Mature olfactory receptor neurons express connexin 43

The expression of the gap junction subunit connexin 43 was studied in the olfactory epithelium of adult mice. In agreement with conclusions from previous immunohistochemical studies, we observed expression of mRNA encoding for connexin 43 in layers of the epithelium containing nuclei belonging to sustentacular cells. However, we also observed expression of connexin 43 mRNA in the layers containing nuclei belonging to mature olfactory receptor neurons (ORNs), immature ORNs, and basal cells. Connexin 43 mRNA expression was low in dorsomedial regions of the nasal cavity but higher ventrally. This differential regional distribution was consistent with expression in a transgenic mouse of a LacZ reporter gene driven by the proximal 6.5 kb of the connexin 43 promoter. LacZ was expressed in cells colabeled with antibody against olfactory marker protein (OMP), corroborating that mature ORNs express connexin 43. LacZ staining also was observed in sustentacular and basal cells and in immature ORNs. Double-label studies with antibodies against connexin 43 and OMP and expression of connexin 43 in the epithelium of bulbectomized mice were also consistent with expression of connexin 43 in mature ORNs. This is the first report of expression of a connexin subunit in mature ORNs. Our findings of connexin subunits in mature ORNs raise the novel possibility that gap junctions may play a fundamental role in information processing in the olfactory epithelium.