarpine-induced convulsions. The goal was to explore the association between short-term cholinergic convulsions, brain PI signaling, and changes in the brain morphology in the young and the old rats. Pilocarpine caused convulsions in young rats at a dose of 300 mg/kg, whereas a dose of 175 mg/kg was required to obtain the same effect in old rats. A dose of 5 mg/kg of diazepam was used to terminate the convulsions 2 hr after their initiation; the rats were then examined on Day 5 postpilocarpine. Inositol and inositol monophosphate levels were similar in both the young and the old control rats. Pilocarpine-induced convulsions decreased cerebral inositol and increased inositol-1-phosphate in both the young and the old rats. Inositol-4-phosphate was stable in the young rats but increased in the frontal cortex and the hippocampus in the old rats. Delayed neuronal death also occurred in the convulsing rats, i.e., a variable proportion of neurons appeared shrunken with eosinophilic cytoplasm and pyknotic nuclei. The hippocampus was the most severely affected brain area. These results show that old rats are more sensitive than young ones to short-term pilocarpine convulsions, associated with sustained PI turnover, and brain injury. Mechanisms in addition to cholinergic ones are likely to be involved in the prolonged cerebral effects of cholinergic convulsions in rats.