Abstracts

Continuous spike-wave discharges during sleep (CSWS) is associated with a decline in IQ, marked reduction in language function and disturbances in behavior. There are no animal models of the condition. The goal of this study was to investigate spatial memory in rats after induced spike-wave discharges in the hippocampal region during sleep. To mimic interictal spikes a bipolar twist stimulation electrode was implanted in the ventral hippocampal commisure and a recording microelecrode [ndash] in the CA1 region. For behavioral testing a modified version of the Morris Water Maze task was used. Rats were trained for three trials and then placed in their home cages. At the beginning of sleep spike-wave patterns were induced using series of electrical pulses 20 msec in duration with a current of 0.2 mA and frequency 1 Hz during the first 60 minutes of stimulation; 0.5 Hz during the next 60 minutes; 2 Hz during the next 30 minutes and 1 Hz during the last 60 minutes (210 minutes altogether). Control rats received sham stimulation. Animals were sleeping more than 85% of the stimulation time. After stimulation or sham stimulation, rats were subjected to three additional water maze trials. For each trial, latency to reach the platform was recorded. On the first day increased mean latency was shown in the experimental group from 30,9[plusmn]8,6 sec after the first three trials to 53,6[plusmn]10,6 sec after the second three trials. In the control group mean latency decreased from 54,2[plusmn]10,3 to 30,1[plusmn]8,4 sec. On the second day mean latency before and after stimulation in the experimental group did not change, while in the control group latency decreased from 46,0[plusmn]11,3 sec to 35,2[plusmn]11,4 sec. On the third and fouth days mean latency declined in both the control and experimental groups. The hippocampus serves a critical role in memory formation, forming a temporally ordered retrieved code for neocortically stored information. The hippocampus receives convergent afferents from virtually all cortical association areas. These afferent inputs are widely distributed onto the cell population of the hippocampus and during sleep the sequence of signals are transmitted to the cortex. Induction of spike-wave discharges in the hippocampus during sleep appears to interrupt memory consolidation from hippocampus to cortex leading to impairment at spatial memory. (Supported by a grant from the National Institutes of Health entitled, [quot]Predictors of Seizure-Induced Memory Impairment[quot] (R01 NS044295).)