Abstract <p>An immunohistochemical study on Wistar rats demonstrated thelocalization of claudin-2, a tight junction protein characteristicof epithelial cells, in neurons across various brain regions. Thehighest density of claudin-2-immunopositive structures was detectedin cells of the cerebral cortex, hypothalamic structures, the hippocampus,cells of the nucleus of the solitary tract in the medulla oblongata.Real-time PCR results demonstrate stable expression of the geneencoding claudin-2 in the cerebral cortex and hypothalamus, andWestern blot results demonstrate the presence of claudin-2 proteinin these brain regions. Double fluorescent immunolabeling analysisin the hypothalamus indicates localization of claudin-2 in bothPOMC-positive and POMC-negative cells in the arcuate nucleus ofthe hypothalamus, and in vasopressin-positive and vasopressin-negativecells of the supraoptic and paraventricular nuclei, indicating thepresence of this protein in neurons of various neurochemical types.Not detected of claudin-2 colocalization with GFAP, an astrocyte marker,in hypothalamic nuclei, but colocalization with PSD-95, a postsynapticdensity protein, was demonstrated. These data showed for the firsttime the localization of claudin-2 in brain neurons, providing amorphological basis for studying its functional role in the brain.</p>