Chronic mild stress (CMS) revisited: consistency and behavioural-neurobiological concordance in the effects of CMS

Norepinephrine and Glucocorticoids Modulate Chronic Unpredictable Stress-Induced Increase in the Type 2 CRF and Glucocorticoid Receptors in Brain Structures Related to the HPA Axis Activation

The stress response is multifactorial and enrolls circuitries to build a coordinated reaction, leading to behavioral, endocrine, and autonomic changes. These changes are mainly related to the hypothalamus-pituitary-adrenal (HPA) axis activation and the organism's integrity. However, when self-regulation is ineffective, stress becomes harmful and predisposes the organism to pathologies. The chronic unpredictable stress (CUS) is a widely used experimental model since it induces physiological and behavioral changes and better mimics the stressors variability encountered in daily life. Corticotropin-releasing factor (CRF) and glucocorticoids (GCs) are deeply implicated in the CUS-induced physiological and behavioral changes. Nonetheless, the CUS modulation of CRF receptors and GR and the norepinephrine role in extra-hypothalamic brain areas were not well explored. Here, we show that 14 days of CUS induced a long-lasting HPA axis hyperactivity evidenced by plasmatic corticosterone increase and adrenal gland hypertrophy, which was dependent on both GCs and NE release induced by each stress session. CUS also increased CRF₂ mRNA expression and GR protein levels in fundamental brain structures related to HPA regulation and behavior, such as the lateral septal nucleus intermedia part (LSI), ventromedial hypothalamic nucleus (VMH), and central nucleus of the amygdala (CeA). We also showed that NE participates in the CUS-induced increase in CRF₂ and GR levels in the LSI, reinforcing the locus coeruleus (LC) involvement in the HPA axis modulation. Despite the CUS-induced molecular changes in essential areas related to anxiety-like behavior, this phenotype was not observed in CUS animals 24 h after the last stress session.

Neuroprotective effects of microRNA-211-5p on chronic stress-induced neuronal apoptosis and depression-like behaviours

Findings from recent studies have revealed that microRNAs (miRNAs) are related to numerous neurological disorders. However, whether miRNAs regulate neuronal anomalies involved in the pathogenesis of depression remain unclear. In the present study, we screened miRNA expression profiles in the CA1 hippocampus of a rat model of depression and found that a specific miRNA, microRNA-211-5p, was significantly down-regulated in depressed rats. When miR-211-5p was up-regulated in these rats, neuronal apoptosis within the CA1 area was suppressed, effects which were accompanied with an amelioration of depression-like behaviours in these rats. These neuroprotective effects of miR-211-5p in depressed rats appear to result through suppression of the Dyrk1A/ASK1/JNK signalling pathway within the CA1 area. In further support of this proposal are the findings that knock-down of miR-211-5p within the CA1 area of normal rats activated the Dyrk1A/ASK1/JNK pathway, resulting in the promotion of neuronal apoptosis and display of depression-like behaviours in these rats. Taken together, these results demonstrate that deficits in miR-211-5p contribute to neuronal apoptosis and thus depression-like behaviours in rats. Therefore, the miR-211-5p/Dyrk1A pathway may be critically involved in the pathogenesis of depression and serve as a potential therapeutic target for the treatment of depression.

Catalpol ameliorates depressive-like behaviors in CUMS mice via oxidative stress-mediated NLRP3 inflammasome and neuroinflammation

The purpose of the present study was to investigate whether catalpol exhibited neuroprotective effects in chronic unpredictable mild stress (CUMS) mice through oxidative stress-mediated nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin-domain-containing 3 (NLRP3) inflammasome and neuroinflammation. Deficits in behavioral tests, including open field test (OFT), forced swim test (FST), and elevated plus-maze test (EPM), were ameliorated following catalpol administration. To study the potential mechanism, western blots, quantitative real-time PCR (qRT-PCR) analysis and immunofluorescence imaging were performed on the hippocampus samples. We found that the defects of behavioral tests induced by CUMS could be reversed by the absence of NLRP3 and NLRP3 inflammasome might be involved in the antidepressant effects of catalpol on CUMS mice. Similar to the NLRP3 inflammasome, the expression of interleukin-1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), and inducible nitride oxide synthase (iNOS) were increased after CUMS. The current study demonstrated that catalpol possessed anti-inflammatory effect on CUMS mice and inhibited microglial polarization to the M1 phenotype. In addition, the activity of mitochondrial oxidative stress might be involved in the NLRP3 activation, which was proved by the downregulation of NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), and cleaved IL-1β, after the administration of mitochondrion-targeted antioxidant peptide SS31. Taken together, we provided evidence that catalpol exhibited antidepressive effects on CUMS mice possibly via the oxidative stress-mediated regulation of NLRP3 and neuroinflammation.

Anhedonic Type Behavior and Anxiety Profile of Wistar-UIS Rats Subjected to Chronic Social Isolation

Chronic Social Isolation (CSI) is a model of prolonged stress employed in a variety of studies to induce depression and anxious behavior in rats. The present study aims to evaluate the effect of CSI on male Wistar rats in terms of "anhedonic-type" behavior in the Sucrose Preference Test (SPT) and anxiogenic profile in the elevated-plus-maze (EPM) test, as well as evaluating the effect of resocialization upon sucrose consumption. A total of 24 adolescent male Wistar rats were evaluated. The animals were housed either together (communally) or socially isolated for 21 days, and then exposed for four consecutive days to the SPT test [water vs. a 32% sucrose solution (SS)]. Four days later, they were again subjected to the SPT test (32% vs. 0.7% SS), and then tested on the EPM apparatus 3 days later. Following the completion of the anxiogenic profile of the model, the animals were resocialized for 72 h and then re-tested once again using the SPT (32% vs. 0.7% SS). Twenty-four hours after this final consumption, the animals were euthanized to record the weight of their adrenal glands (AG). It was found that exposure to CSI produces anhedonic-type behavior and an anxiogenic profile in adolescent male rats, as evidenced in both the SPT and EPM tests, as well as in the animals' physiological stress response. It was also demonstrated that resocialization does not reverse the anhedonic-type behavior, nor the physiological response to stress.

Effect of long-term confinement on metabolic and physiological parameters in mice

Long-term and mild confinement or isolation in an enclosed environment can occur in situations such as disasters, specific political, economic or social events, nuclear shelters, seabed exploration, polar expeditions, and space travel. To investigate the effects of stress caused by long-term confinement in an enclosed environment in mammals, we divided 8-week-old C57BL/6J mice into four groups that were housed in a closed environment with a narrow metabolic cage (stress group), normal metabolic cage (control group), conventional cage (conventional group) or conventional cage with wire mesh floor (wire mesh group). The phenotypes of the mice were examined for four weeks, followed by behavioral tests. Weight gain suppression was observed in the stress group. Continuous analysis of these mice every two minutes for four weeks using an implanted measuring device showed a significantly decreased amount of spontaneous activity and subcutaneous temperature in the stress group. After housing in each environment for four weeks, the behavioral tests of mice in the stress group also revealed a shorter latency to fall off in the rotarod test and shorter stride length and interstep distance in the footprint test. Interestingly, the lower spontaneous activity of mice in the stress group was rescued by housing in conventional cages. These results suggest a temporary effect of long-term confinement in an enclosed environment as a chronic and mild stress on homeostasis in mammals.

Baicalin promotes hippocampal neurogenesis via the Wnt/β-catenin pathway in a chronic unpredictable mild stress-induced mouse model of depression

Hippocampal neurogenesis is known to be related to depressive symptoms. Increasing evidence indicates that Wnt/β-catenin signaling regulates multiple aspects of adult hippocampal neurogenesis. Baicalin is a major flavonoid compound with multiple pharmacological effects such as anti-inflammatory, anti-apoptotic, and neuroprotective effects. The current study aimed to explore the antidepressant effects of baicalin and its possible molecular mechanisms affecting hippocampal neurogenesis via the regulation of the Wnt/β-catenin signaling pathway. A chronic mild unpredictable stress (CUMS) model of depression was used in the study. The CUMS-induced mice were treated with baicalin (50 and 100 mg/kg) for 21 days, orally, and the fluoxetine was used as positive control drug. The results indicated that baicalin alleviated CUMS-induced depression-like behaviour, and improved the nerve cells' survival of the hippocampal dentate gyrus (DG) in CUMS-induced depression of model mice and increased Ki-67- and doublecortin (DCX)-positive cells to restore CUMS-induced suppression of hippocampal neurogenesis. The related proteins in the Wnt/β-catenin signaling pathway, which declined in the CUMS-induced depression model of mice, were upregulated after baicalin treatment, including Wingless3a (Wnt3a), dishevelled2 (DVL2), and β-catenin. Further study found that the phosphorylation rate of glycogen synthase kinase-3β (GSK3β) and β-catenin nuclear translocation increased, as the levels of the β-catenin target genes cyclinD1, c-myc, NeuroD1, and Ngn2 upregulated after baicalin treatment. In conclusion, these findings suggest that baicalin may promote hippocampal neurogenesis, thereby exerting the antidepressant effect via regulation of the Wnt/β-catenin signaling pathway.

Estrogen administration attenuates post-stroke depression by enhancing CREB/BDNF/TrkB signaling in the rat hippocampus

A previous study demonstrated that 17β-estradiol (E2), which is an antidepressant, can ameliorate post-stroke depression (PSD); however, the underlying mechanisms governing this remain largely unknown. Therefore, the present study developed a PSD model in rats, which was induced by left middle cerebral artery occlusion followed by exposure to chronic mild stress for 2 weeks. The results revealed that the activity of the cAMP response element-binding protein (CREB), a cellular transcription factor, and the associated brain-derived neurotrophic factor (BDNF)/tyrosine kinase B (TrkB) signaling were all attenuated in the hippocampus in PSD rats. The depression-like behaviors were significantly improved after treatment with E2, along with increased CREB and the BDNF/TrkB signaling activity. These results provide novel insight into the molecular basis of PSD, and suggest the potential involvement of CREB/BDNF/TrkB signaling in E2-mediated improvement of PSD in rats.

Activation of liver X receptors prevents emotional and cognitive dysfunction by suppressing microglial M1-polarization and restoring synaptic plasticity in the hippocampus of mice

Depression is a long-lasting and persistent mood disorder in which the regulatory mechanisms of neuroinflammation are thought to play a contributing role to the physiopathology of the condition. Previous studies have shown that liver X receptors (LXRs) can regulate the activation of microglia and neuroinflammation. However, the role of LXRs in depression remains to be fully understood. In this study, we hypothesized that stress impairs the function of LXRs and that the LXRs agonist GW3965 plays a potential anti-depressive role by inhibiting neuroinflammation. The anti-depressive effects of GW3965 were evaluated in both chronic unpredictable mild stress (CUMS) and lipopolysaccharide (LPS) models. The LXRs antagonist GSK2033 was also employed to block LXRs. Behavioural tests were performed to measure depression-like phenotypes and learning abilities. Electrophysiological recordings and Golgi staining were used to measure the plasticity of the dentate gyrus synapse. The expression of synapse and neuroinflammation related proteins were evaluated by Western blotting and immunofluorescence. The activation of LXRs by GW3965 prevented emotional and cognitive deficits induced by either CUMS or LPS. GW3965 prevented the decreased level of LXR-β induced by CUMS. The activation of LXRs significantly improved the impairment of synaptic plasticity, prevented the up-regulation of inflammatory factors and inhibited NF-κB phosphorylation and microglial M1-polarization in both models. The antidepressive-like effects of GW3965 were blocked by GSK2033 in the CUMS and LPS models. Our data suggest that inhibition of the LXRs signalling pathway may be a key driver in the pathogenesis of neuroinflammation during depression and that LXRs agonists have a high potential in the treatment of depression.

Food insecurity in older female mice affects food consumption, coping behaviors, and memory

Food insecurity correlates with poor physical and mental health in older individuals, but has not been studied in a laboratory animal model. This explorative study developed a laboratory mouse model for analyzing the impact of food insecurity on food consumption, stress coping mechanisms, exploratory behavior, and memory. 18-month-old CD-1 female mice were assigned to either the food insecurity exposure condition (31 mice, 8 cages) or the control condition (34 mice, 8 cages) by cage. Over four weeks, the mice that were exposed to food insecurity received varied, unpredictable portions of their baseline food consumption (50%, 75%, 125%, 150% of baseline) for four days, followed by ad libitum access for three days, to approximate the inconsistent access to food observed in households experiencing food insecurity. Behavioral tasks were conducted before and after food insecurity exposure. Mice in the food insecurity exposure condition ate less compared to control mice during food insecurity (two-way ANOVA: group x time interaction: F7,93 = 10.95, P < 0.01) but ate more when given access to high fat food (two-way ANOVA, group x time interaction: F1,14 = 11.14, P < 0.01). Mice exposed to food insecurity increased active escaping behaviors in the forced swim test (repeated measures two-way ANOVA, group x time interaction: F1,63 = 5.40, P = 0.023). Exploratory behaviors were unaffected by food insecurity. Mice exposed to food insecurity showed a reduction in memory (repeated measures two-way ANOVA, group x time interaction: F1,61 = 4.81, P = 0.037). These results suggest that exposure to food insecurity is associated with differences in food consumption patterns, active coping mechanisms, and memory. The behavioral changes associated with food insecurity may inform research on food insecurity's impact on health in elderly humans.

Exploratory study on neurochemical effects of low-intensity pulsed ultrasound in brains of mice

There is now a relatively large body of evidence suggesting a relationship between dysfunction of myelin and oligodendrocytes and the etiology of several neuropsychiatric disorders, including depression and schizophrenia, and also suggesting that ultrasound methods may alleviate some of the symptoms of depression. We have applied low-intensity pulsed ultrasound (LIPUS) to the brains of mice treated with the demyelinating drug cuprizone, a drug that has been used as the basis for a rodent model relevant to a number of psychiatric and neurologic disorders including depression, schizophrenia, and multiple sclerosis. Prior to conducting the studies in mice, preliminary studies were carried out on the effects of LIPUS in vitro in neuron-like SH-SY5Y cells and primary glial cells. In subsequent studies in mice, female C57BL/6 mice were restrained in plastic tubes for 20 min daily with the ultrasound transducer near the end of the tube directly above the mouse's head. LIPUS was used at an intensity of 25 mW/cm² once daily for 22 days in control mice and in mice undergoing daily repetitive restraint stress (RRS). Behavioral or neurochemical studies were done on the mice or the brain tissue obtained from them. The studies in vitro indicated that LIPUS stimulation at an intensity of 15 mW/cm² delivered for 5 min daily for 3 days in an enclosed sterile cell culture plate in an incubator increased the viability of SH-SY5Y and primary glial cells. In the studies in mice, LIPUS elevated levels of doublecortin, a marker for neurogenesis, in the cortex compared to levels in the RRS mice and caused a trend in elevation of brain levels of brain-derived neurotrophic factor in the hippocampus relative to control levels. LIPUS also increased sucrose preference (a measure of the attenuation of anhedonia, a common symptom of several psychiatric disorders) in the RRS model in mice. The ability of LIPUS administered daily to rescue damaged myelin and oligodendrocytes was studied in mice treated chronically with cuprizone for 35 days. LIPUS increased cortex and corpus callosum levels of myelin basic protein, a protein marker for mature oligodendrocytes, and neural/glial antigen 2, a protein marker for oligodendrocyte precursor cells, relative to levels in the cuprizone + sham animals. These results of this exploratory study suggest that future comprehensive time-related studies with LIPUS on brain chemistry and behavior related to neuropsychiatric disorders are warranted. Exploratory Study on Neurochemical Effects of Low Intensity Pulsed Ultrasound in Brains of Mice. Upper part of figure: LIPUS device and in-vitro cell experimental set-up. The center image is the LIPUS generating box; the image in the upper left shows the cell experiment set-up; the image in the upper right shows a zoomed-in sketch for the cell experiment; the image in the lower left shows the set-up of repetitive restraint stress (RRS) with a mouse; the image in the lower middle shows the set-up of LIPUS treatment of a mouse; the image in the lower right shows a zoomed-in sketch for the LIPUS treatment of a mouse.

The effectiveness of continuous and interval exercise preconditioning against chronic unpredictable stress: Involvement of hippocampal PGC-1α/FNDC5/BDNF pathway

Various exercise-training types are known to prevent depression, but mechanisms underlying their beneficial effects remain unknown. In the present study, the preconditioning effect of continuous and interval exercise on stress-induced depression was evaluated. Adult male Wistar rats in the exercise groups were made to run on a motorized treadmill, five sessions per week for six weeks. After that, to induce the depression model, the rats were exposed to chronic unpredictable stress for three weeks. Behavioral tests were assessed by open field, elevated plus maze, and forced swim tests. Hippocampal PGC-1α, FNDC5, and BDNF protein expression by Western blot and serum corticosterone by ELISA were detected. In the present results, after continuous and interval exercise periods, locomotor activity, the number of entries and time spent in the open arms were increased, and immobility time was significantly reduced. PGC-1α, FNDC5, and BDNF protein levels had a significant increase, and serum corticosterone did not change. Also, interval exercise training increased PGC-1α and FNDC5 more than continuous. Chronic unpredictable stress reduced the positive changes caused by exercise training, although, except FNDC5, exercise preconditioned groups experienced less significant adverse changes in most variables. These findings showed that both continuous and interval exercise preconditioning with increasing hippocampal PGC-1α, FNDC5, and BDNF proteins and improve the anxiety- and depression-like behaviors have a protective effect against chronic unpredictable stress.

Antidepressant-like effects of helicid on a chronic unpredictable mild stress-induced depression rat model: Inhibiting the IKK/IκBα/NF-κB pathway through NCALD to reduce inflammation

We previously reported that helicid, an active plant monomer of Helicid nilgirica Bedd, had good antidepressant pharmacological activities. However, the potential mechanism of action remains unknown. Current investigation showed the antidepressant-like effects of helicid and its effects on the neurocalcin delta (NCALD) gene, and its mechanism of action through a depression model in rats exposed to chronic unpredictable mild stress (CUMS). We evaluated depression symptoms using the sucrose preference test (SPT), open field test (OFT), and forced swimming test (FST). By silencing NCALD and using rescue experiments, the IL-6, iNOS, IL-1β, COX-2, and TNF-α levels in the hippocampus or peripheral blood were determined using western blotting and ELISAs. The expression of IKKβ, p-IкBα, p-IKKβ, NF-кB p65, and IкBα were tested using western blots of the cytoplasmic or nuclear samples. Helicid and silencing NCALD relieved the CUMS-irritated depressive-like actions of rats, which were shown by increased consumption of sucrose, numbers of rearings, total running distance, zone crossings, and reduced immobility times. Helicid or silencing NCALD reversed the CUMS-induced high levels of IL-1β, COX-2, IL-6, TNF-α, and iNOS in the hippocampus or peripheral blood. Helicid or silencing NCALD also reduced the expressions of p-IκBα and p-IKKβ in the cytoplasm and the expression of nuclear NF-κB p 65 in hippocampus, and simultaneously elevated cytoplasmic expressions of IκBα, IKKβ, and NF-κB p65 in the hippocampus. Notably, after NCALD overexpression, the biochemical indices of rat helicid administration were reversed. In conclusion, the antidepressant action of helicid was mediated through NCALD in rats of CUMS by repressing hippocampal neuro-inflammation and abating the activation of the IKK/IκBα/NF-κB pathway.

Protocatechuic acid attenuates chronic unpredictable mild stress induced-behavioral and biochemical alterations in mice

Amelioration of oxidative stress via promoting the endogenous antioxidant system and enhancement of monoamines in brain were the important underlying antidepressant mechanism of protocatechuic acid (PCA). The aim of the present study is to explore the potential antidepressant mechanism(s) PCA in chronic unpredictable mild stress (CUMS) mice. Mice were subjected to CUMS protocol for 4 weeks, and administered with PCA (100 and 200 mg/kg) and fluoxetine (20 mg/kg) for 24 days (from day 8th to 31st). Behavioral (sucrose preference, immobility time, exploratory behavior), and biochemical alterations such as serum corticosterone, brain derived neurotrophic factor (BDNF), inflammatory cytokines, tumor necrosis factor- α (TNF-α), interleukin-6 (IL-6), and antioxidants parameters were investigated. Experimental findings revealed that CUMS subjected mice exhibited significant impairment in behavioral alterations, such as increased immobility time, impaired preference to the sucrose solution, BDNF levels and, serum corticosterone, cytokines, malondialdehyde (MDA) formation with impaired antioxidants in the hippocampus and cerebral cortex. Administration of PCA to CUMS mice attenuated the immobility time, serum corticosterone, cytokines TNF-α, and IL-6, MDA formation and improved sucrose preference, including restoration of BDNF level. Thus, the present findings demonstrated the antidepressant potential of PCA which is largely achieved probably through maintaining BDNF level, and by modulation of the oxidative stress response, cytokines systems, and antioxidant defense system in mice.

Ursolic acid abrogates depressive-like behavior and hippocampal pro-apoptotic imbalance induced by chronic unpredictable stress

Emerging evidence has shown that ursolic acid exerts antidepressant-like effects, however, its ability to elicit an antidepressant-like response in rodents subjected to stress model that mimics behavioral and neurochemical alterations found in depression remains to be determined. Thus, this study investigated the possible antidepressant-like effect of ursolic acid in mice subjected to chronic unpredictable stress (CUS) for 14 days, and whether this effect could be associated with the modulation of serum corticosterone levels and hippocampal Bcl-2/Bax mRNA expression. Our results indicated that CUS induced a depressive-like behavior, as demonstrated by an increase in the immobility time and latency to first grooming in the tail suspension test and splash test, respectively. Conversely, the repeated administration of ursolic acid (0.1 mg/kg, p.o.) or fluoxetine (10 mg/kg, p.o.) in the last 7 days of CUS completely prevented CUS-induced behavioral alterations, suggesting an antidepressant-like effect. Additionally, CUS significantly increased the mRNA expression of Bax (pro-apoptosis marker), but not Bcl-2 (anti-apoptosis marker) in the hippocampus. Moreover, reduced hippocampal mRNA expression of Bcl-2/Bax ratio was detected in CUS-exposed mice. Ursolic acid, but not fluoxetine, prevented CUS-induced increase in the expression of Bax, but both ursolic acid and fluoxetine prevented CUS-induced reduction on Bcl-2/Bax ratio. Furthermore, neither CUS nor treatments with ursolic acid or fluoxetine altered serum corticosterone levels. Our study unveils the ability of ursolic acid to prevent the depressive-like behavior induced by stress and the modulation of Bcl-2/Bax expression could be associated with this response.

Cognitive effects of the GSK-3 inhibitor "lithium" in LPS/chronic mild stress rat model of depression: Hippocampal and cortical neuroinflammation and tauopathy

Low-dose repeated lipopolysaccharide pre-challenge followed by chronic mild stress (LPS/CMS) protocol has been introduced as a rodent model of depression combining the roles of immune activation and chronic psychological stress. However, the impact of this paradigm on cognitive functioning has not been investigated hitherto.

METHODS

This study evaluated LPS/CMS-induced cognitive effects and the role of glycogen synthase kinase-3β (GSK-3β) activation with subsequent neuroinflammation and pathological tau deposition in the pathogenesis of these effects using lithium (Li) as a tool for GSK-3 inhibition.

RESULTS

LPS pre-challenge reduced CMS-induced neuroinflammation, depressive-like behavior and cognitive inflexibility. It also improved spatial learning but increased GSK-3β expression and exaggerated hyperphosphorylated tau accumulation in hippocampus and prefrontal cortex. Li ameliorated CMS and LPS/CMS-induced depressive and cognitive deficits, reduced GSK-3β over-expression and tau hyperphosphorylation, impeded neuroinflammation and enhanced neuronal survival.

CONCLUSION

This study draws attention to LPS/CMS-triggered cognitive changes and highlights how prior low-dose immune challenge could develop an adaptive capacity to buffer inflammatory damage and maintain the cognitive abilities necessary to withstand threats. This work also underscores the favorable effect of Li (as a GSK-3β inhibitor) in impeding exaggerated tauopathy and neuroinflammation, rescuing neuronal survival and preserving cognitive functions. Yet, further in-depth studies utilizing different low-dose LPS challenge schedules are needed to elucidate the complex interactions between immune activation and chronic stress exposure.

The antidepressant-like effects of the water extract of Panax ginseng and Polygala tenuifolia are mediated via the BDNF-TrkB signaling pathway and neurogenesis in the hippocampus

ETHNOPHARMACOLOGY RELEVANCE

The water extract of Panax ginseng (GT) and Polygala tenuifolia (YT), the main constituents of the commonly used kai-xin-san formula of traditional Chinese medicine, represents SY. It possesses strong neuroprotective effects. Using behavioural tests, we have previously established that the SY formulation exerts superior antidepressant activity than that of GT or YT.

AIM

To elucidate the impact of SY treatment on chronic unpredictable mild stress (CUMS)-induced depressive-like behaviours and the prospective mechanism related to hippocampal neurogenesis and the BDNF signaling pathway.

METHODS

We exposed Sprague-Dawley rats (male; 180-200 g) to CUMS for 35 days. The rats in the experimental treatment groups were daily treated with either fluoxetine (10 mg kg-1d-1) or SY (67.5, 135, or 270 mg kg-1d-1) orally until the behavioural tests (tail suspension test [TST], novelty-suppressed feeding test [NSFT], sucrose preference test [SPT], and forced swim test [FST]) were completed. We assessed the modifications in the hippocampal neurogenesis and the BDNF signaling pathway post-treatment with CUMS and SY. Additionally, K252a, a tyrosine protein kinase inhibitor, was utilized to evaluate the antidepressant mechanisms of SY.

RESULT

s: The results of SPT, NSFT, FST, and TST in CUMS-exposed rats confirmed the antidepressant actions of SY. Additionally, SY treatment induced the BDNF signaling pathway and reversed the hippocampal neurogenesis caused by CUMS. Moreover, we found that the TrkB antagonist K252a blocked SY effects on behavioural improvement, inhibited the incremental effects of SY on hippocampal neurogenesis, and eliminated the impact of SY on BDNF-TrkB signaling activation. Thus, the impact of SY treatment on BDNF signaling molecules (pAkt, pERK1/2, and pCREB) were significantly inhibited by K252a.

CONCLUSIONS

This study showed that SY acted as an antidepressant in rats exhibiting CUMS-induced depressive-like behaviours, and was facilitated by promoting hippocampal neurogenesis and the BDNF signaling pathway activation. Thus, SY could act as a potential novel supplement or adjuvant to prevent or treat clinical depressive disorders.

V1a and V1b vasopressin receptors within the paraventricular nucleus contribute to hypertension in male rats exposed to chronic mild unpredictable stress

Depression is an independent nontraditional risk factor for cardiovascular disease and mortality. The chronic unpredictable mild stress (CMS) rat model is a validated model of depression. Within the paraventricular nucleus (PVN), vasopressin (VP) via V1aR and V1bR have been implicated in stress and neurocardiovascular dysregulation. We hypothesized that in conscious, unrestrained CMS rats versus control, unstressed rats, PVN VP results in elevated arterial pressure (MAP), heart rate, and renal sympathetic nerve activity (RSNA) via activation of V1aR and/or V1bR. Male rats underwent 4 wk of CMS or control conditions. They were then equipped with hemodynamic telemetry transmitters, PVN cannula, and left renal nerve electrode. V1aR or V1bR antagonism dose-dependently inhibited MAP after VP injection. V1aR or V1bR blockers at their ED50 doses did not alter baseline parameters in either control or CMS rats but attenuated the pressor response to VP microinjected into PVN by ∼50%. Combined V1aR and V1bR inhibition completely blocked the pressor response to PVN VP in control but not CMS rats. CMS rats required combined maximally inhibitory doses to block either endogenous VP within the PVN or responses to microinjected VP. Compared with unstressed control rats, CMS rats had higher plasma VP levels and greater abundance of V1aR and V1bR transcripts within PVN. Thus, the CMS rat model of depression results in higher resting MAP, heart rate, and RSNA, which can be mitigated by inhibiting vasopressinergic mechanisms involving both V1aR and V1bR within the PVN. Circulating VP may also play a role in the pressor response.

Positive modulation of NMDA receptors by AGN-241751 exerts rapid antidepressant-like effects via excitatory neurons

Dysregulation of the glutamatergic system and its receptors in medial prefrontal cortex (mPFC) has been implicated in major depressive disorder. Recent preclinical studies have shown that enhancing NMDA receptor (NMDAR) activity can exert rapid antidepressant-like effects. AGN-241751, an NMDAR positive allosteric modulator (PAM), is currently being tested as an antidepressant in clinical trials, but the mechanism and NMDAR subunit(s) mediating its antidepressant-like effects are unknown. We therefore used molecular, biochemical, and electrophysiological approaches to examine the cell-type-specific role of GluN2B-containing NMDAR in mediating antidepressant-like behavioral effects of AGN-241751. We demonstrate that AGN-241751 exerts antidepressant-like effects and reverses behavioral deficits induced by chronic unpredictable stress in mice. AGN-241751 treatment enhances NMDAR activity of excitatory and parvalbumin-inhibitory neurons in mPFC, activates Akt/mTOR signaling, and increases levels of synaptic proteins crucial for synaptic plasticity in the prefrontal cortex. Furthermore, cell-type-specific knockdown of GluN2B-containing NMDARs in mPFC demonstrates that GluN2B subunits on excitatory, but not inhibitory, neurons are necessary for antidepressant-like effects of AGN-241751. Together, these results demonstrate antidepressant-like actions of the NMDAR PAM AGN-241751 and identify GluN2B on excitatory neurons of mPFC as initial cellular trigger underlying these behavioral effects.

Zebrafish Tools for Deciphering Habenular Network-Linked Mental Disorders

Simple Summary

Everything that we think, feel or do depends on the function of neural networks in the brain. These are highly complex structures made of cells (neurons) and their interconnections (axons), which develop dependent on precisely coordinated interactions of genes. Any gene mutation can result in unwanted alterations in neural network formation and concomitant brain disorders. The habenula neural network is one of these important circuits, which has been linked to autism, schizophrenia, depression and bipolar disorder. Studies using the zebrafish have uncovered genes involved in the development of this network. Intriguingly, some of these genes have also been identified as risk genes of human brain disorders highlighting the power of this animal model to link risk genes and the affected network to human disease. But can we use the advantages of this model to identify new targets and compounds with ameliorating effects on brain dysfunction? In this review, we summarise the current knowledge on techniques to manipulate the habenula neural network to study the consequences on behavior. Moreover, we give an overview of existing behavioral test to mimic aspects of mental disorders and critically discuss the applicability of the zebrafish model in this field of research.

Abstract

The prevalence of patients suffering from mental disorders is substantially increasing in recent years and represents a major burden to society. The underlying causes and neuronal circuits affected are complex and difficult to unravel. Frequent disorders such as depression, schizophrenia, autism, and bipolar disorder share links to the habenular neural circuit. This conserved neurotransmitter system relays cognitive information between different brain areas steering behaviors ranging from fear and anxiety to reward, sleep, and social behaviors. Advances in the field using the zebrafish model organism have uncovered major genetic mechanisms underlying the formation of the habenular neural circuit. Some of the identified genes involved in regulating Wnt/beta-catenin signaling have previously been suggested as risk genes of human mental disorders. Hence, these studies on habenular genetics contribute to a better understanding of brain diseases. We are here summarizing how the gained knowledge on the mechanisms underlying habenular neural circuit development can be used to introduce defined manipulations into the system to study the functional behavioral consequences. We further give an overview of existing behavior assays to address phenotypes related to mental disorders and critically discuss the power but also the limits of the zebrafish model for identifying suitable targets to develop therapies.

Identification of 14-3-3 epsilon as a regulator of the neural apoptotic pathway for chronic-stress-induced depression

Major depression is a prevalent and long-lasting psychiatric illness with severe functional impairment and high suicide rate. We have previously shown that the ventrolateral orbital cortex (VLO) plays a key role in the stress responses in mice, but the underlying mechanisms remains unclear. Here, we used proteomic method to identify differentially expressed proteins in VLO of chronic unpredictable mild stress (CUMS) mice. Of 4,953 quantified proteins, 45 proteins were differentially expressed following CUMS. The integrated pathway analyses identified 14-3-3ε and TrkB signaling as differentially downregulated in association with stress-induced depressive-like behaviors. 14-3-3ε overexpression in VLO relieved the depressive-like behaviors by rescue of Bad-mediated apoptosis. Moreover, treatment with the 14-3-3ε stabilizer FC-A precluded neuronal apoptotic signaling in VLO of depressed mice. Because 14-3-3ε provides significant protection against chronic stress, boosting 14-3-3ε expression, pharmacological stabilization of 14-3-3s (e.g. with FC-A) is identified as an exciting therapeutic target for major depression.

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Novel screening of chronic mild stress-induced depression phenotypes in mice

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Proteomics identify 14-3-3ε as a key modulator of depressive behaviors in VLO

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14-3-3ε partially reversed depressive behaviors through neural apoptotic pathway

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14-3-3ε stabilizer FC-A ameliorates depression phenotypes after chronic mild stress

Periodontal diseases and depression: A pre-clinical in vivo study

AIM

To analyse, through a pre-clinical in vivo model, the possible mechanisms linking depression and periodontitis at behavioural, microbiological and molecular levels.

MATERIALS AND METHODS

Periodontitis (P) was induced in Wistar:Han rats (oral gavages with Porphyromonas gingivalis and Fusobacterium nucleatum) during 12 weeks, followed by a 3-week period of Chronic Mild Stress (CMS) induction. Four groups (n = 12 rats/group) were obtained: periodontitis and CMS (P+CMS+); periodontitis without CMS; CMS without periodontitis; and control. Periodontal clinical variables, alveolar bone levels (ABL), depressive-like behaviour, microbial counts and expression of inflammatory mediators in plasma and brain frontal cortex (FC), were measured. ANOVA tests were applied.

RESULTS

The highest values for ABL occurred in the P+CMS+ group, which also presented the highest expression of pro-inflammatory mediators (TNF-α, IL-1β and NF-kB) in frontal cortex, related to the lipoprotein APOA1-mediated transport of bacterial lipopolysaccharide to the brain and the detection of F. nucleatum in the brain parenchyma. A dysregulation of the hypothalamic-pituitary-adrenal stress axis, reflected by the increase in plasma corticosterone and glucocorticoid receptor levels in FC, was also found in this group.

CONCLUSIONS

Neuroinflammation induced by F. nucleatum (through a leaky mouth) might act as the linking mechanism between periodontal diseases and depression.

Resilience to stress and sex-specific remodeling of microglia and neuronal morphology in a rat model of anxiety and anhedonia

Prenatal exposure to stress or glucocorticoids (GC) is associated with the appearance of psychiatric diseases later in life. Microglia, the immune cells of the brain, are altered in stress-related disorders.

Synthetic GC such as dexamethasone (DEX) are commonly prescribed in case of preterm risk labour in order to promote fetal lung maturation. Recently, we reported long-lasting differences in microglia morphology in a model of in utero exposure to DEX (iuDEX), that presents an anxious phenotype. However, it is still unclear if stress differentially affects iuDEX males and females.

In this work, we evaluated how iuDEX animals of both sexes cope with chronic mild stress for 2 weeks. We evaluated emotional behavior and microglia and neuronal morphology in the dorsal hippocampus (dHIP) and nucleus accumbens (NAc), two brain regions involved in emotion-related disorders. We report that males and females prenatally exposed to DEX have better performance in anxiety- and depression-related behavioral tests after chronic stress exposure in adulthood than non-exposed animals. Interestingly, iuDEX animals present sex-dependent changes in microglia morphology in the dHIP (hypertrophy in females) and in the NAc (atrophy in females and hypertrophy in males). After chronic stress, these cells undergo sex-specific morphological remodeling. Paralleled to these alterations in cytoarchitecture of microglia, we report inter-regional differences in dendritic morphology in a sex-specific manner. iuDEX females present fewer complex neurons in the NAc, whereas iuDEX males presented less complex neuronal morphology in the dHIP. Interestingly, these alterations were modified by stress exposure.

Our work shows that stressful events during pregnancy can exert a preserved sex-specific effect in adulthood. Although the role of the observed cellular remodeling is still unknown, sex-specific differences in microglia plasticity induced by long-term stress exposure may anticipate differences in drug efficacy in the context of stress-induced anxiety- or depression-related behaviors.

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iuDEX induces anxiety- and depression-related behavioral in both sexes.

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iuDEX induces sex dependent fine structural alterations in neurons and microglia morphology in the dHIP and in the NAc.

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uCMS in combination to iuDEX normalize the behavior as well the morphology of neurons in the NAc.

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Stressful events during pregnancy can exert a preserved sex-specific effect in adulthood.

Regulatory effect of lithium on hippocampal blood-brain barrier integrity in a rat model of depressive-like behavior

OBJECTIVES

Recent evidence has associated mood disorders with blood-brain barrier (BBB)/ neurovascular unit (NVU) dysfunction, and reduction in blood vessels coverage by the water channel aquaporin-4 (AQP4) immunoreactive astrocytes. Lithium is an established treatment for mood disorders, yet, its mechanism of action is partially understood. We investigated the effects of lithium on BBB integrity and NVU-related protein expression in chronic mild stress (CMS) rat model of depressive-like behavior.

METHODS

Male Wistar rats were exposed for 5 weeks to unpredictable mild stressors with daily co-administration of lithium chloride to half of the stressed and unstressed groups. Sucrose preference and open field tests were conducted to validate the depressive-like phenotype, and dynamic contrast-enhanced MRI analysis was utilized to assess BBB integrity in brain regions relevant to the pathophysiology of depression. Hippocampal AQP4 and claudin-5 expression were studied using immunofluorescence, western blot, and enzyme-linked immunosorbent assays.

RESULTS

Lithium administration to the stressed rats prevented the reductions in sucrose preference and distance traveled in the open field, and normalized the stress-induced hippocampal BBB hyperpermeability, whereas lithium administration to the unstressed rats increased hippocampal BBB permeability. Additionally, lithium treatment attenuated the decrease in hippocampal AQP4 to glial fibrillary acidic protein immunoreactivity ratio in the stressed rats and upregulated hippocampal claudin-5 and BDNF proteins expression.

CONCLUSIONS

Our findings suggest that lithium administration in a rat CMS model of depressive-like behavior is associated with attenuation of stressed-induced hippocampal BBB/NVU disruption. These protective effects may be relevant to the mode of action of lithium in depression.

Sperm microRNAs confer depression susceptibility to offspring

Evidence that offspring traits can be shaped by parental life experiences in an epigenetically inherited manner paves a way for understanding the etiology of depression. Here, we show that F1 offspring born to F0 males of depression-like model are susceptible to depression-like symptoms at the molecular, neuronal, and behavioral levels. Sperm small RNAs, and microRNAs (miRNAs) in particular, exhibit distinct expression profiles in F0 males of depression-like model and recapitulate paternal depressive-like phenotypes in F1 offspring. Neutralization of the abnormal miRNAs in zygotes by antisense strands rescues the acquired depressive-like phenotypes in F1 offspring born to F0 males of depression-like model. Mechanistically, sperm miRNAs reshape early embryonic transcriptional profiles in the core neuronal circuits toward depression-like phenotypes. Overall, the findings reveal a causal role of sperm miRNAs in the inheritance of depression and provide insight into the mechanism underlying susceptibility to depression.

Elevated Brain Fatty Acid Amide Hydrolase Induces Depressive-Like Phenotypes in Rodent Models: A Review

Altered activity of fatty acid amide hydrolase (FAAH), an enzyme of the endocannabinoid system, has been implicated in several neuropsychiatric disorders, including major depressive disorder (MDD). It is speculated that increased brain FAAH expression is correlated with increased depressive symptoms. The aim of this scoping review was to establish the role of FAAH expression in animal models of depression to determine the translational potential of targeting FAAH in clinical studies. A literature search employing multiple databases was performed; all original articles that assessed FAAH expression in animal models of depression were considered. Of the 216 articles that were screened for eligibility, 24 articles met inclusion criteria and were included in this review. Three key findings emerged: (1) FAAH expression is significantly increased in depressive-like phenotypes; (2) genetic knockout or pharmacological inhibition of FAAH effectively reduces depressive-like behavior, with a dose-dependent effect; and (3) differences in FAAH expression in depressive-like phenotypes were largely localized to animal prefrontal cortex, hippocampus and striatum. We conclude, based on the animal literature, that a positive relationship can be established between brain FAAH level and expression of depressive symptoms. In summary, we suggest that FAAH is a tractable target for developing novel pharmacotherapies for MDD.

Corticotropin-releasing hormone 1 receptor antagonism attenuates chronic unpredictable mild stress-induced depressive-like behaviors in rats

Hyperactivity of the hypothalamic-pituitary-adrenal axis and impairment of the central corticotropin-releasing factor system are factors in the pathogenesis of depression. Though several antagonists of the corticotropin-releasing factor 1 receptor were effective in the recognized behavioral tests for antidepressant activity, there is still little information on the potential interactions between corticotropin-releasing factor 1 receptor inhibitors and conventional antidepressant therapy. The aim of our study was to assess the influence of CP154526, a corticotropin-releasing factor 1 receptor blocker, which presented some signs of depression. Our results revealed that CP154526 (5 and 10 mg/kg) or fluoxetine (10 mg/kg) treatment notably improved the sucrose consumption, produced anti-depressive-like behavior in open-field test, as well as immobility time in forced swimming test. The levels of interleukin-6, interleukin-1β, tumor necrosis factor-α, and corticotropin-releasing hormone concentration in the serum were inhibited effectively by CP154526 or fluoxetine administration. Real-time quantitative PCR and western blot analysis showed the upregulated levels of brain-derived neurotrophic factor and growth associated protein 43 (GAP43) in the hypothalamus of the rats exposed to chronic unpredictable mild stress (CUMS), while different degrees of downregulation in their expression were detected after CP154526 (5 and 10 mg/kg) or fluoxetine (10 mg/kg) treatment, respectively. Thus, our data demonstrated that CP154526 exhibited antidepressant effect in CUMS rats, which might be mediated by decreasing the brain-derived neurotrophic factor and GAP43 expression in the hypothalamus.

Animal Models of Depression: What Can They Teach Us about the Human Disease?

Depression is apparently the most common psychiatric disease among the mood disorders affecting about 10% of the adult population. The etiology and pathogenesis of depression are still poorly understood. Hence, as for most human diseases, animal models can help us understand the pathogenesis of depression and, more importantly, may facilitate the search for therapy. In this review we first describe the more common tests used for the evaluation of depressive-like symptoms in rodents. Then we describe different models of depression and discuss their strengths and weaknesses. These models can be divided into several categories: genetic models, models induced by mental acute and chronic stressful situations caused by environmental manipulations (i.e., learned helplessness in rats/mice), models induced by changes in brain neuro-transmitters or by specific brain injuries and models induced by pharmacological tools. In spite of the fact that none of the models completely resembles human depression, most animal models are relevant since they mimic many of the features observed in the human situation and may serve as a powerful tool for the study of the etiology, pathogenesis and treatment of depression, especially since only few patients respond to acute treatment. Relevance increases by the fact that human depression also has different facets and many possible etiologies and therapies.

The effectiveness of Bacopa monnieri (Linn.) Wettst. as a nootropic, neuroprotective, or antidepressant supplement: analysis of the available clinical data

Bacopa monnieri (Linn.) Wettst. has been used in traditional medicine as a drug to enhance and improve memory. In this regard, this study aims to provide B. monnieri's efficacy as a neuroprotective drug and as a nootropic against various neurological diseases. Literatures were collected, following Prisma guidelines, from databases, including Scopus, PubMed, Google Scholar, and Science Direct and were scrutinized using a quality scoring system. Means, standard deviations and 'n' numbers were extracted from the metrics and analyzed. Jamovi computer software for Mac was used to carry out the meta-analysis. The selected studies suggested that the plant extracts were able to show some improvements in healthy subjects which were determined in Auditory Verbal Learning Task, digit span-reverse test, inspection time task and working memory, even though it was not significant, as no two studies found statistically significant changes in the same two tests. B. monnieri was able to express modest improvements in subjects with memory loss, wherein only a few of the neuropsychological tests showed statistical significance. B. monnieri in a cocktail with other plant extracts were able to significantly reduce the effects of Alzheimer's disease, and depression which cannot be solely credited as the effect of B. monnieri. Although in one study B. monnieri was able to potentiate the beneficial effects of citalopram; on the whole, currently, there are only limited studies to establish the memory-enhancing and neuroprotective effects of B. monnieri. More studies have to be done in the future by comparing the effect with standard drugs, in order to establish these effects clinically in the plant and corroborate the preclinical data.

Dentate gyrus activin signaling mediates the antidepressant response

Antidepressants that target monoaminergic systems, such as selective serotonin reuptake inhibitors (SSRIs), are widely used to treat neuropsychiatric disorders including major depressive disorder, several anxiety disorders, and obsessive-compulsive disorder. However, these treatments are not ideal because only a subset of patients achieve remission. The reasons why some individuals remit to antidepressant treatments while others do not are unknown. Here, we developed a paradigm to assess antidepressant treatment resistance in mice. Exposure of male C57BL/6J mice to either chronic corticosterone administration or chronic social defeat stress induces maladaptive affective behaviors. Subsequent chronic treatment with the SSRI fluoxetine reverses these maladaptive affective behavioral changes in some, but not all, of the mice, permitting stratification into persistent responders and non-responders to fluoxetine. We found several differences in expression of Activin signaling-related genes between responders and non-responders in the dentate gyrus (DG), a region that is critical for the beneficial behavioral effects of fluoxetine. Enhancement of Activin signaling in the DG converted behavioral non-responders into responders to fluoxetine treatment more effectively than commonly used second-line antidepressant treatments, while inhibition of Activin signaling in the DG converted responders into non-responders. Taken together, these results demonstrate that the behavioral response to fluoxetine can be bidirectionally modified via targeted manipulations of the DG and suggest that molecular- and neural circuit-based modulations of DG may provide a new therapeutic avenue for more effective antidepressant treatments.

The gut microbiome modulates gut-brain axis glycerophospholipid metabolism in a region-specific manner in a nonhuman primate model of depression

Emerging research demonstrates that microbiota-gut-brain (MGB) axis changes are associated with depression onset, but the mechanisms underlying this observation remain largely unknown. The gut microbiome of nonhuman primates is highly similar to that of humans, and some subordinate monkeys naturally display depressive-like behaviors, making them an ideal model for studying these phenomena. Here, we characterized microbial composition and function, and gut-brain metabolic signatures, in female cynomolgus macaque (Macaca fascicularis) displaying naturally occurring depressive-like behaviors. We found that both microbial and metabolic signatures of depressive-like macaques were significantly different from those of controls. The depressive-like monkeys had characteristic disturbances of the phylum Firmicutes. In addition, the depressive-like macaques were characterized by changes in three microbial and four metabolic weighted gene correlation network analysis (WGCNA) clusters of the MGB axis, which were consistently enriched in fatty acyl, sphingolipid, and glycerophospholipid metabolism. These microbial and metabolic modules were significantly correlated with various depressive-like behaviors, thus reinforcing MGB axis perturbations as potential mediators of depression onset. These differential brain metabolites were mainly mapped into the hippocampal glycerophospholipid metabolism in a region-specific manner. Together, these findings provide new microbial and metabolic frameworks for understanding the MGB axis' role in depression, and suggesting that the gut microbiome may participate in the onset of depressive-like behaviors by modulating peripheral and central glycerophospholipid metabolism.

Chronic Unpredictable Mild Stress Accelerates the Growth of Bladder Cancer in a Xenograft Mouse Model

Objective

Chronic psychological stress is common in patients with bladder cancer. An increasing number of evidence demonstrated that psychiatric disorder leads to worse prognostic outcomes in bladder cancer. This study was to investigate the effects of chronic psychological stress on the growth of bladder cancer and its potential mechanisms.

Methods

A xenograft mouse model was established by subcutaneously implanting the human bladder cancer cell line T24 into nude mice. All of the tumor-bearing mice (N=20) were randomly separated into two groups. Mice in the control group were subjected to normal feeding conditions, while in another group, a chronic unpredictable mild stress (CUMS) model was established, in which mice were exposed to various types of stressors. Various analyses were performed on parameters including the tumor volume, tumor weight, expression of Caspase-3 and VEGF, proportion of Ki-67 positive cells (Ki-67 index), microvessel density (MVD) and serum concentrations of epinephrine and cortisol.

Results

In the CUMS group, the growth of transplanted tumors was distinctly accelerated, with the weight of removed tumors at the end of experiment increased by 34.07% compared to that of the control. Serum levels of epinephrine and cortisol determined by ELISA were significantly increased by CUMS. Immunohistochemistry and Western blot analysis showed that the expression of Caspase-3 was downregulated, whereas the expression of VEGF was upregulated in the CUMS group. Meanwhile, CUMS could increase the Ki-67 index and MVD.

Conclusion

Our research supports the hypothesis that CUMS could affect the growth of bladder cancer in nude mice, indicating that the intervention of chronic psychological stress may be a possible therapeutic strategy for bladder cancer.

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.

Ventral Hippocampal Afferents to Nucleus Accumbens Encode Both Latent Vulnerability and Stress-Induced Susceptibility

BACKGROUND

Stress is a major risk factor for depression, but not everyone responds to stress in the same way. Identifying why certain individuals are more susceptible is essential for targeted treatment and prevention. In rodents, nucleus accumbens (NAc) afferents from the ventral hippocampus (vHIP) are implicated in stress-induced susceptibility, but little is known about how this pathway might encode future vulnerability or specific behavioral phenotypes.

METHODS

We used fiber photometry to record in vivo activity in vHIP-NAc afferents during tests of depressive- and anxiety-like behavior in male and female mice, both before and after a sex-specific chronic variable stress protocol, to probe relationships between prestress neural activity and behavior and potential predictors of poststress behavioral adaptation. Furthermore, we examined chronic variable stress-induced alterations in vHIP-NAc activity in vivo and used ex vivo slice electrophysiology to identify the mechanism of this change.

RESULTS

We identified behavioral specificity of the vHIP-NAc pathway to anxiety-like and social interaction behavior. We also showed that this activity is broadly predictive of stress-induced susceptibility in both sexes, while prestress behavior is predictive only of anxiety-like behavior. We observed a stress-induced increase in in vivo vHIP-NAc activity coincident with an increase in spontaneous excitatory postsynaptic current frequency.

CONCLUSIONS

We implicate vHIP-NAc in social interaction and anxiety-like behavior and identify markers of vulnerability in this neural signal, with elevated prestress vHIP-NAc activity predicting increased susceptibility across behavioral domains. Our findings indicate that individual differences in neural activity and behavior play a role in predetermining susceptibility to later stress, providing insight into mechanisms of vulnerability.

2-Phenylethylamine (PEA) Ameliorates Corticosterone-Induced Depression-Like Phenotype via the BDNF/TrkB/CREB Signaling Pathway

Depression is a serious medical illness that is one of the most prevalent psychiatric disorders. Corticosterone (CORT) increases depression-like behavior, with some effects on anxiety-like behavior. 2-Phenethylamine (PEA) is a monoamine alkaloid that acts as a central nervous system stimulant in humans. Here, we show that PEA exerts antidepressant effects by modulating the Brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB)/cAMP response element binding protein (CREB) signaling pathway in CORT-induced depression. To investigate the potential effects of PEA on CORT-induced depression, we first treated CORT (50 μM)-induced hippocampal neurons with 100 μM PEA for 24 h. We found that treatment with CORT altered dendritic spine architecture; however, treatment with PEA rescued dendritic spine formation via regulation of BDNF/TrkB/CREB signaling. Next, we used a mouse model of CORT-induced depression. Mice were treated with CORT (20 mg/kg) for 21 days, followed by assessments of a battery of depression-like behaviors. During the final four days of CORT exposure, the mice were treated with PEA (50 mg/kg). We found that CORT injection promoted depression-like behavior and significantly decreased BDNF and TrkB expression in the hippocampus. However, treatment with PEA significantly ameliorated the behavioral and biochemical changes induced by CORT. Our findings reveal that PEA exerts antidepressant effects by modulating the BDNF/TrkB/CREB signaling pathway in a mouse model of CORT-induced depression.

Sex differences in endocannabinoid modulation of rat CA1 dendritic neurotransmission

Endocannabinoid sex differences are present in the rat hippocampus. Specifically, at perisomatic GABAergic synapses, tonic anandamide (AEA) and estrogenic-AEA signaling are active in females but not males. Furthermore, in males, hippocampal eCB function varies along the CA1 pyramidal somatodendritic axis. Constitutive CB1 and tonic 2-AG activity are present at perisomatic GABAergic synapses and lacking at dendritic GABAergic synapses. It is unknown if these eCB somatodendritic differences occur at female GABAergic synapses. Moreover, it is unclear whether eCB sex differences occur at hippocampal glutamatergic synapses. In vitro, field potential (fEPSP) recordings were performed to assess eCB sex differences at rat CA3-CA1 dendritic synapses. At female GABAergic synapses, we observed: 1) constitutive CB1 function, 2) tonic AEA, 3) tonic 2-AG and 3) estrogen (ER_α)-driven 2-AG activity. In contrast, only constitutive CB1 and tonic 2-AG activity was observed in males. Sex differences in eCB/CB1 signaling at dendritic synapses appear to shift the basal excitatory/inhibitory balance towards excitation in females and towards inhibition in males. Chronic Mild Stress (CMS) exposure (21 days) in female rats reverses CB1constitutive function and impairs both tonic and ER_α-driven eCB signaling. Endocannabinoid sex differences under both normal and stress conditions may contribute to sexual disparities in stress-related neurobehavioral disorders.

Effects of S100B neutralization on the long-term cognitive impairment and neuroinflammatory response in an animal model of sepsis

The nervous system is one of the first systems to be affected during sepsis. Sepsis not only has a high risk of mortality, but could also lead to cerebral dysfunction and cognitive impairment in long-term survival patients. The receptor for advanced glycation end products (RAGE) can interact with several ligands, and its activation triggers a series of cell signaling events, resulting in the hyperinflammatory condition related to sepsis. Recent studies show that elevated levels of S100B (RAGE ligand) are associated with the pathophysiology of neurodegenerative disorders. They also participate in inflammatory brain diseases and may lead to an increased activation of microglia and astrocytes, leading to neuronal death. This study aimed to determine the effect of S100B inhibition on the neuroinflammatory response in sepsis. Sepsis was induced in Wistar rats by cecal ligation and perforation (CLP). There were three groups: Sham, CLP, and CLP +10 μg/kg of monoclonal antibody (Anti-S100B) administered intracerebroventricularly. The animals were killed 30 days after sepsis following behavioral evaluation by open field, novel object recognition, and splash test. The hippocampus, prefrontal cortex, and amydgala were used for the determination of S100B and RAGE proteins by western blotting and for the evaluation of cytokine levels and verification of the number of microglial cells by immunohistochemistry. On day 30, both the Sham and CLP + anti-S100B groups were capable of recovering the habitual memory in the open field task. Regarding novel object recognition, Sham and CLP + anti-S100B groups increased the recognition index during the test session in comparison to the training session. There was a significant increase in the time of grooming in CLP + anti-S100B in comparison to the CLP group. There was a modulation of cytokine levels and immunohistochemistry showed that the CLP + anti-S100B group had a decrease in the number of microglial cells only in the hippocampus. These results helped to understand the role of S100B protein in the pathophysiology of sepsis-associated encephalopathy and could be helpful to further experimental studies regarding this subject.

An Overview of the Heterogeneity of Major Depressive Disorder: Current Knowledge and Future Prospective

Major depressive disorder (MDD) is estimated to impose maximum debilitating effects on the society by 2030, with its critical effects on health, functioning, quality of life and concomitant high levels of morbidity and mortality. Yet, the disease is inadequately understood, diagnosed and treated. Moreover, with the recent drastic rise in the pace of life, stress has materialized as one of the most potent environmental factors for depression. In this scenario, it is important to understand the modern pathogenetic hypotheses and mechanisms, and possibly try to shift from the traditional approaches in depression therapy. These include the elaboration of pathophysiological changes in heterogeneous systems such as genetic, epigenetic, serotonergic, noradrenergic, gamma-aminobutyric acid, glutamatergic and endocannabinoid systems, neurotrophic factors, HPA axis, immune system as well as cellular stress mechanisms. These components interact with each other in a complex matrix and further elucidation of their mechanism and cascade pathways are needed. This might aid in the identification of MDD subtypes as well as the development of sophisticated biomarkers. Further, characterization might also aid in developing multitargeted therapies that hold much promise as compared to the conventional monoamine based treatment. New candidate pharmacons, refined psychotherapeutic modalities, advanced neuro-surgical and imaging techniques as well as the implementation of pharmacokinetic, pharmacogenetic prescribing guidelines constitute the emerging expanses of MDD treatment.

Antidepressant-Like Effects of Ethanol Extract of Ziziphus jujuba Mill Seeds in Mice

The antidepressant-like activity of ethanol extract of Ziziphus jujuba Mill var. spinosa seeds (Semen Ziziphi Spinosae, SZS) was investigated by behavioral tests, such as a forced swimming test (FST), a tail-suspension test (TST), and an open field test (OFT), using mice exposed to chronic unpredictable mild stress (CUMS). In the TST, immobility times of the extract-treated groups E100 and E300 (CUMS + 100 and 300 mg/kg extract, respectively) were significantly decreased in a dose-dependent manner compared with the negative control (CUMS; p < 0.01, though those of E100 and E300 were higher than those of the positive control (CUMS + 15 mg/kg fluoxetine). In the FST, immobility times of E100 and E300 were decreased compared to the normal control. In the OFT, total and zone distances of E100 and E300 were significantly higher than those of negative controls (p < 0.01) with a dose dependency. In liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis after behavioral tests, norepinephrine (NE) and 5-hydroxytryptamine (5-HT) levels in the hippocampus tissues of E100 and E300 were significantly higher than those of negative controls. Brain-derived neurotrophic factor (BDNF) levels in the hippocampus tissues of E100 and E300 were higher than those of negative controls. From these results, the SZS ethanol extract exhibited significant antidepressant-like effects via immobility decrease, distance increase, hippocampal NE and 5-HT increase, and BDNF expression. These results suggest that the extract could be a potential antidepressant agent.

Associations between disordered gut microbiota and changes of neurotransmitters and short-chain fatty acids in depressed mice

Mounting evidence suggests that gut microbiota can play an important role in pathophysiology of depression, but its specific molecular mechanisms are still unclear. This study was conducted to explore the associations between changes in neurotransmitters and short-chain fatty acids (SCFAs) and altered gut microbiota in depressed mice. Here, the chronic restraint stress (CRS) model of depression was built. The classical behavioral tests were conducted to assess the depressive-like behaviors of mice. The 16S rRNA gene sequence extracted from fecal samples was used to assess the gut microbial composition. Liquid and gas chromatography mass spectroscopy were used to identify neurotransmitters in hypothalamus and SCFAs in fecal samples, respectively. Finally, 29 differential bacteria taxa between depressed mice and control mice were identified, and the most differentially abundant bacteria taxa were genus Allobaculum and family Ruminococcaceae between the two groups. The acetic acid, propionic acid, pentanoic acid, norepinephrine, 5-HIAA and 5-HT were significantly decreased in depressed mice compared to control mice. Genus Allobaculum was found to be significantly positively correlated with acetic acid and 5-HT. Taken together, these results provided novel microbial and metabolic frameworks for understanding the role of microbiota-gut-brain axis in depression, and suggested new insights to pave the way for novel therapeutic methods.

Anxiolytic and antidepressant effects of Ziziphus mucronata hydromethanolic extract in male rats exposed to unpredictable chronic mild stress: Possible mechanisms of actions

ETHNOPHARMACOLOGICAL RELEVANCE

Ziziphus mucronata (ZM) is used traditionally in the treatment of mood and depression. However, no existing scientific data is confirming this traditional claim.

AIM OF THE STUDY

The present study was planned to investigate the anxiolytic and antidepressant-like effects of this plant in a stressed-induced depression model in rats.

MATERIALS AND METHODS

Depressive-like behaviors were induced by exposing rats to different stress paradigms daily for 30 days. A sucrose preference test was performed to assess anhedonia in rats. Anxiety and depression-related behavior were assessed. The oxidative parameters (lipid peroxidation, SOD and catalase activities) were evaluated. Pindolol and Flumazenil were also used to assess the mechanism of action of ZM extract.

RESULTS

The results showed that chronic administration of ZM (150, 300, and 600 mg/kg, p.o., 30 days) and imipramine treatment (20 mg/kg, p.o, 30 days) remarkably (P < 0.05) reversed the UCMS-induced behavioral changes observed in stress vehicle treated rats by reducing sucrose preference, decreased the immobility period in the FST and latency in NSF. Besides, ZM (300 and 600 mg/kg, p.o., 30 days) raised the percentages of time spent and number of open arms entries as well as the number of transitions. Also, ZM (300 mg/kg, (P < 0.05) decreased lipid peroxidation and increased both SOD and catalase activities (300 and 600 mg/kg, (P < 0.05)). These aforementioned behavioral indices were also completely nullified by pindolol a β-adrenoceptors blocker and 5-HT 1A/1B receptor antagonist but not by flumazenil, a benzodiazepine receptors antagonist.

CONCLUSION

ZM improved symptoms of anxiety and depression in behavioral despair paradigm in chronically stressed rats. The observed effects could be due to its capacities to restore the antioxidant status, and probably the modulation of monoamines transmissions.

Alleviation of cognitive deficits and high copper levels by an NMDA receptor antagonist in a rat depression model

BACKGROUND

Major depressive disorder (MDD) is frequently associated with cognitive deficits and high copper levels. Dysfunction of N-methyl-d-aspartate (NMDA) receptors has been postulated to underlie MDD pathogenesis. This study sought to investigate the curative effect of the NMDA receptor antagonist memantine on cognitive deficits in depression and the underlying mechanisms.

METHODS

Adult male Sprague-Dawley rats received corticosterone (CORT) (20 mg/kg) bi-weekly via subcutaneous injection and/or copper gluconate (7 mg/kg) via daily intragastric administration. After 3 weeks, sucrose preference tests and open field tests showed anhedonia and high anxiety in both the CORT and CORT+Cu groups. Memantine intervention (20 mg/kg daily via intragastric administration for 14 days) led to recovery of anhedonia and anxiety behaviors. Memantine also remarkably suppressed serum copper ion levels. Moreover, memantine treatment effectively rescued depression-related spatial memory deficits as shown by the Morris water maze task.

RESULTS

Compared to the pre-memantine treatment results, the results of behavioral tests and cognitive function after memantine treatment were significantly normalized, and the copper concentration was decreased in all groups.

CONCLUSIONS

Collectively, our findings suggest that the NMDA receptor antagonist memantine may improve symptoms of anhedonia and anxiety and the cognitive deficits associated with depression, likely be related to suppress serum copper ion levels.

Chronic stress induces significant gene expression changes in the prefrontal cortex alongside alterations in adult hippocampal neurogenesis

Adult hippocampal neurogenesis is involved in stress-related disorders such as depression, posttraumatic stress disorders, as well as in the mechanism of antidepressant effects. However, the molecular mechanisms involved in these associations remain to be fully explored. In this study, unpredictable chronic mild stress in mice resulted in a deficit in neuronal dendritic tree development and neuroblast migration in the hippocampal neurogenic niche. To investigate molecular pathways underlying neurogenesis alteration, genome-wide gene expression changes were assessed in the prefrontal cortex, hippocampus and the hypothalamus alongside neurogenesis changes. Cluster analysis showed that the transcriptomic signature of chronic stress is much more prominent in the prefrontal cortex compared to the hippocampus and the hypothalamus. Pathway analyses suggested huntingtin, leptin, myelin regulatory factor, methyl-CpG binding protein and brain-derived neurotrophic factor as the top predicted upstream regulators of transcriptomic changes in the prefrontal cortex. Involvement of the satiety regulating pathways (leptin) was corroborated by behavioural data showing increased food reward motivation in stressed mice. Behavioural and gene expression data also suggested circadian rhythm disruption and activation of circadian clock genes such as Period 2. Interestingly, most of these pathways have been previously shown to be involved in the regulation of adult hippocampal neurogenesis. It is possible that activation of these pathways in the prefrontal cortex by chronic stress indirectly affects neuronal differentiation and migration in the hippocampal neurogenic niche via reciprocal connections between the two brain areas.

Epigenetic mechanisms underlying stress-induced depression

Stressful life events are a major contributor to the development of major depressive disorder. Environmental perturbations like stress change gene expression in the brain, leading to altered behavior. Gene expression is ultimately regulated by chromatin structure and the epigenetic modifications of DNA and the histone proteins that make up chromatin. Studies over the past two decades have demonstrated that stress alters the epigenetic landscape in several brain regions relevant for depressive-like behavior in rodents. This chapter will discuss epigenetic mechanisms of brain histone acetylation, histone methylation, and DNA methylation that contribute to adult stress-induced depressive-like behavior in rodents. Several biological themes have emerged from the examination of the brain transcriptome after stress such as alterations in the neuroimmune response, neurotrophic factors, and synaptic structure. The epigenetic mechanisms regulating these processes will be highlighted. Finally, pharmacological and genetic manipulations of epigenetic enzymes in rodent models of depression will be discussed as these approaches have demonstrated the ability to reverse stress-induced depressive-like behaviors and provide proof-of-concept as novel avenues for the treatment of clinical depression.

Stress and signaling pathways regulating autophagy: From behavioral models to psychiatric disorders

Autophagy is a process of degradation and recycling of cytoplasmatic components by the lysosomes. In the central nervous system (CNS), autophagy is involved in cell surveillance, neuroinflammation, and neuroplasticity. Neuropsychiatric conditions are associated with functional disturbances at molecular and cellular levels, causing significant impairments in cell homeostasis. Additionally, emerging evidence supports that dysfunctions in autophagy contribute to the pathophysiology of neurological diseases. However, the studies on autophagy in psychiatric disorders are highly heterogeneous and have several limitations, mainly to assess causality and determine the autophagy flux in animals and human samples. Besides, the role of this mechanism in non-neuronal cells in the CNS is only recently being explored. Thus, this review summarizes and discusses the changes in the autophagy pathway in animal models of psychiatric disorders and the limitations underlying the significant findings. Moreover, we compared these findings with clinical studies. Understanding the involvement of autophagy in psychiatric conditions, and the limitation of our current models may contribute to the development of more effective research approaches and possibly pharmacological therapies.

Antidepressant functions of Jie Yu Chu Fan capsule in promoting hippocampal nerve cell neurogenesis in a mouse model of chronic unpredictable mild stress

Background

Depression is a major public health challenge that imposes a great societal burden. Depression has been attributed to the decreased level of neurotransmitters and brain-derived neurotrophic factor (BDNF) levels. Chinese herbal medicine Jie Yu Chu Fan (JYCF) capsule has been shown to be effective in the management of depression. However, the mechanism has yet to be determined. This study aimed to explore the activity of JYCF against depression by establishing a mouse model of chronic unpredictable mild stress (CUMS) with fluoxetine as the positive control drug.

Methods

The open field test, sucrose preference test, forced swim test, and tail suspension test were carried out to observe the behavioral changes of animals. The levels of norepinephrine (NE), dopamine (DA), and 5-hydroxytryptamine, as well as their respective metabolic products 5-hydroxyindoleacetic acid, homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid in the mouse hippocampi were quantified by high-performance liquid chromatography (HPLC). Cell proliferation and apoptosis, and early and mature nerve cells in the hippocampi were observed by immunofluorescence. Reverse transcription polymerase chain reaction was used to identify BDNF expression in the hippocampi.

Results

After 5 weeks of unpredictable stimulation, a CUMS mouse model was successfully obtained, as indicated by sharply decreased sucrose preference and locomotor activity, as well as an increased immobility time in the forced swim test. Our results demonstrated that treatment with JYCF (1 and 5 g/kg) and fluoxetine (20 mg/kg) dramatically reversed the behavioral abnormalities in CUMS mice. At 1 g/kg, JYCF significantly increased NE, DA, and HVA levels in the hippocampi of CUMS mice. JYCF up-regulated the mRNA expression of BDNF and promoted cell proliferation in hippocampi of CUMS mice.

Conclusions

Our study demonstrated that JYCF exhibits antidepressant activity comparable to that of fluoxetine in CUMS mice. Moreover, the antidepressant-like activity of JYCF was shown to be mediated by enhancing hippocampal nerve cell neurogenesis through increasing the levels of monoamine neurotransmitters and BDNF expression.

The deleterious effect of stress-induced depression on rat liver: Protective role of resveratrol and dimethyl fumarate via inhibiting the MAPK/ERK/JNK pathway

This study aimed to uncover the protective potentiality of resveratrol and dimethyl fumarate (DMF) in the liver of a chronic unpredictable mild stress (CUMS)-induced depression animal model. Resveratrol and DMF significantly alleviated CUMS-induced behavioral abnormalities in stressed rats through improving sucrose preference in sucrose preference test and decreasing immobility time in a forced swimming test. They also mitigated serum corticosterone levels and elevated serum serotonin levels, which were formerly disturbed in CUMS rats. The hepatoprotective effect is evidenced by improvement in hepatic histopathological examinations, as well as normalized serum alanine aminotransferase and aspartate aminotransferase activities. Molecular signaling of resveratrol and DMF was estimated by diminishing hepatic expression of phosphorylated p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK). Consequently, they improved the hepatic antioxidant and anti-inflammatory activities as elaborated by the normalization of total antioxidant capacity, glutathione, malondialdehyde, nuclear factor-κB, tumor necrosis factor-α, and myeloperoxidase levels. In addition, they inhibited hepatocyte apoptosis as evidenced by the increased expression of B-cell lymphoma 2, the decreased expression of Bax, as well as the suppressed activity of caspase-3. In conclusion, resveratrol and DMF purveyed a significant anti-depressant effect, which may be mediated, at least in part, via inhibiting the MAPK/ERK/JNK pathway in the CUMS rat model.

Ketamine, but not guanosine, as a prophylactic agent against corticosterone-induced depressive-like behavior: Possible role of long-lasting pro-synaptogenic signaling pathway

Ketamine has been reported to exert a prophylactic effect against stress-induced depressive-like behavior by modulating the guanosine-based purinergic system. However, the molecular pathways underlying its prophylactic effect and whether guanosine also elicits a similar effect remain to be determined. Here, we investigated the prophylactic effect of ketamine and guanosine against corticosterone (CORT – 20 mg/kg, p.o.)-induced depressive-like behavior in mice. Furthermore, we characterized if the prophylactic response may be associated with mTORC1-driven signaling in the hippocampus and prefrontal cortex. A single administration of ketamine (5 mg/kg, i.p.), but not guanosine (1 or 5 mg/kg, p.o.), given 1 week before the pharmacological stress prevented CORT-induced depressive-like behavior in the tail suspension test (TST) and splash test (SPT). Fluoxetine treatment for 3 weeks did not prevent CORT-induced behavioral effects. A single administration of subthreshold doses of ketamine (1 mg/kg, i.p.) plus guanosine (5 mg/kg, p.o.) partially prevented the CORT-induced depressive-like behavior in the SPT. Additionally, CORT reduced Akt (Ser⁴⁷³) and GSK-3β (Ser⁹) phosphorylation and PSD-95, GluA1, and synapsin immunocontent in the hippocampus, but not in the prefrontal cortex. No alterations on mTORC1/p70S6K immunocontent were found in both regions in any experimental group. CORT-induced reductions on PSD-95, GluA1, and synapsin immunocontent were prevented only by ketamine treatment. Collectively, these findings suggest that ketamine, but not guanosine, exerts a prophylactic effect against depressive-like behavior, an effect associated with the stimulation of long-lasting pro-synaptogenic signaling in the hippocampus.

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CORT induces depressive-like behavior and hippocampal synaptogenic markers deficits.

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Ketamine prevents CORT-induced behavioral and hippocampal synaptogenic alterations.

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Guanosine or fluoxetine are unable to prevent the alterations induced by CORT.

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Ketamine plus guanosine partially prevent CORT-induced reduced self-care behavior.