Mitral and tufted cells of the mouse olfactory bulb possess gap junctions and express connexin43 mRNA.

Analyses of freeze-fracture replicas of mouse olfactory bulb reveal the presence of gap junctions in the plasma membranes of the cell bodies of mitral cells. Due to their localization and morphology we presume that they interconnect mitral and granule cells. Since the quality of electrical transmission between neurons is considered to be determined by the biochemical nature of the gap junction channel forming proteins (connexins) we performed immunohistochemistry and in situ hybridization using probes for connexin43 (Cx43), the most abundant connexin in brain tissue. Attribution of Cx43 immunolabel to specific neurons could not definitely be assessed by means of immunohistochemistry. In situ hybridization, however, using a specific cRNA probe for Cx43 revealed a label confined to cell bodies of mitral and tufted cells of the olfactory bulb. These data indicate that Cx43 is expressed by bulbar neurons and suggest that Cx43 is a molecular constituent of gap junction channels in neurons.