Expression of neuronal acetylcholine nicotinic receptor ?4 and ?2 subunits during postnatal development of the rat brain

Abstract

The expression of the α4 and β2 subunits of neuronal nicotinic acetylcholine receptors (nAChRs) was studied in developing rat brain using in situ hybridization. The levels of both transcripts were already high at birth in cerebral cortex, medial habenula, CA1/CA3 regions of the hippocampus and several thalamic nuclei. In general, the β2 subunit showed a higher density of hybrids than the α4. β2 expression did not change with age in the medial habenula, medial geniculate nucleus or in the hippocampus whereas it decreased in the cortex. The developmental pattern of the hybridization signal for α4 was different according to the brain area considered. The expression of the two transcripts showed a biphasic pattern in some thalamic nuclei: the lowest levels occurring during the first and second postnatal weeks respectively, and the highest levels during the second and fourth postnatal weeks. The ontogenetic profile of the expression of the α4 subunit in the thalamic nuclei coincided with that of [³H]-L-nicotine binding sites. These findings suggest that the two subunits of nAChRs are independently regulated in most of the brain areas examined, and that in some regions, such as the thalamus, the ontogenetic variations reported for the α4 subunit correlate with those observed for the [³H]-L-nicotine binding sites.