Abstracts

Prior studies from our laboratory have demonstrated that status epilepticus (SE) at postnatal (P) 20 results in significant impairment in visual-spatial learning and memory in the water maze. It is not known whether interictal discharges contribute to this cognitive impairment. Our first goal in this study was to determine if SE in immture rats results in impaired visual-spatial memory in the radial eight-arm maze and second, to determine whether interictal discharges influence cognitive ability. Rats (n = 6) underwent lithium-pilocarpine-induced SE at P20 while controls received normal saline (n = 10). On P60, electrodes were implanted in both the SE and the control groups. A recording electrode was implanted in the right CA1 area and the stimulating electrode in the contralateral ventral hippocampus. After a period of one month, the rats were pre-tested with gradually increasing intensity of stimulation. Stimulation at 1 Hz, with a duration of 0.2 millisecond and intensity 50-80 microamperes produced a population spike with an amplitude of 3 millivolts.The rats were monitored for five minutes after this stimulation to confirm there were no afterdischarges. Rats then underwent training in the radial eight-arm maze. To mimic interictal spikes a set of control rats received continuous 1 Hz stimulations using an current sufficient to induce a 3 millivolt population spike through the stimulating electrode during the training pattern while other control rats were not stimulated. Rats with SE showed considerably impaired performance in the radial eight arm maze as compared to the control rats. In control rats receiving 1 Hz stimulations there was a significant impairment in performance in the radial eight-arm compared to non-stimulated controls. SE in P20 rats results in substanial impairment in visual-spatial memory in the radial eight-arm maze (p [lt]0.05). In addition, interictal discharges impaired learning and memory in this behavioral task. Our findings suggest that interictal epileptiform discharges can impair visual-spatial memory. However, even in the absence of interictal epileptiform abnormalities SE in young rats causes cognitive impairment. (Supported by National Institutes of Health, NINDS (NS044296 and NS41595) and the Western Massachusetts Epilepsy Awareness Committee.)