Influence of natural organic matter on the transformation of metal and metal oxide nanoparticles and their ecotoxic potency in vitro

Increased use and production of engineered nanoparticles (NPs) lead to an elevated risk of their diffuse dispersion into the aquatic environment and increased concern on unknown effects induced by their release into the aquatic ecosystem. An improved understanding of the environmental transformation processes of NPs of various surface characteristics is hence imperative for risk assessment and management. This study presents results on effects of natural organic matter (NOM) on the environmental transformation and dissolution of metal and metal oxide NPs of different surface and solubility properties in synthetic freshwater (FW) with and without NOM. Adsorption of NOM was evident on most of the studied NPs, except Sb and Sb₂O₃, which resulted in the formation of negatively charged colloids of higher stability and smaller size distribution compared with the same NPs in FW only. The dissolution rate of the NPs in the presence of NOM correlated with the strength of interactions between the carboxylate group of NOM and the particle surface, and resulted in either no (Mn, Sb, ZnO NPs), increased (Co, Sn NPs) and decreased (Ni, NiO, Sb₂O₃, Y₂O₃ NPs) levels of dissolution. One type of metal NP from each group (Mn, Ni, Sn) were investigated to assess whether observed differences in adsorption of NOM and dissolution would influence their ecotoxic potency. The results showed Mn, Ni, and Sn NPs to generate intracellular reactive oxygen species (ROS) in a time and dose-dependent manner. The extent of ROS generation in FW was similar for both Mn and Ni NPs but higher for Sn NPs. These findings are possibly related to interactions and infiltration of the NPs with the cells, which lead to redox imbalances which could induce oxidative stress and cell damage. At the same time, the presence of NOM generally reduced the intracellular ROS generation by 20-40% for the investigated NPs and also reduced cytotoxicity of Sn NPs, which can be attributed to the stronger interaction of carboxylate groups of NOM with the surface of the NPs.

Differentiating between micronucleus dose-responses induced by whole cigarette smoke solutions with Benchmark Dose potency ranking

Dose-response modeling of in vitro micronucleus test (IVMNT) data was evaluated to determine if the approach has value in discriminating among different tobacco products. Micronucleus responses were generated in L5178Y/Tk+/- mouse lymphoma cells and TK6 human lymphoblastoid cells from a series of whole smoke solutions (WSSs) expected to have different levels of genotoxicity based on differences in their machine-generated smoke constituents. Eight WSSs were prepared by machine smoking different numbers (20 or 60) of two commercial cigarettes (Marlboro Silver or Red) under International Standardization Organization (ISO) or Health Canada Intense (HCI) smoking machine regimens and tested in the two cell lines with and without rat liver S9 activation. The S9-mediated IVMNT dose-response data from the WSSs were evaluated with PROAST software and Benchmark Doses (BMDs) and their upper and lower confidence intervals (CIs) were generated. IVMNT data differed based on the number and type of cigarettes smoked and smoking machine regimen. The IVMNT responses produced in mouse lymphoma cells generally were greater than in TK6 cells, but the ability of the two cell types to differentiate between WSSs was similar. The results indicate that BMD potency ranking was useful for differentiating between IVMNT responses.

Corrosion and transformation of solution combustion synthesized Co, Ni and CoNi nanoparticles in synthetic freshwater with and without natural organic matter

Pure metallic Co, Ni, and their bimetallic compositions of Co3Ni, CoNi, and CoNi3 nanomaterials were prepared by solution combustion synthesis. Microstructure, phase composition, and crystalline structure of these nanoparticles (NPs) were characterized along with studies of their corrosion and dissolution properties in synthetic freshwater with and without natural organic matter (NOM). The nanomaterials consisted of aggregates of fine NPs (3-30 nm) of almost pure metallic and bimetallic crystal phases with a thin surface oxide covered by a thin carbon shell. The nanomaterials were characterized by BET surface areas ranging from ~ 1 to 8 m2/g for the Ni and Co NPs, to 22.93 m2/g, 14.86 m2/g, and 10.53 m2/g for the Co3Ni, CoNi, CoNi3 NPs, respectively. More Co and Ni were released from the bimetallic NPs compared with the pure metals although their corrosion current densities were lower. In contrast to findings for the pure metal NPs, the presence of NOM increased the release of Co and Ni from the bimetallic NPs in freshwater compared to freshwater only even though its presence reduced the corrosion rate (current density). It was shown that the properties of the bimetallic nanomaterials were influenced by multiple factors such as their composition, including carbon shell, type of surface oxides, and the entropy of mixing.

Inhibition of p53/p21 by TWIST alleviates TNF-α induced nucleus pulposus cell senescence in vitro

OBJECTIVE

This study aims to reveal the TWIST protein expression in the degenerated nucleus pulposus (NP), its effect on the TNF-α treated NP cells, and to explore its specific mechanism of anti-senescence.

PATIENTS AND METHODS

NP tissues from spine fracture patients without intervertebral disc degeneration (IDD) and the IDD patients were collected to detect the TWIST1/2 protein expression by Western blot (WB). NP cells isolated from the healthy tissue was treated with TNF-α to induce senescence, and the TWIST1/2 protein expression was also analyzed. We transfected NP cells with the plasmid coding TWIST to upregulate its expression, which was also cultured in the TNF-α condition. Besides, the TNF-α pretreated NP cells were further stimulated with the recombinant human TWIST1/2 protein. The collagen II and senescent marker β-galactosidase (β-gal) were determined by immunofluorescence (IF); the MMP-13, TIMP-3, IL-10, IL-1β mRNA expression level was detected by quantitative Real Time PCR; the cell proliferation was analyzed by CCK8 assay; the cell cycle was measured by flow cytometry.

RESULTS

TWIST1/2 protein was decreased both in the degenerated NP tissue, and TNF-α treated NP cells. The overexpression of TWIST1/2 could prevent the p53, p21, β-gal, MMP-13, and IL-1β expression, moreover, it protected the collagen II, TIMP-3, and IL-10 expression in the TNF-α treated NP cells. Additionally, TWIST overexpression also promoted cell proliferation by ensuring the process of the cell cycle. Furthermore, the supplement of TWIST protein was functional to reverse these senescent phenotypes caused by TNF-α partly.

CONCLUSIONS

TWIST alleviates the TNF-αinduced NP cells senescence via the inhibition of the p53/p21 pathway.

Influence of Biocorona Formation on the Transformation and Dissolution of Cobalt Nanoparticles under Physiological Conditions

Cobalt (Co) nanoparticles (NPs) are produced in different applications and unintentionally generated at several occupational and traffic settings. Their diffuse dispersion may lead to interactions with humans and aquatic organisms via different exposure routes that include their transformation/dissolution in biological media. This paper has investigated the particle stability and reactivity of Co NPs (dispersed by sonication prior to exposure) interacting with selected individual biomolecules (amino acids, polypeptides, and proteins) in phosphate-buffered saline (PBS). No or minor adsorption of amino acids (glutamine, glutamic acid, lysine, and cysteine) was observed on the Co NPs, independent of the functional group and charge. Instead, phosphate adsorption resulted in the formation of a surface layer (a corona) of Co phosphate. The adsorption of larger biomolecules (polyglutamic acid, polylysine, lysozyme, and mucin) was evident in parallel with the formation of Co phosphate. The dissolution of the Co NPs was rapid as 35-55% of the particle mass was dissolved within the first hour of exposure. The larger biomolecules suppressed the dissolution initially compared to exposure in PBS only, whereas the dissolution was essentially unaffected by the presence of amino acids, with cysteine as an exception. The formation of Co phosphate on the NP surface reduced the protective properties of the surface oxide of the Co NPs, as seen from the increased levels of the released Co when compared with the nonphosphate-containing saline. The results underline the diversity of possible outcomes with respect to surface characteristics and dissolution of Co NPs in biological media and emphasize the importance of surface interactions with phosphate on the NP characteristics and reactivity.

Size-separated particle fractions of stainless steel welding fume particles - A multi-analytical characterization focusing on surface oxide speciation and release of hexavalent chromium

Welding fume of stainless steels is potentially health hazardous. The aim of this study was to investigate the manganese (Mn) and chromium (Cr) speciation of welding fume particles and their extent of metal release relevant for an inhalation scenario, as a function of particle size, welding method (manual metal arc welding, metal arc welding using an active shielding gas), different electrodes (solid wires and flux-cored wires) and shielding gases, and base alloy (austenitic AISI 304L and duplex stainless steel LDX2101). Metal release investigations were performed in phosphate buffered saline (PBS), pH 7.3, 37°, 24h. The particles were characterized by means of microscopic, spectroscopic, and electroanalytical methods. Cr was predominantly released from particles of the welding fume when exposed in PBS [3-96% of the total amount of Cr, of which up to 70% as Cr(VI)], followed by Mn, nickel, and iron. Duplex stainless steel welded with a flux-cored wire generated a welding fume that released most Cr(VI). Nano-sized particles released a significantly higher amount of nickel compared with micron-sized particle fractions. The welding fume did not contain any solitary known chromate compounds, but multi-elemental highly oxidized oxide(s) (iron, Cr, and Mn, possibly bismuth and silicon).

Nanoparticles of WC-Co, WC, Co and Cu of relevance for traffic wear particles - Particle stability and reactivity in synthetic surface water and influence of humic matter

Studded tyres made of tungsten carbide cobalt (WC-Co) are in the Northern countries commonly used during the winter time. Tungsten (W)-containing nano- and micron-sized particles have been detected close to busy roads in several European countries. Other typical traffic wear particles consist of copper (Cu). The aims of this study were to investigate particle stability and transformation/dissolution properties of nanoparticles (NPs) of WC-Co compared with NPs of tungsten carbide (WC), cobalt (Co), and Cu. Their physicochemical characteristics (primarily surface oxide and charge) are compared with their extent of sedimentation and metal release in synthetic surface water (SW) with and without two different model organic molecules, 2,3- and 3,4-dihydroxybenzoic acid (DHBA) mimicking certain sorption sites of humic substances, for time periods up to 22 days. The WC-Co NPs possessed a higher electrochemical and chemical reactivity in SW with and without DHBA molecules as compared with NPs of WC, Co, and Cu. Co was completely released from the WC-Co NPs within a few hours of exposure, although it remained adsorbed/bonded to the particle surface and enabled the adsorption of negatively charged DHBA molecules, in contrast with the WC NPs (no adsorption of DHBA). The DHBA molecules were found to rapidly adsorb on the Co and Cu NPs. The sedimentation of the WC and WC-Co NPs was not influenced by the presence of the 2,3- or 3,4-DHBA molecules. A slight influence (slower sedimentation) was observed for the Co NPs, and a strong influence (slower sedimentation) was observed for the Cu NPs in SW with 2,3-DHBA compared with SW alone. The extent of metal release increased in the order: WC < Cu < Co < WC-Co NPs. All NPs released more than 1 wt-% of their metal total mass. The release from the Cu NPs was most influenced by the presence of DHBA molecules.

Textures in polygonal arrangements of square nanoparticles in nematic liquid crystal matrices

A systematic analysis of defect textures in faceted nanoparticles with polygonal configurations embedded in a nematic matrix is performed using the Landau-de Gennes model, homeotropic strong anchoring in a square domain with uniform alignment in the outer boundaries. Defect and textures are analyzed as functions of temperature T, polygon size R, and polygon number N. For nematic nanocomposites, the texture satisfies a defect charge balance equation between bulk and surface (particle corner) charges. Upon decreasing the temperature, the central bulk defects split and together with other -1/2 bulk defects are absorbed by the nanoparticle's corners. Increasing the lattice size decreases confinement and eliminates bulk defects. Increasing the polygon number increases the central defect charge at high temperature and the number of surface defects at lower temperatures. The excess energy per particle is lower in even than in odd polygons, and it is minimized for a square particle arrangement. These discrete modeling results show for first time that, even under strong anchoring, defects are attached to particles as corner defects, leaving behind a low energy homogeneous orientation field that favors nanoparticle ordering in nematic matrices. These new insights are consistent with recent thermodynamic approaches to nematic nanocomposites that predict the existence of novel nematic/crystal phases and can be used to design nanocomposites with orientational and positional order.

Mutagenicity of comfrey (Symphytum Officinale) in rat liver

Comfrey is a rat liver toxin and carcinogen that has been used as a vegetable and herbal remedy by humans. In order to evaluate the mechanisms underlying its carcinogenicity, we examined the mutagenicity of comfrey in the transgenic Big Blue rat model. Our results indicate that comfrey is mutagenic in rat liver and the types of mutations induced by comfrey suggest that its tumorigenicity results from the genotoxicity of pyrrolizidine alkaloids in the plant.

Intranasal absorption of rizatriptan--in vivo pharmacokinetics and bioavailability study in humans

Rizatriptan nasal spray was developed to achieve fast a high effectiveness and to overcome limitations associated with oral formulation. The objective of this study was to investigate the pharmacokinetics and tolerability of a rizatriptan nasal spray compared with an oral formulation in a two treatments, two periods, randomized crossover design. At each phase, each subject received 5 mg rizatriptan as a nasal spray or an oral tablet. Plasma concentrations of rizatriptan were determined by HPLC. Rizatriptan was absorbed more rapidly following nasal spray with detectable plasma concentrations 5 min after dosing. There was no statistically significant difference for AUC or Cmax values between the nasal spray and the oral tablet. The relative bioavailability of nasal formulation to oral formulation was 96%+/-16%. All the formulations were well tolerated and adverse events were generally of short duration and of mild intensity. Thus, rizatriptan nasal spray offers more rapidly absorption compared to the oral route, which may be particularly beneficial to those patients who have gastrointestinal disturbances during their migraine attack or who have difficulty in swallowing a tablet.

Effects of alverine citrate on cat intestinal mechanoreceptor responses to chemical and mechanical stimuli

BACKGROUND

Alverine citrate is commonly used in the treatment of painful affections of the colon.

AIM

To determine whether alverine citrate acts on the vagal sensory endings.

METHODS

Unitary recordings were performed at the level of the vagal fibres in the nodose ganglion of anaesthetized cats using extracellular glass microelectrodes, and the patterns of response to chemical and mechanical stimuli applied to identified vagal intestinal mechanoreceptors were studied.

RESULTS

The intestinal mechanoreceptors located at the endings of type C vagal fibres responded mainly to mechanical stimuli (distension and contraction), but also responded to chemical substances (cholecystokinin and substance P). The most conspicuous effect of alverine (2 mg/kg) was that it significantly inhibited the pattern of vagal activity produced in response to either cholecystokinin (5-10 microg/kg), substance P (5-10 microg/kg) or phenylbiguanide (5-10 microg/kg), a 5-HT3 receptor agonist. On the other hand, the unitary vagal response to the mechanical distension was slightly enhanced by alverine, as was any spontaneous activity present.

CONCLUSIONS

Based on the present data, alverine citrate can be said to decrease the sensitivity of the intestinal mechanoreceptors, which is consistent with its previously established anti-spasmodic effects.

Influence of donor age on the cytotoxicity and mutagenicity of ethylnitrosourea in cultured human T-lymphocytes

The effects of age on the cytotoxicity and mutagenicity of N-ethyl-N-nitrosourea (ENU) in human peripheral blood T-lymphocytes were investigated using colony-forming assay in vitro. ENU was shown to induce a dose-dependent increase in cell killing and in mutation frequencies (MF). No significant correlation between age and ENU-induced 6-thioguanine-resistant (TGr) MF at the hypoxanthine phosphoribosyl transferase (HPRT) locus of the X-chromosome was found after treatment with the same concentration of ENU (1 mM or 2 mM). There were also no significant differences among different donor age groups and the sensitivity parameters for exposure to ENU. As X-rays, the cytotoxic and mutagenic effects of ENU in cultured human T-lymphocytes appear not to be associated with age. These results suggest that the repair of mutagen-induced DNA lesions does not decline with age. Such knowledge has implications for risk assessment and protection against environmental mutagens.

Individual variation and age dependency in the radiosensitivity of peripheral blood T-lymphocytes from normal donors

To investigate individual variation and age dependency in normal cell radiosensitivity, we measured the in vitro radiosensitivity of cultured peripheral blood T-lymphocytes derived from 56 healthy male blood donors. Dose-survival tests using colony formation assay were done with exponential growing T-cells (day 3, PHA-stimulated cells). 6-Thioguanine (6-TG)-resistant mutation assays at the hypoxanthine phosphoribosyl transferase (HPRT) locus were done with G0 phase T-cells (day 0, unstimulated cells). The mean inactivation dose (MID) computed by integration of the fitted survival curves was 1.25 +/- 0.23 Gy (mean +/- SD). The X-ray dose required to kill 90% of the cells (D10) was 2.81 +/- 0.51 Gy. The MID ranged from 0.82 to 1.86 Gy with a coefficient of variation (CV) of 18%. The induced mutation frequencies (MF) per 10(6) cells at 2 Gy of X-rays ranged from 9.10 to 54.80 with a mean +/- SD value of 24.63 +/- 12.51 and a CV of 51%. It appears that the radiosensitivity of cell killing and mutagenicity varies among individuals. Although the spontaneous MF at the HPRT locus increases with age, the induced MF after exposure to 2 or 4 Gy of X-rays was not associated with age. Moreover, there were no significant correlations between age and MID values or the other dose-survival parameters. The findings indicate there is significant inter-individual variation in cellular radiosensitivity, but that in human T-lymphocytes aging does not affect the cytotoxic and mutagenic effects of X-irradiation.

Electrophysiologic evidence showing the existence of sensory receptors within the alveolar bone in anesthetized cats

Single-nerve activities were recorded in the gasserian ganglia of anesthetized cats by glass extracellular micro-electrodes to determine whether sensory endings exist within the alveolar bone. Trigeminal cells responded to mechanical and/or thermal stimulation applied to the maxillary bone. Some were activated by specific kinds of fairly precise mechanical stimuli (moderate forces applied in a preferential direction); others exhibited a coarse mechanical sensitivity. In addition, electrical stimulation was applied to the maxillary bone to determine the conduction velocities of the relevant fibers. These mainly ranged between 1 and 6 m/s, which indicates that the fibers belonged to the small-diameter category (thinnest myelinated and unmyelinated fibers). Similar results were obtained from animals with osseointegrated implants. It was concluded that the alveolar bone is endowed with sensory endings capable of detecting mechanical and thermal changes, and that these receptors may provide compensatory sensitivity in edentulous subjects whose main (periodontal) sensitivity has been eliminated.

Comparison of the frequency of T-cell receptor mutants and thioguanine resistance induced by X-rays and ethylnitrosourea in cultured human blood T-lymphocytes

We have investigated two assays for measuring the induction of mutations using human T-lymphocytes isolated from leukocyte residue buffy coats obtained from normal donors. Variant cell frequency of T-cells defective in the T-cell receptor (TCR) gene expression was measured using a 2-color flow cytometry, and 6-thioguanine-resistant (TGr) cells were determined using a cloning technique at the HPRT gene after treatment with 250 kVp X-rays or ethylnitrosourea (ENU). The frequencies of TCR mutant cells as well as those of TGr cells increased with increasing doses of X-rays or concentrations of ENU studied. For TCR mutants, the induced mutation frequencies at D37 (giving 37% survival) were 31.7 x 10(-4) and 11.0 x 10(-4) for X-rays and ENU, respectively. For TGr T-cells, the induced mutation frequencies at D37 for the same mutagens were 14.4 x 10(-6) and 75.5 x 10(-6), respectively. Over the dose range studied the relationship appears to be linear between the mutation induction of TCR and that of TGr for X-rays or ENU. However, X-rays may induce more TCR mutants against less induction TGr T-cells, and ENU may cause a reverse result. The sensitivity of the assay of each biological endpoint in human blood T-lymphocytes may be different.

Involvement of the vagus nerve, substance P and cholecystokinin in the regulation of intestinal blood flow

Intestinal blood flow was recorded in anesthetized rats and cats using laser-Doppler flowmetry (LDF). This new technique provides continuous and accurate measurements of the intestinal blood flow, without affecting the blood circulation. Electrical stimulation (1 ms, 5-30 V, 5-50 Hz) applied either afferent or efferent vagal fibres elicited changes in the intestinal blood flow consisting mainly of increases. Similar results were obtained upon applying chemical stimulation to intestinal sensory endings using cholecystokinin (CCK) or substrance P (SP; 10-20 micrograms/kg intravenously given). Bilateral vagotomy and atropine treatment markedly reduced or suppressed these vascular effects. In addition experiments in which the activation of gastrointestinal afferents were activated by applying electrical stimulation to the abdominal vagal nerves yielded similar results. Finally, these effects were reduced after selectively severing vagal afferents. It is concluded that intestinal blood changes may be triggered by activation of the sensory endings from the digestive organs through the vagal nerves.

Modification of radio-thermo-chemotherapy by AK-2123 and hydralazine in tumor bearing mice

The effects of chemical modifiers of hypoxic radiosensitizer, a 3-nitrotriazole derivative AK-2123 (200 mg/kg) before treatment, and vasodilator of hydralazine (HDZ; 5.0 mg/kg) after treatment on tumor growth of SCCVII of mice were investigated in the radio-thermotherapy combined with mitomycin C (MMC; 2.0 mg/kg) or adriamycin (ADM; 3 mg/kg). The tumor treated by 10 Gy alone (tumor doubling time = 7.5 days), MMC alone (6.9 days), and hyperthermia (43 degrees C, 30 min; HT) alone (8.0 days) showed a slight growth delay (control: 5.6 days). Prolonged growth delay (23.2 days) was observed by MMC-radio-thermotherapy (MMC-10Gy/HT) than that (12.4 days) by 10 Gy/HT. The modification of MMC-radio-thermotherapy by HDZ administered between 10 Gy and HT (MMC-10 Gy/HDZ/HT) resulted in the significant prolongation of tumor growth delay (31.7 days). AK-2123 administration before this treatment, (MMC-AK-2123)-10 Gy/HDZ/HT), enhanced a further tumor growth delay (37.6 days) which is equal to that by 50 Gy alone and resulted in the highest dose modifying factor (DMF) of 5.2. While modification of ADM-radio-thermotherapy by AK-2123 and HDZ, (ADM-AK-2123)-10 Gy/HDZ/HT, gave the equal tumor growth delay to that by 30 Gy alone (DMF = 3.1). These high efficacies of radio-thermo-chemotherapy modified by AK-2123 and HDZ may be caused by tumor blood flow reduction.

Periodontal and gastric convergences within the hypothalamic ventromedial nucleus area--single unit study on anesthetized rats

Unitary activities were recorded in the ventromedial nucleus of the hypothalamus (VHM) of anesthetized rats. Cells responding to periodontal stimulation (100-200 g disto-mesial traction applied to an upper incisive) were selected. The effects of gastric stimulation (2-5 ml distension) were then investigated. Out of the 40 cells activated (22 cells) or inhibited (18 cells) by periodontal stimulation, only seventeen were influenced by gastric stimulation. Eight of them responded in the same way and nine in the opposite way. Unlike the periodontal stimulation, which elicited specific spatio-temporal patterns, the gastric stimulation had only weak effects. These data nevertheless demonstrate that periodontal-gastric convergences exist in the VHM nucleus, which is consistent with the role previously ascribed to this area in alimentary behaviour.

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.

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.

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.

[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.

Glucose Sensors in Viscera and Control of Blood Glucose Level

In addition to the well-known glucose-responsive neurons in the hypothalamus, recent studies of sensory signals from the visceral area have brought us a new understanding of the mechanisms that control the blood glucose level. The activity of efferent fibres to the pancreas and the liver is precisely modulated, not only by central hypothalamic glucoreceptors but also by peripheral (hepatic and intestinal) glucoreceptors.

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.

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.

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.

Comparison between the properties of the vagal and splanchnic glucoreceptors of the small intestine. Involvement in insulin release

It was recently well established that the vagal intestinal glucoreceptors are involved in insulin release. In this work we demonstrate that the splanchnic glucoreceptors play a unique role in insulin release: their activation induces a decrease, like strong mechanical stimulation. The physiological meaning of this effect is not clear, it may be a non-physiological response, because high glucose concentration is abnormal in the jejuno-ileal lumen. This work represents the first comparison between the properties and role of different kinds of glucoreceptors.

Recent studies on intestinal vagal afferent innervation. Functional implications

Data obtained during recent years have completely changed our understanding of the organization and function of visceral sensitivity. The digestive tract--and especially the small intestine--provides a very good example of this evolution. Classically, it was believed that the sensory innervation of the gut is supplied by both the vagus and the splanchnic nerves. The vagus nerves play the major role in the sensory innervation of the first part of the intestine (all layers of the bowel, except mesentery). These vagal sensory fibers are mostly nonmedullated and generally originate from free endings. Microelectrophysiological techniques have disclosed the existence of a great variety of receptors: mechanoreceptors, chemoreceptors, thermoreceptors and osmoreceptors in the intestinal area. Some receptors like glucoreceptors, are specific receptors since they do not respond to any stimuli other than glucose. Others, like osmosensitive receptors, behave as non-specific or multimodal receptors. The mechanism by which an identical structure (free ending) induces various sorts of signals (mechanical, thermal, chemical etc.) is not yet known, but several hypotheses have been proposed. The discovery of a varied and complex mass of information obtained from studies of the gut finally corroborates the behavioural and clinical data which suggest that the intestinal sensory innervation plays an important role in physiological regulation. Now it is possible to distinguish 3 main kinds of mechanisms involved according to whether they concern digestive motility, homeostasis or alimentary behaviour.

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.

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.

Electrophysiologic properties and role of the vagal thermoreceptors of lower esophagus and stomach of cat

Vagal unitary discharges were elicited in anesthetized cats by thermal stimulation of the lower thoracic esophagus and stomach. Discharges were recorded from the nodose ganglion, using extracellular glass microelectrodes. Three types of receptors were distinguished according to the temperature ranges at which they discharged: the cold receptors (10 degrees-36 degrees C), the warm receptors (39 degrees-50 degrees C), and the mixed receptors (10 degrees-35 degrees C and 40 degrees-50 degrees C). All endings were connected to unmyelinated fibers (conduction velocities around 1 m/s). These receptors are stimulated neither by mechanical (strong distention, localized stroking of mucosa) nor by chemical (acid and glucose solutions) stimuli. Therefore they must be considered as true thermoreceptors. Stimulation of the esophageal and gastric thermoreceptors produced changes both in esophageal motility and in respiratory frequency. It was concluded that they are involved in coordination of digestive activity as well as in thermoregulation.

Afferent and efferent components of the bronchial vagal branches in cats

The composition of the bronchial branches of the vagus nerves was studied in cats using light and electron microscopy. In order to determine the number and the diameter of fibers in the afferent and the efferent components, a unilateral efferent vagotomy was performed. The myelinated and the non-myelinated fibers were counted from the total nerve area and the endoneural area of each one was measured by means of a computer. Composition of "afferent" bronchial nerves (after degeneration following the efferent vagotomy) was compared to that of "entire" nerves. The main results are: (1) efferent fibers represent about 40% of the "entire" bronchial nerve; (2) non-myelinated fibers constitute more than 90% of the total population of the "entire" nerves as well as of the efferent component; (3) the density of myelinated and non-myelinated fibers (i.e. their number per surface unit) was similar in all nerves. However, there were discrepancies between diameter histograms established from different areas of a section. This feature seems to be due to preferential compartmentalization by Schwann cell envelopment of fibers having comparable diameter. This "packing effect" was observed in both efferent and afferent components.

Assessment of true splanchnic glucoreceptors in the jejuno-ileum of the cat

In anesthetized cats, the unitary activity of splanchnic sensory neurons were recorded from T9, T10 and T11 spinal ganglia by means of extracellular glass microelectrodes. Twelve neurons, generally silent, were activated by perfusion of jejuno-ileum with glucose solutions (10, 50, 100 or 200 g/l). The responses indicated that the corresponding receptors belonged to the slowly adapting type. The discharge frequencies were always low (less than 10 Imp/sec), but varied according to the glucose concentration. Saline solutions (NaCl having the same osmotic pressure as glucose ones), acid solutions (HCl, pH 2.7), or mechanical stimulation were unable to stimulate them. These neurons must be associated with true glucoreceptors. These receptors were connected via non-myelinated fibres (conduction velocities-0.8-2.4 m/sec). It is concluded that these splanchnic glucoreceptors are similar to vagal glucoreceptors described previously.

Nervous regulation of insulin release by the intestinal vagal glucoreceptors

In anesthetized cats and rats, it is demonstrated that glucose perfusion of the small intestine produces a rapid increase of insulin secretion (IRI) which precedes glycemia variation. This mechanism involves the autonomic nervous system and originates from intestinal glucoreceptors, the existence of which was recently reported. The nervous pathways are described in this study:(1) the afferent pathway is represented by vagal fibers coming from the intestinal glucoreceptors; (2) the efferent pathway involves both sympathetic fibers (splanchnic nerves) and chiefly parasympathetic fibers (vagal nerves). These results are established after surgical suppression of afferent and efferent vagal fibers, and pharmacological exclusion of parasympathetic or sympathetic fibers. The role of this nervous regulation of insulin secretion is discussed with special reference to other already known mechanisms.

Changes in activity of vagal bronchopulmonary C fibres by chemical and physical stimuli in the cat

1. In eighteen anaesthetized cats, action potentials in non-myelinated vagal afferent neurones were recorded in the nodose ganglion by means of extracellular micro-electrodes. 2. The pulmonary or bronchial origin of these C fibres was assessed in closed chest preparations by injecting phenyl diguanide into either the right atrium or the ascending aorta (bronchial circulation). This was confirmed in two animals by local mechanical stimulation. 3. Eighty per cent of bronchopulmonary C fibres increased their discharge frequency when the end-tidal CO2 concentration (FA,CO2) increased from 0.02 to 0.10. Most of these C endings showed a maximal response when FA,CO2 reached 0.04. For the others a further increase in discharge occurred when CO2 concentration reached 0.08-0.10. Continuous measurement of C fibre discharge frequency indicated that they detected preferentially changes in the inspired CO2 content, but adapted when a high CO2 level was maintained. Their activation by hypercapnia was followed by an increase in lung resistance. 4. Lowering the O2 content of the inspired gas had no effect on the spontaneous activity of bronchopulmonary C endings. 5. When the stroke volume of the pump was doubled, the spontaneous activity of bronchopulmonary C fibres decreased in intact chest preparations. Inflation of the lungs had the opposite effect after the chest was opened. In both cases hyperdeflation was a potent stimulus to these receptors. 6. In tracheotomized cats, the tracheal temperature was 28-29 degrees C. When normal thermal conditions were restored in the tracheal lumen (33-34 degrees C) the spontaneous discharge frequency of some bronchial C fibres was greatly increased. 7. It is concluded that the spontaneous activity of most of the bronchial or pulmonary C fibres was maximal when chemical and physical physiological conditions were restored in the lungs. It appears that changes in alveolar CO2 concentration constitute the usual stimulus for these fibres.

[Vagal acido- and glucoreceptors in the gastro-duodenal region (author's transl)]

Vagal sensitivity to carbohydrates (mainly glucose) and to acids (hydrochloric and acetic acids) was studied in the gastro-duodenal region of anesthetized cats. Action potentials were recorded extracellularly from the nodose ganglion by means of glass microelectrodes. Receptors responding to glucose perfusion were found at this level as well as receptors stimulated by acid perfusion. It is shown that each type of receptor was activated by only one kind of stimulus (carbohydrates and acids, respectively). These receptors must thus be considered as true glucoreceptors or acido-receptors. Being silent before activation, these two types of chemoreceptors discharged at a frequency that varied from 2 to 14 imp/s for the acido-receptors, and from 2 to 30 imp/s for the glucoreceptors. The response could be irregular or regular and might last several minutes. Its latency was short (between 1 and 20 s for both types of chemoreceptors. It was therefore supposed that they were located in the mucosa or neighboring structures. From the conduction velocities (0.8-1.2 m/s), it was concluded that fibers originating from the acido- and glucoreceptors belonged to the C type. Recording of the electromyographic activity from the gastro-duodenal region demonstrated that the gluco- and acid-receptors are involved in the regulation of motility of the gastric and duodenal regions.

[Cutaneous and muscular unmyelinated afferent fibres. Clinical, histological and experimental study. Possible explanation of muscular cramps (author's transl)]

Unmyelinated afferent fibres are the most numerous of the whole afferent component. Their function in nociception is now well established. However some recent data allow to think that their function is much more complex. Cutaneous unmyelinated afferences are evaluated in controls and in 3 groups of patients (painful neuropathies, painless neuropathies with hypesthesia, diabetic neuropathies). Amyelinic myelinic ratio is not in accordance with the gate control theory. Muscular afferent fibres are studied, especially the lateral gastrocnemius soleus nerve of cat. Their predominance is obvious. Our study was conducted by recording single unit activity from a micro electrod inserted in dorsal root ganglia. But 45% of unmyelinated fibres are not activated by various algesic stimuli. It is suggested that they have a function in cardio-pulmonary adaptation to effort and possibly segmental vascular control as homonymous reflex effect on moto-neuron. Their several properties are a possible explanation of muscular cramps.

The composition of the vagus nerve of the cat

The number and caliber of myelinated and non-myelinated fibers of entire and sensory vagal nerves of cats were studied by means of light and electron miscroscopy. The results obtained with electron microscopy show that the non-myelinated component is particularly rich (about 40,000 elements at the cervical level), with clearly higher numbers of fibers than demonstrated thus far with light microscopy. The ratio of myelinated to non-myelinated fibers is on the average 1:4 for the total vagi and only 1:8 for the sensory vaga component. The comparison of the nerve above and below the level of the nodose ganglion shows that (1) mean fiber diameter is usually greater at the infranodose than at the supranodose level, and (2) some myelinated fibers of small diameter occurring below the nodose ganglion become non-myelinated above it. Additionally, the number of non-myelinated fibers per Schwann cell is greater at the supranodose than at the infranodose level; this speaks in favor of a reorganization of the C-fiber population from one level to the other.

Vagal and splanchnic effects at the level of the ventromedian nucleus of the hypothalamus (VMH) in the cat

A systematic study of vagal and splanchnic projections to the VMH area was undertaken in anaesthetized cats by means of macroelectrodes and microelectrodes. Responses elicited by vagal and splanchnic nerve stimulation were recorded from the VMH nucleus and the region situated above it. The fact that they are identical, whatever the nerve stimulated, indicates that the afferences follow a common central pathway. From the response latency and the stimulation parameters, it is assumed that the small vagal and splanchnic fibres (A delta, B and C) are involved. Evoked potentials are generally constituted of two parts: the earlier implies certainly the VPL nucleus (since it disappears definitively after VPL coagulation), whereas the later concerns a different relay probably located in the neighbouring and associative structure (since it persists after VPL coagulation). Similar late responses were simultaneously recorded in VPL nucleus, suggesting that this structure was the same for both nuclei. Its exact location was discussed. On the other hand, effects of gastric distension on the evoked potentials produced by vagal and splanchnic nerve stimulation were studied. The results obtained (decrease or increase in the responses, occurrence of an additional potential) indicated clearly that the gastric afferences projected to the VMH region. This simple method could be used to determine the importance of the sensory innervation of the different parts of the digestive tract.

[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.

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.

[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.

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.