COLOCALIZATION OF MU-OPIOID RECEPTORS WITH GIRK1 POTASSIUM CHANNELS IN THE RAT-BRAIN - AN IMMUNOCYTOCHEMICAL STUDY

Affinity-purified anti-peptide antibodies generated against the carbox y-terminal region of the mu opioid receptor and the GIRK1 (Kir 3.1) io n channel were used to localize these two proteins in the rat brain. M u opioid receptor immunoreactivity was detected in brain regions that were previously found to contain mu opioid binding sites using autorad iography. The distribution of GIRK1 immunoreactivity in the brain corr elated well with a previous in situ hybridization study. Confocal micr oscopy of rat brain sections double-labelled with anti-mu opioid recep tor and anti-GIRK1 antibodies revealed colocalization of GIRK1 and mu opioid receptor immunoreactivities in somata of subpopulations of neur ons in the cerebral cortex, anterior olfactory nucleus, nucleus accumb ens, globus pallidus, substantia nigra, peripeduncular nucleus, hippoc ampal formation, diagonal band, thalamus, locus coeruleus,,dorsal raph e, red nucleus, nucleus of the trapezoid body, reticular nucleus, vest ibular nucleus, inferior colliculus and the mesencephalic trigeminal n ucleus. These anatomical findings suggest that the mu opioid receptor may couple to GIRK1 in some but not all regions of the rat brain.