Midbrain glutamatergic circuit mechanism of resilience to socially transferred allodynia in male mice.

The potential brain mechanism underlying resilience to socially transferred allodynia remains unknown. Here, we utilize a well-established socially transferred allodynia paradigm to segregate male mice into pain-susceptible and pain-resilient subgroups. Brain screening results show that ventral tegmental area glutamatergic neurons are selectively activated in pain-resilient mice as compared to control and pain-susceptible mice. Chemogenetic manipulations demonstrate that activation and inhibition of ventral tegmental area glutamatergic neurons bi-directionally regulate resilience to socially transferred allodynia. Moreover, ventral tegmental area glutamatergic neurons that project specifically to the nucleus accumbens shell and lateral habenula regulate the development and maintenance of the pain-resilient phenotype, respectively. Together, we establish an approach to explore individual variations in pain response and identify ventral tegmental area glutamatergic neurons and related downstream circuits as critical targets for resilience to socially transferred allodynia and the development of conceptually innovative analgesics.

Neuronal and Molecular Mechanisms Underlying Chronic Pain and Depression Comorbidity in the Paraventricular Thalamus.

Patients with chronic pain often develop comorbid depressive symptoms, which makes the pain symptoms more complicated and refractory. However, the underlying mechanisms are poorly known. Here, in a repeated complete Freund's adjuvant (CFA) male mouse model, we reported a specific regulatory role of the paraventricular thalamic nucleus (PVT) glutamatergic neurons, particularly the anterior PVT (PVA) neurons, in mediating chronic pain and depression comorbidity (CDC). Our c-Fos protein staining observed increased PVA neuronal activity in CFA-CDC mice. In wild-type mice, chemogenetic activation of PVA glutamatergic neurons was sufficient to decrease the 50% paw withdrawal thresholds (50% PWTs), while depressive-like behaviors evaluated with immobile time in tail suspension test (TST) and forced swim test (FST) could only be achieved by repeated chemogenetic activation. Chemogenetic inhibition of PVA glutamatergic neurons reversed the decreased 50% PWTs in CFA mice without depressive-like symptoms and the increased TST and FST immobility in CFA-CDC mice. Surprisingly, in CFA-CDC mice, chemogenetically inhibiting PVA glutamatergic neurons failed to reverse the decrease of 50% PWTs, which could be restored by rapid-onset antidepressant S-ketamine. Further behavioral tests in chronic restraint stress mice and CFA pain mice indicated that PVA glutamatergic neuron inhibition and S-ketamine independently alleviate sensory and affective pain. Molecular profiling and pharmacological studies revealed the 5-hydroxytryptamine receptor 1D (Htr1d) in CFA pain-related PVT engram neurons as a potential target for treating CDC. These findings identified novel CDC neuronal and molecular mechanisms in the PVT and provided insight into the complicated pain neuropathology under a comorbid state with depression and related drug development.

Adulthood bisphenol A exposure induces anxiety in male mice via downregulation of alpha-1D adrenergic receptor in paraventricular thalamus.

Bisphenol A (BPA), a ubiquitous endocrine disrupting chemical, is widely used in household plastic products. Large amounts of evidence indicate prenatal and postnatal BPA exposure causes neurodevelopmental disorders such as anxiety and autism. However, the neuronal mechanisms underlying the neurotoxic effects of adulthood BPA exposure remain poorly understood. Here, we provided evidences that adult mice treated with BPA (0.45 mg/kg/day) during 3 weeks exhibited sex-specific anxiety like behaviors. We demonstrated that the BPA-induced anxiety in male mice, but not in female mice, was closely associated with hyperactivity of glutamatergic neurons in the paraventricular thalamus (PVT). Acute chemogenetic activation of PVT glutamatergic neurons caused similar effects on anxiety as observed in male mice exposed to BPA. In contrast, acute chemogenetic inhibition of PVT glutamatergic neurons reduced BPA-induced anxiety in male mice. Concomitantly, the BPA-induced anxiety was related with a down-regulation of alpha-1D adrenergic receptor in the PVT. Taken together, the present study indicated a previously unknown target region in the brain for neurotoxic effects of BPA on anxiety and implicated a possible molecular mechanism of action.

Exposure to tris(2,6-dimethylphenyl) phosphate interferes with sexual differentiation via estrogen receptors 2a and 2b in zebrafish.

Tris(2,6-dimethylphenyl) phosphate (TDMPP), an emerging organophosphate flame retardant, is frequently detected in multiple environmental media. Although TDMPP has been proven as a compound with estrogenic activity, its feminizing effects on reproductive system remain unclear. This study investigated the adverse effects of TDMPP on gonadal development by exposing zebrafish for 105 days from 15 days post-fertilization. Exposure to TDMPP (0.5 and 5 µM, corresponding to about 200 and 2000 µg/L) induced ovarian formation in aromatase mutant (cyp19a1a-/-) line which normally presents all-male phenotype for deficiency of endogenous estrogen (E2), suggesting its feminizing effect on sexual differentiation. In addition, TDMPP also interfered with other aspects of reproduction by delaying puberty onset, retarding sexual maturation, impairing gametogenesis and subfertility. Molecular docking and reporter gene assay indicated that all three nuclear estrogen receptors (nERs) can be binded to and activated by TDMPP. Using a series of nERs mutant lines, we confirmed the indispensable role of esr2a and esr2b in mediating the feminizing effects of TDMPP. Further analysis revealed that the prominent effects of TDMPP on sexual differentiation correlated to upregulation of female-promoting genes and downregulation of male-promoting genes. Taken together, the present study provided unequivocal genetic evidence for estrogenic effects of TDMPP on reproductive system and its molecular mechanisms of action.

Neural and molecular investigation into the paraventricular thalamic-nucleus accumbens circuit for pain sensation and non-opioid analgesia.

The paucity of medications with novel mechanisms for pain treatment combined with the severe adverse effects of opioid analgesics has led to an imperative pursuit of non-opioid analgesia and a better understanding of pain mechanisms. Here, we identify the putative glutamatergic inputs from the paraventricular thalamic nucleus to the nucleus accumbens (PVTGlut→NAc) as a novel neural circuit for pain sensation and non-opioid analgesia. Our in vivo fiber photometry and in vitro electrophysiology experiments found that PVTGlut→NAc neuronal activity increased in response to acute thermal/mechanical stimuli and persistent inflammatory pain. Direct optogenetic activation of these neurons in the PVT or their terminals in the NAc induced pain-like behaviors. Conversely, inhibition of PVTGlut→NAc neurons or their NAc terminals exhibited a potent analgesic effect in both naïve and pathological pain mice, which could not be prevented by pretreatment of naloxone, an opioid receptor antagonist. Anterograde trans-synaptic optogenetic experiments consistently demonstrated that the PVTGlut→NAc circuit bi-directionally modulates pain behaviors. Furthermore, circuit-specific molecular profiling and pharmacological studies revealed dopamine receptor 3 as a candidate target for pain modulation and non-opioid analgesic development. Taken together, these findings provide a previously unknown neural circuit for pain sensation and non-opioid analgesia and a valuable molecular target for developing future safer medication.

The Role of Beta-Adrenergic Receptors in Depression and Resilience.

Norepinephrine is a catecholamine neurotransmitter that has been extensively implicated in the neurobiology of major depressive disorder (MDD). An accumulating body of evidence indicates that investigations into the action of norepinephrine at the synaptic/receptor level hold high potential for a better understanding of MDD neuropathology and introduce possibilities for developing novel treatments for depression. In this review article, we discuss recent advances in depression neuropathology and the effects of antidepressant medications based on preclinical and clinical studies related to beta-adrenergic receptor subtypes. We also highlight a beta-3 adrenergic receptor-involved mechanism that promotes stress resilience, through which antidepressant efficacy is achieved in both rodent models for depression and patients with major depression-an alternative therapeutic strategy that is conceptually different from the typical therapeutic approach in which treatment efficacy is achieved by reversing pathological alterations rather than by enhancing a good mechanism such as natural resilience. Altogether, in this review, we systematically describe the role of beta-adrenergic receptors in depression and stress resilience and provide a new avenue for developing a conceptually innovative treatment for depression.

The antiestrogen-like activity and reproductive toxicity of 2,6-DCBQ on female zebrafish upon sub-chronic exposure.

2,6-Dichloro-1,4-benzoquinone (2,6-DCBQ), an emerging water disinfection by-product, is widely detected in water resources. However, its potential effects on the reproductive system are largely unknown. Here, we investigated the long-term effects of 2,6-DCBQ on gonadal development by exposing zebrafish from 15 to 180 days postfertilization (dpf). Following exposure to 2,6-DCBQ (20 and 100 µg/L), female-specific effects including delayed puberty onset, retarded ovarian growth and breakdown of the zona radiata were observed, resulting in subfertility in adult females. Adverse effects in folliculogenesis disappeared two months after cessation of 2,6-DCBQ administration. In contrast, no adverse impacts were noted in male testes. The effects on females were associated with significant reduction in 17ß-estradiol (E2) level, suggesting a role for 2,6-DCBQ in anti-estrogenic activity. E2 level change in blood was further supported by dysregulated expression of genes (cyp19a1a, fshb, kiss3, esr2b, vtg1, and vtg3) related to the hypothalamic-pituitary-gonad-liver (HPGL) axis. The present study demonstrates for the first time that 2,6-DCBQ induces reproductive impairments in female zebrafish through disrupting 17ß-estradiol level.

Uncovering the 'sphinx' of sphingosine 1-phosphate signalling: from cellular events to organ morphogenesis.

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite, functioning as a signalling molecule in diverse cellular processes. Over the past few decades, studies of S1P signalling have revealed that the physiological activity of S1P largely depends on S1P metabolizing enzymes, transporters and receptors on the plasma membrane, as well as on the intracellular proteins that S1P binds directly to. In addition to its roles in cancer signalling, immunity and inflammation, a large body of evidence has identified a close link of S1P signalling with organ morphogenesis. Here we discuss the vital role of S1P signalling in orchestrating various cellular events during organ morphogenesis through analysing each component along the extracellular and intracellular S1P signalling axes. For each component, we review advances in our understanding of S1P signalling and function from the upstream regulators to the downstream effectors and from cellular behaviours to tissue organization, primarily in the context of morphogenetic mechanisms. S1P-mediated vesicular trafficking is also discussed as a function independent of its signalling function. A picture emerges that reveals a multifaceted role of S1P-dependent pathways in the development and maintenance of organ structure and function.

A Model of Hereditary Sensory and Autonomic Neuropathy Type 1 Reveals a Role of Glycosphingolipids in Neuronal Polarity.

Hereditary sensory and autonomic neuropathy Type 1 (HSAN1) is a rare autosomal dominantly inherited neuropathy, clinically characterized by a loss of distal peripheral sensory and motoneuronal function. Mutations in subunits of serine palmitoyltransferase (SPT) have been linked to the majority of HSAN1 cases. SPTs catalyze the condensation of l-serine with palmitoyl-CoA, the first committed and rate-limiting step in de novo sphingolipid biosynthesis. Despite extensive investigation, the molecular pathogenesis of HSAN1 remains controversial. Here, we established a Caenorhabditis elegans (C. elegans) model of HSAN1 by generating a sptl-1(c363g) mutation, encoding SPTL-1(C121W) and equivalent to human SPTLC1C133W, at the C. elegans genomic locus through CRISPR. The sptl-1(c363g) homozygous mutants exhibited the same larval lethality and epithelial polarity defect as observed in sptl-1(RNAi) animals, suggesting a loss-of-function effect of the SPTL-1(C121W) mutation. sptl-1(c363g)/+ heterozygous mutants displayed sensory dysfunction with concomitant neuronal morphology and axon-dendrite polarity defects, demonstrating that the C. elegans model recapitulates characteristics of the human disease. sptl-1(c363g)-derived neuronal defects were copied in animals with defective sphingolipid biosynthetic enzymes downstream of SPTL-1, including ceramide glucosyltransferases, suggesting that SPTLC1C133W contributes to the HSAN1 pathogenesis by limiting the production of complex sphingolipids, including glucosylceramide. Overexpression of SPTL-1(C121W) led to similar epithelial and neuronal defects and to reduced levels of complex sphingolipids, specifically glucosylceramide, consistent with a dominant-negative effect of SPTL-1(C121W) that is mediated by loss of this downstream product. Genetic interactions between SPTL-1(C121W) and components of directional trafficking in neurons suggest that the neuronal polarity phenotype could be caused by glycosphingolipid-dependent defects in polarized vesicular trafficking.SIGNIFICANCE STATEMENT The symptoms of inherited metabolic diseases are often attributed to the accumulation of toxic intermediates or byproducts, no matter whether the disease-causing enzyme participates in a biosynthetic or a degradation pathway. By showing that the phenotypes observed in a C. elegans model of HSAN1 disease could be caused by loss of a downstream product (glucosylceramide) rather than the accumulation of a toxic byproduct, our work provides new insights into the origins of the symptoms of inherited metabolic diseases while expanding the repertoire of sphingolipid functions, specifically, of glucosylceramides. These findings not only have their most immediate relevance for neuroprotective treatments for HSAN1, they may also have implications for a much broader range of neurologic conditions.