Complexity of sensory environment drives the expression of candidate-plasticity gene,nerve growth factor induced-A

Exposure of animals to an enriched environment triggers widespread modifications in brain circuitry and function. While this paradigm leads to marked plasticity in animals chronically or acutely exposed to the enriched environment, the molecular mechanisms that enable or regulate such modifications require further characterization. To this end, we have investigated the expression profiles of both mRNA and protein products of a candidate-plasticity gene, nerve growth factor induced-A (NGFI-A), in the brains of rats exposed to increased environmental complexity. We found that NGFI-A mRNA is markedly up-regulated throughout the brains of animals exposed to the enriched environment, but not in the brains of either handled-only or undisturbed control groups. The most pronounced effects were observed in the somatosensory and visual cortices, in layers III and V, while more modest increases were observed in all other cortical layers, with the exception of layer I. A striking NGFI-A mRNA up-regulation was also observed in the striatum and hippocampal formation, notably in the CA1 subfield, of animals exposed to the enriched environment paradigm.Immunocytochemistry was also used to investigate the distribution of NGFI-A protein in response to the environmental enrichment protocol. A marked increase in the number of NGFI-A positive nuclei was identified in the enriched environment condition, as compared to undisturbed and handled-only controls, throughout the rat brain. While the greatest number of NGFI-A immunolabeled neurons was found in cortical layers III and V, up-regulation of NGFI-A protein was also detectable in layers II, IV and VI, in both the somatosensory and visual cortices. NGFI-A immunopositive neurons were also more numerous in the CA1 subfield of the hippocampal formation of animals exposed to the enriched environment, but remained at basal levels in both control groups.Our results implicate NGFI-A as one of the possible early genetic signals that ultimately lead to plastic changes in the CNS.     

Chronic unpredictable stress causes attenuation of serotonin responses in cornu ammonis 1 pyramidal neurons

In the present study, serotonin (5-HT) responses of hippocampal pyramidal cornu ammonis 1 (CA1) neurons were studied in rats subjected twice daily for 21 days to unpredictable stressors. In hippocampal tissue from thus stressed rats mRNA expression of the 5-HT(1A) receptor and mineralo- as well as glucocorticoid receptors were examined with in situ hybridization. On average, stressed rats displayed increased adrenal weight and attenuated body weight gain compared with controls, supporting that the animals had experienced increased corticosterone levels due to the stress exposure. One day after the last stressor, under conditions that corticosterone levels were low (predominant mineralocorticoid receptor activation), the 5-HT(1A) receptor mediated hyperpolarization of CA1 neurons in response to 10 microM 5-HT was significantly reduced compared with controls. Basal membrane properties of CA1 cells in stressed rats were comparable to those of controls. The 5-HT(1A) receptor mRNA expression was not changed after chronic stress exposure, in any of the hippocampal areas. A small but significant increase in mineralocorticoid receptor mRNA expression was observed after stress in the dentate gyrus, while glucocorticoid receptor expression was unchanged. The data indicate that unpredictable stress exposure for 3 weeks results in suppression of 5-HT(1A) receptor-mediated responses, possibly due to posttranslational modification of the receptor.     

Use of running wheels regulates the effects of the ovaries on circadian rhythms.

Free-running circadian rhythms in core temperature, wheel-running and general locomotor activity were studied in ovariectomized or intact female rats housed with or without access to a running wheel. No differences in the monitored parameters were found between the intact and ovariectomized rats without a wheel. In the presence of a wheel, however, the intact rats differed from those that had been ovariectomized by displaying a shorter circadian period, an increased amplitude of the temperature rhythm, and strikingly higher rates of wheel-running and general locomotor activity. After estradiol treatment, the ovariectomized rats with a wheel developed a small increase in the temperature amplitude, and also in the correlation between wheel-running and general locomotor activity; these changes were not associated with a significant increase in wheel-running or a shortening of the circadian period. We conclude that some of the differences in circadian function between intact and ovariectomized rats are due to the differential use they make of running wheels, when available, and not directly attributable to the absence or presence of gonadal steroids.     

Selection for aerobic capacity affects corticosterone, monoamines and wheel-running activity

A positive genetic relationship between aerobic capacity and voluntary exercise has been suggested from earlier studies of mice selected for increased wheel-running activity. To further investigate the relationship between aerobic capacity and exercise behavior, wheel-running activity was studied in female rats bidirectionally selected for intrinsic aerobic capacity (high capacity runners - HCR; low capacity runners - LCR). Aerobic capacity was measured using a forced treadmill paradigm; the subpopulations of animals used in this experiment exhibited a 471% difference in endurance capacity. Rats were housed individually, with or without access to running wheels. Wheel-running activity was recorded and analyzed from weeks two through seven during an eight-week trial to determine voluntary activity levels. HCR animals exhibited 33% greater total wheel-running distance per day compared to LCR rats (16,838.7+1337.30 m versus 12,665.8+893.88 m), which was due to the HCR rats exhibiting increases in both running speed and duration over LCR rats. Differences in the intermittency of wheel running were also observed. HCR rats engaged in more bouts of running per day than LCR rats, and trended towards running faster, for more time, and for longer distances during bouts of running than LCR rats. Following the running trial, measurement of plasma corticosterone concentration and striatal dopaminergic activity showed differences between HCR and LCR rats, suggesting a divergence of physiological systems that could potentially influence locomotor behaviors in these lines. These results are consistent with earlier work, and suggest an evolutionarily conserved relationship between physiological capacity and behavioral activity of exercise.     

Ovarian hormone effects on 5-hydroxytryptamine(2A) and 5-hydroxytryptamine(2C) receptor mRNA expression in the ventral hippocampus and frontal cortex of female rats

Alterations in female gonadal hormones are associated with anxiety and mood changes. The aim of the present study was to determine influences of chronic gonadal hormone supplementation on 5-HT(2A) and 5-HT(2C) receptor mRNA levels in the ventral hippocampus and the frontal cerebral cortex. Ovariectomized adult female Sprague-Dawley rats (n=37) received implantation of subcutaneous pellets containing different dosages of 17beta-estradiol alone or in combination with progesterone, or placebo pellets, for 2 weeks. Serotonin receptor mRNA levels were analyzed by in situ hybridization in the ventral hippocampus and 5-HT(2A) receptor mRNA also in the frontal cortex. Estradiol treatment in combination with low-dose progesterone increased 5-HT(2A) receptor mRNA by 43% in the CA2 region of the ventral hippocampus, while estradiol combined with high-dose progesterone increased the expression of this gene by 84% in ventral CA1. 5-HT(2A) mRNA expression in the frontal cortex was not influenced by hormone manipulation. 5-HT(2C) receptor gene expression was in the ventral hippocampus decreased in the CA2, ventral CA1 and the subiculum subregions by high-dose estradiol treatment (8-20% decreases). Effects on mood by gonadal hormones can be mediated, at least partly, through influences on 5-HT(2A) and 5-HT(2C) receptor expression.     

The anorectic effect of fenfluramine is increased by estradiol treatment in ovariectomized rats

The emergence of sex- and estrous cycle-related differences in the anorectic effect of fenfluramine, a serotonin (5-HT) agonist, prompted us to investigate whether these behavioral changes are mediated by estradiol. Rats were ovariectomized and housed in cages that permitted the analysis of feeding and locomotor activity via an automated, computerized system. Using a within-subjects design, we investigated the effects of 1 mg/kg d-fenfluramine and saline vehicle on food intake and wheel running in ovariectomized rats following estradiol benzoate (EB) and oil vehicle treatment. A cyclic regimen of EB treatment was used to mimic the changes in endogenous estradiol secretion over the rat's 4-day estrous cycle. The decrease in food intake following fenfluramine treatment was greater in EB-treated rats, relative to oil-treated rats. Fenfluramine also produced a small but significant decrease in wheel running in ovariectomized rats that was not modulated by EB treatment. Thus, EB's ability to increase the anorectic effect of this dose of fenfluramine appears behaviorally specific. Although the inhibition of food intake by fenfluramine is largely attributed to its ability to increase synaptic levels of 5-HT, additional research involving selective 5-HT receptor agonists and antagonists is necessary to determine whether estradiol interacts with the endogenous 5-HT system to control food intake in the female rat.     

Enriched environment enhances transplanted subventricular zone stem cell migration and functional recovery after stroke

Stroke patients suffer from severe impairments and significant effort is under way to develop therapies to improve functional recovery. Stem cells provide a promising form of therapy to replace neuronal circuits lost to injury. Indeed, previous studies have shown that a variety of stem cell types can provide some functional recovery in animal models of stroke. However, it is unlikely that replacement therapy alone will be sufficient to maximize recovery. The aim of the present study was to determine if rodent stem cell transplants combined with rehabilitation resulted in enhanced functional recovery after focal ischemia in rats. Middle cerebral artery occlusion was induced by injection of the vasoconstrictive peptide endothelin-1 adjacent to the middle cerebral artery. Seven days after stroke the rats received adult neural stem cell transplants isolated from mouse subventricular zone or vehicle injection and then subsequently were housed in enriched or standard conditions. The rats in the enriched housing also had access to running wheels once a week. Enriched housing and voluntary running exercise enhanced migration of transplanted stem cells toward the region of injury after stroke and there was a trend toward increased survival of stem cells. Enrichment also increased the number of endogenous progenitor cells in the subventricular zone of transplanted animals. Finally, functional recovery measured in the cylinder test was facilitated only when the stem cell transplants were combined with enrichment and running exercise 7 days after the transplant. These results suggest that the ability of transplanted stem cells in promoting recovery can be augmented by environmental factors such as rehabilitation.     

Enriched environment influences hormonal status and hippocampal brain derived neurotrophic factor in a sex dependent manner

The present study is aimed at testing the hypothesis that an enriched environment (EE) induces sex-dependent changes in stress hormone release and in markers of increased brain plasticity. The focus was on hypothalamic–pituitary–adrenocortical (HPA) axis activity, plasma levels of stress hormones, gene expression of glutamate receptor subunits and concentrations of brain-derived neurotrophic factor (BDNF) in selected brain regions. Rats exposed to EE were housed in groups of 12 in large cages with various objects, which were frequently changed, for 6 weeks. Control animals were housed four per cage under standard conditions. In females the EE-induced rise in hippocampal BDNF, a neurotrophic factor associated with increased neural plasticity, was more pronounced than in males. Similar sex-specific changes were observed in BDNF concentrations in the hypothalamus. EE also significantly attenuated oxytocin and aldosterone levels only in female but not male rats. Plasma testosterone positively correlated with hippocampal BDNF in female but not male rats housed in EE. In male rats housing in EE led to enhanced levels of testosterone and adrenocorticotropic hormone (ACTH), this was not seen in females. Hippocampal glucocorticoid but not mineralocorticoid receptor levels decreased in rats housed in EE irrespective of sex. Housing conditions failed to modify mRNA levels of glutamate receptor type 1 (Glur1) and metabotropic glutamate receptor subtype 5 (mGlur5) subunits of glutamate receptors in the forebrain. Moreover, a negative association between corticosterone and BDNF was observed in both sexes. The results demonstrate that the association between hormones and changes in brain plasticity is sex related. In particular, testosterone seems to be involved in the regulatory processes related to neuroplasticity in females.     

The role of voluntary exercise in enriched rearing: a behavioral analysis

The effects of postweaning enriched rearing and home cage voluntary wheel-running exercise in adulthood were contrasted on a comprehensive battery of tests designed to assess mnemonic, attentional, emotional, and motor functions. In a 2 x 2 factorial design, female C57BL/6 mice were housed in groups in either standard or enriched cages, which were equipped with either a running or a locked wheel. They were maintained in the corresponding housing conditions for 2 months postweaning prior to, and throughout, testing. Enriched rearing was associated with anxiogenesis, hypolocomotor activity, enhanced motor skills, retarded extinction of conditioned responding, and improved water maze performance. Exercise as such enhanced motor coordination and facilitated extinction of contextual conditioning. Evidence for an interaction between enrichment and exercise was apparent in the open field test, conditioned freezing to a tone stimulus, prepulse inhibition, and acquisition of water maze reference memory. Hence, care should be taken to control for the unique contribution of wheel-running exercise when it is included as an integral component of the enrichment procedure.     

Gene expression profiling of the rat hippocampus one month after focal cerebral ischemia followed by enriched environment

Functional recovery after experimental stroke in rats is enhanced by environmental enrichment by stimulating plastic changes in brain regions outside the lesion, but the molecular mechanisms are not known. We investigated the effect of environmental enrichment after focal cerebral ischemia on cognitive recovery and hippocampal gene expression using microarray analysis. Rats placed in enriched environment (EE) for 1 month after middle cerebral artery occlusion (MCAo) showed significantly improved spatial memory in the Morris water maze compared to rats housed alone after MCAo. Microarray analysis suggested several EE-induced differences in neuronal plasticity-related genes, but these changes could not be confirmed by quantitative real-time PCR. This study highlights some of the potential problems associated with gene expression profiling of brain tissues. Further studies at earlier time points and in additional subregions of the brain are of interest in the search for molecular mechanisms behind EE-induced neuronal plasticity after ischemic stroke.     

Environmental influence on brain-derived neurotrophic factor messenger RNA expression after middle cerebral artery occlusion in spontaneously hypertensive rats

Enriched environment significantly enhances postischemic functional outcome. We have tested the hypothesis that housing in enriched environment stimulates gene expression for brain-derived neurotrophic factor. After ligation of the middle cerebral artery in male spontaneously hypertensive rats, they were housed in individual cages for 30h, then housed either in standard cages or in an enriched environment. The rats were killed two to 30days after the ischemic event. Cryostat coronal sections through the dorsal hippocampus (Bregma -3.3) were processed for in situ hybridization using a rat-brain-derived neurotrophic factor messenger RNA antisense oligonucleotide probe. Postischemic gene expression was significantly higher in standard rats than in enriched rats in contralateral and peri-infarct cortex and in most parts of the hippocampus two, three and 12days after the ischemic event, with a trend for higher-than-baseline levels in standard rats and lower-than-baseline levels in enriched rats. At 20 and 30days the values for both groups were below baseline levels.Contrary to our hypothesis, gene expression in rats postoperatively housed in enriched environment was significantly lower than in standard rats at a time when other studies have reported hyperexcitability in the ipsilateral and contralateral cortex. Should the low messenger RNA levels correspond to low protein synthesis, this might indicate that dampening of the early postischemic hyperexcitability may be beneficial. Low levels in both groups at 20 and 30days may correspond to loss of callosal connections in the opposite hemisphere and to horizontal cortical connections in the lesioned hemisphere.     

Enriched environment promotes efficiency of compensatory movements after cerebral ischemia in rats

Rehabilitation therapy is known to drive motor improvement in stroke patients. However, the interplay of functional recovery and compensation in postischemic motor behavior is poorly understood. This study focused on the time course of functional recovery versus motor compensation in skilled forelimb movements after cerebral ischemia in rats. Young adult male rats underwent a focal cerebral ischemia by unilateral photothrombotic lesion of the motor cortex related to the preferred forelimb. In a first set of experiments animals were exposed to small cortical lesions comprising the forelimb motor cortex (n=8) or to larger lesions additionally extending into the hind limb motor area (n=8). In a second set of experiments animals with large lesion were either housed in standard (n=10) or enriched environment (n=14). Skilled reaching was assessed for 25 to 28 days postischemia. This task allows the distinction between recovery and compensation by parallel quantitative (reaching success) and qualitative (movement pattern) analysis. The results reveal that lesion size determines the initial magnitude of motor deficits, but not the degree of chronic impairments in movement pattern in all experimental groups. Compensatory movements represent the major mechanism of functional improvement and were accompanied by a partial functional restitution. Enriched environment facilitates effective compensation in skilled reaching, while it does not promote restitution of function. In particular, rotating movements of the forelimb during reaching were permanently impaired and required functional compensation through intensified use of the upper body. We conclude an activity dependent postischemic restoration of movement success. Enriched environment provides benefit by increased motor activity mainly due to compensation. Furthermore, these findings emphasize the power of comprehensive movement analysis to gain insight into recovery processes after stroke.     

短暂性前脑缺血后大鼠海马各区NMDA受体亚单位1 mRNA的表达变化

目的观察短暂性前脑缺血后大鼠海马各区N-甲基-D-天门冬氨酸受体(NR)1 mRNA的表达变化。方法采用大鼠前脑缺血15min再灌注0．5h～7d动物模型和原位杂交、图像分析等技术。结果缺血后，海马CA1区NR1 mRNA的表达呈明显上升趋势，至24h达高峰；然后表达开始回落，至缺血后7d降至低谷。在CA3区，NR1 mRNA的表达变化与CA1区类似，但变化幅度明显减小。在齿状回，缺血后0．5h～72h，NR1 mRNA的表达未见显著性变化；缺血后7d，表达亦显著降低。结论短暂性前脑缺血后，大鼠海马各区RN1mRNA的表达变化不同，这种不同可能与海马的选择性易损现象和迟发性细胞死亡有关。     

Serotonin receptor binding and mRNA expression in the hippocampus of fearful amygdala-kindled rats

Amygdala kindling in rats increases fear behavior. The neural correlates of this fear are not well understood. In this experiment, we investigated the relation between serotonin receptor binding and mRNA expression and fearful behavior in amygdala-kindled rats. Rats received either 100 kindling stimulations or sham stimulations, and their fear behavior was subsequently assessed in an unfamiliar open field. Then, the rats were sacrificed and 5-HT transporter binding, 5-HT1A and 5-HT2A receptor binding, and 5-HT1A mRNA expression in several brain regions was assessed. The kindled rats were significantly more fearful in the open field than the sham-stimulated rats. They also had significantly more 5-HT1A receptor binding and mRNA expression in the dentate gyrus than the sham-simulated rats, and these increases in 5-HT1A receptor binding and mRNA expression were significantly correlated to the increases in fear. There were no significant differences between the kindled and sham-stimulated rats in 5-HT transporter binding or 5-HT2A receptor binding. These results suggest that alterations in 5-HT1A receptors in the dentate gyrus may play a role in the expression of kindled fear.     

连续单一应激后大鼠海马5-HT_(1A)受体活性与糖皮质激素受体表达的关系

目的:观察连续单一应激(SPS)大鼠海马糖皮质激素受体(GR)变化与5-HT1A受体的关系,探讨创伤后应激障碍的发病机制。方法:选用雄性成年Wistar大鼠45只,将大鼠随机分为对照组、模型组和阻断组,每组15只。模型组和阻断组给予SPS应激,其中阻断组大鼠在接受SPS前用55-HT1A受体阻断剂WAY100635预处理。采用免疫组织化学和免疫印迹技术测定海马GR水平,采用逆转录-聚合酶链式反应检测GRmRNA表达变化。结果:(1)免疫组织化学结果显示,模型组大鼠海马GR表达高于对照组(P0.01),阻断组则低于模型组(P0.05);(2)WesternBlot结果显示,模型组大鼠海马GR相对表达高于对照组(P0.01),阻断组低于模型组(P0.01);(3)RT-PCR结果表明,与对照组比较,模型组大鼠海马GRmRNA表达增强(P0.01);与模型组比较,阻断组表达量降低(P0.05)。结论:SPS海马GR表达变化与5-HT1A受体有关。