Distribution of nicotinic receptors in cynomolgus monkey brain and ganglia: Localization of α3 subunit mRNA, α-bungarotoxin and nicotine binding sites

Abstract

The distribution of nicotinic receptors in the brain and ganglia of the Cynomolgus monkey was studied by in situ hybridization and receptor autoradiography. A 35S-labeled antisense riboprobe for the mRNA of the α3 subunit of the human nicotinic receptor, [ 3H] l-nicotine and [ 125]α-bungarotoxin were used as markers. The highest levels of α3-mRNA were observed in the hippocampus, the medial habenula, the lateral geniculate, the granular layer of the cerebellum, as well as in the pineal gland; moderate levels were found in other nuclei of the thalamus and in the deeper layers of the cerebral cortex. High-affinity binding sites for [ 3H] l-nicotine were observed mainly in the thalamus. The distribution of [ 125I]α-bungarotoxin binding sites was different from that observed for α3-mRNA and [ 3H] l-nicotine; they were most abundant in a few specific thalamic nuclei, in the medial habenula and in lamina I of the cerebral cortex. The localization of these three markers was also investigated in the sympathetic, parasympathetic and sensory ganglia of the monkey. Intense labeling was observed for α3-mRNA and for [ 125I]α-bungarotoxin in the sympathetic and parasympathetic ganglia, whereas no positive signal was seen in the ganglion of Gasser. [ 3H] l-nicotine binding was not detected in any of the ganglia examined. High levels of mRNA for the α3 subunit of the nicotinic receptor were also detected in human sympathetic ganglia. Comparison between α3-mRNA distribution and [ 3H] l-nicotine binding suggests that in the Cynomolgus monkey brain, the α3 subunit may participate in the formation of more than one nicotinic receptor subtype: a high-affinity binding site for [ 3H] l-nicotine in the thalamus and other sites with low affinity for nicotine in the medial habenula and cerebral cortex. Both the α3-mRNA and the [ 125I]α-bungarotoxin are highly expressed in the sympathetic ganglia; however, since no information is presently available on the intraneuronal cellular localization, it cannot be established whether or not they are both present at synaptic sites.