THE CHANGES OF EPILEPTOGENIC THRESHOLD IN HIPPOCAMPUS DURING NORMAL SLEEP - WAKING CYCLE

Our work aimed to investigate the changes of focal epileptogenic threshold at different stages of sleep-waking cycle (SWC). Experiments were carried out in adult Wistar rats. Under ketalar anesthesia electrodes were implanted stereotaxically into the brain structures, according to Paxinos and Watson atlas coordinates. Epiletiform Discharges (ED) were induced by electrical stimulation of dorsal hippocampus. In addition, reduction of neocortical activity via spreading depression (SD) was induced in the neocortex by bilateral application of 12% KCL solution. It was found that EDs were more durable at the stage of slow sleep than in wakefulness. Consequently, during slow sleep, the hippocampal epileptogenic threshold was lowered. Prolongation of EDs of hippocampal origin during SD was also observed in neocortex. According to the data obtained one of important factors increasing susceptibility of hippocampus to EDs, at the stage of slow sleep, should be the weakening of tonic inhibitory influence of the cortex upon hippocampus, resulting in decreased epileptogenic threshold in the latter.