Exercise, learned helplessness, and the stress-resistant brain

Oral self-administration of EtOH: sex-dependent modulation by running wheel access in C57BL/6J mice

BACKGROUND

The effects of stress, including neuroendocrine and behavioral sequelae aimed at maintaining homeostasis, are associated with increased alcohol consumption. Because both stress and drinking are multifactorial, the mechanisms underlying the relationship are difficult to elucidate. We therefore employed an animal model investigating the influence of blocked access to a running wheel on drinking in C57BL/6J (B6) mice.

METHODS

In the first experiment, naïve, adult male and female subjects were individually housed for 2 weeks with 24-hour access to a running wheel and 12% ethanol (EtOH) in a 2-bottle, free choice paradigm. After determining baseline consumption and preference, experimental subjects had the running wheel placed in a locked position for 6 hours, and the EtOH bottle was removed during the first half of this period. Two subsequent experiments, again in adult, naïve B6 mice, examined the influence of locked running wheels on self-administration of 20% EtOH in a limited access paradigm, and blood EtOH concentrations (BECs) were determined on the final day of this protocol.

RESULTS

In all 3 studies, using both between- and within-subject analyses, females showed transient yet reliable increases in alcohol drinking during blocked access to a rotating activity, while drinking in male mice was largely insensitive to this manipulation, although both sexes showed appreciable BECs (>130 mg/dl in females and 80 mg/dl in males) following a 2-hour EtOH access period.

CONCLUSIONS

These data add to a burgeoning literature suggesting that the factors contributing to excessive alcohol use differ between males and females and that females may be especially sensitive to the influence of wheel manipulation. Elucidating the sex-dependent mechanisms mediating differences in alcohol sensitivity and response is critical to understanding the causes of alcoholism and in developing effective treatments and interventions.

Pathogenesis of depression: Insights from human and rodent studies

Major depressive disorder (MDD) will affect one out of every five people in their lifetime and is the leading cause of disability worldwide. Nevertheless, mechanisms associated with the pathogenesis of MDD have yet to be completely understood and current treatments remain ineffective in a large subset of patients. In this review, we summarize the most recent discoveries and insights for which parallel findings have been obtained in human depressed subjects and rodent models of mood disorders in order to examine the potential etiology of depression. These mechanisms range from synaptic plasticity mechanisms to epigenetics and the immune system where there is strong evidence to support a functional role in the development of specific depression symptomology. Ultimately we conclude by discussing how novel therapeutic strategies targeting central and peripheral processes might ultimately aid in the development of effective new treatments for MDD and related stress disorders.

Exercise is More Effective at Altering Gut Microbial Composition and Producing Stable Changes in Lean Mass in Juvenile versus Adult Male F344 Rats

The mammalian intestine harbors a complex microbial ecosystem that influences many aspects of host physiology. Exposure to specific microbes early in development affects host metabolism, immune function, and behavior across the lifespan. Just as the physiology of the developing organism undergoes a period of plasticity, the developing microbial ecosystem is characterized by instability and may also be more sensitive to change. Early life thus presents a window of opportunity for manipulations that produce adaptive changes in microbial composition. Recent insights have revealed that increasing physical activity can increase the abundance of beneficial microbial species. We therefore investigated whether six weeks of wheel running initiated in the juvenile period (postnatal day 24) would produce more robust and stable changes in microbial communities versus exercise initiated in adulthood (postnatal day 70) in male F344 rats. 16S rRNA gene sequencing was used to characterize the microbial composition of juvenile versus adult runners and their sedentary counterparts across multiple time points during exercise and following exercise cessation. Alpha diversity measures revealed that the microbial communities of young runners were less even and diverse, a community structure that reflects volatility and malleability. Juvenile onset exercise altered several phyla and, notably, increased Bacteroidetes and decreased Firmicutes, a configuration associated with leanness. At the genus level of taxonomy, exercise altered more genera in juveniles than in the adults and produced patterns associated with adaptive metabolic consequences. Given the potential of these changes to contribute to a lean phenotype, we examined body composition in juvenile versus adult runners. Interestingly, exercise produced persistent increases in lean body mass in juvenile but not adult runners. Taken together, these results indicate that the impact of exercise on gut microbiota composition as well as body composition may depend on the developmental stage during which exercise is initiated.

Ultrasonic vocalizations during intermittent swim stress forecasts resilience in a subsequent juvenile social exploration test of anxiety

Current behavioral paradigms of stress resilience traditionally employ forms of prior manipulation or subsequent testing. Recent work has reported adult rat ultrasonic vocalizations (USVs) emitted during intermittent swim stress (ISS) may serve as a predictor of resilience. ISS-induced USVs predicted resilience on several endpoints of behavioral depression and may be considered a forecast of innate resilience. However, a potential problem for these previous findings is the lack of generalizability to other contexts, because both the stress induction and post-stress testing occur in water. The current study tests the generalizability of USVs as a predictor of stress resilience in a non-water-based post-test, the juvenile social exploration test of anxiety. The results provide further support that USVs emitted during ISS predict resilience to depression- and anxiety-like behaviors. Extensions of this work to examine the neurobiology of innate resilience associated with ISS-induced USVs are discussed with comparisons to extant models of learned resilience.

Impairments in cognition and neural precursor cell proliferation in mice expressing constitutively active glycogen synthase kinase-3

Brain glycogen synthase kinase-3 (GSK3) is hyperactive in several neurological conditions that involve impairments in both cognition and neurogenesis. This raises the hypotheses that hyperactive GSK3 may directly contribute to impaired cognition, and that this may be related to deficiencies in neural precursor cells (NPC). To study the effects of hyperactive GSK3 in the absence of disease influences, we compared adult hippocampal NPC proliferation and performance in three cognitive tasks in male and female wild-type (WT) mice and GSK3 knockin mice, which express constitutively active GSK3. NPC proliferation was ~40% deficient in both male and female GSK3 knockin mice compared with WT mice. Environmental enrichment (EE) increased NPC proliferation in male, but not female, GSK3 knockin mice and WT mice. Male and female GSK3 knockin mice exhibited impairments in novel object recognition, temporal order memory, and coordinate spatial processing compared with gender-matched WT mice. EE restored impaired novel object recognition and temporal ordering in both sexes of GSK3 knockin mice, indicating that this repair was not dependent on NPC proliferation, which was not increased by EE in female GSK3 knockin mice. Acute 1 h pretreatment with the GSK3 inhibitor TDZD-8 also improved novel object recognition and temporal ordering in male and female GSK3 knockin mice. These findings demonstrate that hyperactive GSK3 is sufficient to impair adult hippocampal NPC proliferation and to impair performance in three cognitive tasks in both male and female mice, but these changes in NPC proliferation do not directly regulate novel object recognition and temporal ordering tasks.

Exercise, energy intake, glucose homeostasis, and the brain

Here we summarize topics covered in an SFN symposium that considered how and why exercise and energy intake affect neuroplasticity and, conversely, how the brain regulates peripheral energy metabolism. This article is not a comprehensive review of the subject, but rather a view of how the authors' findings fit into a broader context. Emerging findings elucidate cellular and molecular mechanisms by which exercise and energy intake modify the plasticity of neural circuits in ways that affect brain health. By enhancing neurogenesis, synaptic plasticity and neuronal stress robustness, exercise and intermittent energy restriction/fasting may optimize brain function and forestall metabolic and neurodegenerative diseases. Moreover, brain-centered glucoregulatory and immunomodulating systems that mediate peripheral health benefits of intermittent energetic challenges have recently been described. A better understanding of adaptive neural response pathways activated by energetic challenges will enable the development and optimization of interventions to reduce the burden of disease in our communities.

Salivary cortisol levels are elevated in the afternoon and at bedtime in children with prenatal alcohol exposure

Prenatal alcohol exposure can cause dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, which may underlie some of the behavioral and adaptive problems seen in individuals with Fetal Alcohol Spectrum Disorders (FASD). Infants prenatally exposed to alcohol show altered basal and post-stress cortisol levels, but it is unknown if this persists beyond 2 years of age. It is also unknown if cortisol levels can be normalized through intervention programs. In this study, we investigated the effects of a physical activity program for children with FASD to determine: 1) if HPA dysregulation persists in school-age children with FASD, and 2) the effect of our program on cortisol levels. Twenty six children (ages 6-14 years) with FASD participated in an 8 week motor skill development program. Salivary cortisol levels were measured in 24 children and compared at 4 time points: before, immediately after, 3 months, and 1 year after program completion. Cortisol levels were also compared to 32 control children to evaluate the long-term effects of prenatal alcohol exposure on HPA regulation. For each time point, saliva was collected on each of 2 days at 3 times in the diurnal cycle: awakening, after school, and just before bedtime. Cortisol levels were significantly higher in the afternoon and at bedtime in children with FASD with confirmed prenatal exposure to high levels of alcohol (alcohol exposure rank 4), compared with Control children or children with FASD with exposure to low or unknown levels of alcohol (alcohol exposure rank 3). The program did not significantly affect cortisol levels in children with FASD as a group. These results provide support for long-term effects of prenatal alcohol exposure on the HPA system in humans, which could increase vulnerability to mental health issues and diseases later in life.

Hippocampal morphology in a rat model of depression: the effects of physical activity

Accumulating in vivo and ex vivo evidences show that humans suffering from depression have decreased hippocampal volume and altered spine density. Moreover, physical activity has an antidepressant effect in humans and in animal models, but to what extent physical activity can affect hippocampal volume and spine numbers in a model for depression is not known.

In this study we analyzed whether physical activity affects hippocampal volume and spine density by analyzing a rodent genetic model of depression, Flinders Sensitive Line Rats (FSL), with Magnetic Resonance Imaging (MRI) and ex vivo Golgi staining.

We found that physical activity in the form of voluntary wheel running during 5 weeks increased hippocampal volume. Moreover, runners also had larger numbers of thin spines in the dentate gyrus. Our findings support that voluntary wheel running, which is antidepressive in FSL rats, is associated with increased hippocampal volume and spine numbers.

Parameters of hormetic stress and resilience to trauma in rats

Hormesis is the process by which small stresses build resilience to large stresses. We pre-exposed rats to various parameters of mild-to-moderate stress prior to traumatic stress in the present experiments to assess the potential benefits of hormetic training on resilience to traumatic, uncontrollable stress. Rats underwent varying stress pre-training parameters prior to exposure to uncontrollable traumatic stress in the learned helplessness procedure. The ability to prevent the exaggerated fear responding and escape deficits that normally follow experience with traumatic stress were used as a measure of the benefits of hormetic training. Four experiments examined the effects of number of training sessions, stressor severity and pattern of rest between pre-training stress sessions. Repeated exposure to mild restraint stress or moderate shock stress eliminated both the enhanced fear conditioning and shuttle-escape deficits that result from exposure to traumatic, inescapable shock. The pattern of rest did not contribute to resilience when the pre-exposure stressor was mild, but was vital when the pre-exposure stressor was moderate, with an alternation of stress and rest being the most effective procedure. The data also suggest that the level of resilience may increase with the number of pre-exposure sessions.

Swimming reduces the severity of physical and psychological dependence and voluntary morphine consumption in morphine dependent rats

Previous studies have indicated that voluntary exercise decreases the severity of the anxiogenic-like behaviors in both morphine-dependent and withdrawn rats. This study examined the effects of regular swimming exercise during the development of dependency and spontaneous morphine withdrawal on the anxiety-depression profile and voluntary morphine consumption in morphine dependent rats. The rats were chronically treated with bi-daily doses (10 mg/kg, at 12h intervals) of morphine over a period of 14 days. The exercising rats were allowed to swim (45 min/d, five days per a week, for 14 or 21 days) during the development of morphine dependence and withdrawal. Then, rats were tested for the severity of morphine dependence, the elevated plus-maze (EPM), sucrose preference test (SPT) and voluntary morphine consumption using a two-bottle choice paradigm in animal models of craving. The results showed that withdrawal signs were decreased in swimmer morphine dependent rats than sedentary rats (P<0.05). Also, the swimmer morphine-dependent and withdrawn rats exhibited an increase in EPM open arm time and entries (P<0.05), higher levels of sucrose preference (P<0.001) than sedentary rats. Voluntary consumption of oral morphine was less in the swimmer morphine-withdrawn rats than the sedentary groups during four periods of the intake of drug (P<0.01). We conclude that regular swimming exercise reduces the severity of morphine dependence and voluntary morphine consumption with reducing anxiety and depression in morphine-dependent and withdrawn rats. Thus, swimming exercise may be a potential method to ameliorate some of the deleterious behavioral consequences of morphine dependence.

Challenging oneself intermittently to improve health

Humans and their predecessors evolved in environments where they were challenged intermittently with: 1) food scarcity; 2) the need for aerobic fitness to catch/kill prey and avoid or repel attackers; and 3) exposure to biological toxins present in foodstuffs. Accordingly, cells and organ systems acquired and retained molecular signaling and metabolic pathways through which the environmental challenges enhanced the functionality and resilience of the cells and organisms. Within the past 60 years there has been a precipitous diminution of such challenges in modern societies because of the development of technologies that provide a continuous supply of energy-dense processed foods and that largely eliminate the need for physical exertion. As a consequence of the modern 'couch potato' lifestyle, signaling pathways that mediate beneficial effects of environmental challenges on health and disease resistance are disengaged, thereby rendering people vulnerable to obesity, diabetes, cardiovascular disease, cancers and neurodegenerative disorders. Reversal of the epidemic of diseases caused by unchallenging lifestyles will require a society-wide effort to re-introduce intermittent fasting, exercise and consumption of plants containing hormetic phytochemicals into daily and weekly routines.

Biological mechanisms underlying the role of physical fitness in health and resilience

Physical fitness, achieved through regular exercise and/or spontaneous physical activity, confers resilience by inducing positive psychological and physiological benefits, blunting stress reactivity, protecting against potentially adverse behavioural and metabolic consequences of stressful events and preventing many chronic diseases. In this review, we discuss the biological mechanisms underlying the beneficial effects of physical fitness on mental and physical health. Physical fitness appears to buffer against stress-related disease owing to its blunting/optimizing effects on hormonal stress responsive systems, such as the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. This blunting appears to contribute to reduced emotional, physiological and metabolic reactivity as well as increased positive mood and well-being. Another mechanism whereby regular exercise and/or physical fitness may confer resilience is through minimizing excessive inflammation. Chronic psychological stress, physical inactivity and abdominal adiposity have been associated with persistent, systemic, low-grade inflammation and exert adverse effects on mental and physical health. The anti-inflammatory effects of regular exercise/activity can promote behavioural and metabolic resilience, and protect against various chronic diseases associated with systemic inflammation. Moreover, exercise may benefit the brain by enhancing growth factor expression and neural plasticity, thereby contributing to improved mood and cognition. In summary, the mechanisms whereby physical fitness promotes increased resilience and well-being and positive psychological and physical health are diverse and complex.

Wheel running in the wild

The importance of exercise for health and neurogenesis is becoming increasingly clear. Wheel running is often used in the laboratory for triggering enhanced activity levels, despite the common objection that this behaviour is an artefact of captivity and merely signifies neurosis or stereotypy. If wheel running is indeed caused by captive housing, wild mice are not expected to use a running wheel in nature. This however, to our knowledge, has never been tested. Here, we show that when running wheels are placed in nature, they are frequently used by wild mice, also when no extrinsic reward is provided. Bout lengths of running wheel behaviour in the wild match those for captive mice. This finding falsifies one criterion for stereotypic behaviour, and suggests that running wheel activity is an elective behaviour. In a time when lifestyle in general and lack of exercise in particular are a major cause of disease in the modern world, research into physical activity is of utmost importance. Our findings may help alleviate the main concern regarding the use of running wheels in research on exercise.

The effects of environmental enrichment on depressive and anxiety-relevant behaviors in socially isolated prairie voles

OBJECTIVES

Social isolation is associated with depression, anxiety, and negative health outcomes. Environmental enrichment, including environmental and cognitive stimulation with inanimate objects and opportunities for physical exercise, may be an effective strategy to include in treatment paradigms for affective disorders as a function of social isolation. In a rodent model-the socially monogamous prairie vole-we investigated the hypothesis that depression- and anxiety-related behaviors after social isolation would be prevented and remediated with environmental enrichment.

METHODS

Experiment 1 investigated the preventive effects of environmental enrichment on negative affective behaviors when administered concurrently with social isolation. Experiment 2 investigated the remediating effects of enrichment on negative affective behaviors when administered after a period of isolation. Behaviors were measured in three operational tests: open field, forced swim test (FST), and elevated plus maze.

RESULTS

In isolated prairie voles, enrichment prevented depression-relevant (immobility in FST, group × housing interaction, p = .049) and anxiety-relevant behaviors (exploration in open field, group × housing interaction, p = .036; exploration in elevated plus maze, group × housing interaction, p = .049). Delayed enrichment also remediated these behaviors in isolated animals (immobility in FST, main effect of housing, p = .001; exploration in open field, main effect of housing, p = .047; exploration in elevated plus maze, main effect of housing, p = .001) and was slightly more effective than physical exercise alone in remediating anxiety-relevant behaviors.

CONCLUSIONS

These findings provide insight into the beneficial effects of an enriched environment on depression- and anxiety-relevant behaviors using a translational rodent model of social isolation.

Physical weight loading induces expression of tryptophan hydroxylase 2 in the brain stem

Sustaining brain serotonin is essential in mental health. Physical activities can attenuate mental problems by enhancing serotonin signaling. However, such activity is not always possible in disabled individuals or patients with dementia. Knee loading, a form of physical activity, has been found to mimic effects of voluntary exercise. Focusing on serotonergic signaling, we addressed a question: Does local mechanical loading to the skeleton elevate expression of tryptophan hydroxylase 2 (tph2) that is a rate-limiting enzyme for brain serotonin? A 5 min knee loading was applied to mice using 1 N force at 5 Hz for 1,500 cycles. A 5-min treadmill running was used as an exercise (positive) control, and a 90-min tail suspension was used as a stress (negative) control. Expression of tph2 was determined 30 min – 2 h in three brain regions ––frontal cortex (FC), ventromedial hypothalamus (VMH), and brain stem (BS). We demonstrated for the first time that knee loading and treadmill exercise upregulated the mRNA level of tph2 in the BS, while tail suspension downregulated it. The protein level of tph2 in the BS was also upregulated by knee loading and downregulated by tail suspension. Furthermore, the downregulation of tph2 mRNA by tail suspension can be partially suppressed by pre-application of knee loading. The expression of tph2 in the FC and VMH was not significantly altered with knee loading. In this study we provided evidence that peripheral mechanical loading can activate central tph2 expression, suggesting that physical cues may mediate tph2-cathalyzed serotonergic signaling in the brain.

Stress-protective neural circuits: not all roads lead through the prefrontal cortex

Exposure to an uncontrollable stressor elicits a constellation of physiological and behavioral sequel in laboratory rats that often reflect aspects of anxiety and other emotional disruptions. We review evidence suggesting that plasticity within the serotonergic dorsal raphe nucleus (DRN) is critical to the expression of uncontrollable stressor-induced anxiety. Specifically, after uncontrollable stressor exposure subsequent anxiogenic stimuli evoke greater 5-HT release in DRN terminal regions including the amygdala and striatum; and pharmacological blockade of postsynaptic 5-HT(2C) receptors in these regions prevents expression of stressor-induced anxiety. Importantly, the controllability of stress, the presence of safety signals, and a history of exercise mitigate the expression of stressor-induced anxiety. These stress-protective factors appear to involve distinct neural substrates; with stressor controllability requiring the medial prefrontal cortex, safety signals the insular cortex and exercise affecting the 5-HT system directly. Knowledge of the distinct yet converging mechanisms underlying these stress-protective factors could provide insight into novel strategies for the treatment and prevention of stress-related psychiatric disorders.

Generating new neurons to circumvent your fears: the role of IGF signaling

Extinction of fear memory is a particular form of cognitive function that is of special interest because of its involvement in the treatment of anxiety and mood disorders. Based on recent literature and our previous findings (EMBO J 30(19):4071-4083, 2011), we propose a new hypothesis that implies a tight relationship among IGF signaling, adult hippocampal neurogenesis and fear extinction. Our proposed model suggests that fear extinction-induced IGF2/IGFBP7 signaling promotes the survival of neurons at 2-4 weeks old that would participate in the discrimination between the original fear memory trace and the new safety memory generated during fear extinction. This is also called "pattern separation", or the ability to distinguish similar but different cues (e.g., context). To understand the molecular mechanisms underlying fear extinction is therefore of great clinical importance.

Neuronal-glial mechanisms of exercise-evoked stress robustness

Stress robustness by definition, incorporates both stress resistance (organisms endure greater stressor intensity or duration before suffering negative consequences) and stress resilience (organisms recover faster after suffering negative consequences). Factors that influence stress robustness include the nature of the stressor, (i.e., controllability, intensity, chronicity) and features of the organism (i.e., age, genetics, sex, and physical activity status). Here we present a novel hypothesis for how physically active versus sedentary living promotes stress robustness in the face of intense uncontrollable stress. Advances in neurobiology have established microglia as an active player in the regulation of synaptic activity, and recent work has revealed mechanisms for modulating glial function, including cross talk between neurons and glia. This chapter presents supporting evidence that the physical activity status of an organism may modulate stress-evoked neuronal-glial responses by changing the CX3CL1-CX3CR1 axis. Specifically, we propose that sedentary animals respond to an intense acute uncontrollable stressor with excessive serotonin (5-HT) and noradrenergic (NE) activity and/or prolonged down-regulation of the CX3CL1-CX3CR1 axis resulting in activation and proliferation of hippocampal microglia in the absence of pathogenic signals and consequent hippocampal-dependent memory deficits and reduced neurogenesis. In contrast, physically active animals respond to the same stressor with constrained 5-HT and NE activity and rapidly recovering CX3CL1-CX3CR1 axis responses resulting in the quieting of microglia, and protection from negative cognitive and neurobiological effects of stress.

Trophic Mechanisms for Exercise-Induced Stress Resilience: Potential Role of Interactions between BDNF and Galanin

Current concepts of the neurobiology of stress-related disorders, such as anxiety and depression emphasize disruptions in neural plasticity and neurotrophins. The potent trophic actions of exercise, therefore, represent not only an effective means for prevention and treatment of these disorders, they also afford the opportunity to employ exercise paradigms as a basic research tool to uncover the neurobiological mechanisms underlying these disorders. Novel approaches to studying stress-related disorders focus increasingly on trophic factor signaling in corticolimbic circuits that both mediate and regulate cognitive, behavioral, and physiological responses to deleterious stress. Recent evidence demonstrates that the neural plasticity supported by these trophic mechanisms is vital for establishing and maintaining resilience to stress. Therapeutic interventions that promote these mechanisms, be they pharmacological, behavioral, or environmental, may therefore prevent or reverse stress-related mental illness by enhancing resilience. The present paper will provide an overview of trophic mechanisms responsible for the enhancement of resilience by voluntary exercise with an emphasis on brain-derived neurotrophic factor, galanin, and interactions between these two trophic factors.

Exercise as a novel treatment for drug addiction: a neurobiological and stage-dependent hypothesis

Physical activity, and specifically exercise, has been suggested as a potential treatment for drug addiction. In this review, we discuss clinical and preclinical evidence for the efficacy of exercise at different phases of the addiction process. Potential neurobiological mechanisms are also discussed focusing on interactions with dopaminergic and glutamatergic signaling and chromatin remodeling in the reward pathway. While exercise generally produces an efficacious response, certain exercise conditions may be either ineffective or lead to detrimental effects depending on the level/type/timing of exercise exposure, the stage of addiction, the drug involved, and the subject population. During drug use initiation and withdrawal, its efficacy may be related to its ability to facilitate dopaminergic transmission, and once addiction develops, its efficacy may be related to its ability to normalize glutamatergic and dopaminergic signaling and reverse drug-induced changes in chromatin via epigenetic interactions with brain-derived neurotrophic factor (BDNF) in the reward pathway. We conclude with future directions, including the development of exercise-based interventions alone or as an adjunct to other strategies for treating drug addiction.

Sensorimotor modulation of mood and depression: in search of an optimal mode of stimulation

Depression involves a dysfunction in an affective fronto-limbic circuitry including the prefrontal cortices, several limbic structures including the cingulate cortex, the amygdala, and the hippocampus as well as the basal ganglia. A major emphasis of research on the etiology and treatment of mood disorders has been to assess the impact of centrally generated (top-down) processes impacting the affective fronto-limbic circuitry. The present review shows that peripheral (bottom-up) unipolar stimulation via the visual and the auditory modalities as well as by physical exercise modulates mood and depressive symptoms in humans and animals and activates the same central affective neurocircuitry involved in depression. It is proposed that the amygdala serves as a gateway by articulating the mood regulatory sensorimotor stimulation with the central affective circuitry by emotionally labeling and mediating the storage of such emotional events in long-term memory. Since both amelioration and aggravation of mood is shown to be possible by unipolar stimulation, the review suggests that a psychophysical assessment of mood modulation by multimodal stimulation may uncover mood ameliorative synergisms and serve as adjunctive treatment for depression. Thus, the integrative review not only emphasizes the relevance of investigating the optimal levels of mood regulatory sensorimotor stimulation, but also provides a conceptual springboard for related future research.

Beneficial effects of fluoxetine, reboxetine, venlafaxine, and voluntary running exercise in stressed male rats with anxiety- and depression-like behaviors

Rodents exposed to mild but repetitive stress may develop anxiety- and depression-like behaviors. Whether this stress response could be alleviated by pharmacological treatments or exercise interventions, such as wheel running, was unknown. Herein, we determined anxiety- and depression-like behaviors in restraint stressed rats (2h/day, 5 days/week for 4 weeks) subjected to acute diazepam treatment (30min prior to behavioral test), chronic treatment with fluoxetine, reboxetine or venlafaxine (10mg/kg/day for 4 weeks), and/or 4-week voluntary wheel running. In elevated plus-maze (EPM) and forced swimming tests (FST), stressed rats spent less time in the open arms and had less swimming duration than the control rats, respectively, indicating the presence of anxiety- and depression-like behaviors. Stressed rats also developed learned fear as evaluated by elevated T-maze test (ETM). Although wheel running could reduce anxiety-like behaviors in both EPM and ETM, only diazepam was effective in the EPM, while fluoxetine, reboxetine, and venlafaxine were effective in the ETM. Fluoxetine, reboxetine, and wheel running, but not diazepam and venlafaxine, also reduced depression-like behavior in FST. Combined pharmacological treatment and exercise did not further reduce anxiety-like behavior in stressed rats. However, stressed rats treated with wheel running plus reboxetine or venlafaxine showed an increase in climbing duration in FST. In conclusion, regular exercise (voluntary wheel running) and pharmacological treatments, especially fluoxetine and reboxetine, could alleviate anxiety- and depression-like behaviors in stressed male rats.

Treadmill exercise exerts ameliorating effect on isolation-induced depression via neuronal activation

Maternal isolation has been used as a valid animal model of early life stress, and it induces depression to offspring. Exercise ameliorates the incidence and severity of stress-related mood disorders, such as depression and anxiety. Here in this study, we investigated the effects of treadmill exercise on brain neuronal excitation in the rat pups with maternal isolation-induced depression. Forced swimming test and immunohistochemistry for glucocorticoid receptor and c-Fos in the hippocampal dentate gyrus and hypothalamic paraventricular nucleus were conducted. Maternal isolation lasted for 6 hours per day and was continued from postnatal day 1 to postnatal day 30. The rat pups in the exercise group were forced to run on a treadmill for 30 min once a day for 10 consecutive days, starting from the postnatal day 21 until the postnatal day 30. In the present results, treadmill exercise alleviated depressive state in the maternal separated rat pups, as potently as fluoxetine treatment. Treadmill exercise also restored the expressions of glucocorticoid receptor and c-Fos in the hippocampal dentate gyrus and hypothalamic paraventricular nucleus of the maternal separated rat pups near to the control level, as fluoxetine treatment. The present study suggests the possibility that treadmill exercise can be used as the therapeutic strategy for the childhood depression induced by disturbed mother-child relationship.

Glucocorticoids orchestrate divergent effects on mood through adult neurogenesis

Both social defeat stress and environmental enrichment stimulate adrenal glucocorticoid secretion, but they have opposing effects on hippocampal neurogenesis and mood. Hypothalamic-pituitary-adrenal axis dysregulation and decreased neurogenesis are consequences of social defeat. These outcomes are correlated with depressive states, but a causal role in the etiology of depression remains elusive. The antidepressant actions of environmental enrichment are neurogenesis-dependent, but the contribution of enrichment-elevated glucocorticoids is unexplored. Importantly, for both social defeat and environmental enrichment, how glucocorticoids interact with neurogenesis to alter mood is unknown. Here, we investigate causal roles of glucocorticoids and neurogenesis in induction of depressive-like behavior and its amelioration by environmental enrichment in mice. By blocking neurogenesis and surgically clamping adrenal hormone secretions, we showed that neurogenesis, via hypothalamic-pituitary-adrenal axis interactions, is directly involved in precipitating the depressive phenotype after social defeat. Mice adrenalectomized before social defeat showed enhanced behavioral resiliency and increased survival of adult-born hippocampal neurons compared with sham-operated defeated mice. However, mice lacking hippocampal neurogenesis did not show protective effects of adrenalectomy. Moreover, glucocorticoids secreted during environmental enrichment promoted neurogenesis and were required for restoration of normal behavior after social defeat. The data demonstrate that glucocorticoid-dependent declines in neurogenesis drive changes in mood after social defeat and that glucocorticoids secreted during enrichment promote neurogenesis and restore normal behavior after defeat. These data provide new evidence for direct involvement of neurogenesis in the etiology of depression, suggesting that treatments promoting neurogenesis can enhance stress resilience.

Exercise benefits brain function: the monoamine connection

The beneficial effects of exercise on brain function have been demonstrated in animal models and in a growing number of clinical studies on humans. There are multiple mechanisms that account for the brain-enhancing effects of exercise, including neuroinflammation, vascularization, antioxidation, energy adaptation, and regulations on neurotrophic factors and neurotransmitters. Dopamine (DA), noradrenaline (NE), and serotonin (5-HT) are the three major monoamine neurotransmitters that are known to be modulated by exercise. This review focuses on how these three neurotransmitters contribute to exercise affecting brain function and how it can work against neurological disorders.

Exercise-induced stress resistance is independent of exercise controllability and the medial prefrontal cortex

Exercise increases resistance against stress-related disorders such as anxiety and depression. Similarly, the perception of control is a powerful predictor of neurochemical and behavioral responses to stress, but whether the experience of choosing to exercise, and exerting control over that exercise, is a critical factor in producing exercise-induced stress resistance is unknown. The current studies investigated whether the protective effects of exercise against the anxiety- and depression-like consequences of stress are dependent on exercise controllability and a brain region implicated in the protective effects of controllable experiences, the medial prefrontal cortex. Adult male Fischer 344 rats remained sedentary, were forced to run on treadmills or motorised running wheels, or had voluntary access to wheels for 6 weeks. Three weeks after exercise onset, rats received sham surgery or excitotoxic lesions of the medial prefrontal cortex. Rats were exposed to home cage or uncontrollable tail shock treatment three weeks later. Shock-elicited fear conditioning and shuttle box escape testing occurred the next day. Both forced and voluntary wheel running, but not treadmill training, prevented the exaggerated fear conditioning and interference with escape learning produced by uncontrollable stress. Lesions of the medial prefrontal cortex failed to eliminate the protective effects of forced or voluntary wheel running. These data suggest that exercise controllability and the medial prefrontal cortex are not critical factors in conferring the protective effects of exercise against the affective consequences of stressor exposure, and imply that exercise perceived as forced may still benefit affect and mental health.

Vascular endothelial growth factor-dependent spinogenesis underlies antidepressant-like effects of enriched environment

Current antidepressant treatments remain limited by poor efficacy and a slow onset of action. Increasing evidence demonstrates that enriched environment (EE) treatment can promote structural and behavioral plasticity in the brain and dampen stress-induced alterations of neuroplasticity. Here, we have examined whether short term exposure to EE is able to produce antidepressant-like effects. Our results show that housing adult mice in an EE cage for 7 days led to antidepressant-like behavioral profiles and a significant increase in the number of dendritic spines in hippocampal CA1 pyramidal neurons. These EE-induced antidepressant-like effects are primarily attributed to increased vascular endothelial growth factor (VEGF) expression through a hypoxia-inducible factor-1α (HIF-1α)-mediated transcriptional mechanism. Blockade of HIF-1α synthesis by lentiviral infection with HIF-1α small hairpin RNAs completely blocked the increase in expression of VEGF and the antidepressant-like effects induced by EE. Moreover, no significant antidepressant-like effects were observed with EE treatment in VEGF receptor 2 (Flk-1) knock-out mice. The increase in HIF-1α expression in the hippocampus induced by EE was associated with a decrease in endogenous levels of microRNA-107 (miR-107). Overexpression of miR-107 in the hippocampus completely blocked EE-induced HIF-1α expression and the antidepressant-like effects. These results support a model in which the down-regulation of miR-107, acting through HIF-1α, mediates VEGF-dependent spinogenesis to underlie the EE-induced antidepressant-like effects.

Exercise offers anxiolytic potential: a role for stress and brain noradrenergic-galaninergic mechanisms

Although physical activity reduces anxiety in humans, the neural basis for this response is unclear. Rodent models are essential to understand the mechanisms that underlie the benefits of exercise. However, it is controversial whether exercise exerts anxiolytic-like potential in rodents. Evidence is reviewed to evaluate the effects of wheel running, an experimental mode of exercise in rodents, on behavior in tests of anxiety and on norepinephrine and galanin systems in neural circuits that regulate stress. Stress is proposed to account for mixed behavioral findings in this literature. Indeed, running promotes an adaptive response to stress and alters anxiety-like behaviors in a manner dependent on stress. Running amplifies galanin expression in noradrenergic locus coeruleus (LC) and suppresses stress-induced activity of the LC and norepinephrine output in LC-target regions. Thus, enhanced galanin-mediated suppression of brain norepinephrine in runners is supported by current literature as a mechanism that may contribute to the stress-protective effects of exercise. These data support the use of rodents to study the emotional and neurobiological consequences of exercise.

Integrative physiology of depression and antidepressant drug action: implications for serotonergic mechanisms of action and novel therapeutic strategies for treatment of depression

Major depressive disorder (MDD) is predicted to be the second leading cause of disability worldwide by the year 2020. Currently available treatments for MDD are suboptimal. Only 50% of MDD patients recover in less than 12 weeks with adequate treatment, and up to 20% of patients will fail to adequately respond to all currently available interventions. Moreover, current treatments come at the cost of significant central nervous system (CNS) side effects, further highlighting the need for more effective treatments with fewer side effects. A greater mechanistic understanding of MDD and the actions of antidepressant drugs would provide opportunities for development of novel therapeutic approaches to treatment. With this aim in mind, we explore the novel, but empirically supported, hypothesis that an evolutionarily ancient thermoafferent pathway, signaling via the spinoparabrachial pathway from serotonergic sensory cells in the skin and other epithelial linings to serotonergic neurons and depression-related circuits in the brain, is dysfunctional in MDD and that antidepressant therapies, including antidepressant drugs and exercise, act by restoring its function.

Chronic activation of corticotropin-releasing factor type 2 receptors reveals a key role for 5-HT1A receptor responsiveness in mediating behavioral and serotonergic responses to stressful challenge

BACKGROUND

The corticotropin-releasing factor type 2 receptor (CRFR2) is suggested to play an important role in aiding recovery from acute stress, but any chronic effects of CRFR2 activation are unknown. CRFR2 in the midbrain raphé nuclei modulate serotonergic activity of this key source of serotonin (5-HT) forebrain innervation.

METHODS

Transgenic mice overexpressing the highly specific CRFR2 ligand urocortin 3 (UCN3OE) were analyzed for stress-related behaviors and hypothalamic-pituitary-adrenal axis responses. Responses to 5-HT receptor agonist challenge were assessed by local cerebral glucose utilization, while 5-HT and 5-hydroxyindoleacetic acid content were quantified in limbic brain regions.

RESULTS

Mice overexpressing urocortin 3 exhibited increased stress-related behaviors under basal conditions and impaired retention of spatial memory compared with control mice. Following acute stress, unlike control mice, they exhibited no further increase in these stress-related behaviors and showed an attenuated adrenocorticotropic hormone response. 5-HT and 5-hydroxyindoleacetic acid content of limbic nuclei were differentially regulated by stress in UCN3OE mice as compared with control mice. Responses to 5-HT type 1A receptor challenge were significantly and specifically reduced in UCN3OE mice. The distribution pattern of local cerebral glucose utilization and 5-HT type 1A receptor messenger RNA expression levels suggested this effect was mediated in the raphé nuclei.

CONCLUSIONS

Chronic activation of CRFR2 promotes an anxiety-like state, yet with attenuated behavioral and hypothalamic-pituitary-adrenal axis responses to stress. This is reminiscent of stress-related atypical psychiatric syndromes such as posttraumatic stress disorder, chronic fatigue, and chronic pain states. This new understanding indicates CRFR2 antagonism as a potential novel therapeutic target for such disorders.

Rodent estrous cycle response to incomplete spinal cord injury, surgical interventions, and locomotor training

Estrous cycle disruption after spinal cord injury (SCI) in female rats is a common phenomenon. It remains unknown, however, if the aberrant estrous cycle is a result of an injury to the spinal cord itself or due to the general stress associated with surgical interventions. We addressed this issue by determining estrous cyclicality in female rats after a spinal cord hemisection (HX), implantation of EMG wires into selected hind limb muscles, and/or injections of tracer dyes into the spinal cord. Because it is known that aerobic exercise can enhance the recovery of locomotor function in rodents with an incomplete SCI, we also determined if locomotor training positively impacts the disrupted estrous cycle after an HX. Estrous cycle assessments were made during a 5-8 week period in 27 female rats before and after HX, EMG, and/or dye injection surgeries and in HX rats that recovered spontaneously or underwent locomotor training. Our results show that estrous cyclicality was disrupted (cycle length >5 days) in approximately 76%, 46%, and 50% of the rats after HX, EMG, and dye injection surgeries, respectively. The cyclicality, however, was disrupted for a longer period after HX than after EMG or dye injection surgeries. Furthermore, estrous cycle mean length was shorter in the trained than nontrained HX group. These results suggest that estrous cycle disruption after a major SCI is a consequence of both the direct injury to the spinal cord and to the associated stress. Moreover, moderate aerobic exercise initiated early after a spinal cord HX returns the duration of the estrous cycle toward normal.

Taking the Perspective that a Depressive State Reflects Inflammation: Implications for the Use of Antidepressants

This paper reviews both the evidence that supports the characterization of depression as an inflammatory disorder and the different biochemical mechanisms that have been postulated for the connection between inflammation and depression. This association offers credible explanation for the short term efficacy of antidepressants, which have short term anti-inflammatory effects. Evidence for those anti-inflammatory effects is discussed. Evidence of the contrary long-term effects of antidepressants, which increase rather than decrease inflammation, is also reviewed. It is argued that this increase in inflammation would predict an increase in chronicity among depressed patients that have been treated with antidepressants drugs, which has been noted in the literature. A brief discussion of alternatives for decreasing inflammation, some of which have demonstrated efficacy in ameliorating depression, is presented.

Effect of baseline self-efficacy on physical activity and psychological stress after a one-week pedometer intervention

Physical activity and psychological stress were hypothesized to improve more in participants with high self-efficacy than in those with low and medium self-efficacy after a one-week intervention. 39 female university students participated. The intervention had two steps: a lecture on self-monitoring and goal setting (160 min.) and a one-week pedometer intervention. Analyses were conducted on tertile groups according to self-efficacy at baseline. Pedometer step counts were higher in the high self-efficacy group than in the low self-efficacy group after intervention. Helplessness decreased time dependently after intervention only in the high-self-efficacy group. Because physical activity improved more in the high self-efficacy group after a one-week intervention, one hypothesis was supported.

Voluntary exercise offers anxiolytic potential and amplifies galanin gene expression in the locus coeruleus of the rat

Although exercise improves anxiety in humans, it is controversial whether exercise is anxiolytic in rodents. We tested the hypothesis that stress influences the effect of exercise on anxiety-like and defensive behaviors. To explore the neurobiological mechanisms of exercise, we also examined whether exercise alters gene expression for the stress-related peptide galanin. Rats were housed in the presence or absence of a running wheel for 21 d. A subset of these rats were (1) not injected or received a single high, dose of the β-carboline FG7142 (inverse agonist at the benzodiazepine receptor site) immediately prior to testing or (2) were injected repeatedly with vehicle or FG7142 during the last 10d of exercise. On day 22, anxiety-like and defensive behaviors were measured in the elevated plus maze, shock probe defensive burying, and defensive withdrawal tests. Locus coeruleus prepro-galanin mRNA was measured by in situ hybridization. Exercise and sedentary rats that were not injected exhibited similar behavior in all tests, whereas FG7142 injected immediately prior to the test battery produced intense avoidance and immobility consistent with an anxiety-like response. However, exercise produced anxiolytic-like and active defensive behaviors in the test battery relative to the sedentary condition in rats injected repeatedly with vehicle or FG7142. Exercise also increased prepro-galanin mRNA in the locus coeruleus relative to sedentary controls. These data suggest that the emergence of enhanced adaptive behavior after chronic voluntary exercise is influenced by stress. Our data support a role for galanin in the beneficial consequences of wheel running.

Little things on which happiness depends: microRNAs as novel therapeutic targets for the treatment of anxiety and depression

Anxiety and depression are devastating mental illnesses that are a significant public health concern. Selective serotonin-reuptake inhibitors are the first-line treatment strategy for these disorders, which despite being a significant advantage over older treatments, are hampered by a limited efficacy in a significant subset of patients, delayed onset of action and side effects that affect compliance. Thus, there is much impetus to develop novel therapeutic strategies. However, this goal can only be rationally realised with a better understanding of the molecular pathophysiology of these disorders. MicroRNAs (miRNAs) are a newly discovered class of gene-expression regulators that may represent a novel class of therapeutic targets to treat a variety of disorders including psychiatric diseases. miRNAs are heavily involved in regulating many physiological processes including those fundamental to the functioning of the central nervous system. Evidence collected to date has already demonstrated that miRNA-expression levels are altered in patients suffering from depression and anxiety and in pre-clinical models of psychological stress. Furthermore, increasing evidence suggests that psychoactive agents including antidepressants and mood stabilisers utilise miRNAs as downstream effectors. Altering miRNA levels has been shown to alter behaviour in a therapeutically desirable manner in pre-clinical models. This review aims to outline the evidence collected to date demonstrating miRNAs role in anxiety and depression, the potential advantages of targeting these small RNA molecules as well as some of the hurdles that will have to be overcome to fully exploit their therapeutic potential.

The many faces of insulin-like peptide signalling in the brain

Central and peripheral insulin-like peptides (ILPs), which include insulin, insulin-like growth factor 1 (IGF1) and IGF2, exert many effects in the brain. Through their actions on brain growth and differentiation, ILPs contribute to building circuitries that subserve metabolic and behavioural adaptation to internal and external cues of energy availability. In the adult brain each ILP has distinct effects, but together their actions ultimately regulate energy homeostasis - they affect nutrient sensing and regulate neuronal plasticity to modulate adaptive behaviours involved in food seeking, including high-level cognitive operations such as spatial memory. In essence, the multifaceted activity of ILPs in the brain may be viewed as a system organization involved in the control of energy allocation.

Adolescent female rats exhibiting activity-based anorexia express elevated levels of GABA(A) receptor α4 and δ subunits at the plasma membrane of hippocampal CA1 spines

Activity-based anorexia (ABA) is an animal model for anorexia nervosa that has revealed genetic links to anxiety traits and neurochemical characteristics within the hypothalamus. However, few studies have used this animal model to investigate the biological basis for vulnerability of pubertal and adolescent females to ABA, even though the great majority of the anorexia nervosa cases are females exhibiting the first symptoms during puberty. GABAergic inhibition of the hippocampus strongly regulates anxiety as well as plasticity throughout life. We recently showed that the hippocampal CA1 of female mice undergo a dramatic change at puberty onset--from expressing virtually none of the nonsynaptic α4βδ GABA(A) receptors (GABARs) prepubertally to expressing these GABARs at ~7% of the CA1 dendritic spine membranes at puberty onset. Furthermore, we showed that this change underlies the enhanced modulation of anxiety, neuronal excitability, and NMDA receptor-dependent synaptic plasticity in the hippocampus by the stress neurosteroid, THP (3α-OH-5α[β]-pregnan-20-one or [allo]pregnanolone). Here, we used quantitative electron microscopy to determine whether ABA induction in female rats during adolescence also elevates the expression of α4 and δ subunits of α4βδ GABARs, as was observed at puberty onset for mice. Our analysis revealed that rats also exhibit a rise of α4 and δ subunits of α4βδ GABARs at puberty onset, in that these subunits are detectable at ~6% of the dendritic spine membranes of CA1 pyramidal cells at puberty onset (postnatal day 32-36; P32-36) but this drops to about 2% by P40-P44. The levels of α4 and δ subunits at the CA1 spines remained low following exposure of females to either of the two environmental factors needed to generate ABA--food restriction and access to a running wheel for 4 days--from P40 to P44. This pattern contrasted greatly from those of ABA animals, for which the two environmental factors were combined. Within the hippocampus of ABA animals, 12% of the spine profiles were labeled for α4, reflecting a sixfold increase, relative to hippocampi of age-matched (P44) control females (p < 0.005). Concurrently, 7% of the spine profiles were labeled for δ, reflecting a 130% increase from the control values of 3% (p = 0.01). No measurable change was detected for spine size. The observed magnitude of increase in the α4 and δ subunits at spines is sufficient to increase both tonic inhibition of hippocampus and anxiety during stress, thereby likely to exacerbate hyperactivity and weight loss.

The use of a running wheel to measure activity in rodents: relationship to energy balance, general activity, and reward

Running wheels are commonly employed to measure rodent physical activity in a variety of contexts, including studies of energy balance and obesity. There is no consensus on the nature of wheel-running activity or its underlying causes, however. Here, we will begin by systematically reviewing how running wheel availability affects physical activity and other aspects of energy balance in laboratory rodents. While wheel running and physical activity in the absence of a wheel commonly correlate in a general sense, in many specific aspects the two do not correspond. In fact, the presence of running wheels alters several aspects of energy balance, including body weight and composition, food intake, and energy expenditure of activity. We contend that wheel-running activity should be considered a behavior in and of itself, reflecting several underlying behavioral processes in addition to a rodent's general, spontaneous activity. These behavioral processes include defensive behavior, predatory aggression, and depression- and anxiety-like behaviors. As it relates to energy balance, wheel running engages several brain systems-including those related to the stress response, mood, and reward, and those responsive to growth factors-that influence energy balance indirectly. We contend that wheel-running behavior represents factors in addition to rodents' tendency to be physically active, engaging additional neural and physiological mechanisms which can then independently alter energy balance and behavior. Given the impact of wheel-running behavior on numerous overlapping systems that influence behavior and physiology, this review outlines the need for careful design and interpretation of studies that utilize running wheels as a means for exercise or as a measurement of general physical activity.

MicroRNA expression in rat brain exposed to repeated inescapable shock: differential alterations in learned helplessness vs. non-learned helplessness

MicroRNA (miRNA) expression was measured within frontal cortex of male Holtzman rats subjected to repeated inescapable shocks at days 1 and 7, tested for learned helplessness (LH) at days 2 and 8, and sacrificed at day 15. We compared rats that did vs. did not exhibit LH, as well as rats that were placed in the apparatus and tested for avoidance but not given shocks (tested controls, TC). Non-learned helpless (NLH) rats showed a robust adaptive miRNA response to inescapable shock whereas LH rats showed a markedly blunted response. One set of 12 miRNAs showed particularly large, significant down-regulation in NLH rats relative to tested controls (mir-96, 141, 182, 183, 183*, 298, 200a, 200a*, 200b, 200b*, 200c, 429). These were encoded at a few shared polycistronic loci, suggesting that the down-regulation was coordinately controlled at the level of transcription. Most of these miRNAs are enriched in synaptic fractions. Moreover, almost all of these share 5'-seed motifs with other members of the same set, suggesting that they will hit similar or overlapping sets of target mRNAs. Finally, half of this set is predicted to hit Creb1 as a target. We also identified a core miRNA co-expression module consisting of 36 miRNAs that are highly correlated with each other across individuals of the LH group (but not in the NLH or TC groups). Thus, miRNAs participate in the alterations of gene expression networks that underlie the normal (NLH) as well as aberrant (LH) response to repeated shocks.

Exercise, stress resistance, and central serotonergic systems

Voluntary exercise reduces the incidence of stress-related psychiatric disorders in humans and prevents serotonin-dependent behavioral consequences of stress in rodents. Evidence reviewed herein is consistent with the hypothesis that exercise increases stress resistance by producing neuroplasticity at multiple sites of the central serotonergic system, which all help to limit the behavioral impact of acute increases in serotonin during stressor exposure.

Short natural sleep is associated with higher T cell and lower NK cell activities

Short sleep duration increases the risk of several diseases, possibly involving compromised immune function. However, most previous studies are based on experimentally induced sleep deprivation, and only a few have studied natural variations in sleep duration. Thus our aim was to study how natural variations in sleep duration affect immune function. In total, 36 healthy men and women, aged 20-54, donated blood; 29 on three consecutive mornings, and seven on one morning. Each morning, participants self-reported sleep duration the night prior to blood draw. General sleep patterns, physical activity and stress were also assessed. A flow-cytometric assay was used to measure natural killer cell activity (NKCA), T cell function (in response to PHA, influenza, and SEA+B), and B cell function (in response to PWM) per volume whole blood. Short sleep duration prior to blood draw (<7 h) was associated with 49% higher PHA-induced T cell function (95% CI 7/109%) and 30% lower NKCA compared with normal prior sleep (7-9 h) (95% CI -46/-8%). In addition, high perceived stress was associated with 39% higher PHA-induced T cell function (95% CI 0/94%). High general physical activity was associated with 47% increased numbers of B cells and 28% increased numbers of T cells, but not with immune function. Our results suggest strong relationships between short sleep duration and T- and NK-cell functions. The stability of the findings as well as the clinical consequences of the link between short sleep and immune function should be explored in future studies.

5-hydroxytryptamine 2C receptors in the dorsal striatum mediate stress-induced interference with negatively reinforced instrumental escape behavior

Uncontrollable stress can interfere with instrumental learning and induce anxiety in humans and rodents. While evidence supports a role for serotonin (5-HT) and serotonin 2C receptors (5-HT(2C)R) in the behavioral consequences of uncontrollable stress, the specific sites of action are unknown. These experiments sought to delineate the role of 5-HT and 5-HT(2C)R in the dorsal striatum (DS) and the lateral/basolateral amygdala (BLA) in the expression of stress-induced instrumental escape deficits and exaggerated fear, as these structures are critical to instrumental learning and fear behaviors. Using in vivo microdialysis, we first demonstrated that prior uncontrollable, but not controllable, stress sensitizes extracellular 5-HT in the dorsal striatum, a result that parallels prior work in the BLA. Additionally, rats were implanted with bi-lateral cannula in either the DS or the BLA and exposed to uncontrollable tail shock stress. One day later, rats were injected with 5-HT(2C)R antagonist (SB242084) and fear and instrumental learning behaviors were assessed in a shuttle box. Separately, groups of non-stressed rats received an intra-DS or an intra-BLA injection of the 5-HT(2C)R agonist (CP809101) and behavior was observed. Intra-DS injections of the 5-HT(2C)R antagonist prior to fear/escape tests completely blocked the stress-induced interference with instrumental escape learning; a partial block was observed when injections were in the BLA. Antagonist administration in either region did not influence stress-induced fear behavior. In the absence of prior stress, intra-DS administration of the 5-HT(2C)R agonist was sufficient to interfere with escape behavior without enhancing fear, while intra-BLA administration of the 5-HT(2C)R agonist increased fear behavior but had no effect on escape learning. Results reveal a novel role of the 5-HT(2C)R in the DS in the expression of instrumental escape deficits produced by uncontrollable stress and demonstrate that the involvement of 5-HT(2C)R activation in stress-induced behaviors is regionally specific.

The neurogenesis hypothesis of affective and anxiety disorders: are we mistaking the scaffolding for the building?

Hypotheses are scaffoldings erected in front of a building and then dismantled when the building is finished. They are indispensable for the workman; but you mustn't mistake the scaffolding for the building. Johann Wolfgang von Goethe. The neurogenesis hypothesis of affective disorders - in its simplest form - postulates that the generation of neurons in the postnatal hippocampal dentate gyrus is involved in the etiology and treatment efficacy of major depressive disorder (MDD). The hypothesis was established in the 1990s but was built on a broad foundation of earlier research on the hippocampus, serotonin and MDD. It has gone through several growth phases fueled by discoveries both correlative and causative in nature. Recently, the hypothesis has also been broadened to also include potential relevance for anxiety disorders, like post-traumatic stress disorder (PTSD). As any hypothesis should be, it has been tested and challenged, sometimes vigorously. Here we review the current standing of the neurogenesis hypothesis of affective and anxiety disorders, noting in particular how a central postulate - that decreased neurogenesis results in depression or anxiety - has, in general, been rejected. We also review the controversies on whether treatments for these disorders, like antidepressants, rely on intact neurogenesis for their efficacy, and the existence of neurogenesis-dependent and -independent effects of antidepressants. In addition, we review the implications that the hypothesis has for the response to stress, PTSD, and the neurobiology of resilience, and highlight our own work showing that adult-generated neurons are functionally important for the behavioral response to social stress. We conclude by emphasizing how advancements in transgenic mouse technology, rodent behavioral analyses, and our understanding of the neurogenesis process will allow us to refine our conclusions and perform ever more specific experiments. Such scrutiny is critical, since if we "mistake the scaffolding for the building" we could overlook opportunities for translational impact in the clinic. This article is part of a special Issue entitled 'Anxiety and Depression'.

Wheel running can accelerate or delay extinction of conditioned place preference for cocaine in male C57BL/6J mice, depending on timing of wheel access

Aerobic exercise may represent a useful intervention for drug abuse in predisposed individuals. Exercise increases plasticity in the brain that could be used to reverse learned drug associations. Previous studies have reported that exposing mice to a complex environment including running wheels after drug conditioning abolishes conditioned place preference (CPP) for cocaine, whereas running can enhance CPP when administered before conditioning. The purpose of the present study was to test the hypothesis that timing of exercise relative to conditioning has opposing effects on cocaine CPP. Male C57BL/6J mice experienced 30 days of running or sedentary treatments either before or after cocaine conditioning. Control animals always received saline and never cocaine, but otherwise underwent the same conditioning and exercise treatments. Animals were given bromodeoxyuridine injections at the onset of conditioning or exercise, and euthanized at the end of the study to quantify survival of new neurons in the hippocampus as a marker of plasticity. Wheel running accelerated extinction of CPP when running occurred entirely after drug conditioning, whereas running delayed extinction when administered before conditioning. A single conditioning day after running was sufficient to abolish the accelerated extinction observed when all conditioning preceded running. Running approximately doubled adult hippocampal neurogenesis, whereas cocaine had no effect. These results suggest that exercise-induced plasticity can facilitate learning that context is no longer associated with drug. However, if drug exposure occurs after exercise, running-induced plasticity may strengthen drug associations. The results provide insights into the interaction between exercise and drug conditioning that could have implications for drug abuse treatments.

Exercise therapy for stress-related mental disorder, a randomised controlled trial in primary care

BACKGROUND

to investigate whether a structured physical exercise programme (PEP) improves the recovery of general health in patients suffering from Stress-related Mental Disorder (SMD).

METHOD

STUDY DESIGN

randomised open trial in general practice. Patients from two regions in the Netherlands were included between September 2003 and December 2005, and followed up for 12 weeks.

INTERVENTION

the patients were referred to a physical therapist for instruction in and monitoring of physical exercise of an intermediate intensity. Following the Dutch Guidelines for Healthy Physical Exercise, the patients were instructed to exercise at least five times a week, for at least 30 minutes per day.

CONTROL GROUP

usual care from the GP OUTCOME: Primary: improvement of general health after 6 weeks according to the 'general health' dimension of the Short-Form 36.Secondary: total days off work, percentage that resumed work after 6 and 12 weeks, change in distress score and change in remaining SF36 dimensions after 6 and 12 weeks.

RESULTS

out of 102 randomised patients (mean age 43, 60 (59%) female), 70 (68%) completed the trial, of whom 31 were in the intervention group. After 6 weeks, the mean (SD) general health score was 54.6 (22.1) for the intervention group and 57.5 (19.2) for the controls. The corresponding effect size (Cohen's d with 95% confidence interval) from analysis of covariance was -0.06 (-0.41, 0.30) indicating no effect on general health. No significant effects of the intervention were detected for any secondary outcome parameter either.

CONCLUSION

Notwithstanding the relatively high drop-out rate, our results suggest that referral to a physical therapist for structured physical exercise is not likely to be very effective in improving recovery from SMD.

TRIAL REGISTRY

Current Controlled Trials ISRCTN15609105.

Environmental enrichment confers stress resiliency to social defeat through an infralimbic cortex-dependent neuroanatomical pathway

Enriched environmental (EE) housing dampens stress-induced alterations in neurobiological systems, promotes adaptability, and extinguishes submissive behavioral traits developed during social defeat stress (SD). In the present study, we hypothesized that enrichment before SD can confer stress resiliency and, furthermore, that neuronal activity in the prefrontal cortex (PFC) is requisite for this resiliency. To test these hypotheses, mice were housed in EE, standard (SE), or impoverished (IE) housing and then exposed to SD. EE conferred resilience to SD as measured in several behavioral tasks. EE-housed mice expressed elevated FosB/ΔFosB immunostaining in areas associated with emotional regulation and reward processing, i.e., infralimbic, prelimbic, and anterior cingulate cortices, amygdala, and nucleus accumbens, and this expression was mostly preserved in mice receiving EE followed by SD. In contrast, in SE- or IE-housed animals, SD increased maladaptive behaviors and greatly reduced FosB/ΔFosB staining in the forebrain. We tested the putative involvement of the PFC in mediating resilience by lesioning individual regions of the PFC either before or after EE housing and then exposing the mice to SD. We found that discrete lesions of the infralimbic but not prelimbic or cingulate cortex made before but not after EE abolished the behavioral resiliency to stress afforded by EE and attenuated FosB/ΔFosB expression in the accumbens and amygdala while increasing it in the paraventricular hypothalamic nucleus. These data suggest that pathological ventromedial PFC outputs to downstream limbic targets could predispose an individual to anxiety disorders in stressful situations, whereas enhanced ventromedial PFC outputs could convey stress resilience.