Presence Of Neural Blockade Research Articles

Induction of rhythmic transient depolarizations associated with waxing and waning of slow wave activity in intestinal smooth muscle.

Cannon described in 1902 the segmentation motor activity of the small intestine (Canon WB. J Med Res 7: 72-75, 1902). This motor pattern can arise when low-frequency transient depolarizations are evoked in the interstitial cells of Cajal associated with the deep muscular plexus (ICC-DMP) network, which then affect the omnipresent slow wave activity: changing its regular amplitude into a waxing and waning pattern. The objective of the present study was to investigate physiological stimuli that could induce the low-frequency component. Intracellular recordings were obtained from circular muscle with or without attached mucosa. Decanoic acid (1 mM) and butyric acid (10 mM) both evoked low-frequency transient depolarizations but through different mechanisms. Decanoic acid-induced waxing and waning was initiated by purely myogenic means when perfused onto exposed circular muscle. Butyric acid required the intact mucosa and uninhibited neural activity to elicit the low-frequency response. Evidence is provided that the transient rhythmic depolarizations occur in the absence of interstitial cells of Cajal associated with the myenteric plexus (ICC-MP). Onset of the slow transient depolarizations was stimulated by addition of N(ω)-nitro-l-arginine (l-NNA; 100 μM); thus the low-frequency component seems to be under chronic inhibition by nitric oxide. Excitatory tachykinergic stimulation induced the low-frequency component since substance P (0.5 μM) evoked it in the presence of neural blockade. In summary, interplay between two networks of myogenic pacemakers, neural activity, and nutrient factors such as fatty acids plays a role in the generation of the rhythmic low-frequency component that is essential for the development of the checkered segmentation motor pattern.

Neurogenic and Myogenic Properties of Pan-Colonic Motor Patterns and Their Spatiotemporal Organization in Rats

Background and AimsBetter understanding of intrinsic control mechanisms of colonic motility will lead to better treatment options for colonic dysmotility. The aim was to investigate neurogenic and myogenic control mechanisms underlying pan-colonic motor patterns.MethodsAnalysis of in vitro video recordings of whole rat colon motility was used to explore motor patterns and their spatiotemporal organizations and to identify mechanisms of neurogenic and myogenic control using pharmacological tools.ResultsStudy of the pan-colonic spatiotemporal organization of motor patterns revealed: fluid-induced or spontaneous rhythmic propulsive long distance contractions (LDCs, 0.4–1.5/min, involving the whole colon), rhythmic propulsive motor complexes (RPMCs) (0.8–2.5/min, dominant in distal colon), ripples (10–14/min, dominant in proximal colon), segmentation and retrograde contractions (0.1–0.8/min, prominent in distal and mid colon). Spontaneous rhythmic LDCs were the dominant pattern, blocked by tetrodotoxin, lidocaine or blockers of cholinergic, nitrergic or serotonergic pathways. Change from propulsion to segmentation and distal retrograde contractions was most prominent after blocking 5-HT3 receptors. In the presence of all neural blockers, bethanechol consistently evoked rhythmic LDC-like propulsive contractions in the same frequency range as the LDCs, indicating the existence of myogenic mechanisms of initiation and propulsion.ConclusionsNeurogenic and myogenic control systems orchestrate distinct and variable motor patterns at different regions of the pan-colon. Cholinergic, nitrergic and serotonergic pathways are essential for rhythmic LDCs to develop. Rhythmic motor patterns in presence of neural blockade indicate the involvement of myogenic control systems and suggest a role for the networks of interstitial cells of Cajal as pacemakers.

A 5-HT3 receptor agonist induces a chloride secretory response in the presence of neural blockade in rat distal colon

Abstract Introduction: Serotonin (5-HT) is a well-described intestinal secretagogue. The 5-HT3 receptor is one of many 5-HT subtypes and is generally accepted to reside at the level of the enteric neuron. We hypothesize that a further subtype of the 5-HT3 receptor may be found on a nonneural cell in rat colon. Methods: Partial-thickness sheets of rat distal colon (n = 9) were mounted in Ussing chambers and short-circuited. The selective 5-HT3 receptor agonist, 2-met-5-HT (50 micromol), was added in the presence or absence of 1 micromol of the neural sodium channel blocker, tetrodotoxin (TTX). Control tissue received no drug. Changes in short-circuit current (Isc), a measure of electrogenic chloride secretion, was measured continuously. Results: Histologic examination of the stripped colon revealed intact mucosa and muscularis mucosa, scant submucosa, and virtually no neural ganglia (HE ANOVA) or TTX alone (p Conclusions: In this in vitro preparation of rat colon, the selective 5-HT3 receptor agonist, 2-met-5-HT, induced a chloride secretory response that was TTX-insensitive. These findings suggest the presence of a nonneural 5-HT3 receptor located at the level of the mucosa. TableMean (+/− SEM) changes in Isc from baseline in microamps/cm 2 MinControl2Met5HT∗2Met5HT + TTX∗TTX5−1.3 ± 0.911.3 ± 2.28.1 ± 3.0−0.3 ± 0.210−1.8 ± 1.912.0 ± 3.37.3 ± 1.9−0.8 ± 0.315−3.3 ± 3.09.3 ± 1.86.7 ± 1.6−0.8 ± 0.430−4.3 ± 4.18.6 ± 1.95.2 ± 1.2−0.9 ± 0.660−5.0 ± 4.35.5 ± 2.12.0 ± 0.8−1.1 ± 0.7∗p

Neural control of cardiovascular responses and of ventilation during dynamic exercise in man.

1. Nine subjects performed dynamic knee extension by voluntary muscle contractions and by evoked contractions with and without epidural anaesthesia. Four exercise bouts of 10 min each were performed: three of one-legged knee extension (10, 20 and 30 W) and one of two-legged knee extension at 2 x 20 W. Epidural anaesthesia was induced with 0.5% bupivacaine or 2% lidocaine. Presence of neural blockade was verified by cutaneous sensory anaesthesia below T8-T10 and complete paralysis of both legs. 2. Compared to voluntary exercise, control electrically induced exercise resulted in normal or enhanced cardiovascular, metabolic and ventilatory responses. However, during epidural anaesthesia the increase in blood pressure with exercise was abolished. Furthermore, the increases in heart rate, cardiac output and leg blood flow were reduced. In contrast, plasma catecholamines, leg glucose uptake and leg lactate release, arterial carbon dioxide tension and pulmonary ventilation were not affected. Arterial and venous plasma potassium concentrations became elevated but leg potassium release was not increased. 3. The results conform to the idea that a reflex originating in contracting muscle is essential for the normal blood pressure response to dynamic exercise, and that other neural, humoral and haemodynamic mechanisms cannot govern this response. However, control mechanisms other than central command and the exercise pressor reflex can influence heart rate, cardiac output, muscle blood flow and ventilation during dynamic exercise in man.

Adaptation of Cholinergic Enteric Neuromuscular Transmission in Diabetic Rat Small Intestine

Representative longitudinal muscle strips (6 x 10 mm) from distal small intestine were obtained from rats after 1, 2, and 3 mo of streptozocin-induced diabetes. The strips were stretched to their optimum lengths and subjected to electrical field stimulation (1-ms pulse duration, 30-270 mA, 10 Hz) in the presence of Krebs solution and Krebs solution plus 10(-6) M atropine. Field stimulation produced atropine-sensitive and atropine-resistant contractions in all strips. After 1 mo, significant differences in the amplitudes of the atropine-sensitive contractions were found between the diabetic rats and nondiabetic controls. Insulin-treated diabetic rats showed contraction responses that were intermediate in amplitude. After 2 mo, the difference between the control and diabetic groups was less evident but still significant. After 3 mo, the previously noted difference in the atropine-sensitive contractions between the diabetic and control groups had resolved. No significant differences among the three groups were noted in the amplitudes of the atropine-resistant contractions. Field stimulation delivered at pulse durations of 50 ms in the presence of neural blockade with tetrodotoxin (5 x 10(-6) M) produced similar contraction amplitudes among the three groups at any respective time phase of the study. Dose-response studies of intestinal muscle after 3 mo of untreated diabetes showed normal tension development to both bethanechol chloride and physostigmine. These results indicate that streptozocin-induced diabetes is acutely associated with defective cholinergic neuromuscular transmission in the myenteric plexus of the distal small intestine. The abnormality is less evident after 2 mo of untreated diabetes and resolves spontaneously after 3 mo. Insulin treatment appears to accelerate this resolution.

Ion transport abnormalities in inflamed rat jejunum: Involvement of mast cells and nerves

Basal and stimulated changes in ion transport in vitro were examined in jejunal mucosa from rats during inflammation produced after infection with the nematode Nippostrongylus brasiliensis. The gut was acutely inflamed at days 7 and 10 when net secretion of Na+ and Cl− ions was evident. Serum levels of rat mast cell protease II were elevated, providing evidence for mast cell activation. In addition, the magnitude of the short-circuit current responses to electrical transmural stimulation of enteric nerves (but not to histamine in the presence of neural blockade) were significantly reduced (p < 0.01) to 17%–33% of control values, suggesting abnormalities of mucosal nerves. Following worm expulsion, serum levels of rat mast cell protease II and ion transport returned to normal. However, mastocytosis was apparent in gut mucosa and parasite antigen stimulated net secretion. In the absence of antigen, short-circuit current responses to nerve stimulation were increased (to 122% of controls; p < 0.05). These findings suggest that changes in mast cells and enteric nerves occur during inflammation in this model and implicate neural and mast cell interactions with the epithelium in producing the ion-transport abnormalities.

Ion transport abnormalities in inflamed rat jejunum

Abstract Basal and stimulated changes in ion transport in vitro were examined in jejunal mucosa from rats during inflammation produced after infection with the nematode Nippostrongylus brasiliensis . The gut was acutely inflamed at days 7 and 10 when net secretion of Na + and Cl − ions was evident. Serum levels of rat mast cell protease II were elevated, providing evidence for mast cell activation. In addition, the magnitude of the short-circuit current responses to electrical transmural stimulation of enteric nerves (but not to histamine in the presence of neural blockade) were significantly reduced (p

Effect of Neural Blockade on Somatostatin-Induced Inhibition of Exocrine Pancreatic Secretion

In vivo somatostatin inhibits exocrine pancreatic secretion. In in vitro experiments, such as the isolated perfused pancreas, somatostatin fails to inhibit exocrine pancreatic secretion. This suggests an indirect action of somatostatin, such as modulation of neural regulation. In the anesthetized rat we tested the inhibitory capacity of somatostatin in the presence of neural blockade in vivo. Neither the drugs given intravenously--phentolamine, propranolol, atropine and naloxone--nor vagotomy were able to prevent somatostatin-induced inhibition of exocrine pancreatic secretion. We conclude that somatostatin-induced inhibition of exocrine pancreatic secretion is not dependent on intact extrinsic innervation.

β-Adrenoceptors on duodenal mucosal cells mediate venous serotonin release

We have previously documented predominant intraluminal release of serotonin (5-HT) following activation of muscarinic receptors on enterochromaffin cells. Gronstad et al. reported that portal venous release of 5-HT in response to vagal stimulation was mediated by β-adrenergic receptors. The purpose of this study was to determine whether 5-HT release induced by the β-adrenergic agonist, isoproterenol, is mediated by enteric nerves or is a direct action at the enterochromaff in cell level. We mounted rabbit duodenal mucosal sheets stripped of muscularis in modified Ussing chambers and measured release of 5-HT in response to 10 −5 M isoproterenol, in the presence and absence of the neural conduction blocker tetrotoxin, 10 −6 M. Serotonin was measured in the buffer bathing the mucosal and submucosal surfaces by HPLC. In the presence of isoproterenol, total (mucosal and submucosal) 5-HT release (21.0 ± 4.9 ng/cm 2/45 min) was significantly ( P < 0.05) greater than that in untreated controls (7.8 ± 2.7 ng/cm 2/45 min); release was predominantly toward the submucosal surface. In the presence of tetrodotoxin alone, net 5-HT release was significantly ( P < 0.05) increased to 12.8 ± 2.8 ng/cm 2/45 min. In tetrodotoxin-treated mucosa, isoproterenol increased 5-HT release to 28.6 ± 5.3 ng/cm 2/45 min which was significantly greater ( P < 0.05) than that with tetrodotoxin alone. Since 5-HT release was increased even in the presence of neural blockade, these results suggest that activation of β-adrenergic receptors on or near enterochromaffin cells induces release of 5-HT predominantly toward the submucosal surface.

Serotonin release is mediated by muscarinic receptors on duodenal mucosal cells

Serotonin (5-HT), found in abundance in intestinal enterochromaffin cells, has been shown to be released in response to neural, humoral, and intraluminal stimuli but the mechanisms controlling release are poorly understood. The purpose of this study was to determine whether 5-HT release induced by the muscarinic agonist, methacholine, is mediated by enteric nerves or is a direct action at the mucosal cell level. We mounted rabbit mucosal sheets containing intact submucosal neural elements, but stripped of muscularis propria and myenteric plexus, in modified Ussing chambers and measured the release of 5-HT in response to 5 × 10 −5 M methacholine added to both mucosal and serosal surface bathing solutions, in the presence and absence of selective neural blockade with 1 × 10 −6 M tetrodotoxin. 5-HT release in control tissues (no drugs) as measured by radioimmunoassay was 25.7 ± 6 ng/cm 2/30 min (mean ± SEM). In the presence of mucosal and serosal methacholine, total 5-HT release increased significantly ( P < 0.05) to 66.7 ± 9 ng/cm 2/30 min. When tetrodotoxin alone was applied, 5-HT release significantly increased to 55.2 ± 9 ng/cm 2/30 min compared to matched control. In the presence of tetrodotoxin, methacholine increased 5-HT release to 79.3 ± 9 ng/cm 2/30 min, which was significantly greater than with tetrodotoxin alone. These results provide evidence of an inhibitory neural regulation of basal 5-HT release since release increased in the presence of neural blockade. They also suggest that a muscarinic receptor at or near the enterochromaffin cells mediates mucosal 5-HT release since 5-HT is further increased by methacholine even in the presence of neural blockade.

Evidence for abnormal cholinergic neuromuscular transmission in diabetic rat small intestine

Proximal and distal rat small intestine from control, diabetic, and insulin-treated diabetic rats was cut into strips measuring 6.0 × 10.0 mm. Strips cut along the oral-caudal axis were called longitudinal strips, while those cut 90 ° to that axis were called circular strips. The strips were stretched to their optimum lengths and subjected to electrical field stimulation (0.1–1.0-ms pulse duration, 30–270 mA, 1–26 Hz) in the presence of Krebs' solution and Krebs' solution plus 10−6 M atropine. Field stimulation produced atropine-sensitive and atropineresistant contractions in all strips. Significant differences among the three groups were found in the amplitudes of atropine-sensitive contractions in strips from distal longitudinal muscle. Controls showed the highest amplitude contractions and diabetics the lowest, whereas the insulin-treated diabetics showed contractions intermediate in amplitude. No significant differences were noted among the atropine-resistant contractions. Field stimulation delivered at pulse durations of 5.0 and 50.0 ms in the presence of neural blockade with tetrodotoxin (5 × 10−6 M) produced similar contraction amplitudes among the three groups. These results suggest that streptozotocin-induced diabetes mellitus is associated with defective cholinergic neuromuscular transmission in the myenteric plexus of the distal small intestine. Insulin therapy seems to improve the abnormality.