Bihemispheric reduction of GABAA receptor binding following focal cortical photothrombotic lesions in the rat brain.

Focal brain lesions may lead to neuronal dysfunctions in remote (exofocal) brain regions. In the present study, focal lesions were induced in the hindlimb representation area of the parietal cerebral cortex in rats using the technique of photothrombosis. Photothrombosis occurs after illumination of the brain through the intact skull following intravenous injection of the photosensitive dye Rose Bengal. This resulted in cortical lesions with a diameter of about 2 mm. Quantitative receptor autoradiography was used to study alterations in the density of [3H]muscimol binding sites to GABAA receptors seven days after lesion induction. A reduced GABAA receptor binding (-13 to -27% of the control value) was found in layers II and III of remote exofocal regions in the ipsi- and contralateral cortex. The reduction was consistently more intense in the ipsilateral cortical areas than in those of the contralateral hemisphere. Using extracellular recordings, significant correlations between GABAA receptor binding and paired pulse inhibition could be demonstrated. The present investigation demonstrates that focal brain lesions cause a widespread, functionally effective down-regulation of GABAA receptors. These postlesional changes may result from lesion-induced alterations in cortical connectivity.