Central regulatory mechanisms of visceral sensation in response to colonic distension with special reference to brain orexin

Role and therapeutic target of P2X2/3 receptors in visceral pain

Visceral pain (VP) is caused by internal organ disease. VP is involved in nerve conduction and related signaling molecules, but its specific pathogenesis has not yet been fully elucidated. Currently, there are no effective methods for treating VP. The role of P2X2/3 in VP has progressed. After visceral organs are subjected to noxious stimulation, cells release ATP, activate P2X2/3, enhance the sensitivity of peripheral receptors and the plasticity of neurons, enhance sensory information transmission, sensitize the central nervous system, and play an important role in the development of VP. However, antagonists possess the pharmacological effect of relieving pain. Therefore, in this review, we summarize the biological functions of P2X2/3 and discuss the intrinsic link between P2X2/3 and VP. Moreover, we focus on the pharmacological effects of P2X2/3 antagonists on VP therapy and provide a theoretical basis for its targeted therapy.

Brain Neuropeptides, Neuroinflammation, and Irritable Bowel Syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by chronic abdominal symptoms, but its pathogenesis is not fully understood.

SUMMARY

We have recently shown in rats that neuropeptides such as orexin, ghrelin, and oxytocin act in the brain to improve the intestinal barrier dysfunction, which is a major pathophysiology of IBS. We have additionally shown that the neuropeptides injected intracisternally induced a visceral antinociceptive action against colonic distension. Since it has been known that intestinal barrier dysfunction causes visceral hypersensitivity, the other main pathophysiology of IBS, the neuropeptides act centrally to reduce leaky gut, followed by improvement of visceral sensation, leading to therapeutic action on IBS. It has been recently reported that there is a bidirectional relationship between neuroinflammation in the brain and the pathophysiology of IBS. For example, activation of microglia in the brain causes visceral hypersensitivity. Accumulating evidence has suggested that orexin, ghrelin, or oxytocin could improve neuroinflammation in the CNS. All these results suggest that neuropeptides such as orexin, ghrelin, and oxytocin act in the brain to improve intestinal barrier function and visceral sensation and also induce a protective action against neuroinflammation in the brain.

KEY MESSAGES

We therefore speculated that orexin, ghrelin, or oxytocin in the brain possess dual actions, improvement of visceral sensation/leaky gut in the gut, and reduction of neuroinflammation in the brain, thereby inducing a therapeutic effect on IBS in a convergent manner.

Pharmacotherapy for gastric and intestinal cramping pain: ‎ current and emerging therapies

INTRODUCTION

Acute gastrointestinal cramping pain (GICP) is a debilitating condition that affects many people worldwide, significantly reducing their quality of life. As such, prompt treatment is crucial.

AREAS COVERED

This article will explore relevant literature from databases such as PubMed, Scopus, Google Scholar, Cochrane Library, and Web of Science. Additionally, we searched ClinicalTrials.gov and the WHO ICTRP database for the latest clinical trials.

EXPERT OPINION

Consensus dictates that antispasmodics such as hyoscine-N-butyl bromide and mebeverine should be the primary treatment for GICP. If these prove ineffective, patients can switch to an antispasmodic with a different mode of action or add acetaminophen/NSAIDs for more severe cases. Currently, several antispasmodics are undergoing clinical trials, including drotaverine, alverine, pinaverium, otilonium bromide, fenoverine, tiropramide, otilonium bromide, trimebutine, and peppermint oil. Well-designed head-to-head studies are necessary to evaluate current antispasmodics' safety, efficacy, pharmacokinetic, and pharmacoeconomics profiles. Recent studies have shown that fixed-dose combinations of antispasmodics + NSAIDs or two different antispasmodics can improve patient compliance and synergistically reduce GICP. Therefore, it is recommended that the global availability and accessibility of these products be enhanced.

Activation of basal forebrain cholinergic neurons improves colonic hyperpermeability through the vagus nerve and adenosine A2B receptors in rats

Intestinal barrier dysfunction, a leaky gut, contributes to the pathophysiology of various diseases such as dementia and irritable bowel syndrome (IBS). We recently clarified that orexin, ghrelin, or adenosine A2B signaling in the brain improved leaky gut through the vagus nerve. The present study was performed to clarify whether basal forebrain cholinergic neurons (BFCNs) are implicated in the central regulation of intestinal barrier function. We activated BFCNs using benzyl quinolone carboxylic acid (BQCA), a positive muscarinic M1 allosteric modulator, and evaluated colonic permeability by quantifying the absorbed Evans blue in rat colonic tissue. Intracisternal (not intraperitoneal) injection of BQCA blocked the increased colonic permeability in response to lipopolysaccharide. Vagotomy blocked BQCA-induced improvement of colonic hyperpermeability. Intracisternally administered pirenzepine, a muscarinic M1 selective antagonist, prevented intestinal barrier function improvement by intravenously administered 2-deoxy-d-glucose, central vagal stimulant. Adenosine A2B receptor antagonist but not dopamine or opioid receptor antagonist prevented BQCA-induced blockade of colonic hyperpermeability. Additionally, intracisternal injection of pirenzepine blocked orexin- or butyrate-induced intestinal barrier function improvement. These results suggest that BFCNs improve leaky gut through adenosine A2B signaling and the vagal pathway. Furthermore, BFCNs mediate orexin- or butyrate-induced intestinal barrier function improvement. Since BFCNs play a role in cognitive function and a leaky gut is associated with dementia, the present finding may lead us to speculate that BFCNs are involved in the development of dementia by regulating intestinal barrier function.

Oxytocin acts centrally in the brain to improve leaky gut through the vagus nerve and a cannabinoid signaling in rats

Brain oxytocin plays a role in gastrointestinal functions. Among them, oxytocin acts centrally to modulate gastrointestinal motility and visceral sensation. Intestinal barrier function, one of important gut functions, is also regulated by the central nervous system. Little is, however, known about a role of central oxytocin in the regulation of intestinal barrier function. The present study was performed to clarify whether brain oxytocin is also involved in regulation of intestinal barrier function and its mechanism. Colonic permeability was estimated in vivo by quantifying the absorbed Evans blue in colonic tissue in rats. Intracisternal injection of oxytocin dose-dependently abolished increased colonic permeability in response to lipopolysaccharide while intraperitoneal injection of oxytocin at the same dose failed to block it. Either atropine or surgical vagotomy blocked the central oxytocin-induced improvement of colonic hyperpermeability. Cannabinoid 1 receptor antagonist but not adenosine or opioid receptor antagonist prevented the central oxytocin-induced blockade of colonic hyperpermeability. In addition, intracisternal injection of oxytocin receptor antagonist blocked the ghrelin- or orexin-induced improvement of intestinal barrier function. These results suggest that oxytocin acts centrally in the brain to reduce colonic hyperpermeability. The vagal cholinergic pathway or cannabinoid 1 receptor signaling plays a vital role in the process. The oxytocin-induced improvement of colonic hyperpermeability mediates the central ghrelin- or orexin-induced improvement of intestinal barrier function. We would therefore suggest that activation of central oxytocin signaling may be useful for leaky gut-related diseases such as irritable bowel syndrome and autism.