Autoradiographic distribution of [3H]nicotine binding in human cortex: relative abundance in subicular complex.
Distinct patterns of [3H]nicotine (3 nM) binding were apparent in various regions of adult human neo- and archicortex. Receptor binding was greatest in the subicular complex--particularly presubiculum--and entorhinal cortex, where it was prominent in the characteristic parvo- and magnocellular islands of these regions and in middle layers of entorhinal cortex. In somatosensory cortex (Brodmann areas 3, 1 and 2) and occipital (area 17) cortex binding was highest in the upper and lower layers, and relatively sparse in the sensory input, layer IV. In primary motor (area 4) and temporal (area 21) cortex, binding in the outer half of the cortical ribbon was denser than that in the inner half and a distinct band was apparent in temporal and cingulate (area 32) in the lower portion of layer III. In prefrontal association cortex the pattern of binding was less distinct although slightly higher in the lower architectonic layers. There was generally little binding in the hippocampus (areas CA1-4) and dentate gyrus with the exception of the stratum lacunosum moleculare in CA2-3 and, to a lesser extent, supra- and subgranule zones of the dentate. These patterns of reactivity, which are distinct from that of the major cortical cholinergic innervation, suggest that the nicotinic receptor, detected using nanomolar concentrations of [3H]nicotine, may primarily be associated with intracortical circuitry in the neocortex. The relatively high density in entorhinal and subicular regions may be related to the extensive phylogenetic development of these regions which has occurred in conjunction with the development of multimodal association circuitry in the human cortex.