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Biomedical subjects

A Jean

Publications and source records attributed to A Jean.

At least 19 recordsLinked to original sources
PubMed2006

Neurogenesis and neural stem cells in the dorsal vagal complex of adult rat brain: new vistas about autonomic regulations--a review.

The dorsal vagal complex (DVC) of the brainstem is the major reflex center of autonomic nervous system. Several neuroplasticity effectors have been identified in the DVC of adult rat, such as PSA-NCAM, GAP-43, BDNF and its receptor TrkB; moreover, acute vagal stimulation was found to induce c-fos and to down-regulate western-blot-assayed tissular concentration of PSA-NCAM. Adult neurogenesis was first shown in rat DVC by BrdU incorporation combined with phenotypic labelling in situ; new neurons are generated in equal proportions with new astrocytes and at a lower rate than in olfactory bulb or hippocampus. Intrinsic proliferative cells were then detected within the DVC of adult rat by means of Ki-67 immunohistochemistry and western-blot of D-cyclins. The presence of neural stem cells within DVC was directly demonstrated by applying the in vitro neurosphere assay on microdissected adult DVC explants; DVC-derived neurospheres display lower proliferation rate and neurogenic potential than forebrain ones. Vagotomy in adult promotes massive and transient increase of neurogenic and microglial proliferations within DVC, the kinetics and location of which were analyzed by Ki-67 immunohistochemistry and cyclin D western blot. These mechanisms shed light on so far unknown plasticity potential in DVC, which brings novel cues about physiological adaptations of autonomic reflexes in adult mammals.

Animals↗
PubMed2006

Involvement of central microsomal prostaglandin E synthase-1 in IL-1beta-induced anorexia.

In response to infection or inflammation, individuals develop a set of symptoms referred to as sickness behavior, which includes a decrease in food intake. The characterization of the molecular mechanisms underlying this hypophagia remains critical, because chronic anorexia may represent a significant health risk. Prostaglandins (PGs) constitute an important inflammatory mediator family whose levels increase in the brain during inflammatory states, and their involvement in inflammatory-induced anorexia has been proposed. The microsomal PGE synthase (mPGES)-1 enzyme is involved in the last step of PGE2 biosynthesis, and its expression is stimulated by proinflammatory agents. The present study attempted to determine whether an upregulation of mPGES-1 gene expression may account for the immune-induced anorexic behavior. We focused our study on mPGES-1 expression in the hypothalamus and dorsal vagal complex, two structures strongly activated during peripheral inflammation and involved in the regulation of food intake. We showed that mPGES-1 gene expression was robustly upregulated in these structures after intraperitoneal and intracerebroventricular injections of anorexigenic doses of IL-1beta. This increase was correlated with the onset of anorexia. The concomitant reduction in food intake and central mPGES-1 gene upregulation led us to test the feeding behavior of mice lacking mPGES-1 during inflammation. Interestingly, IL-1beta failed to decrease food intake in mPGES-1(-/-) mice, although these animals developed anorexia in response to a PGE2 injection. Taken together, our results demonstrate that mPGES-1, which is strongly upregulated during inflammation in central structures involved in feeding control, is essential for immune anorexic behavior and thus may constitute a potential therapeutic target.

Animals↗
PubMed2005

Characterization of neural stem cells in the dorsal vagal complex of adult rat by in vivo proliferation labeling and in vitro neurosphere assay.

The dorsal vagal complex, located in the brainstem, is the major integrative center of the autonomic nervous system. By combining in vivo bromodeoxyuridine incorporation and phenotypic immunolabeling, we have previously reported that neurogenesis occurs in the adult rat dorsal vagal complex [Bauer S, Hay M, Amilhon B, Jean A, Moyse E (2005) In vivo neurogenesis in the dorsal vagal complex of the adult rat brainstem. Neuroscience 130:75-90.]. In the present study we asked whether adult dorsal vagal complex contains proliferative and/or neural stem cells. Using Ki-67 immunolabeling and cyclin D1 Western blot, we showed intrinsic cell proliferation in the dorsal vagal complex and its stimulation by vagotomy. Detailed time-course analysis revealed that vagotomy-induced proliferation in the dorsal vagal complex peaked three days after lesion. In order to directly assess the presence of intrinsic stem cells, primary cell cultures from adult rat dorsal vagal complex were performed in the presence of epidermal growth factor and basic fibroblast growth factor (neurosphere assay). A discrete subpopulation of dorsal vagal complex cells proliferated as neurospheres, self-renewed when passaged, and differentiated into neurons, astrocytes and oligodendrocytes. Proliferation and neuron-differentiating potentials of dorsal vagal complex neurospheres were both lower than those of subventricular zone neurospheres from the same rats. The relationship between in vitro neurosphere-forming cells of dorsal vagal complex and in vivo dorsal vagal complex neurogenesis is discussed and remains to be directly addressed. The present data demonstrate the occurrence of neural stem cells in the dorsal vagal complex of adult rat brain.

Animals↗
PubMed2005

In vivo neurogenesis in the dorsal vagal complex of the adult rat brainstem.

The dorsal vagal complex (DVC) encompasses the nucleus tractus solitarii (NTS), the dorsal motor nucleus of the vagus nerve (DMX) and the area postrema (AP), that altogether provide the major integrative center for the mammalian autonomic nervous system. The adult rat DVC has been reported to contain afferent-dependent concentration of the plasticity-promoting polysialylated form of neural cell adhesion molecule [J Neurosci 21 (2001) 4721; Eur J Neurosci 14 (2001) 1194]. This prompted us to assess the occurrence of neurogenesis in the DVC of adult rats. Cumulative in vivo labeling of cell proliferation with i.p. bromodeoxyuridine (BrdU) injections was combined with phenotypic markers and confocal microscopy on serial brainstem sections throughout the DVC extent. In basal condition, sparse BrdU+ nuclei were selectively detected in the DVC according to a discrete and reproducible pattern. Some of them were found to colocalize with the neuronal markers doublecortin, HuC/D, or neuronal-specific antigen (NeuN), demonstrating that neurogenesis does occur within the DVC of adult rat. In the NTS, 10% of the BrdU+ nuclei were also NeuN+. A comparable proportion of astrogliogenesis was found in the DVC. Nestin immunohistochemistry yielded a highly specific labeling pattern at the border between AP and NTS. These data may relate to the neural stem cells that have been reported in the floor of the IVth ventricle [J Neurosci 16 (1996) 7599]. In order to assess a possible modulation of neurogenesis by afferent input in vivo, unilateral vagotomy was performed prior to cumulative BrdU treatment. Such DVC deafferentation triggered a large increase of BrdU incorporation in the ipsilateral DVC, which was associated with microglial proliferation in the DMX and with increased genesis of neurons and astrocytes in the NTS. These findings establish DVC as a novel model of adult neurogenesis that is reactive to deafferentation.

Animals↗
PubMed2002

Microleakage of class V composite restorations following Er:YAG and Nd:YAP laser irradiation compared to acid-etch: an In vitro study.

This study compared microleakage at enamel/composite and dentine/composite interfaces following Er:YAG laser, Nd:YAP laser, or acid-etch preparation. Class V cavities produced on the lingual and buccal surfaces of 20 extracted carie- and restoration-free human teeth were randomly assigned to four groups of 10 cavities. Teeth were treated with 37% phosphoric acid and primer (group 1), irradiated with an Er:YAG laser (group 2) or an Nd:YAP laser (group 3), or served as controls (group 4). The specimens were restored with Scotchbond Multipurpose/Z100 (3M), stored in physiological solution at 37 degrees C for 7 days, thermocycled 500 times between 5 degrees C and 55 degrees C, placed in a 0.5% solution of basic fuchsin for 48 h, embedded in resin, and sectioned. Microleakage was assessed according to the depth of dye penetration along the restorative composite. The results showed that irradiation with Er:YAG and Nd:YAP lasers did not produce a good seal. Mean microleakage was greater than with acid-etch and statistically comparable to that of control cavities (Kruskal-Wallis test).

Acid Etching, Dental↗
PubMed2001

NMDA receptor and nitric oxide synthase activation regulate polysialylated neural cell adhesion molecule expression in adult brainstem synapses.

Here we report that synapses in the adult dorsal vagal complex, a gateway for many primary afferent fibers, express a high level of the polysialylated neural cell adhesion molecule (PSA-NCAM). We show that electrical stimulation of the vagal afferents causes a rapid decrease of PSA-NCAM expression both in vivo and in acute slices. Inhibition of NMDA receptor activity completely prevented the decrease. Blockade of calmodulin activation, neuronal nitric oxide (NO) synthase, or soluble guanylyl cyclase and chelation of extracellular NO mimicked this inhibition. Our data provide a mechanistic framework for understanding how activity-linked stimulation of the NMDA-NO-cGMP pathway induces rapid changes in PSA-NCAM expression, which may be associated with long-term depression.

Animals↗
PubMed2001

Dual effects of NMDA receptor activation on polysialylated neural cell adhesion molecule expression during brainstem postnatal development.

Here we show a dual role of N-methyl-d-aspartate receptor (NMDAR) activation in controlling polysialylated neural cell adhesion molecule (PSA-NCAM) dynamic expression in the dorsal vagal complex (DVC), a gateway for many primary afferent fibres. In this structure the overall expression of PSA-NCAM decreases during the first 2 weeks after birth to persist only at synapses in the adult. Electrical stimulation of the vagal afferents causes a rapid increase of PSA-NCAM expression both in vivo and in acute slices before postnatal day (P) 14 whereas a similar stimulation induces a decrease after P15. Inhibition of NMDAR activity in vitro completely prevented these changes. These regulations depend on calmodulin activation and cGMP production at all stages. By contrast, blockade of neuronal nitric oxide synthase (nNOS) prevented these changes only after P10 in agreement with its late expression in the DVC. The pivotal role of NMDAR is also supported by the observation that chronic blockade induces a dramatic decrease in PSA-NCAM expression.

Aging↗
PubMed2001

Brain stem control of swallowing: neuronal network and cellular mechanisms.

Swallowing movements are produced by a central pattern generator located in the medulla oblongata. It has been established on the basis of microelectrode recordings that the swallowing network includes two main groups of neurons. One group is located within the dorsal medulla and contains the generator neurons involved in triggering, shaping, and timing the sequential or rhythmic swallowing pattern. Interestingly, these generator neurons are situated within a primary sensory relay, that is, the nucleus tractus solitarii. The second group is located in the ventrolateral medulla and contains switching neurons, which distribute the swallowing drive to the various pools of motoneurons involved in swallowing. This review focuses on the brain stem mechanisms underlying the generation of sequential and rhythmic swallowing movements. It analyzes the neuronal circuitry, the cellular properties of neurons, and the neurotransmitters possibly involved, as well as the peripheral and central inputs which shape the output of the network appropriately so that the swallowing movements correspond to the bolus to be swallowed. The mechanisms possibly involved in pattern generation and the possible flexibility of the swallowing central pattern generator are discussed.

Animals↗
PubMed2000

Analgesic and antiinflammatory activities of an extract from Parkia biglobosa used in traditional medicine in the Ivory Coast.

In the Ivory coast, Parkia biglobosa (Mimosaceae) is used in traditional medicine as an analgesic drug, especially against dental pain. Of the three extracts obtained from the plant bark, the hexane fraction was studied to determine its analgesic and/or antiinflammatory activities. The results show that this extract possesses a marked analgesic activity when evaluated with the abdominal writhing test in mice, but, like paracetamol, was ineffective with the hot-plate method, a feature suggesting a peripheral mechanism of action. This activity was accompanied by an antiinflammatory effect, somewhat weaker than the analgesic one.

Analgesics↗
PubMed2000

Temperature rise during Er:YAG and Nd:YAP laser ablation of dentin.

This in vitro study compared temperature rises during cavity preparation with an Er:YAG laser, Nd:YAP laser, and a high-speed handpiece. Eighteen teeth were sectioned longitudinally and divided into six groups: group 1 was treated with a carbide bur on a high-speed dental handpiece; group 2 was treated with an Er:YAG laser with an energy of 140 mJ, a pulse repetition rate of 4 Hz; and group 3 was treated with an Nd:YAP laser with an energy of 240 mJ, a pulse repetition rate of 10 Hz. In these groups no water cooling was used. Groups 4 to 6 were treated in the same way, but with water spray. Temperature increases were measured at different dentin thicknesses by a microthermocouple attached to the inner side of the pulp chamber. Water cooling was essential to reduce temperature effects in all groups. Nd:YAP laser induced significantly higher temperature rises than Er:YAG or handpiece. Temperature response to the Er:YAG laser and the handpiece seemed to be similar.

Aluminum Silicates↗
PubMed1999

Scanning electron microscopic analysis of diseased and healthy dental hard tissues after Er:YAG laser irradiation: in vitro study.

The aim of this study was to treat carious lesions, sound dentin, and enamel either with conventional methods or with an Er:YAG laser and to compare the results. Thirty freshly extracted carious human teeth were divided into two groups. In the first group, lesions were treated with burs in a dental handpiece; in the second group, we used the Er:YAG laser with parameters recommended by the manufacturer (Kavo). After treatment, the teeth were prepared for scanning electron microscopic observation. On laser-treated teeth, scaly, flaky, rough surfaces were seen: surfaces were clean with several morphological reliefs that may enhance bonding resin restoration. The Er:YAG laser beam can ablate carious dentin with an energy level of 250 mJ at 2 Hz. Sound dentin can be cut at 300 mJ and 2 Hz; for enamel, 350 mJ and 3 Hz are required. The Er:YAG laser seems to be effective in the treatment of carious lesions and in cavity preparation in vitro.

Dental Caries↗
PubMed1999

Ultrastructural properties of laser-irradiated and heat-treated dentin.

Previous studies using scanning electron microscopy and infrared absorption spectroscopy reported that laser irradiation causes compositional changes in enamel. The purpose of this study was to evaluate the ultrastructural and compositional changes in dentin caused by irradiation with a short-pulse laser (Q-switched Nd:YAG). The irradiated and non-irradiated areas of the lased dentin samples were investigated by scanning (SEM) and transmission electron microscopy (TEM), micro-micro electron diffraction, and electron microprobe analysis of dispersive energy (EDX). Heat-treated dentin was similarly investigated. This study demonstrated that laser irradiation resulted in the recrystallization of dentin apatite and in the formation of additional calcium phosphate phases consisting of magnesium-substituted beta-tricalcium phosphate, beta-TCMP, beta-(Ca,Mg)3(PO4)2, and tetracalcium phosphate, TetCP, Ca4(PO4)O. TEM analyses of the modified and unmodified zones of the irradiated areas showed two types of crystal populations: much larger crystals from the modified zone and crystals with size and morphology similar to those of dentin apatite in the unmodified zone. The morphology of crystals in the modified zones in the irradiated dentin resembled those of dentin sintered at 800 or 950 degrees C. In the irradiated areas (modified and unmodified zones), the Ca/P ratio was lower compared with that in the non-irradiated dentin. The Mg/Ca ratio in the modified zones was higher than that in the unmodified zones and in the non-irradiated dentin. In sintered dentin, the Mg/Ca ratio increased as a function of sintering temperature. The ultrastructural and compositional changes observed in laser-irradiated dentin may be attributed to high temperature and high pressure induced by microplasma during laser irradiation. These changes may alter the solubility of the irradiated dentin, making it less susceptible to acid dissolution or to the caries process.

Calcium↗
PubMed1998

[Deglutition: physiologic and neurophysiologic aspects].

Swallowing is a complex motor sequence involving the coordinated contraction of many muscles of the buccopharyngeal cavity, the larynx and the oesophagus. Most of the muscles are striated except those of the distal oesophagus which, in human and some other species, are of the smooth type. During swallowing, usually divided into a buccopharyngeal and an oesophageal stage (peristalsis), the sequential activity of the muscles results from motor orders programmed by a rhombencephalic swallowing centre and conveyed to the periphery by efferent fibres belonging to various pairs of cranial nerves (Vth, VIIth, Xth, XIIth). Apart from the motor nuclei of the cranial nerves, the swallowing centre contains an interneurone network responsible for the programming of deglutition. During swallowing, these interneurones (INs) exhibit a sequential activity quite parallel to that of muscles, and persisting in the absence of sensory feedback. The "swallowing INs" are located in two medullary regions: (1) a dorsal region including the nucleus of the solitary tract and the adjacent reticular formation, (2) a ventral region corresponding to the reticular formation surrounding the nucleus ambiguus. The dorsal INs are involved in the initiation and the programming of swallowing. The ventral INs receive their swallowing input from the dorsal neurones and are probably switching neurones that distribute the swallowing excitation to the various pools of motoneurones. The swallowing program can be triggered by inputs originating from either the peripheral reflexogenic areas or the supramedullary structures (cerebral cortex, basal ganglia and hypothalamus). Under physiological circumstances swallowing program is continuously modified by peripheral afferents (expecially muscular) that adjust the force and the timming of contractions to the size of the swallowed bolus. In addition, an important operating feature of the programming network consists of a functionnal polarization so that the activity of proximal portions of the swallowing tract inhibits that of distal portions. This polarization implies the existence of inhibitory connections between interneurones, that could be responsible for the series of delays typical fo swallowing contractile sequence, by generating delayed desinhibitions followed by post inhibitory excitations. Lastly, the sensitive messages that trigger and adjust the swallowing program are at the same time conveyed to higher nervous structures allowing the so called "voluntary" swallow and the integration of swallowing in the ingestive behavior. Disruption of this central loop is likely the source of swallowing disorders (dysphagia) following lesion of cortical or subcortical structures.

Animals↗
PubMed1997

Immunohistochemical detection of glutamate in rat vagal sensory neurons.

Vagal primary afferent neurons have their cell bodies located in the nodose (inferior) and jugular (superior) vagal ganglia and send terminals into the nucleus tractus solitarii (NTS) which lies in the dorsomedial medulla. The presence of glutamate (Glu)-containing neurons in the rat nodose ganglion was investigated using immunohistochemistry. Glu-immunoreactivity on nodose sections was found in neuronal perikarya and nerve fibers, but not in non-neuronal elements such as Schwann cells and satellite cells. Both immunoreactive and non-immunoreactive ganglion cells were observed. The immunoreactive ganglion cells amounted to about 60% of the nodose population. No specific intraganglionic localization was observed for the non-immunoreactive cells. Immunoreactive perikarya were slightly smaller than the non-immunoreactive ones, but no relationship was found between size and staining intensities of immunoreactive neurons. The present data indicate that immunodetectable Glu is present in a large population of vagal afferent neurons. They therefore add to a growing body of evidence suggesting that Glu may be the main neurotransmitter released by vagal afferent terminals within the nucleus tractus solitarii.

Animals↗
PubMed1997

Postnatal ontogeny of glutamate receptors in the rat nucleus tractus solitarii and ventrolateral medulla.

The nucleus tractus solitarii and the ventrolateral medulla are two brainstem regions involved in regulation of autonomic functions. Glutamate (Glu) receptors localized within these two regions play a key role in neural control of swallowing and breathing and in blood pressure regulation. In the present study, postnatal changes in global [3H]Glu binding and in [3H]Glu binding to N-methyl-D-aspartate (NMDA) receptors were analyzed in the nucleus tractus solitarii and the ventrolateral medulla using in vitro receptor autoradiography. Similar results were obtained in both regions. When expressed as density values (fmol/mg tissue), both global and NMDA-sensitive Glu binding increased by approximately 50-70% between birth and postnatal day 9 (P9) and then decreased until P30. When expressed as binding per nucleus (i.e., after correction for tissue growth), global Glu binding still increased between birth and P9 and decreased between P9 and P30 whereas NMDA-sensitive binding increased until P9 and remained stable thereafter. Saturation studies showed a postnatal increase in Glu receptor number per nucleus, which occurred mainly between birth and P9, and a decrease in Glu receptor affinity between P9 and adulthood. These results indicate that dramatic changes in glutamatergic neurotransmission occur in the nucleus tractus solitarii and the ventrolateral medulla during the first month of postnatal life. They suggest that both neonates and young animals may not be fully mature as regard to central regulation of autonomic functions.

Animals↗
PubMed1997

Fourier-transform infrared spectroscopy study of an organic-mineral composite for bone and dental substitute materials.

A new injectable biomaterial for bone and dental surgery is a composite consisting of a polymer as a matrix and bioactive calcium phosphate (CaP) ceramics as fillers. The stability of the polymer is essential in the production of a ready-to-use injectable sterilized biomaterial. The purpose of this study was to detect possible polymer degradation which may have been caused by the interaction with the fillers using Fourier transform infrared spectroscopy. Composites containing CaP fillers (biphasic calcium phosphate, hydroxyapatite and peroxidized hydroxyapatite) and polymer (hydroxypropyl methyl cellulose) were prepared. To investigate the properties of the polymer, the inorganic and organic phases of the composite were separated using several extraction methods. The difficulty in separating the organic (polymer) from the mineral (CaP fillers) phases in the composite investigated in this study suggested the presence of strong interactions between the two phases. Spectra of extracted polymers showed new absorption bands of low intensities and indications that some chemical modifications of the original polymers have occurred. Results also indicated that the filler composition has an effect on the integrity of the polymer.

Journal Article↗
PubMed1997

Scanning electron microscopic evaluation of the effects of an air-abrasive system on dental implants: a comparative in vitro study between machined and plasma-sprayed titanium surfaces.

An in vitro comparative study was conducted in order to evaluate the effects of an air-abrasive system on dental implant surfaces. Eight new titanium dental implants, four standard machined implants (machined group), and four standard plasma-sprayed implants (plasma-sprayed group) were selected for investigation. Both neck and body surfaces of the implants were analyzed. Each pair of implants in each group was treated as follows: the spray of the air-abrasive unit was applied to each area for 5 seconds on the first implant and 15 seconds on the second implant. A total of 24 areas were observed: 16 test implants and 8 controls. Scanning electron photomicrographs were analyzed by 3 examiners using a category rating scale (kappa = 0.594). The images were also computerized for texture analysis. The results indicate that a single air-powder abrasive treatment of the dental implants selected for this study modified their exposed surfaces. After treatment, the threaded neck surface of a machined group implant was least affected, whereas the body was the most altered. In the plasma-sprayed group, comparisons between implant surfaces showed little change. In the machined group, more change was observed in both neck and body areas. In all specimens, a 5-second exposure to the air-powder abrasive did not induce deep changes in the surfaces. A 15-second exposure modified all the specimen surfaces. Further studies are needed to evaluate the effect of these changes on the biological osseointegration process.

Air↗