Functional and immunocytochemical identification of glutamate autoreceptors of an NMDA type in crayfish neuromuscular junction

N-Methyl-D-aspartate (NMDA) reduces release from crayfish excitatory nerve terminals. We show here that polyclonal and monoclonal antibodies raised ag ainst the mammalian postsynaptic NMDA receptor subunit 1 stain specifically the presynaptic membrane of release boutons of the crayfish neuromuscular junction. In crayfish ganglionic membranes, the polyclonal antibody recogni zes a single protein band that is somewhat larger (by similar to 30 kD) tha n the molecular weight of the rat receptor. Moreover, the monoclonal (but n ot the polyclonal) antibody abolishes the physiological effect of NMDA on g lutamate release. The monoclonal antibody did not prevent the presynaptic e ffects of glutamate, which also reduces release by activation of quisqualat e presynaptic receptors. Only when 6-cyano-7-nitroquinoxatine-2,3,dione (CN QX) was added together with the monoclonal antibody was the presynaptic eff ect of glutamate blocked. These results show that presynaptic glutamate rec eptors of the crayfish NMDA type are involved in the regulation of neurotra nsmitter release in crayfish axon terminals. Although the crayfish receptor differs in its properties from the mammalian NMDA receptor, the two recept ors retained some structural similarity.