Environmental enrichment alters nerve growth factor-induced gene A and glucocorticoid receptor messenger RNA expression after middle cerebral artery occlusion in rats

Housing rats in an enriched environment after focal brain ischemia improves functional outcome without changes in infarct volume, suggesting neuroplas tic changes outside the lesion. In this study, permanent occlusion of the m iddle cerebral artery was followed by housing in an enriched or a standard environment. Nerve growth factor-induced gene A and glucocorticoid receptor messenger RNA expression were determined by in situ hybridization two to 3 0 days after middle cerebral artery occlusion. Stroke induced a decrease in nerve growth factor-induced gene A messenger RNA expression in cortical ar eas outside the ischemic lesion and in the CA1 subregion of the hippocampus two to three days after ischemia. This decrease was more prolonged with en vironmental enrichment, lasting until 20 days. However, 30 days after focal cerebral ischemia, environmental enrichment increased nerve growth factor- induced gene A expression compared to standard housing. A reduction of hipp ocampal glucocorticoid receptor (type II) messenger RNA two to 12 days afte r stroke in standard housed rats was restored by environmental enrichment. These data suggest that improved functional outcome induced by environmenta l enrichment after middle cerebral artery occlusion is associated with dyna mically altered expression of nerve growth factor-induced gene A messenger RNA in brain regions outside the ischemic lesion, and sustained levels of h ippocampal glucocorticoid receptor messenger RNA expression. (C) 1999 IBRO. Published by Elsevier Science Ltd.