ISCHEMIA-INDUCED CELLULAR REDISTRIBUTION OF THE ASTROCYTIC GAP JUNCTIONAL PROTEIN CONNEXIN43 IN RAT-BRAIN

The distribution and levels of the astrocytic gap junction protein, co nnexin-43 (Cx43) was analyzed in various regions of brain as a functio n of time after neuronal loss and consequent reactive gliosis induced by bilateral carotid occlusion in rats. In the striatum 2 days after i nduction of ischemia, immunostaining intensity for Cx43 increased in a nimals exhibiting mild to moderate striatal damage, whereas areas of r educed staining surrounded by elevated levels of Cx43 immunoreactivity were observed in animals with severe ischemic damage. Immunolabelling of glial cell bodies was evident in ischemic, but not normal, striatu m. Similar, though less dramatic, changes were seen at 7 days post-isc hemia. Compared with the fine punctate pattern of Cx43 staining seen i n normal striatum, ischemic striatal areas contained large aggregates of punctate profiles. In the hippocampus, increased immunostaining was seen at 2 and 7 days post-ischemia and, unlike normal hippocampus, ne urons in the CA3 pyramidal cell layer were surrounded by a network of Cx43-immunoreactive puncta at the latter survival time. Immuno-EM anal ysis of ischemic tissue revealed numerous immunolabelled gap junctions among astrocytic processes in the vicinity of degenerating neurons an d elevated levels of intracellular Cx43 immunoreactivity in astrocytic processes and cell bodies. No differences in protein levels or phosph orylation states of Cx43 were detected in either hippocampus or striat um by Western blot analyses of ischemic and control tissue. These resu lts suggest that astrocytes respond to an ischemic insult by reorganiz ing their gap junctions, that the qualitative nature of their response is dependent on the severity of neuronal damage or loss, and that a p ool of Cx43 normally undetectable by immunohistochemistry may contribu te to the ischemia-induced elevations of immunolabelling for this prot ein.