LONG-TERM BEHAVIORAL DEFICITS FOLLOWING PILOCARPINE SEIZURES IN IMMATURE RATS

The effect of seizures on subsequent long-term behavior was studied in immature rats. A similar severity of seizures were induced in 20-day old rats (P20) and 45-day old rats (P45) by intraperitoneal injections of pilocarpine at doses of 200 mg/kg and 380 mg/kg, respectively. Imm ediately after injection of pilocarpine, prolonged seizures with elect roencephalographic ictal discharges were observed in both groups of ra ts. These seizures were followed by seemingly complete neurological re covery. In rats that received pilocarpine at P45 spontaneous recurrent seizures appeared after 4-10 days and persisted until completion of t he study at P100. Behavioral tests performed when the rats were fully mature demonstrated that they were more aggressive when handled, more active in open field, and had deficits in learning platform position i n the water maze as compared to controls. Furthermore, flurothyl seizu re latency was significantly lower in pilocarpine-treated P45 rats tha n controls. Histology examination showed gross cell loss in the CA3 su bfield of the hippocampus in four out of six pilocarpine-treated rats while no cell loss was found in control rats. Rats that received piloc arpine at P20, despite having more severe seizures than the P45 rats, had no histological lesions, did not develop spontaneous recurrent sei zures, and had no significant difference in the flurothyl seizure late ncy Lest when compared to their controls. While there was no differenc e between the control and pilocarpine-treated rats in the handling and open field test, P20 rats receiving pilocarpine were slower in learni ng platform position in the water maze than the controls. Rats receivi ng pilocarpine at P45 performed significantly more poorly than rats tr eated at P20 in the water maze. These results suggest that prolonged s eizures in immature rats can cause long-term behavioral deficits. Howe ver, the severity and nature of these deficits are highly age dependen t.