Effects of amino acid neurotransmitter candidates on an identified insect motoneurone.

The cell body of the fast coxal depressor motoneurone (Df) was used to examine the effects of a group of putative amino acid neurotransmitters. gamma-Aminobutyric acid (GABA) elicited a biphasic hyperpolarizing response, each component having a separate reversal potential. Both components were affected by the GABA antagonist picrotoxinin. L-Glutamate produced a hyperpolarizing response with a reversal potential of between -80 and -85 mV, and L-aspartate gave a similar but less potent effect. Kainic acid and quisqualic acid elicited depolarizing responses of up to 10 mV in amplitude. beta-Alanine and taurine produced a single hyperpolarization with a reversal potential similar to glutamate. Glycine was ineffective on motoneurone Df.