Different effects of ω-conotoxin GVIA at excitatory and inhibitory synapses in rat CA1 hippocampal neurons

The nature of the coupling mechanism of presynaptic calcium channels involved in the release of neurotransmitters in the mammalian central nervous system is unknown. Using intracellular recordings from CAI neurons in the rat hippocampal slice preparation, we show that the N-type calcium channels antagonist omega-conotoxin GVIA (omega-CgTx) blocks partially the excitatory (EPSP) and totally the inhibitory (IPSP) synaptic transmission in CAI hippocampal pyramidal neurons. In addition, the inhibitory effect of omega-CgTx on IPSPs is strongly depressed by intrahippocampal 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 excitatory or inhibitory terminals.