Myogenic peristalsis in isolated preparations of chicken oesophagus

Neuromuscular mechanisms of primary peristalsis

Primary peristalsis of the esophagus is initiated by the act of swallowing. Control of the orderly contraction must take into account coordination of the activity in the esophageal body with the sphincters at either end, integration of activity between the striated and smooth muscle portions of the esophagus, and the central and peripheral neural and muscular control mechanisms present. Peristalsis in the striated section is directed by sequential vagal excitation arising in a brainstem "Central Program Generator." Peristalsis in the smooth muscle section involves the interaction of central and peripheral neural mechanisms and probably the interaction between these neural mechanisms and smooth muscle properties. Coordination of activity between the striated and smooth muscle portions has similar multifaceted neural and mechanical components. In the smooth muscle, 2 main neural mechanisms, a cholinergic excitatory one and a nonadrenergic, noncholinergic (NANC) inhibitory one interact together and with central and local influences to regulate the amplitude, velocity, and direction of propagation of the peristaltic contraction.

Distribution of alpha-vascular smooth muscle actin in the smooth muscle cells of the gastrointestinal tract of the chicken

Immunoreactivity specific for alpha-vascular smooth muscle actin (ASMA) was examined in the enteric smooth muscle cells along the entire length of the gastrointestinal tract of the chicken. Specificity for gamma-smooth muscle actin (GSMA) and desmin was also examined. All smooth muscle layers, i.e. the muscularis mucosae, and the circular and longitudinal muscle layers, showed immunoreactivity specific for GSMA and desmin throughout the gastrointestinal tract whereas immunoreactivity for ASMA differed between regions and muscle layers. In the oesophagus and crop, immunoreactivity for ASMA was observed in the muscularis mucosae and the inner and outer muscle layers, together with staining for GSMA and desmin. In the proventriculus, immunoreactivity for ASMA was observed in all smooth muscle cells in the inner layer of the muscularis mucosae and the longitudinal muscle layer. In the outer layer of the muscularis mucosae, immunoreactivity for ASMA on smooth muscle cells was observed on the luminal side and decreased in the serosal direction. In the intermediate muscles, immunoreactivity for ASMA was observed in the luminal portion, the intensity of staining decreasing gradually in the serosal direction. In contrast to the intermediate muscles, the latter muscles were negative for ASMA. In the pyloric region, the outer part was weakly immunopositive, while the inner part was intensely positive. In the small and large intestines, the muscularis mucosae and the longitudinal muscle layer were positive for ASMA. The outer part of the circular muscle layer was immunonegative for ASMA whereas the inner part was positive. The complex structure and contractile functions of each organ and muscle layers may be related to the difference patterns of expression of ASMA molecules in the smooth muscle cells.

The role of the L-arginine-nitric oxide pathway in relaxation of the opossum lower oesophageal sphincter

1. The role of the L-arginine-nitric oxide pathway in lower oesophageal sphincter (LOS) relaxation and oesophageal peristalsis was investigated. 2. Twenty four adult opossums were anaesthetized and the right vagus nerve was isolated in the neck and sectioned. Electrical stimulation, applied to the peripheral end of the nerve, resulted in a frequency-dependent relaxation of the LOS, and peristaltic and non-peristaltic contractions in the oesophageal body. 3. N omega-nitro-L-arginine (L-NNA, 10(-8)-10(-5) mol kg-1), an inhibitor of the L-arginine-nitric oxide pathway, inhibited LOS relaxation in a dose-dependent manner, but did not affect resting LOS pressure. At the highest dose of L-NNA no relaxation of the LOS was elicited in response to vagal stimulation. The effect of L-NNA, (10(-5) mol kg-1) was fully reversed by infusion of 10(-4) mol kg-1 L-arginine. Peristaltic velocity and amplitude of contractions in the oesophageal body were unaffected by L-NNA. 4. Infusion of sodium nitroprusside reduced LOS pressure to zero, and the drug was equally potent in control animals (-log ED50:8.1 +/- 0.2 mol kg-1) and in animals pretreated with L-NNA (-log ED50:8.2 +/- 0.3 mol kg-1). This suggests that the effect of L-NNA was not directly on guanylate cyclase. 5. A significant elevation of blood pressure was recorded after administration of L-NNA (10(-5) mol kg-1). 6. It is suggested that the L-arginine-nitric oxide pathway plays an important functional role for relaxation of the LOS, but not for oesophageal peristalsis. Whether the active substance is nitric oxide or a related nitroso-compound remains to be settled.

The avian oesophageal motor function and its nervous control: some physiological, pharmacological and comparative aspects

1. This paper deals with the avian oesophageal motor function and it attempts to draw some comparative aspects between neural regulation of the avian and mammalian oesophagus. 2. Different from the mammalian oesophagus, the avian oesophagus, presents at rest electrical activity associated to spontaneous contractions. 3. Swallowing elicits peristaltic contraction, characterized by an inhibitory and an excitatory component. 4. Non-adrenergic, non-cholinergic neurons are responsible for the inhibitory component. 5. Contrarily to what observed in mammals, where the peripheral mechanism are important for the peristaltic sequence, the primary peristaltism of birds seems to be entirely mediated by extrinsic nervous system.

Intrinsic reflexes underlying peristalsis in the small intestine of the domestic fowl

Peristalsis in the chicken small intestine was studied using either a modified Trendelenburg method or a technique in which changes in circular muscle activity were recorded in response to application of a localized radial distension. A localized radial distension had no effect on either the resting tension or the spontaneous activity of the circular muscle on the oral side of distension. On the aboral side of the distension a transient contraction was recorded in the ileum and jejunum after a mean delay of 2.74 s at 37 degrees C. In about a third of the preparations a tonic contraction was also present which persisted for as long as distension was maintained. The transient contraction was blocked by hyoscine (0.6-2.3 microM) and hexamethonium (275 microM); whereas the tonic contraction persisted in the presence of hyoscine. Both types of contraction were blocked by tetrodotoxin (0.31 microM). No such responses were recorded in the duodenum. The descending excitatory reflex responses were followed in all preparations by a fall in the amplitude and frequency of spontaneous contractions and in a few preparations by a concomitant fall in the tone of the circular muscle lasting for up to 3 min. This inhibitory component of the descending reflex was not blocked by guanethidine (3-10 microM). The transient contraction, which originated most frequently at the site of distension, always propagated aborally at a mean speed of 14.2 mm s-1. Surgical interruption of the longitudinal muscle and myenteric plexus effectively blocked the transmission of the excitatory and inhibitory components of the descending reflex past the site of the lesion. In the modified Trendelenburg apparatus raising the intraluminal pressure elicited peristalsis in the isolated ileum. Peristaltic contractions never started at the most oral end of the preparation but appeared instead at any other point on the ileum. This resulted in several contractions contributing to each emptying cycle. Peristalsis was blocked by tetrodotoxin (0.31 microM). These results are discussed in the terms of the organization of the descending reflex. It is suggested that within the enteric nervous system of the ileum and jejunum of the chicken, there are cholinergic and non-cholinergic excitatory neurones and non-adrenergic inhibitory neurones. The results of this study demonstrate that neurogenic peristalsis in the avian small intestine does not conform to the 'law of the intestine' as originally postulated by Bayliss & Starling (1899).

Actions of putative transmitters in the chicken vagus nerve/oesophagus and Remak nerve/rectum preparations

1 Histamine (0.02-0.1 mug/ml) contracted the chicken rectum preparation. This effect was antagonized by mepyramine (0.01 mug/ml) but not by hyoscine (0.02 mug/ml).2 5-Hydroxytryptamine (0.05-0.25 mug/ml) relaxed the rectum preparation and at higher concentration produced a biphasic response. These responses were not antagonized by methysergide (0.01 mug/ml), and the relaxation was not antagonized by tetrodotoxin (0.1 mug/ml) or a combination of propranolol (0.05 mug/ml) and phentolamine (0.1 mug/ml).3 Neither mepyramine (0.1 mug/ml) nor methysergide (0.01 mug/ml) antagonized the contractions produced by nerve stimulation in vagus nerve/oesophagus and Remak nerve/rectum preparations.4 5-Hydroxytryptamine (2 mug/ml) in the presence of methysergide (0.01 mug/ml), inhibited the contractions produced by nerve stimulation in Remak nerve/rectum and vagus nerve/oesophagus preparations.5 Adenosine, adenosine 5'-phosphate (AMP), adenosine 5'-diphosphate (ADP) and adenosine 5'-triphosphate (ATP), in order of decreasing potency, produced slow contractions in most oesophagus preparations. The action of ATP in this preparation was antagonized by tetrodotoxin (0.1 mug/ml), hyoscine (0.1 mug/ml) and strychnine (5 mug/ml).6 Desensitization of the vagus nerve/oesophagus preparation to ATP did not produce any antagonism of the contractions to nerve stimulation.7 Adenosine and AMP produced relaxations and ADP and ATP contractions in the rectum preparation. ATP was about 100 times as potent as ADP in producing fast contractions which were not antagonized by tetrodotoxin, hyoscine or strychnine.8 Desensitization of the Remak nerve/rectum preparation to ATP resulted in the contractions to nerve stimulation and acetylcholine being inhibited to the same extent.9 Prostaglandin E(2) produced slow contractions in the oesophagus and rectum preparations which were not antagonized by tetrodotoxin (0.1 mug/ml). Polyphloretin phosphate (10 mug/ml) antagonized spontaneous movements and responses to prostaglandin E(2) in the rectum but not the oesophagus.10 Neither polyphloretin phosphate (60 mug/ml) nor indomethacin (20-100 mug/ml) antagonized the contractions produced by nerve stimulation in vagus nerve/oesophagus (with hyoscine in the bathing solution) and Remak nerve/rectum preparations.11 These experiments seem to exclude histamine, 5-hydroxytryptamine, adenosine and its nucleotides and prostaglandin E(2) as possible motor transmitters in synapses and neuromuscular junctions in the chicken vagus nerve/oesophagus and Remak nerve/rectum preparations.