Multiple opiate receptor in human brain: an autoradiographic investigation

The pharmacologically defined kappa agonist 3H-(-)-bremazocine and the mu-agonists 3H-dihydromorphine and 3H-D-Ala2,MePhe4, Gly-ol5-enkephalin bind to unique sites in microtome sections of human brain tissue. Kappa binding sites were visualized by autoradiography under conditions where mu- and delta-sites were blocked by D-Ala2,MePhe4,Gly-ol5 and D-Ala2,D-Leu5-enkephalin. A heterogenous distribution of opiate binding sites was found with the neocortical and cerebellar cortices being very rich, brainstem generally poor and white matter very poor in opiate receptor sites. A clear difference in anatomical distribution of opiate binding types was observed. In the midbrain the ventral tegmental area was enriched in mu- and the substantia nigra in kappa-sites. The deep laminae of the neocortex were enriched in kappa-, whereas the molecular layer of the cerebellum contained predominantly mu-sites. Within the hippocampal formation the stratum lacunosum moleculare was enriched in kappa- and the dentate gyrus in delta-sites.