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 α4 and β2 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 α4 and β2 signals with the exception of some basal ganglia regions and the reticular thalamic nucleus which were devoid of α4 signal. α6 and β3 mRNA signals were selectively concentrated in the substantia nigra and the medial habenula. The strongest signals for α3 or β4 mRNAs were found in the epithalamus (medial habenula and pineal gland), whereas there were no specific α3 or β4 signals in mesencephalic dopaminergic nuclei. α5 and α7 mRNA signals were found in several brain areas, including cerebral cortex, thalamus and substantia nigra, although at a lower level than α4 and β2. The distribution of α3, α4, α5, α6, α7, β2, β3 and β4 subunit mRNAs in the monkey is substantially similar to that observed in rodent brain. Surprisingly, α2 mRNA signal was largely distributed in the Macaca brain, at levels comparable with those of α4 and β2. This observation represents the main difference between rodent and Macaca subunit mRNA distribution and suggests that, besides α4β2*, α2β2* nAChRs constitute a main nAChR isoform in primate brain.