Opioid peptide enkephalin: immunohistochemical mapping in rat central nervous system.

Using specific antisera to methionine-enkephalin and leucine-enkephalin, we have visualized apparent enkephalin-containing neuronal fibers and terminals throughout the central nervous system of the rat. Immunoreactive enkephalin displays sharply defined localizations. Regions of highest immunofluorescent density include the laminae I and II of the spinal cord, the substantia gelatinosa of the caudal nucleus of nerve V, the vagal nuclei of the medulla, the periventricular and periaqueductal areas of the upper medulla and midbrain, dorsomedial thalamic regions, specific hypothalamic nuclei, the basal ganglia, particularly the globus pallidus and the central nucleus of the amygdala, and the lateral septum. In certain regions enkephalin immunofluorescence corresponds closely with the distribution of autoradiographic opiate receptor grains.