Autonomic Nerve Regulation of Colonic Peristalsis in Guinea Pigs

BACKGROUND/AIMS: Colonic peristalsis is mainly regulated via intrinsic neurons in guinea pigs. However, autonomic regulation of colonic motility is poorly understood. We explored a guinea pig model for the study of extrinsic nerve effects on the distal colon. METHODS: Guinea pigs were sacrificed, their distal colons isolated, preserving pelvic nerves (PN) and inferior mesenteric ganglia (IMG), and placed in a tissue bath. Fecal pellet propagation was conducted during PN and IMG stimulation at 10 Hz, 0.5 ms and 5 V. Distal colon was connected to a closed circuit system, and colonic motor responses were measured during PN and IMG stimulation. RESULTS: PN stimulation increased pellet velocity to 24.6 +/- 0.7 mm/sec (n = 20), while IMG stimulation decreased it to 2.0 +/- 0.2 mm/sec (n = 12), compared to controls (13.0 +/- 0.7 mm/sec, P < 0.01). In closed circuit experiments, PN stimulation increased the intraluminal pressure, which was abolished by atropine (10(-6) M) and hexamethonium (10(-4) M). PN stimulation reduced the incidence of non-coordinated contractions induced by NG-nitro-L-arginine methyl ester (L-NAME; 10(-4) M). IMG stimulation attenuated intraluminal pressure increase, which was partially reversed by alpha-2 adrenoceptor antagonist (yohimbine; 10(-6) M). CONCLUSIONS: PN and IMG input determine speed of pellet progression and peristaltic reflex of the guinea pig distal colon. The stimulatory effects of PN involve nicotinic, muscarinic and nitrergic pathways. The inhibitory effects of IMG stimulation involve alpha-2 adrenoceptors.

Regional Difference in Colonic Motility Response to Electrical Field Stimulation in Guinea Pig

BACKGROUND/AIMS: In isolated guinea-pig colon, we investigated regional differences in peristalsis evoked by intrinsic electrical nerve stimulation. METHODS: Four colonic segments from mid and distal colon of Hartley guinea pigs, were mounted horizontally in an organ bath. Measurement of pellet propulsion time, intraluminal pressure, electrical field stimulation (EFS; 0.5 ms, 60 V, 10 Hz), and response of pharmacological antagonists, were performed to isolated segments of colon to determine the mechanisms underlying peristaltic reflexes evoked by focal electrical nerve stimuli. RESULTS: In fecal pellet propulsion study, the velocity of pellet propulsion was significantly faster in the distal colon and decreased gradually to the proximal part of the mid colon. Intraluminal pressure recording studies showed that luminal infusion initiated normal peristaltic contractions (PCs) in 82% trials of the distal colon, compared to that of mid colon. In response to EFS, the incidence of PCs was significantly increased in the distal colon in contrast, the incidence of non-peristaltic contractions (NPCs) was significantly higher in the middle-mid colon, distal-mid colon and distal colon, compared to that of proximal-mid colon. Addition of L-NAME into the bath increased the frequency of NPCs. EFS failed to cause any PCs or NPCs contractions in the presence of hexamethonium, atropine or tetrodotoxin. CONCLUSIONS: This study has revealed that electrical nerve stimulation of distal colon is the most likely region to elicit a peristaltic wave, compared with the mid or proximal colon. Our findings suggest that EFS-evoked PCs can be modulated by endogenous nitric oxide.

Mechanism of Interdigestive Migrating Motor Complex

Migrating motor complex (MMC) is well characterized by the appearance of gastrointestinal contractions in the interdigestive state. This review article discussed the mechanism of gastrointestinal MMC. Luminal administration of 5-hydroxytryptamine (5-HT) initiates duodenal phase II followed by gastrointestinal phase III with a concomitant increase of plasma motilin release in conscious dogs. Duodenal 5-HT concentration is increased during gastric phase II and phase III. Intravenous infusion of motilin increases luminal 5-HT content and induces gastrointestinal phase III. 5-HT4 antagonists significantly inhibits both of gastric and intestinal phase III, while 5-HT3 antagonists inhibited only gastric phase III. These suggest that gastrointestinal MMC cycle is mediated via the interaction between motilin and 5-HT by the positive feedback mechanism. Gastric MMC is regulated via vagus, 5-HT3/4 receptors and motilin, while intestinal MMC is regulated via intrinsic primary afferent neurons and 5-HT4 receptors. Stress is highly associated with the pathogenesis of functional dyspepsia. Acoustic stress attenuates gastric phase III without affecting intestinal phase III in conscious dogs, via reduced vagal activity and increased sympathetic activity. It has been shown that subset of functional dyspepsia patients show reduced vagal activity and impaired gastric phase III. The physiological importance of gastric MMC is a mechanical and chemical cleansing of the empty stomach in preparation for the next meal. The impaired gastric MMC may aggravate dyspeptic symptoms following a food ingestion. Thus, maintaining gastric MMC in the interdigestive state is an important factor to prevent the postprandial dyspeptic symptoms.

Mechanism of acupuncture-induced gastric motility / 全日本鍼灸学会雑誌

Effects of acupuncture on gastric motility in anesthetized rats<BR>Acupuncture has been used to treat gastrointestinal symptoms in. China for more than 3, 000 years. However, the mechanism of the beneficial effects of acupuncture remains mysterious. Strain gage transducers were implanted on the serosal surface of the stomach to record circular muscle contractions in thiobutabarbialanesthetized rats. Acupuncture on the right lower abdomen caused a transient relaxation of the stomach. Acupuncture-induced gastric relaxations were abolished by guanethidine, propranolol, splanchnic ganglionectomy, spinal cord transection, and spino-medullary transection. In contrast, NG-nitro-L-arginine, phentolamine, truncal vagotomy and ponto-medullary transection had no effect. Acupuncture increased the number of c-Fos immunopositive cells at the rostral ventrolateral medulla (RVLM). It is concluded that acupuncture-induced gastric relaxations are mediated via somato-sympathetic reflex. Its afferent limb is composed of abdominal cutaneous and muscle afferent nerves. Its efferent limb is the gastric sympathetic nerve and the reflex center is within the medulla. RVLM neurons may play an important role in mediating this reflex.<BR>Effects of acupuncture on gastric motility in conscious rats<BR>Of 35 rats studied, 60% showed no cyclic groupings of strong contractions (type A) and 10 rats (40%) showed the cyclic phase III-like contractions (type B) in conscious rats. In 73 % of type A rats, acupuncture on the hind limb (ST36), but not on the back, produced strong cyclic contractions lasting for more than 3 hrs. Acupuncture failed to produce phase III-like contractions in type A rats treated with atropine, hexamethonium and vagotomy. Pretreatment with naloxone significantly shortened the duration of enhanced phase III-like contractions. In 60 % of type B rats, acupuncture suppressed phase III-like contractions. These results suggest that the acupuncture on the ST36 induces dual effects, either stimulatory or inhibitory effects, on gastric motility. The stimulatory effects of acupuncture on the hind limb are mediated via wagal efferent pathway and opioid pathway.<BR>Effects of acupuncture on vasopressin-induced emesis in conscious dogs<BR>Arginine vasopressin (AVP) is a posterior pituitary hormone and recent evidence implies an involvement of AVP in vomiting and nausea of humans and animals. Vasopressin was intravenously infused at a dose of 0.1U/kg/min. Number of retching and vomiting were visually counted during the experiment. Intravenous administration of vasopressin induced retching and vomiting in all dogs tested. Retrograde peristaltic contractions (RPCs) occurred before the retching and vomiting.<BR>Electro-acupuncture (EA) of 10 HZ at PC6 decreased the number of retching and vomiting induced by vasopressin. EA also suppressed the RPCs. EA at the PC6 significantly reduced the number of episodes of retching and vomiting to 20-30 % compared to that without EA, while EA at BL21 had no significant effects on the number of episodes of retching and vomiting induced by vasopressin.<BR>To investigate whether opioid pathway is involved in EA-induced anti-nociceptive effects, naloxone was administered before EA and vasopressin infusion. EA at PC6 had no more inhibitory effects on vasopressininduced nausea and vomiting when naloxone was given. This suggests that anti-emetic effects of acupuncture is mediated via (central) opioid pathway.<BR>Effects of acupuncture on EGG in healthy volunteers<BR>The point of PC6 and ST36 are the common points for the treatment of gastric symptoms. We compared the effect of EA between PC6 and ST36 on gastric myoelectrical activity using surface electrogastrography (EGG). Eight healthy volunteers were fasted for 12 hours. On the separate days, four sessions of EA (1 Hz, 30 min) were randomly performed to each subject. The percentage of normal slow waves and tachygastria, peak dominant frequency (PDF) and peak dominant power