MU-OPIATE RECEPTOR IMMUNOREACTIVITY IN RAT CENTRAL-NERVOUS-SYSTEM

Immunoreactivity corresponding to the C-terminus of the rat mu opiate receptor can be detected by light microscopy in fiber- and terminal-li ke patterns in a number of rat brain and spinal cord regions, and in i mmunoreactive perikarya in several of these regions. Especially abunda nt fiber- and terminal-like patterns were localized to superficial lay ers of the spinal cord dorsal horn and nucleus caudalis of the spinal tract of the trigeminal, the nucleus of the solitary tract, nucleus am biguous, locus coeruleus, interpeduncular nucleus, medial aspect of th e lateral habenular nucleus, presumed ''striasomes'' of the caudate-pu tamen and nucleus accumbens. Moderate fiber and terminal densities wer e found in the ventral tegmental area, more medial aspects of the thal amus and hypothalamus, and several amygdaloid nuclei. Immunostained pe rikarya were prominent in the nucleus accumbens and also observed in t he middle layers of the cerebral cortex, septum and diagonal band, pre optic area, medial thalamic and habenular nuclei, locus coeruleus, nuc leus ambiguous, nucleus of the solitary tract, trigeminal nucleus caud alis, and spinal cord substantia gelatinosa zones. Many of these local izations correspond well with the previously-determined autoradiograph ic distributions of mu opiate receptor ligand binding, and with report s of mu opiate receptor immunoreactivity determined using other antise ra. Electron microscopic immunohistochemical studies reveal details of the membrane distribution of the mu receptor in nucleus accumbens, ca udate/putamen, locus coeruleus, and spinal cord. These results suggest largely neuronal and largely extrasynaptic distributions of mu recept ors that show differential patterns of perikaryal, dendritic, and/or a xonal immunostaining in different central nervous system zones. Identi fication of these distributions adds substantially to data identifying the cellular localization of the principal opiate receptor involved i n both analgesic and addictive processes.