Heterogeneous expression of connexin 36 in the olfactory epithelium and glomerular layer of the olfactory bulb

Gap junctions regulate a variety of cell functions by directly connecting two cells through intercellular channels. Connexins are gap junction channel-forming protein subunits. In this study, we studied the expression of connexin 36 (Cx36) in the olfactory epithelium and olfactory bulb of adult mice. In situ hybridization revealed that mRNA for Cx36 was expressed in the olfactory sensory epithelium, main olfactory bulb and accessory olfactory bulb. Expression of mRNA encoding Cx36 was observed in the olfactory epithelium mainly in ventral and lateral regions of the turbinates. Immunohistochemical determination of Cx36 protein expression showed sparse punctuate staining in the olfactory epithelial layer. Intense Cx36-like immunostaining was found in the olfactory nerve bundles underlying the olfactory epithelium and in the olfactory nerve layer and glomerular layer of the olfactory bulb. Mapping of the intensity of Cx36-like immunofluorescence in glomeruli throughout the main olfactory bulb indicated a heterogeneous distribution. A set of approximately 50 glomeruli located in the anterior and posterior limits of the olfactory bulb was more intensely labeled than other glomeruli. There was intense immunofluorescence signal in the glomerular layer of the accessory olfactory bulb and in the vomeronasal nerve. beta-Galactosidase distribution in the olfactory epithelium and olfactory bulb in Cx36 knockout mice (Deans et al. [2001] Neuron 31:477-485) supported the findings with immunofluorescence. Cx36-like immunofluorescence was absent in the olfactory nerve bundles in Cx36 knockout mice. The immunolocalization of Cx36 to the olfactory and vomeronasal nerves, and a subset of olfactory glomeruli suggest a functional role for Cx36 in odor coding.