Laminar distribution of the multiple opioid receptors in the human cerebral cortex

Quantitative autoradiographic assessment of cerebral cortical laminar distribution of mu, delta and kappa opioid receptors was carried out in coronal sections of five post-mortem human brains obtained at autopsy. The cortical areas studied were: cingulate, frontal, insular, parietal, parahippocampal, temporal, occipitotemporal, occipital and striate area. In general, the laminar patterns of distribution for the three types of receptors are distinctive. Peak levels of delta opioid binding are in laminae I, II, and IIIa. mu-Receptors are located in lamina III followed by I and II in cingulate, frontal, insular and parietal cortices and lamina IV in temporal and occiptotemporal cortices. kappa-Receptors are found concentrated in laminae V and VI. The patterns of opioid binding in cortical laminae showed remarkable consistency in all five brains examined. In contrast to other cortical areas, the parahippocampal gyrus, at the level of the amygdaloid formation, demonstrated peak kappa receptor density in laminae I, II and III. mu-Opioid binding was undetectable in the lateral occipital cortex and in the striate area.