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 distributi on of immunoreactivity, which included immunolabeled perikarya and bea ded processes, was achieved using an immunoaffinity purified polyclona l antibody, Ab165, which recognizes the amino acid sequence, IRNLRQDRS KYY, found in the mu-opioid binding protein purified in our laboratory . Immunohistochemical staining with Ab165 was carried out by the avidi n-biotin procedure. Antibody, preabsorbed with antigen, served as cont rol. Extensive immunoreactivity was seen in the hippocampal formation, the amygdaloid complex, the striatal complex, cortical regions, selec t areas of the thalamus and hypothalamus and in laminae I and II of th e dorsal horn in spinal cord. The distribution of immunoreactivity in the rat brain of antibody 165, which mu-opioid binding protein, is con cordant with the distribution of mu-opioid binding sites as determined by other laboratories in autoradiographic, electrophysiological and i mmunocytochemical studies. These findings have enabled us to distingui sh areas possessing large fields of mu-opioid receptor containing cell bodies from areas possessing dense networks of immunolabeled neuronal processes or mixtures of both.