Repeated Short-term (2h×14d) Emotional Stress Induces Lasting Depression-like Behavior in Mice

Antidepressant activity of phytochemicals of Mangifera indica seeds assisted by integrated computational analysis

Mangifera indica L., also known as mango, is a tropical fruit that belongs to the Anacardiaceae family and is prized for its juiciness, unique flavour, and worldwide popularity. The current study aimed to probe into antidepressant power (ADP) of MIS in animals and confirmation of ADP with in silico induced-fit molecular docking. The depression model was prepared by exposing mice to various stressors from 9:00 am to 2:00 pm during 42 days study period. MIS extract and fluoxetine were given daily for 30 min before exposing animals to stressors. ADP was evaluated by various behavioural tests and biochemical analysis. Results showed increased physical activity in mice under behavioural tests, plasma nitrite and malondialdehyde (MDA) levels and monoamine oxidase A (MAO-A) activity decreased dose-dependently in MIS treated mice and superoxide dismutases (SOD) levels increased in treated groups as compared to disease control. With the peculiar behaviour and significant interactions of the functional residues of target proteins with selected ligands along with the best absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties, it is concluded that catechin could be the best MAO-A inhibitor at a binding energy of -8.85 kcal/mol, and two hydrogen bonds were generated with Cys406 (A) and Gly443 (A) residues of the active binding site of MAO-A enzyme. While catechin at -6.86 kcal/mol generated three hydrogen bonds with Ala263 (A) and Gly434 (A) residues of the active site of monoamine oxidase B (MAO-B) enzyme and stabilized the best conformation. Therefore, it is highly recommended to test the selected lead-like compound catechin in the laboratory with biological system analysis to confirm its activity as MAO-A and MAO-B inhibitors so it can be declared as one of the novel therapeutic options with anti-depressant activity. Our findings concluded that M. indica seeds could be a significant and alternative anti-depressant therapy.

Behavioral Engagement With Playable Objects Resolves Stress-Induced Adaptive Changes by Reshaping the Reward System

BACKGROUND

The reward system regulates motivated behavior, and repeated practice of specific motivated behavior might conversely modify the reward system. However, the detailed mechanisms by which they reciprocally regulate each other are not clearly understood.

METHODS

Mice subjected to chronic restraint stress show long-lasting depressive-like behavior, which is rescued by continual engagement with playable objects. A series of molecular, pharmacological, genetic, and behavioral analyses, combined with microarray, liquid chromatography, and chemogenetic tools, are used to investigate the neural mechanisms of antidepressive effects of playable objects.

RESULTS

Here, we show that repeated restraint induces dopamine surges into the nucleus accumbens-lateral shell (NAc-lSh), which cause upregulation of the neuropeptide PACAP in the NAc-lSh. As repeated stress is continued, the dopamine surge by stressors is adaptively suppressed without restoring PACAP upregulation, and the resulting enhanced PACAP inputs from NAc-lSh neurons to the ventral pallidum facilitate depressive-like behaviors. Continual engagement with playable objects in mice subjected to chronic stress remediates reduced dopamine response to new stressors, enhanced PACAP upregulation, and depressive-like behaviors. Overactivation of dopamine D₁ receptors over the action of D₂ receptors in the NAc-lSh promotes depressive-like behaviors. Conversely, inhibition of D₁ receptors or PACAP upregulation in the NAc-lSh confers resilience to chronic stress-induced depressive-like behaviors. Histochemical and chemogenetic analyses reveal that engagement with playable objects produces antidepressive effects by reshaping the ventral tegmental area-to-NAc-lSh and NAc-lSh-to-ventral pallidum circuits.

CONCLUSIONS

These results suggest that behavioral engagement with playable objects remediates depressive-like behaviors by resolving stress-induced maladaptive changes in the reward system.

Mice can recognise water depths and will avoid entering deep water

Rodents are averse to bodies of water, and this aversion has been exploited in experiments designed to study stress in mice. However, a few studies have elucidated the characteristics of murine water aversion. In this study, we investigated how mice behave in and around areas filled with water. Using variants of the open field test that contained pools of water at corners or sides of the field, we recorded the movements of mice throughout the field under various conditions. When the water was 8 mm deep, the mice explored the water pool regardless of whether an object was placed within it, but when the water was 20 mm deep, the mice were less willing to enter it. When the mice were placed on a dry area surrounded by 3 mm-deep water, they explored the water, but when they were surrounded by 8 mm-deep water, they stayed within the dry area. Our results indicate that mice exhibit exploratory behaviours around water, they can recognise water depths and avoid unacceptably deep water, and their willingness to enter water may be reduced by situational anxiety. Our experimental method could be used to investigate water-related anxiety-like behaviours in mice.

A novel mouse model of postpartum depression using emotional stress as evaluated by nesting behavior

Postpartum depression is an important mental health issue not only for the mother but also for the child’s development, other family members, and the society. An appropriate animal model is desired to elucidate the pathogenesis of postpartum depression. However, methods for stress loading during pregnancy have not been established. Behavioral experiments to investigate postpartum depression-like behaviors should be conducted without stress because behavioral tests affect rearing behaviors such as lactation. Therefore, we developed a new mouse model of postpartum depression using a psychological stress method. Mating partners were made to witness their partners experiencing social defeat stress and then listen to their cries. Emotional stress loading during pregnancy significantly increased postpartum depression-like behaviors. Postpartum depression also affected nurturing behaviors and caused disturbances in pup care. Furthermore, nesting behavior was impaired in the stressed group, suggesting that the observation of nesting behavior may be useful for assessing social dysfunction in postpartum depression. These results demonstrate the utility of this new mouse model of postpartum depression.

Pharmacological Screening of Mangifera indica Seeds for Antidepressant-like Action Along with a Mechanistic Study

Depression is emerging as a major global issue. There are several antidepressants available in the market, but their efficacy is usually unpredictable. Therefore, there is a need to find an alternative therapeutic agent with better therapeutic efficacy and availability. In the current investigation, the antidepressant-like action of the aqueous methanolic extract of Mangifera indica seeds (25, 50, and 100 mg/kg) was evaluated by two predictive models like the tail suspension test and forced swimming test along with the determination of the mechanism of action working behind this action. The results of the acute treatment with the extract show a dose-dependent reduction in the duration of immobility in both models. The antidepressant-like action of the extract (100 mg/kg) was blocked by the administration of p-chlorophenyl alanine, α-methyl-p-tyrosine, prazosin, and sulpiride while remaining unaffected with propranolol. In contrast, the administration of d-serine along with the extract (a full agonist of glycine/N-methyl-d-aspartate, NMDA, receptors) diminished the anti-immobility action. The administration of the extract along with nitro-l-arginine-methyl ester synergizes into the anti-immobility action of the extract, and intake of l-arginine remained unable to effect this action, whereas sildenafil blocks the effect. The antidepressant-like action of the extract is probably due to the involvement of serotonergic and adrenergic (mainly α receptors are involved) systems, an NMDA receptor complex, and the nitric oxide pathway.

The impact of handling technique and handling frequency on laboratory mouse welfare is sex-specific

Handling is a well-known source of stress to laboratory animals and can affect variability of results and even compromise animal welfare. The conventional tail handling in mice has been shown to induce aversion and anxiety-like behaviour. Recent findings demonstrate that the use of alternative handling techniques, e.g. tunnel handling, can mitigate negative handling-induced effects. Here, we show that technique and frequency of handling influence affective behaviour and stress hormone release of subjects in a sex-dependent manner. While frequent tail handling led to a reduction of wellbeing-associated burrowing and increased despair-like behaviour in male mice, females seemed unaffected. Instead, they displayed a stress response to a low handling frequency, which was not detectable in males. This could suggest that in terms of refinement, the impact in handling could differ between the sexes. Independently from this observation, both sexes preferred to interact with the tunnel. Mice generally explored the tunnel more often than the tail-handling hands of the experimenter and showed more positively rated approaches, e.g. touching or climbing, and at the same time, less defensive burrowing, indicating a strong preference for the tunnel.

Erinacine A-Enriched Hericium erinaceus Mycelium Produces Antidepressant-Like Effects through Modulating BDNF/PI3K/Akt/GSK-3β Signaling in Mice

Antidepressant-like effects of ethanolic extract of Hericium erinaceus (HE) mycelium enriched in erinacine A on depressive mice challenged by repeated restraint stress (RS) were examined. HE at 100, 200 or 400 mg/kg body weight/day was orally given to mice for four weeks. After two weeks of HE administration, all mice except the control group went through with 14 days of RS protocol. Stressed mice exhibited various behavioral alterations, such as extending immobility time in the tail suspension test (TST) and forced swimming test (FST), and increasing the number of entries in open arm (POAE) and the time spent in the open arm (PTOA). Moreover, the levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) were decreased in the stressed mice, while the levels of interleukin (IL)-6 and tumor necrosis factor (TNF)-α were increased. These changes were significantly inverted by the administration of HE, especially at the dose of 200 or 400 mg/kg body weight/day. Additionally, HE was shown to activate the BDNF/TrkB/PI3K/Akt/GSK-3β pathways and block the NF-κB signals in mice. Taken together, erinacine A-enriched HE mycelium could reverse the depressive-like behavior caused by RS and was accompanied by the modulation of monoamine neurotransmitters as well as pro-inflammatory cytokines, and regulation of BDNF pathways. Therefore, erinacine A-enriched HE mycelium could be an attractive agent for the treatment of depressive disorders.

Physical Exercise Counteracts Stress-induced Upregulation of Melanin-concentrating Hormone in the Brain and Stress-induced Persisting Anxiety-like Behaviors

Chronic stress induces anxiety disorders, whereas physical exercise is believed to help people with clinical anxiety. In the present study, we investigated the mechanisms underlying stress-induced anxiety and its counteraction by exercise using an established animal model of anxiety. Mice treated with restraint for 2 h daily for 14 days exhibited anxiety-like behaviors, including social and nonsocial behavioral symptoms, and these behavioral impairments lasted for more than 12 weeks after the stress treatment was removed. Despite these lasting behavioral changes, wheel-running exercise treatment for 1 h daily from post-stress days 1 - 21 counteracted anxiety-like behaviors, and these anxiolytic effects of exercise persisted for more than 2 months, suggesting that anxiolytic effects of exercise stably induced. Repeated restraint treatment up-regulated the expression of the neuropeptide, melanin-concentrating hormone (MCH), in the lateral hypothalamus, hippocampus, and basolateral amygdala, the brain regions important for emotional behaviors. In an in vitro study, treatment of HT22 hippocampal cells with glucocorticoid increased MCH expression, suggesting that MCH upregulation can be initially triggered by the stress hormone, corticosterone. In contrast, post-stress treatment with wheel-running exercise reduced the stress-induced increase in MCH expression to control levels in the lateral hypothalamus, hippocampus and basolateral amygdala. Administration of an MCH receptor antagonist (SNAP94847) to stress-treated mice was therapeutic against stress-induced anxiety-like behaviors. These results suggest that repeated stress produces long-lasting anxiety-like behaviors and upregulates MCH in the brain, while exercise counteracts stress-induced MCH expression and persisting anxiety-like behaviors.

Chronic Antidepressant Treatment in Normal Mice Induces Anxiety and Impairs Stress-coping Ability

Antidepressants are clinically used for patients with major depression. Antidepressant treatments in certain groups of patients are effective for relieving depression as well as anxiety disorder. However, it is not clearly known whether the use of current antidepressants in healthy persons is beneficial for upcoming depression- and anxiety-inducing life events. To address this question, normal mice were intraperitoneally administered with imipramine or fluoxetine for more than 2 weeks, and behaviors related to anxiety and depression were evaluated. Mice treated with imipramine or fluoxetine for more than 14 days exhibited significantly decreased immobility time in the forced swim test and tail suspension test, but these mice exhibited enhanced anxiety in several behavioral tests. Furthermore, chronic antidepressant treatments followed by sub-threshold level of stress in normal mice profoundly aggravated antidepressant-induced anxiety-like behaviors without further affecting depression-related behaviors. Chronic antidepressant treatments followed by sub-threshold level of stress produced swollen vesicles and ulcerations on the lips as well as a watery and inflammatory nose. Mice given chronic antidepressant treatments displayed intestinal abnormalities evidenced by a highly enlarged and inflamed small intestine full of defecation materials. These results suggest that chronic antidepressant treatment in normal mice provokes anxiety-like behaviors and impairs their stress-coping ability.

Chronic stress impairs α1-adrenoceptor-induced endocannabinoid-dependent synaptic plasticity in the dorsal raphe nucleus

Alpha 1-adrenergic receptors (α1-ARs) control the activity of dorsal raphe nucleus (DRn) serotonin (5-HT) neurons and play crucial role in the regulation of arousal and stress homoeostasis. However, the precise role of these receptors in regulating glutamate synapses of rat DRn 5-HT neurons and whether chronic stress exposure alters such regulation remain unknown. In the present study, we examined the impact of chronic restraint stress on α1-AR-mediated regulation of glutamate synapses onto DRn 5-HT neurons. We found that, in the control condition, activation of α1-ARs induced an inward current and long-term depression (LTD) of glutamate synapses of DRn 5-HT neurons. The α1-AR LTD was initiated by postsynaptic α1-ARs but mediated by a decrease in glutamate release. The presynaptic expression of the α1-AR LTD was signaled by retrograde endocannabinoids (eCBs). Importantly, we found that chronic exposure to restraint stress profoundly reduced the magnitude of α1-AR LTD but had no effect on the amplitude of α1-AR-induced inward current. Chronic restraint stress also reduced the CB1 receptor-mediated inhibition of EPSC and the eCB-mediated depolarization-induced suppression of excitation. Collectively, these results indicate that chronic restraint stress impairs the α1-AR LTD by reducing the function of presynaptic CB1 receptors and reveal a novel mechanism by which noradrenaline controls synaptic strength and plasticity in the DRn. They also provide evidence that chronic stress impairs eCB signaling in the DRn, which may contribute, at least in part, to the dysregulation of the stress homeostasis.

Inhibition of stress-induced hepatic tryptophan 2,3-dioxygenase exhibits antidepressant activity in an animal model of depressive behaviour

The role of hepatic tryptophan 2,3 dioxygenase (TDO) was assessed in the provocation of stress-induced depression-related behaviour in the rat. TDO drives tryptophan metabolism via the kynurenine pathway (KP) and leads to the production of neuroactive metabolites including kynurenine. A single 2 h period of restraint stress in adult male Sprague-Dawley rats provoked an increase in circulating concentrations of the glucocorticoid corticosterone and induction of hepatic TDO expression and activity. Repeated exposure to stress (10 d of 2 h restraint each day) provoked an increase in immobility in the forced swimming test (FST) indicative of depression-related behaviour. Immobility was accompanied by an increase in the circulating corticosterone concentrations, expression and activity of hepatic TDO and increase in the expression of TDO in the cerebral cortex. Increased TDO activity was associated with raised circulating kynurenine concentrations and a reduction in circulating tryptophan concentrations indicative of KP activation. Co-treatment with the TDO inhibitor allopurinol (20 mg/kg, i.p.), attenuated the chronic stress-related increase in immobility in the FST and the accompanying increase in circulating kynurenine concentrations. These findings indicate that stress-induced corticosterone and consequent activation of hepatic TDO, tryptophan metabolism and production of kynurenine provoke a depression-related behavioural phenotype. Inhibition of stress-related hepatic TDO activity promotes antidepressant activity. TDO may therefore represent a promising target for the treatment of depression associated with stress-related disorders in which there is evidence for KP activation.

Anti-Depressant Like Effect of Methyl Gallate Isolated from Acer barbinerve in Mice

In the present study, the anti-depressant like effect of methyl gallate (MG) isolated from the stem bark of Acer barbinerve was examined in ICR mice. Body weight (BDW) and blood glucose (BDG) levels significantly decreased in the repeated restraint stress (RRS) group (2 h/day for 14 days) compared to the no stress (NS) group. To examine the effect of MG on RS-induced BDW loss and hypoglycemia, MG (10 mg/kg) and the anti-depressant fluoxetine (10 mg/kg) were administered daily for 14 days. Orally administered MG and fluoxetine significantly attenuated the RS-induced BDW loss and hypoglycemia. Interestingly, MG administered mice showed increased BDG levels in the normal and glucose feeding condition. Chronic RS-subjected mice showed immobilized and depressed behaviors. The effect of MG on the depressed behaviors was evaluated using the tail-suspension test (TST) and the forced swimming test (FST). In both tests, RS-induced immobilized behaviors were significantly reversed in MG and fluoxetine administered groups. Taken together, MG significantly attenuated the RS-induced BDW loss, hypoglycemia, and depressed behaviors. Considering that decreased BDG levels (hypoglycemia) can cause depression, MG may exert its anti-depressant like effect by preventing hypoglycemia. Our results suggest that MG isolated from A. barbinerve can exert anti-depressant like effect, and could be used as a new and natural anti-depressant therapy.

1-Methyl-1,2,3,4-tetrahydroisoquinoline, an endogenous Neuroprotectant and MAO inhibitor with antidepressant-like properties in the rat

Oxidative stress is a major contributing factor in a range of brain pathologies and in the etiology of depression. 1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) is an endogenous substance which is present in the mammalian brain and exhibits neuroprotective, and monoamine oxidase (MAO)-inhibiting properties. In the present study, in order to investigate the potential role of 1MeTIQ as an antidepressant, we tested antidepressant-like effects of 1MeTIQ in comparison with desipramine (a classic antidepressant) in the forced swimming test (FST), and using HPLC methodology, we measured the concentrations of monoamines (dopamine, noradrenaline, serotonin) and the rate of their metabolism. 1MeTIQ given alone as well as in combination with desipramine produced an antidepressant-like effect and decreased the immobility time in the FST. Neurochemical data have shown that 1MeTIQ like desipramine, activated the noradrenergic system. However, the mechanism of action of 1MeTIQ is broader than the actions of desipramine, and 1MeTIQ inhibits the MAO-dependent oxidation of dopamine and serotonin in all investigated structures. We can conclude that 1MeTIQ exhibits antidepressant-like activity in the FST in the rat. The mechanism of its antidepressant action differs from desipramine and seems to be mostly associated with the inhibition of the catabolism of monoamines and their increased concentrations in the brain. 1MeTIQ seems to be very beneficial from the clinical point of view as a reversible MAO inhibitor with a significant antidepressant effects.

Ketamine elicits sustained antidepressant-like activity via a serotonin-dependent mechanism

RATIONALE

Behavioural antidepressant-like effects of ketamine have been reported in the forced swimming test (FST). The mechanisms mediating such effects are unknown.

OBJECTIVES

As serotonin (5-HT) is an important transmitter mediating antidepressant responsiveness in the FST, the influence of 5-HT depletion on the antidepressant-like effect of ketamine was assessed.

METHODS

The effect of ketamine (25 mg/kg, i.p., 1 or 24 h prior to test) was assessed in the FST in naive rats or animals subjected to 5-HT depletion, repeated stress or following a combination of 5-HT depletion and stress. Endogenous 5-HT was depleted using the tryptophan hydroxylase inhibitor para-chlorophenylalanine (3 × 150 mg/kg, i.p.). Stress was induced by physical restraint (2 h/day for 10 days).

RESULTS

In naive rats, ketamine administered 24 or 1 h prior to test produced a characteristic antidepressant-like reduction in immobility time in the FST. Depletion of 5-HT blocked this reduction in immobility when ketamine was administered 24 h prior FST, indicative of 5-HT dependency. The increase in immobility provoked by repeated restraint stress (2 h/day for 10 days) was blocked by ketamine when administered 24 h prior to FST, but this effect dissipated when animals were subjected to 5-HT depletion.

CONCLUSIONS

These observations are consistent with a role for 5-HT in mediating sustained antidepressant activity of ketamine in the FST. Molecular and cellular changes induced by ketamine may produce a rapid adaptation of 5-HT transmission which underlies the antidepressant response.

NADPH oxidase mediates depressive behavior induced by chronic stress in mice

Stress is a potent risk factor for depression, yet the underlying mechanism is not clearly understood. In the present study, we explored the mechanism of development and maintenance of depression in a stress-induced animal model. Mice restrained for 2 h daily for 14 d showed distinct depressive behavior, and the altered behavior persisted for >3 months in the absence of intervention. Acute restraint induced a surge of oxidative stress in the brain, and stress-induced oxidative stress progressively increased with repetition of stress. In vitro, the stress hormone glucocorticoid generated superoxide via upregulation of NADPH oxidase. Consistently, repeated restraints increased the expression of the key subunits of NADPH oxidase, p47phox and p67phox, in the brain. Moreover, stressed brains markedly upregulated the expression of p47phox to weak restress evoked in the poststress period, and this molecular response was reminiscent of amplified ROS surge to restress. Pharmacological inhibition of NADPH oxidase by the NADPH oxidase inhibitor apocynin during the stress or poststress period completely blocked depressive behavior. Consistently, heterozygous p47phox knock-out mice (p47phox(+/-)) or molecular inhibition of p47phox with Lenti shRNA-p47phox in the hippocampus suppressed depressive behavior. These results suggest that repeated stress promotes depressive behavior through the upregulation of NADPH oxidase and the resultant metabolic oxidative stress, and that the inhibition of NADPH oxidase provides beneficial antidepression effects.