Localization of nAChR subunit mRNAs in the brain of Macaca mulatta

We present here a systematic mapping of nAChR subunit mRNAs in Macaca mulatta brain. A fragment, from the transmembrane segments MIII to MIV of Macaca neuronal nAChR subunits was cloned, and shown to exhibit high identity (around 95%) to the corresponding human subunits. Then, specific oligodeoxynucleotides were synthesized for in situ hybridization experiments. Both alpha 4 and beta 2 mRNA signals were widely distributed in the brain, being stronger in the thalamus and in the dopaminergic cells of the mesencephalon. Most brain nuclei displayed both alpha 4 and beta 2 signals with the exception of some basal ganglia regions and the reticular thalamic nucleus which were devoid of alpha 4 signal. alpha 6 and beta 3 mRNA signals were selectively concentrated in the substantia nigra and the medial habenula. The strongest signals for alpha 3 or beta 4 mRNAs were found in the epithalamus (medial habenula and pineal gland), whereas there were no specific alpha 3 or beta 4 signals in mesencephalic dopaminergic nuclei. alpha 5 and alpha 7 mRNA signals were found in several brain areas, including cerebral cortex, thalamus and substantia nigra, although at a lower level than alpha 4 and beta 2. The distribution of alpha 3, alpha 4, alpha 5, alpha 6, alpha 7, beta 2, beta 3 and beta 4 subunit mRNAs in the monkey is substantially similar to that observed in rodent brain. Surprisingly, alpha 2 mRNA signal was largely distributed in the Macaca brain, at levels comparable with those of alpha 4 and beta 2. This observation represents the main difference between rodent and Macaca subunit mRNA distribution and suggests that, besides alpha 4 beta 2*, alpha 2 beta 2* nAChRs constitute a main nAChR isoform in primate brain.