Regular moderate or intense exercise prevents depression-like behavior without change of hippocampal tryptophan content in chronically tryptophan-deficient and stressed mice

The role of exercise in the treatment of depression: biological underpinnings and clinical outcomes

Globally, depression is a leading cause of disability and has remained so for decades. Antidepressant medications have suboptimal outcomes and are too frequently associated with side effects, highlighting the need for alternative treatment options. Although primarily known for its robust physical health benefits, exercise is increasingly recognized for its mental health and antidepressant benefits. Empirical evidence indicates that exercise is effective in treating individuals with depression; however, the mechanisms by which exercise exerts anti-depressant effects are not fully understood. Acute bouts of exercise have been shown to transiently modulate circulating levels of serotonin and norepinephrine, brain-derived neurotrophic factor, and a variety of immuno-inflammatory mechanisms in clinical cohorts with depression. However, exercise training has not been demonstrated to consistently modulate such mechanisms, and evidence linking these putative mechanisms and reductions in depression is lacking. The complexity of the biological underpinnings of depression coupled with the intricate molecular cascade induced by exercise are significant obstacles in the attempt to disentangle exercise's effects on depression. Notwithstanding our limited understanding of these effects, clinical evidence uniformly argues for the use of exercise to treat depression. Regrettably, exercise remains underutilized despite being an accessible, low-cost alternative/adjunctive intervention that can simultaneously reduce depression and improve overall health. To address the gaps in our understanding of the clinical and molecular effects of exercise on depression, we propose a model that leverages systems biology and multidisciplinary team science with a large-scale public health investment. Until the science matches the scale of complexity and burden posed by depression, our ability to advance knowledge and treatment will continue to be plagued by fragmented, irreproducible mechanistic findings and no guidelines for standards of care.

Thymoquinone-Enriched Naringenin-Loaded Nanostructured Lipid Carrier for Brain Delivery via Nasal Route: In Vitro Prospect and In Vivo Therapeutic Efficacy for the Treatment of Depression

In the current research, a thymoquinone-enriched naringenin (NGN)-loaded nanostructured lipid carrier (NLC) was developed and delivered via the nasal route for depression. Thymoquinone (TQ) oil was used as the liquid lipid and provided synergistic effects. A TQ- and NGN-enriched NLC was developed via the ultrasonication technique and optimized using a central composite rotatable design (CCRD). The optimized NLC exhibited the following properties: droplet size, 84.17 to 86.71 nm; PDI, 0.258 to 0.271; zeta potential, −8.15 to −8.21 mV; and % EE, 87.58 to 88.21%. The in vitro drug release profile showed the supremacy of the TQ-NGN-NLC in comparison to the NGN suspension, with a cumulative drug release of 82.42 ± 1.88% from the NLC and 38.20 ± 0.82% from the drug suspension. Ex vivo permeation study displayed a 2.21-fold increase in nasal permeation of NGN from the NLC compared to the NGN suspension. DPPH study showed the better antioxidant potential of the TQ-NGN-NLC in comparison to NGN alone due to the synergistic effect of NGN and TQ oil. CLSM images revealed deeper permeation of the NGN-NLC (39.9 µm) through the nasal mucosa in comparison to the NGN suspension (20 µm). Pharmacodynamic studies, such as the forced swim test and the locomotor activity test, were assessed in the depressed rat model, which revealed the remarkable antidepressant effect of the TQ-NGN-NLC in comparison to the NGN suspension and the marketed formulation. The results signify the potential of the TQ-enriched NGN-NLC in enhancing brain delivery and the therapeutic effect of NGN for depression treatment.

Effect of Regular Physical Exercise on Gut Microbiota and Depressive Behaviors in Rats

Objective. The gut microbiota, as the critical mediator of the gut-brain axis, can produce and transport neuroactive substances, thus playing a significant role in the pathogenesis of depression. Although regular physical exercise is an important nondrug antidepressant, its specific effector mechanism is still unclear. Methods. Rats were randomly divided into four different groups (n = 10 for each group) as follows: normal group (G1), depression group (G2), fluoxetine treatment group (G3), and regular exercise treatment group (G4). All rats underwent forced swimming tests, tail suspension tests, open field tests, and elevated plus-maze tests to detect behavioristics. Then, corticosterone levels were detected by ELISA. Additionally, taxonomic analysis of the gut microbiota in all rats was performed after they were exercised regularly for 60 days. Results. Compared with the G1 group, the rats in the G2 group showed significant depression-like behaviors, with increased serum corticosterone levels. The proportions of Bacteroides, Actinomycetes, Proteobacteria, Saccharomyces, and Cyanobacteria in rats of the G2 group were lower than those in the G1 group, while the proportions of Firmicutes, Tenicotte, Deferrobacteria, and Fusobacteria were increased. Furthermore, after regular exercise treatment, the gut microbiota of rats was effectively improved, almost returning to the level of the G1 group, and depressive behavior and corticosterone levels were also restored, which was almost the same as the effect of fluoxetine treatment. Conclusion. Regular physical exercise could alleviate depressive-like behaviors by modulating the species and function of the gut microbiota.

A Bird's-Eye View of Exercise Intervention in Treating Depression Among Teenagers in the Last 20 Years: A Bibliometric Study and Visualization Analysis

Background: Exercise is medicine. Multiple studies on the effects and mechanisms of exercise in treating depression among teenagers and adolescents have been widely reported. However, literature involving scientometric analysis of this topic is sparse. Here, we endeavored to conduct a bibliometric study and visualization analysis to give a bird's-eye view of publications between 2000 and 2020 on exercise therapy treating depression. Methods: Relevant original publications were obtained from the Science Citation Index Expanded in the Web of Science Core Collection (WoSCC) database between 2000 and 2020. CiteSpace (5.7.R 5) and VOSviewer (1.6.16) software were used to perform bibliometric analysis of countries, institutions, categories, journals, authors, references, and keywords involved in this topic. Results: A total number of 975 articles on this field were retrieved from the WoSCC database and we identified an overall increase in the amount of publications over the past two decades, with the United States and Harvard University leading the field. Most related publications were published in the journals with a focus on sport, medicine, rehabilitation, psychology, and health, as represented by the dual-map overlay. A series of authors and co-cited authors were identified as main contributors in the exercise-depression-teenager domain. Three major clusters were explored based on the reference co-citation analysis: "exercise," "suicide," and "concussion". Conclusions: Current concerns and hotspots of exercise intervention in depression treatments were summarized by "individual level," "social level," "role of exercise," and "research quality." We considered that the following four directions were potential future perspectives: "research on the effect of specific exercise intervention," "research on the essence of exercise and sports," "research on the combination mode of 'exercise + X'," and "research on the micro and molecular level," which should receive more attention.

Low Levels of Serum Tryptophan Underlie Skeletal Muscle Atrophy

Sarcopenia is a poor prognosis factor in some cancer patients, but little is known about the mechanisms by which malignant tumors cause skeletal muscle atrophy. Tryptophan metabolism mediated by indoleamine 2,3-dioxygenase is one of the most important amino acid changes associated with cancer progression. Herein, we demonstrate the relationship between skeletal muscles and low levels of tryptophan. A positive correlation was observed between the volume of skeletal muscles and serum tryptophan levels in patients with diffuse large B-cell lymphoma. Low levels of tryptophan reduced C2C12 myoblast cell proliferation and differentiation. Fiber diameters in the tibialis anterior of C57BL/6 mice fed a tryptophan-deficient diet were smaller than those in mice fed a standard diet. Metabolomics analysis revealed that tryptophan-deficient diet downregulated glycolysis in the gastrocnemius and upregulated the concentrations of amino acids associated with the tricarboxylic acid cycle. The weights and muscle fiber diameters of mice fed the tryptophan-deficient diet recovered after switching to the standard diet. Our data showed a critical role for tryptophan in regulating skeletal muscle mass. Thus, the tryptophan metabolism pathway may be a promising target for preventing or treating skeletal muscle atrophies.

Neurobiological effects of aerobic exercise, with a focus on patients with schizophrenia

Schizophrenia is a severe neuropsychiatric disease that is associated with neurobiological alterations in multiple brain regions and peripheral organs. Negative symptoms and cognitive deficits are present in about half of patients and are difficult to treat, leading to an unfavorable functional outcome. To investigate the impact of aerobic exercise on various neurobiological parameters, we conducted a narrative review. Add-on aerobic exercise was shown to be effective in improving negative and general symptoms, cognition, global functioning, and quality of life in schizophrenia patients. Based on findings in healthy individuals and animal models, this qualitative review gives an overview of different lines of evidence on how aerobic exercise impacts brain structure and function and molecular mechanisms in patients with schizophrenia and how its effects could be related to clinical and functional outcomes. Structural magnetic resonance imaging studies showed a volume increase in the hippocampus and cortical regions in schizophrenia patients and healthy controls after endurance training. However, results are inconsistent and individual risk factors may influence neuroplastic processes. Animal studies indicate that alterations in epigenetic mechanisms and synaptic plasticity are possible underlying mechanisms, but that differentiation of glial cells, angiogenesis, and possibly neurogenesis may also be involved. Clinical and animal studies also revealed effects of aerobic exercise on the hypothalamus-pituitary-adrenal axis, growth factors, and immune-related mechanisms. Some findings indicate effects on neurotransmitters and the endocannabinoid system. Further research is required to clarify how individual risk factors in schizophrenia patients mediate or moderate the neurobiological effects of exercise on brain and cognition. Altogether, aerobic exercise is a promising candidate in the search for pathophysiology-based add-on interventions in schizophrenia.

Treadmill Exercise Reverses Depression Model-Induced Alteration of Dendritic Spines in the Brain Areas of Mood Circuit

Depression is one of the most prevalent psychiatric disorders. Exercise has been shown to be effective in the amelioration of depression, but the underlying mechanism remains largely unknown. Alterations in the density and morphology of dendritic spines are associated with psychiatric diseases. Chronic unpredictable mild stress (CUMS) is an established animal model of depression. The aim of this study was to determine whether treadmill exercise reverses CUMS-induced both depression-like behaviors and alterations in spine density and morphology of the principal neurons in the brain areas of the mood circuits including the hippocampus, medial prefrontal cortex (mPFC), nucleus accumbens (NAc) and basolateral amygdala (BLA). Male rats were randomly divided into four groups: control, CUMS, exercise, and CUMS+exercise. CUMS-induced depression-like behaviors were evaluated by the sucrose preference test (SPT). Golgi staining was used to visualize dendritic spines. Our results showed that CUMS-induced depression-like behaviors characterized by a decrease in sucrose consumption were accompanied by a decrease in spine density and a change in spine morphology in the pyramidal neurons of both the hippocampal CA3 area and the mPFC, and an increase in spine density and an alteration in spine shape in both the NAc medium spiny neurons (MSNs) and the BLA neurons; exercise reversed both CUMS-induced depression-like behaviors and alterations in dendritic spines. This study provides important information for understanding the mechanism through which exercise ameliorates CUMS-induced depression-like behaviors.

The role of tryptophan metabolism in postpartum depression

The Postpartum depression (PPD) is the most common postpartum psychiatric disorder, afflicting approximately 10%-20% of new mothers. Clinical symptoms of the PPD include depressive disorder, agitation, insomnia, anxiety and confusion, resulting in an increase in suicidal tendencies, thereby having significant impacts on the puerpera, newborn and their family. A growing body of data indicate a role for alterations in tryptophan metabolism in the PPD. The metabolism of tryptophan produces an array of crucial factors that can differentially regulate key physiological processes linked to the PPD. Importantly, an increase in stress hormones and immune-inflammatory activity drives tryptophan to the production of neuroregulatory kynurenine pathway products and away from the serotonin and melatonin pathways. This links the PPD to other disorders of depressed mood, which are classically associated with decreased serotonin and melatonin, coupled to increases in kynurenine pathway products. Several kynurenine pathway products, such as kynurenic acid and quinolinic acid, can have neuroregulatory effects, with consequences pathological underpinnings of the PPD. The current article reviews the role of alterations in tryptophan metabolism in the PPD.

On the Run for Hippocampal Plasticity

Accumulating research in rodents and humans indicates that exercise benefits brain function and may prevent or delay onset of neurodegenerative conditions. In particular, exercise modifies the structure and function of the hippocampus, a brain area important for learning and memory. This review addresses the central and peripheral mechanisms underlying the beneficial effects of exercise on the hippocampus. We focus on running-induced changes in adult hippocampal neurogenesis, neural circuitry, neurotrophins, synaptic plasticity, neurotransmitters, and vasculature. The role of peripheral factors in hippocampal plasticity is also highlighted. We discuss recent evidence that systemic factors released from peripheral organs such as muscle (myokines), liver (hepatokines), and adipose tissue (adipokines) during exercise contribute to hippocampal neurotrophin and neurogenesis levels, and memory function. A comprehensive understanding of the body-brain axis is needed to elucidate how exercise improves hippocampal plasticity and cognition.

Intermittent intense exercise protects against cognitive decline in a similar manner to moderate exercise in chronically stressed mice

It is well known that regular low or mild exercise helps to improve and maintain cognition. On the other hand, ever thought many people prefer high-intensity exercise (e.g., running, swimming, biking, soccer, basketball, etc.) to get rid of stress or improve their health, the previous studies reported that intense exercise either impairs cognition or has no effect on cognitive function. However, we previously showed that intermittent intense exercise prevents stress-induced depressive behavior in mice in a similar manner to moderate exercise. On the basis of this finding, we investigated the effect of intermittent intense exercise on cognitive deficit in chronically stressed mice. A total of forty mice were evenly divided into control, stressed, stressed with moderate exercise, and stressed with intense exercise groups. The stressed mice were chronically exposed a restraint stress (10 h/day, 6 days/week for 7 weeks). The exercised mice were subjected to intermittent intense or endurance moderate running on the treadmill three times a week. Cognition was evaluated using the Morris water maze test and the object recognition test. Chronic stress decreased cognition, and newborn cell survival and blood vessel density in the hippocampus. However, both regular intense and moderate exercise prevented decrease of cognition, improved newborn cell survival and blood vessel density. These findings suggest that intermittent intense exercise may protect against decrease of cognition in a similar manner to moderate exercise and that both exercise-induced protection of decrease of cognition is closely related to newborn cell survival and angiogenesis in the hippocampus.

Stereological Study on the Positive Effect of Running Exercise on the Capillaries in the Hippocampus in a Depression Model

Running exercise is an effective method to improve depressive symptoms when combined with drugs. However, the underlying mechanisms are not fully clear. Cerebral blood flow perfusion in depressed patients is significantly lower in the hippocampus. Physical activity can achieve cerebrovascular benefits. The purpose of this study was to evaluate the impacts of running exercise on capillaries in the hippocampal CA1 and dentate gyrus (DG) regions. The chronic unpredictable stress (CUS) depression model was used in this study. CUS rats were given 4 weeks of running exercise from the fifth week to the eighth week (20 min every day from Monday to Friday each week). The sucrose consumption test was used to measure anhedonia. Furthermore, stereological methods were used to investigate the capillary changes among the control group, CUS/Standard group and CUS/Running group. Sucrose consumption significantly increased in the CUS/Running group. Running exercise has positive effects on the capillaries parameters in the hippocampal CA1 and DG regions, such as the total volume, total length and total surface area. These results demonstrated that capillaries are protected by running exercise in the hippocampal CA1 and DG might be one of the structural bases for the exercise-induced treatment of depression-like behavior. These results suggest that drugs and behavior influence capillaries and may be considered as a new means for depression treatment in the future.

Monoamines and cortisol as potential mediators of the relationship between exercise and depressive symptoms

A randomized controlled trial was conducted to assess the effects of exercise plus pharmacotherapy on monoamine neurotransmitters (dopamine, noradrenaline, adrenaline, serotonin) and cortisol levels. A total of 26 women with clinical depression were randomly assigned to one of the two groups: aerobic exercise plus pharmacotherapy or only pharmacotherapy. The exercise program consisted of aerobic exercise, 45-50 min/session, three times/week, for 16 weeks. The biological parameters were measured before and after the exercise program. Adding exercise to pharmacotherapy had no additional effects on monoamines and cortisol plasma levels. These data are preliminary outcomes from a small sample and should be replicated.

Running exercise protects the capillaries in white matter in a rat model of depression

Running has been shown to improve depressive symptoms when used as an adjunct to medication. However, the mechanisms underlying the antidepressant effects of running are not fully understood. Changes of capillaries in white matter have been discovered in clinical patients and depression model rats. Considering the important part of white matter in depression, running may cause capillary structural changes in white matter. Chronic unpredictable stress (CUS) rats were provided with a 4-week running exercise (from the fifth week to the eighth week) for 20 minutes each day for 5 consecutive days each week. Anhedonia was measured by a behavior test. Furthermore, capillary changes were investigated in the control group, the CUS/Standard group, and the CUS/Running group using stereological methods. The 4-week running increased sucrose consumption significantly in the CUS/Running group and had significant effects on the total volume, total length, and total surface area of the capillaries in the white matter of depression rats. These results demonstrated that exercise-induced protection of the capillaries in white matter might be one of the structural bases for the exercise-induced treatment of depression. It might provide important parameters for further study of the vascular mechanisms of depression and a new research direction for the development of clinical antidepressant means. J. Comp. Neurol. 524:3577-3586, 2016. © 2016 Wiley Periodicals, Inc.

Exercise amelioration of depression-like behavior in OVX mice is associated with suppression of NLRP3 inflammasome activation in hippocampus

Exercise has benefit for perimenopause women in many ways, such as affective disorders. Our previous study has demonstrated that inflammation in hippocampus contributes to development of depression-like behavior in ovariectomized (OVX) rats. Recently, oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome has been implicated to be involved in lipopolysaccharide (LPS)- and chronic stress-induced depression-like behavior in rodents. We sought to investigate whether ovariectomy-induced depression-like behavior is associated with NLRP3 inflammasome activation in brain and the effect of exercise on NLRP3 inflammasome activation in this model. The results showed that ovariectomy resulted in depression-like behavior in mice and an increase in levels of IL-1β and IL-18 in hippocampus. Exercise ameliorated the depression-like behavior and decreased levels of IL-1β and IL-18 in hippocampus. The level of IL-1β and IL-18 in hippocampus correlated to depression-like behavior in OVX mice. The levels of NLRP3, cleaved caspase-1 P10 and CD11b in hippocampus were increased in OVX mice compared with control group. Exercise could reduce the levels of NLRP3, cleaved caspase-1 P10 and CD11b in OVX mice. Our study suggests that NLRP3 inflammasome activation contribute to inflammation in hippocampus upon to deprivation of ovary. Exercise amelioration of depression-like behavior is associated with suppression of NLRP3 inflammasome activation in hippocampus of this model.

Intranasal delivery of paroxetine nanoemulsion via the olfactory region for the management of depression: formulation, behavioural and biochemical estimation

Paroxetine is a selective serotonin reuptake inhibitor (SSRI) and is used for the treatment of depression and anxiety problems, but suffers from the drawback of poor oral bioavailability (less than 50%) due to its extensive first pass metabolism. The objective of the present study was to develop a paroxetine loaded nanoemulsion (o/w type) for direct nose-to-brain delivery. Nanoemulsions were prepared by the spontaneous emulsification technique using Capmul MCM, Solutol HS 15 and propylene glycol as oil phase, surfactant and co-surfactant, respectively, for delivery of drug directly to the brain through the nasal route for better management of depression. Formulations were studied for droplet size, polydispersity index (PDI), percentage transmittance, refractive index, viscosity, zeta potential, surface morphology and in vitro permeation study. TEM images of optimized formulation showed spherical droplets with a mean diameter of 58.47 ± 3.02 nm, PDI of 0.339 ± 0.007 and zeta potential values of -33 mV. The formulation showed good results for transmittance (100.60 ± 0.577%), refractive index (1.412 ± 0.003) and viscosity (40.85 ± 6.40 cP). Permeation studies revealed a 2.57-fold enhancement in permeation as compared to the paroxetine suspension. Behavioural studies such as the forced swimming test and locomotor activity test were done on Wistar rats to study the antidepressant effect of the optimized formulation. Treatment of depressed rats with paroxetine nanoemulsion (administered intranasally) significantly improved the behavioural activities in comparison to paroxetine suspension (orally administered). Biochemical estimation results revealed that the prepared nanoemulsion was effective in enhancing the depressed levels of glutathione and decreasing the elevated levels of TBARS.

The use of animal models to decipher physiological and neurobiological alterations of anorexia nervosa patients

Extensive studies were performed to decipher the mechanisms regulating feeding due to the worldwide obesity pandemy and its complications. The data obtained might be adapted to another disorder related to alteration of food intake, the restrictive anorexia nervosa. This multifactorial disease with a complex and unknown etiology is considered as an awful eating disorder since the chronic refusal to eat leads to severe, and sometimes, irreversible complications for the whole organism, until death. There is an urgent need to better understand the different aspects of the disease to develop novel approaches complementary to the usual psychological therapies. For this purpose, the use of pertinent animal models becomes a necessity. We present here the various rodent models described in the literature that might be used to dissect central and peripheral mechanisms involved in the adaptation to deficient energy supplies and/or the maintenance of physiological alterations on the long term. Data obtained from the spontaneous or engineered genetic models permit to better apprehend the implication of one signaling system (hormone, neuropeptide, neurotransmitter) in the development of several symptoms observed in anorexia nervosa. As example, mutations in the ghrelin, serotonin, dopamine pathways lead to alterations that mimic the phenotype, but compensatory mechanisms often occur rendering necessary the use of more selective gene strategies. Until now, environmental animal models based on one or several inducing factors like diet restriction, stress, or physical activity mimicked more extensively central and peripheral alterations decribed in anorexia nervosa. They bring significant data on feeding behavior, energy expenditure, and central circuit alterations. Animal models are described and criticized on the basis of the criteria of validity for anorexia nervosa.

Hippocampal UCP2 is essential for cognition and resistance to anxiety but not required for the benefits of exercise

Uncoupling protein-2 (UCP2) reduces oxidative stress by facilitating the influx of protons into mitochondrial matrix, thus dissociating mitochondrial oxidation from ATP synthesis. UCP2 is expressed abundantly in brain areas and plays a key role in neuroprotection. Here, we sought to determine if UCP2 deficiency produces cognitive impairment and anxiety in young mice, and to determine if hippocampal UCP2 is essential for the beneficial effects of voluntary exercise. Antisense oligonucleotide (ASO) was used to produce UCP2 knockdown in mice. Our results firstly showed that UCP2-targeted ASO significantly reduced UCP2 mRNA and protein expression in the hippocampus. ASO treatment impaired learning and memory of the mice in Y-maze, T-maze, and object recognition tests (ORT). ASO-treated mice exhibited more anxiously in OPT, light/dark box test, and elevated plus maze (EPM) than the control mice. We also found that wheel running ameliorated cognitive dysfunction and anxiety-like behaviors in ASO-treated mice. Furthermore, voluntary exercise reversed ASO-induced changes in hippocampal levels of serotonin (5-HT), dopamine (DA), and norepinephrine (NE). However, UCP2 protein in the hippocampus was not correlated with cognitive and anxiolytic benefits of exercise. These findings suggest that hippocampal UCP2 is essential for cognitive function and the resistance to anxiety of mice, but not required for the beneficial effects of exercise.