Histochemical localization of opiate receptors and the enkephalins

It is possible to localize opiate receptors and opioid peptides by light microscopic histochemical methods. The receptors have been mapped by autoradiography with specifically bound 3H-diprenorphine. They are found in anatomical areas associated with physiologic functions known to be altered by opiate administration, as well as in other areas. There appear to be opiate receptors on axons and nerve terminals; some of these are probably for axo-axonic synapses in glomeruli. Some electrophysiologic studies are supportive of the autoradiographic results. Enkephalin-containing neurons can be revealed by immunohistochemistry. Often, although not always, the distribution of enkephalin-like immunoreactivity is similar to that of the opiate receptors. These results are compatible with the notion that the enkephalins are the endogenous substrates of the opiate receptors.