Circadian rhythms and depression: effects of exercise in an animal model

A computational analysis of mouse behavior in the sucrose preference test

The sucrose preference test (SPT) measures the relative preference of sucrose over water to assess hedonic behaviors in rodents. Yet, it remains uncertain to what extent the SPT reflects other behavioral components, such as learning, memory, motivation, and choice. Here, we conducted an experimental and computational decomposition of mouse behavior in the SPT and discovered previously unrecognized behavioral subcomponents associated with changes in sucrose preference. We show that acute and chronic stress have sex-dependent effects on sucrose preference, but anhedonia was observed only in response to chronic stress in male mice. Additionally, reduced sucrose preference induced by optogenetics is not always indicative of anhedonia but can also reflect learning deficits. Even small variations in experimental conditions influence behavior, task outcome and interpretation. Thus, an ostensibly simple behavioral task can entail high levels of complexity, demonstrating the need for careful dissection of behavior into its subcomponents when studying the underlying neurobiology.

Circadian rhythms-related disorders in diurnal fat sand rats under modern lifestyle conditions: A review

Modern lifestyle reduces environmental rhythmicity and may lead to circadian desynchrony. We are exposed to poor day-time lighting indoors and excessive night-time artificial light. We use air-conditioning to reduce ambient temperature cycle, and food is regularly available at all times. These disruptions of daily rhythms may lead to type 2 diabetes mellitus (T2DM), obesity, cardiometabolic diseases (CMD), depression and anxiety, all of which impose major public health and economic burden on societies. Therefore, we need appropriate animal models to gain a better understanding of their etiologic mechanisms, prevention, and management.We argue that the fat sand rat (Psammomys obesus), a diurnal animal model, is most suitable for studying the effects of modern-life conditions. Numerous attributes make it an excellent model to study human health disorders including T2DM, CMD, depression and anxiety. Here we review a comprehensive series of studies we and others conducted, utilizing the fat sand rat to study the underlying interactions between biological rhythms and health. Understanding these interactions will help deciphering the biological basis of these diseases, which often occur concurrently. We found that when kept in the laboratory (compared with natural and semi-wild outdoors conditions where they are diurnal), fat sand rats show low amplitude, nocturnal or arrhythmic activity patterns, dampened daily glucose rhythm, glucose intolerance, obesity and decreased survival rates. Short photoperiod acclimation exacerbates these pathologies and further dampens behavioral and molecular daily rhythms, resulting in CMD, T2DM, obesity, adipocyte dysfunction, cataracts, depression and anxiety. Increasing environmental rhythmicity by morning bright light exposure or by access to running wheels strengthens daily rhythms, and results in higher peak-to-trough difference in activity, better rhythmicity in clock genes expression, lower blood glucose and insulin levels, improved glucose tolerance, lower body and heart weight, and lower anxiety and depression. In summary, we have demonstrated that fat sand rats living under the correspondent of “human modern lifestyle” conditions exhibit dampened behavioral and biological rhythms and develop circadian desynchrony, which leads to what we have named “The Circadian Syndrome”. Environmental manipulations that increase rhythmicity result in improvement or prevention of these pathologies. Similar interventions in human subjects could have the same positive results and further research on this should be undertaken.

Beneficial effects of voluntary wheel running on activity rhythms, metabolic state, and affect in a diurnal model of circadian disruption

Emerging evidence suggests that disruption of circadian rhythmicity contributes to development of comorbid depression, cardiovascular diseases (CVD), and type 2 diabetes mellitus (T2DM). Physical exercise synchronizes the circadian system and has ameliorating effects on the depression- and anxiety-like phenotype induced by circadian disruption in mice and sand rats. We explored the beneficial effects of voluntary wheel running on daily rhythms, and the development of depression, T2DM, and CVD in a diurnal animal model, the fat sand rat (Psammomys obesus). Voluntary exercise strengthened general activity rhythms, improved memory and lowered anxiety- and depressive-like behaviors, enhanced oral glucose tolerance, and decreased plasma insulin levels and liver weight. Animals with access to a running wheel had larger heart weight and heart/body weight ratio, and thicker left ventricular wall. Our results demonstrate that exercising ameliorates pathological-like daily rhythms in activity and blood glucose levels, glucose tolerance and depressive- and anxiety-like behaviors in the sand rat model, supporting the important role of physical activity in modulating the “circadian syndrome” and circadian rhythm-related diseases. We suggest that the utilization of a diurnal rodent animal model may offer an effective way to further explore metabolic, cardiovascular, and affective-like behavioral changes related to chronodisruption and their underlying mechanisms.

Voluntary wheel running behaviour as a tool to assess the severity in a mouse pancreatic cancer model

Laboratory animals frequently undergo routine experimental procedures such as handling, restraining and injections. However, as a known source of stress, these procedures potentially impact study outcome and data quality. In the present study, we, therefore, performed an evidence-based severity assessment of experimental procedures used in a pancreatic cancer model including surgical tumour induction and subsequent chemotherapeutic treatment via repeated intraperitoneal injections. Cancer cell injection into the pancreas was performed during a laparotomy under general anaesthesia. After a four-day recovery phase, mice received either drug treatment (galloflavin and metformin) or the respective vehicle substances via daily intraperitoneal injections. In addition to clinical scoring, an automated home-cage monitoring system was used to assess voluntary wheel running (VWR) behaviour as an indicator of impaired well-being. After surgery, slightly elevated clinical scores and minimal body weight reductions, but significantly decreased VWR behaviour were observed. During therapy, body weight declined in response to chemotherapy, but not after vehicle substance injection, while VWR activity was decreased in both cases. VWR behaviour differed between treatment groups and revealed altered nightly activity patterns. In summary, by monitoring VWR a high impact of repeated injections on the well-being of mice was revealed and substance effects on well-being were distinguishable. However, no differences in tumour growth between treatment groups were observed. This might be due to the severity of the procedures uncovered in this study, as exaggerated stress responses are potentially confounding factors in preclinical studies. Finally, VWR was a more sensitive indicator of impairment than clinical scoring in this model.

Can animals develop depression? An overview and assessment of ‘depression-like’ states

Describing certain animal behaviours as ‘depression-like’ or ‘depressive’ has become common across several fields of research. These typically involve unusually low activity or unresponsiveness and/or reduced interest in pleasure (anhedonia). While the term ‘depression-like’ carefully avoids directly claiming that animals are depressed, this narrative review asks whether stronger conclusions can be legitimate, with animals developing the clinical disorder as seen in humans (cf., DSM-V/ICD-10). Here, we examine evidence from animal models of depression (especially chronically stressed rats) and animals experiencing poor welfare in conventional captive conditions (e.g., laboratory mice and production pigs in barren environments). We find troubling evidence that animals are indeed capable of experiencing clinical depression, but demonstrate that a true diagnosis has yet to be confirmed in any case. We thus highlight the importance of investigating the co-occurrence of depressive criteria and discuss the potential welfare and ethical implications of animal depression.

Light at night during development in mice has modest effects on adulthood behavior and neuroimmune activation

Exposure to light at night (LAN) can disrupt the circadian system, thereby altering neuroimmune reactivity and related behavior. Increased exposure to LAN affects people of all ages - and could have particularly detrimental effects during early-life and adolescence. Despite this, most research on the behavioral and physiological effects of LAN has been conducted in adult animals. Here we evaluated the effects of dim LAN during critical developmental windows on adulthood neuroimmune function and affective/sickness behaviors. Male and female C57BL/6 J mice were exposed to dim LAN [12:12 light (150 lx)/dim (15 lx) cycle] during early life (PND10-24) or adolescence (PND30-44) [control: 12:12 light (150 lx)/dark (0 lx) cycle]. Behaviors were assessed during juvenile (PND 42-44) and adult (PND60) periods. Contrary to our hypothesis, juvenile mice that were exposed to dim LAN did not exhibit changes in anxiety- or depressive-like behaviors. By adulthood, adolescent LAN-exposed female mice showed a modest anxiety-like phenotype in one behavioral task but not another. Adolescent LAN exposure also induced depressive-like behavior in a forced swim task in adulthood in both male and female mice. Additionally, developmental LAN exacerbated the hippocampal cytokine response (IL-1β) following peripheral LPS in female, but not male mice. These results suggest female mice may be more susceptible to developmental LAN than male mice: LAN female mice had a modest anxiety-like phenotype in adulthood, and upon LPS challenge, higher hippocampal IL-1β expression. Taken together, developmental LAN exposure in mice promotes a modest increase in susceptibility to anxiety- and depressive-like symptoms.

Sex differences in resilience: Experiential factors and their mechanisms

Adverse life events can lead to stable changes in brain structure and function and are considered primary sources of risk for post-traumatic stress disorder, depression and other neuropsychiatric disorders. However, most individuals do not develop these conditions following exposure to traumatic experiences, and research efforts have identified a number of experiential factors associated with an individual's ability to withstand, adapt to and facilitate recovery from adversity. While multiple animal models of stress resilience exist, so that the detailed biological mechanisms can be explored, studies have been disproportionately conducted in male subjects even though the prevalence and presentation of stress-linked disorders differ between sexes. This review focuses on (a) the mechanisms by which experiential factors (behavioral control over a stressor, exercise) reduce the impact of adverse events as studied in males; (b) whether other manipulations (ketamine) that buffer against stress-induced sequelae engage the same circuit features; and (c) whether these processes operate similarly in females. We argue that investigation of experiential factors that produce resistance/resilience rather than vulnerability to adversity will generate a unique set of biological mechanisms that potentially underlie sex differences in mood disorders.

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.

Prospects for circadian treatment of mood disorders

Disruption of circadian clocks is strongly associated with mood disorders. Chronotherapies targeting circadian rhythms have been shown to be very effective treatments of mood disorders, but still are not widely used in clinical practice. The mechanisms by which circadian disruption leads to mood disorders are poorly characterized and, therefore, may not convince clinicians to apply chronotherapies. Hence, in this review, we describe specific potential mechanisms, in order to make this connection more credible to clinicians. We believe that four major features of disrupted clocks may contribute to the development of mood disorders: (1) loss of synchronization to environmental 24-h rhythms, (2) internal desynchronization among body clocks, (3) low rhythm amplitude, and (4) changes in sleep architecture. Discussing these attributes and giving plausible examples, we will discuss prospects for relatively simple chronotherapies addressing these features that are easy to implement in clinical practice. Key messages In this review, we describe specific potential mechanisms by which disrupted clocks may contribute to the development of mood disorders: (1) loss of synchronization to environmental 24-h rhythms, (2) internal desynchronization among body clocks, (3) low rhythm amplitude, and (4) changes in sleep architecture. We provide prospects for relatively simple chronotherapies addressing these features that are easy to implement in clinical practice.

Running in the wheel: Defining individual severity levels in mice

The fine-scale grading of the severity experienced by animals used in research constitutes a key element of the 3Rs (replace, reduce, and refine) principles and a legal requirement in the European Union Directive 2010/63/EU. Particularly, the exact assessment of all signs of pain, suffering, and distress experienced by laboratory animals represents a prerequisite to develop refinement strategies. However, minimal and noninvasive methods for an evidence-based severity assessment are scarce. Therefore, we investigated whether voluntary wheel running (VWR) provides an observer-independent behaviour-centred approach to grade severity experienced by C57BL/6J mice undergoing various treatments. In a mouse model of chemically induced acute colitis, VWR behaviour was directly related to colitis severity, whereas clinical scoring did not sensitively reflect severity but rather indicated marginal signs of compromised welfare. Unsupervised k-means algorithm–based cluster analysis of body weight and VWR data enabled the discrimination of cluster borders and distinct levels of severity. The validity of the cluster analysis was affirmed in a mouse model of acute restraint stress. This method was also applicable to uncover and grade the impact of serial blood sampling on the animal’s welfare, underlined by increased histological scores in the colitis model. To reflect the entirety of severity in a multidimensional model, the presented approach may have to be calibrated and validated in other animal models requiring the integration of further parameters. In this experimental set up, however, the automated assessment of an emotional/motivational driven behaviour and subsequent integration of the data into a mathematical model enabled unbiased individual severity grading in laboratory mice, thereby providing an essential contribution to the 3Rs principles.

Animal-based biomedical research is often accompanied by experience of discomfort or pain by the animal. Recognition of disturbed animal welfare is mandatory, and the classification and assessment of its severity is a crucial part of the legislative framework in the European Union (EU). In the present study, we analysed voluntary wheel running (VWR) behaviour as a measure of compromised welfare in a mouse colitis model. Unsupervised mathematical clustering of clinical and VWR data enabled us to allocate and classify severity levels. This cluster model was verified using VWR data from a restraint stress model and allowed us to uncover the impact of routine experimental procedures on these mice. We propose that clustering of VWR behaviour provides a useful method for assessing the severity level of experimental procedures conducted on mice.

Making Sense of Rodent Models of Anhedonia

A markedly reduced interest or pleasure in activities previously considered pleasurable is a main symptom in mood disorder and psychosis and is often present in other psychiatric disorders and neurodegenerative diseases. This condition can be labeled as "anhedonia," although in its most rigorous connotation the term refers to the lost capacity to feel pleasure that is one aspect of the complex phenomenon of processing and responding to reward. The responses to rewarding stimuli are relatively easy to study in rodents, and the experimental conditions that consistently and persistently impair these responses are used to model anhedonia. To this end, long-term exposure to environmental aversive conditions is primarily used, and the resulting deficits in reward responses are often accompanied by other deficits that are mainly reminiscent of clinical depressive symptoms. The different components of impaired reward responses induced by environmental aversive events can be assessed by different tests or protocols that require different degrees of time allocation, technical resources, and equipment. Rodent models of anhedonia are valuable tools in the study of the neurobiological mechanisms underpinning impaired behavioral responses and in the screening and characterization of drugs that may reverse these behavioral deficits. In particular, the antianhedonic or promotivational effects are relevant features in the spectrum of activities of drugs used in mood disorders or psychosis. Thus, more than the model, it is the choice of tests that is crucial since it influences which facets of anhedonia will be detected and should be tuned to the purpose of the study.

Hormonal Regulation of Hippocampal Neurogenesis: Implications for Depression and Exercise

Adult hippocampal neurogenesis exists in all mammalian species, including humans, and although there has been considerable research investigating the function and regulation of neurogenesis, there remain many open questions surrounding the complexity of this phenomenon. This stems partially from the fact that neurogenesis is a multistage process that involves proliferation, differentiation, migration, survival, and eventual integration of new cells into the existing hippocampal circuitry, each of which can be independently influenced. The function of adult neurogenesis in the hippocampus is related to stress regulation, behavioral efficacy of antidepressants, long-term spatial memory, forgetting, and pattern separation. Steroid hormones influence the regulation of hippocampal neurogenesis, stress regulation, and cognition and differently in males and females. In this chapter, we will briefly tap into the complex network of steroid hormone modulation of neurogenesis in the hippocampus with specific emphasis on stress, testosterone, and estrogen. We examine the possible role of neurogenesis in the etiology of depression and influencing treatment by examining the influence of both pharmacological (selective serotonin reuptake inhibitors, tricyclic antidepressants) treatments and non-pharmacological (exercise) remedies.

Assessing mouse behaviour throughout the light/dark cycle using automated in-cage analysis tools

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Automated assessment of mouse home-cage behaviour is robust and reliable.

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Analysis over multiple light/dark cycles improves ability to classify behaviours.

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Combined RFID and video analysis enables home-cage analysis in group housed animals.

An important factor in reducing variability in mouse test outcomes has been to develop assays that can be used for continuous automated home cage assessment. Our experience has shown that this has been most evidenced in long-term assessment of wheel-running activity in mice. Historically, wheel-running in mice and other rodents have been used as a robust assay to determine, with precision, the inherent period of circadian rhythms in mice. Furthermore, this assay has been instrumental in dissecting the molecular genetic basis of mammalian circadian rhythms. In teasing out the elements of this test that have determined its robustness – automated assessment of an unforced behaviour in the home cage over long time intervals – we and others have been investigating whether similar test apparatus could be used to accurately discriminate differences in distinct behavioural parameters in mice. Firstly, using these systems, we explored behaviours in a number of mouse inbred strains to determine whether we could extract biologically meaningful differences. Secondly, we tested a number of relevant mutant lines to determine how discriminative these parameters were. Our findings show that, when compared to conventional out-of-cage phenotyping, a far deeper understanding of mouse mutant phenotype can be established by monitoring behaviour in the home cage over one or more light:dark cycles.

α9-nAChR knockout mice exhibit dysregulation of stress responses, affect and reward-related behaviour

The α9α10-subtype of nicotinic acetylcholine receptor (nAChR) has recently garnered interest in biomedicine and is being pursued as an analgesic target. However, the receptor exhibits diverse tissue distribution, the function of which is known to varying degrees, and targeting this receptor for clinical treatments without a broad understanding of its function may have adverse consequences. The α9α10-nAChR is expressed in the adrenal and pituitary glands, suggesting a potential role in the stress response, but little is known about its function in this tissue. Here we determined a role for the α9α10-nAChR in behavioural and physiological stress responses, by comparing the stress- and affect-related phenotypes of wildtype and α9-nAChR knockout mice. Naïve knockout mice exhibited largely normal behaviour on standard tests of affective behaviour. However, after sub-chronic restraint stress knockout mice showed significantly decreased stress-induced arousal and increased anxiety-like behaviour when compared to wildtype animals. Physiologically, corticosterone responses were muted in knockout mice after an acute stressor, but exaggerated in response to the same stressor after undergoing sub-chronic stress. Behavioural profiling of the α9-nAChR knockout mice in the home-cage revealed that circadian patterns of activity were altered when compared to wildtype controls. Furthermore, knockout mice showed altered responses to a period of reward discounting, resulting in anhedonia-like behaviour in a sucrose preference test where WT mice continued to seek reward. These experiments uncover a novel role for the α9α10-nAChR in mounting a normal stress response and in the regulation of affective- and reward-related behaviour, and suggest that pursuing the receptor for clinical treatments may not be as straightforward as has been suggested.

Exercise increases mTOR signaling in brain regions involved in cognition and emotional behavior

Exercise can enhance learning and memory and produce resistance against stress-related psychiatric disorders such as depression and anxiety. In rats, these beneficial effects of exercise occur regardless of exercise controllability: both voluntary and forced wheel running produce stress-protective effects. The mechanisms underlying these beneficial effects of exercise remain unknown. The mammalian target of rapamycin (mTOR) is a translation regulator important for cell growth, proliferation, and survival. mTOR has been implicated in enhancing learning and memory as well as antidepressant effects. Moreover, mTOR is sensitive to exercise signals such as metabolic factors. The effects of exercise on mTOR signaling, however, remain unknown. The goal of the present study was to test the hypothesis that exercise, regardless of controllability, increases levels of phosphorylated mTOR (p-mTOR) in brain regions important for learning and emotional behavior. Rats were exposed to 6 weeks of either sedentary (locked wheel), voluntary, or forced wheel running conditions. At 6 weeks, rats were sacrificed during peak running and levels of p-mTOR were measured using immunohistochemistry. Overall, both voluntary and forced exercise increased p-mTOR-positive neurons in the medial prefrontal cortex, striatum, hippocampus, hypothalamus, and amygdala compared to locked wheel controls. Exercise, regardless of controllability, also increased numbers of p-mTOR-positive glia in the striatum, hippocampus, and amygdala. For both neurons and glia, the largest increase in p-mTOR positive cells was observed after voluntary running, with forced exercise causing a more modest increase. Interestingly, voluntary exercise preferentially increased p-mTOR in astrocytes (GFAP+), while forced running increased p-mTOR in microglia (CD11+) in the inferior dentate gyrus. Results suggest that mTOR signaling is sensitive to exercise, but subtle differences exist depending on exercise controllability. Increases in mTOR signaling could contribute to the beneficial effects of exercise on cognitive function and mental health.

Physical Exercise for Treatment of Mood Disorders: A Critical Review

PURPOSE OF THE REVIEW

The purpose of this review is to critically assess the evidence for exercise as an adjunct intervention for major depressive disorder and bipolar disorder, chronic conditions characterized by frequent comorbid conditions as well as interepisodic symptoms with poor quality of life and impaired functioning. Individuals with these mood disorders are at higher risk of cardiovascular disease and premature death in part because of increased rates of obesity, inactivity, and diabetes mellitus compared to the general population. Exercise may not only mitigate the increased risk of cardiovascular disease, but could also potentially improve the long term outcomes of mood disorders.

RECENT FINDINGS

We conducted a literature review on the impact of exercise on mood disorders and associated comorbid conditions as well as possible biological mechanisms. We found that exercise impacts both the physical health parameters of mood disorders as well as mental health outcomes. Exercise also positively impacts conditions frequently comorbid with mood disorders (i.e. anxiety, pain, and insomnia). There are multiple candidate biomarkers for exercise, with brain-derived neurotrophic factor and oxidative stress as two main promising components of exercise's anti-depressant effect.

SUMMARY

Exercise appears to be a promising adjunct treatment for mood disorders. We conclude with recommendations for future research of exercise as an adjunct intervention for mood disorders.

Effects of creatine monohydrate supplementation and exercise on depression-like behaviors and raphe 5-HT neurons in mice

[Purpose]

The effects of creatine and exercise on chronic stress-induced depression are unclear. In the present study, we identified the effects of 4-week supplementation of creatine monohydrate and/or exercise on antidepressant behavior and raphe 5-HT expression in a chronic mild stress-induced depressed mouse model.

[Methods]

Seven-week-old male C57BL/6 mice (n=48) were divided randomly into 5 groups: (1) non-stress control (CON, n=10), (2) stress control (ST-CON, n=10), (3) stress and creatine intake (ST-Cr, n=10), (4) stress and exercise (ST-Ex, n=9), and (5) combined stress, exercise, and creatine intake (ST-Cr+Ex, n=9). After five weeks’ treatment, we investigated using both anti-behavior tests (the Tail Suspension Test (TST) and the Forced Swimming Test (FST)), and 5-HT expression in the raphe nuclei (the dorsal raphe (DR) and median raphe (MnR)).

[Results]

Stress for 4 weeks significantly increased depressive behaviors in the mice. Treatment with creatine supplementation combined with exercise significantly decreased depressive behaviors as compared with the CON-ST group in both the TST and FST tests. With stress, 5-HT expression in the raphe nuclei decreased significantly. With combined creatine and exercise, 5-HT positive cells increased significantly and had a synergic effect on both DR and MnR.

[Conclusion]

The present study found that even a single treatment of creatine or exercise has partial effects as an antidepressant in mice with chronic mild stress-induced depression. Furthermore, combined creatine and exercise has synergic effects and is a more effective prescription than a single treatment.

Anxiety and depression with neurogenesis defects in exchange protein directly activated by cAMP 2-deficient mice are ameliorated by a selective serotonin reuptake inhibitor, Prozac

Intracellular cAMP and serotonin are important modulators of anxiety and depression. Fluoxetine, a selective serotonin reuptake inhibitor (SSRI) also known as Prozac, is widely used against depression, potentially by activating cAMP response element-binding protein (CREB) and increasing brain-derived neurotrophic factor (BDNF) through protein kinase A (PKA). However, the role of Epac1 and Epac2 (Rap guanine nucleotide exchange factors, RAPGEF3 and RAPGEF4, respectively) as potential downstream targets of SSRI/cAMP in mood regulations is not yet clear. Here, we investigated the phenotypes of Epac1 (Epac1(-/-)) or Epac2 (Epac2(-/-)) knockout mice by comparing them with their wild-type counterparts. Surprisingly, Epac2(-/-) mice exhibited a wide range of mood disorders, including anxiety and depression with learning and memory deficits in contextual and cued fear-conditioning tests without affecting Epac1 expression or PKA activity. Interestingly, rs17746510, one of the three single-nucleotide polymorphisms (SNPs) in RAPGEF4 associated with cognitive decline in Chinese Alzheimer's disease (AD) patients, was significantly correlated with apathy and mood disturbance, whereas no significant association was observed between RAPGEF3 SNPs and the risk of AD or neuropsychiatric inventory scores. To further determine the detailed role of Epac2 in SSRI/serotonin/cAMP-involved mood disorders, we treated Epac2(-/-) mice with a SSRI, Prozac. The alteration in open field behavior and impaired hippocampal cell proliferation in Epac2(-/-) mice were alleviated by Prozac. Taken together, Epac2 gene polymorphism is a putative risk factor for mood disorders in AD patients in part by affecting the hippocampal neurogenesis.

Neurochemical and behavioural indices of exercise reward are independent of exercise controllability

Brain reward circuits are implicated in stress-related psychiatric disorders. Exercise reduces the incidence of stress-related disorders, but the contribution of exercise reward to stress resistance is unknown. Exercise-induced stress resistance is independent of exercise controllability; both voluntary running (VR) and forced running (FR) protect rats against the anxiety-like and depression-like behavioural consequences of stress. Voluntary exercise is a natural reward, but whether rats find FR rewarding is unknown. Moreover, the contribution of dopamine (DA) and striatal reward circuits to exercise reward is not well characterized. Adult, male rats were assigned to locked wheels, VR, or FR groups. FR rats were forced to run in a pattern resembling the natural wheel running behavior of rats. Both VR and FR increased the reward-related plasticity marker ΔFosB in the dorsal striatum and nucleus accumbens, and increased the activity of DA neurons in the lateral ventral tegmental area, as revealed by immunohistochemistry for tyrosine hydroxylase and pCREB. Both VR and FR rats developed conditioned place preference (CPP) to the side of a CPP chamber paired with exercise. Re-exposure to the exercise-paired side of the CPP chamber elicited conditioned increases in cfos mRNA in direct-pathway (dynorphin-positive) neurons in the dorsal striatum and nucleus accumbens in both VR and FR rats, and in tyrosine hydroxylase-positive neurons in the lateral ventral tegmental area of VR rats only. The results suggest that the rewarding effects of exercise are independent of exercise controllability and provide insight into the DA and striatal circuitries involved in exercise reward and exercise-induced stress resistance.

Role of the dorsal medial habenula in the regulation of voluntary activity, motor function, hedonic state, and primary reinforcement

The habenular complex in the epithalamus consists of distinct regions with diverse neuronal populations. Past studies have suggested a role for the habenula in voluntary exercise motivation and reinforcement of intracranial self-stimulation but have not assigned these effects to specific habenula subnuclei. Here, we have developed a genetic model in which neurons of the dorsal medial habenula (dMHb) are developmentally eliminated, via tissue-specific deletion of the transcription factor Pou4f1 (Brn3a). Mice with dMHb lesions perform poorly in motivation-based locomotor behaviors, such as voluntary wheel running and the accelerating rotarod, but show only minor abnormalities in gait and balance and exhibit normal levels of basal locomotion. These mice also show deficits in sucrose preference, but not in the forced swim test, two measures of depression-related phenotypes in rodents. We have also used Cre recombinase-mediated expression of channelrhodopsin-2 and halorhodopsin to activate dMHb neurons or silence their output in freely moving mice, respectively. Optical activation of the dMHb in vivo supports intracranial self-stimulation, showing that dMHb activity is intrinsically reinforcing, whereas optical silencing of dMHb outputs is aversive. Together, our findings demonstrate that the dMHb is involved in exercise motivation and the regulation of hedonic state, and is part of an intrinsic reinforcement circuit.

Voluntary wheel running does not affect lipopolysaccharide-induced depressive-like behavior in young adult and aged mice

OBJECTIVE(S)

Peripheral stimulation of the innate immune system with lipopolysaccharide (LPS) causes prolonged depressive-like behavior in aged mice that is dependent on indoleamine 2,3 dioxygenase (IDO) activation. Regular moderate-intensity exercise training has been shown to exert neuroprotective effects that might reduce depressive-like behavior in aged mice. The purpose of this study was to test the hypothesis that voluntary wheel running (VWR) would attenuate LPS-induced depressive-like behavior and brain IDO gene expression in 4- and 22-month-old C57BL/6J mice.

METHODS

Mice were housed with a running wheel (VWR) or no wheel (standard) for 30 (young adult mice) or 70 days (aged mice), after which they were intraperitoneally injected with LPS (young adult mice: 0.83 mg/kg; aged mice: 0.33 mg/kg).

RESULTS

Young adult VWR mice ran on average 6.9 km/day, while aged VWR mice ran on average 3.4 km/day. Both young adult and aged VWR mice increased their forced exercise tolerance compared to their respective standard control groups. VWR had no effect on LPS-induced anorexia, weight loss, increased immobility in the tail suspension test and decreased sucrose preference in either young adult or aged mice. Four (young adult mice) and 24 h (aged mice) after injection of LPS, mRNA transcripts for TNF-α, IL-1β, IL-6, and IDO were upregulated in the whole brain independently of VWR.

CONCLUSION

Prolonged physical exercise has no effect on the neuroinflammatory response to LPS and its behavioral consequences in young adult and aged mice.

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.

Clinical classification in mental health at the cross-roads: which direction next?

BACKGROUND

After 30 years of consensus-derived diagnostic categories in mental health, it is time to head in new directions. Those categories placed great emphasis on enhanced reliability and the capacity to identify them via standardized checklists. Although this enhanced epidemiology and health services planning, it failed to link broad diagnostic groupings to underlying pathophysiology or specific treatment response.

DISCUSSION

It is time to adopt new goals that prioritize the validation of clinical entities and foster alternative strategies to support those goals. The value of new dimensions (notably clinical staging), that are both clinically relevant and directly related to emerging developmental and neurobiological research, is proposed. A strong emphasis on 'reverse translation' (that is, working back from the clinic to the laboratory) underpins these novel approaches. However, it relies on using diagnostic groupings that already have strong evidence of links to specific risk factors or patterns of treatment response.

SUMMARY

The strategies described abandon the historical divides between clinical neurology, psychiatry and psychology and adopt the promotion of pathways to illness models.

Effect of rolipram, a phosphodiesterase enzyme type-4 inhibitor, on γ-amino butyric acid content of the frontal cortex in mice exposed to chronic mild stress

OBJECTIVES

To investigate the alterations in GABA levels by rolipram in the model of depression.

MATERIALS AND METHODS

The alteration of GABA content by rolipram as a phosphodiesterase enzyme type-4 inhibitor in the frontal cortex (FCx; as a brain region crucial for the control of emotion and cognition) obtained from male mice exposed to chronic mild stress (CMS)-induced anhedonia (the loss of pleasure or lack of sensitivity to pleasure stimuli) was recorded.

RESULTS

The results demonstrated the reversal of CMS-induced anhedonia after 3 weeks per os of rolipram in a dose of 0.1 mg/kg/day dissolved in distilled water. Furthermore, rolipram showed a significant reduction in duration of immobility in long-term behavioral changes recorded by the FST. Additionally, there was a significant increase in the GABA content of the FCx of rolipram-treated mice exposed to CMS-induced anhedonia.

CONCLUSIONS

The present study suggested that GABA levels may be decreased in an animal model of depression and its reversal together with the behaviour improvement by rolipram could support the hypothesis that modification in GABAergic activity has a role in mood disorders. These effects may complement the antidepressant effect of rolipram that is originally mediated via inhibition of phosphodiesterase enzyme type-4 [PDE4] that increases cyclic adenosine monophosphate signalling the pharmacotherapy of depression.

5-HT2C receptors in the basolateral amygdala and dorsal striatum are a novel target for the anxiolytic and antidepressant effects of exercise

Physical activity reduces the incidence and severity of psychiatric disorders such as anxiety and depression. Similarly, voluntary wheel running produces anxiolytic- and antidepressant-like effects in rodent models. The specific neurobiological mechanisms underlying the beneficial properties of exercise, however, remain unclear. One relevant pharmacological target in the treatment of psychiatric disorders is the 5-HT(2C) receptor (5-HT(2C)R). Consistent with data demonstrating the anxiogenic consequences of 5-HT(2C)R activation in humans and rodents, we have previously reported that site-specific administration of the selective 5-HT(2C)R agonist CP-809101 in the lateral/basolateral amygdala (BLA) increases shock-elicited fear while administration of CP-809101 in the dorsal striatum (DS) interferes with shuttle box escape learning. These findings suggest that activation of 5-HT(2C)R in discrete brain regions contributes to specific anxiety- and depression-like behaviors and may indicate potential brain sites involved in the anxiolytic and antidepressant effects of exercise. The current studies tested the hypothesis that voluntary wheel running reduces the behavioral consequences of 5-HT(2C)R activation in the BLA and DS, specifically enhanced shock-elicited fear and interference with shuttle box escape learning. After 6 weeks of voluntary wheel running or sedentary conditions, the selective 5-HT(2C)R agonist CP-809101 was microinjected into either the BLA or the DS of adult Fischer 344 rats, and shock-elicited fear and shuttle box escape learning was assessed. Additionally, in-situ hybridization was used to determine if 6 weeks of voluntary exercise changed levels of 5-HT(2C)R mRNA. We found that voluntary wheel running reduced the behavioral effects of CP-809101 and reduced levels of 5-HT(2C)R mRNA in both the BLA and the DS. The current data indicate that expression of 5-HT(2C)R mRNA in discrete brain sites is sensitive to physical activity status of the organism, and implicates the 5-HT(2C)R as a target for the beneficial effects of physical activity on mental health.

Treatment of depressive-like behaviour in Huntington's disease mice by chronic sertraline and exercise

BACKGROUND AND PURPOSE

Depression is the most common psychiatric disorder in Huntington's disease (HD) patients. Women are more prone to develop depression and such susceptibility might be related to 5-hydroxytryptaminergic (serotonergic) dysregulation.

EXPERIMENTAL APPROACH

We performed tests of depression-related behaviours on female R6/1 HD mice that had been chronically treated with sertraline or provided with running-wheels. Functional assessments of 5-HT(1A) and 5-HT(2A) receptors were performed by measuring behavioural and physiological responses following administration of specific agonists, in combination with analysis of hippocampal gene expression. Finally we assessed the effect of exercise on hippocampal cell proliferation.

KEY RESULTS

Female HD mice recorded increased immobility time in the forced-swimming test, reduced saccharin preference and a hyperthermic response to stress compared with wild-type animals. These alterations were improved by chronic sertraline treatment. Wheel-running also resulted in similar improvements with the exception of saccharin preference but failed to correct the hippocampal cell proliferation deficits displayed by HD mice. The benefits of sertraline treatment and exercise involved altered 5-HT(1A) autoreceptor function, as demonstrated by modulation of the exaggerated 8-OH-DPAT-induced hypothermia exhibited by female HD mice. On the other hand, sertraline treatment was unable to restore the reduced 5-HT(1A) and 5-HT(2) heteroceptor function observed in HD animals.

CONCLUSIONS AND IMPLICATIONS

We report for the first time a crucial role for 5-HT(1A) autoreceptor function in mediating the sex-specific depressive-like phenotype of female R6/1 HD mice. Our data further support a differential effect of chronic sertraline treatment and exercise on hippocampal cell proliferation despite common behavioural benefits.

Withdrawal from chronic, intermittent access to a highly palatable food induces depressive-like behavior in compulsive eating rats

The increased availability of highly palatable foods is a major contributing factor toward the development of compulsive eating in obesity and eating disorders. It has been proposed that compulsive eating may develop as a form of self-medication to alleviate the negative emotional state associated with withdrawal from highly palatable foods. This study was aimed at determining whether withdrawal from chronic, intermittent access to a highly palatable food was responsible for the emergence of depressive-like behavior. For this purpose, a group of male Wistar rats was provided a regular chow diet 7 days a week (Chow/Chow), whereas a second group of rats was provided chow for 5 days a week, followed by a 2-day access to a highly palatable sucrose diet (Chow/Palatable). Following 7 weeks of diet alternation, depressive-like behavior was assessed during withdrawal from the highly palatable diet and following renewed access to it, using the forced swim test, the sucrose consumption test, and the intracranial self-stimulation threshold procedure. It was found that Chow/Palatable rats withdrawn from the highly palatable diet showed increased immobility time in the forced swim test and decreased sucrose intake in the sucrose consumption test compared with the control Chow/Chow rats. Interestingly, the increased immobility in the forced swim test was abolished by renewing access to the highly palatable diet. No changes were observed in the intracranial self-stimulation threshold procedure. These results validate the hypothesis that withdrawal from highly palatable food is responsible for the emergence of depressive-like behavior, and they also show that compulsive eating relieves the withdrawal-induced negative emotional state.

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.

Effect of enhanced voluntary physical exercise on brain levels of monoamines in Huntington disease mice

Using the R6/1 mouse model of Huntington disease (HD), we have recently shown that voluntary physical activity was able to correct the depressive-like behaviours exhibited by the HD animals at a pre-motor symptomatic stage of the disease. Using the high performance liquid chromatography system, we have now evaluated the effect of exercise on monoamine metabolism in HD mice. We found that serotonin and its metabolite as well as dopamine and noradrenaline were reduced across several brain regions in female R6/1 animals. Our data also suggest that some of these neurochemical deficits were modulated by physical activity, in a genotype-region dependent manner. These newly identified changes could account for some of the behavioural effects of exercise previously reported in HD mice.

Different regulation of adult hippocampal neurogenesis in Western house mice (Mus musculus domesticus) and C57BL/6 mice

Adult hippocampal neurogenesis (AHN) of laboratory rodents is enhanced by physical exercise in a running wheel. However, little is known about modulation of AHN in wild-living rodent species. The finding that AHN cannot be modulated by voluntary exercise in wild wood mice suggests that AHN may be regulated differently under natural conditions than in laboratory adapted animals. In order to minimize genetic influences, we aimed to investigate the genetically closest wild-living relatives of laboratory mice. Here, C57BL/6 mice and F1 offspring of wild house mice (Mus musculus domesticus) were tested in two different running paradigms: voluntary running and running-for-food--a condition in which mice had to run for their daily allowance of food. In house mice, we found a non-significant trend towards increased numbers of proliferating cells and doublecortin-positive immature neurons in both voluntary runners and runners-for-food. Voluntary running in C57BL/6 mice resulted in a 30% increase in cell proliferation and a pronounced 70% increase in doublecortin-positive cells. C57BL/6 runners-for-food ran as much as voluntary runners, but they showed no enhancement of cell proliferation, a small increase in the number of doublecortin-positive cells and more pyknotic cells compared to controls. Taken together, these findings suggest that motivational aspects of running are critical determinants of the increased cell proliferation in C57BL/6 mice. In contrast, running has smaller and context-independent effects in house mice. The findings imply a difference in the regulation of AHN in C57BL/6 mice and their wild-derived conspecifics.

Antidepressant-like Effect of l-perillaldehyde in Stress-induced Depression-like Model Mice through Regulation of the Olfactory Nervous System

Perillae Herba (a leaf of Perilla frutescens) has been prescribed as one of the component herbs in certain Kampo (Japanese herbal) medicines that are used clinically for the improvement of depressive mood. l-Perillaldehyde (PAH) is a major component in the essential oil containing in Perillae Herba, but its antidepressant-like effect has not been reported. To clarify the antidepressant-like effect of PAH, the inhaled effect of PAH on stress-induced depression-like model mice prepared by subjection to a combination of forced swimming and chronic mild stresses was investigated. The degree of the depression-like state was measured by the animal's duration of immobility using a forced swimming test. Inhalation of PAH (0.0965 and 0.965 mg/mouse/day, 9 days) significantly shortened the duration of immobility of the depression-like model mice and did not affect locomotor activity. However, another odor substance, cinnamaldehyde containing in Cinnamomi Cortex, exhibited no reduction in the immobility. The reduction in the immobility induced by the inhalation of PAH was prevented on anosmia-induced mice prepared by intranasal irrigation with zinc sulfate. These results suggest that the inhalation of PAH shows antidepressant-like activity through the olfactory nervous function.

The role of exercise in facilitating basal ganglia function in Parkinson's disease

Epidemiological and clinical studies have suggested that exercise is beneficial for patients with Parkinson's disease (PD). Through research in normal (noninjured) animals, neuroscientists have begun to understand the mechanisms in the brain by which behavioral training and exercise facilitates improvement in motor behavior through modulation of neuronal function and structure, called experience-dependent neuroplasticity. Recent studies are beginning to reveal molecules and downstream signaling pathways that are regulated during exercise and motor learning in animal models of PD and that are important in driving protective and/or adaptive changes in neuronal connections of the basal ganglia and related circuitry. These molecules include the neurotransmitters dopamine and glutamate (and their respective receptors) as well as neurotrophic factors (brain-derived neurotrophic factor). In parallel, human exercise studies have been important in revealing 'proof of concept' including examining the types and parameters of exercise that are important for behavioral/functional improvements and brain changes; the feasibility of incorporating and maintaining an exercise program in individuals with motor disability; and, importantly, the translation and investigation of exercise effects observed in animal studies to exercise effects on brain and behavior in individuals with PD. In this article we highlight findings from both animal and human exercise studies that provide insight into brain changes of the basal ganglia and its related circuitry and that support potentially key parameters of exercise that may lead to long-term benefit and disease modification in PD. In addition, we discuss the current and future impact on patient care and point out gaps in our knowledge where continuing research is needed. Elucidation of exercise parameters important in driving neuroplasticity, as well as the accompanying mechanisms that underlie experience-dependent neuroplasticity may also provide insights towards new therapeutic targets, including neurorestorative and/or neuroprotective agents, for individuals with PD and related neurodegenerative disorders.

Exercise effects on motor and affective behavior and catecholamine neurochemistry in the MPTP-lesioned mouse

This study used 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP) in mice to determine if exercise improves behavior and dopamine (DA) and serotonin (5HT) content. Male C57BL/6 mice received MPTP (4 x 20mg/kg) or saline. They remained sedentary or exercised by treadmill or voluntary running wheel for 6 weeks (n=8/group). Saline-treated mice ran significantly faster on running wheels (22.8+/-1.0m/min) than on treadmill (8.5+/-0.5m/min), and MPTP lesion did not reduce voluntary exercise (19.3+/-1.5m/min, p>0.05). There was a significant effect of both lesion and exercise on overall Rotarod performance (ORP): MPTP lesion reduced ORP, while treadmill exercise increased ORP vs sedentary mice (p<0.05). MPTP increased anxiety in the marble-burying test: sedentary lesioned mice buried more marbles (74.0+/-5.2%) than sedentary controls (34.8+/-11.8%, p<0.05). Conversely, exercise reduced anxiety on the elevated plus maze. Among saline-treated mice, those exposed to voluntary wheel-running showed an increased percent of open arm entries (49.8+/-3.5%, p<0.05) relative to sedentary controls (36.2+/-4.0%, p<0.05). Neither MPTP nor exercise altered symptoms of depression measured by sucrose preference or tail suspension. MPTP significantly reduced DA in striatum (in sedentary lesioned mice to 42.1+/-3.0% of saline controls), and lowered 5HT in amygdala and striatum (in sedentary lesioned mice to 86.1+/-4.1% and 66.5+/-8.2% of saline controls, respectively); exercise had no effect. Thus, exercise improves behavior in a model of DA depletion, without changes in DA or 5HT.

Mental Health Benefits of Strength Training in Adults

This review summarizes evidence from randomized controlled trials to examine whether strength training influences anxiety, chronic pain, cognition, depression, fatigue symptoms, self-esteem, and sleep. The weight of the available evidence supported the conclusion that strength training is associated with reductions in anxiety symptoms among healthy adults (5 trials); reductions in pain intensity among patients with low back pain (5 trials), osteoarthritis (8 trials), and fibromyalgia (4 trials); improvements in cognition among older adults (7 trials); improvements in sleep quality among depressed older adults (2 trials); reductions in symptoms of depression among patients with diagnosed depression (4 trials) and fibromyalgia (2 trials); reductions in fatigue symptoms (10 trials); and improvements in self-esteem (6 trials). The evidence indicates that larger trials with a greater range of patient samples are needed to better estimate the magnitude and the consistency of the relationship between strength training and these mental health outcomes. Plausible social, psychological, and neural mechanisms by which strength training could influence these outcomes rarely have been explored. This review revealed the high-priority research need for animal and human research aimed at better understanding the brain mechanisms underlying mental health changes with strength training.

Sini tang prevents depression-like behavior in rats exposed to chronic unpredictable stress

Sini Tang, a Chinese traditional prescription containing three herbs, has been widely used for Yang-deficiency. Recent clinical studies have shown that Sini Tang could treat and improve depression symptoms, but the mechanisms underlying the antidepressant effect of Sini Tang remains unknown. In rats with chronic unpredictable stress (CUS), we examined the effects of Sini Tang on sucrose preference and open field exploratory behavior. The levels of corticosterone level in plasma and corticotropin-releasing hormone (CRH) mRNA expression in hypothalamus were also measured by enzyme-linked immunosorbent assays (ELISA) and real-time reverse transcription PCR (RT-PCR), respectively. Rats subjected to CUS exhibited decreases in sucrose preference and ambulation in the open field test. These were all attenuated by Sini Tang in a dose-dependent manner. Biochemically, Sini Tang also reversed CUS-induced increases in corticosterone in plasma and CRH mRNA in the hypothalamus. The behavioral effects of the Sini Tang were correlated to the biochemical actions. These results suggest that Sini Tang produces an antidepressant-like effect, which appears to involve CRH in the brain.

Circadian clock genes: non-circadian roles in sleep, addiction, and psychiatric disorders?

Elucidation of the cellular and molecular mechanisms of the circadian clock, along with the realization that these mechanisms are operative in both central and peripheral tissues, has revolutionized circadian biology. Further, these observations have resulted in an explosion of interest in the health implications of circadian organization and disorganization at both molecular and physiological levels. Thus, recent research has implicated mutations and polymorphisms of circadian clock genes in diabetes and obesity, cardiovascular disease, and cancer. At the neuro-behavioral level, circadian clock genes have also been implicated in sleep disorders, drug and alcohol addiction, and other psychiatric conditions. While such findings are frequently described as revealing "non-circadian" effects of clock genes, it remains possible that most of these non-circadian effects are in fact secondary to the loss of cellular and systemic rhythmicity. This review summarizes the evidence linking circadian clock genes to biobehavioral dysregulation, and considers criteria for defining a pleiotropic clock gene effect as non-circadian.

Effects of Rhodiola rosea L. extract on behavioural and physiological alterations induced by chronic mild stress in female rats

Rhodiola rosea L. is one of the most popular adaptogen and an antistress plant in European and Asiatic traditional medicine. Our previous studies have confirmed the adaptogenic and antistress properties of a single administration of R. rosea L. extract in rats exposed to acute stress. There is increasing evidence that prolonged exposure to stressful life events and depression are both related to significant behavioural, endocrinological and neurobiological changes in human and animal subjects. The aim of this study was to determine whether chronic treatment with a hydroalcoholic R. rosea extract (RHO) standardized in 3% rosavin and 1% salidroside can prevent alterations induced in female rats following 6 weeks of a chronic mild stress (CMS) procedure. This was analysed through the behavioural and physiological parameters of consumption of 1% sucrose solution, locomotor and exploratory activities, body weight gain and oestrous cycle length. After the first 3 weeks of stress, RHO was administered daily by gavage at doses of 10, 15 and 20 mg/kg for the remaining 3 weeks. In addition, the antidepressant drug fluoxetine (10 mg/kg os), which has been shown to reverse CMS-induced disruptions, was used as the reference treatment. Rats subjected to the CMS procedure demonstrated decreased sucrose intake, reduced moving behaviour, minimized weight gain and dysregulation of their oestrous cycle. Treatment with RHO completely reverted all of these changes. The effects of RHO were comparable to those of fluoxetine. Interestingly, neither RHO nor fluoxetine influence the behavioural and physiological parameters tested in non-stressed animals. These findings strongly showed that chronic administration of RHO results in potent inhibition of the behavioural and physiological changes induced by chronic exposure to mild stressors.

Differential behavioral and neurochemical effects of exercise, reboxetine and citalopram with the forced swim test

AIMS

In this study, we investigated whether short-term exercise, known to promote hippocampal brain-derived neurotrophic factor (BDNF) expression, would also enhance activity in the Porsolt forced swim test (FST), a model for assessing antidepressant efficacy. We also wished to determine whether exercise combined with antidepressants would be more effective at modifying behavior in the FST than either intervention alone. In parallel with this, we also expected that these interventions would preserve post-stress levels of BDNF, and that antidepressants designed to selectively enhance noradrenergic or serotonergic neurotransmission (reboxetine or citalopram, respectively) would have differential effects on behavior and BDNF expression.

MAIN METHODS

Male Sprague-Dawley rats were treated with exercise (voluntary wheel running), reboxetine, citalopram, or the combination of exercise and each antidepressant, for 1 week. At the end of this period, a subset of animals from each treatment group underwent the FST. Post-stress levels of hippocampal BDNF mRNA were then quantified via in situ hybridization.

KEY FINDINGS

Our results indicate that while both exercise and antidepressant treatment preserved post-stress levels of hippocampal BDNF mRNA, each intervention led to a unique behavioral profile in the FST. We found that antidepressant treatment increased swimming time in the FST, but that exercise decreased swimming time. While the combination of reboxetine-plus-exercise led to an increase in climbing and diving, citalopram-plus-exercise reduced these behaviors.

SIGNIFICANCE

It is possible that active behaviors during the FST, though specific to antidepressant medications, may not reflect increased hippocampal BDNF expression or other survival- associated benefits.

Exercise reverses chronic stress-induced Bax oligomer formation in the cerebral cortex

Chronic stress may lead to neuronal atrophy and functional impairments within the CNS, and increasing evidence indicates that exercise can protect the brain from these changes. Bax is a key protein of the B-cell lymphoma (Bcl) family that complexes within the mitochondrial membrane and forms pores to initiate cellular apoptosis. Herein, we measured cortical Bax levels following chronic and acute stress via immunoblotting. We reveal that chronic, but not acute, stress increases cortical levels of Bax oligomer 270, a complex revealed in previous studies to be associated with apoptosis. Several recent studies have revealed that physical exercise can protect rodents from neurochemical and/or behavioral changes occurring with stress. Previous studies have also revealed that voluntary exercise enhances the expression and activation of cellular proteins associated with enhanced neuronal survival. Herein, we reveal that 3 weeks of daily restraint led to increased oligomerization of Bax within the cerebral cortex, and that chronic corticosterone administration had a similar effect. Voluntary wheel running, concurrent with chronic restraint, prevented an increase in Bax oligomer 270. Analysis of subcellular fractions also revealed that the combination of exercise with chronic stress reduced the percent of total Bax localized to the mitochondria. Ours is the first study to investigate dynamic molecule complexes associated with the initiation of apoptosis with stress, and the influence of exercise upon the levels of these complexes, suggesting that exercise is an effective preventative measure that can promote neuronal survival and protect the brain against the damaging effects of chronic stress.

Exercise, learned helplessness, and the stress-resistant brain

Exercise can prevent the development of stress-related mood disorders, such as depression and anxiety. The underlying neurobiological mechanisms of this effect, however, remain unknown. Recently, researchers have used animal models to begin to elucidate the potential mechanisms underlying the protective effects of physical activity. Using the behavioral consequences of uncontrollable stress or "learned helplessness" as an animal analog of depression- and anxiety-like behaviors in rats, we are investigating factors that could be important for the antidepressant and anxiolytic properties of exercise (i.e., wheel running). The current review focuses on the following: (1) the effect of exercise on the behavioral consequences of uncontrollable stress and the implications of these effects on the specificity of the "learned helplessness" animal model; (2) the neurocircuitry of learned helplessness and the role of serotonin; and (3) exercise-associated neural adaptations and neural plasticity that may contribute to the stress-resistant brain. Identifying the mechanisms by which exercise prevents learned helplessness could shed light on the complex neurobiology of depression and anxiety and potentially lead to novel strategies for the prevention of stress-related mood disorders.

Social isolation disrupts autonomic regulation of the heart and influences negative affective behaviors

BACKGROUND

There is a documented association between affective disorders (e.g., depression and anxiety) and cardiovascular disease in humans. Chronic social stressors may play a mechanistic role in the development of behavioral and cardiac dysregulation. The current study investigated behavioral, cardiac, and autonomic responses to a chronic social stressor in prairie voles, a rodent species that displays social behaviors similar to humans.

METHODS

Female prairie voles were exposed to 4 weeks of social isolation (n = 8) or pairing (control conditions; n = 7). Electrocardiographic parameters were recorded continuously during isolation, and behavioral tests were conducted during and following this period.

RESULTS

Isolation induced a significant increase in resting heart rate, reduction in heart rate variability (standard deviation of normal-to-normal intervals and amplitude of respiratory sinus arrhythmia), and exaggerated cardiac responses during an acute resident-intruder paradigm. Isolation led also to both depression-like and anxiety-like behaviors in validated operational tests. These changes in response to social isolation showed predictable interrelations and were mediated by a disruption of autonomic balance including both sympathetic and parasympathetic (vagal) mechanisms.

CONCLUSIONS

These findings indicate that social isolation induces behavioral, cardiac, and autonomic alterations related to those seen after other stressors and which are relevant to cardiovascular disease and affective disorders. This model may provide insight into the mechanisms that underlie these co-occurring conditions.

Learned helplessness is independent of levels of brain-derived neurotrophic factor in the hippocampus

Reduced levels of brain-derived neurotrophic factor (BDNF) in the hippocampus have been implicated in human affective disorders and behavioral stress responses. The current studies examined the role of BDNF in the behavioral consequences of inescapable stress, or learned helplessness. Inescapable stress decreased BDNF mRNA and protein in the hippocampus of sedentary rats. Rats allowed voluntary access to running wheels for either 3 or 6 weeks prior to exposure to stress were protected against stress-induced reductions of hippocampal BDNF protein. The observed prevention of stress-induced deceases in BDNF, however, occurred in a time course inconsistent with the prevention of learned helplessness by wheel running, which is evident following 6 weeks, but not 3 weeks, of wheel running. BDNF suppression in physically active rats was produced by administering a single injection of the selective serotonin reuptake inhibitor fluoxetine (10 mg/kg) just prior to stress. Despite reduced levels of hippocampal BDNF mRNA following stress, physically active rats given the combination of fluoxetine and stress remained resistant against learned helplessness. Sedentary rats given both fluoxetine and stress still demonstrated typical learned helplessness behaviors. Fluoxetine by itself reduced BDNF mRNA in sedentary rats only, but did not affect freezing or escape learning 24 h later. Finally, bilateral injections of BDNF (1 mug) into the dentate gyrus prior to stress prevented stress-induced reductions of hippocampal BDNF but did not prevent learned helplessness in sedentary rats. These data indicate that learned helplessness behaviors are independent of the presence or absence of hippocampal BDNF because blocking inescapable stress-induced BDNF suppression does not always prevent learned helplessness, and learned helplessness does not always occur in the presence of reduced BDNF. Results also suggest that the prevention of stress-induced hippocampal BDNF suppression is not necessary for the protective effect of wheel running against learned helplessness.

Animal models of depression in drug discovery: a historical perspective

Over the course of the last 50 years many models of major depressive disorder have been developed on the basis of theoretical aspects of this disorder. These models and procedures have been crucial in the discovery and development of clinically-effective drugs. Notwithstanding, there is presently great concern about the discrepancy between positive outcomes of new candidate drugs in animal models and apparent lack of efficacy in humans i.e., the predictive validity of animal models. Some reasons for this concern lie in the over-reliance in the face value of behavioural models, design of clinical trials, placebo responses, genetic variations in response to drugs, species differences in bioavailability and toxicology, and not least, disinterest of pharmaceutical sponsors to continue developing certain drugs. Present model development is focusing on endophenotypic aspects of behaviours rather than trying to model whole syndromes. This essay traces the origins and theoretical bases of our animal models of depression or depressed-like behaviours in humans and indicates how they have evolved from behavioural assays used to measure the potency and efficacy of potential candidate drugs to tools by which endophenotypes of depression may be identified and verified pharmacologically. A cautionary note is included though to indicate that the true predictive validity of our models will not be fully assessed until we can determine the attrition rate of molecules discovered from new drug targets translating into clinically-effective drugs.

Chronic mild stress (CMS) revisited: consistency and behavioural-neurobiological concordance in the effects of CMS

The chronic mild stress (CMS) model of depression has high validity but has in the past been criticized for being difficult to replicate. However, a large number of recent publications have confirmed that CMS causes behavioural changes in rodents that parallel symptoms of depression. This review summarizes studies from over sixty independent research groups that have reported decreases in reactivity to rewards, and a variety of other depression-like behaviours, in rats or mice, following exposure to CMS. Together, these changes are referred to as a 'depressive' behavioural profile. Almost every study that has examined the effects of chronic antidepressant treatment in these procedures has reported that antidepressants were effective in reversing or preventing these 'depressive' behavioural changes. (The single exception is a study in which the duration of treatment was too brief to constitute an adequate trial.) There are also a handful of reports of CMS causing significant effects in the opposite direction, termed here an 'anomalous' behavioural profile. There are six neurobiological parameters that have been studied in both 'anhedonic' and 'anomalous' animals: psychostimulant and place-conditioning effects of dopamine agonists; dopamine D2 receptor number and message; inhibition of dopamine turnover by quinpirole, and beta-adrenergic receptor binding. On all six measures, CMS caused opposite effects in animals displaying 'depressive' and 'anomalous' profiles. Thus, there is overwhelming evidence that under appropriate experimental conditions, CMS can cause antidepressant-reversible depressive-like effects in rodents; however, the 'anomalous' profile that is occasionally reported appears to be a genuine phenomenon, and these two sets of behavioural effects appear to be associated with opposite patterns of neurobiological changes.

Chronic mild stress induces behavioral and physiological changes, and may alter serotonin 1A receptor function, in male and cycling female rats

RATIONALE

Interactions among stress, serotonin 1A (5-HT(1A)) receptors, and the hypothalamic-pituitary-adrenocortical (HPA) system have been proposed to influence the development of depression in humans. The investigation of depression-relevant behaviors and physiological responses to environmental stressors in animal models of depression may provide valuable insight regarding these mechanisms.

OBJECTIVES

The purpose of these experiments was to investigate the interactions among central 5-HT(1A) receptors, endocrine function, and behavior in an animal model of depression, chronic mild stress (CMS).

METHODS

The current study examined behavioral responses to a pleasurable stimulus (sucrose), estrous cycle length (in female rats), and plasma hormone levels following systemic administration of a selective 5-HT(1A) receptor agonist [(+)8-hydroxy-N,N-dipropyl-2-aminotetralin hydrobromide (8-OH-DPAT); 40 mug/kg, s.c.; administered 15 min prior to sacrifice], in male and female rats exposed to 4 weeks of CMS.

RESULTS

Four weeks of CMS produced a reduction in the intake of 1% sucrose (anhedonia), as well as attenuated adrenocorticotropic hormone (ACTH) responses to 8-OH-DPAT in both male and female rats (22 and 18% lower than the control groups, respectively). Corticosterone and oxytocin responses to 8-OH-DPAT were not altered by exposure to CMS. In female rats, CMS induced a lengthening of the estrous cycle by approximately 40%.

CONCLUSIONS

CMS produces minor HPA disruptions along with behavioral disruptions. Alterations in 5-HT(1A) receptor function in specific populations of neurons in the central nervous system may be associated with the CMS model. The current findings contribute to our understanding of the relations that stress and neuroendocrine function have to depressive disorders.

Neuroendocrine and cytokine profile of chronic mild stress-induced anhedonia

A bidirectional relationship exists between depression and cardiovascular disease. Patients with major depression are more likely to develop cardiac events, and patients with myocardial infarction and heart failure are more likely to develop depression. A feature common to both clinical syndromes is activation of proinflammatory cytokines and stress hormones, including the hypothalamic-pituitary-adrenal axis and the renin-angiotensin-aldosterone system. In the present study we examined the hypothesis that exposure to chronic mild stress (CMS), an experimental model of depression that induces anhedonia in rats, is sufficient to activate the production of proinflammatory cytokines and stress hormones that are detrimental to the heart and vascular system. Four weeks of exposure of male, Sprague-Dawley rats to mild unpredictable environmental stressors resulted in anhedonia which was operationally defined as a reduction in sucrose intake without a concomitant effect on water intake. Humoral assays indicated increased plasma levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), plasma renin activity, aldosterone, and corticosterone in the CMS exposed rats. Tissue TNF-alpha and IL-1beta were increased in the hypothalamus, and TNF-alpha was increased in the pituitary gland. These humoral responses to CMS, associated with anhedonia as an index of depression in the rat, are likely to be associated with neurohumoral mechanisms that may contribute to adverse cardiac events. The findings provide a basis for examining more directly the interactions among the central, endocrine, and immune systems in depression associated with heart disease.

Effects of chronic activity wheel running and imipramine on masculine copulatory behavior after olfactory bulbectomy

We examined the effects of chronic activity wheel running and imipramine administration on appetitive behavior after olfactory bulbectomy (OBX). Male Long-Evans rats were randomly assigned to the following conditions using a 2 x 2 x 2 design: (1) bilateral OBX or sham surgery, (2) voluntary activity wheel running or sedentary home cage, and (3) daily imipramine or saline injections. After 21 days of treatment, animals underwent behavioral testing for copulatory activity and sucrose preference. Bulbectomized animals exhibited decrements in copulatory performance and reductions in sucrose intake compared to sham animals. Within the bulbectomized groups, imipramine-treated rats either did not copulate or had reduced ejaculation frequencies. However, activity wheel running attenuated the copulatory deficits induced by OBX. The findings encourage studies of physical activity and male sexual dysfunction among depressed men being treated by pharmacotherapy.

Chronic psychosocial stress persistently alters autonomic function and physical activity in mice

We investigated heart rate (HR), temperature (T), and physical activity (Act) (by means of radiotelemetry) in male mice subjected to chronic psychosocial stress. Resident/intruder dyads lived in sensory contact for 15 days with the possibility to physically interact daily during the light phase for a maximum of 15 min. Intruders becoming dominants (InD) or subordinates (InS) were investigated here. The aims were to investigate; if a daily aggressive interaction would result in adaptation of autonomic responses; the effects of the social stress on daily rhythmicity and the way these effects change over time; whether acute and long-term autonomic changes do correlate; to compare dominants and subordinates. InD and InS showed a strong autonomic activation during the interactions, with moderate (InS) or no (InD) habituation over time. On the long term, InD showed tachycardia and marked hyperthermia but normal physical activity, while InS showed tachycardia, slight hyperthermia, and depressed physical activity. No correlation emerged between the acute and the long-term autonomic responses. These results highlight the existence of a sustained autonomic activation under chronic stress, which was also affected by mice social status.