Expression of neural connexins and pannexin1 in the hippocampus and inferior olive: a quantitative approach

Electrical synapses (or neuronal gap junctions) are thought to be essential for the generation of synchronous oscillatory activities in various areas of the brain. In this study, we quantified the steady state mRNA expression levels of two neuronal gap junction proteins, connexin36 (Cx36) and connexin45 (Cx45), as well as of pannexin1, a member of a novel class of communicative junction forming proteins, and of connexin47 (Cx47) which is expressed in oligodendrocytes. The expression levels of these genes were compared in two regions known for oscillatory activity and which are equipped with electrically coupled neurons. Assessment of the levels of mRNA expression in the hippocampus and the nuclear complex of the inferior olive (IO) was achieved by means of laser microdissection (LMM) in combination with real time RT-PCR. Our results demonstrate the differential expression of Cx36, Cx45, pannexin1 and Cx47 in the hippocampus, with pannexin1 showing the highest level of expression followed by Cx36, Cx47, and Cx45. In the IO, pannexin1 showed a comparable expression level as in the hippocampus, but connexin expression levels were increased. Upon direct comparison, the combination of LMM and real time RT-PCR data generated specific, robust and reproducible results consistent with recent data reported about connexin expression in the nervous system. We conclude that the analytical strategy shown here provides a technological solution to overcome the less sensitive and notoriously less specific analysis of connexin expression by in situ hybridization.