Following focal ischemic injury, several mechanisms lead to secondary expansion of the affected area and therefore increase the initial damage. We thoroughly investigated the expression of astrocytic connexin 43 (Cx43) after photothrombosis in rat brain. The temporal profile of Cx43 mRNA as well as protein expression was studied in remote, structurally uninjured cortical and hippocampal areas. The hippocampal formation revealed an increased number of Cx43 mRNA positive astrocytes and an up-regulated protein expression exclusively in the ipsilateral stratum oriens. We assume a participation of this region in glia scar formation. While Cx43 mRNA positive cells were transiently increased, immunoreactivity was reduced in the somatosensory cortex of injured hemispheres. The observed decrease of Cx43 protein in the post-ischemic cerebral cortex implies an impairment of gap junctional intercellular communication which might be detrimental to the brain.