Evidence for L-glutamate as the neurotransmitter of the squid giant synapse

The effect of a spider toxin (JSTX), a specific blocker of glutamate receptors, was studied in the squid stellate ganglion. JSTX irreversibly blocked the excitatory postsynaptic potential in a dose-dependent manner. The toxin neither affected the spike in the postsynaptic nor the presynaptic fibers. Spontaneous miniature potentials recorded from thin stellate nerves were suppressed by the toxin. Iontophoretically applied L-glutamate depolarized the postsynaptic membrane of the giant axon and this potential was also blocked by JSTX. Kainic acid also depolarized the postsynaptic membrane but this was partially blocked by JSTX, indicating that JSTX differentiated kainate receptor from glutamate one. The results strongly suggest that L-glutamate is the neurotransmitter in the giant synapse of squid.