Suppression of hippocampal synaptic transmission by the spider toxin omega-agatoxin-IV-A.

Effects of omega-agatoxin-IV-A (AGTX) on synaptic transmissions were examined in thin transverse sections of the guinea pig hippocampus. AGTX suppressed, in a dose-dependent manner, field potentials elicited by mossy fiber stimulation in CA3 pyramidal cell layer. AGTX also suppressed field potentials elicited by perforant fiber stimulation in granular layer without marked changes in antidromic responses. These results suggest that Ca2+ entry into presynaptic terminals via P-like calcium channels is at least partly responsible for release of glutamate.