Ultrastructural localization of enkephalin immunoreactivity in the substantia nigra of the monkey

Localization of enkephalin-like immunoreactivity in the substantia nigra of the Japanese red-faced monkey was investigated by light and electron microscopy using the peroxidase-anti-peroxidase method. Immunoreactive precipitates were predominantly distributed in the nerve fibers of the substantia nigra pars reticulata but not in the perikarya, and a low density of immunoreactive enkephalin was found in the pars compacta of this nucleus. Electron microscopic observations showed that enkephalin-immunoreactive precipitates were located in axon terminals containing numerous small clear vesicles either with or without labeled large granular vesicles and formed predominantly axo-dendritic synapses.