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Actions of Putative Amino Acid Neurotransmitters on the Neuropile Arborizations of Locust Flight Motoneurones
1 Zoologisches Institut der Universität Rheinsprung 9, CH-4051 Basel, Switzerland
To characterize the receptors for putative amino acid neurotransmitters present on the dendritic arborizations of flight motoneurones in Locusta migratoria, the effects of pressure applications of glutamate, 
-aminobutyric acid (GABA), aspartate, taurine, glycine and cysteine were studied using an animal preparation in which neuropile intracellular recordings could be made during expression of the flight motor output. A majority of cells responded to glutamate, GABA, aspartate and taurine. At resting potential, glutamate and GABA caused, in different cells, a depolarization, a hyperpolarization or, in a few cells, a biphasic response, all accompanied by a decrease in the size of the evoked and spontaneous postsynaptic potentials (PSPs). At spiking threshold, the responses were always hyperpolarizing. Activation of a chloride conductance mediated the effects of both glutamate and GABA. In some cells, the response to glutamate or GABA desensitized during long-lasting applications, but in most cells the amplitude of the response did not decrease during applications lasting several minutes. Responses to aspartate and glutamate had identical reversal potentials and cross-desensitized. Responses to GABA and taurine had more negative reversal potentials and did not cross-desensitize with those elicited by glutamate or aspartate. Only a few neurones responded to applications of glycine or cysteine at resting potential; they responded with an inhibition of spiking at depolarized potentials. These data suggest that a variety of amino acid receptors are present on the neuropile arborizations of flight motoneurones.
Key words: locust, neurones, amino acid neurotransmitters, GABA, L-glutamate, receptors, insects, Locusta migratoria
Accepted on August 13, 1990
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