Melanin-concentrating hormone promotes anxiety and intestinal dysfunction via basolateral amygdala in mice

The GABAergic pathway from anterior cingulate cortex to lateral hypothalamus area regulates irritable bowel syndrome in mice and its underlying mechanism

Irritable bowel syndrome (IBS), which is characterized by chronic abdominal pain, has a high global prevalence. The anterior cingulate cortex (ACC), which is a pivotal region involved in pain processing, should be further investigated regarding its role in the regulation of visceral sensitivity and mental disorders. A C57BL/6J mouse model for IBS was established using chronic acute combining stress (CACS). IBS-like symptoms were assessed using behavioral tests, intestinal motility measurements, and abdominal withdrawal reflex scores. Fluoro-Gold retrograde tracing and immunohistochemistry techniques were employed to investigate the projection of ACC gamma-aminobutyric acid-producing (GABAergic) neurons to the lateral hypothalamus area (LHA). Chemogenetic approaches enabled the selective activation or inhibition of the ACC-LHA GABAergic pathway. Enzyme-linked immunosorbent assay (ELISA) and western blot analyses were conducted to determine the expression of histamine, 5-hydroxytryptamine (5-HT), and transient receptor potential vanilloid 4 (TRPV4). Our findings suggest that CACS induced IBS-like symptoms in mice. The GABA type A receptors (GABAAR) within LHA played a regulatory role in modulating IBS-like symptoms. The chemogenetic activation of ACC-LHA GABAergic neurons elicited anxiety-like behaviors, intestinal dysfunction, and visceral hypersensitivity in normal mice; however, these effects were effectively reversed by the administration of the GABAAR antagonist Bicuculline. Conversely, the chemogenetic inhibition of ACC-LHA GABAergic neurons alleviated anxiety-like behaviors, intestinal dysfunction, and visceral hypersensitivity in the mouse model for IBS. These results highlight the crucial involvement of the ACC-LHA GABAergic pathway in modulating anxiety-like behaviors, intestinal motility alterations, and visceral hypersensitivity, suggesting a potential therapeutic strategy for alleviating IBS-like symptoms.

Exploratory Rearing Is Governed by Hypothalamic Melanin-Concentrating Hormone Neurons According to Locus Ceruleus

Information seeking, such as standing on tiptoes to look around in humans, is observed across animals and helps survival. Its rodent analog-unsupported rearing on hind legs-was a classic model in deciphering neural signals of cognition and is of intense renewed interest in preclinical modeling of neuropsychiatric states. Neural signals and circuits controlling this dedicated decision to seek information remain largely unknown. While studying subsecond timing of spontaneous behavioral acts and activity of melanin-concentrating hormone (MCH) neurons (MNs) in behaving male and female mice, we observed large MN activity spikes that aligned to unsupported rears. Complementary causal, loss and gain of function, analyses revealed specific control of rear frequency and duration by MNs and MCHR1 receptors. Activity in a key stress center of the brain-the locus ceruleus noradrenaline cells-rapidly inhibited MNs and required functional MCH receptors for its endogenous modulation of rearing. By defining a neural module that both tracks and controls rearing, these findings may facilitate further insights into biology of information seeking.

Regulation of the MCHergic Neural Circuit to Dorsal Raphe Nucleus on Emotion-Related Behaviors and Intestinal Dysfunction in Mice Model of Irritable Bowel Syndrome with Diarrhea

INTRODUCTION

Irritable bowel syndrome with diarrhea (IBS-D) is frequently accompanied by depression and anxiety, resulting in a reduced quality of life and increased medical expenditures. Although psychological factors are known to play an important role in the genesis and development of IBS-D, an understanding of the central neural control of intestinal dysfunction remains elusive. Melanin-concentrating hormone (MCH) is a gut-brain peptide involved in regulating feeding, sleep-wake rhythms, and emotional states.

METHODS

This study investigated the regulation of the MCHergic neural circuit from the lateral hypothalamic area (LHA) to the dorsal raphe nucleus (DRN) on anxiety- and depression-like behaviors, intestinal motility, and visceral hypersensitivity in a mice model of IBS-D. The models of IBS-D were prepared by inducing chronic unpredictable mild stress.

RESULTS

Chemogenetic activation of the MCH neurons in the LHA could excite serotonin (5-HT) neurons in the DRN and induce anxiety- and depression-like behaviors and IBS-D-like symptoms, which could be recovered by microinjection of the MCH receptor antagonist SNAP94847 into the DRN. The mice model of IBS-D showed a reduction of 5-HT and brain-derived neurotrophic factor (BDNF) expression in the DRN, while an elevation of 5-HT and BDNF was observed in the colon through immunofluorescent staining, ELISA, and Western blot analysis. SNAP94847 treatment in the DRN alleviated anxiety- and depression-like behaviors, improved intestinal motility, and alleviated visceral hypersensitivity responses by normalizing the 5-HT and BDNF expression in the DRN and colon.

CONCLUSION

This study suggests that the activation of MCH neurons in the LHA may induce IBS-D symptoms via the DRN and that the MCH receptor antagonist could potentially have therapeutic effects.

CHTOP Promotes Microglia-Mediated Inflammation by Regulating Cell Metabolism and Inflammatory Gene Expression

During the initiation of the inflammatory response of microglia, the expression of many inflammation- and cell metabolism-related genes alters. However, how the transcription of inflammation- and metabolism-related genes are coordinately regulated during inflammation initiation is poorly understood. In this study, we found that LPS stimulation induced the expression of the chromatin target of PRMT1 (protein arginine methyltransferase 1) (CHTOP) in microglia. Knocking down CHTOP in microglia decreased proinflammatory cytokine expression. In addition, CHTOP knockdown altered cell metabolism, as both the upregulated genes were enriched in cell metabolism-related pathways and the metabolites profile was greatly altered based on untargeted metabolomics analysis. Mechanistically, CHTOP could directly bind the regulatory elements of inflammation and cell metabolism-related genes to regulate their transcription. In addition, knocking down CHTOP increased neuronal viability in vitro and alleviated microglia-mediated neuroinflammation in a systemic LPS treatment mouse model. Collectively, these data revealed CHTOP as a novel regulator to promote microglia-mediated neuroinflammation by coordinately regulating the transcription of inflammation and cell metabolism-related genes.

Hypothalamic MCH Neurons: From Feeding to Cognitive Control

Modern neuroscience is progressively elucidating that the classic view positing distinct brain regions responsible for survival, emotion, and cognitive functions is outdated. The hypothalamus demonstrates the interdependence of these roles, as it is traditionally known for fundamental survival functions like energy and electrolyte balance, but is now recognized to also play a crucial role in emotional and cognitive processes. This review focuses on lateral hypothalamic melanin-concentrating hormone (MCH) neurons, producing the neuropeptide MCH-a relatively understudied neuronal population with integrative functions related to homeostatic regulation and motivated behaviors, with widespread inputs and outputs throughout the entire central nervous system. Here, we review early findings and recent literature outlining their role in the regulation of energy balance, sleep, learning, and memory processes.

Protective Role and Functional Engineering of Neuropeptides in Depression and Anxiety: An Overview

Behavioral disorders, such as anxiety and depression, are prevalent globally and touch children and adults on a regular basis. Therefore, it is critical to comprehend how these disorders are affected. It has been demonstrated that neuropeptides can influence behavior, emotional reactions, and behavioral disorders. This review highlights the majority of the findings demonstrating neuropeptides' behavioral role and functional engineering in depression and anxiety. Gut-brain peptides, hypothalamic releasing hormone peptides, opioid peptides, and pituitary hormone peptides are the four major groups of neuropeptides discussed. Some neuropeptides appear to promote depression and anxiety-like symptoms, whereas others seem to reduce it, all depending on the receptors they are acting on and on the brain region they are localized in. The data supplied here are an excellent starting point for future therapy interventions aimed at treating anxiety and depression.

Loss of glutamatergic signalling from MCH neurons reduced anxiety-like behaviours in novel environments

Melanin-concentrating hormone (MCH) neurons within the hypothalamus are heterogeneous and can coexpress additional neuropeptides and transmitters. The majority of MCH neurons express vesicular transporters to package glutamate for synaptic release, and MCH neurons can directly innervate downstream neurons via glutamate release. Although glutamatergic signalling from MCH neurons may support physiological and behavioural roles that are independent of MCH (e.g., in glucose homeostasis and nutrient-sensing), it can also mediate similar roles to MCH in the regulation of energy balance. In addition to energy balance, the MCH system has also been implicated in mood disorders, as MCH receptor antagonists have anxiolytic and anti-depressive effects. However, the contribution of glutamatergic signalling from MCH neurons to mood-related functions have not been investigated. We crossed Mch-cre mice with floxed-Vglut2 mice to delete the expression of the vesicular glutamate transporter 2 (Vglut2) and disable glutamatergic signalling specifically from MCH neurons. The resulting Mch-Vglut2-KO mice showed Vglut2 deletion from over 75% of MCH neurons, and although we did not observe changes in depressive-like behaviours, we found that Mch-Vglut2-KO mice displayed anxiety-like behaviours. Mch-Vglut2-KO mice showed reduced exploratory activity when placed in a new cage and were quicker to consume food placed in the centre of a novel open arena. These findings showed that Vglut2 deletion from MCH neurons resulted in anxiolytic actions and suggested that the anxiogenic effects of glutamate are similar to those of the MCH peptide. Taken together, these findings suggest that glutamate and MCH may synergize to regulate and promote anxiety-like behaviour.