The skeletal muscle of members of Orthoptera and Diptera receives an innervation which is probably glutaminergic1-3. Recent study of the ventral muscle fibres in the larvae of the beetle, Tenebrio molitor, has revealed that the transmitter action can be mimicked by the iontophoretic application of L-glutamate to the junctional sites at which the extracellular excitatory postsynaptic potentials (e.p.s.ps) could be recorded (D.Y. and H.W., unpublished observation). Contrary to the evidence favouring glutamate as a transmitter of junctional excitation in insects, some investigators have found that curare (+)tubocrarine, TC), a classic acetylcholine (ACh) antagonist, suppresses the neurally evoked muscle potentials in the fly Sarcophaga 4,5, and Tenebrio6. Here, we have analysed the action of curare on the neuromuscular junction of Tenebrio larvae and found that curare blocked the glutaminergic transmission by antagonising the transmitter at the postsynaptic site.
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