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N Clerc

Publications and source records attributed to N Clerc.

33 records · Page 2Linked to original sources
PubMed1997

Ultrastructural relationships of spinal primary afferent fibres with neuronal and non-neuronal cells in the myenteric plexus of the cat oesophago-gastric junction.

Spinal primary afferent fibres innervating the myenteric area in the oesophago-gastric junction of the cat were selectively labelled by anterogradely transported cholera toxin B subunit-horseradish peroxidase conjugate injected into thoracic dorsal root ganglia. The ultrastructure of these labelled primary afferent fibres was studied in order to determine whether they display close relationships with specific cell types in the myenteric plexus. Horseradish peroxidase was revealed with tetramethylbenzidine stabilized with ammonium heptamolybdate or with the tetramethylbenzidine/tungstate reaction in order to visualize the cytoplasmic organelles and the axolemma, respectively. The labelled primary afferent fibres were unmyelinated. Two kinds of profiles of labelled fibres containing vesicles and mitochondrial accumulations were found: (i) fibres running in myenteric connectives in isolated nerve bundles, and (ii) fibres within the myenteric ganglia. The first kind had small areas of axolemma with no glial cell covering, whereas the second kind had little or no glial cell covering (termed naked primary afferent fibres). In addition, labelled fibres containing few vesicles and mitochondria and running in nerve bundles surrounded by perineurium were numerous. Within the myenteric ganglia, naked primary afferent fibres contacted myenteric neurons. The contacts were mainly axosomatic. No synaptic specializations were distinguished. In the interganglionic area, some labelled fibres terminated close to blood vessels. The intraganglionic naked primary afferent fibres are suggested to be mechanoreceptors. Their exposed axolemma might allow both mechanotransduction and release of neurotransmitters which could act on myenteric neurons. Because they are protected by their glial cell sheath and by bundles of collagen fibrils, interganglionic primary afferent fibres are likely to be less exposed to deformation.

Afferent Pathways↗
PubMed1996

Immunochemical study of galanin in the cat digestive tract and autonomic ganglia.

The presence of galanin was examined in the cat gut and related autonomic nervous structures using radioimmunoassay (RIA) and high performance liquid chromatography (HPLC). In the gut wall, the concentration of galanin-like immunoreactivity (GAL-Lt) was assayed separately in the muscular layers with the nervous plexuses and in the mucosa and ranged from 0.35 to 0.55 pmol/g wet tissue. In the autonomic nervous structures, GAL-L1 concentrations ranged from 0.22 (thoracic spinal ganglia) to 0.81 (inferior mesenteric ganglion) pmol/g wet tissue. The presence of galanin was checked by HPLC in the antrum, intestine, and colon. HPLC of extractable material revealed a major peak coeluting with the synthetic porcine peptide and minor earlier peaks representing likely different molecular forms of galanin. Our study strengthens the notion that galanin acts in nervous control of the cat gut functions.

Animals↗
PubMed1994

Morphological relationships of choleragenoid horseradish peroxidase-labeled spinal primary afferents with myenteric ganglia and mucosal associated lymphoid tissue in the cat esophagogastric junction.

The goal of the present study was to gain insight into the environmental factors influencing the activity of primary spinal afferent fibers in the different layers of the esophagogastric junction of the cat and, thus, to analyze the relationships of these afferents with various cellular components. Spinal primary afferent fibers were selectively labeled by anterogradely transported choleragenoid horseradish peroxidase conjugate (B-HRP). B-HRP was injected into the thoracic dorsal root ganglion at the T8-T13 levels. 6-Hydroxydopamine-induced sympathectomy was performed prior to B-HRP injection in order to prevent otherwise unavoidable labeling of sympathetic fibers in the gut wall. Numerous labeled fibers ran between, around, and within the myenteric ganglia. Others crossed the muscle layers directly and entered the mucosa, where some ran near granulocytes and around or through solitary lymphoid follicles. Labeled fibers were observed in the squamous esophageal epithelium but not in the fundic glandular epithelium. The fibers in the myenteric area are probably connected to the muscular tension receptors that have been detected by electrophysiologic techniques. This assumption is based on the observation that only a few fibers appear to terminate in muscle layers and on the fact that the myenteric area is very narrow and subject to powerful forces. Fibers in the myenteric ganglia could be involved in local efferent functions. Fibers in the mucosa could act as nociceptors and might be involved in local immunological responses.

Afferent Pathways↗
PubMed1993

Inhibition of peripheral fast synaptic inputs to celiac ganglion neurons by splanchnic preganglionic fibers in the cat.

Fast nicotinic transmission was studied in vitro in isolated cat celiac ganglion neurons using intracellular recording techniques. Fast synaptic activation was evoked by stimulation (0.1 Hz) of the anterior peripheral rami. A long-lasting inhibition of this response was triggered by repetitive splanchnic stimulation (30-50 Hz) for 10 s. Evidence is given that this inhibition occurs at presynaptic level. Our results indicate that central inputs modulate transmission of fast synaptic peripheral inputs to prevertebral ganglionic neurons. This would be another integrative mechanism in the prevertebral ganglia.

Animals↗
PubMed1988

Patterns of fast synaptic cholinergic activation of neurons in the celiac ganglia of cats.

Fast nicotinic transmission was studied in vitro in neurons of isolated cat celiac ganglia. In the absence of nerve stimulation, neurons could be classified into three types: silent neurons, synaptically activated neurons, and spontaneously discharging neurons. In all three types, fast synaptic activation could be obtained in single neurons by stimulating with a single pulse both the splanchnic nerves or one of the peripheral nerves connected to the ganglia. During repetitive nerve stimulation, a gradual depression of the central and peripheral fast nicotinic activation occurred, which was not affected by phentolamine plus propranolol, domperidone, atropine, or naloxone. Repetitive nerve stimulation was followed by a long lasting discharge of excitatory postsynaptic potentials and action potentials that decreased gradually with time. This discharge, which was probably due to presynaptic or prejunctional facilitation of acetylcholine release from cholinergic terminals, was reduced by the application of phentolamine plus propranolol, domperidone, or atropine and increased with naloxone. The existence of the mechanisms described in this study reflects the complexity of the integrative processes at work in neurons of the cat celiac ganglia that involve fast synaptic cholinergic activation.

Action Potentials↗
PubMed1987

Selective labeling of vagal sensory nerve fibers in the lower esophageal sphincter with anterogradely transported WGA-HRP.

Wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) injected into the nodose ganglion was anterogradely transported into the vagal sensory terminal fibers that were further visualized in the lower esophageal sphincter (LES) of the cat. The distribution pattern of the labeled fibers in the LES wall was investigated. All the labeled fibers came from the serosa and penetrated between the bundles of longitudinal muscle fibers. Then the labeled fibers took two different pathways: they either ran, and probably ended, between the longitudinal and circular muscle layers, or they ran directly from the longitudinal to the circular muscle layer. Between the longitudinal and circular muscle layers, they followed a sinuous pathway. In contrast, when they crossed the circular muscle layer toward the mucosa, they ran perpendicular to the orientation of the muscle fibers. After having entered the mucosa, they became twisted and penetrated deeply into the epithelium. These two populations of vagal sensory labeled fibers might correspond respectively to the muscular and mucosal receptors classically described in previous electrophysiological studies.

Animals↗
PubMed1986

[Met]- and [Leu]enkephalin-like immunoreactive cell bodies and nerve fibres in the coeliac ganglion of the cat.

The occurrence and distribution of methionine- and leucine-enkephalin-like immunoreactivity were investigated in the cat coeliac ganglion using either the indirect immunoperoxidase method or the peroxidase-antiperoxidase technique. Several antisera raised to methionine- and leucine-enkephalin were used. Their specificity was assessed by incubating sections of the coeliac ganglion with increasing dilutions of antisera and with antisera saturated with their respective antigen. The present study was performed both in untreated and in colchicine-treated cats. Immunoreactive methionine- and leucine-enkephalin-like cell bodies were only visualized in colchicine-treated cats. Two types of labeled cells were observed. The first type had a size similar to that of unlabeled principal ganglion cells. These labeled cells were numerous and scattered throughout the ganglion; they probably represented enkephalin-containing ganglion cells. The second type of immunoreactive cells were of a much smaller size. They were always gathered in small clusters of about 5-15 cells and were not numerous; they presumably represented enkephalin-containing small intensely fluorescent cells. Immunoreactive nerve fibres were mainly observed in untreated cats and accessorily in colchicine-treated cats. In untreated animals dense networks of methionine- and leucine-enkephalin-like immunoreactive fibres were found in the coeliac ganglion. These fibres had numerous varicosities which often closely surrounded unlabeled principal ganglion cells. In colchicine-treated cats some immunoreactive fibres surrounded labeled principal ganglion cell bodies. The present results establish for the first time the presence of enkephalin-like immunoreactive principal ganglion cells in a mammalian sympathetic prevertebral ganglion. The presence of enkephalin-containing principal ganglion cells, small intensely fluorescent cells and nerve terminals, supports an important role of enkephalins in the integrative synaptic activities of cat coeliac ganglion cells.

Animals↗
PubMed1983

Afferent innervation of the lower oesophageal sphincter of the cat. An HRP study.

Labeling of afferent neurons by the retrograde axonal transport of horseradish peroxidase (HRP) was performed on anaesthetized cats in order to examine the afferent innervation of the lower oesophageal sphincter (LOS), involving both the vagal and the sympathetic nerves. The labeled cells, whose fibres follow the sympathetic pathways were found in dorsal root ganglia from T1 to L2. Nerve section experiments indicated that the main pathways involved were the splanchnic nerves, as expected from classical data. Additional pathways passing through the sympathetic cardiac branch emerging from the stellate ganglion and the thoracic sympathetic branches were also evidenced. This work corroborated the electrophysiological data showing the richness of the LOS sensory vagal innervation. Nevertheless, in this case the difficulties related to the HRP technique are particularly enhanced since the abdominal sensory vagal fibres can be affected by HRP injections.

Animals↗
PubMed1983

Thoracic esophageal mechanoreceptors connected with fibers following sympathetic pathways.

The existence of splanchnic mechanoreceptors was demonstrated in the esophagus including the lower esophageal sphincter of anesthetized cats. For this purpose, unitary activities were recorded in T9, T10 and T11 spinal ganglia by means of extracellular glass microelectrodes. Two types of receptors were evidenced according to their location: the muscular and the serosal receptors. The muscular mechanoreceptors usually exhibited a weak spontaneous discharge (0.8-18 imp/sec) and adapted slowly to mechanical stimulations (distension, contraction, digital compression). The potent physiological stimulus resulted in distension for the receptors situated in the thoracic esophagus and contraction for the receptors located in the lower esophageal sphincter. The serosal mechanoreceptors were always silent and belonged to the rapidly adapting type. They responded mainly to touching the serous membrane, but strong distension or stretching was sometimes efficient. A comparison with the vagal receptors already described in this region is drawn, and the role of splanchnic mechanoreceptors is discussed.

Action Potentials↗
PubMed1983

Vagal mechanoreceptors located in the lower oesophageal sphincter of the cat.

In anaesthetized cats, sixty-two vagal sensory units with afferent endings in the lower oesophageal sphincter were recorded by means of extracellular glass micro-electrodes implanted in the nodose ganglion. All the receptors had non-medullated fibres, with conduction velocities ranging from 0.8 to 1.2 m/s. From the direct stimulation of the lower oesophageal sphincter, three types of mechanoreceptors were identified. Thirty-one were activated by natural stimuli:tonic contraction of the sphincter and distension elicited by the passage of a bolus. Artificial stimulation effected by digital compression was also effective. These receptors were similar to muscular endings already described in the digestive tract. Their main characteristic, i.e. their slow adaptation, suggests that they act as sensors of sphincter opening and closure. This was corroborated by observations obtained during distension of the cervical or thoracic oesophagus; a maximum decrease occurred in the lower oesophageal sphincter mechanoreceptor discharge when the distension was produced between 9 and 12 cm from the lower oesophageal sphincter. Twenty-nine endings were found in the superficial layers (mucosae). Contrary to the muscular receptors, the mucosal receptors were not affected by normal contractions or distensions of the lower oesophageal sphincter. They were activated only by strong stimuli like digital compression or distension achieved with a balloon. In addition, mucosal stroking was a potent stimulus. Whatever the stimulus used, the mucosal receptors showed rather rapidly adapting discharges. These receptors should be considered to be sensors of bolus consistency. Two mechanoreceptors, located in the serous membrane of the lower oesophageal sphincter, were identified by touching or by stretching. Their discharges showed that they belonged to the rapidly adapting type. A comparison of the three types of receptors found in the lower oesophageal sphincter is made with known digestive endings and their possible role is discussed.

Action Potentials↗
PubMed1983

Histological characteristics of the lower oesophageal sphincter in the cat.

The structure of the lower oesophageal sphincter (LOS) of the cat was investigated in comparison with that of the oesophagus. The following two main results were collected: (1) The muscularis mucosae of the lower oesophageal sphincter is much thicker than at oesophageal level (221 micron as compared with 17.8 micron on average). This thickening is particularly marked at the most prominent foldings of the mucosa. (2) Numerous annulospiral thin elastic fibres were found, in the circular layer of the LOS. These structures will coil spirally around muscular bundles and then wrap themselves around adjacent bundles so that they present an oblique orientation with regard to muscular fibres. Therefore it is concluded that in this species, the LOS is morphologically differentiated from the oesophagus.

Animals↗
PubMed1981

[Demonstration of mucous mechanoreceptors in the lower esophageal sphincter. Comparison with muscle mechanoreceptors].

In anaesthetized cats, vagal unitary discharges originating from the Lower Oesophageal Sphincter (L.O.S.) were recorded in nodose ganglia by means of glass microelectrodes. Numerous mechanoreceptors located both in mucosa and muscular layers were found in L.O.S. The mucus mechanoreceptors (high threshold receptors) were activated by strong compressions and distensions, by rapid passage of liquid through the oesophagus and by striking the mucosa. The muscular mechanoreceptors (low threshold receptors) responded to contraction and distension of L.O.S. Both receptors were connected to nonmyelinated fibres (conduction velocity: 0.9-1.4 m/sec).

Action Potentials↗
PubMedDate not supplied

Afferent innervation of the lower esophageal sphincter of the cat. Pathways and functional characteristics.

The sensory vagal and 'sympathetic' innervation of the lower esophageal sphincter (LES) has been investigated in cats using both electrophysiological and histochemical techniques. Histochemical studies produced evidence that 'sympathetic' afferents run in: (i) the splanchnic nerves; (ii) the sympathetic thoracic nerves; and (iii) the sympathetic cardiac branch. Electrophysiological studies allowed us to describe different kinds of LES receptors: (i) mucosal vagal receptors acting as rapidly adapting mechanoreceptors or as slowly adapting chemoreceptors; (ii) vagal and 'sympathetic' endings located in the muscular layers, adapting slowly and mainly activated by LES contractions; and (iii) vagal and 'sympathetic' endings located in the serous membrane behaving as rapidly adapting receptors sensitive to stretching.

Animals↗
PubMedDate not supplied

Enteropathogens associated with acute diarrhea in hospitalized infants.

Thirty-five infants of low socioeconomic status who were living in urban Santiago were hospitalized for acute diarrhea were prospectively evaluated for the presence of enteropathogens associated with the episode. Some degree of malnutrition was evident in 20 infants (57.1%); 15 of these (75%) were under 6 months of age. Mean duration of the hospital stay was 11.8 days for well-nourished patients and 15.7 days for the malnourished patients. One or more enteropathogens were found in 60% of the cases studied: in 17 cases (48.6%) these were bacteria and in four cases (11.4%) it was rotavirus. Parasites were not detected. In three patients, two different pathogens were demonstrated. Among the bacteria, 12 isolates (34.3%) were enteropathogenic E. coli (EPEC) and two (5.7%) were Shigella. Campylobacter jejuni was also isolated from two different cases (5.7%) and Salmonella from one case (2.9%). The recovery of pathogens was independent of the nutritional status. Mean age of detection of EPEC was 3.2 months among well-nourished infants and 6.2 months among the malnourished (p less than 0.001). Half of the EPEC strains isolated were multiresistant to antibiotics. One of these strains transferred some of its resistance in vitro to E. coli K12. Ampicillin and kanamycin were the antibiotics to which EPEC showed the greatest resistance. The other bacterial pathogens were mostly sensitive to antibiotics. Campylobacter jejuni, together with Shigella, was the second most frequent pathogen isolated during episodes of diarrhea. Campylobacter should be included in the routine study of diarrheal episodes in our setting.

Acute Disease↗