Enhancement of neurogenesis by running wheel exercises is suppressed in mice lacking NMDA receptor epsilon 1 subunit

Molecular mechanisms underlying physical exercise-induced brain BDNF overproduction

Accumulating evidence supports that physical exercise (EX) is the most effective non-pharmacological strategy to improve brain health. EX prevents cognitive decline associated with age and decreases the risk of developing neurodegenerative diseases and psychiatric disorders. These positive effects of EX can be attributed to an increase in neurogenesis and neuroplastic processes, leading to learning and memory improvement. At the molecular level, there is a solid consensus to involve the neurotrophin brain-derived neurotrophic factor (BDNF) as the crucial molecule for positive EX effects on the brain. However, even though EX incontestably leads to beneficial processes through BDNF expression, cellular sources and molecular mechanisms underlying EX-induced cerebral BDNF overproduction are still being elucidated. In this context, the present review offers a summary of the different molecular mechanisms involved in brain's response to EX, with a specific focus on BDNF. It aims to provide a cohesive overview of the three main mechanisms leading to EX-induced brain BDNF production: the neuronal-dependent overexpression, the elevation of cerebral blood flow (hemodynamic hypothesis), and the exerkine signaling emanating from peripheral tissues (humoral response). By shedding light on these intricate pathways, this review seeks to contribute to the ongoing elucidation of the relationship between EX and cerebral BDNF expression, offering valuable insights into the potential therapeutic implications for brain health enhancement.

Effects of early exercise intervention and exercise cessation on neuronal loss and neuroinflammation in a senescence-accelerated mouse prone 8

Physical exercise is beneficial for preventing Alzheimer's disease (AD) and cognitive decline through several mechanisms, including suppression of neuroinflammation and neuronal loss in the hippocampus. Despite these exercise-induced benefits in AD pathology, less attention has been paid to the importance of maintaining exercise and the consequences of detraining. This study aimed to investigate the effects of early exercise intervention and detraining on age-related cognitive decline and its protective mechanisms using senescence-accelerated mouse prone 8 (SAMP8). These mice were divided to four groups: no-exercise (No-Ex, n = 9), 4 months (4M)-detraining (n = 11), 2 months (2M)-detraining (n = 11), and long-term exercise (LT-Ex, n = 13). Age-related cognitive decline was prevented in the LT-Ex group compared with the No-Ex group through the suppression of neuronal loss, enhanced brain-derived neurotrophic factor (BDNF), and inhibition of neuroinflammation corresponding to reduced M1 and increased M2 microglia in the hippocampus. No significant differences were observed in cognitive function between the detraining and No-Ex groups. However, the 2M-detraining group showed increased BDNF positive area in the CA1 region and the enhancement of anti-inflammatory M2 phenotype microglia. In contrast, no statistically beneficial exercise-induced changes in the hippocampus were observed in the 4M-detrainig group. These results showed that early exercise intervention prevented age-related cognitive deficits in AD progression by suppressing neuronal loss and neuroinflammation in the hippocampus. Exercise-induced benefits, including the anti-inflammation in the hippocampus, may be retained after exercise cessation, even if exercise-induced beneficial effects decline in a time-dependent manner.

Beneficial effects of enriched environment on behavior, cognitive functions, and hippocampal brain-derived neurotrophic factor level following postnatal serotonin depletion in male rats

The neurotransmitter serotonin (5-HT) is one of the most important modulators of neural circuitry and has a critical role in neural development and functions. Previous studies indicated that changes in serotonergic system signaling in early life critically impact mental health, behavior, the morphology of hippocampal neurons, and cognitive functions across the lifespan. The enriched environment (EE) has indicated beneficial effects on behavior and cognitive functions in the developmental period of life, but its impacts on cognitive impairments and behavioral changes following postnatal serotonin depletion are unknown. Therefore, the present study aimed to evaluate the influences of the EE housing (postnatal days [PNDs] 21-60) following postnatal serotonin depletion (by para-chlorophenylalanine [PCPA], 100 mg/kg, s.c, in PNDs 10-20) on anxiety-related behaviors, cognitive functions, and brain-derived neurotrophic factor (BDNF) mRNA expression in the hippocampus of male rats. Memory and behavioral parameters were examined in early adulthood and after that, the hippocampi of rats were removed to determine the BDNF mRNA expression by PCR (PNDs 60-70). The findings of the present work indicated that adolescent EE exposure alleviated memory impairment, decreased BDNF levels, and anxiety disorders induced by experimental depletion of serotonin. Overall, these results indicate that serotonergic system dysregulation during the developmental periods can be alleviated by adolescent EE exposure.

Exercise to spot the differences: a framework for the effect of exercise on hippocampal pattern separation in humans

Exercise has a beneficial effect on mental health and cognitive functioning, but the exact underlying mechanisms remain largely unknown. In this review, we focus on the effect of exercise on hippocampal pattern separation, which is a key component of episodic memory. Research has associated exercise with improvements in pattern separation. We propose an integrated framework mechanistically explaining this relationship. The framework is divided into three pathways, describing the pro-neuroplastic, anti-inflammatory and hormonal effects of exercise. The pathways are heavily intertwined and may result in functional and structural changes in the hippocampus. These changes can ultimately affect pattern separation through direct and indirect connections. The proposed framework might guide future research on the effect of exercise on pattern separation in the hippocampus.

Adolescent enriched environment exposure alleviates cognitive impairment in sleep-deprived male rats: Role of hippocampal BDNF

Developmental life experience has long-lasting influences on the brain and behavior. The present study aims to examine the long-term effects of the enriched environment (EE), which was imposed during the adolescence period of life, on their passive avoidance and recognition memories as well as anxiety-like behaviors and hippocampal brain-derived neurotrophic factor (BDNF) levels, in sleep-deprived male rats. In the present study, the male pups were separated from their mothers in postnatal day 21 (PND21) and were housed in the standard or EE for 40 days. In PND 61, the rats were allocated in four groups: control, SD (sleep deprivation), EE, and EE+SD groups. Sleep deprivation was induced in rats by a modified multiple platform model for 24 hours. Open field, novel object recognition memory, and passive avoidance memory tests were used to examine behavior and cognitive ability. The expression of hippocampal BDNF levels was determined by PCR. The results revealed that SD increased anxiety-like behaviors and impaired cognitive ability, while adolescent EE housing alleviated these changes. In addition, EE reversed SD-induced changes in hippocampal BDNF level. We also demonstrated that EE not only has beneficial effects on the cognitive functions of normal rats but also declined memory deficits induced by sleep deprivation. In conclusion, our results suggest that housing in EE during the adolescence period of life reduces cognitive impairment induced by SD. The increase of the BDNF level in the hippocampus is a possible mechanism to alleviate cognitive performance in sleep-deprived rats.

Sex-dependent effects of postweaning exposure to an enriched environment on novel objective recognition memory and anxiety-like behaviors: The role of hippocampal BDNF level

Exposure to enriched environment (EE) has been indicated to enhance cognitive functions, hippocampal neural plasticity, neurogenesis, long-term potentiation, and levels of the brain-derived neurotrophic factor (BDNF) in laboratory animals. Also, studies on the sex-dependent effects of exposure to EE during adolescence on adult cognitive functions are less. This is important because the beneficial effects of EE may be predominant in the adolescence stage. Therefore, the present study was designed to compare the effects of EE during adolescence (PND21-PND60) on novel objective recognition memory (NORM), anxiety-like behaviors, and hippocampal BDNF mRNA level in the adult male and female rats. Assessment of NORM and anxiety-like behaviors has been done by novel objective recognition task, open field (OF), and elevated plus maze (EPM), respectively. The expression of BDNF mRNA level was also evaluated by quantitative RT-PCR. Our findings demonstrated that housing in the EE during adolescence improves NORM in adult male rats. Also, exposure to EE during adolescence had a different effect on anxiety-like behaviors in both sexes. Additionally, our results indicated an augmented BDNF level in the hippocampus of male and female rats. In conclusion, adolescent exposure to EE has sex-dependent effects on cognitive functions and anxiety-like behaviors and increases BDNF mRNA expression in the hippocampus of both male and female rats; thus, BDNF is an important factor that can mediate the beneficial effects of EE and running exercise on cognitive functions and psychiatric traits.

Effects of exercise on proactive interference in memory: potential neuroplasticity and neurochemical mechanisms

Proactive interference occurs when consolidated memory traces inhibit new learning. This kind of interference decreases the efficiency of new learning and also causes memory errors. Exercise has been shown to facilitate some types of cognitive function; however, whether exercise reduces proactive interference to enhance learning efficiency is not well understood. Thus, this review discusses the effects of exercise on proactive memory interference and explores potential mechanisms, such as neurogenesis and neurochemical changes, mediating any effect.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

Postnatal changes in constitutive cyclooxygenase‑2 expression in the mice hippocampus and its function in synaptic plasticity

Although the expression of cyclooxygenase-2 (COX-2) is closely associated with inflammation in the brain, it is constitutively expressed in the brain, and its expression is regulated by synaptic activity. The present study investigated postnatal expression of COX-2 in the hippocampus in C57BL/6 mice at postnatal days (P) 1, 7, 14, 28, and 56. In addition, the presented study examined the effects of COX-2 on synaptic plasticity through Arc, phosphorylated cAMP response element-binding protein (pCREB), N-methyl-d-aspartate receptor 1 (GluN1), and GluN2A/2B immunohistochemistry, which was performed on COX-2 knockout (KO) and wild-type (WT) mice. Extremely weak COX-2 immunoreactivity was detected in the hippocampal CA1-3 areas in addition to the dentate gyrus at P1. Conversely, COX-2 immunoreactivity was observed in the stratum pyramidale of the CA1-3 regions and in the outer granule cell layer of the dentate gyrus at P7. Additionally, although peak COX-2 immunoreactivity was observed in all hippocampal sub-regions, including the dentate gyrus at P14, it was significantly decreased at P14. Finally, COX-2 immunoreactivity and the distribution pattern seen at P56 in the hippocampal CA1-3 regions were similar to those observed at P28, whereas, they were identified in the inner half of the granule cell layer of the dentate gyrus. The western blot analysis revealed that the COX-2 protein levels peaked at P14 and were decreased at P28 and P56. Additionally, the number of Arc and pCREB immunoreactive cells as well as GluN1 and GluN2A/2B immunoreactivity of COX-2 KO mice were significantly decreased in the dentate gyrus when compared with that in WT mice. Taken together, the results of the present study suggest that COX-2 serves an important role in synaptic plasticity in the dentate gyrus and changes in the levels of its constitutive expression are associated with the hippocampal dentate gyrus postnatal development.

Dexras1 is a homeostatic regulator of exercise-dependent proliferation and cell survival in the hippocampal neurogenic niche

Adult hippocampal neurogenesis is highly responsive to exercise, which promotes the proliferation of neural progenitor cells and the integration of newborn granule neurons in the dentate gyrus. Here we show that genetic ablation of the small GTPase, Dexras1, suppresses exercise-induced proliferation of neural progenitors, alters survival of mitotic and post-mitotic cells in a stage-specific manner, and increases the number of mature newborn granule neurons. Dexras1 is required for exercise-triggered recruitment of quiescent neural progenitors into the cell cycle. Pharmacological inhibition of NMDA receptors enhances SGZ cell proliferation in wild-type but not dexras1-deficient mice, suggesting that NMDA receptor-mediated signaling is dependent on Dexras1. At the molecular level, the absence of Dexras1 abolishes exercise-dependent activation of ERK/MAPK and CREB, and inhibits the upregulation of NMDA receptor subunit NR2A, bdnf, trkB and vegf-a expression in the dentate gyrus. Our study reveals Dexras1 as an important stage-specific regulator of exercise-induced neurogenesis in the adult hippocampus by enhancing pro-mitogenic signaling to neural progenitor cells and modulating cell survival.

Effects of acute voluntary loaded wheel running on BDNF expression in the rat hippocampus

[Purpose]

Voluntary loaded wheel running involves the use of a load during a voluntary running activity. A muscle-strength or power-type activity performed at a relatively high intensity and a short duration may cause fewer apparent metabolic adaptations but may still elicit muscle fiber hypertrophy. This study aimed to determine the effects of acute voluntary wheel running with an additional load on brain-derived neurotrophic factor (BDNF) expression in the rat hippocampus.

[Methods]

Ten-week old male Wistar rats were assigned randomly to a (1) sedentary (Control) group; (2) voluntary exercise with no load (No-load) group; or (3) voluntary exercise with an additional load (Load) group for 1-week (acute period). The expression of BDNF genes was quantified by real-time PCR.

[Results]

The average distance levels were not significantly different in the No-load and Load groups. However, the average work levels significantly increased in the Load group. The relative soleus weights were greater in the No-load group. Furthermore, loaded wheel running up-regulated the BDNF mRNA level compared with that in the Control group. The BDNF mRNA levels showed a positive correlation with workload levels (r=0.75), suggesting that the availability of multiple workload levels contributes to the BDNF-related benefits of loaded wheel running noted in this study.

[Conclusion]

This novel approach yielded the first set of findings showing that acute voluntary loaded wheel running, which causes muscular adaptation, enhanced BDNF expression, suggesting a possible role of high-intensity short-term exercise in hippocampal BDNF activity.

NASCIDOS PARA CORRER: A IMPORTÂNCIA DO EXERCÍCIO PARA A SAÚDE DO CÉREBRO

RESUMO A hipótese evolutiva da corrida de resistência afirma que o movimento teve um papel crucial no aparecimento de características anatômicas tipicamente humanas, assim como na modelação da estrutura e forma do cérebro humano. A íntima ligação entre exercício e evolução humana é evidenciada pelo fato de a inatividade nos tornar doentes. Efetivamente, o corpo humano, incluindo o cérebro, evoluiu para suportar períodos prolongados de estresse cardiovascular. O movimento é de tal modo essencial para o cérebro, que a atividade física regular é imprescindível para que funcione de modo adequado. Estudos vêm demonstrando que o exercício aeróbico aumenta a proliferação de neurônios, a síntese de fatores neurotróficos, gliogênese, sinaptogênese, regula sistemas de neurotransmissão e neuromodulação, além de reduzir a inflamação sistêmica. Todos esses efeitos têm impacto significativo no sentido de melhorar a saúde mental, reduzir o declínio de massa cinzenta associado à idade e melhorar as funções cognitivas. Deste modo, o objetivo deste artigo é apresentar uma atualização sobre a temática de exercício físico e saúde mental. Dados os recentes avanços apresentados neste original, sobre a neurobiologia do exercício e seu potencial terapêutico e econômico para a população em geral, espera-se que pesquisas futuras que correlacionem estudos básicos a variáveis psicológicas e estudos de imagem possam elucidar os mecanismos pelos quais o exercício melhora a saúde cerebral.

Adult hippocampal neurogenesis: an important target associated with antidepressant effects of exercise

Depression is a prevalent devastating mental disorder that affects the normal life of patients and brings a heavy burden to whole society. Although many efforts have been made to attenuate depressive/anxiety symptoms, the current clinic antidepressants have limited effects. Scientists have long been making attempts to find some new strategies that can be applied as the alternative antidepressant therapy. Exercise, a widely recognized healthy lifestyle, has been suggested as a therapy that can relieve psychiatric stress. However, how exercise improves the brain functions and reaches the antidepressant target needs systematic summarization due to the complexity and heterogeneous feature of depression. Brain plasticity, especially adult neurogenesis in the hippocampus, is an important neurophysiology to facilitate animals for neurogenesis can occur in not only humans. Many studies indicated that an appropriate level of exercise can promote neurogenesis in the adult brains. In this article, we provide information about the antidepressant effects of exercise and its implications in adult neurogenesis. From the neurogenesis perspective, we summarize evidence about the effects of exercise in enhancing neurogenesis in the hippocampus through regulating growth factors, neurotrophins, neurotransmitters and metabolism as well as inflammations. Taken together, a large number of published works indicate the multiple benefits of exercise in the brain functions of animals, particularly brain plasticity like neurogenesis and synaptogenesis. Therefore, a new treatment method for depression therapy can be developed by regulating the exercise activity.

Limiting exercise inhibits neuronal recovery from neurological disorders

Patients who are bedridden often suffer from muscular atrophy due to reduced daily activities and can become depressed. However, patients who undergo physical therapy sometimes demonstrate positive benefits including a reduction of stressful and depressed behavior. Regenerative medicine has seen improvements in two stem cell-based therapies for central nervous system disorders. One therapy is through the transfer of exogenous stem cells. The other therapy is a more natural method and focuses on the increasing endogenous neurogenesis and restoring the neurological impairments. This study overviews how immobilization-induced disuse atrophy affects neurogenesis in rats, specifically hypothesizing that immobilization diminishes circulating trophic factor levels, like vascular endothelial growth factors or brain-derived neurotrophic factor, which in turn limits neurogenesis. This hypothesis requires the classification of the stem cell microenvironment by probing growth factors in addition to other stress-related proteins that correlate with exercise-induced neurogenesis. There is research examining the effects of increased exercise on neurogenesis while limiting exercise, which better demonstrates the pathological states of immobile stroke patients, remains relatively unexplored. To examine the effects of immobilization on neurogenesis quantitative measurements of movements, 5-bromo-2deoxyuridine labeling of proliferative cells, biochemical assays of serum, cerebrospinal fluid and neurological levels of trophic factors, growth factors, and stress-related proteins will indicate levels of neurogenesis. In further research, studies are needed to show how in vivo stimulation, or lack thereof, affects stem cell microenvironments to advance treatment procedures for strengthening neurogenesis in bedridden patients. This paper is a review article. Referred literature in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors' experiences.

Pcdhαc2 is required for axonal tiling and assembly of serotonergic circuitries in mice

Serotonergic neurons project their axons pervasively throughout the brain and innervate various target fields in a space-filling manner, leading to tiled arrangements of their axon terminals to allow optimal allocation of serotonin among target neurons. Here we show that conditional deletion of the mouse protocadherin α (Pcdhα) gene cluster in serotonergic neurons disrupts local axonal tiling and global assembly of serotonergic circuitries and results in depression-like behaviors. Genetic dissection and expression profiling revealed that this role is specifically mediated by Pcdhαc2, which is the only Pcdhα isoform expressed in serotonergic neurons. We conclude that, in contrast to neurite self-avoidance, which requires single-cell identity mediated by Pcdh diversity, a single cell-type identity mediated by the common C-type Pcdh isoform is required for axonal tiling and assembly of serotonergic circuitries.

Negative rebound in hippocampal neurogenesis following exercise cessation

Physical exercise can improve brain function, but the effects of exercise cessation are largely unknown. This study examined the time-course profile of hippocampal neurogenesis following exercise cessation. Male C57BL/6 mice were randomly assigned to either a control (Con) or an exercise cessation (ExC) group. Mice in the ExC group were reared in a cage with a running wheel for 8 wk and subsequently placed in a standard cage to cease the exercise. Exercise resulted in a significant increase in the density of doublecortin (DCX)-positive immature neurons in the dentate gyrus (at week 0). Following exercise cessation, the density of DCX-positive neurons gradually decreased and was significantly lower than that in the Con group at 5 and 8 wk after cessation, indicating that exercise cessation leads to a negative rebound in hippocampal neurogenesis. Immunohistochemistry analysis suggests that the negative rebound in neurogenesis is caused by diminished cell survival, not by suppression of cell proliferation and neural maturation. Neither elevated expression of ΔFosB, a transcription factor involved in neurogenesis regulation, nor increased plasma corticosterone, were involved in the negative neurogenesis rebound. Importantly, exercise cessation suppressed ambulatory activity, and a significant correlation between change in activity and DCX-positive neuron density suggested that the decrease in activity is involved in neurogenesis impairment. Forced treadmill running following exercise cessation failed to prevent the negative neurogenesis rebound. This study indicates that cessation of exercise or a decrease in physical activity is associated with an increased risk for impaired hippocampal function, which might increase vulnerability to stress-induced mood disorders.

Effects of inducing exercise on growing mice by means of three-dimensional structure in rearing environment

We reared ICR mice during a growth period (3 to 10 weeks of age) and examined the effect of exercise induction, by enriching the rearing environment with obstacles such as ladders, compared to the standard environment. Environmental enrichment significantly increased the amount of exercise in both sexes (P<0.01). Enriched exercise mice had higher body weight than control mice at 6 to 9 weeks of age in males and 8 weeks of age in females (P<0.05). The sexual maturation of female enriched exercise mice was significantly advanced compared to the control (P<0.001). Enriched exercise mice showed decreased anxiety-like behavior in the open field test and lower plasma corticosterone levels in both sexes compared to the control, and differences were statistically significant in males (P<0.05). In both sexes, enriched exercise appeared to increase natural killer cells in blood compared to the control, but no statistical differences was detected. In conclusion, we confirmed that daily low-stress exercise could be induced using a three-dimensional rearing environment in growing mice. In addition, we suggest that exercise has beneficial effects on physical growth, sexual maturation and anxiety-like behavior. Furthermore, environmental enrichment might be more effective in male than female in group-housed mice.

Detrimental effects of physical inactivity on neurogenesis

Patients diagnosed with neurological disorders exhibit a variety of physical and psychiatric symptoms, including muscle atrophy, general immobility, and depression. Patients who participate in physical rehabilitation at times show unexpected clinical improvement, which includes diminished depression and other stress-related behaviors. Regenerative medicine has advanced two major stem cell-based therapies for central nervous system (CNS) disorders, transplantation of exogenous stem cells, and enhancing the endogenous neurogenesis. The latter therapy utilizes a natural method of re-innervating the injured brain, which may mend neurological impairments. In this study, we examine how inactivity-induced atrophy, using the hindlimb suspension model, alters neurogenesis in rats. The hypothesis is that inactivity inhibits neurogenesis by decreasing circulation growth or trophic factors, such as vascular endothelial growth or neurotrophic factors. The restriction modifies neurogenesis and stem cell differentiation in the CNS, the stem cell microenvironment is examined by the trophic and growth factors, including stress-related proteins. Despite growing evidence revealing the benefits of “increased” exercise on neurogenesis, the opposing theory involving “physical inactivity,” which simulates pathological states, continues to be neglected. This novel theory will allow us to explore the effects on neurogenesis by an intransigent stem cell microenvironment likely generated by inactivity. 5-bromo-2-deoxyuridine labeling of proliferative cells, biochemical assays of serum, cerebrospinal fluid, and brain levels of trophic factors, growth factors, and stress-related proteins are suggested identifiers of neurogenesis, while evaluation of spontaneous movements will give insight into the psychomotor effects of inactivity. Investigations devised to show how in vivo stimulation, or lack thereof, affects the stem cell microenvironment are necessary to establish treatment methods to boost neurogenesis in bedridden patients.

Spatial learning and neurogenesis: Effects of cessation of wheel running and survival of novel neurons by engagement in cognitive tasks

Physical exercise stimulates cell proliferation in the adult dentate gyrus and facilitates acquisition and/or retention of hippocampal-dependent tasks. It is established that regular physical exercise improves cognitive performance. However, it is unclear for how long these benefits last after its interruption. Independent groups of rats received both free access to either unlocked (EXE Treatment) or locked (No-EXE Treatment) running wheels for 7 days, and daily injections of bromodeoxyuridine (BrdU) in the last 3 days. After a time delay period of either 1, 3, or 6 weeks without training, the animals were tested in the Morris water maze (MWM) either in a working memory task dependent on hippocampal function (MWM-HD) or in a visible platform searching task, independent on hippocampal function (MWM-NH). Data confirmed that exposure of rats to 7 days of spontaneous wheel running increases cell proliferation and neurogenesis. In contrast, neurogenesis was not accompanied by significant improvements of performance in the working memory version of the MWM. Longer time delays between the end of exercise and the beginning of cognitive training in the MWM resulted in lower cell survival; that is, the number of novel surviving mature neurons was decreased when this delay was 6 weeks as compared with when it was 1 week. In addition, data showed that while exposure to the MWM-HD working memory task substantially increased survival of novel neurons, exposure to the MWM-NH task did not, thus indicating that survival of novel dentate gyrus neurons depends on the engagement of this brain region in performance of cognitive tasks. © 2015 Wiley Periodicals, Inc.

Running Improves Pattern Separation during Novel Object Recognition

Running increases adult neurogenesis and improves pattern separation in various memory tasks including context fear conditioning or touch-screen based spatial learning. However, it is unknown whether pattern separation is improved in spontaneous behavior, not emotionally biased by positive or negative reinforcement. Here we investigated the effect of voluntary running on pattern separation during novel object recognition in mice using relatively similar or substantially different objects.We show that running increases hippocampal neurogenesis but does not affect object recognition memory with 1.5 h delay after sample phase. By contrast, at 24 h delay, running significantly improves recognition memory for similar objects, whereas highly different objects can be distinguished by both, running and sedentary mice. These data show that physical exercise improves pattern separation, independent of negative or positive reinforcement. In sedentary mice there is a pronounced temporal gradient for remembering object details. In running mice, however, increased neurogenesis improves hippocampal coding and temporally preserves distinction of novel objects from familiar ones.

Behavioral experiences as drivers of oligodendrocyte lineage dynamics and myelin plasticity

Many behavioral experiences are known to promote hippocampal neurogenesis. In contrast, the ability of behavioral experiences to influence the production of oligodendrocytes and myelin sheath formation remains relatively unknown. However, several recent studies indicate that voluntary exercise and environmental enrichment can positively influence both oligodendrogenesis and myelination, and that, in contrast, social isolation can negatively influence myelination. In this review we summarize studies addressing the influence of behavioral experiences on oligodendrocyte lineage cells and myelin, and highlight potential mechanisms including experience-dependent neuronal activity, metabolites, and stress effectors, as well as both local and systemic secreted factors. Although more study is required to better understand the underlying mechanisms by which behavioral experiences regulate oligodendrocyte lineage cells, this exciting and newly emerging field has already revealed that oligodendrocytes and their progenitors are highly responsive to behavioral experiences and suggest the existence of a complex network of reciprocal interactions among oligodendrocyte lineage development, behavioral experiences, and brain function. Achieving a better understanding of these relationships may have profound implications for human health, and in particular, for our understanding of changes in brain function that occur in response to experiences. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Autocrine action of BDNF on dendrite development of adult-born hippocampal neurons

Dendrite development of newborn granule cells (GCs) in the dentate gyrus of adult hippocampus is critical for their incorporation into existing hippocampal circuits, but the cellular mechanisms regulating their dendrite development remains largely unclear. In this study, we examined the function of brain-derived neurotrophic factor (BDNF), which is expressed in adult-born GCs, in regulating their dendrite morphogenesis. Using retrovirus-mediated gene transfection, we found that deletion and overexpression of BDNF in adult-born GCs resulted in the reduction and elevation of dendrite growth, respectively. This effect was mainly due to the autocrine rather than paracrine action of BDNF, because deletion of BDNF only in the newborn GCs resulted in dendrite abnormality of these neurons to a similar extent as that observed in conditional knockout (cKO) mice with BDNF deleted in the entire forebrain. Furthermore, selective expression of BDNF in adult-born GCs in BDNF cKO mice fully restored normal dendrite development. The BDNF autocrine action was also required for the development of normal density of spines and normal percentage of spines containing the postsynaptic marker PSD-95, suggesting autocrine BDNF regulation of synaptogenesis. Furthermore, increased dendrite growth of adult-born GCs caused by voluntary exercise was abolished by BDNF deletion specifically in these neurons and elevated dendrite growth due to BDNF overexpression in these neurons was prevented by reducing neuronal activity with coexpression of inward rectifier potassium channels, consistent with activity-dependent autocrine BDNF secretion. Therefore, BDNF expressed in adult-born GCs plays a critical role in dendrite development by acting as an autocrine factor.

No pain, no gain: lack of exercise obstructs neurogenesis

Bedridden patients develop atrophied muscles, their daily activities greatly reduced, and some display a depressive mood. Patients who are able to receive physical rehabilitation sometimes show surprising clinical improvements, including reduced depression and attenuation of other stress-related behaviors. Regenerative medicine has advanced two major stem cell-based therapies for CNS disorders, namely, transplantation of exogenous stem cells and amplification of endogenous neurogenesis. The latter strategy embraces a natural way of reinnervating the damaged brain and correcting the neurological impairments. In this study, we discussed how immobilization-induced disuse atrophy, using the hindlimb suspension model, affects neurogenesis in rats. The overarching hypothesis is that immobilization suppresses neurogenesis by reducing the circulating growth or trophic factors, such as vascular endothelial growth factor or brain-derived neurotrophic factor. That immobilization alters neurogenesis and stem cell differentiation in the CNS requires characterization of the stem cell microenvironment by examining the trophic and growth factors, as well as stress-related proteins that have been implicated in exercise-induced neurogenesis. Although accumulating evidence has revealed the contribution of "increased" exercise on neurogenesis, the reverse paradigm involving "lack of exercise," which mimics pathological states (e.g., stroke patients are often immobile), remains underexplored. This novel paradigm will enable us to examine the effects on neurogenesis by a nonpermissive stem cell microenvironment likely produced by lack of exercise. BrdU labeling of proliferative cells, biochemical assays of serum, cerebrospinal fluid and brain levels of trophic factors, growth factors, and stress-related proteins are proposed as indices of neurogenesis, while quantitative measurements of spontaneous movements will reveal psychomotor components of immobilization. Studies designed to reveal how in vivo stimulation, or lack thereof, alters the stem cell microenvironment are needed to begin to develop treatment strategies for enhancing neurogenesis in bedridden patients.

Role of adult hippocampal neurogenesis in cognition in physiology and disease: pharmacological targets and biomarkers

Adult hippocampal neurogenesis is a remarkable form of brain structural plasticity by which new functional neurons are generated from adult neural stem cells/precursors. Although the precise role of this process remains elusive, adult hippocampal neurogenesis is important for learning and memory and it is affected in disease conditions associated with cognitive impairment, depression, and anxiety. Immature neurons in the adult brain exhibit an enhanced structural and synaptic plasticity during their maturation representing a unique population of neurons to mediate specific hippocampal function. Compelling preclinical evidence suggests that hippocampal neurogenesis is modulated by a broad range of physiological stimuli which are relevant in cognitive and emotional states. Moreover, multiple pharmacological interventions targeting cognition modulate adult hippocampal neurogenesis. In addition, recent genetic approaches have shown that promoting neurogenesis can positively modulate cognition associated with both physiology and disease. Thus the discovery of signaling pathways that enhance adult neurogenesis may lead to therapeutic strategies for improving memory loss due to aging or disease. This chapter endeavors to review the literature in the field, with particular focus on (1) the role of hippocampal neurogenesis in cognition in physiology and disease; (2) extrinsic and intrinsic signals that modulate hippocampal neurogenesis with a focus on pharmacological targets; and (3) efforts toward novel strategies pharmacologically targeting neurogenesis and identification of biomarkers of human neurogenesis.

Bilateral Agenesis of the Hippocampal Dentate Gyrus in a Neurologically Normal Adult

Background:

Ontogenic development of granule cells in the hippocampal dentate gyrus is influenced by genes including WNT3, EMX2, NEUROD, and LEF1. Dentate granule cells continue to be generated from stem cell precursors postnatally and during adult life, and are implicated in normal and abnormal neurological function. Developmental privation of dentate granule cells is rare and essentially always occurs in the context of other neurodevelopmental abnormalities. We have found no previous reports of severe, selective agenesis of dentate granule cells in humans.

Methods:

A gross and microscopic examination of the brain included appropriate histochemical and immunohistochemical preparations and examination of the hippocampal formation at multiple levels bilaterally.

Results:

This neurologically normal 82-year-old man was found to have bilateral agenesis of the hippocampal dentate gyrus, no identifiable dentate granule cells, and moderate disorganization of the pyramidal cell layer of Ammon's horn. We found no neurodevelopmental abnormalities outside the hippocampus.

Conclusion:

The hippocampal architectural alterations in this patient are similar to those associated with a murine Lef1 mutation, but our human case does not have the other congenital deficits reported in the Lef1-null mouse. Bilateral agenesis of the hippocampal dentate gyrus, and apparent failure of regeneration of dentate granule cells from stem cells in adult life, may occur without overt clinical neurological deficits.

Treadmill exercise inhibits hippocampal apoptosis through enhancing N-methyl-D-aspartate receptor expression in the MK-801-induced schizophrenic mice

Schizophrenia is a severe mental disorder characterized by abnormal mental functioning and disruptive behaviors. Abnormal expression of N-methyl-D-aspartate (NMDA) receptor, one of the glutamate receptor subtypes, has also been suggested to contribute to the symptoms of schizophrenia. The effect of treadmill exercise on schizophrenia-induced apoptosis in relation with NMDA receptor has not been evaluated. In the present study, we investigated the effect of treadmill exercise on neuronal apoptosis in the hippocampus using MK-801-induced schizophrenic mice. MK-801 was intraperitoneally injected once a day for 2 weeks. The mice in the exercise groups were forced to run on a treadmill exercise for 60 min, once a day for 2 weeks. In the present results, repeated injection of the NMDA receptor antagonist MK-801 reduced expression of NMDA receptor in hippocampal CA2-3 regions. MK-801 injection increased casapse-3 expression and enhanced cytochrome c release in the hippocampus. The ratio of Bax to Bcl-2 was higher in the MK-801-induced schizophrenia mice than the normal mice. In contrast, treadmill exercise enhanced NMDA receptor expression, suppressed caspae-3 activation and cytochrome c release, and inhibited the ratio of Bax to Bcl-2. Based on present finding, we concluded that NMDA receptor hypofunctioning induced neuronal apoptosis in MK-801-induced schizophrenic mice. Treadmill exercise suppressed neuronal apoptosis through enhancing NMDA receptor expression in schizophrenic mice.

Deletion of the NMDA receptor GluN2A subunit significantly decreases dendritic growth in maturing dentate granule neurons

It is known that NMDA receptors can modulate adult hippocampal neurogenesis, but the contribution of specific regulatory GluN2 subunits has been difficult to determine. Here we demonstrate that mice lacking GluN2A (formerly NR2A) do not show altered cell proliferation or neuronal differentiation, but present significant changes in neuronal morphology in dentate granule cells. Specifically, GluN2A deletion significantly decreased total dendritic length and dendritic complexity in DG neurons located in the inner granular zone. Furthermore, the absence of GluN2A also resulted in a localized increase in spine density in the middle molecular layer, a region innervated by the medial perforant path. Interestingly, alterations in dendritic morphology and spine density were never seen in dentate granule cells located in the outer granular zone, a region that has been hypothesized to contain older, more mature, neurons. These results indicate that although the GluN2A subunit is not critical for the cell proliferation and differentiation stages of the neurogenic process, it does appear to play a role in establishing synaptic and dendritic morphology in maturing dentate granule cells localized in the inner granular zone.

α4βδ-GABAARs in the hippocampal CA1 as a biomarker for resilience to activity-based anorexia

Anorexia nervosa (AN) is a psychiatric illness characterized by restricted eating and an intense fear of gaining weight. Most individuals with AN are females, diagnosed first during adolescence, 40-80% of whom exhibit excessive exercise, and an equally high number with a history of anxiety disorder. We sought to determine the cellular basis for individual differences in AN vulnerability by using an animal model, activity-based anorexia (ABA), that is induced by combining food restriction (FR) with access to a running wheel that allows voluntary exercise. Previously, we showed that by the fourth day of FR, the ABA group of adolescent female rats exhibit >500% greater levels of non-synaptic α4βδ-GABAARs at the plasma membrane of hippocampal CA1 pyramidal cell spines, relative to the levels found in age-matched controls that are not FR and without wheel access. Here, we show that the ABA group exhibits individual differences in body weight loss, with some losing nearly 30%, while others lose only 15%. The individual differences in weight loss are ascribable to individual differences in wheel activity that both precedes and concurs with days of FR. Moreover, the increase in activity during FR correlates strongly and negatively with α4βδ-GABAAR levels (R=-0.9, p<0.01). This negative correlation is evident within 2days of FR, before body weight loss approaches life-threatening levels for any individual. These findings suggest that increased shunting inhibition by α4βδ-GABAARs in spines of CA1 pyramidal neurons may participate in the protection against the ABA-inducing environmental factors of severe weight loss by suppressing excitability of the CA1 pyramidal neurons which, in turn, is related indirectly to suppression of excessive exercise. The data also indicate that, although exercise has many health benefits, it can be maladaptive to individuals with low levels of α4βδ-GABAARs in the CA1, particularly when combined with FR.

Treadmill exercise enhances NMDA receptor expression in schizophrenia mice

Schizophrenia is a serious psychiatric disorder with several symptoms including cognitive dysfunction. Although the causes of schizophrenia are still unclear, there is a strong suspicion that the abnormality in N-methyl-D-aspartate (NMDA) receptor may contribute to schizophrenia symptoms. In the present study, the effect of treadmill exercise on the NMDA receptor expression was evaluated using MK-801-induced schizophrenia mice. Immunohistochemistry for expressions of NMDA receptor tyrosine hydroxylase (TH) was conducted. Western blot for brain-derived neurotrophic factor (BDNF) was also performed. In the present results, the mice in the MK-801-treated group displayed reduced NMDA receptor expression. Enhanced TH expression and suppressed BDNF expression were also observed in the MK-801-treated mice. Treadmill exercise improved NMDA receptor expression in the MK-801-induced schizophrenia mice. Treadmill exercise also suppressed TH expression and enhanced BDNF expression in the MK-801-induced schizophrenia mice. The present study showed that down-regulation of NMDA receptor demonstrated schizophrenia-like parameters, meanwhile treadmill running improved schizophrenia-related parameters through enhancing NMDA receptor expression.

Role of adult neurogenesis in hippocampal-cortical memory consolidation

Acquired memory is initially dependent on the hippocampus (HPC) for permanent memory formation. This hippocampal dependency of memory recall progressively decays with time, a process that is associated with a gradual increase in dependency upon cortical structures. This process is commonly referred to as systems consolidation theory. In this paper, we first review how memory becomes hippocampal dependent to cortical dependent with an emphasis on the interactions that occur between the HPC and cortex during systems consolidation. We also review the mechanisms underlying the gradual decay of HPC dependency during systems consolidation from the perspective of memory erasures by adult hippocampal neurogenesis. Finally, we discuss the relationship between systems consolidation and memory precision.

GluN2A-/- Mice Lack Bidirectional Synaptic Plasticity in the Dentate Gyrus and Perform Poorly on Spatial Pattern Separation Tasks

The different secondary subunits of the N-methyl-d-aspartate (NMDA) receptor each convey unique biophysical properties to the receptor complex, and may be key in determining the functional role played by NMDA receptors. In the hippocampus, the GluN2A and GluN2B subunits are particularly abundant; however, their exact roles in synaptic plasticity and behavior remain controversial. Here, we show that mice carrying a deletion for the GluN2A subunit (GluN2A(-/-)) demonstrate a severely compromised NMDA to AMPA receptor current ratio in granule cells from the dentate gyrus (DG), while granule cell morphology is unaltered. This deficit is accompanied by significant impairments in both LTP and LTD in the DG, whereas only minor impairments are observed in the CA1. In accordance with these hippocampal region-specific deficits, GluN2A(-/-) mice show impaired performance on the DG-associated task of spatial pattern separation. In contrast, GluN2A(-/-) mice show no deficit in temporal pattern separation, a process associated with CA1 functioning. Thus, our results establish the GluN2A subunit as a significant contributor to both bidirectional synaptic plasticity and spatial pattern separation in the DG.

Regulation of adult hippocampal neurogenesis: relevance to depression

Recent hypotheses suggest that depression may involve an inability to mount adaptive structural changes in key neuronal networks. In particular, the addition of new neurons within the hippocampus, a limbic region implicated in mood disorders, is compromised in animal models of depression. Adult hippocampal neurogenesis is also a target for chronic antidepressant treatments, and an increase in adult hippocampal neurogenesis is implicated in the behavioral effects of antidepressants in animal models. The 'neurogenic' hypothesis of depression raises the intriguing possibility that hippocampal neurogenesis may contribute to the pathogenesis and treatment of depressive disorders. While there remains substantial debate about the precise relevance of hippocampal neurogenesis to mood disorders, this provocative hypothesis has been the focus of many recent studies. In this review, we discuss the pathways that may mediate the effects of depression models and antidepressants on adult hippocampal neurogenesis, and the promise of these studies in the development of novel antidepressants.

Variable alteration of regional tissue oxygen pressure in rat hippocampus by acute swimming exercise

One of the events in the brain is an increasing cerebral blood flow during exercise. The tissue oxygen level may be increased because blood flow correlates with tissue oxygen level. However, it is little known whether the tissue oxygen pressure in hippocampal region (Hip-pO2) will be affected by exercise.

AIMS

The aim of this study is to examine Hip-pO2 levels in the hippocampus and its changes during exercise.

MAIN METHODS

We applied improved Clark-type electrodes to measure Hip-pO2 level in the hippocampus of rats that were subjected to three groups, 2h swimming without weights (low intensity, n=6), 2h swimming with a 5 g weight (moderate intensity, n=6), and 2h swimming with a 10 g weight (high intensity, n=6).

KEY FINDINGS

Exercise affected the Hip-pO2 level, the responses varied with the exercise intensity and duration. Interestingly during and after the Low intensity swimming the Hip-pO2 level showed long lasting enhancement (10-20% above resting level). But the moderate and high intensity swimming increased Hip-pO2 level at the start of the swimming (50%, P<0.05 and slightly above resting level, respectively, at 10 min of 2h swimming) and then began to decrease (at 120 min and 10 min of 2h swimming, respectively), and suppressed the Hip-pO2 levels during post exercise resting period (2h) (85-95% of resting level, NS and 60-70% of resting level P<0.05, respectively).

SIGNIFICANCE

We propose that exercise-induced hippocampal hyper/hypo oxygen condition may participate in beneficial exercise effects on brain function.

Activity-dependent, stress-responsive BDNF signaling and the quest for optimal brain health and resilience throughout the lifespan

During development of the nervous system, the formation of connections (synapses) between neurons is dependent upon electrical activity in those neurons, and neurotrophic factors produced by target cells play a pivotal role in such activity-dependent sculpting of the neural networks. A similar interplay between neurotransmitter and neurotrophic factor signaling pathways mediates adaptive responses of neural networks to environmental demands in adult mammals, with the excitatory neurotransmitter glutamate and brain-derived neurotrophic factor (BDNF) being particularly prominent regulators of synaptic plasticity throughout the central nervous system. Optimal brain health throughout the lifespan is promoted by intermittent challenges such as exercise, cognitive stimulation and dietary energy restriction, that subject neurons to activity-related metabolic stress. At the molecular level, such challenges to neurons result in the production of proteins involved in neurogenesis, learning and memory and neuronal survival; examples include proteins that regulate mitochondrial biogenesis, protein quality control, and resistance of cells to oxidative, metabolic and proteotoxic stress. BDNF signaling mediates up-regulation of several such proteins including the protein chaperone GRP-78, antioxidant enzymes, the cell survival protein Bcl-2, and the DNA repair enzyme APE1. Insufficient exposure to such challenges, genetic factors may conspire to impair BDNF production and/or signaling resulting in the vulnerability of the brain to injury and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Further, BDNF signaling is negatively regulated by glucocorticoids. Glucocorticoids impair synaptic plasticity in the brain by negatively regulating spine density, neurogenesis and long-term potentiation, effects that are potentially linked to glucocorticoid regulation of BDNF. Findings suggest that BDNF signaling in specific brain regions mediates some of the beneficial effects of exercise and energy restriction on peripheral energy metabolism and the cardiovascular system. Collectively, the findings described in this article suggest the possibility of developing prescriptions for optimal brain health based on activity-dependent BDNF signaling.

Voluntary resistance running induces increased hippocampal neurogenesis in rats comparable to load-free running

Recently, we reported that voluntary resistance wheel running with a resistance of 30% of body weight (RWR), which produces shorter distances but higher work levels, enhances spatial memory associated with hippocampal brain-derived neurotrophic factor (BDNF) signaling compared to wheel running without a load (WR) [17]. We thus hypothesized that RWR promotes adult hippocampal neurogenesis (AHN) as a neuronal substrate underlying this memory improvement. Here we used 10-week-old male Wistar rats divided randomly into sedentary (Sed), WR, and RWR groups. All rats were injected intraperitoneally with the thymidine analogue 5-Bromo-2'-deoxuridine (BrdU) for 3 consecutive days before wheel running. We found that even when the average running distance decreased by about half, the average work levels significantly increased in the RWR group, which caused muscular adaptation (oxidative capacity) for fast-twitch plantaris muscle without causing any negative stress effects. Additionally, immunohistochemistry revealed that the total BrdU-positive cells and newborn mature cells (BrdU/NeuN double-positive) in the dentate gyrus increased in both the WR and RWR groups. These results provide new evidence that RWR has beneficial effects on AHN comparable to WR, even with short running distances.

All about running: synaptic plasticity, growth factors and adult hippocampal neurogenesis

Accumulating evidence from animal and human research shows exercise benefits learning and memory, which may reduce the risk of neurodegenerative diseases, and could delay age-related cognitive decline. Exercise-induced improvements in learning and memory are correlated with enhanced adult hippocampal neurogenesis and increased activity-dependent synaptic plasticity. In this present chapter we will highlight the effects of physical activity on cognition in rodents, as well as on dentate gyrus (DG) neurogenesis, synaptic plasticity, spine density, neurotransmission and growth factors, in particular brain-derived nerve growth factor (BDNF).

Running-induced anxiety is dependent on increases in hippocampal neurogenesis

Exercise, specifically voluntary wheel running, is a potent stimulator of hippocampal neurogenesis in adult mice. In addition, exercise induces behavioral changes in numerous measures of anxiety in rodents. However, the physiological underpinnings of these changes are poorly understood. To investigate the role of neurogenesis in exercise-mediated anxiety, we examined the cellular and behavioral effects of voluntary wheel running in mice with a reduction in hippocampal neurogenesis, achieved through conditional deletion of ataxia telangiectasia-mutated and rad-3-related protein (ATR), a cell cycle checkpoint kinase necessary for normal levels of neurogenesis. Following hippocampal microinjection of an adeno-associated virus expressing Cre recombinase to delete ATR, mice were exposed to 4 weeks of voluntary wheel running and subsequently evaluated for anxiety-like behavior. Wheel running resulted in increased cell proliferation and neurogenesis, as measured by bromodeoxyuridine and doublecortin, respectively. Wheel running also resulted in heightened anxiety in the novelty-induced hypophagia, open field and light-dark box tests. However, both the neurogenic and anxiogenic effects of wheel running were attenuated following hippocampal ATR deletion, suggesting that increased neurogenesis is an important mediator of exercise-induced anxiety.

Hippocampal functional hyperemia mediated by NMDA receptor/NO signaling in rats during mild exercise

Current studies have demonstrated that exercise increases regional cerebral blood flow (rCBF), an index of neuronal activity. However, neuronal regulation of the increased rCBF in the brain parenchyma is poorly understood. We developed a running model with rats for monitoring hippocampal cerebral blood flow (Hip-CBF) and found that mild treadmill running increases Hip-CBF in a tetrodotoxin-dependent manner, suggesting that functional hyperemia, an increase in rCBF in response to neuronal activation, occurs in the running rat's hippocampus (Nishijima T and Soya H. Neurosci Res 54: 186–191, 2006). To further support our hypothesis, it was important to discover the neurogenic pathways behind the increase in Hip-CBF that occurred during running. Here, we examine the possible role of N-methyl-d-aspartate (NMDA) receptor/nitric oxide (NO) signaling and group I metabotropic glutamate receptors in mediating the Hip-CBF increase. Hip-CBF during running was measured by laser-Doppler flowmetry. Intrahippocampal drug administration was performed by microdialysis. Mild treadmill running (10 m/min) increased Hip-CBF, which was remarkably attenuated by either NMDA receptor antagonists (1 mM MK-801) or NO synthase inhibitors (2 mM NG-nitro-l-arginine methyl ester). However, group I metabotropic glutamate receptor antagonists {1 mM 7-(hydroxyimino)cyclopropa[ b]chromen-1a-carboxylate ethyl ester + 1 mM 2-methyl-6-(phenylethynyl)pyridine hydrochloride} augmented the running-induced Hip-CBF increase. We also found that rCBF in the olfactory bulb was unchanged with running. These results strongly suggest that Hip-CBF during mild exercise is regulated locally under hippocampal neuronal activity, mediated mainly through NMDA receptor/NO signaling. Collectively, these results, together with our previous findings, support our hypothesis that mild exercise elicits neuronal activation, which then triggers functional hyperemia in the rat hippocampus.

Changes in mRNA levels for brain-derived neurotrophic factor after wheel running in rats selectively bred for high- and low-aerobic capacity

We evaluated levels of exercise-induced brain-derived neurotrophic factor (BDNF) messenger RNA (mRNA) within the hippocampal formation in rats selectively bred for 1) high intrinsic (i.e., untrained) aerobic capacity (High Capacity Runners, HCR), 2) low intrinsic aerobic capacity (Low Capacity Runners, LCR), and 3) unselected Sprague-Dawley (SD) rats with or without free access to running wheels for 3 weeks. The specific aim of the study was to determine whether a dose-response relationship exists between cumulative running distance and levels of BDNF mRNA. No additional treatments or behavioral manipulations were used. HCR, LCR, and SD rats were grouped by strain and randomly assigned to sedentary or activity (voluntary access to activity wheel) conditions. Animals were killed after 21 days of exposure to the assigned conditions. Daily running distances (mean ± standard deviation meters/day) during week three were: HCR (4726 ± 3220), SD (2293 ± 3461), LCR (672 ± 323). Regardless of strain, levels of BDNF mRNA in CA1 were elevated in wheel runners compared to sedentary rats and this difference persisted after adjustment for age (p=0.040). BDNF mRNA was not affected by intrinsic aerobic capacity and was not related to total running distance. The results support that BDNF mRNA expression is increased by unlimited access to activity wheel running for 3 weeks but is not dependent upon accumulated running distance.

Running is the neurogenic and neurotrophic stimulus in environmental enrichment

Environmental enrichment (EE) increases dentate gyrus (DG) neurogenesis and brain-derived neurotrophic factor (BDNF) levels. However, running is considered an element of EE. To dissociate effects of physical activity and enrichment on hippocampal neurogenesis and BDNF levels, young female C57Bl/6 mice were housed under control, running, enrichment, or enrichment plus running conditions, and injected with bromodeoxyuridine. Cell genesis was assessed after 12 d and differentiation was analyzed 1 mo later. In addition, locomotor activity in the open field and hippocampal mature BDNF peptide levels were measured. Open-field adaptation was improved in all groups, compared to controls, but more so with running. New cell proliferation, survival, neuron number, and neurotrophin levels were enhanced only when running was accessible. We conclude that exercise is the critical factor mediating increased BDNF levels and adult hippocampal neurogenesis.

Physical exercise alleviates debilities of normal aging and Alzheimer's disease

Both healthy aging and the pathologic incidence of disorders associated with aging involve an array of debilities. Physical exercise harnesses implicit and inherent biologic characteristics amenable to the putative interventional influences under clinical, institutional or laboratory conditions. The neurodegenerative and pathophysiologic progressions that constitute Alzheimer's disease (AD), amnestic mild cognitive impairment (aMCI), normal aging, and different animal models of AD have shown the existence of several putative mechanisms. A large variety of moderating factors have demonstrated that the ever-proliferating plethora of neurotrophic factors, neurogenesis as observed through generality of expression and neuronal arborization. The insistent efficacy of brain vascular angiogenesis may delay also the comorbid incidence of depressive disorders with dementia pathology. The pathogenesis of aging may be contained by selective treatments: these diverse conditions, linked to the basis of the aging concept, have been shown, to greater or lesser extents, to respond to a variety of scheduled applications of physical exercise. The range of reports that provide accounts of the mechanisms mediating the positive progressive response to exercise intervention is far-ranging; these studies indicate that subtle changes at molecular, neuronal, vascular and epigenetic levels may exert notable consequence at functional expression and, perhaps most essentially, offer convincing expectancy of significant benefits.

Exercise is not beneficial and may accelerate symptom onset in a mouse model of Huntington's disease

Exercise benefits both general health and brain function in rodents and humans. However, it is less clear whether physical activity prevents or ameliorates neurodegenerative diseases. The aim of the present study was to determine whether voluntary wheel running can delay the onset or reduce the severity of Huntington’s disease (HD) in a mouse model. To investigate whether running may delay HD symptoms lifespan, disease onset, locomotor activity, glucose levels, weight, striatal volume, inclusions, cognition and hippocampal neurogenesis were studied in male N171-82Q transgenic HD mice. Running started in pre-symptomatic (44±1 days old) male HD mice, did not improve function and appeared to accelerate disease onset. In particular, HD runners had an earlier onset of disease symptoms (shaking, hunched back and poor grooming), reduced striatal volume and impaired motor behavior, including a shorter latency to fall from the rotarod compared to sedentary controls. Furthermore, weight loss, reduced lifespan, hyperglycemia, Morris water maze learning deficits, diminished hippocampal neurogenesis, deficits in immature neuronal morphology, intranuclear inclusions and decreased dentate gyrus volume were refractory to physical activity. Taken together our research indicates that exercise is not beneficial, and may be detrimental to a vulnerable nervous system.

Neurobiological alterations induced by exercise and their impact on depressive disorders [corrected]

BACKGROUND

The impact of physical activity on brain metabolic functions has been investigated in different studies and there is growing evidence that exercise can be used as a preventive and rehabilitative intervention in the treatment of depressive disorders. However, the exact neuronal mechanisms underlying the latter phenomenon have not been clearly elucidated. The present article summarises key results derived from studies that focussed on the neurobiological impact of exercise on brain metabolic functions associated with depressive disorders. Since major depressive disorder (MDD) is a life threatening disease it is of great significance to find reliable strategies to prevent or to cure this illness. Therefore, the aim of this paper is to review (1) the physiological relationship between physical activity and depressive disorders and (2) the potential neurobiological alterations induced by exercise that might lead to the relief of mental disorders like depression.

METHODS

We searched electronic databases for literature concerning the relationship between exercise and depression from 1963 until 2009.

RESULTS

The data suggests an association between physical inactivity and higher levels of depressive symptoms. Properly designed studies could show that exercise training can be as effective as antidepressive medications.

CONCLUSION

The exact mechanisms how exercise affects the brain are not fully understood and the literature lacks of well designed studies concerning the effects of exercise training on depressive disorders. But the observed antidepressant actions of exercise are strong enough that it already can be used as an alternative to current medications in the treatment of depressive disorders.