Amygdala dynorphin/κ opioid receptor system modulates depressive-like behavior in mice following chronic social defeat stress

Comparative transcriptional analyses of the striatum in the chronic social defeat stress model in C57BL/6J male mice and the gut microbiota-dysbiosis model in Kumming mice

Depression is a complex disorder with multiple contributing factors, and chronic stress has previously been recognized as a major causative factor, while gut microbes have also been found to be involved in depression recently. However, gene expression in depression models with different etiologies is unclear. Here, we compared the transcriptomes of the striatum in chronic social defeat stress (CSDS) model of C57BL/6J male mice and fecal microbiota transplant (FMT) model of Kumming male mice. We found that the proportion of shared differentially expressed genes (DEGs) between the two models was only 24 %. The specific DEGs of FMT model were enriched in immune and inflammatory, and are associated with changes in vascular and ciliated ependymal cells. The specific DEGs of CSDS model were enriched in neuron and synapse. The results of network analysis suggested the expression patterns and biological function of depressive-like behaviors-related modules in the two models are different. Further, the alternative splicing events of CSDS are more than FMT. Our results suggested models of depression induced by different etiologies differ significantly in gene expression and biological function. Our study also suggested us to pay attention to the characteristics of models of depression of different etiologies and provided a more comprehensive understanding of the heterogeneity of depression.

Social Homeostasis and Psychoactive Drugs: What Can We Learn From Opioid and Amphetamine Drug Challenge Studies in Humans?

Social disequilibrium, or disrupted social homeostasis, underlies many behavioral disorders, including problematic drug use. One way to study the relationship between drug use and social homeostasis is to determine whether single doses of psychoactive drugs relieve some of the discomfort of social isolation and promote social connection. In this narrative review, we discuss challenges and opportunities in studying the relationship between psychoactive drugs and social homeostasis. Using the examples of opioids and amphetamines, we discuss the evidence that drugs alleviate dysphoria related to lack of social connection or produce prosocial effects that improve connection. With regard to opioid drugs, we report that mu opioid agonists and kappa opioid antagonists reduce distress from social isolation, and mu opioid agonists enhance social reward. Amphetamine-like stimulant drugs, including MDMA, do not seem to act by reducing the distress of social isolation, but they have notable prosocial effects that increase both motivation for social contact and the pleasure derived from interacting socially. Many questions remain in understanding interactions between drugs and social equilibrium, including whether these effects contribute to problematic drug use. We identify gaps in knowledge, including the effects of drug withdrawal or dependence on social function or the responses of individuals with psychiatric symptomatology. Understanding these actions on social processes will help to develop novel pharmacological treatments for clinical problems related to social disequilibrium.

The Antidepressant Effect of Magnolol on Depression-Like Behavior of CORT-Treated Mice

Although the antidepressant-like effect of magnolol has been revealed in previous reports, the mechanism remains unclear. In this study, the antidepressant-like effect of magnolol on corticosterone-induced (CORT-induced) mice was investigated in vivo. After 21 days of CORT induction, the mice showed marked depressive-like behaviors, with a decrease in sucrose preference score and an increase in immobility time in the tail suspension test (TST) and forced swimming test (FST). Pretreatment with either magnolol (50 mg/kg, i.p.) or the kappa opioid receptor (KOR) antagonist nor-BNI (10 mg/kg, i.p.) prevented CORT-induced depression-like behavior and reduced CORT-induced dynorphin (DYN A) elevation in the hippocampal ventral DG. However, no depression-like behavior was observed in mice with KOR downregulation in the ventral DG. We further found that upregulation of DYN A in the DG caused depression-like behavior, which was blocked by intraperitoneal injection of nor-BNI and modulated by magnolol. The present study demonstrated that magnolol could ameliorate CORT-induced depression-like behaviors, by modulating the DYN A/KOR system in the ventral DG of the hippocampus.

Endogenous opiates and behavior: 2022

This paper is the forty-fifth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2022 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Kappa opioid receptor in nucleus accumbens regulates depressive-like behaviors following prolonged morphine withdrawal in mice

Prolonged withdrawal from opioids leads to negative emotions. Kappa opioid receptor (KOR) plays an important role in opioid addiction and affective disorders. However, the underlying mechanism of KOR in withdrawal-related depression is still lacking. We found that escitalopram treatment had a limited effect in improving depression symptoms in heroin-dependent patients. In mice, we demonstrated prolonged (4 weeks) but not acute (24 h) withdrawal from morphine induced depressive-like behaviors. The number of c-Fos positive cells and the expression of KOR in the nucleus accumbens (NAc), were significantly increased in the prolonged morphine withdrawal mice. Conditional KOR knockdown in NAc significantly improved depressive-like behaviors. Repeated but not acute treatment with the KOR antagonist norBNI improved depressive-like behaviors and reversed PSD95, synaptophysin, p-ERK, p-CREB, and BDNF in NAc. This study demonstrated the important role of striatal KOR in morphine withdrawal-related depressive-like behaviors and offered therapeutic potential for the treatment of withdrawal-related depression.

Social Psychopharmacology: Novel Approaches to Treat Deficits in Social Motivation in Schizophrenia

BACKGROUND AND HYPOTHESIS

Diminished social motivation is a negative symptom of schizophrenia and leads to severe functional consequences for many patients suffering from the illness. However, there are no effective medications available to treat this symptom. Despite the lack of approved treatments for patients, there is a growing body of literature on the effects of several classes of drugs on social motivation in healthy volunteers that may be relevant to patients. The aim of this review is to synthesize these results in an effort to identify novel directions for the development of medications to treat reduced social motivation in schizophrenia.

STUDY DESIGN

In this article, we review pharmacologic challenge studies addressing the acute effects of psychoactive drugs on social motivation in healthy volunteers and consider how these findings may be applied to deficits in social motivation in schizophrenia. We include studies testing amphetamines and 3,4-methylenedioxymethamphetamine (MDMA), opioids, cannabis, serotonergic psychedelics, antidepressants, benzodiazepines, and neuropeptides.

STUDY RESULTS

We report that amphetamines, MDMA, and some opioid medications enhance social motivation in healthy adults and may represent promising avenues of investigation in schizophrenia.

CONCLUSIONS

Given the acute effects of these drugs on behavioral and performance-based measures of social motivation in healthy volunteers, they may be particularly beneficial as an adjunct to psychosocial training programs in patient populations. It remains to be determined how these medications affect patients with deficits in social motivation, and in which contexts they may be most effectively administered.

Stress-Induced Changes in the Endogenous Opioid System Cause Dysfunction of Pain and Emotion Regulation

Early life stress, such as child abuse and neglect, and psychosocial stress in adulthood are risk factors for psychiatric disorders, including depression and anxiety. Furthermore, exposure to these stresses affects the sensitivity to pain stimuli and is associated with the development of chronic pain. However, the mechanisms underlying the pathogenesis of stress-induced depression, anxiety, and pain control remain unclear. Endogenous opioid signaling is reportedly associated with analgesia, reward, addiction, and the regulation of stress responses and anxiety. Stress alters the expression of various opioid receptors in the central nervous system and sensitivity to opioid receptor agonists and antagonists. μ-opioid receptor-deficient mice exhibit attachment disorders and autism-like behavioral expression patterns, while those with δ-opioid receptor deficiency exhibit anxiety-like behavior. In contrast, deficiency and antagonists of the κ-opioid receptor suppress the stress response. These findings strongly suggest that the expression and dysfunction of the endogenous opioid signaling pathways are involved in the pathogenesis of stress-induced psychiatric disorders and chronic pain. In this review, we summarize the latest basic and clinical research studies on the effects of endogenous opioid signaling on early-life stress, psychosocial stress-induced psychiatric disorders, and chronic pain.

Up-regulation of BDNF/TrkB signaling by δ opioid receptor agonist SNC80 modulates depressive-like behaviors in chronic restraint-stressed mice

Depressive disorder is a psychiatric disease characterized by its main symptoms of low mood and anhedonia. Due to its complex etiology, current clinical treatments for depressive disorder are limited. In this study, we assessed the role of the δ opioid receptor (δOR) system in the development of chronic-restraint-stressed (CRS)-induced depressive behaviors. We employed a 21-day CRS model and detected the c-fos activation and protein levels' changes in enkephalin (ENK)/δOR. It was found that the hippocampus and amygdala were involved in CRS-induced depression. The expression of pro-enkephalin (PENK), the precursors of the endogenous ligand for δOR, was significantly decreased in the hippocampus and amygdala following CRS. We then treated the mice with SNC80, a specific δOR agonist, to examine its anti-depressant effects in the tail suspension test (TST), forced swimming test (FST), and sucrose preference test (SPT). SNC80 administration significantly reversed depressive-like behaviors, and this antidepressant effect could be blocked by a TrkB inhibitor: ANA-12. Although ANA-12 treatment had no significant effect on the expression of ENK/δOR, it blocked the promoting effects of brain-derived neurotrophic factor (BDNF)/tyrosine kinase B(TrkB) signaling by SNC80 in the hippocampus and amygdala. Therefore, the present study demonstrates that SNC80 exerts anti-depressant effects by up-regulating the BDNF/TrkB signaling pathway in the hippocampus and amygdala in CRS-induced depression and provides evidence that δOR's agonists may be potential anti-depressant therapeutic agents.

Changes in mRNA and miRNA expression in the prelimbic cortex related to depression-like syndrome induced by chronic social defeat stress in mice

Major depressive disorder is a complex psychiatric disorder with a high prevalence rate worldwide. Previous studies have demonstrated the involvement of the prelimbic cortex (PL) in mediating depressive-like behavior, however, the exact molecular mechanism taking place in the PL remains unclear. In the present study, we conducted high-throughput sequencing of mRNAs and miRNAs in PL tissue harvested from chronic social defeat stress (CSDS) susceptible male mice. We identified 59 differentially expressed mRNAs and 6 differentially expressed miRNAs, in which 40 mRNAs and 3 miRNAs were up-regulated, while 19 mRNAs and 3 miRNAs were down-regulated. Integrated analysis of miRNA-mRNA networks suggested that GPR35 signaling might be involved in CSDS-induced depressive-like behaviors. RT-PCR and western blot assays validated that Abra, Sell and GPR35 were up-regulated. Functionally, inhibition of GPR35 in the PL ameliorated CSDS-induced depressive-like behaviors. Thus, the present study provided a global view of mRNA and miRNA profiles in the PL of male stress susceptible mice, and suggested that GPR35 signaling was associated with CSDS-induced depressive-like behaviors. These results may be valuable for further investigations of the molecular regulatory mechanisms in stress-induced depression.

Regulation of Cortico-Thalamic JNK1/2 and ERK1/2 MAPKs and Apoptosis-Related Signaling Pathways in PDYN Gene-Deficient Mice Following Acute and Chronic Mild Stress

The crosstalk between the opioidergic system and mitogen-activated protein kinases (MAPKs) has a critical role in mediating stress-induced behaviors related to the pathophysiology of anxiety. The present study evaluated the basal status and stress-induced alterations of cortico-thalamic MAPKs and other cell fate-related signaling pathways potentially underlying the anxiogenic endophenotype of PDYN gene-deficient mice. Compared to littermates, PDYN knockout (KO) mice had lower cortical and or thalamic amounts of the phospho-activated MAPKs c-Jun N-terminal kinase (JNK1/2) and extracellular signal-regulated kinase (ERK1/2). Similarly, PDYN-KO animals displayed reduced cortico-thalamic densities of total and phosphorylated (at Ser191) species of the cell fate regulator Fas-associated protein with death domain (FADD) without alterations in the Fas receptor. Exposure to acute restraint and chronic mild stress stimuli induced the robust stimulation of JNK1/2 and ERK1/2 MAPKs, FADD, and Akt-mTOR pathways, without apparent increases in apoptotic rates. Interestingly, PDYN deficiency prevented stress-induced JNK1/2 and FADD but not ERK1/2 or Akt-mTOR hyperactivations. These findings suggest that cortico-thalamic MAPK- and FADD-dependent neuroplasticity might be altered in PDYN-KO mice. In addition, the results also indicate that the PDYN gene (and hence dynorphin release) may be required to stimulate JNK1/2 and FADD (but not ERK1/2 or Akt/mTOR) pathways under environmental stress conditions.

Dynorphin participates in interaction between depression and non-erosive reflux disease

BACKGROUND

To explore the relationships between anxiety/depression and NERD, we focused on dynorphin (Dyn), an important member of visceral hypersensitivity, and its related pathways.

METHODS

Pearson's correlation analysis on patients with NERD and in vivo experiment on NERD rat model. Part 1: Pearson's correlation analysis among serum levels of Dyn, clinical symptoms and HADS scores of NERD patients were carried on. Part 2: Wistar rats were randomly divided into 2 groups: control group and model group. The data of pH value, immobility time, serum Dyn concentration, NMDAR1 and SP expression were, respectively, derived from automatic pH recorder, tail suspension test, enzyme-linked immunosorbent assay, immunohistochemistry and immunofluorescence.

RESULTS

Part 1: Pearson's correlation analysis showed that there was a linear correlation between Clinical Symptom (CS) score and HADS score (HAD-A, HAD-D), and the correlation coefficients were 0.385 and 0.273 respectively; the correlation coefficient between lg (Dyn) and lg (CS score) was r = 0.441, P = 0.002; the correlation coefficient between lg(Dyn) and lg (HAD-D score) was r = 0.447, P = 0.002. Part 2: The pH value of the lower esophagus in the model group was lower than that in the control group (P < 0.01). The tail suspension immobility time of model group was significantly longer than that of control group (P < 0.01). The serum Dyn concentration and the expression level of NMDAR1 in spinal cord and SP in lower esophageal mucosa of model group were significantly higher than those of control group (P < 0.05).

CONCLUSION

Increased serum dynorphin level may be a sign of correlation between depression and NERD.

Dynorphin/kappa opioid receptor system regulation on amygdaloid circuitry: Implications for neuropsychiatric disorders

Amygdaloid circuits are involved in a variety of emotional and motivation-related behaviors and are impacted by stress. The amygdala expresses several neuromodulatory systems, including opioid peptides and their receptors. The Dynorphin (Dyn)/kappa opioid receptor (KOR) system has been implicated in the processing of emotional and stress-related information and is expressed in brain areas involved in stress and motivation. Dysregulation of the Dyn/KOR system has also been implicated in various neuropsychiatric disorders. However, there is limited information about the role of the Dyn/KOR system in regulating amygdala circuitry. Here, we review the literature on the (1) basic anatomy of the amygdala, (2) functional regulation of synaptic transmission by the Dyn/KOR system, (3) anatomical architecture and function of the Dyn/KOR system in the amygdala, (4) regulation of amygdala-dependent behaviors by the Dyn/KOR system, and (5) future directions for the field. Future work investigating how the Dyn/KOR system shapes a wide range of amygdala-related behaviors will be required to increase our understanding of underlying circuitry modulation by the Dyn/KOR system. We anticipate that continued focus on the amygdala Dyn/KOR system will also elucidate novel ways to target the Dyn/KOR system to treat neuropsychiatric disorders.