Pharmacological modulation of the behavioral effects of social defeat in memory and learning in male mice

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response. Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region-specific, particularly involving the corticolimbic system, including the ventral tegmental area, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus. Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology. In this review, we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression. We focused on associated molecular pathways and neural circuits, with special attention to the brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling pathway and the ventral tegmental area-nucleus accumbens dopamine circuit. We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature, severity, and duration of stress, especially in the above-mentioned brain regions of the corticolimbic system. Therefore, BDNF might be a biological indicator regulating stress-related processes in various brain regions.

Therapeutic role of mesenchymal stem cell-derived extracellular vesicles in neuroinflammation and cognitive dysfunctions induced by binge-like ethanol treatment in adolescent mice

BACKGROUND

Extracellular vesicles (EVs) are heterogeneous membrane vesicles secreted by cells in extracellular spaces that play an important role in intercellular communication under both normal and pathological conditions. Mesenchymal stem cells (MSC) are anti-inflammatory and immunoregulatory cells capable of secreting EVs, which are considered promising molecules for treating immune, inflammatory, and degenerative diseases. Our previous studies demonstrate that, by activating innate immune receptors TLR4 (Toll-like receptor 4), binge-like ethanol exposure in adolescence causes neuroinflammation and neural damage.

AIMS

To evaluate whether the intravenous administration of MSC-derived EVs is capable of reducing neuroinflammation, myelin and synaptic alterations, and the cognitive dysfunction induced by binge-like ethanol treatment in adolescent mice.

MATERIALS & METHODS

MSC-derived EVs obtained from adipose tissue were administered in the tail vein (50 microg/dose, one weekly dose) to female WT adolescent mice treated intermittently with ethanol (3.0 g/kg) during two weeks.

RESULTS

MSC-derived EVs from adipose tissue ameliorate ethanol-induced up-regulation of inflammatory genes (e.g., COX-2, iNOS, MIP-1α, NF-κB, CX3CL1, and MCP-1) in the prefrontal cortex of adolescent mice. Notably, MSC-derived EVs also restore the myelin and synaptic derangements, and the memory and learning impairments, induced by ethanol treatment. Using cortical astroglial cells in culture, our results further confirm that MSC-derived EVs decrease inflammatory genes in ethanol-treated astroglial cells. This, in turn, confirms in vivo findings.

CONCLUSION

Taken together, these results provide the first evidence for the therapeutic potential of the MSC-derived EVs in the neuroimmune response and cognitive dysfunction induced by binge alcohol drinking in adolescence.

Oleoylethanolamide attenuates the stress-mediated potentiation of rewarding properties of cocaine associated with an increased TLR4 proinflammatory response

The lipid-derived messenger oleoylethanolamide (OEA) has been involved in multiple physiological functions including metabolism and the immune response. More recently, OEA has been observed to affect reward-related behavior. Stress is a major risk factor for drug use and a predictor of drug relapse. In the laboratory, social stress has been largely studied using the social defeat (SD) model. Here, we explored the effects of different OEA administration schedules on the increased rewarding properties of cocaine induced by SD. In addition, we evaluated the anti-inflammatory action of OEA pretreatment in TLR4 expression caused by SD in the cerebellum, a novel brain structure that has been involved in the development of cocaine addiction. Adult OF1 mice were assigned to an experimental group according to the stress condition (exploration or SD) and treatment (OEA before SD, OEA before conditioning or subchronic OEA treatment). Mice were administered with OEA i.p (10 mg/kg) 10 min previously to the corresponding event. Three weeks after the last SD encounter, conditioned place preference (CPP) was induced by a subthreshold cocaine dose (1 mg/kg). As expected, socially defeated mice presented greater vulnerability to the cocaine reinforcing effects and expressed CPP. Conversely, this effect was not observed under a non-stressed condition. Most importantly, we observed that OEA pretreatment before SD or before conditioning prevented cocaine CPP in defeated mice. Biochemical analysis showed that OEA administration before SD decreased proinflammatory TLR4 upregulation in the cerebellum caused by social stress. In summary, our results suggest that OEA may have a protective effect on stress-induced increased cocaine sensitivity by exerting an anti-inflammatory action.

Early Life Adversity and Neuropsychiatric Disease: Differential Outcomes and Translational Relevance of Rodent Models

It is now well-established that early life adversity (ELA) predisposes individuals to develop several neuropsychiatric conditions, including anxiety disorders, and major depressive disorder. However, ELA is a very broad term, encompassing multiple types of negative childhood experiences, including physical, sexual and emotional abuse, physical and emotional neglect, as well as trauma associated with chronic illness, family separation, natural disasters, accidents, and witnessing a violent crime. Emerging literature suggests that in humans, different types of adverse experiences are more or less likely to produce susceptibilities to certain conditions that involve affective dysfunction. To investigate the driving mechanisms underlying the connection between experience and subsequent disease, neuroscientists have developed several rodent models of ELA, including pain exposure, maternal deprivation, and limited resources. These studies have also shown that different types of ELA paradigms produce different but somewhat overlapping behavioral phenotypes. In this review, we first investigate the types of ELA that may be driving different neuropsychiatric outcomes and brain changes in humans. We next evaluate whether rodent models of ELA can provide translationally relevant information regarding links between specific types of experience and changes in neural circuits underlying dysfunction.

Downregulation of lncRNA GAS5 prevents mitochondrial apoptosis and hypoxic-ischemic brain damage in neonatal rats through the microRNA-128-3p/Bax/Akt/GSK-3β axis

OBJECTIVE

Hypoxic/ischemic brain damage (HIBD) results in increased neonatal mortality and serious neurologic morbidity. Long noncoding RNAs (lncRNAs) are shown as essential modulators of various neurological diseases. Here, we determined the mechanisms of lncRNA GAS5 in mitochondrial apoptosis in HIBD rats.

METHODS

The HIBD neonatal rat model was established and treated with shRNA-GAS5 or antagomir miR-128-3p. The morphological changes and apoptosis rate were observed by histological staining. Expressions of GAS5, miR-128-3p, and Bax mRNA in brain tissues of HIBD neonatal rats were determined. The binding relationships between GAS5 and miR-128-3p, and miR-128-3p and Bax were confirmed by dual-luciferase assay. Subsequently, the mitochondrial membrane potential and apoptosis-related factors in brain tissues of HIBD neonatal rats were detected. Western blot analysis was performed to detect the expression of Akt/GSK3β pathway-associated proteins.

RESULTS

The neurons in the brain tissue of HIBD neonatal rats decreased with disordered arrangement, and showed vacuolization and nuclear pyknosis, obvious brain damage, increased neuronal apoptosis, and enhanced mitochondrial apoptotic pathway. Downregulated miR-128-3p and upregulated GAS5 and Bax mRNA were found in HIBD neonatal rats. There were binding relationships between GAS5 and miR-128-3p, and miR-128-3p and Bax mRNA. Inhibition of lncRNA GAS5 in HIBD neonatal rats suppressed mitochondrial apoptosis. miR-128-3p knockdown annulled the inhibitory effect of inhibiting lncRNA GAS5 on mitochondrial apoptosis. Silencing GAS5 increased the phosphorylation levels of Akt and GSK3β.

CONCLUSION

Downregulation of lncRNA GAS5 prevents mitochondrial apoptosis in neonatal HIBD rats by regulating the miR-128-3p/Bax/Akt/GSK-3β axis.

Ethanol intake in male mice exposed to social defeat: Environmental enrichment potentiates resilience

Large preclinical evidence shows that exposure to social defeat (SD) increases vulnerability to drug abuse, increasing the consumption of ethanol. However, not all subjects are equally affected by the changes induced by stress. Previous reports have evidenced that the resilient phenotype to depressive-like behaviors after SD is associated with the resistant phenotype to cocaine-increased rewarding effects and the smaller neuroinflammatory response. The aim of the present study was to further clarify whether the resilient profile to depressive-like behavior also predicts a protection against the increase in ethanol intake induced by SD. The neuroinflammatory profile was studied after the end of the oral ethanol self-administration (SA) procedure, measuring levels of the pro-inflammatory cytokine IL-6 and the chemokine CX3CL1 or fractalkine in the striatum and prefrontal cortex. Previous studies have shown that environmental enrichment (EE) is an effective mechanism to dimish the detrimental effects of social stress. In a second study, we aimed to evaluate if EE housing before exposure to SD could potentiate resilience. Our results showed that mice with a phenotype susceptible to SD-induced depressive-like behaviors showed increased ethanol consumption and increased neuroinflammatory signaling. In contrast, despite the lack of effect on depressive-like behaviors, defeated mice previously housed under EE conditions did not show an increase in ethanol SA or an increase in immune response. To sum up, the resilient phenotype to SD develops at different levels, such as depressive-like behaviors, ethanol consumption and the neuroinflammatory response. Our results also point to the protective role of EE in potentiating resilience to SD effects.

Chronic Social Defeat During Adolescence Induces Short- and Long-Term Behavioral and Neuroendocrine Effects in Male Swiss-Webster Mice

Chronic stress exposure during adolescence is a significant risk factor for the development of depression. Chronic social defeat (CSD) in rodents is an animal model of depression with excellent ethological, predictive, discriminative, and face validity. Because the CSD model has not been thoroughly examined as a model of stress-induced depression within the adolescence stage, the present study analyzed the short- and long-term behavioral and neuroendocrine effects of CSD during early adolescence. Therefore, adolescent male Swiss-Webster (SW) mice were exposed to the CSD model from postnatal day (PND) 28 to PND37. Twenty-four hours (mid-adolescence) or 4 weeks (early adulthood) later, mice were tested in two models of depression; the social interaction test (SIT) and forced swimming test (FST); cognitive deficits were evaluated in the Barnes maze (BM). Finally, corticosterone and testosterone content was measured before, during, and after CSD exposure, and serotonin transporter (SERT) autoradiography was studied after CSD in adolescent and adult mice. CSD during early adolescence induced enduring depression-like behaviors as inferred from increased social avoidance and immobility behavior in the SIT and FST, respectively, which correlated in an age-dependent manner with SERT binding in the hippocampus; CSD during early adolescence also induced long-lasting learning and memory impairments in the Barnes maze (BM). Finally, CSD during early adolescence increased serum corticosterone levels in mid-adolescence and early adulthood and delayed the expected increase in serum testosterone levels observed at this age. In conclusion: (1) CSD during early adolescence induced long-lasting depression-like behaviors, (2) sensitivity of SERT density during normal brain development was revealed, (3) CSD during early adolescence induced enduring cognitive deficits, and (4) results highlight the vulnerability of the adolescent brain to social stressors on the adrenal and gonadal axes, which emphasizes the importance of an adequate interaction between both axes during adolescence for normal development of brain and behavior.

The antidepressant-like effects of Shen Yuan: Dependence on hippocampal BDNF-TrkB signaling activation in chronic social defeat depression-like mice

The Shen Yuan prescription (SY) comprises Panax ginseng (GT) and Polygala tenuifolia (YT), elicited superior antidepressant activity compared with that of GT or YT alone. The aim of this paper is to elucidate the effects of SY treatment on chronic social defeat stress (CSDS)-induced depression-like symptoms and the related mechanism. Our results indicated that SY treatment reverses the depressive-like behaviors induced by CSDS as measured by the social interaction test, sucrose preference test, forced swim test, and tail suspension test. SY decreased the serum levels of CORT and increased hippocampal neurotransmitters (5-HT, DA, and NE) in CSDS mice. Meanwhile, SY upregulated the brain-derived neurotrophic factor (BDNF) signaling pathway and reversed the decreased hippocampal neurogenesis caused by CSDS. In addition, we found that the TrkB antagonist K252a fully blocked the SY effects on behavioral improvement and eliminated the promoting effects of SY on hippocampal neurogenesis and BDNF-TrkB signaling (including the downstream ERK and Akt pathways) activation, thus further demonstrating that BDNF-TrkB signaling was necessary for the SY effects. In conclusion, our study showed that SY acted as an antidepressant in mice exhibiting CSDS-induced depression-like symptoms, and its effect was facilitated by promoting hippocampal neurogenesis and BDNF signaling pathway activation.

Unique effects of social defeat stress in adolescent male mice on the Netrin-1/DCC pathway, prefrontal cortex dopamine and cognition (Social stress in adolescent vs. adult male mice)

For some individuals, social stress is a risk factor for psychiatric disorders characterised by adolescent onset, prefrontal cortex (PFC) dysfunction and cognitive impairments. Social stress may be particularly harmful during adolescence when dopamine (DA) axons are still growing to the PFC, rendering them sensitive to environmental influences. The guidance cue Netrin-1 and its receptor, DCC, coordinate to control mesocorticolimbic DA axon targeting and growth during this age. Here we adapted the accelerated social defeat (AcSD) paradigm to expose male mice to social stress in either adolescence or adulthood and categorised them as "resilient" or "susceptible" based on social avoidance behaviour. We examined whether stress would alter the expression of DCC and Netrin-1 in mesolimbic dopamine regions and would have enduring consequences on PFC dopamine connectivity and cognition. While in adolescence the majority of mice are resilient but exhibit risk-taking behaviour, AcSD in adulthood leads to a majority of susceptible mice without altering anxiety-like traits. In adolescent, but not adult mice, AcSD dysregulates DCC and Netrin-1 expression in mesolimbic DA regions. These molecular changes in adolescent mice are accompanied by changes in PFC DA connectivity. Following AcSD in adulthood, cognitive function remains unaffected, but all mice exposed to AcSD in adolescence show deficits in inhibitory control when they reach adulthood. These findings indicate that exposure to AcSD in adolescence vs. adulthood has substantially different effects on brain and behaviour and that stress-induced social avoidance in adolescence does not predict vulnerability to deficits in cognitive performance.Significance statement During adolescence, dopamine circuitries undergo maturational changes which may render them particularly vulnerable to social stress. While social stress can be detrimental to adolescents and adults, it may engage different mechanisms and impact different domains, depending on age. The accelerated social defeat (AcSD) model implemented here allows exposing adolescent and adult male mice to comparable social stress levels. AcSD in adulthood leads to a majority of socially avoidant mice. However, the predominance of AcSD-exposed adolescent mice does not develop social avoidance, and these resilient mice show risk-taking behaviour. Nonetheless, in adolescence only, AcSD dysregulates Netrin-1/DCC expression in mesolimbic dopamine regions, possibly disrupting mesocortical dopamine and cognition. The unique adolescent responsiveness to stress may explain increased psychopathology risk at this age.

Dammarane sapogenins attenuates stress-induced anxiety-like behaviors by upregulating ERK/CREB/BDNF pathways

Dammarane sapogenins (DS), an extract derived from ginseng by alkaline hydrolysis of total ginsenosides, possesses high pharmacological activity and higher bioavailability than ginsenosides. The present study was designed to investigate the anxiolytic-like effects of DS in a mouse model of chronic social defeat stress (CSDS). DS (40 and 80 mg/kg) significantly ameliorated social avoidance and anxiety-like behavior in four test models of CSDS, showing increased time in the interaction zone in the social interaction test and in the center of the field in the open field test, an increased percentage of entries and open arm time in the elevated plus maze, and reduced latency to eat in the novelty-suppressed feeding test. Biochemical analyses showed that DS significantly reduced serum corticosterone levels and increased brain concentration of neurotransmitter 5-HT and noradrenaline in CSDS mice. Treatment with DS significantly upregulated BDNF (brain-derived neurotrophic factor), p-CREB/CREB and p-ERK1/2/ERK1/2 protein expression in the hippocampus and prefrontal cortex of CSDS mice. Collectively, these results suggest that DS exerts anxiolytic-like effects in CSDS model mice and the action is mediated, at least in part, by modulating the HPA (hypothalamic-pituitary-adrenal) axis and monoamine neurotransmitter levels, and via ERK/CREB/BDNF signaling pathway.

Ginsenoside Rg1 ameliorates chronic social defeat stress-induced depressive-like behaviors and hippocampal neuroinflammation

Chronic social defeat stress (CSDS) is an ethologically relevant psychosocial stress animal model and has been widely used in depression studies. Ginsenoside Rg1 (Rg1) is the major active ingredients of ginseng with low toxicity and neuroprotective effects. The present study aims to investigate the antidepressant effects of Rg1 in CSDS mice and explore its molecular mechanism. We found that Rg1 (20 or 40 mg/kg, i.g.) administration significantly alleviated depressive-like behaviors caused by 4-week CSDS exposure, as measured by social interaction test and sucrose preference test, tail suspension test and forced swim test. Additionally, Rg1 treatment inhibited CSDS-induced production of IL-6, TNF-α and IL-1β, decreased the expression of iNOS, COX2, and caspase-9 and -3, and inhibited microglial activation (Iba1) in the hippocampus. Rg1 was found to significantly downregulate p-JNK1/2 and p-P38 MAPK levels, upregulate p-ERK1/2 levels and inhibit the expression of phosphorylated NF-κB in the hippocampus. Meanwhile, Rg1 regulated SIRT1 and decreased the levels of acetylated p65 (ac-p65) in the hippocampus. Moreover, the reduction in adult hippocampal neurogenesis in CSDS mice was reversed by Rg1 treatment. In conclusion, our findings suggest that Rg1 prevents depressive-like behavior in CSDS-exposed mice, partially through the downregulation of hippocampal neuroinflammation and the upregulation of adult hippocampal neurogenesis and that these changes presumably occur through increased anti-inflammatory effects and the inhibition of proinflammatory cytokine and neurotoxic mediator expression and microglial activation, which is partly mediated by the regulation of the MAPK and SIRT1 signaling pathways and results in the inhibition of NF-κB transcriptional activity.