Nicotinic receptors promote susceptibility to social stress in female mice linked with neuroadaptations within VTA dopamine neurons

Electroacupuncture Alleviates Neuropathic Pain and Negative Emotion in Mice by Regulating Gut Microbiota

Background

Neuropathic pain (NP) is a prevalent chronic condition frequently accompanied by adverse emotional states. Previous research has demonstrated the clinical efficacy of electroacupuncture (EA) in mitigating neuropathic pain and its associated mood disorders. Recent studies have underscored a correlation between gut microbiota and both NP and negative emotional states. Nevertheless, the relationship between the modulation of gut microbiota by EA and the amelioration of NP remains inadequately understood.

Methods

Mice were randomly assigned to one of the three groups: the Control (Con) group, the EA group, and the Chronic Constrictive Injury (CCI) group (n = 12 each). Starting from the 8th day post-CCI induction, the EA group underwent EA treatment once every two days, for a total of 20 sessions. To investigate the impact of gut microbiota on CCI mice, we employed a variety of methods, including various behavioral tests and 16S ribosomal DNA (rDNA) sequencing.

Results

The results indicated that EA significantly ameliorated mechanical allodynia and emotional dysfunction induced by CCI in mice. Analysis through 16S rDNA sequencing revealed that the gut microbiota of NP model mice exhibited a marked increase in diversity. However, EA could partially reverse changes in the diversity of gut microbiota. The abundance of Alloprevotella, A2, Roseburia, Muribaculum, Ruminiclostridium, and Rikenella was increased, and the abundance levels of Bacteroides were decreased at the genus level in CCI mice. Following EA treatment, the relative abundance of Alistipes, A2, Roseburia, and Rikenella was decreased, whereas the relative abundance of Alloprevotella and Parabacteroides was increased in EA group when compared with the CCI group.

Conclusion

These findings suggested that EA exerted a significant therapeutic effect on NP, potentially through modulation of the gut microbiota.

Ventral tegmental area glutamate neurons mediate nonassociative consequences of stress

Exposure to trauma is a risk factor for the development of a number of mood disorders, and may enhance vulnerability to future adverse life events. Recent data demonstrate that ventral tegmental area (VTA) neurons expressing the vesicular glutamate transporter 2 (VGluT2) signal and causally contribute to behaviors that involve aversive or threatening stimuli. However, it is unknown whether VTA VGluT2 neurons regulate transsituational outcomes of stress and whether these neurons are sensitive to stressor controllability. This work adapted an operant mouse paradigm to examine the impact of stressor controllability on VTA VGluT2 neuron function as well as the role of VTA VGluT2 neurons in mediating transsituational stressor outcomes. Uncontrollable (inescapable) stress, but not physically identical controllable (escapable) stress, produced social avoidance and exaggerated fear in male mice. Uncontrollable stress in females led to exploratory avoidance of a novel brightly lit environment. Both controllable and uncontrollable stressors increased VTA VGluT2 neuronal activity, and chemogenetic silencing of VTA VGluT2 neurons prevented the behavioral sequelae of uncontrollable stress in male and female mice. Further, we show that stress activates multiple genetically-distinct subtypes of VTA VGluT2 neurons, especially those that are VGluT2+VGaT+, as well as lateral habenula neurons receiving synaptic input from VTA VGluT2 neurons. Our results provide causal evidence that mice can be used for identifying stressor controllability circuitry and that VTA VGluT2 neurons contribute to transsituational stressor outcomes, such as social avoidance, exaggerated fear, or anxiety-like behavior that are observed within trauma-related disorders.

Serotonin transporter knockdown relieves depression-like behavior and ethanol-induced CPP in mice after chronic social defeat stress

Patients with stress-triggered major depression disorders (MDD) can often seek comfort or temporary relief through alcohol consumption, as they may turn to it as a means of self-medication or coping with overwhelming emotions. The use of alcohol as a coping mechanism for stressful events can escalate, fostering a cycle where the temporary relief it provides from depression can deepen into alcohol dependence, exacerbating both conditions. Although, the specific mechanisms involved in stress-triggered alcohol dependence and MDD comorbidities are not well understood, a large body of literature suggests that the serotonin transporter (SERT) plays a critical role in these abnormalities. To further investigate this hypothesis, we used a lentiviral-mediated knockdown approach to examine the role of hippocampal SERT knockdown in social defeat stress-elicited depression like behavior and ethanol-induced place preference (CPP). The results showed that social defeat stress-pro depressant effects were reversed following SERT knockdown demonstrated by increased sucrose preference, shorter latency to feed in the novelty suppressed feeding test, and decreased immobility time in the tail suspension and forced swim tests. Moreover, and most importantly, social stress-induced ethanol-CPP acquisition and reinstatement were significantly reduced following hippocampal SERT knockdown using short hairpin RNA shRNA-expressing lentiviral vectors. Finally, we confirmed that SERT hippocampal mRNA expression correlated with measures of depression- and ethanol-related behaviors by Pearson's correlation analysis. Taken together, our data suggest that hippocampal serotoninergic system is involved in social stress-triggered mood disorders as well as in the acquisition and retrieval of ethanol contextual memory and that blockade of this transporter can decrease ethanol rewarding properties.

Folic Acid Ameliorates Anxiety- and Depressive-Like Behavior Induced by Nicotine Withdrawal Through Restoration of Behavioral and Biochemical Alterations in Adolescent Male Rats

BACKGROUND

The present study aimed to assess the efficacy of folic acid (FA) on withdrawal following nicotine (Nic) administration in adolescent male rats.

AIMS AND METHODS

Adolescent male rats were divided into two groups: (1) vehicle and (2) Nic (Nic-2 mg/kg), and were under treatment from 21 to 42 days of age. After that, they continued the experiment without treatment and returned to a regular diet, except for one of those who received Nic. The rats were divided into four groups where they were treated with different doses of FA (5, 10, and 15 mg/kg) and bupropion (Bup) by oral gavage, and the final group included normal rats that received only FA (15 mg/kg) from 42 days of age for three weeks during which withdrawal occurred.

RESULTS

Results showed that adolescent Nic exposure exacerbated the behavioral indices of anxiety- and depression-like behaviors, while FA attenuated the effects of Nic withdrawal on anxiety and depression as well as Bup. In support, the biochemical results demonstrated a balance between oxidant and antioxidant mediators in addition to the increase and decrease of serotonin and monoamine oxidase (MAO) activity in cortical tissue. TNF-α as an inflammatory agent was decreased, whereas IL-10 as an anti-inflammatory parameter was increased.

CONCLUSIONS

The present findings suggest anxiety and depression caused by Nic withdrawal were attenuated by FA more likely through the reduction activity of MAO, the important enzyme responsible for serotonin metabolism along with balance between oxidant/antioxidant and pro-inflammatory/anti-inflammatory mediators. However, various mechanisms might be involved, which requires further investigation.

IMPLICATIONS

Nic withdrawal-induced depression and anxiety like behavior in rats followed by neuro-oxidative damage and neuro-inflammation. FA supplementation as well as Bup improved cognitive disorders induced by Nic withdrawal by increasing neuro-inflammation and neuro-oxidative damage.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic- and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice 24 h post-treatment. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than anxiolytic effects.

Hidden variables in stress neurobiology research

Among the central goals of stress neurobiology research is to understand the mechanisms by which stressors change neural circuit function to precipitate or exacerbate psychiatric symptoms. Yet despite decades of effort, psychiatric medications that target the biological substrates of the stress response are largely lacking. We propose that the clinical advancement of stress response-based therapeutics for psychiatric disorders may be hindered by 'hidden variables' in stress research, including considerations of behavioral study design (stressors and outcome measures), individual variability, sex differences, and the interaction of the body's stress hormone system with endogenous circadian and ultradian rhythms. We highlight key issues and suggest ways forward in stress neurobiology research that may improve the ability to assess stress mechanisms and translate preclinical findings.

Reduction of p11 in dorsal raphe nucleus serotonergic neurons mediates depression-like behaviors

The pathology of depression is related to the imbalance of various neurotransmitters. The dorsal raphe nucleus (DRN), the main brain region producing 5-HT, is crucially involved in the pathophysiology of depression. It contains several neuron types, in which GABAergic neurons are activated by stimuli associated with negative experiences and 5-HT neurons are activated by reward signals. However, little is known about its underlying molecular mechanisms. Here, we found that p11, a multifunctional protein associated with depression, was down-regulated by chronic social defeat stress in 5-HTDRN neurons. Knockdown of p11 in DRN induced depression-like behaviors, while its overexpression in 5-HTDRN neurons alleviated depression-like behavior caused by chronic social defeat stress. Further, p11 regulates membrane trafficking of glutamate receptors in 5-HTDRN neurons, suggesting a possible molecular mechanism underlying the participation of p11 in the pathological process of depression. This may facilitate the understanding of the molecular and cellular basis of depression.

Ethopharmacological evaluation of antidepressant-like effect of serotonergic psychedelics in C57BL/6J male mice

Serotonergic psychedelics such as psilocybin, lysergic acid diethylamide, and DOI exert a hallucinatory effect through serotonin 5-HT 2A receptor (5-HT2A) activation. Recent studies have revealed that serotonergic psychedelics have therapeutic potential for neuropsychiatric disorders, including major depressive and anxiety-related disorders. However, the involvement of 5-HT2A in mediating the therapeutic effects of these drugs remains unclear. In this study, we ethopharmacologically analyzed the role of 5-HT2A in the occurrence of anxiolytic-and antidepressant-like effects of serotonergic psychedelics such as psilocin, an active metabolite of psilocybin, DOI, and TCB-2 in mice. Mice with acute intraperitoneal psychedelic treatment exhibited significantly shorter immobility times in the forced swimming test (FST) and tail-suspension test (TST) than vehicle-treated control mice 24 h post-treatment. These effects were eliminated by pretreatment with volinanserin, a 5-HT2A antagonist. Surprisingly, the decreasing immobility time in the FST in response to acute psilocin treatment was sustained for at least three weeks. In the novelty-suppressed feeding test (NSFT), the latency to feed, an indicator of anxiety-like behavior, was decreased by acute administration of psilocin; however, pretreatment with volinanserin did not diminish this effect. In contrast, DOI and TCB-2 did not affect the NSFT performance in mice. Furthermore, psilocin, DOI, and TCB-2 treatment did not affect the spontaneous locomotor activity or head-twitch response, a hallucination-like behavior in rodents. These results suggest that 5-HT2A contributes to the antidepressant effects of serotonergic psychedelics rather than an anxiolytic effects.

Acute Effects of Intravenous Sub-Anesthetic Doses of Ketamine and Intranasal Inhaled Esketamine on Suicidal Ideation: A Systematic Review and Meta-Analysis

Purpose

Suicide is a major public health concern with currently no validated and efficacious treatments approved. Preliminary evidence suggests that intravenous ketamine has rapid and sustained antidepressant effects, making it a candidate with therapeutic potential for depressed patients at risk for suicide. We conducted a meta-analysis to evaluate the efficacy of ketamine and esketamine in reducing suicidal ideation (SI), as well as their respective onset and duration of action.

Data Sources

We searched PubMed, Embase, Ovid, Cochrane, and Web of Science databases for studies published from inception to September 29, 2022.

Study Eligibility Criteria

We conducted a systematic review of all parallel randomized controlled trials (RCTs) examining the effect and duration of ketamine or esketamine on SI. Our primary outcome measure was the Suicide Scale score, which was measured using the Scale for Suicidal Ideation (SSI), Beck Scale for Suicide Ideation (BSS), Beck Depression Inventory (BDI), or Modified Scale for Suicidal Ideation (MSSI). To obtain effect sizes (Cohen's d), we calculated the difference in Suicide Scale scores before and after administration in each group.

Results

Our study showed that intravenous sub-anesthetic doses of ketamine and intranasal inhaled esketamine had a significant anti-SI effect. Specifically, ketamine produced a large degree of anti-SI effect within the 4-6 hours (Cohen's d = 1.16, 95% CI: 0.50, 1.81) and a medium-large degree in the 24 hours (Cohen's d = 0.95, 95% CI: 0.48, 1.41). Esketamine, on the other hand, produced a small-medium degree of anti-SI effect within the 4-6 hours timeframe (Cohen's d = 0.26, 95% CI: 0.09, 0.44) and the 24 hours (Cohen's d = 0.30, 95% CI: 0.17, 0.47).

Conclusion

Intravenous sub-anesthetic doses of ketamine and intranasal inhaled esketamine could reduce SI within 4 hours and last for 24 hours.