Sven‐Anders Bergström

Cognitive impairment is common after ischemic stroke. In rodent stroke models using occlusion of the middle cerebral artery (MCA) this is reflected by impaired spatial memory associated with the size of the ischemic lesion. Housing in an enriched environment enhances brain plasticity and improves recovery of sensorimotor functions after experimental stroke in rats. In this study we report that postischemic housing in an enriched environment also attenuates the long-term spatial memory impairment after MCA occlusion and extinguishes the association between spatial memory and infarct volume. An enriched environment did not significantly alter the expression of selected neuronal plasticity-associated genes 1 month after MCA occlusion, indicating that most of the adaptive changes induced by an enriched environment have already occurred at this time point. We conclude that the attenuated memory impairment induced by environmental enrichment after MCA occlusion provides a useful model for further studies on the neurobiological mechanisms of recovery of cognitive functions after ischemic stroke.

Circulating levels of glucocorticoids show a circadian rhythm. Obesity is associated with a flattening of the diurnal rhythm; plasma cortisol levels are slightly increased during the trough, although they are normal or low in the morning. Studies in humans and in leptin-resistant Zucker rats suggest that tissue-specific alterations in glucocorticoid exposure might play a key role for development of obesity and obesity-associated dysregulation of the hypothalamic-pituitary-adrenal axis. We hypothesized that there is a circadian rhythm in prereceptor metabolism of glucocorticoids exerted by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) in brain and/or peripheral tissues (liver, fat, and muscle) that might be abrogated in obesity. The present study demonstrates a circadian rhythm in 11beta-HSD1 mRNA expression (35-45% increase at morning vs. evening, P < 0.05) in dentate gyrus granular layer and CA1 subregions of the hippocampus in lean Zucker rats that was lost in the obese rats. Sprague Dawley rats also revealed a diurnal rhythm in hippocampal 11beta-HSD1 mRNA expression. There was no circadian variation in 11beta-HSD enzyme activity in peripheral tissues, although obese Zucker rats had a decreased enzyme activity in liver and epididymal fat (by approximately 40%, P < 0.05) compared with lean rats. In Sprague Dawley rats, 11beta-HSD activity in adipose tissue was higher in retroperitoneal and epididymal vs. sc fat (P < 0.001). In summary, obese Zucker rats lack a circadian rhythm of 11beta-HSD1 gene expression in the hippocampus, which may contribute to increased activity of the hypothalamic-pituitary-adrenal axis and altered diurnal variation of circulating corticosterone levels.

Proteomic analysis has the potential to yield vast amounts of data. The available proteomic methods have been hampered by methodological errors in quantification due to large gel‐to‐gel variations. The inclusion of an internal standard greatly reduces this variation, and therefore the purpose of this investigation was: 1) to develop a sample preparation protocol for human skeletal muscle for two‐dimensional differentiated gel electrophoresis (DIGE) and 2) to investigate the repeatability of one particular system, the Ettan™ DIGE. To test repeatability, nine aliquots from the same homogenate were labelled with three different CyDye™ dyes (Cy2, Cy3, Cy5). Samples were run on 18×24 cm gels, scanned with a Typhoon™ 9410 laser scanner and analysed in the DeCyder™ software. When selecting spots appearing only in triplicate (n = 1314), the mean error was 1.7 % (SD: 10.5 %; 95 % CI: 1.1–2.4 %). When setting the significance level to 99 %, no false‐positive changes in protein volume ratios were detected. In the protocol presented here, only 0.5 mg tissue was used and separation of >2500 distinct protein spots in the pH range 3–11 and MW 10–200 kDa. Changes in protein abundance of <20 % could be detected. The method is especially useful when comparing muscle proteins between different conditions; for example, healthy and diseased tissue, before and after treatment or different exercise protocols.