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Biomedical subjects

N Mei

Publications and source records attributed to N Mei.

At least 55 records · Page 3Linked to original sources
PubMed1980

[Role of vagal intestinal glucoreceptors in insulin regulation].

This paper summarizes recent data on the existence of insulin nervous regulation by duodenal glucoreceptors which are connected to non-medullated fibres included in the vagal nerves. These glucoreceptors respond to intestinal perfusion of glucose or other carbohydrates, but other conventional mechanical stimuli are unable to activate them; therefore, they must be considered as true specific glucoreceptors. Their activation produces an immediate increase of insulin which precedes changes in glycemia. From bivagotomy experiments and from experiments which pharmacologically exclude the efferent parasympathetic or sympathetic fibres, it has been shown that this regulation is chiefly mediated by the vagal nerves. On the other hand, it was found that glucoreceptor afferents project on the hypothalamic nuclei (VMH and LHA) like the whole splanchnic and vagal afferents. The physiological importance and the role of insulin nervous regulation are discussed.

Afferent Pathways↗
PubMed1980

[Electrophysiology of the peripheral effect of two analgesics: aspirin and dibencozide].

The peripheral effect of two analgesics (aspirin and dibencozide) was studied on anaesthetized cats. Several types of neurons and stimulations were performed in this work: traction for periodontal mechanoreceptors connected to small-sized trigeminal fibres, distension for the muscular intestinal mechanoreceptors connected to non-myelinated vagal fibres, chemical stimulation by means of phenyldiguanide for the non-myelinated vagal fibres, electrical stimulation of the myelinated and non-myelinated vagal fibres. In all cases, unitary activities were recorded into corresponding ganglia (nodose or gasserian) with extracellular glass microelectrodes. After injection of analgesics, a decrease of control responses were observed till 30 minutes but the maximum occurred between 1 and 5 minutes. This effect concerned the non-myelinated neurones as well as the myelinated ones. It can be explained by a direct action of analgesics on the ending excitability.

Animals↗
PubMed1980

[Assessment of the reflex vagal origin of broncho-constrictor effects of hypercapnia in cats (author's transl)].

Breath-by-breath measurements of pulmonary resistance (RL) were used to study the bronchomotor effects produced by the inhalation of a CO2-enriched gas mixture in anaesthetized, spontaneously breathing cats. A significant increase in RL occurred from the second inhalation of the hypercapnic gas mixture. This bronchoconstrictor effect lasted about 18 seconds, then a marked decrease in RL was observed. The secondary bronchodilatation persisted during the entire hypercapnic test (4 min). After surgical suppression of the sensory vagal component at the level of the nodose ganglion (bilateral sensory vagotomy), the early bronchoconstrictor effect of CO2 disappeared, but the secondary bronchodilatation was unchanged. In other experiments, after procaine block of the nervous conduction in non-myelinated vagal fibers, the bronchomotor effects of CO2 were the same as those observed after sensory vagotomy. In contrast, an electrotonic block of both vagus nerves, which abolished nervous conduction in myelinated fibers, did not suppress the bronchoconstrictor response to hypercapnia. Thus, the early increase in RL, which follows inhalation of a hypercapnic gas mixture, seems to be reflexly mediated by vagal afferents, especially by non-myelinated fibers.

Animals↗
PubMed1980

[Preliminary data on intestinal chemoreceptor responses to amino acids].

Intestinal chemoreceptor responses to amino acids in the small intestine were investigated in anaesthetized cats with a microelectrophysiological technique, i.e. vagal units in the nodose ganglion were recorded by extracellular glass microelectrodes. About 400 neurons were tested by infusing the small intestine with a mixture of several amino acids at 38 degrees C. Fifty neurons, which were generally silent before the first infusion, were activated by amino acid solutions with a short latency of a few seconds. Their discharge frequency was always low (less than 10 Hz). The corresponding fibres were non-medullated (conduction velocity: 0.8-1.4 m/s). These receptors did not respond to osmotic or mechanical stimuli. Moreover, some of them were not activated by glucose infusion and must thus be considered as specific amino acid receptors. The others which responded to both amino acids and glucose infusions were non-specific receptors. The properties of these two types of amino receptors and their roles in the nervous regulations of feeding behaviour, in particular protein satiety, are discussed.

Amino Acids↗
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↗
PubMed1978

[Sensory innervation of the gastro-intestinal junction: new electrophysiological, histological and histochemical data].

The sensory innervation of the small intestine was studied in the cat with electrophysiological, histological and histochemical techniques. Thanks to the histochemical technique (peroxydase method) the exact number and proportion of splanchnic and vagal fibres was determined : the latter being about 9 times more numerous than the former. On the other hand the exact position of the corresponding cells was defined in the nodose and spinal ganglia by means of the previous technique and the microelectrophysiological method (recording of single units into the ganglia with extracellular glass microelectrodes). The splanchnic neurones were found in the T9, T10 and T11 ganglia whereas the vagal ones were chiefly located in the lower half of the nodose ganglia. The histological studies using electronic microscope showed many non-medullated endings, which were often found beneath the epithelium and in the lamina propria of the villi close to the blood vessels. This result is certainly the proof that numerous receptors (mechanoreceptors, chemoreceptors and even thermoreceptors do exist in the small intestine.

Animals↗
PubMed1977

[Visceral, vagal, and splanchnic projections in the region of the ventro-medial nucleus of the hypothalamus in cats].

In anaesthetized cats, evoked or unitary potentials were produced in the hypothalamus by electrical stimulation of splanchnic and vagus nerves. Responses were recorded bilaterally in an area corresponding to the median nucleus. They were greater for the splanchnic stimulation than for the vagal one. The stimulation parameters and the response latencies suggested that the afferent fibres involved belonged chiefly to B and C nerve components. From this preliminary study, it will be possible to analyze the effects of different splanchnic and vagal afferents on the unitary activity of the ventro-median nucleus.

Afferent Pathways↗
PubMed1976

Conduction velocity along the afferent vagal dendrites: a new type of fibre.

1. We systematically calculated the conduction velocity along the peripheral extensions of sensory vagal neurones in cats (the dendrites). In addition, a study of excitability cycle and light microscopic investigation were also conducted on these neurones. 2. The conduction velocity of the three known types of fibres (A, B and C) remains uniform along the dendrites. 3. Another mixed type of fibres exists with a C conduction velocity (mean value 1-5 m/sec) along its distal pathway and a B conduction velocity (mean value 6 m/sec) along its proximal pathway. The change in conduction velocity progressively occurs in the thoraco-cervical portion of the vagus nerve at least 20 mm from the receptor and at least 40 mm from the T cell. 4. The mixed fibres exhibited a C type excitability cycle in their peripheral pathway and a B type excitability cycle in their central pathway. 5. The histological study using the teasing method demonstrated the existence of unmyelinated fibres, in the thoraco-cervical region of the vagus nerve, becoming progressively myelinated from the periphery to the nodose ganglion. These fibres are likely to be the ones showing mixed electrophysiological properties. They represent (approximately) 10% of the vagal nerve population. 6. We propose to call the mixed fibres BC because they present electrophysiological and morphological properties of C fibres in their distal part and properties of B fibres in their proximal part.

Action Potentials↗