Cognitive functions after pilocarpine-induced status epilepticus: Changes during silent period precede appearance of spontaneous recurrent seizures

Purpose: To study the possible relation between spontaneous recurrent seizu res (SRS) and the derangement of cognitive memory. Methods: Status epilepticus (SE) was induced in adult Long-Evans rats by pi locarpine (320 mg/kg, i.p.) and interrupted after 2 h by clonazepam (CZPs m g/kg, i.p.). In addition to the animals that were given pilocarpine and CZP (group P), two groups received ketamine (100 mg/kg, i.p.): the first group 15 minutes after SE onset (group K15), and the second immediately after th e CZP (group K120). Control groups were formed from animals not treated wit h pilocarpine as well as animals that received pilocarpine but did not deve lop motor seizures. Spatial cognitive memory was tested in the Morris water maze. Results: Testing was impossible for more than 6 days after SE in group P. K etamine shortened this period for the two groups that received it. During t he silent period, deteriorated cognitive memory progressively improved, but the performance of group P started to worsen before the appearance of SRS. Group K120 only expressed a tendency toward declining performance, whereas group K15 never developed SRS, and the behavior of these animals did not d iffer from that of the controls after the postseizure period was over. Hist ologically, massive hippocampal cell loss was seen in group P. Ketamine pro tected hippocampal cells in a time-dependent manner; group K15 did not exhi bit any obvious necrosis in the hippocampus. Conclusions: There is no close relation between cognitive functions and the appearance of SRS, because ketamine, administered 120 min after the beginn ing of SE, prevented the derangment of cognitive functions but not the appe arance of SRSs.