Forestomach Motility Research Articles

The effect of central sympathectomy by 6-hydroxydopamine (6-OHDA) on the response to morphine in conscious sheep.

When morphine, an opioid mu-agonist, was administered in vivo into the third cerebral ventricle (ICV) of conscious sheep at 20 and 40 micrograms/kg body weight, it caused psychomotor excitability for 2-3 h and a significant decrease in the reticuloruminal frequency for 45 min and in the mean amplitude of the primary contractions for 65 min. From 60 min after infusion, the same doses of morphine caused a significant increase in the average amplitude of the contractions for 45 min. This suggests that an inhibitory mu-opioid acceptor is involved in the central control of forestomach motility and general behaviour in sheep. All the effects of morphine were completely prevented by pretreatment with 18.2 micrograms/kg body weight 6-OHDA ICV. These results suggest that both morphine-induced inhibition of rumen motility and psychomotor excitability are due to central noradrenergic descending system activation. The exact location of the noradrenergic system remains to be determined.

Modification by 6-hydroxydopamine (6-OHDA) of the inhibition of extrinsic rumen contractions in sheep produced by beta-endorphin.

In sheep, beta-endorphin (1 and 2 micrograms/kg) administered into the third cerebral ventricle caused a significant inhibition of the frequency of rumen contractions. The amplitude of the first rumen contractions, following immediately after the end of infusion, and the average amplitude of primary rumen contractions, were inhibited. Beta-endorphin caused general psychomotor excitability. These results suggest that an inhibitory mu and delta opioid system is involved in the control of forestomach motility and general behaviour in sheep. All effects of beta-endorphin were completely prevented by i.c.v. 6-hydroxydopamine (6-OHDA, 18.2 micrograms/kg) pre-treatment. These results suggest that beta-endorphin-induced inhibition of rumen motility is due to central noradrenergic system activation. The exact location of this noradrenergic system remains to be determined.

Opioid inhibitory control of the ruminant stomach motility: functional importance of the hypothalamus.

In conscious sheep, Leu-enkephalin (10 and 20 micrograms.kg-1) administered into the third cerebral ventricle caused a psychosedative action and a significant inhibition of the frequency of rumen contractions. The amplitude of the first rumen contractions, following immediately after the end of the Leu-enkephalin's infusion (at a dose of 20 micrograms) and the average amplitude of primary rumen contractions were also significantly inhibited. The hypothalamic isolation prevented both the inhibitory effect of Leu-enkephalin on the rumen motility and the drug induced psychosedative action. In contrast, Leu-enkephalin (20 micrograms.kg-1), significantly enhanced phasic contractions of the rumen after hypothalamic isolation. However the hypothalamic isolation did not prevent Leu-enkephalin induced inhibition of the mean amplitude of rumen contractions, but this inhibition was not significant (NS). The character of the histopathological changes induced by the isolation of the hypothalamus showed descending degenerative changes of the neuronal pathways connecting the hypothalamus to the pons and lower to the medulla. These results do suggest that the isolation of the hypothalamus causes the degeneration of the descending inhibitory opioid pathways connecting the hypothalamus to the gastric centers of the medulla and point act out the functional importance of descending tonic opioid inhibitory control of ruminant forestomach motility.

Inhibition of Food Intake and Reticulo‐Rumen Motility of Sheep by the Alpha‐2 Adrenoreceptor Agonist Clonidine

The investigation of the effect of intravenous clonidine, an alpha-2 adrenoreceptor agonist, was carried out in sheep with recording of forestomach motility for 3 h and intake of chopped hay for 8 h after drug administration. Motility and food intake were inhibited by clonidine at 2 micrograms.kg-1 and at 5 micrograms.kg-1. The effects of the lower dose were prevented by idazoxan, an alpha-2 antagonist, at 0.1 mg.kg-1 but not by prazosin, an alpha-1 antagonist, at 0.1 mg.kg-1. Minor effects of the antagonists alone were noted. Blood glucose concentration was measured in all the experiments and the possibility discussed that changes in concentration, not absolute values, may have contributed to inhibitory effects. Vagal stimulation in anaesthetised sheep indicated that inhibition of motility was a central neural effect, not an effect on forestomach muscle.

Inhibition of reticulo-rumen motility by gammaendorphin in sheep

Effects of gamma-endorphin, the mu- and delta-opioid receptor's agonist on amplitude and frequency of reticulo-ruminal contractions of conscious sheep were determined. Gamma-endorphin (1.0 and 2.0 μg kg −1 BW) administered into the third cerebral ventricle caused significant decreases in frequency of reticulo-ruminal contractions. Gamma-endorphin (2.0 μg kg −1 BW) depressed frequency and amplitude, and caused general neuroleptic-like action. A 1.0 μg kg −1 BW dose increased amplitude of contractions and provoked psychomotor-excitability action. Naloxone (12.5 μg kg −1 BW) prevented response to gamma-endorphin. Results suggest that an inhibitory mu- and delta-opioid system is involved in the control of forestomach motility and general behavior in sheep.

Circadian Changes of Forestomach Motility and of Rumination in Camels

Circadian Changes of Forestomach Motility and of Rumination in Camels

Loss of Forestomach Motility in Sheep Experiencing Ruminal Lactic Acidosis is not Dependent on Duodenal Acidification by Lactic Acid

Reticuloruminal motility, duodenal myoelectrical activity, and the pH and lactic acid concentrations of ruminal and duodenal contents were monitored in rumen fistulated sheep that were intraruminally loaded with finely ground wheat (50 g/kg). Following ruminal loading, reticuloruminal motility was enhanced. However, within 6 hours of loading, forestomach motility was impaired and within 9 hours ruminal stasis occurred. During loss of forestomach motility, lactic acid concentrations in ruminal contents increased and may, in part, have contributed to the decrease in pH of ruminal fluids. The levels of lactic acid within duodenal contents also rose, however, the pH of duodenal contents remained unchanged. During the loss of reticuloruminal motility, premature regular spiking activity (RSA) and/or abnormal patterns of migrating myoelectric complexes (MMC) were not observed on the duodenum. These findings indicate that loss of forestomach motility in ruminal lactic acidosis may not be a consequence of acidification of the proximal duodenum by lactic acid produced in the forestomach.

Ruminal lactic acidosis: forestomach epithelial receptor activation by undissociated volatile fatty acids and rumen fluids collected during loss of reticuloruminal motility

Forty-three reticuloruminal epithelial receptors, with excitatory receptive fields within the reticulum, were isolated in 19 anaesthetised sheep. The responsiveness of these receptors to acetic, propionic, butyric and DL-lactic acids were assessed as well as their ability to be activated by rumen fluids obtained from sheep with induced ruminal lactic acidosis. Eighteen (41.9 per cent) receptors were excited by all three volatile fatty acids (VFAs) and 17 (39.5 per cent) responded to two VFAs. Butyric acid was the most potent volatile fatty acid eliciting responses in 41 (95.3 per cent) receptors. Acetic acid activated 33 (76.7 per cent) receptors and propionic acid excited 22 (53.5 per cent) receptors. DL-lactic acid only activated 13 (30.2 per cent) receptors, six of which required concentrations of 200 mM to be activated. Rumen fluids obtained when forestomach motility was impaired, activated 37 (81.1 per cent) of the 43 receptors, whereas rumen fluids obtained when forestomach motility was normal did not activate any receptors. Despite the high levels of lactic acid in rumen fluids which activated epithelial receptors, this acid was not responsible for receptor excitation.

Anorexia during febrile conditions in dwarf goats. The effect of diazepam, flurbiprofen and naloxone.

The most common sign of febrile diseases is anorexia, which develops at a time when adequate caloric and micronutrient availability may be critical. In order to study the relationship of fever and anorexia, feed intake in dwarf goats was studied under conditions of fever and antipyresis. Furthermore, experiments were done to establish whether a feed intake stimulant would override the anorexia during febrile conditions. Infection with Ehrlichia phagocytophila and i.v. injection of Escherichia coli endotoxin (0(111) B4, 0.1 microgram/kg body weight) both resulted in increased rectal temperatures and significant reductions in feed intake. Administration of the antipyretic drug flurbiprofen (1 mg/kg) to febrile animals inhibited the temperature responses, but food intake was still suppressed. Diazepam (0.06 mg/kg), a feed intake stimulant, did not override the anorexia associated with fever. Blocking the febrile response of E. coli LPS-injected goats with flurbiprofen plus diazepam or with flurbiprofen plus naloxone (0.1 mg/kg) did not antagonise their reduced feed intake either. The effects of these drugs and of endotoxin on rumen motility adds an interesting aspect to their activities in the CNS, since the CNS has been shown to regulate various aspects of forestomach motility, which in turn could alter feeding behaviour. Moreover, our findings are consistent with the hypothesis that the suppression of feed intake might depend on the release of interleukin-1.

On the Effect of Xylazine on Forestomach Motility in Sheep

SummaryForestomach motility during sedation induced by xylazine (0.3 mg/kg body weight i. m.) was studied in sheep by means of electromyography.The response of the reticulum to xylazine lasted 80 min; it started with a 45 min period of inactivity followed by a period of decreased activity.The ruminal response was manifested by a 70 min period of decreased activity which was characterized mainly by a decrease in frequency of the primary contractions, so that they became less frequent than the secondary ones. This explains the absence of development of bloat.The differences in response between reticulum and rumen are though to be linked to a difference in alpha2‐adrenergic receptors, in the CNS, which may exist between the motoneurones which innervate the reticulum and those which innervate the rumen.The omasal motor response to xylazine lasted 70 min and was opposite to that of the reticulo‐rumen. Since xylazine excites omasal motility through its action of the CNS, this supports the suggestion that although the motility of the omasum is considered to be mainly intrinsic, a possible CNS inhibitory control on its activity should not be disregarded.ZusammenfassungÜber die Wirkungen von Xylazin auf die Vormagenmotilität beim SchafMittels Elektromyographie wurde die Vormagenmotilität bei Schafen nach Sedierung mit Xylazin (0,3 mg/Kg KGW, i. m.) überprüft. Die Reaktion des Netzmagens auf Xylazin dauerte 80 Minuten; sie begann mit einer Phase der Inaktivität (45 min) und war gefolgt von einer Phase herabgesetzter Motilität.Der Pansen reagierte während 70 min in Form einer herabgesetzten Aktivität, hauptsächlich gekennzeichnet durch eine Abnahme der Frequenz von primären Kontraktionen, die dadurch weniger häufiger als die sekundären waren. Dies erklärt das Ausbleiben von Blähungen.Die unterschiedlichen Reaktionen von Netzmagen und Pansen werden auf Unterschiede der α2‐adrenergischen Rezeptoren im ZNS zurückgeführt, die möglicherweise bestehen zwischen den Motoneuronen, die den Netzmagen bzw. den Pansen innervieren.Die Reaktion des Psalters auf Xylazin dauerte 70 min und war entgegengesetzt derjenigen von Netzmagen und Pansen. Da Xylazin über seine Wirkung auf das ZNS die Psaltermotilität anregt, wird darauf hingewiesen, daß ungeachtet der weitgehenden Intrinsic‐Motilität des Psalters eine mögliche inhibitorische Kontrolle des ZNS in Betracht zu ziehen ist.

Forestomach motility in the camel ( Camelus dromedarius)

1. 1. There is a cyclical pattern of motility in compartments 1 and 2 of the forestomach of the camel which can be categorized into A- and B- contractions. 2. 2. An average motility cycle is composed of 7 A- and 5 B-contractions and lasts 5 min, including a pause of 2.3 min. 3. 3. The glandular sacs within the caudal sac of compartment 1 contract 1.7 sec earlier than the caudal sac. 4. 4. The proximal part of the canal between compartment 2 and 3 contracts 1.2 sec prior to the distal part. 5. 5. Forestomach motility is stimulated by distention of the cranial sac of compartment 1 and inhibited by distention of the tubiform portion of compartment 3.

Effects of calcitonin and CGRP alone or in combination on food intake and forestomach (reticulum) motility in sheep

The effects of intracerebroventricular (ICV) and intravenous (IV) administration of calcitonin and calcitonin gene-related peptide (CGRP) on feeding behavior and reticular motility were investigated in sheep. ICV calcitonin at a dose of 2 to 200 mU/kg reduced, in a dose-related manner, the immediate (0–60 min) food intake. The daily food intake was also significantly ( p<0.05) decreased for doses up to 20 mU/kg, and the frequency of reticular contractions during the first hour of eating was decreased by 27.9%. Calcitonin at the highest IV dose (200 mU/kg) did not affect feeding behavior or reticular motility. In contrast, CGRP given ICV did not affect the first 3 hour period of food intake, while a significant increase (27.8%) in daily food intake was observed at a dose of 20 ng/kg despite immediate inhibitory effects on reticular frequency. No effect on feeding behavior and forestomach motiliy was noticed for a 25 times higher dose IV administered. Furthermore, CGRP given ICV (100 ng/kg) did not antagonize the immediate anorectic effects of calcitonin (200 mU/kg), although it delayed commencement of rumination and partially restored the daily food intake. These results suggest that calcitonin and CGRP play opposite roles in the central control of food intake in sheep, probably by acting on different brain structures, yet have a similar effect on reticular motility.

Central and local actions of opioids upon reticulo-ruminal motility in sheep

The effects of opioids and naloxone on cyclical forestomach motility were determined in anaesthetized and conscious sheep. To assess central or peripheral opioid actions, differential routes of administration were used. Possible dynamic effects along the innervating vagovagal reflex arc were investigated electrophysiologically at the cervical level of the vagus nerve. Further, direct influences on the smooth muscle were evaluated in vitro on isolated longitudinal reticular strips. Additionally, the effects of some spasmogenic agents were studied for comparative purposes. In anaesthetized sheep, opioids depressed in an identical manner both the amplitude of spontaneous cyclical contractions and contractions evoked by electrical stimulation of the distal end of the cut cervical vagus. In conscious sheep, low doses of normorphine and loperamide inhibited frequency and amplitude centrally (20 micrograms/kg and 4 micrograms/kg via carotid artery respectively), whereas locally higher dose levels (200 micrograms/kg and 10 micrograms/kg via coeliac artery respectively) affected only the amplitude of cyclical contractions. Furthermore the opioid peptides Leu-, Met-enkephalin and [D-Ala2-Met5]-enkephalinamide preferentially depressed the amplitude of cyclical motility most efficiently if administrated via the coeliac artery. These results indicate the presence both of a central opioid action depressing frequency and amplitude and of a local opioid action depressing only the amplitude of cyclical reticulo-ruminal motility. Opioids did not alter the resting discharge of afferent tension units and similarly failed to modulate tone of reticular strips in vitro, suggesting that the opioids act locally on the intramural neuronal plexus, possibly by diminishing the output of excitatory transmitter. Whether substance P could play a role as a vagal excitatory transmitter besides the classically implicated acetylcholine has been discussed. The central opioid mechanism is probably not situated within the gastric centres but elsewhere in the brain. Naloxone (greater than or equal to 100 micrograms/kg, jugular vein) stimulated the frequency of cyclical ruminal motility only in well-defined experimental conditions, probably via a central mechanism.

Central and peripheral serotonergic control of forestomach motility in sheep.

Participation of tryptaminergic receptors in the control of forestomach motility was investigated in conscious sheep using strain-gauges and chronically implanted electrodes. Two hours after feeding the sheep, serotonin (5-HT) was infused into the jugular vein (i.v.), or the carotid artery (i.c.), or into the lateral cerebral ventricles (i.c.v.), over a 10-min period. An i.v. dose of 16 micrograms/kg/min abolished the cyclic propagated contractions throughout the forestomach, increased ruminoreticular tone, and induced simultaneous contractions of all the parts of the rumen. A dose of 1.6 micrograms/kg/min i.c. or i.v. 5-HT inhibited phasic contractions. The effects of 5-HT were blocked completely by i.c.v. administration of methysergide (20 micrograms/kg) and imipramine (200 micrograms/kg), and blocked partially by naloxone (25 micrograms/kg), but unaffected by atropine (50 micrograms/kg). The inhibitory effects of i.v. 5-HT were antagonized by methysergide (200 micrograms/kg, i.v.) but unaffected by imipramine (2 mg/kg, i.v.) and atropine (250 micrograms/kg, i.v.). Only the i.v. administration of methysergide blocked the inhibition induced by i.c. infusion (1.6 micrograms/kg/min) of 5-HT. It is suggested that 5-HT exhibits an inhibitory control on forestomach phasic contractions through hypothalamic and bulbar 5-HT receptors, and exerts peripheral excitatory effects on the tone of the rumen wall.

Influence of regimen (roughage vs. concentrates) on satiety and forestomach motility in sheep

The influence of concentrate intake on the subsequent intake of hay was investigated in sheep fitted with a rumen cannula and electrodes on the reticulum wall to measure volatile fatty acids concentration and reticular motility, respectively. In sheep fasted during night time, a previous meal of concentrates given 30, 60 or 120 min before feeding hay, did not modify significantly ( p<0.05) the first hour and the first 3 hour intake of hay despite a large increase in ruminal total volatile fatty acid concentration. However, the daily intake of hay was significantly ( p<0.05) reduced. Similarly, the reticular motility in response to feeding hay was not affected by the previous meals of concentrate. It is concluded that in fasted sheep on a hay ration the short-term satiation of a hay meal is not affected by foregoing intake of concentrates and that the hay intake is not controlled by ruminal volatile fatty acid levels.

Contrôle nerveux de la motricité du réticulo-rumen

This paper reviews the nervous mechanisms involved in the control of motility of the forestomach compartments in ruminants. The first part of the review reports the efferent vagal discharge which consists of several distinct and independent types of urinary activity and passes from the gastric centres to the reticulo-rumen. The patterns of each of these activities are temporally related to the contractions of special parts of the forestomach and occur in a sequence which could produce the coordinated series of movements found in the reticulum and rumen. The orderly sequence of motor events that constitutes the gastric cycle is due to this coordination of efferent vagal outputs arising in the gastric centres. The focal point of the second part of the paper is sensory feedback from the complex stomach to the centres. Four types of receptor have been identified according to their location and stimulus; these are tension receptors and epithelial receptors in the reticulo-rumen and tension receptors and mucosal receptors in the abomasum. Mechanical or chemical stimulation of these distinct receptor types leads to either facilitation or inhibition of reticulo-ruminal motility. The third part of the paper deals with the organization of the medullary gastric centres. The gastric vagal motoneurons are controlled by interneurons organized in two functionally distinct networks. The "rate" network for which the periodicity of its activity depends on the cumulative integrated afferent inputs from central and peripheral sources, determines the rhythm of gastric cycles. It is postulated to drive the "amplitude and form" network which adjusts vagal output to instantaneous gastric afferents, enabling the amplitude of gastric contractions to be adapted to peripheral stimulations. The role of the sensory feedback from the complex stomach in the control of the "frequency" network is discussed, taking into account new experiments on vagal deafferentation and the concept of an oscillating generator that would be more or less permanently inhibited by vagal afferents is reviewed. The respective roles of local regulation mechanisms, mediated in the intramural plexus, and of central mechanisms, in the control of forestomach motility, are briefly discussed.

INHIBITION OF FORESTOMACH MOTILITY BY SHORT-CHAIN VOLATILE FATTY ACIDS IN SHEEP

Ruminal infusions of volatile fatty acids (VFAs) abolished intrinsic forestomach contractions (vagotomized sheep) and secondary ruminal and reticular contractions at similar concentrations. Lower VFA concentrations abolished primary ruminal contractions. VFA mixtures were inhibitory by summation of individual VFA effects. Inhibition may involve direct effects on the forestomach musculature or myenteric plexus. Key words: Sheep, forestomach motility, volatile fatty acids

MODULATION OF RETICULO-RUMINAL MOTILITY IN GOATS AND SHEEP BY OPIOID MECHANISMS

Normorphine and naloxone were administered via selective routes in sheep and goats. The results with normorphine indicate the presence of both (1) a central action depressing frequency and amplitude and, (2) a peripheral action — probably on the intramural plexus — depressing only the amplitude of the cyclical reticulo-ruminal contractions. Key words: Sheep, goat, normorphine, naloxone, forestomach motility

FORESTOMACH EPITHELIAL RECEPTOR ACTIVATION BY GRAIN OVERLOAD RUMEN FLUIDS

Rumen fluids, obtained during the loss of forestomach motility in sheep experiencing ruminal lactic-acidosis, activated reticulo-ruminal epithelial receptors when applied to the receptive fields of these receptors. Rumen fluids which contained the highest levels of undissociated volatile fatty acids (VFAs) were the most effective. Since the levels of undissociated VFAs in effective rumen fluids were, in some cases, lower than the determined VFA thresholds of the receptors, receptor activation in these instances may have been facilitated by the levels of free lactic acid within these samples. Key words: Grain overload, epithelial receptors, ruminal stasis

Opioid control of the ruminant stomach motility: Functional importance of μ, κ and δ receptors

In sheep, the subcutaneous (SC) or intracerebroventricular (ICV) administration of the μ-type opioid agonists, fentanyl and morphine, evokes a blockade of the cyclic contractions of the reticulum. A similar inhibition of forestomach motility was recorded following the administration of the two enkephalin analogs, DAla 2Met 5enkephalinamide (DAMA) and DAla 2DLeu 5enkephalin (DADLE) which are mixed μ - σ opioid agonists. In contrast, the reticular contractions were enhanced by the SC or ICV administration of the κ type agonist, ethylketazocine (EKC) and U - 50 488 H. The proximal duodenum motor activity was transiently increased resulting in the occurrence of a phase III-like activity by these opioid agonists, regardless of the subtypes. The effects of the opioid agonists on reticular motility were prevented by the injection of naloxone but not by the quaternary parent compound methylnaloxone which does not cross the blood-brain barrier. The duodenal motor effects elicited by the opioid agonists were antagonized by both naloxone and methylnaloxone. The results suggest that the inhibition of the ruminant stomach motility is centrally mediated by μ - δ type opioid agonists and are consistent with opposite effects from κ type opioid agonists. The stimulatory effect of peptide and non-peptide opioid agonists on the duodenum may result in part from direct opioid receptor-mediated actions on smooth muscle.