EFFECT OF KAINIC ACID ON UNIT DISCHARGE IN CA1 AREA OF HIPPOCAMPAL SLICE OF DBA AND C57 MICE

Spontaneous unit discharges in stratum pyramidale of CA1 area of hippo campal slices from DBA and C57 mice at different ages were recorded ex tracellularly. The average rate and amplitude of the spontaneous disch arges from CA1 area of hippocampal slices bathed in artificial cerebro spinal fluid (aCSF) were not different between DBA and C57 mice at eit her 3-4 or 5-6 weeks of age. Bath application of kainic acid (KA) in c oncentrations of 0.5-1.0 mu M produced different responses in CA1 area from these two strains of mice. In DBA mice at age 3-4 weeks, when th ey are most susceptible to audiogenic seizures, KA perfusion induced h igh-frequency repetitive single spikes and bursts of multiple populati on spikes in CA1 area. Very high-frequency discharges (10-fold higher than most responses) were also observed in 20% of all slices. In audio genic seizure resistant C57 mice at age 3-4 weeks, KA perfusion at the same doses induced only the repetitive single spikes. The rate of spo ntaneous discharges was much lower than that in DBA mice. No burst of multiple population spikes nor very high-frequency responses were reco rded in C57 mice. At age 5-6 weeks, when both DBA and C57 mice are res istant to audiogenic seizures, the rate of spontaneous discharges reco rded from the CA1 area during and after KA perfusion was lower than th at at age 3-4 weeks, and there was no significant difference between D BA and C57 mice. Pretreatment of hippocampal slices with AMPA/kainate receptor antagonist CNQX(10 mu M) markedly reduced the rate and amplit ude of spontaneous discharges in CAI area during and after KA perfusio n, whereas competitive N-methyl-D-aspartate (NMDA) receptor antagonist D-APS had no effect. These results indicate that the responses in spo ntaneous discharges recorded extracellularly from stratum pyramidale i n CAI area of hippocampal slices to KA perfusion correlate with suscep tibility to audiogenic seizures in DBA and C57 mice.