Differential blocking effects of a spider toxin on synaptic and glutamate responses in the afferent synapse of the acoustico-lateralis receptors of Plotosus

The hypothesis that glutamate is the afferent transmitter in the acoustico-lateralis receptors was examined in Plotosus electroreceptors. JSTX, a spider toxin known to specifically block glutamate receptors, irreversibly abolished afferent impulse discharges induced by iontophoretically applied glutamate, whereas those induced synaptically by focal stimulation of receptor cells were little affected. Such differential blocking effects by JSTX, complementary to other biochemical data, further provide pharmacological evidence against the glutamate hypothesis.