Effect of chronic stress on short and long-term plasticity in dentate gyrus; Study of recovery and adaptation

Cannabidiol/cannabidiolic acid-rich hemp (Cannabis sativa L.) extract attenuates cognitive impairments and glial activations in rats exposed to chronic stress

ETHNOPHARMACOLOGICAL RELEVANCE

Hemp (Cannabis sativa L.) is increasingly being recognized for its medicinal properties beside utilizing it for food, oil, and textile fibers. The high level of cannabidiol (CBD) content in hemp's flowers shows promising neuroprotective properties without causing psychotomimetic or addictive effects. Recently, products containing CBD and its precursor, cannabidiolic acid (CBDA), have been used to treat stress-related cognitive impairment. However, the therapeutic potential of hemp extract remains inadequately explored.

AIM OF THE STUDY

To investigate the effect of CBD/CBDA-rich hemp extract on learning and memory, neuroendocrine alterations, and hippocampal neuropathological changes in the chronic restraint stress model.

MATERIALS AND METHODS

Chronic restraint stress (CRS) was induced in male Wistar rats by immobilizing them in a restrainer for 6 h per day for 21 consecutive days. CBD/CBDA-rich hemp extract (10 and 30 mg/kg, intraperitoneal injection) was administered daily, 1 h before restraint. After the last day of CRS, behavioral tests for cognition were conducted using the Y-maze and object recognition tests. Serum corticosterone (CORT) levels were measured by ELISA. Histopathological changes, neuronal density, and the activation of microglia and astrocytes were visualized using cresyl violet and immunohistochemical staining.

RESULTS

A high dose of CBD/CBDA-rich hemp extract effectively ameliorated CRS-induced cognitive impairment and reversed HPA axis hyperactivity in CRS rats by reducing CORT levels and adrenal gland weight. Additionally, CBD/CBDA-rich hemp extract protected CRS-induced damage to hippocampal neurons. Further analysis showed that CBD/CBDA-rich hemp extract reduced specific markers of microglial activation (ionized calcium-binding adaptor molecule-1, Iba-1) and astrocytic structural protein (glial fibrillary acidic protein, GFAP) in CRS rats.

CONCLUSION

CBD/CBDA-rich hemp extracts remarkably reversed the stress-induced behavioral perturbations and hippocampal damage, suggesting its ameliorative effect on stress response.

Effects of chronic empathic stress on synaptic efficacy, as well as short-term and long-term plasticity at the Schaffer collateral/commissural- CA1 synapses in the dorsal hippocampus of rats

Empathy, the ability to comprehend and share others' emotional states, impacts brain functions. This in vivo electrophysiological study explored the influence of chronic empathic stress on synaptic efficacy, as well as short-term and long-term plasticity at the Schaffer collateral/Commissural - CA1 synapses in the dorsal hippocampus of rats, in situations of social equality and inequality. Forty-eight male rats were randomized into six groups: control, pseudo-observer, pseudo-demonstrator, observer, demonstrator, and co-demonstrator (Co, Pse-Ob, Pse-De, Ob, De, Co-De) groups. Stress induction (2h/day, 21 days) was performed in situations of equality and inequality. Serum corticosterone levels, slope, amplitude, and area under the curve (AUC) of field excitatory postsynaptic potentials (fEPSPs) were assessed in the hippocampal CA1 area using input-output (I/O) functions, paired-pulse (PP) responses with different interpulse intervals (IPIs), and long-term potentiation (LTP) after high-frequency stimulation (HFS). The fEPSP slope, amplitude, and AUC significantly decreased in all stress groups, especially in the De and Pse-De groups. These parameters were significantly increased in the Co-De and Ob groups compared to the De group. Notably, the corticosterone levels strongly confirmed the electrophysiological findings. Chronic empathic stress could disrupt synaptic efficacy and plasticity in the CA1 area. Empathic stress, involving the presence of cagemates in situations of social equality and inequality, can modify long-term plasticity and serum corticosterone levels in demonstrators and co-demonstrators. Under empathic stress related to situations of inequality, freely moving observers may influence the demonstrators' stress experience. Therefore, the presence of a conspecific in the social inequality conditions had significant suppressive effects on long-term plasticity, while conversely, under equality conditions, long-term plasticity was favorably improved through social buffering.

Comparing the Efficacy of Escitalopram with and without Crocin in Restoring I/O Functions and LTP within the Hippocampal CA1 Region of Stressed Rats

Background

Escitalopram, a pharmacological compound, and crocin, the active compound of saffron, influence brain functions and serotonin levels. This study examined the efficacy of escitalopram with and without crocin in restoring the input-output (I/O) functions and long-term potentiation (LTP) within the hippocampal cornu ammonis 1 (CA1) region of stressed rats.

Materials and Methods

Rats were divided into six groups: control (Co), sham (Sh), stress-recovery (St-Rec), stress-escitalopram (St-Esc), stress-crocin (St-Cr), and stress-escitalopram-crocin (St-Esc-Cr) groups. They underwent 14 days of restraint stress (6 h/day). After being subjected to stress, they received 14 days of escitalopram (20 mg/kg) and crocin (30 mg/kg), as well as co-administration of these two compounds during the next 14 days. The field excitatory postsynaptic potential (fEPSP) slope and amplitude were measured using I/O functions and LTP induction in the CA1 region. Corticosterone (CORT) levels were also evaluated.

Results

The fEPSPs slope and amplitude in the I/O functions and LTP induction significantly decreased in stressed rats without therapeutic intervention. These variables in the I/O functions declined in rats with escitalopram administration alone. All electrophysiological parameters showed an increase in rats treated with crocin alone compared to stressed subjects without any treatment. Serum CORT levels decreased only with crocin treatment for stressed rats.

Conclusion

Neural excitability and memory within the CA1 region were severely disrupted among stressed rats without any treatment. Furthermore, administering crocin alone improved neural excitability and memory post-chronic stress. Treatment with escitalopram alone also impaired neural excitability within the CA1 region. The use of escitalopram with and without crocin did not enhance memory under chronic stress.

Acute stress causes sex-dependent changes to ventral subiculum synapses, circuitry, and anxiety-like behavior

Experiencing a single severe stressor is sufficient to drive sexually dimorphic psychiatric disease development. The ventral subiculum (vSUB) emerges as a site where stress may induce sexually dimorphic adaptations due to its sex-specific organization and pivotal role in stress integration. Using a 1-hr acute restraint stress model, we uncover that stress causes a net decrease in vSUB activity in females that is potent, long-lasting, and driven by adrenergic receptor signaling. By contrast, males exhibit a net increase in vSUB activity that is transient and driven by corticosterone signaling. We further identified sex-dependent changes in vSUB output to the bed nucleus of the stria terminalis and in anxiety-like behavior in response to stress. These findings reveal striking changes in psychiatric disease-relevant brain regions and behavior following stress with sex-, cell-type, and synapse-specificity that contribute to our understanding of sex-dependent adaptations that may shape stress-related psychiatric disease risk.

In vivo synaptic potency, short-term and long-term plasticity at the hippocampal Schaffer collateral-CA1 synapses: Role of different light-dark cycles in male rats

The changes in the light-dark(L/D) cycle could modify cellular mechanisms in some brain regions. The present study compared the effects of various L/D cycles on invivo synaptic potency, short-term and long-term plasticity in the hippocampal CA1 area, adrenal glands weight(AGWs), corticosterone (CORT) levels, and body weight differences(BWD) in male rats. Male rats were assigned into different L/D cycle groups: L4/D20, L8/D16, L12/D12(control), L16/D8, and L20/D4. The slope, amplitude, and the area under curve(AUC) related to the field excitatory postsynaptic potentials(fEPSPs) were assessed, using the input-output(I/O) functions, paired-pulse(PP) responses at different interpulse intervals, and after the induction of long-term potentiation(LTP) in the hippocampal CA1 area. Also, the CORT levels, AGWs, and BWDs were measured in all groups. The slope, amplitude, and AUC of fEPSP in the I/O functions, all three phases of PP, before and after the LTP induction, were significantly decreased in all experimental groups, especially in the L20/D4 and L4/D20 groups. As such, the CORT levels and AGWs were significantly increased in all experimental groups, especially in the L20/D4 group. Overall, the uncommon L/D cycles (minimum and particularly maximum durations of light) significantly reduced the cellular mechanism of learning and memory. Also, downtrends were observed in synaptic potency, as well as short-term and long-term plasticity. The changes in PP with high interpulse intervals, or activity of GABAB receptors, were more significant than the changes in other PP phases with different L/D durations. Additionally, the CORT levels, adrenal glands, and body weight gain occurred time-independently concerning different L/D lengths.

Neurocognitive effects of stress: a metaparadigm perspective

Stressful experiences, both physical and psychological, that are overwhelming (i.e., inescapable and unpredictable), can measurably affect subsequent neuronal properties and cognitive functioning of the hippocampus. At the cellular level, stress has been shown to alter hippocampal synaptic plasticity, spike and local field potential activity, dendritic morphology, neurogenesis, and neurodegeneration. At the behavioral level, stress has been found to impair learning and memory for declarative (or explicit) tasks that are based on cognition, such as verbal recall memory in humans and spatial memory in rodents, while facilitating those that are based on emotion, such as differential fear conditioning in humans and contextual fear conditioning in rodents. These vertically related alterations in the hippocampus, procedurally observed after subjects have undergone stress, are generally believed to be mediated by recurrently elevated circulating hypothalamic-pituitary-adrenal (HPA) axis effector hormones, glucocorticoids, directly acting on hippocampal neurons densely populated with corticosteroid receptors. The main purposes of this review are to (i) provide a synopsis of the neurocognitive effects of stress in a historical context that led to the contemporary HPA axis dogma of basic and translational stress research, (ii) critically reappraise the necessity and sufficiency of the glucocorticoid hypothesis of stress, and (iii) suggest an alternative metaparadigm approach to monitor and manipulate the progression of stress effects at the neural coding level. Real-time analyses can reveal neural activity markers of stress in the hippocampus that can be used to extrapolate neurocognitive effects across a range of stress paradigms (i.e., resolve scaling and dichotomous memory effects issues) and understand individual differences, thereby providing a novel neurophysiological scaffold for advancing future stress research.

Isorhynchophylline ameliorates stress-induced emotional disorder and cognitive impairment with modulation of NMDA receptors

Introduction

Isorhynchophylline is one of the main active ingredients from Uncaria rhynchophylla, the effects and mechanisms of isorhynchophylline on stress-induced emotional disorders and cognitive impairment remain unclear.

Methods

Long-term potentiation (LTP) in vivo was used for synaptic plasticity evaluation; chronic unpredictable mild stress (CUMS) model was used to evaluate the effect of isorhynchophylline on stress induced emotional disorders and cognitive impairment; sucrose preference test (SPT), open field test (OFT), and elevated plus maze (EPM) were used to evaluate emotional disorders; morris water maze (MWM) test was used to evaluate cognitive impairment; Western blotting (WB) was used to the expression of proteins; high performance liquid chromatography (HPLC) was used to quantify neurotransmitters; Nissl staining was used to identify pathological changes induced by stress.

Results

In this study, we found that isorhynchophylline improved corticosterone-induced in vivo LTP impairment significantly, indicating positive effects on stress. Therefore, 28-day CUMS model was adopted to evaluate the anti-stress effects of isorhynchophylline. The results showed that isorhynchophylline improved CUMS-induced weight loss, anxiety- and depression-like behaviors, and spatial memory impairment. Isorhynchophylline reduced CUMS-induced corticosterone elevation. N-methyl-D-aspartic acid (NMDA) receptors play an important role in the process of emotion and memory. Glutamate and the expression of GluN2B increased in the CUMS mice, while D-serine and the expression of serine racemase (SR) decreased significantly, and isorhynchophylline restored these changes to normal level.

Conclusion

These results indicated that isorhynchophylline ameliorated stress-induced emotional disorders and cognitive impairment, modulating NMDA receptors might be one of the underlying mechanisms.

The impact of different dark chocolate dietary patterns on synaptic potency and plasticity in the hippocampal CA1 area of the rats under chronic isolation stress

INTRODUCTION

Although, stress causes brain dysfunction, consumption of dark chocolate (DC) has positive effects on brain functions. The current study investigated the impact of different DC dietary patterns on synaptic potency and plasticity in the hippocampal CA1 area, as well as food intake and body weight in rats under chronic isolation stress.

METHODS

Thirty-five rats were allocated into five groups of control, stress, and stress accompanied by three DC dietary patterns (stress-compulsory, -optional, and -restricted DC). The stressed rats on a compulsory diet only received DC and the ones on an optional diet received unlimited chow and/or DC. Also, the stressed rats on a restricted diet each received chow freely and only 4 g DC daily. Subsequently, the slope and amplitude of field excitatory postsynaptic potentials (fEPSPs) were assessed based on the Input-Output (I/O) curves and after the longterm potentiation (LTP). Moreover, food intake and body weight were measured for all groups.

RESULTS

The fEPSP slope and amplitude in the I/O curves and after LTP decreased significantly in the stress group compared to the control group. Although the slope and amplitude both enhanced non-significantly in the optional DC diet, these parameters changed significantly in both compulsory and restricted DC dietary patterns compared to the stress group. Also, food intake and body weight decreased significantly in all DC groups.

CONCLUSION

The compulsory and restricted DC dietary patterns reversed the harmful effects of chronic isolation stress on the hippocampal synaptic potency, plasticity, learning, and memory. All DC diets, especially compulsory and restricted ones, reduced food intake and body weight.

Comparing the effects of crocin at different doses on excitability and long-term potentiation in the CA1 area, as well as the electroencephalogram responses of rats under chronic stress

Stress adversely affects the cellular and electrophysiological mechanisms of memory; however, crocin has beneficial effects on brain functions. Nonetheless, the electrophysiological effects of using this active saffron component at different doses are not yet studied in rats under chronic restraint stress. Therefore, this study compared the impact of crocin at different doses on the excitability and long-term potentiation (LTP) in the CA1 area of rats, as well as their electroencephalogram (EEG) responses, hippocampal and frontal cortical glucose levels under chronic restraint stress (an emotional stress model). Forty rats were allocated into five groups of control, sham, restraint stress (6 h/day/21 days), and two stress groups receiving intraperitoneal injections of crocin (30, 60 mg/kg/day). Besides measuring the slope and amplitude of field excitatory postsynaptic potentials (fEPSPs) in the input-output and LTP curves, the EEG waves and hippocampal and frontal cortical glucose levels were assessed in all groups. Chronic restraint stress significantly decreased the fEPSP slope and amplitude in the input-output curves and after LTP induction. Both doses of crocin (60 and particularly 30 mg/kg) significantly improved fEPSP slope and amplitude in the stressed groups. Also, stress and crocin only at a dose of 30 mg/kg altered the EEG waves. Hippocampal and frontal cortical glucose levels displayed no significant differences in the experimental groups. Crocin at doses of 60 mg/kg/day and particularly 30 mg/kg/day reversed the harmful effects of chronic restraint stress on LTP as a cellular memory-related mechanism. However, only the lower dose of crocin affected the electrical brain activity in EEG.

Behavioral profiling reveals an enhancement of dentate gyrus paired pulse inhibition in a rat model of PTSD

We recently introduced behavioral profiling as a translational approach to increase the validity of animal models of posttraumatic stress disorder (PTSD). Behavioral profiling utilizes the response of a 'normal population' of control animals and compares the performance of animals with a history of traumatic stress in different behavioral tests that can capture PTSD-like symptoms. Thus, affected, PTSD-like individuals can be subdivided from resilient trauma-exposed animals. While in our recent study we focused mainly on tests for activity and anxiety, we now expand the behavioral tests battery and include also fear memory and extinction tasks as well as a spatial object recognition test in our behavioral profiling approach. Utilizing underwater trauma as the traumatic event, we found that only a small subset of animals exposed to underwater trauma showed lasting increases in anxiety-like behavior and heightened emotional memory formation. Adding juvenile stress as a model for childhood adversity increased the prevalence of such affected animals and furthermore and induced additional cognitive deficits in a subgroup of such emotionally affected individuals. In addition, multiple affected individual rats displayed increased local circuit activity in the dorsal dentate gyrus, as measured in vivo with paired pulse protocols in anesthetized animals. Together, our findings highlight behavioral profiling, refined by including multiple behavioral tests, as a valid tool to identify PTSD-like vs. resilient individual animals and further suggest that enhanced local inhibition in specific circuits of the dorsal dentate gyrus may be associated with the observed symptoms.

Norepinephrine in the dentate gyrus is involved in spatial learning and memory alteration induced by chronic restraint stress in aged rats

The role of norepinephrine of the hippocampal dentate gyrus in spatial learning and memory alteration induced by chronic restraint stress (CRS, 3 h/day, 6 weeks) was investigated in aged rats. Spatial learning and memory were assessed by the Morris water maze (MWM), and the extracellular concentration of norepinephrine and amplitude of field excitatory postsynaptic potential (fEPSP) were measured in the dentate gyrus during MWM test in freely-moving rats. Next, the involvement of β-adrenoceptors in spatial learning and memory of CRS rats was examined by microinjection of its antagonist (propranolol) into the dentate gyrus. In addition, we observed the expression of brain-derived neurotrophic factor (BDNF) protein and activation of cAMP-response element binding protein (CREB) in the dentate gyrus. Compared with the control group, the basal level of norepinephrine, BDNF expression and CREB activation in the dentate gyrus were increased, and the spatial learning and memory abilities were enhanced in CRS rats. In the control group, the norepinephrine concentration and fEPSP amplitude in the dentate gyrus were increased on the second to fourth days of MWM test, and these responses were significantly enhanced in CRS rats. Furthermore, in CRS rats, propranolol significantly decreased the spatial learning and memory abilities, and attenuated the fEPSP response during MWM test, and the BDNF expression and CREB activation in the dentate gyrus. Our results suggest that norepinephrine activation of β-adrenoceptors in the hippocampal dentate gyrus is involved in spatial learning and memory enhancement induced by CRS in aged rats, in part via modulations of synaptic efficiency and CREB-BDNF signaling pathway.

Changes in Hippocampal Plasticity in Depression and Therapeutic Approaches Influencing These Changes

Depression is a common neurological disease that seriously affects human health. There are many hypotheses about the pathogenesis of depression, and the most widely recognized and applied is the monoamine hypothesis. However, no hypothesis can fully explain the pathogenesis of depression. At present, the brain-derived neurotrophic factor (BDNF) and neurogenesis hypotheses have highlighted the important role of plasticity in depression. The plasticity of neurons and glial cells plays a vital role in the transmission and integration of signals in the central nervous system. Plasticity is the adaptive change in the nervous system in response to changes in external signals. The hippocampus is an important anatomical area associated with depression. Studies have shown that some antidepressants can treat depression by changing the plasticity of the hippocampus. Furthermore, caloric restriction has also been shown to affect antidepressant and hippocampal plasticity changes. In this review, we summarize the latest research, focusing on changes in the plasticity of hippocampal neurons and glial cells in depression and the role of BDNF in the changes in hippocampal plasticity in depression, as well as caloric restriction and mitochondrial plasticity. This review may contribute to the development of antidepressant drugs and elucidating the mechanism of depression.

Deficit of Long-Term Potentiation Induction, but Not Maintenance, in the Juvenile Hippocampus after Neonatal Proinflammatory Stress

CA3-CA1 long-term potentiation (LTP) in the hippocampal slices from juvenile Wistar rats was studied to reveal factors potentially contributing to different sensitivity to neonatal proinflammatory stress (NPS). NPS was induced by intra-peritoneal injections of bacterial lipopolysaccharide (LPS) to neonatal rats (two injections of LPS, or saline in the control group, consecutively on postnatal days 3 and 5 [PND3 and PND5]). In females, a significant effect of NPS on hippocampus development was associated with modifications of long-term synaptic plasticity, the synapses becoming more resistant to LTP induction. LTP deficit in the slices of the NPS group was not associated with a decrease in LTP maintenance, since late LTP generally corresponded to early LTP magnitude, similar in all groups. Moreover, partial correlation revealed significantly higher residual LTP 1 h after high-frequency stimulation in the NPS groups compared to the corresponding value of early LTP in the control groups, suggesting improved consolidation. Both effects were evident in NPS females. A number of males responded to NPS similarly to females, while others were relatively resistant to NPS exposure, a significant increase in variability of LTP magnitude being revealed in NPS males compared to respective females and the control groups. We suggest that postnatal development of long-term plasticity after NPS is similar in animals of both sexes; however, additional specific factor(s) may promote a relative resistance of the male brain.

Resilience to chronic stress is associated with specific neurobiological, neuroendocrine and immune responses

Research into the molecular basis of stress resilience is a novel strategy to identify potential therapeutic strategies to treat stress-induced psychopathologies such as anxiety and depression. Stress resilience is a phenomenon which is not solely driven by effects within the central nervous system (CNS) but involves multiple systems, central and peripheral, which interact with and influence each other. Accordingly, we used the chronic social defeat stress paradigm and investigated specific CNS, endocrine and immune responses to identify signatures of stress-resilience and stress susceptibility in mice. Our results showed that mice behaviourally susceptible to stress (indexed by a reduction in social interaction behaviour) had higher plasma corticosterone levels and adrenal hypertrophy. An increase in inflammatory circulating monocytes was another hallmark of stress susceptibility. Furthermore, prefrontal cortex mRNA expression of corticotrophin-releasing factor (Crf) was increased in susceptible mice relative to resilient mice. We also report differences in hippocampal synaptic plasticity between resilient and susceptible mice. Ongoing studies will interpret the functional relevance of these signatures which could potentially inform the development of novel psychotherapeutic strategies.

Effects of Crocin on Learning and Memory in Rats Under Chronic Restraint Stress with Special Focus on the Hippocampal and Frontal Cortex Corticosterone Levels

Background:

Chronic stress adversely influences brain functions while crocin, as an effective component of saffron, exhibits positive effects on memory processes. This study investigated the effects of different doses of crocin on the improvement of learning and memory as well as corticosterone (CORT) levels in the hippocampus and frontal cortex of rats subjected to chronic stress.

Materials and Methods:

Forty male rats were randomly allocated to five different groups (n = 8): Control, sham; stress (6 h/day for 21 days) groups, and two groups receiving daily intraperitoneal injections of one of two doses (30 and 60 mg/kg) of crocin accompanied by 21 days of restraint stress. Latency was evaluated as a brain function using the passive avoidance test before and one-day after a foot shock. CORT levels were measured in the homogenized hippocampus and frontal cortex.

Results:

Results revealed that chronic stress had a significantly (P < 0.01) negative effect on memory. Crocin (30 and 60 mg/kg), however, gave increase to significantly (P < 0.01 and P < 0.05; respectively) improved memory functions in the stressed rats. Furthermore, the CORT levels in the hippocampus and frontal cortex declined significantly (P < 0.05) in the stress group compared to the control. Only a crocin dose of 30 mg/kg was observed modulate significantly (P < 0.05) the CORT levels in the hippocampus and frontal cortex in the stressed group.

Conclusions:

It was found that the lower crocin dose (30 mg/kg) had more beneficial effects than its higher (60 mg/kg) dose on learning and memory under chronic stress conditions. Moreover, it was speculated that different doses of crocin act on different neurotransmitters and biochemical factors in the brain.

High-intensity treadmill running impairs cognitive behavior and hippocampal synaptic plasticity of rats via activation of inflammatory response

Although appropriate exercise is beneficial for enhancing brain functions, high-intensity exercise (HIE)-induced cognitive dysfunction is causing more and more concerns nowadays. In the present study, we observed the effects of high-intensity treadmill running on the spatial learning of the adult Sprague Dawley male rats in Y-maze (n = 16 per group), and investigated its possible electrophysiological and molecular mechanisms by examining in vivo hippocampal long-term potentiation (LTP), central inflammatory responses, and JNK/p38/ERK signal pathway. The Y-maze active avoidance test showed that high-intensity treadmill running impaired spatial learning ability of rats, with increased error times and prolonged training time in recognizing safety condition. Associated with the cognitive dysfunction, the induction and maintenance of hippocampal LTP were also impaired by the HIE. Furthermore, accompanied by elevated levels of inflammatory factors IL-1β, TNF-α, and iNOS, overactivation of microglia and astrocytes was also found in the CA1 region of hippocampus in the excessive exercise group, indicating an inflammatory response induced by HIE. In addition, Western blot assay showed that the phosphorylation of JNK/p38/ERK proteins was enhanced in the exercise group. These results suggest that exercise stress-induced neuronal inflammatory responses in the hippocampus are associated with HIE-induced cognitive deficits, which may be involved in the upregulation of the JNK/p38/ERK pathway. © 2016 Wiley Periodicals, Inc.

The Effect of Preventive, Therapeutic and Protective Exercises on Hippocampal Memory Mediators in Stressed Rats

BACKGROUND

Exercise plays a significant role in learning and memory. The present study focuses on the hippocampal corticosterone (CORT), interleukin-1 beta (IL-1β), glucose, and brain-derived neurotrophic factor (BDNF) levels in preventive, therapeutic, and protective exercises in stressful conditions.

METHODS

Forty male rats were randomly divided into four groups: the control group and the preventive, therapeutic, and protective exercise groups. The treadmill running was applied at a speed of 20-21m/min and a chronic stress of 6 hours/day for 21 days. Subsequently, the variables were measured in the hippocampus.

RESULTS

The findings revealed that the hippocampal CORT levels in the preventive exercise group had a significant enhancement compared to the control group. In the protective and particularly the therapeutic exercise groups, the hippocampal CORT levels declined. Furthermore, the hippocampal BDNF levels in the preventive and the therapeutic exercise groups indicated significantly decreased and increased, respectively, in comparison with the control group. In the preventive exercise group, however, the hippocampal glucose level turned out to be substantially higher than that in the control group.

CONCLUSION

It appears that the therapeutic exercise group had the best exercise protocols for improving the hippocampal memory mediators in the stress conditions. By contrast, the preventive exercise group could not improve these mediators that had been altered by stress. It is suggested that exercise time, compared to stress, can be considered as a crucial factor in the responsiveness of memory mediators.

Stress biomarker responses to different protocols of forced exercise in chronically stressed rats

Stress is one of the most significant causes of major health problems on a global scale. The beneficial effects of exercise on combating stress, however, are well-established. The present study investigated the stress biomarker responses, such as serum corticosterone, interlukin-1β, and glucose levels, to different (preventive, therapeutic, protective, and continuous) protocols of forced exercise under stress. Male rats were randomly allocated to the following five groups: stressed, preventive, therapeutic, protective, and continuous (and/or pre-stress, post-stress, stress-accompanied, and both pre-stress and stress-accompanied exercise respectively) exercise groups. Stress was applied 6 h/day for 21 days and the treadmill running was employed at a speed of 20-21 m/min for 21 and 42 days. The findings showed that the therapeutic, protective, and continuous exercises led to reduced corticosterone and glucose levels. Whereas, the preventive exercise did not reverse the stress responses, and that the therapeutic exercise led to a significant decline in serum interlukin-1β. It is concluded that protective, therapeutic, and, particularly, continuous exercises lead to significant reductions in serum corticosterone and the associated stress-induced hyperglycemia. Moreover, it appears that the timing and duration of exercise are the two factors contributing to changes in stress biomarker responses.

Shifts in excitatory/inhibitory balance by juvenile stress: A role for neuron-astrocyte interaction in the dentate gyrus

Childhood trauma is a well-described risk factor for the development of stress-related psychopathology such as posttraumatic stress disorder or depression later in life. Childhood adversity can be modeled in rodents by juvenile stress (JS) protocols, resulting in impaired coping with stressful challenges in adulthood. In the current study, we investigated the long-lasting impact of JS on the expression of molecular factors for glutamate and γ-aminobutyric acid (GABA) uptake and turnover in sublayers of the dentate gyrus (DG) using laser microdissection and quantitative real-time polymerase chain reaction. We observed reduced mRNA expression levels after JS for factors mediating astrocytic glutamate and GABA uptake and degradation. These alterations were prominently observed in the dorsal but not ventral DG granule cell layer, indicating a lasting change in astrocytic GABA and glutamate metabolism that may affect dorsal DG network activity. Indeed, we observed increased inhibition and a lack of facilitation in response to paired-pulse stimulation at short interstimulus intervals in the dorsal DG after JS, while no alterations were evident in basal synaptic transmission or forms of long-term plasticity. The shift in paired-pulse response was mimicked by pharmacologically blocking the astrocytic GABA transporter GAT-3 in naïve animals. Accordingly, reduced expression levels of GAT-3 were confirmed at the protein level in the dorsal granule cell layer of rats stressed in juvenility. Together, these data demonstrate a lasting shift in the excitatory/inhibitory balance of dorsal DG network activity by JS that appears to be mediated by decreased GABA uptake into astrocytes.

Sex-specific impairment and recovery of spatial learning following the end of chronic unpredictable restraint stress: potential relevance of limbic GAD

Chronic restraint stress alters hippocampal-dependent spatial learning and memory in a sex-dependent manner, impairing spatial performance in male rats and leaving intact or facilitating performance in female rats. Moreover, these stress-induced spatial memory deficits improve following post-stress recovery in males. The current study examined whether restraint administered in an unpredictable manner would eliminate these sex differences and impact a post-stress period on spatial ability and limbic glutamic acid decarboxylase (GAD65) expression. Male (n=30) and female (n=30) adult Sprague-Dawley rats were assigned to non-stressed control (Con), chronic stress (Str-Imm), or chronic stress given a post-stress recovery period (Str-Rec). Stressed rats were unpredictably restrained for 21 days using daily non-repeated combinations of physical context, duration, and time of day. Then, all rats were tested on the radial arm water maze (RAWM) for 2 days and given one retention trial on the third day, with brains removed 30min later to assess GAD65 mRNA. In Str-Imm males, deficits occurred on day 1 of RAWM acquisition, an impairment that was not evident in the Str-Rec group. In contrast, females did not show significant outcomes following chronic stress or post-stress recovery. In males, amygdalar GAD65 expression negatively correlated with RAWM performance on day 1. In females, hippocampal CA1 GAD65 positively correlated with RAWM performance on day 1. These results demonstrate that GABAergic function may contribute to the sex differences observed following chronic stress. Furthermore, unpredictable restraint and a recovery period failed to eliminate the sex differences on spatial learning and memory.