Synaptic contact between mechanosensory neuron and withdrawal interneuron in terrestrial snail is mediated by L-glutamate-like transmitter.

The properties of the monosynaptic input from mechanosensory neurons to withdrawal interneurons were examined in Helix lucorum. The instantaneous I-V relation of the excitatory postsynaptic current in withdrawal interneurons was nonlinear, having a plateau region between -40 and -60 mV. On application of the blocker of vertebrate N-methyl-D-aspartate (NMDA) receptors AP5, or reduction of the Mg(2+) concentration, the current-voltage relation became more linear, suggesting that Mg(2+) may partially block the ion channel underlying the EPSC at voltages ranging from -40 to around -60 mV and the involvement of NMDA-like receptors. DNQX and 6-cyano-7-nitroquinoxaline-2,3-dione, which are known to block the glutamate non-NMDA receptors in mammals, significantly depress in a dose-dependent manner the actions of the natural transmitter. Exogenous L-glutamate applications mimicked the action of the mechanosensory neuron transmitter.