Optimized animal model to mimic the reality of stress-induced depression in the clinic

A comparative analysis of depressive-like behavior: Exploring sex-related differences and insights

Profiling the variability related to the estrous cycle is essential for assessing depressive-like behavior and screening drugs. This study compares circulating plasma corticosterone levels [CORT] and behavioral alterations in mice exposed to sucrose preference, forced swimming, and tail suspension tests (SPT, FST, and TST, respectively). While SPT exposure did not significantly alter [CORT], FST and TST showed notable changes. Mice in the TST exhibited increased movement and decreased immobility time compared to FST, suggesting a lower likelihood of depressive-like behavior in male mice. Notably, during the proestrus phase, female mice displayed the highest tendency for depressive-like behavior and elevated [CORT], but similar response to antidepressants (imipramine and fluoxetine). The inherent stress of the FST and TST tasks appears to influence [CORT] as well as depressant and antidepressant effects. These comparisons provide valuable insights for further behavioral phenotyping, model sensitivity assessment, and deepen our neurobiological understanding of depression in the context of drug screening.

Chronic Inhibition of Aggressive Behavior Induces Behavioral Change in Mice

Suppression of anger is more common than its expression among Asian individuals. Emotional suppression is considered an unhealthy emotional regulation. Most studies on emotional suppression have concluded that suppression adversely affects social outcomes, with approximately 5% of the world's population suffering from emotional disorders. However, anger suppression has not received academic attention, and details of the effects of chronic anger suppression on the central nervous system remain unclear. In this study, we performed the resident-intruder test to investigate the effect of chronic suppression of aggressive behavior in mice using a behavioral test battery and to clarify whether suppression of this aggressive behavior is stressful for mice. Mice chronically inhibited aggressive behavior and lost weight. Mice with inhibited aggressive behavior showed a reduced percentage of immobility time during the tail suspension test as well as no changes in activity, anxiety-like behavior, muscle strength, or temperature sensitivity. This study provides scientific evidence for the effects of chronic aggressive behavior inhibition on the body and central nervous system.

Study of the Effects of Cordia myxa Fruit Extract on Induced Animal Model of Depression in Male Rats

Depression is one of the most common mental illnesses. Herbal medications such as ginseng and peony have recently gained popularity in treating depression due to their safety, efficacy, and cost-effectiveness. Therefore, the present study aimed to evaluate the actions of Cordia myxa (C. myxa) fruit extract on the model of chronic unpredictable mild stress (CUMS) and antioxidant enzymes system in male rats' brains. Sixty male rats were divided into six groups (n=10). Group 1 (control) was neither exposed to CUMS nor received any treatment, while group 2 was exposed to CUMS for 24 days with normal saline treatment for 14 days, group 3 was exposed to CUMS for 24 days and received 10 mg/kg fluoxetine daily on day 10 for 14 days, and group 4, 5, and 6 were exposed to CUMS for 24 days and received C. myxa extract (125, 250, and 500 mg/kg, respectively) on day 10 for 14 days. The antidepressant effect of fluoxetine and C. myxa extract was evaluated using a forced swim test (FST). At the end of the experiments, animals were sacrificed by decapitation; and antioxidant enzyme levels, catalase (CAT), and superoxide dismutase (SOD) were determined by enzyme-linked immunosorbent assays kits (ELISA) on rats' brain tissues. All groups subjected to CUMS showed a significant rise in duration of immobility on the tenth day compared to day zero. The CUMS showed a decrease in antioxidant enzyme levels, and groups treated with extract showed significant rise in enzyme levels (SOD and CAT) compared to group 2. According to this recent study, C. myxa may have an antidepressant-like action.

Pedicularis resupinata Extract Prevents Depressive-like Behavior in Repeated Corticosterone-Induced Depression in Mice: A Preliminary Study

Excessive corticosterone (CORT), resulting from a dysregulated hypothalamic–pituitary–adrenal (HPA) axis, is associated with cognitive impairment and behavioral changes, including depression. In Korean oriental medicine, Pedicularis resupinata is used for the treatment of inflammatory diseases such as rheumatoid arthritis. However, the antidepressant properties of P. resupinata have not been well characterized. Here, the antidepressant-like effects of P. resupinata extract (PRE) were evaluated in terms of CORT-induced depression using in vivo models. HPLC confirmed that acteoside, a phenylethanoid glycoside, was the main compound from PRE. Male ICR mice (8 weeks old) were injected with CORT (40 mg/kg, i.p.) and orally administered PRE daily (30, 100, and 300 mg/kg) for 21 consecutive days. Depressive-like behaviors were evaluated using the open-field test, sucrose preference test, passive avoidance test, tail suspension test, and forced swim test. Treatment with a high dose of PRE significantly alleviated CORT-induced, depressive-like behaviors in mice. Additionally, repeated CORT injection markedly reduced brain-derived neurotrophic factor levels, whereas total glucocorticoid receptor (GR) and GR phosphorylation at serine 211 were significantly increased in the mice hippocampus but improved by PRE treatment. Thus, our findings suggest that PRE has potential antidepressant-like effects in CORT-induced, depressive-like behavior in mice.

Maternal Deprivation Increased Vulnerability to Depression in Adult Rats Through DRD2 Promoter Methylation in the Ventral Tegmental Area

OBJECTIVE

Early life adversity is a risk factor for depression in adulthood; however, the underlying mechanisms are not well understood. This study aims to investigate the effect of DNA methylation of DRD2 gene on early life stress-induced depression in adult rats.

METHODS

Newborn Sprague-Dawley rats were randomly assigned to four groups: maternal deprivation group (MD), chronic unpredictable stress (CUS) group, maternal deprivation plus chronic unpredictable stress (MD/CUS) group, and normal control group (NOR). Behaviors were measured by open field test (OFT), sucrose preference test (SPT), and Original Research Article forced swimming test (FST). Fecal CORT level was detected by ELISA. Bisulfite amplicon sequencing PCR was used to assess methylation levels of DRD2 promoter.

RESULTS

CUS and MD/CUS rats had a significantly shorter total distance, longer immobility time, and higher CORT level, while MD and MD/CUS rats had a significantly lower percentage of central distance, more feces, lower rate of sucrose preference, and lower levels of DRD2 protein and mRNA in the VTA than NOR rats. CUS rats showed a significantly higher DRD2 mRNA and protein levels in the VTA than NOR rats. CUS, MD, and MD/CUS rats showed a significantly higher level of DRD2 promoter methylation than NOR rats. CORT level was significantly correlated with the sucrose preference rate in SPT, the immobility time in FST, the total distance, and the number of fecal pellets in OFT. DRD2 protein level was significantly correlated with the sucrose preference rate and the number of fecal pellets. DRD2 mRNA level was significantly correlated with the percentage of central distance and the number of fecal pellets in OFT. The level of DRD2 promoter methylation was significantly correlated with the sucrose preference rate, immobility time, total distance, the percentage of central distance, and the number of fecal pellets.

CONCLUSIONS

Early life MD increased vulnerability to stress-induced depressive-like behavior in adult rats. Enhanced DRD2 promoter methylation in the VTA may increase the susceptibility to depression.

Antidepressant-like effect of flaxseed in rats exposed to chronic unpredictable stress

INTRODUCTION

Depression is a serious mental illness. However, a significant proportion of patients with depression fail to achieve remission with antidepressant therapies. This study was conducted to explore the antidepressant-like effect of flaxseed oil and flour in an animal model with depression-like behaviors induced by chronic unpredictable stress (CUS).

METHODS

Rats were randomly divided into five groups: normal control (Sham-Sham), CUS plus saline (S-SN), CUS plus escitalopram (S-Esc), CUS plus flaxseeds oil (S-FO), and CUS plus flaxseed flour (S-FF). Behaviors were tested using sucrose preference test and forced swimming test. The serum BDNF concentration, hippocampal BDNF mRNA, and protein expression were measured by enzyme-linked immunosorbent assay, real-time PCR, and Western blot, respectively.

RESULTS

The sucrose preference rate was significantly higher in S-FO and S-FF rats than in S-SN and S-Esc rats (p < .01), and lower in S-Esc rats than in Sham-Sham rats (p < .01). The immobility time was significantly shorter in S-FO and S-FF rats than in S-SN rats (p < .01), and shorter in S-Esc rats than in S-SN rats (p < .01). Plasma BDNF concentrations were significantly lower in S-FO, S-FF, and S-Esc rats than in Sham-Sham rats (p < .01); BDNF was lower in S-FO, S-FF, and S-SN rats than in S-Esc rats. The hippocampal BDNF protein expression was significantly higher in S-Esc rats than in S-SN rats (p < .05). The hippocampal BDNF mRNA expression was significantly higher in S-Esc rats than in S-SN rats (p < .01). The BDNF gene expression in plasma and the hippocampus negatively correlated with the immobility time (p < .05), but BDNF gene expression in the hippocampus positively correlated with the sucrose preference rate (p < .05).

CONCLUSION

Flaxseed oil and flaxseed flour exert antidepressant-like effect in rats exposed to chronic stress. Flaxseed may have a therapeutic effect on depression.

mGluR5 Facilitates Long-Term Synaptic Depression in a Stress-Induced Depressive Mouse Model

BACKGROUND

Glutamatergic system has been known to play a role in the pathogenesis of major depression disorder by inducing N-methyl-d-aspartate receptor-dependent long-term depression (LTD) or metabotropic glutamate receptors (mGluR)-dependent LTD. Here, we characterized the LTD in a chronic social defeat stress (CSDS)-induced depressive mouse model.

METHODS

CSDS was used to induce the depressive-like behaviors in C57BL/6 male mice, which were assessed using sucrose preference test and social interaction test. The synaptic strength including LTD and long-term potentiation (LTP) induced by paired-pulse low frequency stimulation (PP-LFS) was measured using whole-cell recording technique.

RESULTS

CSDS induced depressive-like behaviors and facilitated PP-LFS-induced LTD in hippocampal CA3-CA1 pathway in the susceptible mice. Interestingly, mGluR5 but not N-methyl-d-aspartate receptor mediated the PP-LFS-induced LTD. In addition, mGluR5 agonist dihydroxyphenylglycine promoted PP-LFS-induced LTD specifically in susceptible mice, which was diminished by activating the BDNF/TrkB signaling pathway.

CONCLUSIONS

Our results suggest that mGluR5-dependent LTD might be responsible for the development of depressive-like behaviors in CSDS-induced depression mice model.

Resilient Phenotype in Chronic Mild Stress Paradigm Is Associated with Altered Expression Levels of miR-18a-5p and Serotonin 5-HT1a Receptor in Dorsal Part of the Hippocampus

Disturbed serotonergic signaling in the hippocampus observed in many individuals vulnerable to stress has been suggested as one of the primary factors contributing to the development of depression. However, little is known about the physiology of the brain in the resilient phenotype. Resilient subjects maintain a positive mood and psychological balance despite being under the stress influence. In our study, we generated stress-vulnerable and resilient rats by using a chronic mild stress (CMS) paradigm. Using different molecular approaches, we revealed that resilient animals exhibited a significantly decreased expression level of miR-18a-5p and, in the same time, an elevated level of 5-HT1AR in dorsal, but not ventral, part of the hippocampus. Described biochemical changes were not observed in animals behaviorally vulnerable to stress. Further, in vitro analysis showed that miR-18a-5p may be a negative epigenetic regulator of 5-HT1AR since the treatment of adult hippocampal neurons with miR-18a-5p mimic significantly lowered the expression level of mRNA encoding 5-HT1AR. Moreover, bioinformatic analysis of potential target genes expressed in the hippocampus and being regulated by miR-18a-5p showed that this microRNA may regulate biological processes, such as axonogenesis, which are important in the functioning of the hippocampus in both rats and humans. All these molecular features may contribute to serotonergic homeostatic balance at the level of serotonin turnover observed in hippocampi of resilient but not stress-vulnerable rats. Delineation of further molecular and biochemical markers underlying resilience to stress may contribute to the development of new antidepressant strategies which will restore resilient phenotype in depressed patients.

Anti-depressive-like effect of 2-phenylethanol inhalation in mice

Rose oil has traditionally been used to treat psychiatric disorders, but the scientific basis of this treatment remains poorly understood. The main odor component of rose oil is 2-phenylethanol (2-PE), but the neuropsychological effects of 2-PE have not been investigated in detail. Thus, we aimed to investigate the effects of 2-PE on mouse behavior. We first investigated whether 2-PE is attractive or repulsive to mice. After 2-PE inhalation, the mice underwent a series of behavioral experiments, such as the elevated plus maze, open field, Y-maze, tail-suspension, and Porsolt forced-swim tests. Mice did not have a strong interest in 2-PE but were not repelled by it nor were fearful. In the open field test, mice that had inhaled 2-PE spent less time in the center area, while in the tail suspension test, their immobility time decreased. There was no change in cognitive function, activity level, muscle strength, or aggression in these mice. Our results suggest that 2-PE elicits neuropsychological effects that alter the behavior of mice and may also elicit anti-depressive effects. Inhalation of rose oil containing 2-PE may be effective against depression and stress-related diseases.

Treatment with escitalopram modulates cardiovascular function in rats

Considering depression is three times more common in cardiac patients compared to the normal population and selective serotonin reuptake inhibitors (SSRI) as drug of choice for treating patients with cardiovascular disease and depression, our work aims to evaluate the cardiovascular effects of treatment for 21 days with escitalopram (5 mg/kg/day, ip) in rats. The treatment caused an increase in mean arterial pressure concomitant with a decrease in heart rate. Concerning heart rate variability, there was a significant reduction in the sympathetic component and an elevation of the parasympathetic component, indicating that escitalopram caused an autonomic imbalance with parasympathetic predominance. In addition, we observed a decrease in both low and very low frequency power in blood pressure variability. The cardiac autonomic blockade indicated an increase in parasympathetic modulation to the heart with escitalopram chronic treatment. However, no change was observed on baroreflex activity. On the other hand, there was a decrease in pressure response during acute restraint stress with no changes in the tachycardia response. These findings showed that despite the escitalopram be a relatively safe drug it can cause tonic effects on cardiovascular function as well as during aversive situations.

Alterations of DNA Methylation at GDNF Gene Promoter in the Ventral Tegmental Area of Adult Depression-Like Rats Induced by Maternal Deprivation

Objective: To study the expression and DNA methylation of the Glial cell line-derived neurotrophic factor (GDNF) gene in the development of depression-like behaviors in rats experiencing maternal deprivation stress in early life. Methods: Newborn SD rats were randomly assigned to a normal control group (NOR) or maternal deprivation group (MD). An open field test (OPT), sucrose preference test (SPT), and a forced swimming test (FST) were used to evaluate rats' behaviors. Protein, mRNA, and methylation levels were measured by ELISA/Western blot, real-time PCR, and BiSulfte Amplicon sequencing PCR, respectively. Results: MD rats had significantly shorter total distance and more fecal pellets in OPT, a lower sucrose preference rate in SPT, and a longer immobility time in FST than NOR rats. Compared with NOR rats, MD rats showed a significantly higher plasma corticosterone (CORT) level. The levels of plasma dopamine (DA) and the GDNF were significantly lower in the MD rats than in NOR rats. In the ventral tegmental area (VTA) tissues, MD rats had a significantly higher level of methylation at the GDNF gene promoter than NOR rats. The expression of the GDNF mRNA and protein were significantly lower in MD rats than in NOR rats. The total distance was significantly correlated with plasma DA and GDNF, the DNA methylation level at the GDNF promoter and the GDNF mRNA level in the VTA. Fecal pellets showed a significant correlation with plasma CORT. The sucrose preference rate was significantly correlated with plasma DA, the DNA methylation level at the GDNF promoter and the GDNF mRNA level in the VTA. Immobility time showed a significant correlation with the plasma DA, the plasma GDNF and the GDNF mRNA level in the VTA. Conclusion: up-regulation of DNA methylation at the GDNF gene promotor and the subsequent down-regulation of the GDNF gene expression in the VTA, may be involved in the development of depression-like behaviors in rats experiencing MD in early life.