The effect of repeated physical exercise on hippocampus and brain cortex in stressed rats

The Impact of Chronic Stress on Behavior and Body Mass in New Animal Models

(1) Background: Exposure to different sources of stress can have a significant effect on both psychological and physical processes. (2) Methods: The study took place over a period of 34 days and included a total of 40 animals. Regarding the exposure to chronic stressors, we opted for physiological, non-invasive stressors, e.g., running, swimming, and changes in the intensity of light. An unforeseen stress batch was also created that alternated all these stress factors. The animals were divided into five experimental groups, each consisting of eight individuals. In the context of conducting the open field test for behavioral assessment before and after stress exposure, we aimed to investigate the impact of stress exposure on the affective traits of the animals. We also monitored body mass every two days. (3) Results: The control group exhibited an average increase in weight of approximately 30%. The groups exposed to stress factors showed slower growth rates, the lowest being the running group, recording a rate of 20.55%, and the unpredictable stress group at 24.02%. The anxious behavior intensified in the group with unforeseen stress, in the one with light variations, and in the running group. (4) Conclusions: Our research validates the animal model of intermittent light exposure during the dark phase as a novel method of inducing stress. The modification of some anxiety parameters was observed; they vary according to the type of stress. Body mass was found to increase in all groups, especially in the sedentary groups, likely due to the absence of cognitive, spatial, and social stimuli except for cohabitation.

Running from Stress: Neurobiological Mechanisms of Exercise-Induced Stress Resilience

Chronic stress, even stress of a moderate intensity related to daily life, is widely acknowledged to be a predisposing or precipitating factor in neuropsychiatric diseases. There is a clear relationship between disturbances induced by stressful stimuli, especially long-lasting stimuli, and cognitive deficits in rodent models of affective disorders. Regular physical activity has a positive effect on the central nervous system (CNS) functions, contributes to an improvement in mood and of cognitive abilities (including memory and learning), and is correlated with an increase in the expression of the neurotrophic factors and markers of synaptic plasticity as well as a reduction in the inflammatory factors. Studies published so far show that the energy challenge caused by physical exercise can affect the CNS by improving cellular bioenergetics, stimulating the processes responsible for the removal of damaged organelles and molecules, and attenuating inflammation processes. Regular physical activity brings another important benefit: increased stress robustness. The evidence from animal studies is that a sedentary lifestyle is associated with stress vulnerability, whereas a physically active lifestyle is associated with stress resilience. Here, we have performed a comprehensive PubMed Search Strategy for accomplishing an exhaustive literature review. In this review, we discuss the findings from experimental studies on the molecular and neurobiological mechanisms underlying the impact of exercise on brain resilience. A thorough understanding of the mechanisms underlying the neuroprotective potential of preconditioning exercise and of the role of exercise in stress resilience, among other things, may open further options for prevention and therapy in the treatment of CNS diseases.

Exposure to 2.45 GHz Radiation Triggers Changes in HSP-70, Glucocorticoid Receptors and GFAP Biomarkers in Rat Brain

Brain tissue may be especially sensitive to electromagnetic phenomena provoking signs of neural stress in cerebral activity. Fifty-four adult female Sprague-Dawley rats underwent ELISA and immunohistochemistry testing of four relevant anatomical areas of the cerebrum to measure biomarkers indicating induction of heat shock protein 70 (HSP-70), glucocorticoid receptors (GCR) or glial fibrillary acidic protein (GFAP) after single or repeated exposure to 2.45 GHz radiation in the experimental set-up. Neither radiation regime caused tissue heating, so thermal effects can be ruled out. A progressive decrease in GCR and HSP-70 was observed after acute or repeated irradiation in the somatosensory cortex, hypothalamus and hippocampus. In the limbic cortex; however, values for both biomarkers were significantly higher after repeated exposure to irradiation when compared to control animals. GFAP values in brain tissue after irradiation were not significantly different or were even lower than those of nonirradiated animals in all brain regions studied. Our results suggest that repeated exposure to 2.45 GHz elicited GCR/HSP-70 dysregulation in the brain, triggering a state of stress that could decrease tissue anti-inflammatory action without favoring glial proliferation and make the nervous system more vulnerable.

Treadmill running improves long-term potentiation (LTP) defects in streptozotocin-induced diabetes at dentate gyrus in rats

OBJECTIVES

It has been demonstrated that exercise has neuroprotective effects in the central nervous system (CNS), especially in hippocampus. Previous studies have indicated that diabetes mellitus affects synaptic plasticity in the hippocampus leading to impairments in learning and memory. The aim of this study was to evaluate the effects of treadmill running on synaptic plasticity at dentate gyrus (DG) of streptozotocin-induced diabetic rats.

STUDY DESIGN

Experimental groups were the control, the diabetes and the diabetes-exercise groups. Long-term potentiation (LTP) in perforant path-DG synapses was assessed (by 400Hz tetanization) in order to investigate the effect of exercise on synaptic plasticity. Field excitatory post-synaptic potential (fEPSP) slope and population spike (PS) amplitude were measured.

RESULTS

With respect to the control group, fEPSP were significantly decreased in the diabetes group. However, there were no differences between responses of the diabetes-exercise group and the control.

CONCLUSION

The present results suggest that LTP induction in the dentate gyrus is affected under diabetic conditions and that treadmill running prevents these effects. The data suggest that treadmill running protect against diabetes-induced decrease of learning ability and memory function of the hippocampus.

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.

Coping with a challenging environment: effects of seasonal variability and reproductive status on glucocorticoid concentrations of female baboons (Papio cynocephalus)

Environmental stressors impact physiology and behavior in many species of animals. These effects are partly mediated through changing concentrations of glucocorticoids, which also vary with reproductive state and social conditions. Prior research has focused largely on seasonal breeders, but the close temporal linkage between season and reproductive state in these species hinders ability to disentangle environmental effects from those of the animal's reproductive status. Here we assessed the effects of environmental challenges on the fecal glucocorticoid (fGC) levels of non-seasonal breeders, female baboons (Papio cynocephalus) of Amboseli, Kenya. Amboseli is characterized by a long dry season, during which food and water become scarce, and by extreme temperatures above 40 degrees C in the shade during some months of the year. We found that after accounting for female reproductive status and individual variability, females exhibited higher fGC levels during the dry season than during the wet season. Further, during the wet season, fGC levels were higher in months of high average daily maximum temperatures. During the dry season, fGC levels were elevated both in hotter months and in months during which the baboons spent a relatively high proportion of time feeding. In spite of these stressors, female baboons reproduce during all months of the year in Amboseli, unlike most other mammals in this environment. This may be attributable to their extreme adaptability, specifically their diversified diet, and their ability to modify their behavior, including their activity profiles.

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.