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Rat connexin-36 (Cx36) is the first gap junction protein shown to be expressed predominantly in neuronal cells of the mammalian central nervous system. As a prerequisite for studies devoted to the investigation of the possible role of this connexin in human neurological diseases, we report the cloning and sequencing of the human Cx36 gene, its chromosomal localization, and its pattern of expression in the human brain analyzed by radioactive in situ hybridization. The determination of the human gene sequence revealed that the coding sequence of Cx36 is highly conserved (98% identity at the protein level with the mouse and rat Cx36 and 80% with the ortholog perch and skate Cx35), and that the gene structure is that typical of the Cx35/36 subgroup observed in the other species (presence of a single intron located within the coding region, 71 bp after the translation initiation site). The distribution of Cx36 in several regions of the human central nervous system is similar to that previously observed in rat brain. The most intense signal among the cerebral areas examined by in situ hybridization was observed in the inferior olivary complex, both in principal and accessory nuclei. A moderate labeling was also observed in several myelencephalic nuclei, in specific cells of the the cerebellar cortex, in a relatively large subpopulation of cells in the cerebral cortex, in the hilus of the dentate gyrus, and in the strata radiatum and oriens of hippocampal subfields. Moreover, labeled cells were revealed in all the lamina of the spinal cord gray matter. The chromosomal localization of the human Cx36 gene was determined by fluorescence in situ hybridization. The results allowed assignment of the gene to band 15q14, thus making it a possible candidate gene for a form of familial epilepsy previously linked to the same chromosomal band. The knowledge of the human Cx36 gene sequence, of its chromosomal localization, and of its pattern of expression opens new avenues for the analysis of its possible involvement in human genetic and acquired neuropathology.

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The levels of glial fibrillary acidic protein mRNA were analysed by in situ hybridization during the first 6 h in experimental models of status epilepticus in the rat. Two different models of status epilepticus were studied: one is produced by the administration of pilocarpine to lithium-treated rats and the other by the intracerebroventricular administration of kainate. Results obtained in the present study showed a very rapid (as early as 1.5 h in periventricular zones of hypothalamus, cerebral cortex, and hippocampal area) up-regulation of GFAP mRNA levels following the pharmacological induction of seizures. Several other areas showed a GFAP activation starting at 3 h such as septum, habenular nuclei, corpus callosum, and cingulum. The comparison of the results obtained in the two models of status epilepticus revealed interesting differences in some brain areas, such as cerebellum and striatum, which can be related to the specific neurotransmitter receptors and neurochemical pathways stimulated by the drugs. Interestingly, some brain areas whose neurons are strongly activated by pilocarpine and kainate (amygdala and CA3 hippocampal field) and that undergo neuronal degeneration did not show the early GFAP response. An interesting spatial feature was observed in several brain regions examined (striatum, septum, and hypothalamus): the response first appeared in the periventricular zones and then diffused to the rest of the brain area. In general GFAP responses in the periventricular zones were early and intense.

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