Paraventricular thalamus-insular cortex circuit mediates colorectal visceral pain induced by neonatal colonic inflammation in mice.

AIMS: Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder, but its pathogenesis remains incompletely understood, particularly the involvements of central nervous system sensitization in colorectal visceral pain. Our study was to investigate whether the paraventricular thalamus (PVT) projected to the insular cortex (IC) to regulate colorectal visceral pain in neonatal colonic inflammation (NCI) mice and underlying mechanisms. METHODS: We applied optogenetic, chemogenetic, or pharmacological approaches to manipulate the glutamatergicPVT-IC pathway. Fiber photometry was used to assess neuronal activity. Electromyography activities in response to colorectal distension (CRD) were measured to evaluate the colorectal visceral pain. RESULTS: NCI enhanced c-Fos expression and calcium activity upon CRD in the ICGlu, and optogenetic manipulation of them altered colorectal visceral pain responses accordingly. Viral tracing indicated that the PVTGlu projected to the ICGlu. Optogenetic manipulation of PVTGlu changed colorectal visceral pain responses. Furthermore, selective optogenetic modulation of PVT projections in the IC influenced colorectal visceral pain, which was reversed by chemogenetic manipulation of downstream ICGlu. CONCLUSIONS: This study identified a novel PVT-IC neural circuit playing a critical role in colorectal visceral pain in a mouse model of IBS.

Rab27a-mediated exosome secretion in anterior cingulate cortex contributes to colorectal visceral pain in adult mice with neonatal maternal deprivation.

Chronic visceral pain is a common symptom of irritable bowel syndrome (IBS). Exosomes are involved in the development of pain. Rab27a can mediate the release of exosomes. The purpose of this study is to investigate how Rab27a-mediated exosome secretion in the anterior cingulate cortex (ACC) regulates visceral hyperalgesia induced with neonatal maternal deprivation (NMD) in adult mice. The colorectal distension method was adopted to measure visceral pain. The BCA protein assay kit was applied to detect the exosome protein concentration. Western blotting, quantitative PCR, and immunofluorescence technique were adopted to detect the expression of Rab27a and the markers of exosomes. Exosomes extracted from ACC were more in NMD mice than in control (CON) mice. Injection of the exosome-specific inhibitor GW4869 in ACC attenuated colorectal visceral pain of NMD mice. Injection of NMD-derived exosomes produced colorectal visceral pain in CON mice. Rab27a was upregulated in ACC of NMD mice. Rab27a was highly expressed in ACC neurons of NMD mice, rather than astrocytes and microglia. Injection of Rab27a-siRNA reduced the release of exosomes and attenuated the colorectal visceral pain in NMD mice. This study suggested that overexpression of Rab27a increased exosome secretion in ACC neurons, thus contributing to visceral hyperalgesia in NMD mice.NEW & NOTEWORTHY This work demonstrated that the expression of Rab27a in the anterior cingulate cortex was upregulated, which mediated multivesicular bodies trafficking to the plasma membrane and led to the increased release of neuronal exosomes, thus contributing to colorectal visceral pain in neonatal maternal deprivation (NMD) mice. Blocking the release of exosomes or downregulation of Rab27a could alleviate colorectal visceral pain in NMD mice. These data may provide a promising strategy for the treatment of visceral pain in irritable bowel syndrome patients.

Folic acid attenuates chronic visceral pain by reducing clostridiales abundance and hydrogen sulfide production.

Irritable bowel syndrome (IBS) related chronic visceral pain affects 20% of people worldwide. The treatment options are very limited. Although the scholarly reviews have appraised the potential effects of the intestinal microbiota on intestinal motility and sensation, the exact mechanism of intestinal microbiota in IBS-like chronic visceral pain remains largely unclear. The purpose of this study is to investigate whether Folic Acid (FA) attenuated visceral pain and its possible mechanisms. Chronic visceral hyperalgesia was induced in rats by neonatal colonic inflammation (NCI). 16S rDNA analysis of fecal samples from human subjects and rats was performed. Patch clamp recording was used to determine synaptic transmission of colonic-related spinal dorsal horn. Alpha diversity of intestinal flora was increased in patients with IBS, as well as the obviously increased abundance of Clostridiales order (a main bacteria producing hydrogen sulfide). The hydrogen sulfide content was positive correlation with visceral pain score in patients with IBS. Consistently, NCI increased Clostridiales frequency and hydrogen sulfide content in feces of adult rats. Notably, the concentration of FA was markedly decreased in peripheral blood of IBS patients compared with non-IBS human subjects. FA supplement alleviated chronic visceral pain and normalized the Clostridiales frequency in NCI rats. In addition, FA supplement significantly reduced the frequency of sEPSCs of neurons in the spinal dorsal horn of NCI rats. Folic Acid treatment attenuated chronic visceral pain of NCI rats through reducing hydrogen sulfide production from Clostridiales in intestine.

Neonatal Colonic Inflammation Increases Spinal Transmission and Cystathionine ß-Synthetase Expression in Spinal Dorsal Horn of Rats with Visceral Hypersensitivity.

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterized by chronic abdominal pain and alteration of bowel movements. The pathogenesis of visceral hypersensitivity in IBS patients remains largely unknown. Hydrogen sulfide (H2S) is reported to play an important role in development of visceral hyperalgesia. However, the role of H2S at spinal dorsal horn level remains elusive in visceral hypersensitivity. The aim of this study is designed to investigate how H2S takes part in visceral hypersensitivity of adult rats with neonatal colonic inflammation (NCI). Visceral hypersensitivity was induced by neonatal colonic injection of diluted acetic acid. Expression of an endogenous H2S synthesizing enzyme cystathionine ß-synthetase (CBS) was determined by Western blot. Excitability and synaptic transmission of neurons in the substantia gelatinosa (SG) of spinal cord was recorded by patch clamping. Here, we showed that expression of CBS in the spinal dorsal horn was significantly upregulated in NCI rats. The frequency of glutamatergic synaptic activities in SG was markedly enhanced in NCI rats when compared with control rats. Application of NaHS increased the frequency of both spontaneous and miniature excitatory post-synaptic currents of SG neurons in control rats through a presynaptic mechanism. In contrast, application of AOAA, an inhibitor of CBS, dramatically suppressed the frequency of glutamatergic synaptic activities of SG neurons of NCI rats. Importantly, intrathecal injection of AOAA remarkably attenuated visceral hypersensitivity of NCI rats. These results suggest that H2S modulates pain signaling likely through a presynaptic mechanism in SG of spinal dorsal horn, thus providing a potential therapeutic strategy for treatment for chronic visceral pain in patients with IBS.