Immunohistochemical localization of enkephalin in rat forebrain.

Discrete localization of enkephalin immunoreactive sites in the rat forebrain was undertaken using animals with and without colchicine pretreatment. Both the immunofluorescence and unlabeled PAP antibody techniques were employed using antisera directed against methionine-enkephalin. We have found several areas of enkephalin fiber and cell localizations not previously described, as well as confirming the results of other researchers. Thus, we found large amounts of perikaryal enkephalin immunoreactivity in the lateral septal nucleus, bed nucleus of the stria terminalis, the preoptic nuclei, the ventral premammillary nucleus, prelateral mammillary nucleus, the medial mammillary nucleus, paraventricular nucleus, the periventricular, ventromedial, dorsomedial and posterior nuclei of the hypothalamus, the arcuate nucleus, and the ventral nucleus of the lateral geniculate body. High concentrations of immunoreactive neuronal fibers not immediately associated with enkephalin perikarya were seen in the nucleus accumbens, medial forebrain bundle, globus pallidus, mammillothalamic tract, the subthalamic nucleus, and the caudal portion of the zona incerta. Many of the areas presented in this study correspond with areas known to exert some regulation over neuroendocrine function as well as various motor and sensory functions. Nuclei with high immunoreactive fiber content also correspond in many instances with areas reported to have high concentrations of opiate receptors. Possible enkephalin-containing tracts and the relationships of enkephalin-containing cells in fiber bundles are also pointed out.