Opiate receptors: some anatomical and physiological aspects.

It is possible to localize opiate receptors by light microscopic autoradiography using techniques developed for the autoradiographic localization of small diffusible molecules. The receptors are found in the neuropil of anatomical areas associated with various physiologic functions known to be altered by opiates. In some areas, opiate receptors are associated with the axons of small diameter fibers. Many kinds of studies, especially electrophysiologic studies, provide evidence that receptors revealed in these studies have a physiological function. Electrophysiological and immunohistochemical studies of the enkephalins provide results which are compatible with the notion that the enkephalins are the endogenous substrates of the opiate receptors.