DIFFERENT EFFECTS OF OMEGA-CONOTOXIN GVIA AT EXCITATORY AND INHIBITORY SYNAPSES IN RAT CA1 HIPPOCAMPAL-NEURONS

The nature of the coupling mechanism of presynaptic calcium channels i nvolved in the release of neurotransmitters in the mammalian central n ervous system is unknown. Using intracellular recordings from CAI neur ons in the rat hippocampal slice preparation, we show that the N-type calcium channels antagonist omega-conotoxin GVIA (omega-CgTx) blocks p artially the excitatory (EPSP) and totally the inhibitory (IPSP) synap tic transmission in CAI hippocampal pyramidal neurons. In addition, th e inhibitory effect of omega-CgTx on IPSPs is strongly depressed by in trahippocampal injection of PTX, while the effect on EPSP is not. The results suggest that the nature or the regulation of calcium channels might be different, depending on the location of these channels on exc itatory or inhibitory terminals.