DISTRIBUTION OF NICOTINIC RECEPTORS IN THE HUMAN HIPPOCAMPUS AND THALAMUS

Neuronal nicotinic acetylcholine receptors consist of different subuni ts, alpha and beta, with different subtype arrangement corresponding t o distinct pharmacological and functional properties. The expression o f alpha 3, alpha 7 and beta 2 mRNA in the human brain was studied by i n situ hybridization and compared to [H-3]nicotine, [H-3]cytisine and [I-125]alpha-bungarotoxin binding in contiguous sections. The beta 2 p robe showed a strong hybridization signal in the granular layer of the dentate gyrus and in the CA2/CA3 region of the hippocampus and in the insular cortex, and a signal of lower intensity in the subicular comp lex and entorhinal cortex. The alpha 3 probe showed strong hybridizati on in the dorsomedial, lateral posterior, ventroposteromedial and reti cular nuclei of the thalamus, and a weak signal in the hippocampal reg ion and in the entorhinal, insular and cingular cortex. The amount of alpha 7 mRNA was high at the level of the dentate granular layer and t he CA2/CA3 region of the hippocampus, in the caudate nucleus and in th e pulvinar and ventroposterolateral nuclei of the thalamus. [H-3]Nicot ine and [H-3]cytisine binding appeared to be identical in anatomical d istribution and relative intensity. It was high in the thalamic nuclei , the putamen and in the hippocampal formation in the subicular comple x and the stratum lacunosum moleculare. The level of [I-125]alpha-bung arotoxin binding was particularly high in the hippocampus and in the p yramidal cells of the CA1 region, but was relatively low in the subicu lar complex. Our data indicate that in the human brain nicotinic recep tor subtypes have discrete distributions, which are in part different from those of other species.