Abstract: Objective To study the effects of acute weak vagus nerve stimulation on hippocampal CA1 unit discharges and field potentials of normal and epileptiform discharging rats. Methods The experiments were performed on 55 male Sprague-Dawley rats weighing 180-250g, SPF grade. All the animals were divided into normal (n=45) 基金项目：上海市优秀青年教师科研基金（2006A-74） * 通讯作者：xianwen2004@yahoo.com.cn and regularly epileptiform discharging (n=10) groups. The normal rat group: Separate the left neck vagus nerve and ligate the peripheral end. Acute weak electrical stimulation (10Hz, 0.5ms, 1.5-5.0V, 15-20 unit /train) were administered to the left neck vagus nerve central end. Once every five minutes, 20 trains in all. Record the unit discharges of right hippocampal CA1 and field potentials of bilateral hippocampal CA1. The epileptiform discharging group: Gelatin spongia contains penicillin(400u～600u∕mm3) was put onto the left cortex to induce epileptiform discharges. After 30min stable regularly discharging, continue with the procedure in the first group. Results Cyclical theta oscillation (about 3-6.5Hz) appeared in bilateral hippocampal CA1 of normal rats after the stimulation (strain m=5-7, 38/45,84.4%). With the oscillation, there is unit discharging. It has two kinds: theta-on (n=30) and theta-off (n=5). The sharp wave amplitude can be inhibited while the sharp wave interval increased following the acute weak vagus nerve stimulation(n=10) in epileptiform discharging rats. Theta oscillation was induced during the sharp wave. With the oscillation, there is tonic unit discharging (n=10). The number of action potential spikes positively correlate with the sharp wave intervals (p<0.001), but there were no correlation with the sharp wave potential amplitude. Conclusion The inhibition of epileptiform activity by the acute weak stimulation maybe due to the appearing of theta oscillation. The theta-on cell is very important to the field sharp waves frequency inhibition.

Key words: neural network, theta oscillation, vagus nerve, hippocampus, epilepsy, rat