Voluntary running improves depressive behaviours and the structure of the hippocampus in rats: A possible impact of myokines

Major Depressive Disorder and Gut Microbiota: Role of Physical Exercise

Major depressive disorder (MDD) has a high prevalence and is a major contributor to the global burden of disease. This psychiatric disorder results from a complex interaction between environmental and genetic factors. In recent years, the role of the gut microbiota in brain health has received particular attention, and compelling evidence has shown that patients suffering from depression have gut dysbiosis. Several studies have reported that gut dysbiosis-induced inflammation may cause and/or contribute to the development of depression through dysregulation of the gut-brain axis. Indeed, as a consequence of gut dysbiosis, neuroinflammatory alterations caused by microglial activation together with impairments in neuroplasticity may contribute to the development of depressive symptoms. The modulation of the gut microbiota has been recognized as a potential therapeutic strategy for the management of MMD. In this regard, physical exercise has been shown to positively change microbiota composition and diversity, and this can underlie, at least in part, its antidepressant effects. Given this, the present review will explore the relationship between physical exercise, gut microbiota and depression, with an emphasis on the potential of physical exercise as a non-invasive strategy for modulating the gut microbiota and, through this, regulating the gut-brain axis and alleviating MDD-related symptoms.

Environmental enrichment promotes resilience to neuropathic pain-induced depression and correlates with decreased excitability of the anterior cingulate cortex

Depression is a common comorbidity of chronic pain with many patients being affected. However, efficient pharmacological treatment strategies are still lacking. Therefore, it is desirable to find additional alternative approaches. Environmental enrichment has been suggested as a method to alleviate pain-induced depression. However, the neuronal mechanisms of its beneficial effects are still elusive. The anterior cingulate cortex (ACC) plays a central role in processing pain-related negative affect and chronic pain-induced plasticity in this region correlates with depressive symptoms. We studied the consequences of different durations of environmental enrichment on pain sensitivity and chronic pain-induced depression-like behaviors in a mouse model of neuropathic pain. Furthermore, we correlated the behavioral outcomes to the activity levels of pyramidal neurons in the ACC by analyzing their electrophysiological properties ex vivo. We found that early exposure to an enriched environment alone was not sufficient to cause resilience against pain-induced depression-like symptoms. However, extending the enrichment after the injury prevented the development of depression and reduced mechanical hypersensitivity. On the cellular level, increased neuronal excitability was associated with the depressive phenotype that was reversed by the enrichment. Therefore, neuronal excitability in the ACC was inversely correlated to the extended enrichment-induced resilience to depression. These results suggest that the improvement of environmental factors enhanced the resilience to developing chronic pain-related depression. Additionally, we confirmed the association between increased neuronal excitability in the ACC and depression-like states. Therefore, this non-pharmacological intervention could serve as a potential treatment strategy for comorbid symptoms of chronic pain.

Structural changes and neurotrophic factors upregulation in submandibular gland in a rat model of depression: proposed correlation with stress indicators during and after the relief of depression

This study evaluated the structural changes, the immunohistochemical and gene expression of neurotrophic factors in submandibular gland in a rat model of depression, and their correlation with depression parameters during and after relief of depression by voluntary running. Forty-eight male Wistar rats were divided into control, control-exercise, depression, and depression-exercise groups. Depression was induced using forced swimming protocol, while the relief of depression was induced using the rat voluntary running wheels. The depressive state of rats was evaluated by measuring the immobility duration and the serum corticosterone level. The immune expression was evaluated by measuring the optical densities (ODs) using ImageJ software, and the gene expression levels were investigated. In the depression group, the convoluted ducts appeared dilated with numerous secretory granules. The number of PCNA-stained cells was significantly decreased in the depression group as compared to control group and then significantly increased in the depression-exercise group when compared to the depression group with a negative correlation to stress indicator. The ODs of immuno-expression for the brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) increased significantly in the depression group as compared to control group. Both BDNF and VEGF immuno-expression displayed positive correlation with the stress indicators. Both BDNF and VEGF gene expression results confirmed their immunohistochemical results. The findings of this study explored the role of submandibular gland in secreting neurotrophic factors and raise a flag for the possibility of using salivary secretions as dependable and easy parameter for estimation of chronic stressed patients.Mini AbstractThe submandibular gland neurotrophic factors immuno-expression can be used in estimating chronic depressive disorders as they are correlated with stress indicators during and after the relief of depression.

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.

Effect of Voluntary Wheel-Running Exercise on the Endocrine and Inflammatory Response to Social Stress: Conditioned Rewarding Effects of Cocaine

The present paper evaluates the effect of physical activity on the increase of the conditioned rewarding effects of cocaine induced by intermittent social stress and on the neuroinflammatory response that contributes to the enhancement of drug response. For that purpose, three studies were designed in which social stress was induced in different samples of mice through a social-defeat protocol; the mice underwent an increase of physical activity by different modalities of voluntary wheel running (continuous and intermittent access). The results showed that continuous access to running wheels prior to stress enhanced the establishment of cocaine place preference, whereas an intermittent access exerted a protective effect. Wheel running contingent to cocaine administration prevented the development of conditioned preference, and if applied during the extinction of drug memories, it exerted a dual effect depending on the stress background of the animal. Our biological analysis revealed that increased sensitivity to cocaine may be related to the fact that wheel running promotes inflammation though the increase of IL-6 and BDNF levels. Together, these results highlight that physical exercise deeply impacts the organism’s response to stress and cocaine, and these effects should be taken into consideration in the design of a physical intervention.

An overview of the molecular and physiological antidepressant mechanisms of physical exercise in animal models of depression

BACKGROUND

Depression is a global disease that affects the physical and mental health of people of all ages. Non-pharmacological and unconventional methods of treatment, such as regular physical exercise, have been recommended to treat depression.

METHODS

Here, we briefly review the literature about the physiological and molecular mechanisms of exercise antidepressants in depressive-like behavior in animal models of depression.

RESULTS

The main hysiological and molecular mechanisms of physical exercise in depression include blood flow changes in several areas of the brain, increase in brain serotonin synthesis, increase in antioxidant enzymes, increase in serum and brain brain-derived neuro factor (BDNF) levels, decrease in cortisol levels and reduced inflammation in peripheral and brain tissues. Physical exercise also leads to increased activation of the phosphatidylinositol-3-kinase (PI3K), PGC-1α/FNDC5/Irisin pathway, BDNF concentrations (serum and cerebral), extracellular signal-regulated kinase and cAMP-response element binding protein (mainly in neurons of the hippocampus and prefrontal cortex), which together contribute to fight or inhibit the development of depression symptoms. These molecular and physiological mechanisms work in synchrony, further enhancing their effects.

CONCLUSION

Physical exercise can be used as a safe and effective non-pharmacological treatment in depression.

Exercise inhibits JNK pathway activation and lipotoxicity via macrophage migration inhibitory factor in nonalcoholic fatty liver disease

The macrophage migration inhibitory factor (MIF) expressed in hepatocytes can limit steatosis during obesity. Lipotoxicity in nonalcoholic fatty liver disease is mediated in part by the activation of the stress kinase JNK, but whether MIF modulates JNK in lipotoxicity is unknown. In this study, we investigated the role of MIF in regulating JNK activation and high-fat fostered liver lipotoxicity during simultaneous exercise treatment. Fifteen mice were equally divided into three groups: normal diet, high-fat diet, and high-fat and exercise groups. High-fat feeding for extended periods elicited evident hyperlipemia, liver steatosis, and cell apoptosis in mice, with inhibited MIF and activated downstream MAPK kinase 4 phosphorylation and JNK. These effects were then reversed following prescribed swimming exercise, indicating that the advent of exercise could prevent liver lipotoxicity induced by lipid overload and might correlate to the action of modulating MIF and its downstream JNK pathway. Similar detrimental effects of lipotoxicity were observed in in vitro HepG2 cells palmitic acid treatment. Suppressed JNK reduced the hepatocyte lipotoxicity by regulating the BCL family, and the excess JNK activation could also be attenuated through MIF supplementation or exacerbated by MIF siRNA administration. The results found suggest that exercise reduces lipotoxicity and inhibits JNK activation by modulating endogenous hepatic MIF in NAFLD. These findings have clinical implications for the prevention and intervention of patients with immoderate diet evoked NAFLD.

The Effects of Nordic Walking With Poles With an Integrated Resistance Shock Absorber on Cognitive Abilities and Cardiopulmonary Efficiency in Postmenopausal Women

Late adulthood is associated with atrophy of brain areas, which contribute to cognitive deterioration and increase the risk of depression. On the other hand, aerobic exercise can improve learning and memory function, ameliorate mood, and prevent neurodegenerative changes. This study demonstrates the effect of Nordic walking (NW) and NW with poles with an integrated resistance shock absorber (NW with RSA) on aerobic capacity and body composition in postmenopausal women. It also measures the brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) serum levels and determines correlations with cognitive functions and depression symptoms. These relationships with the use of NW with RSA as a new form of exercise have not been described thus far. In this study, 31 women (NW - 16, NW with RSA - 15) participated in eight weeks of training. The findings showed that only NW with RSA training caused a significant decrease in body mass and body mass index (p < 0.05). There were no significant changes in GDNF levels between groups studied. Regarding BDNF, a significant decrease (p < 0.05) in the NW group and an increase (not statistically significant) in the NW with RSA group was found. A comparative analysis of cognitive and depression outcomes and changes in BDNF and GDNF concentration showed no significant differences in the efficacy of either form of training. Training loads resulted in a significant increase in VO₂max in both the NW (p < 0.01) and NW with RSA (p < 0.05) groups. This indicates an improvement in cardiopulmonary efficiency of the examined women.

Effect of voluntary running on expression of myokines in brains of rats with depression

This study aimed to demonstrate the histopathology and immunoexpression of exercise-derived myokines in dentate gyrus (DG), medial prefrontal cortex (mPFC) and cerebellum of depressed Wistar rats during depression and after practising voluntary running. Depression was developed by forced swimming for 2 weeks. Voluntary running was performed by voluntary running for 3 weeks. Brain sections were processed and immunostained to detect brain-derived neurotrophic factor (BDNF), macrophage migration inhibitory factor (MIF), vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6). ImageJ software was used to measure the optical density (OD). BDNF was expressed in neurons in DG, mPFC and granular and Purkinje cells in cerebellum. MIF was expressed in neurons of sub-granular zone in DG, mPFC and Purkinje cells. VEGF was expressed in many neurons in DG, mPFC and Purkinje cells. IL-6 was expressed in some neurons in DG, in neuropil of mPFC and in Purkinje cells. In depression, the OD of studied myokines significantly decreased in all examined areas. After voluntary running, the OD of myokines significantly increased in all areas. This study defines the immunohistochemical expression of myokines in brain areas in depression and after voluntary running and reveals the involvement of the mPFC and cerebellum in the pathophysiology of depression.

Roles of myokines in exercise-induced improvement of neuropsychiatric function

Exercise is a well-known non-pharmacological intervention to improve brain functions, including cognition, memory, and motor coordination. Contraction of skeletal muscles during exercise releases humoral factors that regulate the whole-body metabolism via interaction with other non-muscle organs. Myokines are muscle-derived effectors that regulate body metabolism by autocrine, paracrine, or endocrine action and were reportedly suggested as "exercise factors" that can improve the brain function. However, several aspects remain to be elucidated, namely the specific activities of myokines related to the whole-body metabolism or brain function, the mechanisms of regulation of other organs or cells, the sources of "exercise factors" that regulate brain function, and their mechanisms of interaction with non-muscle organs. In this paper, we present the physiological functions of myokines secreted by exercise, including regulation of the whole-body metabolism by interaction with other organs and adaptation of skeletal muscles to exercise. In addition, we discuss the functions of myokines that possibly contribute to exercise-induced improvement of brain function. Among several myokines, brain-derived neurotrophic factor (BDNF) is the most studied myokine that regulates adult neurogenesis and synaptic plasticity. However, the source of circulating BDNF and its upstream effector, insulin-like growth factor (IGF-1), and irisin and the effect size of peripheral BDNF, irisin, and IGF-1 released after exercise should be further investigated. Recently, cathepsin B has been reported to be secreted from skeletal muscles and upregulate BDNF following exercise, which was associated with improved cognitive function. We reviewed the level of evidence for the effect of myokine on the brain function. Level of evidence for the association of the change in circulating myokine following exercise and improvement of neuropsychiatric function is lower than the level of evidence for the benefit of exercise on the brain. Therefore, more clinical evidences for the association of myokine release after exercise and their effect on the brain function are required. Finally, we discuss the effect size of the action of myokines on cognitive benefits of exercise, in addition to other contributors, such as improvement of the cardiovascular system or the effect of "exercise factors" released from non-muscle organs, particularly in patients with sarcopenia.

Voluntary exercise and depression-like behavior in rodents: are we running in the right direction?

Acute or chronic exposure to stress can increase the risk to develop major depressive disorder, a severe, recurrent and common psychiatric condition. Depression places an enormous social and financial burden on modern society. Although many depressed patients are treated with antidepressants, their efficacy is only modest, underscoring the necessity to develop clinically effective pharmaceutical or behavioral treatments. Exercise training produces beneficial effects on stress-related mental disorders, indicative of clinical potential. The pro-resilient and antidepressant effects of exercise training have been documented for several decades. Nonetheless, the underlying molecular mechanisms and the brain circuitries involved remain poorly understood. Preclinical investigations using voluntary wheel running, a frequently used rodent model that mimics aspects of human exercise training, have started to shed light on the molecular adaptations, signaling pathways and brain nuclei underlying the beneficial effects of exercise training on stress-related behavior. In this review, I highlight several neurotransmitter systems that are putative mediators of the beneficial effects of exercise training on mental health, and review recent rodent studies that utilized voluntary wheel running to promote our understanding of exercise training-induced central adaptations. Advancements in our mechanistic understanding of how exercise training induces beneficial neuronal adaptations will provide a framework for the development of new strategies to treat stress-associated mental illnesses.

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.

Hyperglycemia Alters the Protein Levels of Prominin-1 and VEGFA in the Retina of Albino Rats

In this study, we addressed the potential relationship between prominin-1 (prom1) and vascular endothelial growth factor (VEGFA) in diabetes-induced retinopathy. In total, we examined 28 retinas from 14 rats with streptozotocin-induced diabetes and 30 retinas from 15 untreated control rats. ELISA was used to measure the level of prom1 and VEGFA in retinal tissue homogenates. Immunohistochemical techniques were used with antibodies directed against prom1, VEGFA, and CASP-3. After 180 days of diabetes induction, we performed light and electron microscopy studies on rat eyes to evaluate histopathological changes and to estimate the de novo metric "Diabetic Retinopathy Histopathological Index" (DRHI). These changes were then correlated to the tissue and immunoexpression levels of prom1 and VEGFA. The data showed a significant upregulation of the tissue levels and optical densities (ODs) of VEGFA and prom1 immunoreactivity in diabetic retinas compared with controls. Both the tissue levels and OD values of prom1 and VEGFA correlated significantly with each other and to the diabetic structural changes as calculated by DRHI. Taken together, these data provide new insight into the potential role of prom1 and VEGFA in the development of diabetic retinopathy.

Molecular Mechanisms Underlying Cardiac Adaptation to Exercise

Exercise elicits coordinated multi-organ responses including skeletal muscle, vasculature, heart, and lung. In the short term, the output of the heart increases to meet the demand of strenuous exercise. Long-term exercise instigates remodeling of the heart including growth and adaptive molecular and cellular re-programming. Signaling pathways such as the insulin-like growth factor 1/PI3K/Akt pathway mediate many of these responses. Exercise-induced, or physiologic, cardiac growth contrasts with growth elicited by pathological stimuli such as hypertension. Comparing the molecular and cellular underpinnings of physiologic and pathologic cardiac growth has unveiled phenotype-specific signaling pathways and transcriptional regulatory programs. Studies suggest that exercise pathways likely antagonize pathological pathways, and exercise training is often recommended for patients with chronic stable heart failure or following myocardial infarction. Herein, we summarize the current understanding of the structural and functional cardiac responses to exercise as well as signaling pathways and downstream effector molecules responsible for these adaptations.