Expression of connexin36 in the adult and developing rat brain

The distribution of connexin36 (Cx36) in the adult rat brain and retina has been analysed at the protein (immunofluorescence) and mRNA (in situ hybrid ization) level. Cx36 immunoreactivity, consisting primarily of round or elo ngated puncta, is highly enriched in specific brain regions (inferior olive and the olfactory bulb), in the retina, in the anterior pituitary and in t he pineal gland, in agreement with the high levels of Cx36 mRNA in the same regions. A lower density of immunoreactive puncta can be observed in sever al brain regions, where only scattered subpopulations of cells express Cx36 mRNA. By combining in situ hybridization for Cx36 mRNA with immunohistoche mistry for a general neuronal marker (NeuN), we found that neuronal cells a re responsible for the expression of Cx36 mRNA in inferior olive, cerebellu m, striatum, hippocampus and cerebral cortex. Cx36 mRNA was also demonstrat ed in parvalbumin-containing GABAergic interneurons of cerebral cortex, str iatum, hippocampus and cerebellar cortex. Analysis of developing brain furt her revealed that Cx36 reaches a peak of expression in the first two weeks of postnatal life, and decreases sharply during the third week. Moreover, i n these early stages of postnatal development Cx36 is detectable in neurona l populations that are devoid of Cx36 mRNA at the adult stage. The developm ental changes of Cx36 expression suggest a participation of this connexin i n the extensive interneuronal coupling which takes place in several regions of the early postnatal brain. (C) 2000 Elsevier Science B.V. All rights re served.