In Vivo Assessment of the Regulatory Mechanism of Cholinergic Neuronal Activity Associated With Motility in Dog Small Intestine

Abstract

ABSTRACT-Intestinal motor activity associated with acetylcholine (ACh) release was assessed in the small intestine of anesthetized dogs by simultaneous measurement of motor activity and local ACh concentrations within the intestinal wall with in vivo microdialysis. Basal concentration of ACh measured in the dialysate was 1.12 ± 0.08 pmol/ 15 min (n = 10), a value that remained constant until 3 h after perfusion. Intraarterial infusion of tetrodotoxin reduced dialysate ACh concentration, while the motor activity accelerated at the early phase after infusion of tetrodotoxin and then decreased, thereby suggesting that the motor activity is regulated by not only excitatory cholinergic neurons, but also inhibitory neurons. Intraarterial infusion of atropine increased dialysate ACh concentration but reduced motor activity, thereby indicating that the cholinergic neurons are tonically active and the muscarinic autoreceptors operate to inhibit the ACh release. Intraarterial infusion of norepinephrine reduced, but yohimbine increased both motor activity and dialysate ACh concentration, thereby indicating that the adrenergic neurons regulate the motor activity due to control of cholinergic neuronal activity. This in vivo microdialysis method demonstrated in the whole body of animals that the activity of cholinergic neurons was physiologically regulated by itself and adrenergic neurons.Keywords: In vivo microdialysis, Acetylcholine release, Tetrodotoxin, Atropine, NorepinephrineThe mechanism underlying changes in gastrointestinal motility induced by many substances were evaluated by measuring mechanical activity and neurotransmitter release in the isolated preparations. However, findings obtained by in vitro experiments do not always correspond to those in vivo, and thus it cannot be elucidated whether the responses obtained in the isolated preparations are physiologically and/ or pathophysiologically important in the whole body. Application of microdialysis to gastrointestinal tissue may offer a potential advantage over traditional methods using isolated preparations because it allows for continuous, long-term sampling of interstitial solute concentration within the region of gastrointestinal tissues in which a dialysis probe has been placed. Prostaglandin E 2 in interstitial fluid of dog gastric submucosa (1) and catabolism of neurotensin in interstitial fluid of rat gastric submucosa (2) were measured by the in vivo microdialysis method. These studies did not analyze neuronal regulation of gastrointestinal motility in the whole body, since the concentrations of substances released into the local area related to the motility were not measured. Recently, it has been shown by the in vivo microdialysis method that stimulation of vagal nerve produces release of nitric oxide at concentrations able to cause inhibition of smooth muscle contractions in the stomach and colonic wall of rabbits (3). We previously suggested that the intestinal motility was associated with acetylcholine (ACh) release from enteric nerves in whole body...

Selective M3 Muscarinic Receptor Antagonist Inhibits Small-Cell Lung Carcinoma Growth in a Mouse Orthotopic Xenograft Model

“…However, J-115311 and darifenacin do have a similar potency for inhibiting carbachol-induced [Ca 2+ ] i influx in the same cell line. It is known that the release of ACh from the parasympathetic nerves is controlled by M 2 autoreceptors located on the nerves (21,22) and that inhibition of these autoreceptors leads to the release of ACh. It is also reported that the M 2 mAChR antagonist significantly increases proliferation of H1694 cells, an SCLC cell line, which suggests that the presence of the M 2 autoreceptor regulates cell proliferation in lung cancer cells (23).…”

Characterization of GABAB Receptors Involved in Inhibition of Motility Associated With Acetylcholine Release in the Dog Small Intestine: Possible Existence of a Heterodimer of GABAB1 and GABAB2 Subunits

“…These results confirmed previous studies in which GABA A receptor and GABA B receptor were shown to be excitatory and inhibitory in the intestinal motor activity of isolated preparations, respectively (20 -22). It has been shown that ACh in the dialysate originates from the enteric cholinergic neuron (26,27); therefore, muscimol and baclofen induced acceleration and inhibition of intestinal motor activity due to modulation of ACh release from the enteric cholinergic neurons, respectively. Thus, the in vitro findings that stimulations of GABA A receptor and GABA B receptor induced contraction and relaxation due to modulation of ACh release, respectively (32,33), were confirmed in the whole body of a dog.…”

“…The motor activity associated with acetylcholine (ACh) release has been demonstrated by measuring simultaneously motor functions and solute concentration of ACh within the region of gastrointestinal tissues in which a dialysis probe has been placed (26,27). Use of such a method facilitates analysis of the mechanism underlying motor functions of the intestine mediated by stimulation of the GABA B receptor in the whole body of an animal.…”

In Vivo Assessment of Acceleration of Motor Activity Associated With Acetylcholine Release via 5-Hydroxytryptamine4 Receptor in Dog Intestine

“…In our previous study, ACh in the dialysate was determined to originate from the enteric cholinergic nerve terminals, based on the findings that intraarterial administration of tetrodotoxin inhibited spontaneous motor acti- vity and ACh release (24) and the nerve-stimulated contractions and increases in ACh release (23). The released ACh, which was associated with motility of circular muscle, was suggested to originate mainly from the cholinergic nerve terminals in the deep muscular plexus of the circular muscle layer (27,28).…”

“…We have shown that the intestinal motor activity was associated with ACh release from enteric nerves in the whole body of dogs using the in vivo microdialysis method (23,24).…”