Effects of postischemic environment on transcription factor and serotonin receptor expression after permanent focal cortical ischemia in rats.

Housing rats in an enriched environment improves functional outcome after ischemic stroke, this may reflect neuronal plasticity in brain regions outside the lesion. Which components of the enriched environment that are of greatest importance for recovery after brain ischemia is uncertain. We have previously found that enriched environment and social interaction alone both improve functional recovery after focal cerebral ischemia, compared with isolated housing with voluntary wheel-running. In this study, the aim was to separate components of the enriched environment and investigate the effects on some potential mediators of improved functional recovery; such as the inducible transcription factors nerve growth factor-induced gene A (NGFI-A) and NGFI-B, and the glucocorticoid and serotonin systems. After permanent middle cerebral artery occlusion, rats were divided into four groups: individually housed with no equipment (deprived group), individually housed with free access to a running wheel (running group), housed together in a large cage with no equipment (social group) or in a large cage furnished with exchangeable bars, chains and other objects (enriched group). mRNA expression of inducible transcription factors, serotonin and glucocorticoid receptors was determined with in situ hybridisation 1 month after cerebral ischemia. Rats housed in enriched or social environments showed significantly higher mRNA expression of NGFI-A and NGFI-B in cortical regions outside the lesion and in the CA1 (cornu ammonis region of the hippocampus), compared with isolated rats with or without a running wheel. NGFI-A and NGFI-B mRNA expression in cortex and in CA1 was significantly correlated to functional outcome. 5-Hydroxytryptamine receptor 1A (5-HT(1A)) mRNA expression and binding, as well as 5-HT(2A) receptor mRNA expression were decreased in the hippocampus (CA4 region) of the running wheel rats. Mineralocorticoid receptor gene expression was increased in the dentate gyrus amongst wheel-running rats. No group differences were found in plasma corticosterone levels or mRNA levels of glucocorticoid receptor, corticotropin-releasing hormone, 5-HT(2C) or c-fos. In conclusion, we have found that social interaction is a major component of the enriched environment regarding the effects on NGFI-A and NGFI-B expression. These transcription factors may be important mediators of improved functional recovery after brain infarctions, induced by environmental enrichment.

Enriched environment influences brain-derived neurotrophic factor levels in rat forebrain after focal stroke.

Tissue levels of brain-derived neurotrophic factor (BDNF) protein were studied using enzyme immunoassay in different forebrain regions in the ipsi- and contralateral hemispheres of rats housed under enriched or standard conditions after the middle cerebral artery ligation. BDNF levels in the ipsilateral to ligation side was significantly higher only in the frontal cortex of standard as compared to enriched rats. However, BDNF overall was more abundant in standard than in enriched group. In addition, BDNF levels detected in the hippocampus and frontal cortex on the ischemic side of standard rats was higher as compared to contralateral side. The present study shows that housing conditions after permanent middle cerebral artery ligation leads to differential regulation of BDNF protein levels in forebrain regions which might have important implication for post-ischemic recovery.

Gender and strain influence on neurogenesis in dentate gyrus of young rats.

To investigate whether rat hippocampal neurogenesis varies with strain and gender, the authors examined proliferating progenitor cells and their progeny in young male and female Sprague-Dawley (SD) and spontaneously hypertensive rats (SHR) using the thymidine analog bromodeoxyuridine (BrdU) combined with immunohistochemistry for the neuronal marker Calbindin D28k and glial fibrillary acidic protein. Rats were given 7 consecutive daily BrdU injections and were killed 1 day or 4 weeks later to allow for discrimination between proliferation and cell survival. Stereologic analysis of the numbers of BrdU-immunoreactive cells in the dentate gyrus revealed both a strain difference with significantly higher cell proliferation and net neurogenesis in SHR than in SD and a gender difference with males from both strains producing significantly more cells than their female counterparts. Whereas the number of progenitors four weeks after BrdU injections was still significantly greater in male than in female SHRs, resulting in a greater net neurogenesis in the male, the number of BrdU-immunoreactive cells did not differ between male and female SD rats, suggesting a greater survival of newly generated cells in the dentate gyrus in female than in male SD rats. No sex or strain difference was observed in the relative ratio of neurogenesis and gliogenesis.

Early training may exacerbate brain damage after focal brain ischemia in the rat.

Early overuse of a lesioned forelimb, induced by immediate immobilization of the intact forelimb after a cortical lesion, has been reported to increase tissue damage and delay functional recovery. To investigate if early training without immobilization of the intact forelimb could increase tissue loss and reduce recovery, the middle cerebral artery was ligated distal to the striatal branches in 25 male spontaneously hypertensive rats. Control rats were housed in standard cages, training rats were transferred to larger cages allowing various activities and received additional special training 1 hour a day starting either 24 hours or 7 days after the ligation. The rats were tested on a rotating pole, in a leg placement test, and in a water maze and they were killed 6 weeks after the ligation. Delayed training resulted in the best overall performance; however, both training groups performed better than standard rats on the rotating pole. The cortical infarct volume was larger in the early training group than in the other two groups (P < .005), possibly related to increased glutamate release and peri-infarct cortical hyperexcitability.

Infarct volume and functional outcome after pre- and postoperative administration of metyrapone, a steroid synthesis inhibitor, in focal brain ischemia in the rat.

High blood levels of glucocorticoids are associated with increased mortality, confusion and poor functional outcome in stroke patients. It has been proposed that inhibition of glucocorticoids in acute stroke might be beneficial, but experimental data are conflicting and no long-term follow-up study has been reported. We have studied whether pre- or postoperative administration of metyrapone, a steroid synthesis inhibitor, can influence long-term outcome after ligation of the right middle cerebral artery (MCA) distal to the striatal branches in hypertensive rats. Metyrapone (200 mg/kg) was administered either 30 min before or 1, 12 and 24 h after MCA occlusion. Limb placements and ability to traverse a rotating pole were evaluated pre- and postoperatively. Infarct size, histology and GFAP immunoreactivity were evaluated on 5 microm coronal sections from brains perfused in situ 4 weeks after the ischemic event. Pretreatment did not influence outcome, whereas postoperative administration of metyrapone significantly increased infarct volume (P < 0.05). Post-treated rats performed significantly worse than vehicle-treated rats on the rotating pole 3 weeks after the operation (P < 0.05). Our results do not support the hypothesis that inhibition of glucocorticoid synthesis improves outcome after cerebral ischemia.