Takuji Hosoya

Localization of TRPV1 and contractile effect of capsaicin in mouse large intestine: high abundance and sensitivity in rectum and distal colon

We investigated immunohistochemical differences in the distribution of TRPV1 channels and the contractile effects of capsaicin on smooth muscle in the mouse rectum and distal, transverse, and proximal colon. In the immunohistochemical study, TRPV1 immunoreactivity was found in the mucosa, submucosal, and muscle layers and myenteric plexus. Large numbers of TRPV1-immunoreactive axons were observed in the rectum and distal colon. In contrast, TRPV1-positive axons were sparsely distributed in the transverse and proximal colon. The density of TRPV1-immunoreactive axons in the rectum and distal colon was much higher than those in the transverse and proximal colon. Axons double labeled with TRPV1 and protein gene product (PGP) 9.5 were detected in the myenteric plexus, but PGP 9.5-immunoreactive cell bodies did not colocalize with TRPV1. In motor function studies, capsaicin induced a fast transient contraction, followed by a large long-lasting contraction in the rectum and distal colon, whereas in the transverse and proximal colon only the transient contraction was observed. The capsaicin-induced transient contraction from the proximal colon to the rectum was moderately inhibited by an NK1 or NK2 receptor antagonist. The capsaicin-induced long-lasting contraction in the rectum and distal colon was markedly inhibited by an NK2 antagonist, but not by an NK1 antagonist. The present results suggest that TRPV1 channels located on the rectum and distal colon play a major role in the motor function in the large intestine.

Distribution of transient receptor potential vanilloid 1 channel-expressing nerve fibers in mouse rectal and colonic enteric nervous system: relationship to peptidergic and nitrergic neurons

In the gut, transient receptor potential vanilloid (TRPV) 1 activation leads to release of neurotransmitters such as neuropeptides and nitric oxide. However, the distribution of TRPV1 nerve fibers and neurotransmitters released form sensory nerve endings in the enteric nervous system are currently not well understood. The present study investigated the immunohistochemical distribution of TRPV1 channels, sensory neuropeptides, and nitric oxide and their co-localization in mouse large intestine. Numerous TRPV1 and calcitonin gene-related peptide (CGRP) immunoreactivities were detected, mainly in the mucosa, submucosal layer, and myenteric plexus. Abundant substance P (SP), neurokinin A (NKA), and neuronal nitric oxide synthase (nNOS)-immunoreactivity were revealed in muscle layers. Motor function studies of circular and longitudinal muscles found that contractile responses to capsaicin in the rectum were most sensitive among the rectum, and distal, transverse, and proximal colon. Double labeling studies were carried out in horizontal sections of mouse rectum. TRPV1/protein gene product (PGP)9.5 double labeled axons were observed, but PGP9.5 and neuronal nuclear protein immunopositive cell bodies did not express TRPV1 immunoreactivity in the myenteric plexus. In the mucosa, submucosal layer, deep muscular plexus, circular muscle, myenteric plexus and longitudinal muscle layer, TRPV1 nerve fibers were found to contain CGRP, SP and nNOS. SP and NKA were almost entirely colocalized at the axons and cell bodies in all layers. Double labeling with c-Kit revealed that TRPV1 nerve fibers localized adjacent to the interstitial cells of Cajal (ICC). These results suggest that the TRPV1-expressing nerve and its neurotransmitters regulate various functions of the large intestine.

Experimental colitis alters expression of 5-HT receptors and transient receptor potential vanilloid 1 leading to visceral hypersensitivity in mice

Abnormalities of primary afferent nerve fibers are strongly associated with the visceral hypersensitivity state in inflammatory bowel disease. Hypersensitivity of afferent fibers occurs during inflammation. Therefore, to gain an insight into the alterations to receptors and channels expressed in primary afferent neurons, the current study aimed to investigate the time-dependent dynamic changes in levels of 5-hydroxytryptamine (5-HT)3 receptors, 5-HT4 receptors, transient receptor potential vanilloid type 1 (TRPV1) channels, and 5-HT regulatory factors in dextran sulfate sodium (DSS)-induced colitis model mice. 5-HT signaling molecules were detected by indirect staining with specific antibodies. TRPV1-immunoreactivity was detected by staining with fluorescein-conjugated tyramide amplification. To assess nociception, visceromotor responses (VMRs) to colorectal distension were measured by electromyography of abdominal muscles. Immunohistochemical analysis and VMRs to colorectal distention were measured during induction of DSS colitis (days 4 and 7). Inflammation led to downregulation of serotonin transporter immunoreactivities with concomitant increases in 5-HT and tryptophan hydroxylase-1-positive cell numbers. TRPV1-expressing nerve fibers gradually increased during DSS treatment. Abundant nonneuronal TRPV1-immunopositive cell-like structures were observed on day 7 of DSS treatment but not on day 4. The number of 5-HT3 receptor-expressing nerve fibers in the mucosa was increased on day 7. On the other hand, the number of 5-HT4 receptor-expressing nerve fibers in the mucosa decreased on day 7. We made the novel observation of increased expression of neuronal/nonneuronal TRPV1 channels and 5-HT3 receptors, and decreased expression of 5-HT4 receptors in the mucosa in a DSS-induced colitis model. Visceral hyperalgesia was observed on day 7 but not on day 4. A TRPV1 antagonist and a 5-HT3 receptor antagonist attenuated the visceral hyperalgesia to the control level. The alterations of 5-HT signaling via 5-HT3 receptors and of TRPV1 channels in mucosa may contribute to the visceral hypersensitivity in colitis model mice.

TRPM8 has a key role in experimental colitis-induced visceral hyperalgesia in mice.

Transient receptor potential channel melastatin 8 (TRPM8) is activated by cold temperatures and cooling agents (menthol and icilin). Recent studies showed TRPM8 is expressed in visceral organs and peripheral sensory pathways. However, the role of TRPM8 in visceral hyperalgesia is poorly understood in pathological states such as inflammatory bowel disease. Hence, we investigated the distribution of TRPM8 and its involvement in visceral hyperalgesia in experimental colitis mice.

Distribution of transient receptor potential cation channel subfamily V member 1-expressing nerve fibers in mouse esophagus

Transient receptor potential cation channel subfamily V member 1 (TRPV1) plays a role in esophageal function. However, the distribution of TRPV1 nerve fibers in the esophagus is currently not well understood. In the present study, we investigated the distribution of TRPV1 and neurotransmitters released from TRPV1 nerve fibers in the mouse lower esophagus. Furthermore, we investigated changes in the presence of TRPV1 in the mouse model of esophagitis. Numerous TRPV1-immunoreactive nerve fibers were seen in both the submucosal layer and myenteric plexus of the lower esophagus and colocalized with calcitonin gene-related peptide (CGRP). TRPV1 colocalized with substance P in axons in the submucosal layer and myenteric plexus. TRPV1 colocalized with neuronal nitric oxide synthase in the myenteric plexus. We observed some colocalization of CGRP with the vesicular acetylcholine (ACh) transporter, packaging of ACh into synaptic vesicles after its synthesis in terminal cytoplasm, in the submucosal layer and myenteric plexus. In the esophagitis model, the number of the TRPV1 nerve fibers did not change, but their immunoreactive intensity increased compared with sham-operated mice. Inhibitory effect of exogenous capsaicin on electrically stimulated twitch contraction significantly increased in esophagitis model compared with the effect in sham-operated mice. Overall, these results suggest that TRPV1 nerve fibers projecting to both the submucosal and muscle layer of the esophagus are extrinsic spinal and vagal afferent neurons. Furthermore, TRPV1 nerve fibers contain CGRP, substance P, nitric oxide, and ACh. Therefore, acid influx-mediated TRPV1 activation may play a role in regulating esophageal relaxation.

Localization of Transient Receptor Potential Melastatin Type-8 (TRPM8) in Normal Mouse Large Intestine and Its Up-Regulation in Inflammatory Bowel Disease Model

colitis model mice, disease activity index, tissue inflammation and amount of 5-HT was gradually increased during 7 days of DSS treatment. The visceral hyperalgesia to mechanical distension was observed on day 7 but not on day 4. The number of 5-HT3 receptorexpressing nerve fibers is significantly increased in mucosa on day 7. On the other hand, number of the 5-HT4 receptor-expressing nerve fibers is significantly decreased on day 7. No significant alteration in the number of 5-HT3 and 5-HT4 receptors was detected on day 4. Progress of the inflammation led to down regulation of SERT immunoreactivities with concomitant increases in 5-HTand TPH-1-positive cell numbers. 5-HTand TPH-1-positive cells were widely distributed in whole mucosa on day 0 and 4. On day 7, these cells were mainly detected in upper part of mucosa. A significant 2-fold increase in number of TRPV1expressing nerve fibers was found inmucosa on day 7. Non-neuronal TRPV1-immunopositive cells were observed on day 7. There is no clear alteration of the immunoreactivities of the 5-HT signaling and the TRPV1 channels in muscle layers of rectum in colitis model mice. CONCLUSION: These results suggest that increased 5-HT, 5-HT3 receptors, TRPV1 channels and decreased 5-HT4 receptors are associated with the pathological conditions of the inflammatory bowel disease.

Role of Neuronal and Non-Neuronal Transient Receptor Potential Vanilloid Type 1 and Sensory Neuropeptides in DSS-Induced Peripheral Inflammatory Changes

BACKGROUND & AIMS: The activation of transient receptor potential vanilloid type 1 (TRPV1) leads to release of sensory neuropeptides such as substance P (SP), neurokinin A (NKA) and calcitonin gene-related peptide (CGRP) from the nerve endings, and these neuropeptides in turn initiate the biochemical cascade known as neurogenic inflammation. TRPV1 channels and the sensory neuropeptides are expressed not only in sensory nerve fibers but also in non-neuronal cells in the mucosa of large intestine. The aim of this study was to investigate alteration of the sensory neuropeptides and TRPV1 channels in mucosa of DSS-induced colitis mice and to characterize their non-neuronal cells. METHODS: Colitis was induced by 3% dextran sulfate sodium (DSS) solution given as drinking water for 7 days in C57BL/6 mice. To evaluate visceral nociception, colorectal distension was performed in mice treated with vehicle or BCTC on day 7 of DSS treatment. Immunohistochemical analysis was performed using rectal tissues of mice. SP, NKA, CGRP, 5-HT, F4/80, keratin, TNF-α, CD11c, and CD4 were detected by indirect staining with their specific antibodies. TRPV1-immunoreactivity was detected by using immunohistochemical staining with fluorescein-conjugated tyramide amplification. RESULTS: TRPV1 antagonist BCTC significantly attenuated the visceral hyperalgesia to control level in DSS-induced colitis model. We compared the number of the nerve fibers and non-neuronal cells expressing TRPV1 channels and sensory neuropeptides in normal and DSS-induced colitis model mice. The number of TRPV1and CGRP-expressing nerve fibers is significantly increased in colitis model. The non-neuronal TRPV1 cells were markedly increased but non-neuronal CGRP-expressing cells were not observed in colitis model. No significant alteration in the number of SP and NKA positive nerve fibers was detected. On the other hand, SP and NKA positive cells were drastically increased in colitis model. Next, double labeling studies were carried out to characterize TRPV1-, SP-, and NKA-expressing cells under inflammatory state. We found two types of non-neuronal TRPV1-expressing cells in mucosa of colitis model. One is keratin positive cells located upper part of mucosa. Another is TNF-α and/or F4/80 positive cells located middle part of the mucosa. Both types of TRPV1-expressing cells did not colocalize with CD4 and CD11c. SP and NKA positive cells almost completely colocalized with 5-HT in experimental colitis model mice. CONCLUSION: These results suggest that TRPV1immunopositive epithelial cells and macrophage are associated with visceral hyperalgesia in colitis.