The pharmacological and physiological profile of glutamate receptors at the Drosophila larval neuromuscular junction

Drosophila larval muscles are commonly used for developmental assessment in regard to various mutations of synaptically relevant molecules. In addition, the molecular sequence of the glutamate receptors on the muscle fibre have been described; however, the pharmacological profiles to known agonists and antagonists have yet to be reported. Here, the responses of N-methyl-D-aspartic acid, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA), L-glutamate, kainate, quisqualic acid, NBQX, AP5 and DNQX are characterized with regard to synaptic transmission and direct effects on the muscle fibres. The muscle fibres depolarize to application of glutamate or quisqualate and the excitatory postsynaptic potential (EPSP) amplitudes are diminished. Kainate does not alter the muscle membrane potential but does reduce the EPSP amplitude. The known antagonists NBQX, AP5 and DNQX have no substantial effect on synaptic transmission at 1 mM, nor do they block the response of quisqualate. Kainate may be acting as a postsynaptic antagonist or via autoreceptors presynaptically to reduce evoked transmission.