Immunohistochemical localization of mu-opioid receptors in rat brain using antibodies generated against a peptide sequence present in a purified mu-opioid binding protein.

Light-microscope visualization in rat brain of a pattern of distribution of immunoreactivity, which included immunolabeled perikarya and beaded processes, was achieved using an immunoaffinity purified polyclonal antibody, Ab165, which recognizes the amino acid sequence, IRNLRQDRSKYY, found in the mu-opioid binding protein purified in our laboratory. Immunohistochemical staining with Ab165 was carried out by the avidin-biotin procedure. Antibody, preabsorbed with antigen, served as control. Extensive immunoreactivity was seen in the hippocampal formation, the amygdaloid complex, the striatal complex, cortical regions, select areas of the thalamus and hypothalamus and in laminae I and II of the dorsal horn in spinal cord. The distribution of immunoreactivity in the rat brain of antibody 165, which recognizes a purified mu-opioid binding protein, is concordant with the distribution of mu-opioid binding sites as determined by other laboratories in autoradiographic, electrophysiological and immunocytochemical studies. These findings have enabled us to distinguish areas possessing large fields of mu-opioid receptor containing cell bodies from areas possessing dense networks of immunolabeled neuronal processes or mixtures of both.