Synaptic binding sites in brain for [(3)H]?-bungarotoxin - A specific probe that perturbs transmitter release

A neurotoxic, [(3)H]labelled derivative of ?-bungarotoxin, known to inhibit neurotransmitter release and to be free of phospholipase activity, was used to demonstrate autoradiographically the distribution and ultrastructural location of its saturable binding component in brain. Light-microscope autoradiography of rat cerebellum and hippocampus showed that it resides primarily in synaptic-rich areas, with much lower densities of sites in other regions containing cell bodies; also, little binding was associated with myelinated tracts. Ultrastructural localisation and sub-fractionation studies on purified cerebrocortical synaptosomes showed that [(3)H]toxin binding sites are located predominantly on brain synaptosomal membranes, consistent with their possible association with transmitter release.