Treadmill running and swimming increase cell proliferation in the hippocampal dentate gyrus of rats

Physical exercise restores adult neurogenesis deficits induced by simulated microgravity

Cognitive impairments have been reported in astronauts during spaceflights and documented in ground-based models of simulated microgravity (SMG) in animals. However, the neuronal causes of these behavioral effects remain largely unknown. We explored whether adult neurogenesis, known to be a crucial plasticity mechanism supporting memory processes, is altered by SMG. Adult male Long-Evans rats were submitted to the hindlimb unloading model of SMG. We studied the proliferation, survival and maturation of newborn cells in the following neurogenic niches: the subventricular zone (SVZ)/olfactory bulb (OB) and the dentate gyrus (DG) of the hippocampus, at different delays following various periods of SMG. SMG exposure for 7 days, but not shorter periods of 6 or 24 h, resulted in a decrease of newborn cell proliferation restricted to the DG. SMG also induced a decrease in short-term (7 days), but not long-term (21 days), survival of newborn cells in the SVZ/OB and DG. Physical exercise, used as a countermeasure, was able to reverse the decrease in newborn cell survival observed in the SVZ and DG. In addition, depending on the duration of SMG periods, transcriptomic analysis revealed modifications in gene expression involved in neurogenesis. These findings highlight the sensitivity of adult neurogenesis to gravitational environmental factors during a transient period, suggesting that there is a period of adaptation of physiological systems to this new environment.

Ageing, Cognitive Decline, and Effects of Physical Exercise: Complexities, and Considerations from Animal Models

In our ageing global population, the cognitive decline associated with dementia and neurodegenerative diseases represents a major healthcare problem. To date, there are no effective treatments for age-related cognitive impairment, thus preventative strategies are urgently required. Physical exercise is gaining traction as a non-pharmacological approach to promote brain health. Adult hippocampal neurogenesis (AHN), a unique form of brain plasticity which is necessary for certain cognitive functions declines with age and is enhanced in response to exercise. Accumulating evidence from research in rodents suggests that physical exercise has beneficial effects on cognition through its proneurogenic capabilities. Given ethical and technical limitations in human studies, preclinical research in rodents is crucial for a better understanding of such exercise-induced brain and behavioural changes. In this review, exercise paradigms used in preclinical research are compared. We provide an overview of the effects of different exercise paradigms on age-related cognitive decline from middle-age until older-age. We discuss the relationship between the age-related decrease in AHN and the potential impact of exercise on mitigating this decline. We highlight the emerging literature on the impact of exercise on gut microbiota during ageing and consider the role of the gut-brain axis as a future possible strategy to optimize exercise-enhanced cognitive function. Finally, we propose a guideline for designing optimal exercise protocols in rodent studies, which would inform clinical research and contribute to developing preventative strategies for age-related cognitive decline.

A Runner's High for New Neurons? Potential Role for Endorphins in Exercise Effects on Adult Neurogenesis

Physical exercise has wide-ranging benefits to cognitive functioning and mental state, effects very closely resembling enhancements to hippocampal functioning. Hippocampal neurogenesis has been implicated in many of these mental benefits of exercise. However, precise mechanisms behind these effects are not well known. Released peripherally during exercise, beta-endorphins are an intriguing candidate for moderating increases in neurogenesis and the related behavioral benefits of exercise. Although historically ignored due to their peripheral release and status as a peptide hormone, this review highlights reasons for further exploring beta-endorphin as a key mediator of hippocampal neurogenesis. This includes possible routes for beta-endorphin signaling into the hippocampus during exercise, direct effects of beta-endorphin on cell proliferation and neurogenesis, and behavioral effects of manipulating endogenous opioid signaling. Together, beta-endorphin appears to be a promising mechanism for understanding the specific ways that exercise promotes adult neurogenesis specifically and brain health broadly.

Sleep deprivation reduces the recovery of muscle injury induced by high-intensity exercise in a mouse model

Sleep is crucial to improve athlete performance and their circadian rhythm, but sleep patterns may be disturbed because athletes participate in several competitions. In addition, intensive training programs can cause muscle pain and psychological stress in athletes, resulting in a lack of sleep. Sleep also plays a critical role in the recovery of muscle injury induced by exercise. The current study evaluated the effect of sleep deprivation on the recovery of muscle injury induced by high-intensity exercise in a mouse model. In this study, 28 mice were randomly assigned to four groups (N = 7): control (Control), exercise (EX), sleep deprivation (SD), and sleep deprivation with exercise (EX+SD). The mice from the EX and EX+SD groups were subjected to high-intensity swimming. The results showed that 72-h sleep deprivation increased food intake and reduced body weight. However, the manipulation of 8-week exercise and/or 72-h sleep deprivation did not have any effect in the elevated plus maze task and tail suspension test. Interestingly, the EX+SD group exhibited improved memory performance in the Morris water maze and impaired motor activity in the open field test. According to the TNF-α level and aspartate aminotransferase (AST), and creatine phosphokinase (CK) activities, only the EX+SD group exhibited muscle impairment. Overall, high-intensity exercise may cause muscle injury, and adequate sleep can recover muscle damage. However, sleep deprivation reduces protein synthesis, which decreases the ability to restore muscle damage and aggravates the harmful effect of high-intensity exercise.

Region-specific and activity-dependent regulation of SVZ neurogenesis and recovery after stroke

Recovery after stroke involves remodeling in brain tissue adjacent to the stroke site. In this remodeling, neurogenesis after stroke involves the formation of new neurons. The role of neurogenesis in stroke recovery and the role of brain and behavioral activity in this process remain undefined. Using orthogonal transgenic mouse tracing and rabies virus approaches, we demonstrate that brain regions unexpectedly compete for new neurons after stroke and that the behavioral or cellular activity establishes this competition. These new neurons synaptically integrate into cortex, and this integration is necessary for poststroke recovery.

Stroke is the leading cause of adult disability. Neurogenesis after stroke is associated with repair; however, the mechanisms regulating poststroke neurogenesis and its functional effect remain unclear. Here, we investigate multiple mechanistic routes of induced neurogenesis in the poststroke brain, using both a forelimb overuse manipulation that models a clinical neurorehabilitation paradigm, as well as local manipulation of cellular activity in the peri-infarct cortex. Increased activity in the forelimb peri-infarct cortex via either modulation drives increased subventricular zone (SVZ) progenitor proliferation, migration, and neuronal maturation in peri-infarct cortex. This effect is sensitive to competition from neighboring brain regions. By using orthogonal tract tracing and rabies virus approaches in transgenic SVZ-lineage-tracing mice, SVZ-derived neurons synaptically integrate into the peri-infarct cortex; these effects are enhanced with forelimb overuse. Synaptic transmission from these newborn SVZ-derived neurons is critical for spontaneous recovery after stroke, as tetanus neurotoxin silencing specifically of the SVZ-derived neurons disrupts the formation of these synaptic connections and hinders functional recovery after stroke. SVZ-derived neurogenesis after stroke is activity-dependent, region-specific, and sensitive to modulation, and the synaptic connections formed by these newborn cells are functionally critical for poststroke recovery.

Effect of regular swimming exercise to duration-intensity on neurocognitive function in cerebral infarction rat model

Objective: This study investigated the effect of regular swimming exercise according to the duration-intensity on neurocognitive function in a cerebral infarction rat model. Methods: Forty male Sprague-Dawley 10-week-old rats, weighing 300 ± 50 g, were subjected to photothrombotic cerebral infarction. The remaining 36 rats were randomly divided into four groups (n = 9 per group: non-exercise (group A); swimming exercise of short duration-intensity (5 min/day, group B); swimming exercise of moderate duration-intensity (10 min/day, group C); and swimming exercise of long duration-intensity (20 min/day, group D). Exercise was performed five times a week for 4 weeks, beginning the day after cerebral infarction. Neurocognitive function was evaluated with the Morris water maze test. Immunohistochemistry and western blot analysis examined brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) at 4 weeks postinfarction. Results: At 4 weeks postinfarction, escape latency was found to be shorter in group C than in any of groups A, B, or D. Immunohistochemistry revealed the most significant immunoreactivity for BDNF and VEGF in group C. Western blot analysis demonstrated that BDNF and VEGF proteins were markedly expressed in group C. Conclusions: Regular swimming exercise of moderate duration-intensity may be the most effective exercise protocol for the recovery of neurocognitive function in cerebral infarction rat model.

Chronic Swimming Exercise Ameliorates Low-Soybean-Oil Diet-Induced Spatial Memory Impairment by Enhancing BDNF-Mediated Synaptic Potentiation in Developing Spontaneously Hypertensive Rats

Exercise and low-fat diets are common lifestyle modifications used for the treatment of hypertension besides drug therapy. However, unrestrained low-fat diets may result in deficiencies of low-unsaturated fatty acids and carry contingent risks of delaying neurodevelopment. While aerobic exercise shows positive neuroprotective effects, it is still unclear whether exercise could alleviate the impairment of neurodevelopment that may be induced by certain low-fat diets. In this research, developing spontaneously hypertensive rats (SHR) were treated with chronic swimming exercise and/or a low-soybean-oil diet for 6 weeks. We found that performance in the Morris water maze was reduced and long-term potentiation in the hippocampus was suppressed by the diet, while a combination treatment of exercise and diet alleviated the impairment induced by the specific low-fat diet. Moreover, the combination treatment effectively increased the expression of brain-derived neurotrophic factor (BDNF) and N-methyl-D-aspartic acid receptor (NMDAR), which were both down-regulated by the low-soybean-oil diet in the hippocampus of developing SHR. These findings suggest that chronic swimming exercise can ameliorate the low-soybean-oil diet-induced learning and memory impairment in developing SHR through the up-regulation of BDNF and NMDAR expression.

Swimming exercise reverses CUMS-induced changes in depression-like behaviors and hippocampal plasticity-related proteins

BACKGROUND

Stress-induced failed resilience of brain plasticity can contribute to the onset and recurrence of depression. Chronic stress has been reported to open windows of epigenetic plasticity in hippocampus. However, how hippocampal plasticity underlies depression-like behaviors and how it adapts in response to stress has not been addressed. The present study aimed to investigate the signaling mechanisms of CUMS affecting hippocampal plasticity-related proteins expression and the regulation of swimming exercise in mice.

METHODS

Male C57BL/6 mice were subjected to chronic unpredictable mild stress (CUMS) for 7 weeks. From the 4th week, CUMS mice were trained in a moderate swimming program for a total of 4 weeks. A videocomputerized tracking system was used to record behaviors of animals for a 5-min session. Real-time PCR and Western Blotting were used to examine gene expression in mouse hippocampus.

RESULTS

Our results demonstrated that CUMS induced depression-like behaviors, which were reversed by swimming exercise. Moreover, the behavioral changes induced by CUMS and exercise were correlated with hippocampal plasticity-related proteins expression of growth-associated protein-43 (GAP-43) and synaptophysin (SYN). The molecular mechanisms regulating this plasticity may include SIRT1/mircoRNA, CREB/BDNF, and AKT/GSK-3β signaling pathways.

LIMITATIONS

We did not establish a correlation between depression-like behaviors induced by chronic stress and epigenetic changes of hippocampal plasticity, either a causal molecular signaling underling this plasticity.

CONCLUSIONS

Our findings have identified swimming exercise effects on CUMS-induced changes in depression-like behaviors and hippocampal plasticity-related proteins, which provide a framework for developing new strategies to treat stress-induced depression.

Exercise pattern and distance differentially affect hippocampal and cerebellar expression of FLK-1 and FLT-1 receptors in astrocytes and blood vessels

Aerobic exercise benefits the body and brain. In the brain, benefits include neuroprotection and improved cognition. These exercise-induced changes are attributed in part to angiogenesis: the growth of new capillaries from preexisting vessels. One critical factor involved in the regulation of angiogenesis is VEGF and its receptors Flk-1 and Flt-1. Although exercise is generally found to be beneficial, there are wide variations in exercise regimens across experiments. This study standardized some of these variations. Rats were assigned to a voluntary or a forced wheel running exercise condition. Within each condition, animals ran for either a long (1000m) or short distance (500m) for up to 24h. Additionally, one voluntary group had unrestricted access to the wheels for the full 24h. Exercising animals were then compared to inactive controls, based on unbiased stereological quantification of Flk-1 and Flt-1 immunohistochemical labeling in the hippocampus and cerebellum. Findings indicated that voluntary exercise, but not forced exercise, could significantly increase Flk-1 and Flt-1 expression in the hippocampus. Interestingly, Flk-1 expression was elevated in astrocytes and Flt-1 in vessels. In the cerebellum long distance forced exercise resulted in the least Flk-1 expression compared to other conditions, and Flt-1 expression in exercising animals either did not change or was suppressed relative to inactive controls.

Comprehensive catwalk gait analysis in a chronic model of multiple sclerosis subjected to treadmill exercise training

BACKGROUND

Multiple sclerosis (MS) is a demyelinating disease with a wide range of symptoms including walking impairment and neuropathic pain mainly represented by mechanical allodynia. Noteworthy, exercise preconditioning may affect both walking impairment and mechanical allodynia. Most of MS symptoms can be reproduced in the animal model named experimental autoimmune encephalomyelitis (EAE). Usually, neurological deficits of EAE are recorded using a clinical scale based on the development of disease severity that characterizes tail and limb paralysis. Following paralysis recovery, subtle motor alterations and even mechanical allodynia investigation are difficult to record, representing sequels of peak disease. The aim of the present study was to investigate the walking dysfunction by the catwalk system (CT) in exercised and non-exercised C57BL/6 mice submitted to EAE with MOG35-55 up to 42 days post-induction (dpi).

METHODS

Twenty-four C57BL/6 female mice were randomly assigned to unexercised (n = 12) or exercised (n = 12) groups. The MOG35-55 induced EAE model has been performed at the beginning of the fifth week of the physical exercise training protocol. In order to characterize the gait parameters, we used the CT system software version XT 10.1 (Noldus Inc., The Netherlands) from a basal time point (before induction) to 42 days post induction (dpi). Statistical analyses were performed with GraphPad Prisma 4.0 software.

RESULTS

Data show dynamic gait changes in EAE mice including differential front (FP) and hind paw (HP) contact latency. Such findings are hypothesized as related to an attempt to maintain balance and posture similar to what has been observed in patients with MS. Importantly, pre-exercised mice show differences in the mentioned gait compensation, particularly at the propulsion sub-phase of HP stand. Besides, we observed reduced intensity of the paw prints as well as reduced print area in EAE subjects, suggestive of a development of chronic mechanical allodynia in spite of being previously exercised.

CONCLUSIONS

Our data suggest that Catwalk system is a useful tool to investigate subtle motor impairment and mechanical allodynia at chronic time points of the EAE model, improving the functional investigation of gait abnormalities and demyelination sequelae.

Leptin receptor knockout-induced depression-like behaviors and attenuated antidepressant effects of exercise are associated with STAT3/SOCS3 signaling

Relatively little has been known about pathophysiological mechanisms contributing to the development of neuropsychiatric symptoms in the context of metabolic syndrome. Impaired leptin signaling activation in db/db mice has been proposed as a potential link between behavioral and metabolic disorders. Our previous studies have shown that exercise has the beneficial effects on a depression-like and insulin-resistant state in mice. The present study aimed to determine whether and how leptin receptor knockout (db/db) induces depression-like behaviors, and to identify the antidepressant effects of swimming exercise in db/db mice. Our results support the validity of db/db mice as an animal model to study depression with metabolic abnormalities, but fail to confirm the improvement of exercise on depression. LepRb knockout-induced depression-like behaviors are associated with STAT3/SOCS3 signaling but independent of IKKβ/NFκB signaling. Our findings suggest the potential importance of LepRb as an exercise-regulated target for depression, also representing a new target underlying treatment-resistant depression.

The effects of hormones and physical exercise on hippocampal structural plasticity

The hippocampus plays an integral role in certain aspects of cognition. Hippocampal structural plasticity and in particular adult hippocampal neurogenesis can be influenced by several intrinsic and extrinsic factors. Here we review how hormones (i.e., intrinsic modulators) and physical exercise (i.e., an extrinsic modulator) can differentially modulate hippocampal plasticity in general and adult hippocampal neurogenesis in particular. Specifically, we provide an overview of the effects of sex hormones, stress hormones, and metabolic hormones on hippocampal structural plasticity and adult hippocampal neurogenesis. In addition, we also discuss how physical exercise modulates these forms of hippocampal plasticity, giving particular emphasis on how this modulation can be affected by variables such as exercise regime, duration, and intensity. Understanding the neurobiological mechanisms underlying the modulation of hippocampal structural plasticity by intrinsic and extrinsic factors will impact the design of new therapeutic approaches aimed at restoring hippocampal plasticity following brain injury or neurodegeneration.

Activity Dependency and Aging in the Regulation of Adult Neurogenesis

Age and activity might be considered the two antagonistic key regulators of adult neurogenesis. Adult neurogenesis decreases with age but remains present, albeit at a very low level, even in the oldest individuals. Activity, be it physical or cognitive, increases adult neurogenesis and thereby seems to counteract age effects. It is, thus, proposed that activity-dependent regulation of adult neurogenesis might contribute to some sort of "neural reserve," the brain's ability to compensate functional loss associated with aging or neurodegeneration. Activity can have nonspecific and specific effects on adult neurogenesis. Mechanistically, nonspecific stimuli that largely affect precursor cell stages might be related by the local microenvironment, whereas more specific, survival-promoting effects take place at later stages of neuronal development and require the synaptic integration of the new cell and its particular synaptic plasticity.

Hormetic effects by exercise on hippocampal neurogenesis with glucocorticoid signaling

Exercise enhances adult hippocampal neurogenesis (AHN), although the exact nature of how this happens remains controversial. The beneficial effects of exercise vary depending upon the exercise condition, especially intensity. Most animal studies, however, have used wheel running, which only evaluates running distance (exercise volume) and does not consider intensity. In our rat model, we have found that exercise-induced neurogenesis varies depending on the intensity of the exercise and have found that exercise-enhanced neurogenesis is more pronounced with mild exercise than with moderate and/or intense exercise. This may be due, at least in part, to increased glucocorticoid (CORT) secretion. To test this hypothesis, we used our special exercise model in mice, with and without a stress response, based on the lactate threshold (LT) in which moderate exercise above the LT increases lactate and adrenocorticotropic hormone (ACTH) release, while mild exercise does not. Adult male C57BL/6J mice were subjected to two weeks of exercise training and AHN was measured with a 5-Bromo-2-deoxyuridine (BrdU) pre-injection and immunohistochemistry. The role of glucocorticoid signaling was examined using intrapertioneal injections of antagonists for the glucocorticoid receptor (GR), mifepristone, and the mineralocorticoid receptor (MR), spironolactone. We found that, while mild exercise increased AHN without elevating CORT blood levels, both MR and GR antagonists abolished mild-exercise-induced AHN, but did not affect AHN under intense exercise. This suggests a facilitative, permissive role of glucocorticoid and mineralocorticoid receptors in AHN during mild exercise (234/250).

Metabolic factors-triggered inflammatory response drives antidepressant effects of exercise in CUMS rats

Chronic stress is a potential contributing factor for depression, accompanying with metabolic and inflammatory response. Exercise is considered as a treatment for depression, but mechanisms underlying its beneficial effects still remain unknown. The objectives of present study were to confirm that metabolic factors-triggered inflammatory response mediates the antidepressant actions of exercise in chronic unpredictable mild stress (CUMS) rats. It has been found that CUMS stimulated expression of ghrelin and its receptor Ghsr, but inhibited expression of leptin and its receptor LepRb. Ghrelin, via binding to Ghsr, induced phosphorylation of GSK-3β on Tyr216 and decreased phosphorylation on Ser9, thus increasing GSK-3β activity. Conversely, ghrelin binding to Ghsr decreased STAT3 activity, through decreasing phosphorylation of STAT3 on Tyr705 and increasing Ser727 phosphorylation. Negatively correlated with ghrelin, leptin binding to LepRb had opposite effects on the activity of GSK-3β and STAT3 via phosphorylation. In addition, decreased leptin level initiated NLRP3 activity via LepRb. Furthermore, GSK-3β inhibited STAT3 activation, thus promoting the expression of NLRP3. Meanwhile, swim improved metabolic and inflammatory response both in CUMS and control rats. Our findings suggest that exercise not only ameliorates metabolic disturbance and inflammatory response in depression, but also contributes to metabolic and inflammatory function in normal conditions.

Neurogenesis within the adult hippocampus under physiological conditions and in depression

Adult neurogenesis can only be observed in some specific brain regions. One of these areas is the dentate gyrus of the hippocampal formation. The progenitor cells located in the subgranular layer of the dentate gyrus proliferate, differentiate, and give rise to young neurons that can become integrated into existing neuronal circuits. Under physiological conditions, hippocampal neurogenesis is linked to hippocampal-dependent learning, whereas deficits in adult hippocampal neurogenesis have been shown to correlate with disturbances in spatial learning and memory. This review summarizes the phenomenon of adult hippocampal neurogenesis and the use of suitable markers for the investigation of adult hippocampal neurogenesis. In addition, we focused on the disturbances in neurogenesis that can be seen in depression. Interestingly, several antidepressants have been found to be capable of increasing the rate of hippocampal neurogenesis. Based on that, it can be speculated that factors, which directly or indirectly increase the rate of hippocampal neurogenesis, may be helpful in the treatment of depression.

Differential effects of exercise on brain opioid receptor binding and activation in rats

Physical exercise stimulates the release of endogenous opioid peptides supposed to be responsible for changes in mood, anxiety, and performance. Exercise alters sensitivity to these effects that modify the efficacy at the opioid receptor. Although there is evidence that relates exercise to neuropeptide expression in the brain, the effects of exercise on opioid receptor binding and signal transduction mechanisms downstream of these receptors have not been explored. Here, we characterized the binding and G protein activation of mu opioid receptor, kappa opioid receptor or delta opioid receptor in several brain regions following acute (7 days) and chronic (30 days) exercise. As regards short- (acute) or long-term effects (chronic) of exercise, overall, higher opioid receptor binding was observed in acute-exercise animals and the opposite was found in the chronic-exercise animals. The binding of [(35) S]GTPγS under basal conditions (absence of agonists) was elevated in sensorimotor cortex and hippocampus, an effect more evident after chronic exercise. Divergence of findings was observed for mu opioid receptor, kappa opioid receptor, and delta opioid receptor receptor activation in our study. Our results support existing evidence of opioid receptor binding and G protein activation occurring differentially in brain regions in response to diverse exercise stimuli. We characterized the binding and G protein activation of mu, kappa, and delta opioid receptors in several brain regions following acute (7 days) and chronic (30 days) exercise. Higher opioid receptor binding was observed in the acute exercise animal group and opposite findings in the chronic exercise group. Higher G protein activation under basal conditions was noted in rats submitted to chronic exercise, as visible in the depicted pseudo-color autoradiograms.

Effects of endurance exercise on expressions of glial fibrillary acidic protein and myelin basic protein in developing rats with maternal infection-induced cerebral palsy

Periventricular leukomalacia (PVL) is a common white matter lesion affecting the neonatal brain. PVL is closely associated with cerebral palsy (CP) and characterized by increase in the number of astrocytes, which can be detected by positivity for glial fibrillary acidic protein (GFAP). Change in myelin basic protein (MBP) is an early sign of white matter abnormality. Maternal or placental infection can damage the neonatal brain. In the present study, we investigated the effects of treadmill walking exercise on GFAP and MBP expressions in rats with maternal lipopolysaccharide (LPS)-induced PVL. Immunohistochemistry was performed for the detection of GFAP and MBP. The present results showed that intracervical maternal LPS injection during pregnancy increased GFAP expression in the striatum and decreased MBP expression in the corpus callosum of rats. The results also showed that treadmill walking exercise suppressed GFAP expression and enhanced MBP expression in the brains of rats with maternal LPS-induced PVL. The present study revealed that treadmill walking exercise is effective for the suppressing astrogliosis and hypomyelination associated with PVL. Here in this study, we showed that treadmill walking exercise may be effective therapeutic strategy for alleviating the detrimental effects of CP.

Beneficial effects of melatonin combined with exercise on endogenous neural stem/progenitor cells proliferation after spinal cord injury

Endogenous neural stem/progenitor cells (eNSPCs) proliferate and differentiate into neurons and glial cells after spinal cord injury (SCI). We have previously shown that melatonin (MT) plus exercise (Ex) had a synergistic effect on functional recovery after SCI. Thus, we hypothesized that combined therapy including melatonin and exercise might exert a beneficial effect on eNSPCs after SCI. Melatonin was administered twice a day and exercise was performed on a treadmill for 15 min, six days per week for 3 weeks after SCI. Immunohistochemistry and RT-PCR analysis were used to determine cell population for late response, in conjunction with histological examination and motor function test. There was marked improvement in hindlimb function in SCI+MT+Ex group at day 14 and 21 after injury, as documented by the reduced size of the spinal lesion and a higher density of dendritic spines and axons; such functional improvements were associated with increased numbers of BrdU-positive cells. Furthermore, MAP2 was increased in the injured thoracic segment, while GFAP was increased in the cervical segment, along with elevated numbers of BrdU-positive nestin-expressing eNSPCs in the SCI+MT+Ex group. The dendritic spine density was augmented markedly in SCI+MT and SCI+MT+Ex groups. These results suggest a synergistic effect of SCI+MT+Ex might create a microenvironment to facilitate proliferation of eNSPCs to effectively replace injured cells and to improve regeneration in SCI.

The impact of duration of one bout treadmill exercise on cell proliferation and central fatigue in rats

The purpose of this study was to investigate the impact of the duration-dependence of the one bout treadmill exercise on cell proliferation, stress, and central fatigue in rats. The animals were randomly divided into five groups: the non-exercise group, 1-h exercise group, 2-h exercise group, 4-h exercise group, and 6-h exercise group. The exercise load consisted of running at speed of 13 meters/min with the 0° inclination. Cell proliferation in the hippocampal dentate gyrus was increased in response to one bout moderate treadmill exercise in all exercise groups. But there was no statistical significance between the exercise duration and cell proliferation. The optical density of glucocorticoid (GR)-positive cells in the hippocampal dentate gyrus was not changed by treadmill exercise at any exercise duration. Expressions of serotonin (5-hydroxytryptamine, 5-HT) and tryptophan hyroxylase (TPH) were increased by treadmill exercise only at 6 h duration. It seemed like that there was no additional benefits on cell proliferation over 2 h exercise due to stressful factors with over exercise dose, and there was no change of GR expression due to early assessment point of time. It can be suggested that the one-bout of moderate treadmill exercise increased cell proliferation, but treadmill exercise prolonged to 6 h induced central fatigue in rats.

Sudden detraining deteriorates swimming training-induced enhancement of short-term and spatial learning memories in mice

In the present study, we investigated the effect of swimming training and sudden detraining on learning ability and spatial memory capability and on neurogenesis and brain-derived neurotrophic factor (BDNF) expression in the hippocampus of mice. Male ICR mice were randomly assigned into three groups (n= 15 in each group): the control group, the swimming training group, and the detraining group. The mice in the swimming training group were made to swim (6 days/week, 60 min/day) for 8 weeks. The mice in the detraining group were accomplished the same swimming program for 4 weeks and then discontinued exercise for 4 weeks. In the present results, enhanced short-term and spatial learning memories and increased hippocampal neurogenesis and BDNF expression were observed in the mice of the swimming training group. In contrast, decreased short-term and spatial learning memories were observed in the mice of the swimming detraining group compared to the control level. Hippocampal neurogenesis and BDNF expression were also decreased in the mice of the detraining group near to the control level. Here in this study, we suggest that sudden cessation of exercise training might bring decline of the brain functions.

Neural plasticity and stress coping in teleost fishes

Physiological and behavioural responses to environmental change are individually variable traits, which manifest phenotypically and are subject to natural selection as correlated trait-clusters (coping styles, behavioural syndromes, or personality traits). Comparative research has revealed a range of neuroendocrine-behavioural associations which are conserved throughout the vertebrate subphylum. Regulatory mechanisms universally mediate a switch between proactive (e.g. active/aggressive) and reactive (e.g. conservation/withdrawal) behaviour in response to unpredictable and uncontrollable events. Thresholds for switching from active coping to behavioural inhibition are individually variable, and depend on experience and genetic factors. Such factors affect physiological stress responses as well as perception, learning, and memory. Here we review the role of an important contributor to neural processing, the set of biochemical, molecular, and structural processes collectively referred to as neural plasticity. We will concentrate on work in teleost fishes, while also elucidating conserved aspects. In fishes, environmental and physiological control of brain cell proliferation and neurogenesis has received recent attention. This work has revealed that the expression of genes involved in CNS plasticity is affected by heritable variation in stress coping style, and is also differentially affected by short- and long-term stress. Chronic stress experienced by subordinate fish in social hierarchies leads to a marked suppression of brain cell proliferation. Interestingly, typically routine dependent and inflexible behaviour in proactive individuals is also associated with low transcription of neurogenesis related genes. The potential for these findings to illuminate stress-related neurobiological disorders in other vertebrates is also discussed.

Swimming exercise ameliorates depression-like behaviors induced by prenatal exposure to glucocorticoids in rats

Prenatal exposure to glucocorticoids (GCs) leads to affective dysfunction in adulthood, which may be associated with the alterations in hypothalamic-pituitary-adrenal (HPA) axis. Physical exercise has been shown to ameliorate depressive symptoms. The objectives of present study were to investigate whether prenatal exposure to GCs induces depression-like behaviors in adult offspring rats, and determine whether swimming exercise alleviates the depression-like behaviors induced by this paradigm. Pregnant rats received dexamethasone (DEX) (0.1mg/kg/day) in the last third of pregnancy or vehicle. DEX treatment reduced body weight in 1, 3, 6, 9-week old male offspring, and 3, 6, 9-week old female offspring. DEX treatment resulted in an elevated level of serum corticosterone in adult offspring (9weeks). Female and male adult offspring rats exhibited decreased number of poking into holes and rearing and decreased central distance traveled in open field test (OFT), and reduced sucrose consumption, suggesting prenatal DEX exposure increase depression-like behaviors in the adult offspring rats. Four-week swimming exercise reduced serum corticosterone levels, and alleviated the depressive behavior by reversing the decreased number of poking into holes and rearing as well as decreased central distance traveled, and reversing the reduced sucrose consumption in male and female adult offspring. These findings suggested prenatal exposure to GCs increase the activity of HPA axis and depression-like behaviors of adult offsprings. Swimming exercise decreases HPA activity and ameliorates depression in rats exposed to DEX prenatally.

HIV-1 alters neural and glial progenitor cell dynamics in the central nervous system: coordinated response to opiates during maturation

HIV-associated neurocognitive disorders (HANDs) are common sequelae of human immunodeficiency virus (HIV) infection, even when viral titers are well controlled by antiretroviral therapy. Evidence in patients and animal models suggests that neurologic deficits are increased during chronic opiate exposure. We have hypothesized that central nervous system (CNS) progenitor cells in both adult and developing CNS are affected by HIV infection and that opiates exacerbate these effects. To examine this question, neural progenitors were exposed to HIV-1 Tat(1-86) in the developing brain of inducible transgenic mice and in vitro. We examined whether Tat affected the proliferation or balance of progenitor populations expressing nestin, Sox2, and Olig2. Disease relevance was further tested by exposing human-derived progenitors to supernatant from HIV-1 infected monocytes. Studies concentrated on striatum, a region preferentially targeted by HIV and opiates. Results were similar among experimental paradigms. Tat or HIV exposure reduced the proliferation of undifferentiated (Sox2(+)) progenitors and oligodendroglial (Olig2(+)) progenitors. Coexposure to morphine exacerbated the effects of Tat or HIV-1(SF162) supernatant, but partially reversed HIV-1(IIIB) supernatant effects. Populations of Sox2(+) and Olig2(+) cells were also reduced by Tat exposure, although progenitor survival was unaffected. In rare instances, p24 immunolabeling was detected in viable human progenitors by confocal imaging. The vulnerability of progenitors is likely to distort the dynamic balance among neuron/glial populations as the brain matures, perhaps contributing to reports that neurologic disease is especially prevalent in pediatric HIV patients. Pediatric disease is atypical in developed regions but remains a serious concern in resource-limited areas where infection occurs commonly at birth and through breast feeding.

Dietary folic acid intake differentially affects methionine metabolism markers and hippocampus morphology in aged rats

PURPOSE

Folic acid (FA) is an emerging nutritional factor in the pathogenesis of diverse neurodegenerative disorders by still unknown mechanisms. The hippocampus is altered during the loss of cognitive abilities in humans and selectively affected when homocysteine increases. The aim was to evaluate the potential protective role of folic acid in the maintenance of biochemical markers related to the methionine cycle, as well as the integrity of the hippocampus as part of the brain in aged rats.

METHODS

Male Sprague-Dawley rats (18 months old) were assigned to four different folic acid groups (0 mg FA/kg diet, deficient; 2 mg FA/kg diet, control; 8 mg FA/kg diet, moderate supplementation; 40 mg FA/kg diet, extra supplementation) for 30 days. We evaluated several parameters related to the methionine cycle. In addition, hippocampus areas were immunostained for specific neuronal markers and astrocytes.

RESULTS

Serum folate levels increased according to FA dietary level (p < 0.01). There was a significant increase in the serum homocysteine concentrations in the folic acid-deficient diet group (p < 0.01). However, brain S-adenosylmethionine and S-adenosylhomocysteine did not differ significantly between the folic acid groups. Consequently, the methylation ratio was also unchanged. The morphometric analysis did not show any differences in the number of neurons and astrocytes between groups, except when comparing the folic acid-deficient diet versus folic acid-supplemented diet in the striatum of the hippocampus.

CONCLUSIONS

Clearly, the dietary FA deficiency negatively affects the methionine metabolism biomarkers, while excessive supplementation seems to be unnecessary for optimal maintenance of the methylation cycle and hippocampus integrity.

The effect of combined therapy of exercise and nootropic agent on cognitive function in focal cerebral infarction rat model

Objective

To investigate the effect of combined therapy of exercise and nootropic agent on cognitive function in a focal cerebral infarction rat model.

Method

Forty 10-week old male Sprague-Dawley rats were subjected to photothrombotic cerebral infarction of the left parietal lobe. All rats were randomly divided into 4 groups: group A was photothrombotic cerebral infarction rats without any treatment (n=10); group B was photothrombotic cerebral infarction rats with swimming exercise (n=10); group C was photothrombotic cerebral infarction rats with oral administration of acetyl-L-carnitine (n=10); group D was photothrombotic cerebral infarction rats with swimming exercise and oral administration of acetyl-L-carnitine (n=10). Cognitive function was evaluated using the Morris water maze test on the 1st day, and the 1st, 2nd, and 4th week after the induction of cerebral infarction. The activity of superoxide dismutase (SOD) and the level of malondialdehyde (MDA) in the hippocampus were measured. The neuronal cells of the hippocampus were histopathologically evaluated.

Results

The escape latency was shorter in groups B, C, and D than in group A. However, the differences were not statistically significant at the 1st, 2nd and 4th week. The activity of SOD was the highest in group D. The level of MDA was the lowest in group D. We observed more normal neuronal cells in groups B, C, and D.

Conclusion

The combined therapy of exercise and nootropic agent was helpful in ameliorating oxidative stress in the focal cerebral infarction rat model. However, the effect did not translate into improvement of cognitive function.

From pattern to purpose: how comparative studies contribute to understanding the function of adult neurogenesis

The study of adult neurogenesis has had an explosion of fruitful growth. Yet numerous uncertainties and challenges persist. Our review begins with a survey of species that show evidence of adult neurogenesis. We then discuss how neurogenesis varies across brain regions and point out that regional specializations can indicate functional adaptations. Lifespan and aging are key life-history traits. Whereas 'adult neurogenesis' is the common term in the literature, it does not reflect the reality of neurogenesis being primarily a 'juvenile' phenomenon. We discuss the sharp decline with age as a universal trait of neurogenesis with inevitable functional consequences. Finally, the main body of the review focuses on the function of neurogenesis in birds and mammals. Selected examples illustrate how our understanding of avian and mammalian neurogenesis can complement each other. It is clear that although the two phyla have some common features, the function of adult neurogenesis may not be similar between them and filling the gaps will help us understand neurogenesis as an evolutionarily conserved trait to meet particular ecological pressures.

Effects of physical exercise on spatial memory and astroglial alterations in the hippocampus of diabetic rats

Type 1 diabetes mellitus (T1DM) is associated with neurocognitive dysfunction and astrogliosis. Physical exercise prevents cognitive impairments and induces important brain modifications. The aim of our study was to investigate the effect of treadmill exercise on spatial memory and astrocytic function in the hippocampus of a T1DM model. Fifty-seven Wistar rats were divided into four groups: trained control (TC) (n = 15), non-trained control (NTC) (n = 13), trained diabetic (TD) (n = 14) and non-trained diabetic (NTD) (n = 15). One month after streptozotocin-induced diabetes, exercise groups were submitted to 5 weeks of physical training, and then, all groups were assessed in the novel object-placement recognition task. Locomotor activity was analyzed in the open field apparatus using Any-maze software. The expression of glial fibrillary acidic protein (GFAP) and S100B in hippocampus and cerebrospinal fluid were measured using ELISA assay, and hippocampal GFAP immunoreactivity was evaluated by means of immunohistochemistry and optical densitometry. The results showed that physical exercise prevents and/or reverts spatial memory impairments observed in NTD animals (P < 0.01). Decreased locomotor activity was observed in both the NTD and TD groups when compared with controls (P < 0.05). ELISA and immunohistochemistry analyzes showed there was a reduction in GFAP levels in the hippocampus of NTD animals, which was not found in TD group. ELISA also showed an increase in S100B levels in the cerebrospinal fluid from the NTD group (P < 0.01) and no such increase was found in the TD group. Our findings indicate that physical exercise prevents and/or reverts the cognitive deficits and astroglial alterations induced by T1DM.

Immunohistological markers for proliferative events, gliogenesis, and neurogenesis within the adult hippocampus

Biologists long believed that, once development is completed, no new neurons are produced in the forebrain. However, as is now firmly established, new neurons can be produced at least in two specific forebrain areas: the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampal formation. Neurogenesis within the adult DG occurs constitutively throughout postnatal life, and the rate of neurogenesis within the DG can be altered under various physiological and pathophysiological conditions. The process of adult neurogenesis within the DG is a multi-step process (proliferation, differentiation, migration, targeting, and synaptic integration) that ends with the formation of a post-mitotic functionally integrated new neuron. Various markers are expressed during specific stages of adult neurogenesis. The availability of such markers allows the time-course and fate of newly born cells to be followed within the DG in a detailed and precise fashion. Several of the available markers (e.g., PCNA, Ki-67, PH3, MCM2) are markers for proliferative events, whereas others are more specific for early phases of neurogenesis and gliogenesis within the adult DG (e.g., nestin, GFAP, Sox2, Pax6). In addition, markers are available allowing events to be distinguished that are related to later steps of gliogenesis (e.g., vimentin, BLBP, S100beta) or neurogenesis (e.g., NeuroD, PSA-NCAM, DCX).

Short-term sleep deprivation may alter the dynamics of hippocampal cell proliferation in adult rats

Long-term (>48 h) sleep deprivation (SD) reduces adult rat hippocampal cell proliferation and neurogenesis, yet reported effects of short-term (<24 h) SD are inconsistent. We systematically assessed the effects of various durations of SD on adult rat hippocampal cell proliferation. Rats were sleep-deprived for 6, 12, 24, 36 or 48 h and injected with 5-bromo-2'-deoxyuridine (BrdU) 2 h before the end of SD. Immunolabeling for BrdU in the hippocampal subgranular zone increased significantly after 12 h SD but tended to decrease after 48 h SD relative to respective Controls. Surprisingly, SD did not alter immunolabeling for Ki67 protein (Ki67) or proliferating cell nuclear antigen (PCNA), two intrinsic cell proliferation markers. SD did not affect BrdU or Ki67 labeling in the subventricular zone, nor did it affect serum corticosterone levels. Because immunoreactivity for Ki67 and PCNA can identify cells in all phases of the ∼25 h cell cycle in adult rat hippocampus, whereas BrdU labels only cells in S-phase (∼9.5 h), this discrepancy suggests that 12 h SD might have affected cell cycle dynamics. A separate group of rats were injected with BrdU 10 h before the end of 12 h SD, which would allow some time for labeled cells to divide; the results were consistent with an acceleration of the timing of hippocampal progenitor cell division during 12 h SD. These results suggest that short-term (12 h) SD transiently produces more hippocampal progenitor cells via cell cycle acceleration, and confirm the importance of using multiple cell cycle markers or BrdU injection paradigms to assess potential changes in cell proliferation.

Hippocampal mossy fiber sprouting induced by forced and voluntary physical exercise

Alterations in the function and organization of synapses have been proposed to induce learning and memory. Previous studies have demonstrated that mossy fiber induced by overtraining in a spatial learning task can be related with spatial long-term memory formation. In this work we analyzed whether physical exercise could induce mossy fiber sprouting by using a zinc-detecting histologic technique (Timm). Rats were submitted to 3 and 5days of forced or voluntary exercise. Rat brains were processed for Timm's staining to analyze mossy fiber projection at 7, 12 and 30days after the last physical exercise session. A significant increase of mossy fiber terminals in the CA3 stratum oriens region was observed after 5days of forced or voluntary exercise. Interestingly, the pattern of Timm's staining in CA3 mossy fibers was significantly altered when analyzed 12days after exercise but not at 7days post-exercise. In contrast, animals trained for only 3days did not show increments of mossy fiber terminals in the stratum oriens. Altogether, these results demonstrate that sustained or programmed exercise can alter mossy fiber sprouting. Further Investigations are necessary to determine whether mossy fiber sprouting induced by exercise is also involved in learning and memory processes.

Opioid modulation of cell proliferation in the ventricular zone of adult zebra finches (Taenopygia guttata)

Besides modulating pain, stress, physiological functions, motivation, and reward, the opioid system has been implicated in developmental and adult mammalian neurogenesis and gliogenesis. In adult male songbirds including zebra finches, neurons generated from the ventricular zone (VZ) of the lateral ventricles are incorporated throughout the telencephalon, including the song control nuclei, HVC, and area X. Although the endogenous opioid met-enkephalin is present in neurons adjacent to the VZ and is upregulated in song control regions during singing, it is not known whether the opioid system can modulate adult neurogenesis/gliogenesis in zebra finches. We used quantitative RT-PCR and in situ hybridization to demonstrate that μ- and δ-opioid receptors are expressed by the VZ of adult male zebra finches. Treating cultured VZ cells from male birds with the opioid antagonist naloxone led to an increase in cell proliferation measured by 5-bromo-2-deoxyuridine incorporation, whereas administering met-enkephalin had the opposite effect, compared with saline-treated cultures. Systemically administering naloxone (2.5 mg/kg body wt) to adult male zebra finches for 4 d also led to a significant increase in cell proliferation in the ventral VZ of these birds, compared with saline-treated controls. Our results show that cell proliferation is augmented by naloxone in the VZ adjacent to the anterior commissure, suggesting that the endogenous opioids modulate adult neurogenesis/gliogenesis by inhibiting cell proliferation in songbirds.

Social isolation prevents exercise-induced proliferation of hippocampal progenitor cells in female rats

Social isolation negatively affects the behavior and health of laboratory rats. Recently, it has been found that social isolation retards exercise-induced neurogenesis in the hippocampal dentate gyrus (DG) of male rats (Stranahan et al. (2006) Nat Neurosci 9:526-533). Since male and female rats react differently to housing changes and exercise opportunities, we investigated whether social isolation would also suppress the exercise-dependent increase in proliferation of dentate gyrus progenitor cells in females. Accordingly, female rats were housed either alone (isolated) or in groups (social) with (exercise) or without (sedentary) the opportunity to run in an exercise wheel. Proliferating progenitor cells were labeled with bromodeoxyuridine (BrdU). As expected, exercise increased the number of BrdU+ cells in socially housed animals. However, isolation prevented this running-induced increase. Our results expand upon previous findings by showing that the female brain is also susceptible to the suppressive effect of social isolation on exercise-induced neurogenesis.

Additive effects of physical exercise and environmental enrichment on adult hippocampal neurogenesis in mice

Voluntary physical exercise (wheel running, RUN) and environmental enrichment both stimulate adult hippocampal neurogenesis but do so by different mechanisms. RUN induces precursor cell proliferation, whereas ENR exerts a survival-promoting effect on newborn cells. In addition, continued RUN prevented the physiologically occurring age-related decline in precursor cell in the dentate gyrus but did not lead to a corresponding increase in net neurogenesis. We hypothesized that in the absence of appropriate cognitive stimuli the potential for neurogenesis could not be realized but that an increased potential by proliferating precursor cells due to RUN could actually lead to more adult neurogenesis if an appropriate survival-promoting stimulus follows the exercise. We thus asked whether a sequential combination of RUN and ENR (RUNENR) would show additive effects that are distinct from the application of either paradigm alone. We found that the effects of 10 days of RUN followed by 35 days of ENR were additive in that the combined stimulation yielded an approximately 30% greater increase in new neurons than either stimulus alone, which also increased neurogenesis. Surprisingly, this result indicates that although overall the amount of proliferating cells in the dentate gyrus is poorly predictive of net adult neurogenesis, an increased neurogenic potential nevertheless provides the basis for a greater efficiency of the same survival-promoting stimulus. We thus propose that physical activity can “prime” the neurogenic region of the dentate gyrus for increased neurogenesis in the case the animal is exposed to an additional cognitive stimulus, here represented by the enrichment paradigm.

A reward increases running-wheel performance without changing cell proliferation, neuronal differentiation or cell death in the dentate gyrus of C57BL/6 mice

Exercise is one of the best-known stimulators of adult hippocampal neurogenesis, but it is not known if voluntary changes in the intensity of exercise are accompanied by changes in neurogenesis. In this study we investigated whether a reward influences the performance in a running wheel and the rate of cell proliferation, neuronal differentiation and cell death in C57BL/6 mice. Mice had free access to a running wheel during the first week of the experiment. In the second week, animals were rewarded for their performance and compared to normal voluntary running and control mice. A reward significantly increased the performance by 78% when compared to the non-rewarded performance of the first week. The performance of the non-rewarded runners remained relatively constant. Fourteen days of exercise significantly increased cell proliferation by 27% and the number of doublecortin immunoreactive cells by 46%. A reward and the associated increase of performance did not modulate proliferation, cell death or the number of cells entering the neuronal lineage. We suggest that, in C57BL/6 mice, either exercise increases adult hippocampal neurogenesis to a ceiling value, which is reached by a performance at or below the level achieved by voluntary wheel running, or that a possible positive effect of increased running-wheel activity is balanced by stress resulting from rewarded running, which is no longer performed on a strictly voluntary basis.

Effect of voluntary running on adult hippocampal neurogenesis in cholinergic lesioned mice

Background

Cholinergic neuronal dysfunction of the basal forebrain is observed in patients with Alzheimer's disease and dementia, and has been linked to decreased neurogenesis in the hippocampus, a region involved in learning and memory. Running is a robust inducer of adult hippocampal neurogenesis. This study aims to address the effect of running on hippocampal neurogenesis in lesioned mice, where septohippocampal cholinergic neurones have been selectively eliminated in the medial septum and diagonal band of Broca of the basal forebrain by infusion of mu-p75-saporin immunotoxin.

Results

Running increased the number of newborn cells in the dentate gyrus of the hippocampus in cholinergic denervated mice compared to non-lesioned mice 24 hours after injection of bromodeoxyuridine (BrdU). Although similar levels of surviving cells were present in cholinergic depleted animals and their respective controls four weeks after injection of BrdU, the majority of progenitors that proliferate in response to the initial period of running were not able to survive beyond one month without cholinergic input. Despite this, the running-induced increase in the number of surviving neurones was not affected by cholinergic depletion.

Conclusion

The lesion paradigm used here models aspects of the cholinergic deficits associated with Alzheimer's Disease and aging. We showed that running still increased the number of newborn cells in the adult hippocampal dentate gyrus in this model of neurodegenerative disease.

Glucocorticoid signaling and exercise-induced downregulation of the mineralocorticoid receptor in the induction of adult mouse dentate neurogenesis by treadmill running

Physical exercise is known to promote adult neurogenesis, although the underlying mechanisms remain unclear. Glucocorticoid (corticosterone in rodents) is a factor that is known to affect neurogenesis. As physical exercise modulates corticosterone secretion, we hypothesized that corticosterone signaling is involved in exercise-induced adult neurogenesis. We chose treadmill running (TR) to accurately define the intensity and duration of exercise. Our results showed that 5 weeks of TR increased the doublecortin (DCX)-positive neuronal progenitor cells (NPCs) in adult hippocampus and transiently increased the serum corticosterone level at the end of the TR protocol. This protocol reduced the levels of hippocampal mineralocorticoid receptor (MR); however, glucocorticoid receptor levels were unaltered. We then investigated whether reducing corticosterone levels by bilateral adrenalectomy (ADX) attenuated the TR-enhanced adult neurogenesis. Our results showed that ADX not only blocked the TR-induced downregulation of MR, but also reduced the number of TR-enhanced NPCs. In order to examine the role of MR downregulation in TR-induced adult neurogenesis, animals were treated repeatedly with a selective MR antagonist, spironolactone, for 3 weeks. The results revealed that spironolactone increased the number of spontaneously occurring and TR-induced NPC in the dentate area. Further analysis revealed that spironolactone treatment did not alter precursor cell proliferation, but increased the number of DCX-positive NPCs, suggesting that blockage of MR signaling either facilitates the differentiation of progenitor cells towards neurons and/or enhances the survival of NPCs. Taken together, the data indicated that induction of NPCs in the dentate area of adult hippocampus by TR is partly due to the downregulation of glucocorticoid/MR signaling, which subsequently enhances differentiation along a neuronal lineage and/or NPC survival.

Forced and voluntary exercise differentially affect brain and behavior

The potential of physical exercise to decrease body weight, alleviate depression, combat aging and enhance cognition has been well-supported by research studies. However, exercise regimens vary widely across experiments, raising the question of whether there is an optimal form, intensity and duration of exertion that would produce maximal benefits. In particular, a comparison of forced and voluntary exercise is needed, since the results of several prior studies suggest that they may differentially affect brain and behavior. In the present study, we employed a novel 8-week exercise paradigm that standardized the distance, pattern, equipment and housing condition of forced and voluntary exercisers. Exercising rats were then compared with sedentary controls on measures previously shown to be influenced by physical activity. Our results indicate that although the distance covered by both exercise groups was the same, voluntary exercisers ran at higher speed and for less total time than forced exercisers. When compared with sedentary controls, forced but not voluntary exercise was found to increase anxiety-like behaviors in the open field. Both forms of exercise increased the number of surviving bromodeoxyuridine (BrdU)+ cells in the dentate gyrus after 8 weeks of exercise, although forced exercisers had significantly more than voluntary exercisers. Phenotypic analysis of BrdU+ cells showed no difference between groups in the percentage of newborn cells that became neurons, however, because forced exercise maximally increased the number of BrdU+ cells, it ultimately produced more neurons than voluntary exercise. Our results indicate that forced and voluntary exercise are inherently different: voluntary wheel running is characterized by rapid pace and short duration, whereas forced exercise involves a slower, more consistent pace for longer periods of time. This basic difference between the two forms of exercise is likely responsible for their differential effects on brain and behavior.

Voluntary exercise-induced neurogenesis in the postischemic dentate gyrus is associated with spatial memory recovery from stroke

Spatial cognitive impairment is common after stroke insults. Voluntary exercise could improve the impaired spatial memory. Newly generated neurons in the dentate gyrus are necessary for the acquisition of new hippocampus-dependent memories. However, it is not well known whether voluntary exercise after stroke promotes neurogenesis in the adult dentate gyrus, thereby promoting spatial memory recovery. Here, we examined in mice subjected to focal cerebral ischemia the effect of voluntary or forced exercise on neurogenesis in the ischemic dentate gyrus and spatial memory. Exposure to voluntary wheel running after stroke enhanced newborn cell survival and up-regulated the phosphorylation of cAMP response element binding protein (CREB) in the dentate gyrus and reversed ischemia-induced spatial memory impairment. However, the enhanced newborn cell survival and CREB phosphorylation in the dentate gyrus and improved spatial memory were not observed in the mice exposed to forced swimming. Moreover, there was a significant correlation between the total number of surviving newborn cells in the dentate gyrus and the ability of mice to locate the platform in the Morris water maze. These results suggest that, in the adult mice, exposure to voluntary exercise after ischemic stroke may promote newborn cells survival in the dentate gyrus by up-regulating CREB phosphorylation and consequently restore impaired hippocampus-dependent memory.