Immunohistochemical evidence for dysregulation of the GABAergic system ipsilateral to photochemically induced cortical infarcts in rats

Abstract

Deficits of GABAergic transmission have been reported to occur in tissue surrounding ischemic cortical lesions between a few days and several weeks after the insult. In the present experiments, we used immunohistochemistry with antibodies aagainst parvalbumin and two major subunits of the GABA A receptor (α1, α2) to characterize the events that underlie these changes at different levels of circuit organization. Neocortical infarcts (∼2 mm diameter) consistently affecting medial parts of the primary somatosensory cortex were induced photochemically in adult male Wistar rats; animals were allowed to recover for one week before perfusion–fixation. When compared to controls the pattern of immunoreactivity had changed for the α1 subunit of the GABA A receptor seven days after the insult. Ipsilateral to the ischemic lesions, we found a decrease in staining intensity reaching up to 4 mm laterally, resulting in a partial or complete absence of the normal laminar staining pattern. No consistent changes were observed for the α2 subunit. Parvalbumin staining revealed pathological alterations in a rim of tissue surrounding the infarct, measuring up to 1 mm from the border of the infarcts. Parvalbumin-positive interneurons in this region showed signs of degeneration; both a reduction of the number of dendrites and, to a lesser extent and only immediately adjacent to the ischemic lesions, a reduction of the number of parvalbumin-positive neurons was readily apparent. The results provide evidence for both a differential regulation of two GABA A receptor subunits and degenerative changes of parvalbumin-containing interneurons ipsilateral to cortical infarcts. The relevance of these findings for mechanisms underlying long-term recovery, transient functional deficits and postinfarct seizures warrants further investigation.