L-glutamate Receptors on the Cell Body Membrane of an Identified Insect Motor Neurone

Current-clamp experiments on an identified neurone have demonstrated the presence of L-glutamate receptors in the insect central nervous system. The cell body of the fast coxal depressor motor neurone (Df) in the metathoracic ganglion of the cockroach Periplaneta americana exhibits a hyperpolarizing response to L-glutamate, accompanied by an increase in membrane conductance. The response is dependent on both intracellular and extracellular chloride concentration, but is not affected by changes in potassium concentration. The hyperpolarization reverses at — 82mV (the equilibrium potential for chloride), is mimicked by the action of L-aspartate, blocked by the antagonists picrotoxin and y-D-glutamylglycine (y-DGG) at high concentrations (1-Oxl0~moll~), and is enhanced by L-amino phosphonobutyTate (L-APB). The response is insensitive to glutamate diethyl ester (GDEE), cis-2,3-piperazine dicarboxylic acid (cis-2,3PDA) and D-amino phosphonobutyrate (D-APB). The L-glutamate-activated increase in chloride conductance does not cross-desensitize with the y-aminobutyric acid (GAB A) response on the same cell. It is less sensitive than the GAB A response to block by picrotoxin. In addition, y-DGG specifically blocks the L-glutamate receptor.