The mechanism underlying the intestinal fluid loss in rotavirus diarrhea, which often afflicts children in developing countries, is not known. One hypothesis is that the rotavirus evokes intestinal fluid and electrolyte secretion by activation of the nervous system in the intestinal wall, the enteric nervous system (ENS). Four different drugs that inhibit ENS functions were used to obtain experimental evidence for this hypothesis in mice in vitro and in vivo. The involvement of the ENS in rotavirus diarrhea indicates potential sites of action for drugs in the treatment of the disease.

Background and aims: The mechanisms underlying intestinal secretion in rotavirus diarrhoea remain to be established. We previously reported that rotavirus evokes intestinal fluid and electrolyte secretion by activation of the enteric nervous system. We now report that antagonists for the 5-hydroxytryptamine 3 receptor (5-HT 3 ) and vasoactive intestinal peptide (VIP) receptor, but not antagonists for 5-hydroxytryptamine 4 receptor or the muscarinic receptor, attenuate rotavirus induced diarrhoea. Methods: Neurotransmitter antagonists were administered to wild-type or neurokinin 1 receptor knockout mice infected with homologous (EDIM) or heterologous (RRV) rotavirus. Results: While RRV infected mice had diarrhoea for 3.3 (0.2) days (95% confidence interval (CI) 3.04-3.56), the 5-HT 3 receptor antagonist (granisetron) and the VIP receptor antagonist (4Cl-D-Phe 6 ,Leu 17 )-VIP both reduced the total number of days of RRV induced diarrhoea to 2.1 (0.3) (95% CI 1.31-2.9) (p,0.01). EDIM infected mice treated with granisetron had a significantly shorter duration of diarrhoea (5.6 (0.4) days) compared with untreated mice (8.0 (0.4) days; p,0.01). Experiments with neurokinin 1 receptor antagonists suggest that this receptor may possibly be involved in the secretory response to rotavirus. On the other hand, rotavirus diarrhoea was not attenuated in the neurokinin 1 receptor knockout mice. Conclusions: Our results suggest that the neurotransmitters serotonin and VIP are involved in rotavirus diarrhoea; observations that could imply new principles for treatment of this disease with significant global impact.

Cholera toxin (CT) may induce uncontrolled firing in recurrent networks of secretomotor neurons in the submucous plexus. This hypothesis was tested in chloralose-anesthetized rats in vivo. The secretory reflex response to graded intestinal distension was measured with or without prior exposure to luminal CT. The transmural potential difference (PD) was used as a marker for electrogenic chloride secretion. In controls, distension increased PD, and this response was reduced by the neural blocker tetrodotoxin given serosally and the vasoactive intestinal peptide (VIP) receptor antagonist [4Cl-d-Phe(6),Leu(17)]VIP (2 mug.min(-1).kg(-1) iv) but unaffected by the serotonin 5-HT(3) receptor antagonist granisetron, by the nicotinic receptor antagonist hexamethonium, by the muscarinic receptor antagonist atropine, or by the cyclooxygenase inhibitor indomethacin. Basal PD increased significantly with time in CT-exposed segments, an effect blocked by granisetron, by indomethacin, and by [4Cl-d-Phe(6),Leu(17)]VIP but not by hexamethonium or atropine. In contrast, once the increased basal PD produced by CT was established, [4Cl-d-Phe(6),Leu(17)]VIP and indomethacin had no significant effect, whereas granisetron and hexamethonium markedly depressed basal PD. CT significantly reduced the increase in PD produced by distension, an effect reversed by granisetron, indomethacin, and atropine. CT also activated a specific motility response to distension, repeated cluster contractions, but only in animals pretreated with granisetron, indomethacin, or atropine. These data are compatible with the hypothesis that CT induces uncontrolled activity in submucous secretory networks. Development of this state depends on 5-HT(3) receptors, VIP receptors, and prostaglandin synthesis, whereas its maintenance depends on 5-HT(3) and nicotinic receptors but not VIP receptors. The motility effects of CT (probably reflecting myenteric activity) are partially suppressed via a mechanism involving 5-HT(3) and muscarinic receptors and prostaglandin synthesis.

In contrast to humans, adult but not infant small animals are resistant to rotavirus diarrhea. The pathophysiological mechanism behind this age-restricted diarrhea is currently unresolved, and this question was investigated by studying the secretory state of the small intestines of adult mice infected with rotavirus. Immunohistochemistry and histological examinations revealed that rotavirus (strain EDIM) infects all parts of the small intestines of adult mice, with significant numbers of infected cells in the ilea at 2 and 4 days postinfection. Furthermore, quantitative PCR revealed that 100-fold more viral RNA was produced in the ilea than in the jejuna or duodena of adult mice. In vitro perfusion experiments of the small intestine did not reveal any significant changes in net fluid secretion among mice infected for 3 days or 4 days or in those that were noninfected (37 ؎ 9 l · h ؊1 · cm ؊1 , 22 ؎ 13 l · h ؊1 · cm ؊1 , and 33 ؎ 6 l · h ؊1 · cm ؊1 , respectively) or in transmucosal potential difference (4.0 ؎ 0.3 mV versus 3.9 ؎ 0.4 mV), a marker for active chloride secretion, between control and rotavirus-infected mice. In vivo experiments also did not show any differences in potential difference between uninfected and infected small intestines. Furthermore, no significant differences in weight between infected and uninfected small intestines were found, nor were any differences in fecal output observed between infected and control mice. Altogether, these data suggest that rotavirus infection is not sufficient to stimulate chloride and water secretion from the small intestines of adult mice.Rotavirus (RV) is an important cause of acute gastroenteritis in young children and is also an important pathogen in several animal species. In contrast to the situation in humans, where symptomatic reinfections do occur in adults (1,23,30), most adult small animals show an age-dependent resistance to symptomatic RV infections (4,5,12,38). The pathophysiological mechanisms behind this age-dependent resistance are currently unresolved, but it has been proposed that they are due to compensatory fluid absorption by the larger colons of older animals. It has also been suggested that the low expression of proteolytic enzymes in newborn mice is a possible mechanism (13). Furthermore, an interesting observation is that the agedependent resistance in adult mice correlates with the lack of chemokine responses (28). We have previously shown that in infant mice, rotavirus infection gives rise to an increased fluid secretion and an increased transmucosal potential difference (PD), a marker for active chloride secretion (16). The aim of this study was to investigate the secretory state of the small intestines of adult mice. Using established (16,32,33) in vivo and in vitro methods, we measured net fluid transport and PD and found that in spite of virus infection, there was no evidence for chloride or water secretion from the small intestines of murine rotavirus-infected adult mice. This suggests that rotavirus infection in adult mice, in...