PubMed Health⌕ Search

Biomedical subjects

N Mei

Publications and source records attributed to N Mei.

At least 19 recordsLinked to original sources
PubMed1992

Current data and ideas on digestive sensitivity.

Remarkable advances have recently been made in the study of visceral sensitivity. Both electrophysiological and histological data emphasize the richness and the complexity of information elicited in the visceral area including the digestive tract. In addition these afferents are largely involved in physiological mechanisms which are not only restricted to the visceral area. The current knowledge of visceral sensitivity leads us to reconsider the classical ideas and concepts previously accepted in this field and raises questions to help gain a better comprehension of sensory physiology in general.

Animals↗
PubMed1991

Intestinal effects of the products of lipid digestion on gastric electrical activity in the cat. Possible involvement of vagal intestinal receptors sensitive to lipids.

The relationship between the lipid content of the intestinal lumen and gastric motor activity was studied in anesthetized cats. For this purpose the electromyographic activity was recorded in the antrum whereas the small intestine (duodenum and first part of jejunum or ileum) was perfused with various solutions including calcium propionate, tributyrin, sodium caprylate, potassium oleate, mixtures containing linoleic acid, monolein, triolein, mixture of triglycerides, and glycerol. Long-chain lipids and glycerol both induced a decrease in the rate of basal antral activity. This effect was found to depend on the state of lipid hydrolysis (triglycerides, monoglycerides, and fatty acids) and was most marked with monolein, linoleic acid, and glycerol. With the middle-chain lipids used, these effects were only slight; short-chain lipids did not induce any visible changes in gastric activity. All these effects were prevented by cervical bivagotomy. It was concluded that the two types of lipid-sensitive vagal receptors, which we recently showed to exist in the small intestine, trigger an inhibitory enterogastric reflex that contributes to the regulation of gastric emptying.

Animals↗
PubMed1991

Effects of periodontal stimulation on VHM neurones in anesthetized rats.

In anesthetized rats, mechanical stimulations, the direction and intensity of which could be modified, were applied to the superior incisive while single neurone activities were recorded within the VHM region by means of extracellular glass microelectrodes. The great sensitivity of periodontal receptors to the direction and the intensity of the stimulations was demonstrated at this level. This finding, which is reported here in detail for the first time, suggests that the periodontal afferents might be involved in physiological mechanisms including food intake regulation and osteomorphogenesis.

Action Potentials↗
PubMed1990

[Intestinal sensitivity disorders and irritable bowel syndrome].

Long neglected in the past, the study of visceral sensitivity (interoception) has progressed in recent years because of advances in neurobiological techniques. Dealing with the structure or the function of single neurons, these techniques have profoundly increased our knowledge about the sensitive mechanisms in the digestive tract. According to recent data, the visceral sensitivity organs are richer and more complex than imagined previously. Microphysiological techniques have shown that intestinal sensitive terminations are capable of transmitting information concerning visceral activity and physicochemical modifications of intestinal contents directly to the central nervous system. This means that visceral sensitivity intervenes under physiological as well as pathological conditions. This notion is new and of great interest. As progress was being made concerning the morphologic and electrophysiologic aspects and contemporaneous studies were establishing the richness of visceral, and particularly, intestinal, sensitive receptors, basic science research in humans and animals have emphasized the diversity of the implication of the extrinsic nervous system in pain, regulation of digestive motility, homeostasis and alimentary behaviour. Our present knowledge on the nervous and neurohumoral mechanisms has shed new light on the determinisms in digestive tract pathology. This is especially true in the irritable bowel syndrome which can be considered as an extrinsic nervous system derangement. Due to abnormal sensitivity by modification of the threshold values of sensitivity to distension, and/or to stimulation by substances such as cholecystokinin, for example, motor disorders occur. Other factors, such as stress, can be responsible for revelation or exacerbation of neurohumoral disorders.

Colonic Diseases, Functional↗
PubMed1988

[Morphologic and functional peculiarities of the visceral protoneuron reexamined in light of recent data].

The recent works showing the richness and complexity of the sensory innervation of viscera raise various questions which are of general interest for modern physiology. 1 - The primary afferent neurons are much more numerous and heterogeneous than it was usually expected. Moreover, another category of neurones, namely the sensory intrinsic neurons, must be taken in consideration. These neurones end either in the intrinsic plexuses of viscera or in the prevertebral ganglia. 2 - Another major question concerns the mechanisms responsible for the functional diversity of interoceptors including the chemoreceptors. Several hypothesis have been proposed involving the presence of membrane receptors, the release of neurotransmitters by chromaffin cells and the deformation of tissue. In any way, the functional characteristics of interoceptors do not result in morphological differentiation since free endings are mainly found in the visceral area. 3 - Does the functional properties of primary afferent neurons are related to their morphological (diameter of fibres, size of cell bodies) or their biochemical (type of neurotransmitters) characteristics? So far, it is not possible to answer this question. Nevertheless the available data suggest that a such relationship partly exists. 4 - The visceral afferents are largely implicated in various physiological mechanisms involving visceral motility, homeostasis and behaviour. Therefore, their role in pain appear relatively less important than previously expected. Conversely, the nervous mechanisms induced by the interoceptor activation play a major part in that they prepare and potentialize the effects produced by the other mechanisms.

Animals↗
PubMed1987

Laryngeal afferents activated by phenyldiguanide and their response to cold air or helium-oxygen.

In anesthetized cats, sensory neurons in the superior laryngeal nerves (SLN) were identified with respect to their response to (1) phenyldiguanide (PDG) i.v., (2) mechanical stimulation and (3) lowering temperature in an isolated tracheolaryngeal segment. The activity originating from 107 SLN afferent units activated by PDG was recorded using glass microelectrodes advanced in the nodose ganglion. All tested afferent units increased their discharge rate during direct touching of the airway mucosa. None showed flow or pressure related activity during abrupt changes in constant laryngeal flow or transmural pressure in the isolated segment. Fifteen units were inhibited by cold air. Sixty-two units significantly increased their firing rate when the temperature approached 18 degrees C, reached a peak discharge near 15 degrees C, then their activity decreased or stopped. The response to cold air was compared to cold heliox (79% He-21% O2), which enhanced the respiratory heat loss by conduction. The peak firing rate was significantly higher with heliox (+356% compared to +246% with air), the temperature threshold higher (25 degrees C +/- 1.0 degree C) and the temperature range broader (25-11.5 degrees C). Present results show that a large proportion (58%) of afferent SLN fibres activated by PDG are likely non-proprioceptive units, which are stimulated by cooling the inspired gas. Thermosensitive units in the upper airways may act as sensors of the thermal flux through the airway wall more than as detectors of the absolute value of temperature in the airway lumen.

Action Potentials↗
PubMed1986

Osmosensitive vagal receptors in the small intestine of the cat.

In anesthetized cats, the unitary activity of 66 sensory vagal neurones was recorded with extracellular glass microelectrodes implanted in the nodose ganglia. These neurones had non-medullated afferent fibres with conduction velocities between 0.8 and 1.2 m/s, as do most of the intestinal vagal fibres, and were silent or fired at low frequencies before any simulation. They were activated by perfusion of the small intestine (duodenum and first part of jejunum) with tap water and various solutions (glucose, NaCl and mannitol, in particular) having osmotic pressures ranged between 4 and 1100 mOsm. In general, hypotonic solutions and tap water induced the more marked responses, but differences were observed according to the solution used. Most of these neurones were also excited by other forms of stimulation including stroking of the mucosa and perfusion with warm (39-55 degrees C) and acid (HCl at pH 1) solutions. Therefore they must be considered to be polymodal receptors sensitive to osmotic pressure. The short latency of responses elicited by osmotic stimulations, the marked sensitivity to mucosal stroking and the disappearance of nervous activity after local anesthesia indicate that these receptors are located close to the epithelium. The role of these osmosensitive endings is discussed. Analysis of their general characteristics suggests that they may be involved in the inhibitory entero-gastric reflex modulating gastric emptying.

Action Potentials↗
PubMed1986

Further data on the inhibitory enterogastric reflex triggered by intestinal osmotic changes in cats.

The relationship between osmotic pressure in the intestinal lumen and gastric motor activity was studied in anesthetized cats. For this purpose the EMG was recorded in the antrum while the small intestine (duodenum and the first part of jejunum) was perfused with various solutions: tap water (5 mOsm), NaCl, mannitol and glucose having an osmotic pressure of 70, 138, 275, 550 or 1100 mOsm. Hypotonic and hypertonic solutions both induced a decrease in the gastric activity, i.e. an increase in period of electrical control activity. This effect was found to depend both on the osmolarity value (the osmotic pressures furthest removed from the isotonic value produced the greatest effect) and on the substance used (glucose, mannitol and NaCl, in decreasing order of efficiency). The isotonic solution of glucose and, to a lesser extent, of mannitol was also active, unlike the isotonic solution of NaCl. All these gastric changes were prevented by cervical bivagotomy. It was concluded that the vagal osmosensitive receptors located in the small intestine trigger this inhibitory enterogastric reflex which probably constitutes an important part in the regulation of gastric emptying.

Action Potentials↗
PubMed1986

[Role of the autonomous nervous system in the regulation of the transit, absorption and storage of nutriments].

The possible role of the autonomic nervous system (ANS) in nutrition must be reevaluated in view of recent experimental data. The ANS plays a major part in both initiating and maintaining peristalsis and in coordinating gastrointestinal motility. Intestinal absorption involves extra-epithelial mechanisms such as motility and vasomotricity of the digestive tract. In addition, the ANS (sympathetic fibres) might act directly on enterocytes, or indirectly via the intestinal plexuses through a glucose-dependent mechanism. The control of exocrine and endocrine secretions depends partly on the ANS. In particular the mucous mechanoreceptors, chemoreceptors and thermoreceptors located in the intestinal area supply the sensory information needed in that kind of regulation. The efferent fibres of the ANS intervene in the control of storage of carbohydrates in the liver and of lipids in brown adipose tissue. On the other hand, gastrointestinal afferents might be implicated in this mechanism through the hypothalamic ventro-median nucleus. Finally, these data are consistent with a modern conception suggesting that the ANS is largely involved in the regulation of visceral motility, homeostasis and alimentary behaviour.

Adipose Tissue, Brown↗
PubMed1979

[Vagal thermoreceptors in the gastro-intestinal area. Their role in the regulation of the digestive motility (author's transl)].

In anaesthetized cats, sensory vagal units were recorded in the nodose ganglion by means of extracellular glass microelectrodes. In the antrum and the duodenum we have found receptors tonically activated by warm (38-51 degrees C with an optimum at 46-49 degrees C) or cold (36-10 degrees C with an optimum at 12-10 degrees C) solutions. These receptors did not respond to mechanical stimuli (compression and distension of the viscera) and to chemical ones (perfusion with glucose and acid solutions). Thus they did not belong to polymodal type, but they must be considered as true thermoreceptors, specifically sensitive to warm or cold stimulations. The gastro-duodenal thermoreceptors were connected to non-medullated vagal fibres (conduction velocity: 0.8-1.4 m/s). On the other hand, the role of the gastro-duodenal vagal thermoreceptors in the regulation of the digestive motility was studied. By using several electromyographic recordings, it was possible to show that the cold and warm stimulations of the duodenum which elicited thermoreceptor responses, induced an inhibition of the electrical activity of the antrum. The changes persisted after bisplanchnectomy, but disappeared completely after bivagotomy. From these facts it was concluded that the vagal thermoreceptors were involved in the nervous regulations of the gastro-duodenal motility.

Animals↗
PubMed1979

Assessment of the pulmonary origin of bronchoconstrictor vagal tone.

1. In anaesthetized spontaneously breathing cats, the sensory component of the vagal nerves was sectioned at the level of nodose ganglion, using a method described previously (Mei, 1966; Mei & Dussardier, 1966).2. The strength of the Hering-Breuer reflex (inhibitory ratio, i.e. T(1)/T(0)) provided a test for effectiveness of section of vagal afferents, particularly respiratory afferents. On the other hand, by studying the cardiac and bronchomotor effects induced by electrical stimulation of the supranodose portion of the vagal nerve, it was possible to test the integrity of the efferent vagal component.3. Unilateral right sensory vagotomy was followed by a 29% reduction in total pulmonary resistance.4. Section of the contralateral sensory vagal component (sensory bivagotomy), produced a weak supplementary effect (total decrease of total pulmonary resistance: 31%).5. No additive bronchomotor effect could be observed after the bilateral section of efferent vagal fibres (total bivagotomy).6. In intact cats, blockade of the two vagal nerves by procaine induced a decrease in pulmonary resistance similar to those produced by the sensory bivagotomy (23%). This bronchodilatator effect was concomitant with a complete disappearance of the C wave of the compound vagal potential.7. Intravenous injection of phenyl diguanide, immediately after the blockade of the C vagal fibres by procaine did not modify bronchomotor tone. This result confirms that the C pulmonary afferents, which are activated by phenyl diguanide, are mainly involved in this mechanism.8. The pulmonary irritant receptors seem to play a minor role. In fact, the I.V. administration of histamine under the same conditions, provides evidence that the corresponding neurones (small sized myelinated fibres) are potent during the procaine application.9. From these results, it appears that bronchoconstrictor vagal tone has an exclusive peripheral origin and that pulmonary endings, in particular those connected with non-medullated fibres, are probably involved in this mechanism.

Action Potentials↗
PubMed1978

Vagal glucoreceptors in the small intestine of the cat.

1. In anaesthetized cats, the unitary activity of seventy-eight sensory vagal neurones was recorded in nodose ganglia by means of extracellular glass microelectrodes. 2. These neurones were stimulated by perfusion of the small intestine (duodenum and first part of jejunum) with glucose or other different carbohydrates at concentrations of 1--20 g/l. (i.e. 55--1100 m-osmole/l.). 3. The neurones were slowly adapting to stimulation and their discharge frequency was always low (1--30 Hz). 4. The activity of these neurones depended on the particular carbohydrate used and on its concentration: the discharge frequency generally increased when the concentration rose. 5. The neurones were of the C type (conduction velocities: 0.8--1.4 m/sec; mean, 1.1 m/sec). 6. In contrast with the known neurones connected to the gastro-intestinal tension receptors, they were not obviously activated by intestinal contractions or distensions. 7. In the same way, the stimuli which produced the response of other known endings, i.e. the mucosal receptors, were not effective; these stimuli included in particular stroking of the mucosa, over-distension of the bowel, intestinal perfusion with alkaline or acid solutions. On the other hand, the use of substances other than glucose (KCl and NaCl of the same osmolarity) showed that the osmotic pressure was not directly related to the receptor activation. 8. Therefore it is proposed to call the endings corresponding to these neurones 'glucoreceptors'. 9. The effect of glycaemia and intestinal motility were also studied. These variables acted presumably by changing the intestinal absorption rate. 10. The functional characteristics of the glucoreceptors (in particular the short latency of their response) strongly suggested that they were located close to the intestinal epithelium. 11. An ultrastructural study was performed in an attempt to identify the histological site of the receptors. Many non-medullated fibres were observed in the villi, especially beneath the epithelial layer. They gave complex branchings with abundant swellings. Some of them, at least, belonged to the vagal sensory component, because they were less numerous after unilateral selective sensory vagotomy. Therefore these complex endings could serve as the vagal glucoreceptors. 12. The roles of vagal intestinal glucoreceptors are discussed. Their functional characteristics as well as the clinical and experimental data suggest that they may be involved in the regulation of different types of alimentary behaviour (hunger, thirst, alliesthesia) and energy balance.

Action Potentials↗