Apamin increases excitability of CA1 hippocampal pyramidal neurons

The effects of bath application of apamin, a neurotoxin from bee venom, on CA1 hippocampal pyramidal neurons of young rabbits were examined in vitro u sing the intracellular sharp-electrode recording technique. Apamin dose-dep endently reduced the AHP amplitude [F(5,79) = 3.33, P < 0.009]. The mean pe rcent of AHP reduction at 250 - 1000 nM was <similar to> 20%. A small reduc tion of the spike-frequency adaptation was also observed. These significant , but small and dose-dependent, reductions of both the AHP amplitude and sp ike-frequency adaptation, reflecting increases in hippocampal pyramidal neu ron excitability, may have been overlooked in previous reports. The results suggest that the apamin-sensitive AHP contributes little directly to the l earning-induced reduction of the AHP and accommodation observed in hippocam pal pyramidal neurons, but may contribute indirectly by enhancing cholinerg ic input to the hippocampus.