Tissue slice autoradiography was employed to reveal the brain distribution of the receptor for αlatrotoxin, the presynaptic neurotoxin of the black widow spider venom. The receptor distribution pattern was compared with that of a marker protein for nerve endings, synapsin I, a phosphoprotein known to be present within nerve terminals. The αlatrotoxin receptor and synapsin I were detected in gray matter-containing regions but their relative amounts were not constant. In the cerebral cortex and in the caudatum their distribution was similar, while in the hippocampus they were both abundant, but their distribution varied: synapsin I labeling was heavier in CA4 and CA3,αlatrotoxin receptor labeling in CA1 and dentate gyrus. A dissociation was also observed in the globus pallidus and in the lateral thalamic nuclear complex, where αlatrotoxin receptor labeling was very weak. The most striking dissociation occurred in the cerebellum, where the molecular layer was strongly labeled for synapsin I, but almost unlabeled for the αlatrotoxin receptor, which was more concentrated in the granular layer. Taken as a whole, the data appear compatible with a widespread localization of the αlatrotoxin receptor at synapses. However, they also suggest that either some nerve terminals are insensitive to αlatrotoxin, or the receptor for the toxin is not present at a similar concentration in all presynaptic plasma membranes.
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