Embracing diversity in the 5-HT neuronal system

Tryptophan metabolism and ischemic stroke: An intricate balance

Ischemic stroke, which is characterized by hypoxia and ischemia, triggers a cascade of injury responses, including neurotoxicity, inflammation, oxidative stress, disruption of the blood-brain barrier, and neuronal death. In this context, tryptophan metabolites and enzymes, which are synthesized through the kynurenine and 5-hydroxytryptamine pathways, play dual roles. The delicate balance between neurotoxic and neuroprotective substances is a crucial factor influencing the progression of ischemic stroke. Neuroprotective metabolites, such as kynurenic acid, exert their effects through various mechanisms, including competitive blockade of N-methyl-D-aspartate receptors, modulation of α7 nicotinic acetylcholine receptors, and scavenging of reactive oxygen species. In contrast, neurotoxic substances such as quinolinic acid can hinder the development of vascular glucose transporter proteins, induce neurotoxicity mediated by reactive oxygen species, and disrupt mitochondrial function. Additionally, the enzymes involved in tryptophan metabolism play major roles in these processes. Indoleamine 2,3-dioxygenase in the kynurenine pathway and tryptophan hydroxylase in the 5-hydroxytryptamine pathway influence neuroinflammation and brain homeostasis. Consequently, the metabolites generated through tryptophan metabolism have substantial effects on the development and progression of ischemic stroke. Stroke treatment aims to restore the balance of various metabolite levels; however, precise regulation of tryptophan metabolism within the central nervous system remains a major challenge for the treatment of ischemic stroke. Therefore, this review aimed to elucidate the complex interactions between tryptophan metabolites and enzymes in ischemic stroke and develop targeted therapies that can restore the delicate balance between neurotoxicity and neuroprotection.

Steroid hormones in pain: Mechanistic underpinnings and therapeutic perspectives

Pain is a complex sensory and emotional experience that severely affects an individual's quality of life and health status. Steroid hormones, as important regulatory substances in the human body, are extensively involved in various physiological and pathological processes. In recent years, remarkable progress has been made in the research of steroid hormones in the field of pain. They play a crucial role in the occurrence, development, and treatment of pain. This review comprehensively elaborates on the roles and therapeutic mechanisms of steroid hormones in pain, explores the performances of glucocorticoids, mineralocorticoids, sex hormones, etc. in different pain models, as well as the molecular mechanisms by which they regulate pain through genomic and non-genomic effects, aiming to provide a theoretical basis for the clinical treatment of pain.

Genetic variants of SLC6A4 and risk of coronary artery disease: insights from North Indian population

BACKGROUND

The activity of SLC6A4 is influenced by its polymorphisms, including the length variation in serotonin transporter linked promoter region (5-HTTLPR), a single nucleotide polymorphism (rs25531), and variable number of tandem repeats in serotonin transporter intronic enhancer (STin2). These polymorphisms have been implicated in the development of vascular diseases. Our research aimed to determine whether the bi-allelic 5-HTTLPR, tri-allelic 5-HTTLPR (rs25531), and STin2 polymorphisms of SLC6A4 were associated with an increased risk of coronary artery disease (CAD) in the North Indian population of Jammu region in Jammu and Kashmir state of India.

METHODS

In this study, we performed a large cohort case-control study. Here, we recruited 400 patients clinically diagnosed with CAD, and 400 unrelated healthy individuals with similar sex and age range. We performed Polymerase Chain Reaction (PCR) for genotyping the 5-HTTLPR and STin2 polymorphisms. In addition, PCR- Restriction Fragment Length polymorphism (RFLP) was used to perform restriction fragment length polymorphism for the rs25531. Finally, we performed statistical analysis with the yield data.

RESULTS

The L-allele of 5-HTTLPR was significantly associated with CAD susceptibility, with an odd ratio (OR) of 1.39 and a p-value of 0.01. However, no significant association was identified for the tri-allelic 5-HTTLPR (rs25531) and STin2 polymorphism with the susceptibility of CAD. The haplotype combinations associated with CAD outcomes include L-12 and LA-10.

CONCLUSIONS

Although, majority of the previous studies have evaluated the association of 5-HTTLPR biallelic polymorphism with CAD, our findings suggested that the tri-allelic 5-HTTLPR (rs25531) is a more reliable candidate than the bi-allelic 5-HTTLPR, as studying the bi-allelic version alone may generate association bias. Based on the results of this study, the rs25531 and STin2 polymorphisms indicated that the SLC6A4 gene does not contribute to the development of CAD in the population of the of Jammu region in Jammu and Kashmir state of India.

Perinatal SSRI exposure impacts innate fear circuit activation and behavior in mice and humans

Before assuming its role in the mature brain, serotonin modulates early brain development across phylogenetically diverse species. In mice and humans, early-life SSRI exposure alters the offspring's brain structure and is associated with anxiety and depression-related behaviors beginning in puberty. However, the impact of early-life SSRI exposure on brain circuit function is unknown. To address this question, we examined how developmental SSRI exposure changes fear-related brain activation and behavior in mice and humans. SSRI-exposed mice showed increased defense responses to a predator odor, and stronger fMRI amygdala and extended fear-circuit activation. Likewise, adolescents exposed to SSRIs in utero exhibited higher anxiety and depression symptoms than unexposed adolescents and also had greater activation of the amygdala and other limbic structures when processing fearful faces. These findings demonstrate that increases in anxiety and fear-related behaviors as well as brain circuit activation following developmental SSRI exposure are conserved between mice and humans. These findings have potential implications for the clinical use of SSRIs during human pregnancy and for designing interventions that protect fetal brain development.

Multidimensional mechanisms of anxiety and depression in Parkinson's disease: Integrating neuroimaging, neurocircuits, and molecular pathways

Anxiety and depression are common non-motor symptoms of Parkinson's disease (PD) that significantly affect patients' quality of life. In recent years, our understanding of PD has advanced through multifaceted studies on the pathological mechanisms associated with anxiety and depression in PD. These classic psychiatric symptoms involve complex pathophysiology, with both distinct features and connections to the mechanisms underlying the aetiology of PD. Furthermore, the co-occurrence of anxiety and depression in PD blurs the boundaries between them. Therefore, a comprehensive summary of the pathogenic mechanisms associated with anxiety and depression will aid in better addressing the emergence of these classic psychiatric symptoms in PD. This article integrates neuroanatomical, neural projection, neurotransmitter, neuroinflammatory, brain-gut axis, neurotrophic, hypothalamic-pituitary-adrenal axis, and genetic perspectives to provide a comprehensive description of the core pathological alterations underlying anxiety and depression in PD, aiming to provide an up-to-date perspective and broader therapeutic prospects for PD patients suffering from anxiety or depression.

A prospective code for value in the serotonin system

The in vivo responses of dorsal raphe nucleus serotonin neurons to emotionally salient stimuli are a puzzle1. Existing theories centring on reward2, surprise3, salience4 and uncertainty5 individually account for some aspects of serotonergic activity but not others. Merging ideas from reinforcement learning theory6 with recent insights into the filtering properties of the dorsal raphe nucleus7, here we find a unifying perspective in a prospective code for value. This biological code for near-future reward explains why serotonin neurons are activated by both rewards and punishments3,4,8-13, and why these neurons are more strongly activated by surprising rewards but have no such surprise preference for punishments3,9-observations that previous theories have failed to reconcile. Finally, our model quantitatively predicts in vivo population activity better than previous theories. By reconciling previous theories and establishing a precise connection with reinforcement learning, our work represents an important step towards understanding the role of serotonin in learning and behaviour.

The molecular signature of heat stress in sweat reveals non-invasive biomarker candidates for health monitoring

Heat stress is a significant public health challenge that leads to an increased risk of serious health deterioration, injuries, and loss of economic productivity. While the gold standard for monitoring heat stress continues to remain with population-based measurements, a straight-forward person-centered approach is lacking. Sweat can supply a wealth of molecular information, ranging from protein levels to levels of metabolites; it is thus a promising monitoring biofluid. A thorough investigation of sweat's molecular signature during heat stress is called for. We conducted a cross-over study on healthy participants with personalized heat-stress visits to investigate heat stress's proteomic and molecular signatures in sweat. Through mass-spectrometry analysis, we identified multiple candidate biomarkers ranging from amino acids to microbiome metabolites and proteins. To the best of our knowledge, these biomarker candidates represent the first successful approach to metabolically differentiate between various heat stressors thereby enabling their acute monitoring. While these biomarker candidates need further investigation to confirm their clinical value, many have already been identified as directly associated with heat stress in animals and plants. Once further investigated, next-generation wearable devices for person-centered, on-skin sweat-analysing platforms could be developed that would transform health management during exposure to heat stress.

Exploring the effects of adolescent social isolation stress on the serotonin system and ethanol-motivated behaviors

RATIONALE

Alcohol is one of the most frequently used drugs of abuse and has a major impact on human health worldwide. People assigned female at birth and those with adverse childhood experiences are stress-vulnerable and more likely to report drinking as a means of "self-medication." Prior studies in our laboratory showed that adolescent social isolation stress (SIS) increases vulnerability to ethanol (EtOH) intake and consumption despite negative consequences in female rats.

OBJECTIVES

Here, we explored modulation of the dorsal raphe nucleus (DRN)-serotonin (5-HT) system, a sexually dimorphic neurotransmitter system involved in stress-reward interactions, to determine its contribution to EtOH-motivated behaviors in rats that have undergone SIS.

RESULTS

We employed electrophysiological and functional neuroanatomy strategies to show that both SIS and EtOH exposure induce persistent hypofunction of the DRN 5-HT system, particularly in females. Chemogenetic activation of DRN 5-HT neurons attenuated reward value for both EtOH and sucrose and elevated punished responding for EtOH in a stress-dependent manner.

CONCLUSIONS

Our results highlight an inverse relationship between EtOH consumption and the 5-HT system, the sex- and stress-dependent nature of this relationship, and a connection between DRN 5-HT signaling and acute responding to rewards and punishment. These data support the DRN 5-HT system as a potential target to treat aberrant alcohol consumption and drinking despite negative consequences in stress-vulnerable populations.

In Situ Recovery of Serotonin Synthesis by a Tryptophan Hydroxylase-Like Nanozyme for the Treatment of Depression

Depression is one of the most common mental disorders. The inactivation of tryptophan hydroxylase and the resulting serotonin decrease are the key factors in depression pathology. Herein, we report for the first time that Fe3O4 nanoparticles exhibit tryptophan hydroxylase-like activity and successfully verify their ability to restore serotonin synthesis in the brain for the treatment of depression. To achieve better biocompatibility and brain delivery, the Fe3O4 nanoparticles were functionalized with chitosan (CS) (Fe3O4@CS), enabling their delivery from the nose to the brain. Fe3O4@CS catalyzes the transformation of tryptophan into 5-hydroxytryptophan with the participation of high levels of endogenous ascorbic acid and hydrogen peroxide in stressed neurons, thus compensating for the deactivated tryptophan hydroxylase in the brain. In vivo Fe3O4@CS treatment results in the recovery of 5-hydroxytryptophan and serotonin levels and improvement of neuronal signal transduction ability in a depression mouse model, thus ameliorating depressive-like behaviors. The presented strategy of restoring serotonin synthesis in situ based on a tryptophan hydroxylase-like nanozyme provides a more accurate and efficient approach for the treatment of depression.

The effects of exercise interventions on depressive symptoms in stroke patients: a systematic review and meta-analysis

Purpose

This systematic review and meta-analysis aimed to evaluate the effects of exercise interventions on depressive symptoms in stroke patients.

Methods

Following PRISMA guidelines, We conducted searches in PubMed, Embase, CENTRAL, and Web of Science. The topic was the effect of exercise on depression levels in stroke patients. Patient's performance on depression scales after exercise was assessed using standardized mean difference (SMD) and 95% confidence intervals (95% CI). A random effects model (RE) was used to conduct a meta-analysis and compare the results between subgroups conducted based on adherence to ACSM guidelines and the length of exercise interventions.

Results

The analysis included 24 randomized controlled trials (RCTs) involving 1,757 participants. The meta-analysis revealed that exercise interventions had a significant positive effect on reducing depressive symptoms in stroke patients, with a standardized mean difference (SMD) of -0.43 (95% CI: 0.65, -0.21). Subgroup analysis indicated that high compliance with ACSM guidelines resulted in a more substantial reduction in depressive symptoms (SMD = -0.79, 95% CI: 1.10, -0.49), compared with low or uncertain compliance (SMD = -0.03, 95% CI: 0.16, 0.10). Longer exercise intervention was associated with greater mitigation of depressive symptoms. The differences between intervention groups of different lengths were statistically significant (p < 0.05).

Conclusion

These findings support the integration of tailored exercise programs into post-stroke care to optimize mental health outcomes. Compliance to ACSM-recommended exercise dosages significantly ameliorate depression levels in stroke patients. Further research is warranted to explore standardized exercise regimens in larger, multicenter trials.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/#recordDetails, identifier PROSPERO(CRD42024579095).

Confocal fluorescent study of the fish blood flukes: the serotonergic elements and ultrastructure of the nervous system of adult Sanguinicola plehnae (Digenea: Sanguinicolidae)

The first data on the neurochemical and ultrastructural organisation of the nervous system of the fish blood fluke, suckerless adult Sanguinicola plehnae Warren et Bullard in Warren, Poddubnaya, Zhokhov, Reyda, Choudhury et Bullard, 2023 (Digenea: Aporocotylidae) from the circulatory system of pike, Esox lucius Linnaeus are presented. Based on 5-HT-IP staining, the simple, uniformly developed orthogonal pattern of S. plehnae nervous system is revealed. The ventral and dorsal nerve cords originate from the brain lobes, but the lateral nerve cords originate from anterior nerves at the level of the large serotonergic neurons. In addition, several pairs of such large 5-HT-IP neurons (22-23.5 µm in diameter) are revealed along the ventral nerve cords. Unusual spindle-shaped 5-HT-IP perikarya (7.8-19.8 µm in diameter) are observed along each ventral and lateral nerve cords. The neuroblasts and developing neurons are seen between neurites in S. plehnae along with neuron somata scattered around neuropil periphery, evidencing the renewal of neuron somata population in adult digeneans. The morphological variability of both the orthogonal pattern and neuron somata and types of neurovesicles in adult digeneans are discussed.

Dorsal raphe GABA-ergic neurons regulate the susceptibility to social transfer of pain in mice

Some individuals are more susceptible to developing or suffering from pain states than others. However, the brain mechanisms underlying the susceptibility to pain responses are unknown. In this study, we defined pain susceptibility by recapitulating inter-individual differences in pain responses in mice exposed to a paradigm of socially transferred allodynia (STA), and with a combination of chemogenetic, molecular, pharmacological and electrophysiological approaches, we identified GABA-ergic neurons in the dorsal raphe nucleus (DRN) as a cellular target for the development and maintenance of STA susceptibility. We showed that DRN GABA-ergic neurons were selectively activated in STA-susceptible mice when compared with the unsusceptible (resilient) or control mice. Chemogenetic activation of DRN GABA-ergic neurons promoted STA susceptibility; whereas inhibiting these neurons prevented the development of STA susceptibility and reversed established STA. In in vitro slice electrophysiological analysis, we demonstrated that melanocortin 4 receptor (MC4R) enriched in DRN GABA-ergic neurons was a molecular target for regulating pain susceptibility, possibly by affecting DRN GABA-ergic neuronal activity. These results establish the DRN GABA-ergic neurons as an essential target for controlling pain susceptibility, thus providing important information for developing conceptually innovative and more accurate analgesic strategies.

Coding principles and mechanisms of serotonergic transmission modes

Serotonin-mediated intercellular communication has been implicated in myriad human behaviors and diseases, yet how serotonin communicates and how the communication is regulated remain unclear due to limitations of available monitoring tools. Here, we report a method multiplexing genetically encoded sensor-based imaging and fast-scan cyclic voltammetry, enabling simultaneous recordings of synaptic, perisynaptic, proximate and distal extrasynaptic serotonergic transmission. Employing this method alongside a genetically encoded sensor-based image analysis program (GESIAP), we discovered that heterogeneous firing patterns of serotonergic neurons create various transmission modes in the mouse raphe nucleus and amygdala, encoding information of firing pulse frequency, number, and synchrony using neurotransmitter quantity, releasing synapse count, and synaptic and/or volume transmission. During tonic and low-frequency phasic activities, serotonin is confined within synaptic clefts due to efficient retrieval by perisynaptic transporters, mediating synaptic transmission modes. Conversely, during high-frequency, especially synchronized phasic activities, or when transporter inhibition, serotonin may surpass transporter capacity, and escape synaptic clefts through 1‒3 outlet channels, leading to volume transmission modes. Our results elucidate a mechanism of how channeled synaptic enclosures, synaptic properties, and transporters collaborate to define the coding principles of activity pattern-dependent serotonergic transmission modes.

Early environmental influences on the orbito-frontal cortex function and its effects on behavior

Early-life adversity during pre- and early post-natal phases can impact brain development and lead to maladaptive changes in executive function related behaviors. This increases the risk for a range of psychopathologies and physical diseases. Importantly, exposure to adversities during these periods is also linked to alterations in the orbito-frontal cortex (OFC) which is a key player in these executive functions. The OFC thus appears to be a central node in this association between early life stress and disease risk. Gaining a clear, and detailed understanding of the association between early life stress, OFC function, and executive function, as well as the underlying mechanisms mediating this association is relevant to inform potential therapeutic interventions. In this paper, we begin by reviewing evidence linking early life adversities to 1) alterations in behaviors regulated by the OFC and 2) changes in OFC anatomy and function. We then present insights into the underlying mechanisms for these changes, stemming from early life adversity models, and highlight important future directions for this line of research.

Role of serotonin neurons in the dorsal raphe nucleus in heroin self-administration and punishment

One hallmark of substance use disorder is continued drug use despite negative consequences. When drug-taking behavior is punished with aversive stimuli, i.e. footshock, rats can also be categorized into punishment-resistant or compulsive vs. punishment-sensitive or non-compulsive phenotypes. The serotonin (5-hydroxytryptamine, 5-HT) system modulates responses to both reward and punishment. The goal of the current study was to examine punishment phenotypes in heroin self-administration and to determine the role of dorsal raphe nucleus (DRN) 5-HT neurons in both basal and punished heroin self-administration. First, rats were exposed to punished heroin self-administration and neuronal excitability of DRN 5-HT neurons was compared between punishment-resistant and punishment-sensitive phenotypes using ex vivo electrophysiology. Second, DRN 5-HT neuronal activity was manipulated in vivo during basal and punished heroin self-administration using chemogenetic tools in a Tph2-iCre rat line. While rats separated into punishment-resistant and punishment-sensitive phenotypes for punished heroin self-administration, DRN 5-HT neuronal excitability did not differ between the phenotypes. While chemogenetic inhibition of DRN 5-HT neurons was without effect, chemogenetic activation of DRN 5-HT neurons increased both basal and punished heroin self-administration selectively in punishment-resistant animals. Additionally, the responsiveness to chemogenetic activation of DRN 5-HT neurons in basal self-administration and motivation for heroin in progressive ratio each predicted resistance to punishment. Therefore, our data support the role for the DRN 5-HT system in compulsive heroin self-administration.

Effects of aminooxyacetic acid on learning and memory function and neurochemical changes in chronic alcoholism

OBJECTIVE

This study aimed to investigate the effect of aminooxyacetic acid (AOAA) on cognitive function, particularly learning and memory, in a rat model of chronic alcoholism. Additionally, the study explored changes in cystathionine β-synthase (CBS), hydrogen sulfide (H₂S), and serotonin (5-HT) levels in the prefrontal cortex to understand the potential neurochemical mechanisms involved.

METHODS

Sixty-four male SD rats were randomly divided into four groups, with 16 rats in each: Con, Con + AOAA, Model, and Model + AOAA. The Model group received a 6 % ethanol solution for 28 days. From day 14, the Model + AOAA group was treated with daily intraperitoneal injections of AOAA (5 mg/kg) for 14 consecutive days. Cognitive function was assessed using the Morris water maze, mitochondrial function was evaluated through ATPase activity, and H₂S levels were measured. CBS and 5-HT levels in the prefrontal cortex were analyzed by immunohistochemistry.

RESULTS

Compared to the control groups, rats in the Model group exhibited significant impairments in learning and memory, increased CBS expression, elevated H₂S levels, and decreased 5-HT release. AOAA treatment improved memory performance, reduced CBS expression and H₂S levels, and increased 5-HT release, although these measures did not fully return to baseline. No significant differences were observed between the two control groups.

CONCLUSION

AOAA may alleviate cognitive deficits associated with chronic alcoholism by inhibiting CBS expression, reducing H₂S levels, and enhancing 5-HT release in the prefrontal cortex. These findings suggest AOAA as a potential therapeutic strategy for alcohol-induced cognitive impairments.

HTR1D regulates the PI3K/Akt signaling pathway to impact hepatocellular carcinoma development and resistance to sorafenib

BACKGROUND

Hepatocellular carcinoma (HCC) has a poor prognosis, partly due to resistance to treatments like sorafenib. The 5-hydroxytryptamine receptor 1D (HTR1D) is involved in cancer progression through the PI3K/Akt pathway, but its role in HCC is not well understood. This study investigates HTR1D's expression, function, and potential as a prognostic marker in HCC.

METHODS

First, the correlation between HTR1D and hepatocellular carcinoma was analyzed using the TCGA database, and the expression level of HTR1D in clinical samples was detected by qPCR. Then the siRNA was transfected into Huh-7 and Hep3B cells, and the cell proliferation ability, colony formation ability, migration and invasion ability were detected with or without sorafenib. And the expression of the PI3K/Akt pathway was detected by Western Blot. Finally, the potential of HTR1D as a predictive marker for patient prognosis was evaluated by immunohistochemistry.

RESULTS

Analysis of TCGA data showed that methylation of the HTR1D gene was associated with cancer status. Clinical samples confirmed significant differences in HTR1D expression between HCC and adjacent tissues, with higher expression correlating with poorer patient prognosis. Interference with HTR1D gene expression demonstrated its role in promoting HCC proliferation, migration, and drug resistance through the PI3K/Akt pathway. These findings were validated in a mouse model. Immunohistochemical analysis of clinicopathological samples suggested that HTR1D could be a valuable prognostic marker for HCC.

CONCLUSION

HTR1D is highly expressed in hepatocellular carcinoma tissues, and it can influence hepatocellular carcinoma development and resistance to sorafenib by regulating the PI3K/Akt signaling pathway. In addition, HTR1D has potential as a prognostic indicator.

Deciphering the Functions of Raphe-Hippocampal Serotonergic and Glutamatergic Circuits and Their Deficits in Alzheimer's Disease

Subcortical innervation of the hippocampus by the raphe nucleus is essential for emotional and cognitive control. The two major afferents from raphe to hippocampus originate from serotonergic and glutamatergic neurons, of which the serotonergic control of hippocampal inhibitory network, theta activity, and synaptic plasticity have been extensively explored in the growing body of literature, whereas those of glutamatergic circuits have received little attention. Notably, both serotonergic and glutamatergic circuits between raphe and hippocampus are disrupted in Alzheimer's disease (AD), which may contribute to initiation and progression of behavioral and psychological symptoms of dementia. Thus, deciphering the mechanism underlying abnormal raphe-hippocampal circuits in AD is crucial to prevent dementia-associated emotional and cognitive symptoms. In this review, we summarize the anatomical, neurochemical, and electrophysiological diversity of raphe nuclei as well as the architecture of raphe-hippocampal circuitry. We then elucidate subcortical control of hippocampal activity by raphe nuclei and their role in regulation of emotion and cognition. Additionally, we present an overview of disrupted raphe-hippocampal circuits in AD pathogenesis and analyze the available therapies that can potentially be used clinically to alleviate the neuropsychiatric symptoms and cognitive decline in AD course.

Neurons Are Not All the Same: Diversity in Neuronal Populations and Their Intrinsic Responses to Spinal Cord Injury

Functional recovery following spinal cord injury will require the regeneration and repair of damaged neuronal pathways. It is well known that the tissue response to injury involves inflammation and the formation of a glial scar at the lesion site, which significantly impairs the capacity for neuronal regeneration and functional recovery. There are initial attempts by both supraspinal and intraspinal neurons to regenerate damaged axons, often influenced by the neighboring tissue pathology. Many experimental therapeutic strategies are targeted to further stimulate the initial axonal regrowth, with little consideration for the diversity of the affected neuronal populations. Notably, recent studies reveal that the neuronal response to injury is variable, based on multiple factors, including the location of the injury with respect to the neuronal cell bodies and the affected neuronal populations. New insights into regenerative mechanisms have shown that neurons are not homogenous but instead exhibit a wide array of diversity in their gene expression, physiology, and intrinsic responses to injury. Understanding this diverse intrinsic response is crucial, as complete functional recovery requires the successful coordinated regeneration and reorganization of various neuron pathways.

Activating the Astrocytes of the Dorsal Raphe Nucleus via Its Neural Circuits With the Medial Prefrontal Cortex Improves Depression in Mice

Astrocytes are the primary cell type in the central nervous system, responsible for maintaining the stability of the brain's internal environment and supporting neuronal functions. Researches have demonstrated the close relationship between astrocytes and the pathophysiology and etiology of major depressive disorder. However, the regulatory mechanisms of astrocytes during depression remain unclear. The aim of this study is to examine the alterations of calcium signaling of astrocytes in the dorsal raphe nucleus (DRN), the calcium signaling alterations of neurons in both the DRN and medial prefrontal cortex (mPFC), and the alteration of depressive-like behaviors by activation of DRN astrocytes using chemogenetics in chronic social defeat stress (CSDS) mice. The results showed that the intensity of calcium signaling in DRN astrocytes was decreased and the frequency of calcium signaling was lower after CSDS. The activation of DRN astrocytes increased the calcium signaling of the neurons including CaMKIIα neurons in both DRN and mPFC (via neural circuit between DRN and mPFC). The depressive-like behaviors were improved by activating DRN astrocytes in CSDS mice. Our results suggest that the astrocytes in DRN have an important role in depression and the findings offer new insights for the treatment of depression.

Metformin reprograms tryptophan metabolism via gut microbiome-derived bile acid metabolites to ameliorate depression-Like behaviors in mice

As an adjunct therapy, metformin enhances the efficacy of conventional antidepressant medications. However, its mode of action remains unclear. Here, metformin was found to ameliorate depression-like behaviors in mice exposed to chronic restraint stress (CRS) by normalizing the dysbiotic gut microbiome. Fecal transplants from metformin-treated mice ameliorated depressive behaviors in stressed mice. Microbiome profiling revealed that Akkermansia muciniphila (A. muciniphila), in particular, was markedly increased in the gut by metformin and that oral administration of this species alone was sufficient to reverse CRS-induced depressive behaviors and normalize aberrant stress-induced 5-hydroxytryptamine (5-HT) metabolism in the brain and gut. Untargeted metabolomic profiling further identified the bile acid metabolites taurocholate and deoxycholic acid as direct A. muciniphila-derived molecules that are, individually, sufficient to rescue the CRS-induced impaired 5-HT metabolism and depression-like behaviors. Thus, we report metformin reprograms 5-HT metabolism via microbiome-brain interactions to mitigate depressive syndromes, providing novel insights into gut microbiota-derived bile acids as potential therapeutic candidates for depressive mood disorders from bench to bedside.

Temporal changes of neurobehavior in rats following varied blast magnitudes and screening of serum biomarkers in early stage of brain injury

Blast neurotrauma has been linked to impairments in higher-order cognitive functions, including memory, attention, and mood. Current literature is limited to a single overpressure exposure or repeated exposures at the same level of overpressure. In this study, a rodent model of primary blast neurotrauma was employed to determine the pressure at which acute and chronic neurological alterations occurred. Three pressure magnitudes (low, moderate and high) were used to evaluate injury thresholds. A biology shock tube (BST) was used to simulate shock waves with overpressures of 60 kPa, 90 kPa and 120 kPa respectively. Neurological behavior of the rats was assessed by the Multi-Conditioning System (MCS) at 1 d, 7 d, 28 d and 90 d after shock wave exposure. Serum dopamine (DA), 5-hydroxytryptamine (5-HT), brain-derived neurotrophic factor (BDNF) and gamma-aminobutyric acid (GABA) were measured at the same time points. The proteomic analysis was conducted to identify potentially vulnerable cellular and molecule targets of serum in the immediate post-exposure period. Results revealed that: (1) Anxiety-like behavior increased significantly at 1 d post-exposure in the medium and high overpressure (90 kPa, 120 kPa) groups, returned to baseline at 7 days, and anxiety-like behavior in the high overpressure groups re-emerged at 28 d and 90 d. (2) High overpressure (120 kPa) impaired learning and memory in the immediate post-exposure period. (3) The serum DA levels decreased significantly at 1 d post-exposure in the medium and high overpressure groups; The 5-HT levels decreased significantly at 1 d and 90 d in the high overpressure groups; The BDNF levels decreased significantly at 90 d in the high overpressure groups. (4) Proteomic analysis identified 38, 306, and 57 differentially expressed proteins in serum following low, medium and high overpressure exposures, respectively. Two co-expressed proteins were validated. Functional analysis revealed significant enrichment of 1121, 2096, and 1121 Gene Ontology (GO) items and 33, 47, and 26 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, indicating extensive molecular responses to overpressure in the early phase. These findings suggest that exposure, even at moderate levels, can induce persistent neurobehavioral and molecular alterations, highlighting the need for further research into the long-term consequences of blast neurotrauma.

Gastrointestinal pathophysiology in long COVID: Exploring roles of microbiota dysbiosis and serotonin dysregulation in post-infectious bowel symptoms

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) triggered an unprecedented public health crisis known as the coronavirus disease 2019 (COVID-19) pandemic. Gastrointestinal (GI) symptoms develop in patients during acute infection and persist after recovery from airway distress in a chronic form of the disease (long COVID). A high incidence of irritable bowel syndrome (IBS) manifested by severe abdominal pain and defecation pattern changes is reported in COVID patients. Although COVID is primarily considered a respiratory disease, fecal shedding of SARS-CoV-2 antigens positively correlates with bowel symptoms. Active viral infection in the GI tract was identified by human intestinal organoid studies showing SARS-CoV-2 replication in gut epithelial cells. In this review, we highlight the key findings in post-COVID bowel symptoms and explore possible mechanisms underlying the pathophysiology of the illness. These mechanisms include mucosal inflammation, gut barrier dysfunction, and microbiota dysbiosis during viral infection. Viral shedding through the GI route may be the primary factor causing the alteration of the microbiome ecosystem, particularly the virome. Recent evidence in experimental models suggested that microbiome dysbiosis could be further aggravated by epithelial barrier damage and immune activation. Moreover, altered microbiota composition has been associated with dysregulated serotonin pathways, resulting in intestinal nerve hypersensitivity. These mechanisms may explain the development of post-infectious IBS-like symptoms in long COVID. Understanding how coronavirus infection affects gut pathophysiology, including microbiome changes, would benefit the therapeutic advancement for managing post-infectious bowel symptoms.

Reproductive Toxicity Induced by Serotonin-Norepinephrine Reuptake Inhibitors: A Pharmacovigilance Analysis From 2004 to 2023 Based on the FAERS Database

AIM

Serotonin-norepinephrine reuptake inhibitors (SNRIs) have been extensively utilized for the treatment of depression and anxiety disorders. Clinical trials and real-world data suggest that SNRIs may cause reproductive toxicity. To comprehensively assess this association, we conducted a pharmacovigilance study.

METHODS

We utilized various disproportionality analysis algorithms, including reporting odds ratio (ROR), proportional reporting ratio (PRR), bayesian confidence propagation neural network (BCPNN), and multi-item gamma poisson shrinker (MGPS), to assess the significance of reproductive toxicity-related adverse events (AEs) reported to FDA Adverse Event Reporting System (FAERS) from January 2004 to December 2023, with subgroup analysis conducted by sex and age.

RESULTS

Duloxetine and venlafaxine were associated with 14 and 25 AE signals related to reproductive toxicity, respectively, with erectile dysfunction (ED) and retrograde ejaculation identified as shared important medical events (IMEs). ED had the highest reporting frequency, strongest in venlafaxine-treated patients under 45 years (ROR 4.34, PRR 4.33, IC 2.09, EBGM 4.25). Retrograde ejaculation was newly identified. With decreasing incidence, venlafaxine's median ED onset was 122.5 days and duloxetine's 38 days.

CONCLUSION

Our study provides evidence through an extensive analysis of the large-scale real-world FAERS database, aiding healthcare professionals in mitigating, and prioritizing SNRI-related reproductive toxicity AEs.

Revisiting serotonin's role in spatial memory: A call for sensitive analytical approaches

The serotonergic system is involved in various psychiatric and neurological conditions, with serotonergic drugs often used in treatment. These conditions frequently affect spatial memory, which can serve as a model of declarative memory due to well-known cellular components and advanced methods that track neural activity and behavior with high temporal resolution. However, most findings on serotonin's effects on spatial learning and memory come from studies lacking refined analytical techniques and modern approaches needed to uncover the underlying neuronal mechanisms. This In Focus review critically investigates available studies to identify areas for further exploration. It finds that well-established behavioral models could yield more insights with modern tracking and data analysis approaches, while the cellular aspects of spatial memory remain underexplored. The review highlights the complex role of serotonin in spatial memory, which holds the potential for better understanding and treating memory-related disorders.

Structural and functional remodeling of neural networks in β-amyloid driven hippocampal hyperactivity

Early detection of Alzheimer's disease (AD) is essential for improving the patients outcomes and advancing our understanding of disease, allowing for timely intervention and treatment. However, accurate biomarkers are still lacking. Recent evidence indicates that hippocampal hyperexcitability precedes the diagnosis of AD decades ago, can predict cognitive decline. Thus, could hippocampal hyperactivity be a robust biomarker for early-AD, and what drives hippocampal hyperactivity in early-AD? these critical questions remain to be answered. Increasing clinical and experimental studies suggest that early hippocampal activation is closely associated with longitudinal β-amyloid (Aβ) accumulation, Aβ aggregates, in turn, enhances hippocampal activity. Therefore, in this narrative review, we discuss the role of Aβ-induced altered intrinsic neuronal properties as well as structural and functional remodeling of glutamatergic, GABAergic, cholinergic, noradrenergic, serotonergic circuits in hippocampal hyperactivity. In addition, we analyze the available therapies and trials that can potentially be used clinically to attenuate hippocampal hyperexcitability in AD. Overall, the present review sheds lights on the mechanism behind Aβ-induced hippocampal hyperactivity, and highlights that hippocampal hyperactivity could be a robust biomarker and therapeutic target in prodromal AD.

Mechanisms of neuromodulatory volume transmission

A wealth of neuromodulatory transmitters regulate synaptic circuits in the brain. Their mode of signaling, often called volume transmission, differs from classical synaptic transmission in important ways. In synaptic transmission, vesicles rapidly fuse in response to action potentials and release their transmitter content. The transmitters are then sensed by nearby receptors on select target cells with minimal delay. Signal transmission is restricted to synaptic contacts and typically occurs within ~1 ms. Volume transmission doesn't rely on synaptic contact sites and is the main mode of monoamines and neuropeptides, important neuromodulators in the brain. It is less precise than synaptic transmission, and the underlying molecular mechanisms and spatiotemporal scales are often not well understood. Here, we review literature on mechanisms of volume transmission and raise scientific questions that should be addressed in the years ahead. We define five domains by which volume transmission systems can differ from synaptic transmission and from one another. These domains are (1) innervation patterns and firing properties, (2) transmitter synthesis and loading into different types of vesicles, (3) architecture and distribution of release sites, (4) transmitter diffusion, degradation, and reuptake, and (5) receptor types and their positioning on target cells. We discuss these five domains for dopamine, a well-studied monoamine, and then compare the literature on dopamine with that on norepinephrine and serotonin. We include assessments of neuropeptide signaling and of central acetylcholine transmission. Through this review, we provide a molecular and cellular framework for volume transmission. This mechanistic knowledge is essential to define how neuromodulatory systems control behavior in health and disease and to understand how they are modulated by medical treatments and by drugs of abuse.

Effects of Electroacupuncture at Varied Frequencies on Analgesia and Mechanisms in Sciatic Nerve Cuffing-Induced Neuropathic Pain Mice

Addressing the intricate challenge of chronic neuropathic pain has significant implications for the physical and psychological well-being of patients, given its enduring nature. In contrast to opioids, electroacupuncture (EA) may potentially provide a safer and more efficacious therapeutic alternative. Our objective is to investigate the distinct analgesic effects and potential mechanisms of EA at frequencies of 2 Hz, 100 Hz, and 18 kHz in order to establish more precise frequency selection criteria for clinical interventions. Analgesic efficacy was evaluated through the measurement of mice's mechanical and thermal pain thresholds. Spinal cord inflammatory cytokines and neuropeptides were quantified via Quantitative Real-time PCR (qRT-PCR), Western blot, and immunofluorescence. Additionally, RNA sequencing (RNA-Seq) was conducted on the spinal cord from mice in the 18 kHz EA group for comprehensive transcriptomic analysis. The analgesic effect of EA on neuropathic pain in mice was frequency-dependent. Stimulation at 18 kHz provided superior and prolonged relief compared to 2 Hz and 100 Hz. Our research suggests that EA at frequencies of 2 Hz, 100 Hz, and 18 kHz significantly reduce the release of inflammatory cytokines. The analgesic effects of 2 Hz and 100 Hz stimulation are due to frequency-dependent regulation of opioid release in the spinal cord. Furthermore, 18 kHz stimulation has been shown to reduce spinal neuronal excitability by modulating the serotonergic pathway and downstream receptors in the spinal cord to alleviate neuropathic pain.

Median raphe glutamatergic neuron-mediated enhancement of GABAergic transmission and suppression of long-term potentiation in the hippocampus

The ascending neuromodulatory pathway from the median raphe nucleus (MRN) extends widely throughout midline/para-midline regions and robustly innervates the hippocampus. This neuromodulatory pathway is believed to be critical for regulating emotional and affective behaviors. Although the MRN primarily contains serotoninergic (5-HTergic), GABAergic, and glutamatergic neurons, glutamatergic neurons expressing vesicular glutamate transporter 3 (VGLUT3) form the primary MRN input to the hippocampus. Despite the earlier demonstration of the robust MRN VGLUT3 innervation of the hippocampus, little is known about how this MRN glutamatergic input modulates synaptic transmission and plasticity in the hippocampus. Our studies show that MRN VGLUT3 neurons activate serotonin 3a receptor (5-HT3aR)-expressing GABAergic neurons, including VGLUT3-expressing neurons, at the stratum radiatum (SR)/stratum lacunosum moleculare (SLM) border. This MRN VGLUT3 neuron-mediated glutamatergic transmission onto SR/SLM 5-HT3aR neurons is negatively regulated by 5-HT through 5-HT1B receptors. In agreement with the MRN VGLUT3 neuron-mediated activation of the 5-HT3aR GABAergic neurons, activation of MRN VGLUT3 projections induces a long-lasting increase in GABAergic transmission but not glutamatergic transmission in CA1 pyramidal neurons from male but not female mice. Consistent with the MRN VGLUT3 neuron-mediated enhancement of GABAergic transmission in male mice, activation of MRN VGLUT3 projections suppresses Schaffer collateral (SC)-CA1 long-term potentiation (LTP) in male but not female mice. Thus, our results show that MRN VGLUT3 neurons modulate the dorsal hippocampus by augmenting synaptic inhibition of CA1 pyramidal neurons and by suppressing SC-CA1 LTP in a sex-specific manner.

Serotonergic modulation of swallowing in a complete fly vagus nerve connectome

How the body interacts with the brain to perform vital life functions, such as feeding, is a fundamental issue in physiology and neuroscience. Here, we use a whole-animal scanning transmission electron microscopy volume of Drosophila to map the neuronal circuits that connect the entire enteric nervous system to the brain via the insect vagus nerve at synaptic resolution. We identify a gut-brain feedback loop in which Piezo-expressing mechanosensory neurons in the esophagus convey food passage information to a cluster of six serotonergic neurons in the brain. Together with information on food value, these central serotonergic neurons enhance the activity of serotonin receptor 7-expressing motor neurons that drive swallowing. This elemental circuit architecture includes an axo-axonic synaptic connection from the glutamatergic motor neurons innervating the esophageal muscles onto the mechanosensory neurons that signal to the serotonergic neurons. Our analysis elucidates a neuromodulatory sensory-motor system in which ongoing motor activity is strengthened through serotonin upon completion of a biologically meaningful action, and it may represent an ancient form of motor learning.

A comprehensive study on the regulation of Compound Zaoren Granules on cAMP/CREB signaling pathway and metabolic disorder in CUMS-PCPA induced insomnia rats

ETHNOPHARMACOLOGICAL RELEVANCE

Compound Zaoren Granules (CZG), an optimized herbal formulation based on the traditional Chinese medicine prescription Suanzaoren decoction, are designed specifically for insomnia treatment. However, the mechanisms underlying its efficacy in treating insomnia are not yet fully understood.

AIM OF THE STUDY

The research investigated the mechanisms of CZG's improvement in insomnia by regulating cAMP/CREB signaling pathway and metabolic profiles.

METHODS

The main components of CZG were characterized by liquid chromatography-mass spectrometry (LC-MS). Subsequently, these validated components were applied to network pharmacological analysis to predict signaling pathways associated with insomnia. We evaluated the effect of CZG on BV-2 cells in vitro. We also evaluated the behavioral indexes of CUMS combined with PCPA induced insomnia in rats. HE staining and Nissl staining were used to observe the pathological damage of hippocampus. ELISA was used to detect the levels of various neurotransmitters, orexins, HPA axis, and inflammatory factors in insomnia rats. Then we detected the expression of cAMP/CREB signaling pathway through ELISA, WB, and IHC. Finally, the metabolomics was further analyzed by using UHPLC-QTOF-MS/MS to investigate the changes in the hippocampus of insomnia rats and the possible metabolic pathways were also speculated.

RESULTS

The results of CZG in vitro experiments showed that CZG has protective and anti-inflammatory effects on LPS induced BV-2 cells. A total of 161 chemical components were identified in CZG. After conducting network pharmacology analysis through these confirmed components, we select the cAMP/CREB signaling pathway for further investigate. The behavioral research results on insomnia rats showed that CZG significantly prolonged sleep time, mitigated brain tissue pathological damage, and exhibited liver protective properties. CZG treats insomnia by regulating the content of various neurotransmitters, reducing levels of orexin, HPA axis, and inflammatory factors. It can also treat insomnia by upregulating the expression of the cAMP/CREB signaling pathway. Hippocampus metabolomics analysis identified 69 differential metabolites associated with insomnia. The metabolic pathways related to these differential metabolites have also been predicted.

CONCLUSION

These results indicate that CZG can significantly prolong sleep time. CZG is used to treat insomnia by regulating various neurotransmitters, HPA axis, inflammatory factors, cAMP/CREB signaling pathways, and metabolic disorders.

Serotonergic neuromodulation of synaptic plasticity

Synaptic plasticity constitutes a fundamental process in the reorganization of neural networks that underlie memory, cognition, emotional responses, and behavioral planning. At the core of this phenomenon lie Hebbian mechanisms, wherein frequent synaptic stimulation induces long-term potentiation (LTP), while less activation leads to long-term depression (LTD). The synaptic reorganization of neuronal networks is regulated by serotonin (5-HT), a neuromodulator capable of modify synaptic plasticity to appropriately respond to mental and behavioral states, such as alertness, attention, concentration, motivation, and mood. Lately, understanding the serotonergic Neuromodulation of synaptic plasticity has become imperative for unraveling its impact on cognitive, emotional, and behavioral functions. Through a comparative analysis across three main forebrain structures-the hippocampus, amygdala, and prefrontal cortex, this review discusses the actions of 5-HT on synaptic plasticity, offering insights into its role as a neuromodulator involved in emotional and cognitive functions. By distinguishing between plastic and metaplastic effects, we provide a comprehensive overview about the mechanisms of 5-HT neuromodulation of synaptic plasticity and associated functions across different brain regions.

Potentiation of active locomotor state by spinal-projecting serotonergic neurons

Animals produce diverse motor actions that enable expression of context-appropriate behaviors. Neuromodulators facilitate behavioral flexibility by altering the temporal dynamics and output of neural circuits. Discrete populations of serotonergic (5-HT) neurons target circuits in the brainstem and spinal cord, but their role in the control of motor behavior is unclear. Here we define the pre- and post-synaptic organization of the spinal-projecting serotonergic system and define a role in locomotor control. We show that while forebrain-targeting 5-HT neurons decrease their activity during locomotion, subpopulations of spinal projecting neurons increase their activity in a context-dependent manner. Optogenetic activation of ventrally projecting 5-HT neurons does not trigger initiation of movement, but rather enhances the speed and duration of ongoing locomotion over extended time scales. These findings indicate that the descending serotonergic system potentiates locomotor output and demonstrate a role for serotonergic neurons in modulating the temporal dynamics of motor circuits.

Intrinsic Molecular Proton Sensitivity Underlies GPR4 Effects on Retrotrapezoid Nucleus Neuronal Activation and CO2-Stimulated Breathing

An interoceptive homeostatic reflex monitors levels of CO2/H+ to maintain blood gas homeostasis and rapidly regulate tissue acid-base balance by driving lung ventilation and CO2 excretion-this CO2-evoked increase in respiration is the hypercapnic ventilatory reflex (HCVR). Retrotrapezoid nucleus (RTN) neurons provide crucial excitatory drive to downstream respiratory rhythm/pattern-generating circuits, and their activity is directly modulated by changes in CO2/H+ RTN neurons express GPR4 and TASK-2, global deletion of which abrogates CO2/H+ activation of RTN neurons and the HCVR. It has not been determined if the intrinsic pH sensitivity of these proton detectors is required for these effects. We used CRISPR/Cas9 genome editing to generate mice with mutations in either of two pH-sensing histidine residues in GPR4 to determine effects on RTN neuronal CO2/H+ sensitivity and the HCVR. In global GPR4(H81F) and GPR4(H167F) mice, CO2-stimulated breathing and CO2-induced RTN neuronal activation were strongly blunted, with no effect on hypoxia-stimulated breathing. In brainstem slices from GPR4(H81F) mice, peak firing of RTN neurons during bath acidification was significantly reduced compared with GPR4 wild-type mice, and a subpopulation of RTN neurons was rendered pH-insensitive, phenocopying previous results from GPR4-deleted mice. These effects were independent of changes in RTN number/distribution, neuronal excitability or transcript levels for GPR4 and TASK-2. CO2-stimulated breathing was reduced to a similar extent in GPR4(H81F) and TASK-2-deleted mice, with combined mutation yielding no additional deficit in the HCVR. Together, these data demonstrate that the intrinsic pH sensitivity of GPR4 is necessary for full elaboration of the HCVR.

The role of nitric oxide and hormone signaling in chronic stress, anxiety, depression and post-traumatic stress disorder

This paper provides a summary of the role of nitric oxide (NO) and hormones in the development of chronic stress, anxiety, depression, and post-traumatic stress disorder (PTSD). These mental health conditions are prevalent globally and involve complex molecular interactions. Although there is a significant amount of research and therapeutic options available, the underlying mechanisms of these disorders are still not fully understood. The primary pathophysiologic processes involved in chronic stress, anxiety, depression, and PTSD include dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, the intracellular influence of neuronal nitric oxide synthase (nNOS) on transcription factors, an inflammatory response with the formation of nitrergic oxidative species, and reduced serotonergic transmission in the dorsal raphe nucleus. Despite the extensive literature on this topic, there is a great need for further research to clarify the complexities inherent in these pathways, with the primary aim of improving psychiatric care.

The communication mechanism of the gut-brain axis and its effect on central nervous system diseases: A systematic review

Gut microbiota is involved in intricate and active metabolic processes the host's brain function, especially its role in immune responses, secondary metabolism, and symbiotic connections with the host. Gut microbiota can promote the production of essential metabolites, neurotransmitters, and other neuroactive chemicals that affect the development and treatment of central nervous system diseases. This article introduces the relevant pathways and manners of the communication between the brain and gut, summarizes a comprehensive overview of the current research status of key gut microbiota metabolites that affect the functions of the nervous system, revealing those adverse factors that affect typical communication between the brain-gut axis, and outlining the efforts made by researchers to alleviate these neurological diseases through targeted microbial interventions. The relevant pathways and manners of communication between the brain and gut contribute to the experimental design of new treatment plans and drug development. The factors that may cause changes in gut microbiota and affect metabolites, as well as current intervention methods are summarized, which helps improve gut microbiota brain dialogue, prevent adverse triggering factors from interfering with the gut microbiota system, and minimize neuropathological changes.

Advanced progress of vestibular compensation in vestibular neural networks

Vestibular compensation is the natural process of recovery that occurs with acute peripheral vestibular lesion. Here, we summarize the current understanding of the mechanisms underlying vestibular compensation, focusing on the role of the medial vestibular nucleus (MVN), the central hub of the vestibular system, and its associated neural networks. The disruption of neural activity balance between the bilateral MVNs underlies the vestibular symptoms after unilateral vestibular damage, and this balance disruption can be partially reversed by the mutual inhibitory projections between the bilateral MVNs, and their top-down regulation by other brain regions via different neurotransmitters. However, the detailed mechanism of how MVN is involved in vestibular compensation and regulated remains largely unknown. A deeper understanding of the vestibular neural network and the neurotransmitter systems involved in vestibular compensation holds promise for improving treatment outcomes and developing more effective interventions for vestibular disorders.

Role of the circadian nuclear receptor REV-ERBα in dorsal raphe serotonin synthesis in mood regulation

Affective disorders are frequently associated with disrupted circadian rhythms. The existence of rhythmic secretion of central serotonin (5-hydroxytryptamine, 5-HT) pattern has been reported; however, the functional mechanism underlying the circadian control of 5-HTergic mood regulation remains largely unknown. Here, we investigate the role of the circadian nuclear receptor REV-ERBα in regulating tryptophan hydroxylase 2 (Tph2), the rate-limiting enzyme of 5-HT synthesis. We demonstrate that the REV-ERBα expressed in dorsal raphe (DR) 5-HTergic neurons functionally competes with PET-1-a nuclear activator crucial for 5-HTergic neuron development. In mice, genetic ablation of DR 5-HTergic REV-ERBα increases Tph2 expression, leading to elevated DR 5-HT levels and reduced depression-like behaviors at dusk. Further, pharmacological manipulation of the mice DR REV-ERBα activity increases DR 5-HT levels and affects despair-related behaviors. Our findings provide valuable insights into the molecular and cellular link between the circadian rhythm and the mood-controlling DR 5-HTergic systems.

Long-Term Impact of Early-Life Stress on Serotonin Connectivity

BACKGROUND

Chronic childhood stress is a prominent risk factor for developing affective disorders, yet mechanisms underlying this association remain unclear. Maintenance of optimal serotonin (5-HT) levels during early postnatal development is critical for the maturation of brain circuits. Understanding the long-lasting effects of early-life stress (ELS) on serotonin-modulated brain connectivity is crucial to develop treatments for affective disorders arising from childhood stress.

METHODS

Using a mouse model of chronic developmental stress, we determined the long-lasting consequences of ELS on 5-HT circuits and behavior in females and males. Using FosTRAP mice, we cross-correlated regional c-Fos density to determine brain-wide functional connectivity of the raphe nucleus. We next performed in vivo fiber photometry to establish ELS-induced deficits in 5-HT dynamics and optogenetics to stimulate 5-HT release to improve behavior.

RESULTS

Adult female and male mice exposed to ELS showed heightened anxiety-like behavior. ELS further enhanced susceptibility to acute stress by disrupting the brain-wide functional connectivity of the raphe nucleus and the activity of 5-HT neuron population, in conjunction with increased orbitofrontal cortex (OFC) activity and disrupted 5-HT release in medial OFC. Optogenetic stimulation of 5-HT terminals in the medial OFC elicited an anxiolytic effect in ELS mice in a sex-dependent manner.

CONCLUSIONS

These findings suggest a significant disruption in 5-HT-modulated brain connectivity in response to ELS, with implications for sex-dependent vulnerability. The anxiolytic effect of the raphe-medial OFC circuit stimulation has potential implications for developing targeted stimulation-based treatments for affective disorders that arise from early life adversities.

The nucleus accumbens in reward and aversion processing: insights and implications

The nucleus accumbens (NAc), a central component of the brain's reward circuitry, has been implicated in a wide range of behaviors and emotional states. Emerging evidence, primarily drawing from recent rodent studies, suggests that the function of the NAc in reward and aversion processing is multifaceted. Prolonged stress or drug use induces maladaptive neuronal function in the NAc circuitry, which results in pathological conditions. This review aims to provide comprehensive and up-to-date insights on the role of the NAc in motivated behavior regulation and highlights areas that demand further in-depth analysis. It synthesizes the latest findings on how distinct NAc neuronal populations and pathways contribute to the processing of opposite valences. The review examines how a range of neuromodulators, especially monoamines, influence the NAc's control over various motivational states. Furthermore, it delves into the complex underlying mechanisms of psychiatric disorders such as addiction and depression and evaluates prospective interventions to restore NAc functionality.

Nanoengineered therapeutic strategies targeting SNHG1 for mitigating microglial ischemia-reperfusion injury implications for hypoxic-ischemic encephalopathy

The purpose of this work is to investigate the function of SNHG1, a long non-coding RNA implicated in disease progression, apoptosis, and proliferation, in order to solve the problem of hypoxic-ischemic encephalopathy (HIE) in newborn care. We investigated the impact of overexpressing SNHG1 on hypoxia-induced apoptosis and studied its expression in BV2 microglial cells under hypoxic circumstances. As a result of modifying YY1 expression, SNHG1's overexpression prevents apoptosis, as our data demonstrate that it is considerably downregulated under hypoxia. We demonstrate that SNHG1 might potentially reduce microglial ischemia-reperfusion damage by using sophisticated nanoengineering drug delivery technologies to target it. This provides encouraging information for the therapy of ischemic epilepsy.

Morphometric analysis and functional insights into the serotonergic system of Girardia tigrina (Tricladida, Platyhelminthes)

Using immunocytochemistry, serotonergic nerve elements were documented in the nervous system of the planarian Girardia tigrina. Serotonin-immunopositive components were observed in the brain, ventral, dorsal and longitudinal nerve cords, transverse nerve commissures connecting the nerve cords, and in the nerve plexus. Whole-mount preparations of G. tigrina were analyzed by fluorescent and confocal laser scanning microscopy. An essential quantitative morphometric measurement of serotonin-immunopositive structures was conducted in three body regions (anterior, middle, and posterior) of the planarian. The number of serotonin neurons was maximal in the head region. The ventral nerve cords gradually decreased in thickness from anterior to posterior body ends. Physiological action of exogenously applied serotonin was studied in G. tigrina for the first time. It was found that serotonin (0.1 and 1 µmol L-1) accelerated eye regeneration. The transcriptome sequencing performed for the first time for the planarian G. tigrina revealed the transcripts of the tryptophan hydroxylase (trph), amino acid decarboxylase (aadc) and serotonin transporter (sert) genes. The data obtained indicate the presence of the components of serotonin pathway in G. tigrina. The identified transcripts can take part in serotonin turnover and participate in the realization of biological effects of serotonin in planarians, associated with eyes regeneration and differentiation.

ShuYu capsule alleviates emotional and physical symptoms of premenstrual dysphoric disorder: Impact on ALLO decline and GABAA receptor δ subunit in the PAG area

Premenstrual dysphoric disorder (PMDD) is a severe subtype of premenstrual syndrome in women of reproductive age, with its pathogenesis linked to the heightened sensitivity of type A γ -aminobutyric acid receptors (GABAAR) to neuroactive steroid hormone changes, particularly allopregnanolone (ALLO). While a low dose of fluoxetine, a classic selective serotonin reuptake inhibitor, is commonly used as a first-line drug to alleviate emotional disorders in PMDD in clinical settings, its mechanism of action is related to ALLO-GABAA receptor function. However, treating PMDD requires attention to both emotional and physical symptoms, such as pain sensitivity. This study aims to investigate the efficacy of ShuYu capsules, a traditional Chinese medicine, in simultaneously treating emotional and physical symptoms in a rat model of PMDD. Specifically, our focus centres on the midbrain periaqueductal grey (PAG), a region associated with emotion regulation and susceptibility to hyperalgesia. Considering the underlying mechanisms of ALLO-GABAA receptor function in the PAG region, we conducted a series of experiments to evaluate and define the effects of ShuYu capsules and uncover the relationship between the drug's efficacy and ALLO concentration fluctuations on GABAA receptor function in the PAG region. Our findings demonstrate that ShuYu capsules significantly improved oestrous cycle-dependant depression-like behaviour and reduced stress-induced hyperalgesia in rats with PMDD. Similar to the low dose of fluoxetine, ShuYu capsules targeted and mitigated the sharp decline in ALLO, rescued the upregulation of GABAAR subunit function, and activated PAG neurons in PMDD rats. The observed effects of ShuYu capsules suggest a central mechanism underlying PMDD symptoms, involving ALLO_GABAA receptor function in the PAG region. This study highlights the potential of traditional Chinese medicine in addressing both emotional and physical symptoms associated with PMDD, shedding light on novel therapeutic approaches for this condition.

Regulation of stress-induced sleep perturbations by dorsal raphe VGLUT3 neurons in male mice

Exposure to stressors has profound effects on sleep that have been linked to serotonin (5-HT) neurons of the dorsal raphe nucleus (DR). However, the DR also comprises glutamatergic neurons expressing vesicular glutamate transporter type 3 (DRVGLUT3), leading us to examine their role. Cell-type-specific tracing revealed that DRVGLUT3 neurons project to brain areas regulating arousal and stress. We found that chemogenetic activation of DRVGLUT3 neurons mimics stress-induced sleep perturbations. Furthermore, deleting VGLUT3 in the DR attenuated stress-induced sleep perturbations, especially after social defeat stress. In the DR, VGLUT3 is found in subsets of 5-HT and non-5-HT neurons. We observed that both populations are activated by acute stress, including those projecting to the ventral tegmental area. However, deleting VGLUT3 in 5-HT neurons minimally affected sleep regulation. These findings suggest that VGLUT3 expression in the DR drives stress-induced sleep perturbations, possibly involving non-5-HT DRVGLUT3 neurons.

Dorsal raphe neurons integrate the values of reward amount, delay, and uncertainty in multi-attribute decision-making

The dorsal raphe nucleus (DRN) is implicated in psychiatric disorders that feature impaired sensitivity to reward amount, impulsivity when facing reward delays, and risk-seeking when confronting reward uncertainty. However, it has been unclear whether and how DRN neurons signal reward amount, reward delay, and reward uncertainty during multi-attribute value-based decision-making, where subjects consider these attributes to make a choice. We recorded DRN neurons as monkeys chose between offers whose attributes, namely expected reward amount, reward delay, and reward uncertainty, varied independently. Many DRN neurons signaled offer attributes, and this population tended to integrate the attributes in a manner that reflected monkeys' preferences for amount, delay, and uncertainty. After decision-making, in response to post-decision feedback, these same neurons signaled signed reward prediction errors, suggesting a broader role in tracking value across task epochs and behavioral contexts. Our data illustrate how the DRN participates in value computations, guiding theories about the role of the DRN in decision-making and psychiatric disease.

Sedative and hypnotic effects of the saponins from a traditional edible plant Liriope spicata Lour. in PCPA-induced insomnia mice

ETHNOPHARMACOLOGICAL RELEVANCE

Liriope spicata Lour., a species listed in the catalogue of 'Medicinal and Edible Homologous Species', is traditionally used for the treatment of fatigue, restlessness, insomnia and constipation.

AIM OF THE STUDY

This study is aimed to evaluate the sedative and hypnotic effect of the saponins from a natural plant L. spicata Lour. in vivo.

MATERIALS AND METHODS

The total saponin (LSTS) and purified saponin (LSPS) were extracted from L. spicata, followed by a thorough analysis of their major components using the HPLC-MS. Subsequently, the therapeutic efficacy of LSTS and LSPS was evaluated by the improvement of anxiety and depression behaviors of the PCPA-induced mice.

RESULTS

LSTS and LSPS exhibited similar saponin compositions but differ in their composition ratios, with liriopesides-type saponins accounting for a larger proportion in LSTS. Studies demonstrated that both LSTS and LSPS can extend sleep duration and immobility time, while reducing sleep latency in PCPA-induced mice. However, there was no significant difference in weight change among the various mice groups. Elisa results indicated that the LSTS and LSPS could decrease levels of NE, DA, IL-6, and elevate the levels of 5-HT, NO, PGD2 and TNF-α in mice plasma. LSTS enhanced the expression of neurotransmitter receptors, while LSPS exhibited a more pronounced effect in regulating the expression of inflammatory factors. In conclusion, the saponins derived from L. spicata might hold promise as ingredients for developing health foods with sedative and hypnotic effects, potentially related to the modulation of serotonergic and GABAAergic neuron expression, as well as immunomodulatory process.

Neural cell-types and circuits linking thermoregulation and social behavior

Understanding how social and affective behavioral states are controlled by neural circuits is a fundamental challenge in neurobiology. Despite increasing understanding of central circuits governing prosocial and agonistic interactions, how bodily autonomic processes regulate these behaviors is less resolved. Thermoregulation is vital for maintaining homeostasis, but also associated with cognitive, physical, affective, and behavioral states. Here, we posit that adjusting body temperature may be integral to the appropriate expression of social behavior and argue that understanding neural links between behavior and thermoregulation is timely. First, changes in behavioral states-including social interaction-often accompany changes in body temperature. Second, recent work has uncovered neural populations controlling both thermoregulatory and social behavioral pathways. We identify additional neural populations that, in separate studies, control social behavior and thermoregulation, and highlight their relevance to human and animal studies. Third, dysregulation of body temperature is linked to human neuropsychiatric disorders. Although body temperature is a "hidden state" in many neurobiological studies, it likely plays an underappreciated role in regulating social and affective states.

ER stress in mouse serotonin neurons triggers a depressive phenotype alleviated by ketamine targeting eIF2α signaling

Depression is a devastating mood disorder that causes significant disability worldwide. Current knowledge of its pathophysiology remains modest and clear biological markers are lacking. Emerging evidence from human and animal models reveals persistent alterations in endoplasmic reticulum (ER) homeostasis, suggesting that ER stress-related signaling pathways may be targets for prevention and treatment. However, the neurobiological basis linking the pathways involved in depression-related ER stress remains unknown. Here, we report that an induced model of ER stress in mouse serotonin (5-HT) neurons is associated with reduced Egr1-dependent 5-HT cellular activity and 5-HT neurotransmission, resulting in neuroplasticity deficits in forebrain regions and a depressive-like phenotype. Ketamine administration engages downstream eIF2α signaling to trigger rapid neuroplasticity events that rescue the depressive-like effects. Collectively, these data identify ER stress in 5-HT neurons as a cellular pathway involved in the pathophysiology of depression and show that eIF2α is critical in eliciting ketamine's fast antidepressant effects.

InSpectro-Gadget: A Tool for Estimating Neurotransmitter and Neuromodulator Receptor Distributions for MRS Voxels

Magnetic resonance spectroscopy (MRS) is widely used to estimate concentrations of glutamate and γ -aminobutyric acid (GABA) in specific regions of the living human brain. As cytoarchitectural properties differ across the brain, interpreting these measurements can be assisted by having knowledge of such properties for the MRS region(s) studied. In particular, some knowledge of likely local neurotransmitter receptor patterns can potentially give insights into the mechanistic environment GABA- and glutamatergic neurons are functioning in. This may be of particular utility when comparing two or more regions, given that the receptor populations may differ substantially across them. At the same time, when studying MRS data from multiple participants or timepoints, the homogeneity of the sample becomes relevant, as measurements taken from areas with different cytoarchitecture may be difficult to compare. To provide insights into the likely cytoarchitectural environment of user-defined regions-of-interest, we produced an easy to use tool - InSpectro-Gadget - that interfaces with receptor mRNA expression information from the Allen Human Brain Atlas. This Python tool allows users to input masks and automatically obtain a graphical overview of the receptor population likely to be found within. This includes comparison between multiple masks or participants where relevant. The receptors and receptor subunit genes featured include GABA- and glutamatergic classes, along with a wide range of neuromodulators. The functionality of the tool is explained here and its use is demonstrated through a set of example analyses. The tool is available at https://github.com/lizmcmanus/Inspectro-Gadget .

Mapping the 5-HTergic neural pathways in perimenopausal mice and elucidating the role of oestrogen receptors in 5-HT neurotransmission

Perimenopausal syndrome (PMS) encompasses neuropsychiatric symptoms, such as hot flashes and depression, which are associated with alterations in the 5-HTergic neural pathway in the brain. However, the specific changes and mechanisms underlying these alterations remain unclear. In this study, ovariectomized mice were used to successfully establish a perimenopause model, and the changes in the expression of 5-HT and its receptors (5-HT1AR and 5-HT2AR) across 72 brain regions in these ovariectomized mice were assessed by immunohistochemistry. Although both 5-HT and 5-HT1AR were widely expressed throughout the brain, only a limited number of regions expressed 5-HT2AR. Notably, decreased expression of 5-HT was observed across almost all brain regions in the ovariectomy (OVX) group compared with the Sham group. Altered expression of both receptors was found within areas related to hot flashes (the preoptic area) or mood disorders (the amygdala). Additionally, reduced oestrogen receptor (ER)α/β expression was detected in cells in the raphe nucleus (RN), an area known to regulate body temperature. Results showed that ERα/β positively regulate the transcriptional activity of the enzymes TPH2/MAOA, which are involved in serotonin metabolism during perimenopause. This study revealed the changes in 5-HT neuropathways (5-HT, 5-HT1AR and 5-HT2AR) in perimenopausal mice, mainly in brain regions related to regulation of the body temperature, mood, sleep and memory. This study clarified that the expression of oestrogen receptor decreased in perimenopause, which regulated the transcription levels of TPH2 and MAOA, and ultimately led to the reduction of 5-HT content, providing a new target for clinical diagnosis and treatment of perimenopausal diseases.