Enkephalin-containing nerve cell bodies in the substantia nigra of the rat: Demonstration by immunohistochemistry and in situ hybridization

Abstract

The use of a new and very sensitive immunohistochemical method, combined with intracerebral injections of colchicine, has allowed us to show that a number of nerve cell bodies immunoreactive for Met-enkephalin are present in several mesencephalic nuclei of the rat, including the different subdivisions of the substantia nigra (SN). The existence of numerous neuronal somata of this kind in the medial part of the SN pars compacta and in the lateral half of the pars reticulata is rather new. The latter has been ascertained by demonstrating a perikaryal immunoreactivity for synenkephalin in the same regions of the SN. In addition, by in situ hybridization, we have shown that neuronal cell bodies expressing the preproenkephalin A (PPA) gene are also present in the same regions of the SN. However, the fact that a strong radioautographic reaction was found only in rats which received an intranigral injection of 6-hydroxydopamine indicates that these neurons are probably not dopaminergic and that an induction of the PPA gene occurs in these animals.