In vivo assessment of the regulatory mechanism of cholinergic neuronal activity associated with motility in dog small intestine

Rotavirus Downregulates Tyrosine Hydroxylase in the Noradrenergic Sympathetic Nervous System in Ileum, Early in Infection and Simultaneously with Increased Intestinal Transit and Altered Brain Activities

While rotavirus diarrhea has been considered to occur only due to intrinsic intestinal effects within the enteric nervous system, we provide evidence for central nervous system control underlying the clinical symptomology. Our data visualize infection by large-scale three-dimensional (3D) volumetric tissue imaging of a mouse model and demonstrate that rotavirus infection disrupts the homeostasis of the autonomous system by downregulating tyrosine hydroxylase in the noradrenergic sympathetic nervous system in ileum, concomitant with increased intestinal transit. Interestingly, the nervous response was found to occur before the onset of clinical symptoms. In adult infected animals, we found increased pS6 immunoreactivity in the area postrema of the brain stem and decreased phosphorylated STAT5-immunoreactive neurons in the bed nucleus of the stria terminalis, which has been associated with autonomic control, including stress response. Our observations contribute to knowledge of how rotavirus infection induces gut-nerve-brain interaction early in the disease.

The effects of huperzine A on gastrointestinal acetylcholinesterase activity and motility after single and multiple dosing in mice

The acetylcholinesterase inhibitor (AChEI), huperzine A has been used in the treatment of the cognitive deterioration associated with Alzheimer’s disease (AD). However, the side-effects of huperzine A associated with increased cholinergic activity, particularly in the gastrointestinal system, are evident. It is not yet known how quickly these side-effects become tolerated; this information would provide guidance to doctors on how to use huperzine A so as to attenuate the adverse events. The present study aimed to observe the effects of huperzine A on gastrointestinal motility and acetylcholinesterase (AChE) activity in mice. After oral administration of huperzine A with single and multiple dosing, the gastrointestinal motility and AChE activity of the mice were examined. The results revealed that, following a single dose of huperzine A, the AChE activity in the stomach and duodenum were significantly inhibited and the gastrointestinal motility was significantly increased. However, following multiple doses (7 or 28 doses, one dose per day), no significant changes in the AChE activity and gastrointestinal motility were identified. These findings indicate that the gastrointestinal adverse effects of huperzine A may be well-tolerated relatively quickly and do not recur. Additionally, it suggests that patients with AD are likely to have minimal gastrointestinal side-effects after taking multiple doses of huperzine A.

Selective M3 muscarinic receptor antagonist inhibits small-cell lung carcinoma growth in a mouse orthotopic xenograft model

In small cell lung carcinoma (SCLC), acetylcholine (ACh) is synthesized and secreted, and it acts as an autocrine growth factor through activation of its receptors, muscarinic receptor (mAChR) and nicotinic receptor (nAChR). Alteration of tumor growth by blockade of M(3) mAChR in a human SCLC cell line, NCI-H82, was investigated in the present study. We used a highly selective M(3) muscarinic antagonist, N-(2-[3-([3R]-1-(cyclohexylmethyl)-3-piperidinyl]methylamino)-3-oxopropyl]amino-2-oxoethyl)-3,3,3-triphenyl-propioamide (J-115311). Our results show that J-115311 inhibited the increased intracellular calcium elicited by carbachol, a muscarinic agonist, in SCLC cells. J-115311 also inhibited SCLC cell growth in vitro. In a mouse orthotopic xenograft model, J-115311 dose-dependently reduced tumor growth when NCI-H82 cells were inoculated into the upper left lobe of the lung. These findings indicate that blockade of M(3) mAChR can suppress tumor growth in SCLC, suggesting the potential therapeutic utility of M(3) muscarinic antagonists as anti-cancer agents.

The effect of growth hormone releasing peptide-2 on upper gastrointestinal contractile activity and food intake in conscious dogs

BACKGROUND

The aim of this study was to evaluate the effect of growth hormone releasing peptide (GHRP)-2, a synthetic ligand for the growth hormone secretagogue receptor, on upper gastrointestinal motility and food intake.

METHODS

Five neurally intact dogs and five dogs with vagotomy and pyloroplasty were equipped with strain gauge force transducers on the stomach, duodenum and jejunum. GHRP-2 (0.5-10 microg/kg) was administered intravenously in neurally intact dogs in the interdigestive state and after feeding. To study the mechanism of GHRP-2-induced inhibition on postprandial contractions, various antagonists were administered intravenously prior to GHRP-2. The effect of GHRP-2 on postprandial contractions was also studied in dogs with vagotomy. GHRP-2 was also administered immediately before feeding in each group, and its effect on food intake was assessed.

RESULTS

GHRP-2 did not evoke gastrointestinal contractions in the interdigestive state. GHRP-2 induced contractile inhibition continuing for 2-3 min in neurally intact dogs and dogs with vagotomy. This inhibitory effect was reversed by the alpha- and alpha(2)-blockers. GHRP-2 increased food intake in neurally intact dogs, but not in dogs with vagotomy.

CONCLUSIONS

These results indicate that in the upper gut GHRP-2 inhibits postprandial contractions via alpha(2)-receptors on the enteric nervous system, whereas an intact vagal nerve is necessary for a GHRP-2-induced increase in food intake.

Cholinergic regulation of epithelial ion transport in the mammalian intestine

Acetylcholine (ACh) is critical in controlling epithelial ion transport and hence water movements for gut hydration. Here we review the mechanism of cholinergic control of epithelial ion transport across the mammalian intestine. The cholinergic nervous system affects basal ion flux and can evoke increased active ion transport events. Most studies rely on measuring increases in short-circuit current (ISC = active ion transport) evoked by adding ACh or cholinomimetics to intestinal tissue mounted in Ussing chambers. Despite subtle species and gut regional differences, most data indicate that, under normal circumstances, the effect of ACh on intestinal ion transport is mainly an increase in Cl- secretion due to interaction with epithelial M3 muscarinic ACh receptors (mAChRs) and, to a lesser extent, neuronal M1 mAChRs; however, AChR pharmacology has been plagued by a lack of good receptor subtype-selective compounds. Mice lacking M3 mAChRs display intact cholinergically-mediated intestinal ion transport, suggesting a possible compensatory mechanism. Inflamed tissues often display perturbations in the enteric cholinergic system and reduced intestinal ion transport responses to cholinomimetics. The mechanism(s) underlying this hyporesponsiveness are not fully defined. Inflammation-evoked loss of mAChR-mediated control of epithelial ion transport in the mouse reveals a role for neuronal nicotinic AChRs, representing a hitherto unappreciated braking system to limit ACh-evoked Cl- secretion. We suggest that: i) pharmacological analyses should be supported by the use of more selective compounds and supplemented with molecular biology techniques targeting specific ACh receptors and signalling molecules, and ii) assessment of ion transport in normal tissue must be complemented with investigations of tissues from patients or animals with intestinal disease to reveal control mechanisms that may go undetected by focusing on healthy tissue only.

Characterization of GABA(B) receptors involved in inhibition of motility associated with acetylcholine release in the dog small intestine: possible existence of a heterodimer of GABA(B1) and GABA(B2) subunits

Characterization of the gamma-aminobutyric acid (GABA)(B) receptor involved in the motility of dog small intestine was analyzed by application of the microdialysis method to the small intestine of the whole body of the dog. The reverse transcription-polymerase chain reaction (RT-PCR) was used. Intraarterial administration of muscimol induced acceleration of motility associated with acetylcholine (ACh) release, these responses being antagonized by bicuculline. Intraarterial administration of baclofen induced inhibition of motility associated with ACh release, these responses being antagonized by CGP62349. GABA induced inhibition of motility associated with decrease in ACh release. CGP62349 alone induced acceleration of motility associated with increase in ACh release. RT-PCR revealed the presence of mRNAs for both subunits of GABA(B) receptor, GABA(B1) and GABA(B2), in the dog small intestine, although GABA(B1) subunits were 6 isoforms of GABA(B1) (GABA(B1(a)) - GABA(B1(g))), except GABA(B1(d)). Thus, the GABA(B) receptor located at cholinergic neurons as a heterodimer with subunits of GABA(B1) and GABA(B2) in the dog small intestine operates predominantly relative to the GABA(A) receptor in physiological motility.

In vivo assessment of acceleration of motor activity associated with acetylcholine release via 5-hydroxytryptamine4 receptor in dog intestine

Effect of mosapride, a benzamide, on the motor activity associated with the release of endogenous acetylcholine (ACh) from enteric neurons was examined in the ileum of anesthetized dogs using an in vivo microdialysis method and compared with the effect of 5-hydroxytryptamine (5-HT). Intraarterial administration of 5-HT accelerated intestinal motor activity and increased the concentration of dialysate ACh, and the responses were inhibited by SB204070, a specific 5-HT4-receptor antagonist, but were apparently not affected by methiothepin, ketanserin and granisetron. Intraarterial administration of mosapride, a prokinetic benzamide, accelerated intestinal motor activity and the concentration of dialysate ACh increased. The effects of mosapride were antagonized by SB204070. Specific [125I]SB207710 binding was observed in the myenteric and submucosal plexuses and muscle layers of dog ileum by in vitro receptor autoradiography. High densities of [125I]SB207710 binding sites were detected in the myenteric and submucosal plexuses. Mosapride as well as SB204070 inhibited [125I]SB207710 binding. Thus, in the whole body of dogs, 5-HT and mosapride accelerated the intestinal motor activity due to the increases in ACh release mediated by stimulation of the 5-HT4 receptor.