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Biomedical subjects

A Jean

Publications and source records attributed to A Jean.

At least 55 records · Page 3Linked to original sources
PubMed1990

Selective retrograde labeling of primary vagal afferent cell-bodies after injection of [3H]D-aspartate into the rat nucleus tractus solitarii.

A selective retrograde labeling study was performed using [3H]D-aspartate to identify putative glutamatergic and/or aspartatergic primary vagal afferent fibers. Unilateral microinjection of [3H]D-aspartate into the nucleus tractus solitarii resulted in clear visible labeling of a fraction of the neuronal cell-bodies in the nodose ganglia. The labeled cell-bodies were randomly distributed in the ganglion and more numerous labeled neurons were detected in the ipsilateral than in the contralateral ganglion (4.93% and 0.98% of the neurons sampled within the ipsi- and contralateral ganglia, respectively). These results strongly suggest that primary vagal afferent fibers may utilize excitatory amino acids as transmitters.

Animals↗
PubMed1990

Swallowing responses induced by microinjection of glutamate and glutamate agonists into the nucleus tractus solitarius of ketamine-anesthetized rats.

Swallowing is a patterned motor activity generated by neurons located within the nucleus tractus solitarius (NTS). An excitatory amino acid (EAA) neurotransmitter, such as glutamate (GLU), is suspected of being involved in the initiation of swallowing by NTS neuronal components. However, swallowing can still be elicited in animals anesthetized with ketamine, an antagonist of the N-methyl-D-aspartate (NMDA) subclass of EAA receptors. The present experiments were therefore designed to investigate the influence of EAA administration within the NTS on the swallowing motor activity of rats anesthetized with ketamine. Pressure microinjections of GLU in doses ranging from 25 to 500 pmol elicited swallowing. This effect was dose-dependent and was not reproduced when control injections of the vehicle solution were performed. Microinjections of the GLU agonists, quisqualate (QUIS) and NMDA, in doses ranging between 2.5 and 50 pmol, also induced swallowing motor activities. QUIS, like GLU, elicited a short series of swallows at a brief latency while NMDA generated long-lasting rhythmic swallowing with a longer latency. Swallowing induced by GLU microinjections (100 pmol) was suppressed almost completely by local pretreatment with either the broad spectrum EAA receptor antagonist, gamma-D-glutamylglycine (250 pmol), or the more selective non-NMDA antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (50-100 pmol), but not by pretreatment with the selective NMDA antagonist, DL-2-amino-5-phosponovalerate (250 pmol). On the other hand, pretreatment with DL-2-amino-5-phosphonovalerate (50 pmol) suppressed the deglutitions induced by NMDA microinjections (10 pmol) but not those elicited by QUIS microinjections (10 pmol).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Neurons of the nucleus tractus solitarius, in vitro, generate bursting activities by solitary tract stimulation.

Extracellular recordings of the activity of nucleus tractus solitarius (NTS) neurons were performed on rat brainstem slice preparations. Neurons localized in the medial part of the lateral NTS, which displayed a synaptic response to single pulse stimulation of the tractus solitarius (TS), generated bursting activity following repetitive TS stimulation (20-50 Hz frequency, 100-600 ms duration). According to their patterns of discharge and to the duration and frequency of their bursting activities, these neurons were classified in three groups called type A, B and C. We suggest that different cellular intrinsic properties, rather than local synaptic interactions, might be involved in the generation of these three types of bursting activities. These results are discussed in terms of the role of NTS neurons in the generation of the swallowing motor pattern.

Action Potentials↗
PubMed1988

Central serotonergic projections to the nucleus tractus solitarii: evidence from a double labeling study in the rat.

Projections from several brainstem serotonergic nuclei to the nucleus tractus solitarii were investigated in the rat. Experiments were performed using a double labeling method combining retrograde radioautographic tracing and serotonin immunohistochemistry. After injection of the radioactive tracer ([3H] wheat germ agglutinin) into the lateral nucleus tractus solitarii, nerve cell bodies exhibiting both radioautographic labeling and immunostaining were detected in all the serotonergic nuclei investigated, namely the nucleus raphe magnus, the ventromedial paragigantocellular nucleus, the nuclei raphe pontis, medianus and dorsalis, the medial lemniscus and the reticulotegmental nucleus of the pons. Most of the double labeled perikarya observed were in the nucleus raphe magnus, the adjacent part of the paragigantocellular nucleus and the nucleus raphe dorsalis. Nerve cell bodies retrogradely labeled but devoid of immunostaining were also observed, together with the double labeled perikarya, within serotonergic nuclei. These results provide direct evidence that brainstem serotonergic neurons contribute to the innervation of the nucleus tractus solitarii. They indicate that the nucleus raphe magnus and the nucleus raphe dorsalis constitute two major sources of central serotonergic projections to the nucleus tractus solitarii.

Animals↗
PubMed1988

Simple sequence DNA associated with near sequence identity of the 3'-flanking regions of rat cytochrome P450b and P450e genes.

In rat liver, the two major phenobarbital (PB)-inducible cytochrome P450s, P450b (P450IIB1), and P450e (P450IIB2), are encoded by approximately 2.1-kb mRNAs showing more than 97% nucleotide sequence identity. Almost half of the sequence differences are concentrated in two short divergent segments in exon 7. An additional 4.8-kb P450b/P450e RNA, inducible by Aroclor and by PB, hybridizes with a classical P450b probe and with the 3' extension of the PB23 insert, a cloned P450b-like cDNA (Affolter et al., DNA 5, 209-218, 1986). The 4.8-kb form has now been detected in several rats under a variety of induction conditions. DNA sequencing of the 5' portion of the PB23 insert showed it is derived from a P450b gene. The 4.8-kb RNA hybridized with an oligonucleotide probe that recognizes P450b mRNA, but did not hybridize detectably with one that recognizes P450e mRNA. The 4.8-kb RNA and the PB23 insert doubtless represent P450b RNAs polyadenylated at a downstream site. DNA sequence analysis of the PB23 3' extension (which represents the 3' end of the P450b gene) and of the P450e gene 3'-flanking region demonstrated that the near identity of the P450b and P450e genes extends for at least 920 bp beyond the major polyadenylation site. This region was doubtless part of the original duplication that gave rise to the P450b and P450e genes. A short divergent segment is present in the 3'-flanking region of near sequence identity; the segment is embedded in simple sequence DNA that contains a mixed alternating pyrimidine/purine tract.

Animals↗
PubMed1988

A constitutive member of the rat cytochrome P450IIB subfamily: full-length coding sequence of the P450IIB3 cDNA.

The prototypic members of the rat liver cytochrome P450IIB subfamily, P450b and P450e, have long been the subjects of intense interest, in part because they are highly inducible by phenobarbital (PB). We have previously cloned and sequenced an 858-bp cDNA fragment (the PB24 insert) that encodes the carboxy-terminal portion of a P450b/P450e-like protein, henceforth referred to as P450IIB3. A Bam HI-Eco RI fragment of the PB24 insert hybridizes with a 1.9-kb mRNA present constitutively in rat liver and not inducible by PB (Affolter et al., 1986). We have now obtained, from a lambda gt11 rat liver cDNA library, cDNA inserts corresponding to the complete coding sequence of the IIB3 mRNA. The 491-amino acid IIB3 protein sequence, deduced from the cDNA sequence, is 77% identical to that of P450b. Northern blot analysis, with a IIB3-specific oligonucleotide probe, confirmed the constitutive presence of the polyadenylated 1.9-kb IIB3 mRNA in male rat liver. The IIB3 mRNA was undetectable in the lung, kidney, and prostate. It was constitutively present, and not inducible by PB, in female rat liver. Our results demonstrate unequivocally the existence of a constitutive member of the rat P450IIB subfamily. The remarkable inducibility of the P450b/P450e genes is in striking contrast to the absence of a PB effect on IIB3 gene expression. The molecular basis for this difference remains to be revealed.

Amino Acid Sequence↗
PubMed1988

[Chronic diarrhea caused by Campylobacter jejuni in a patient with AIDS].

We report a case of C. jejuni chronic diarrhea in a homosexual man with AIDS. The antibiotic susceptibility of the bacteria was about normal for the species. Investigating specific immunity, we observed the presence of anti-C. jejuni IgG and the absence of anti-C. jejuni IgA. These findings concord with the hypothesis that specific IgA are necessary for C. jejuni clearance from the digestive tract.

Acquired Immunodeficiency Syndrome↗
PubMed1988

[Course of the resistance of Staphylococcus aureus to pefloxacin. A study based on 782 strains isolated in 1985 and 1986].

We studied the evolution of the resistance of Staphylococcus aureus to pefloxacin during 1985 and 1986 in eight hospital units. The pefloxacin resistant Staphylococcus aureus, which amounted to 8.9% in 1985 reached 27% in 1986. They are found mainly among the methicillin-resistant Staphylococcus. There is no obvious relationship between this resistance and the consumption of pefloxacin in each of the units.

Drug Resistance, Microbial↗
PubMed1987

Possible physico-chemical processes in human dentin caries.

This study correlated ultrastructural observations on the presence of beta-tricalcium phosphate (beta-TCP) in arrested dentin caries with physico-chemical observations on the in vitro formation of Mg-substituted beta-TCP. The ultrastructural studies were made using high-resolution transmission electron microscopy (TEM) with the capability of microdiffraction and microanalysis on sites less than 10 nm in diameter. Mg-substituted beta-TCP was obtained, by a precipitation method, from solutions with Mg/Ca molar ratios of 5/95 and higher. Such correlations led to the postulation of a possible chronological sequence of physico-chemical events occurring at the crystal level during the progress and arrest of caries in human dentin. It is suggested that the initial mechanism for the observed occurrence of large crystals of Mg-substituted beta-TCP and of apatite in the tubule lumen is due to the dissolution of the dentin mineral (a CO3- and Mg-rich calcium OH-apatite) and reprecipitation of Mg-substituted beta-TCP, followed by that of CO3- and Mg-poor apatite.

Calcium Phosphates↗
PubMed1986

Effect of catecholamines on the swallowing reflex after pressure microinjections into the lateral solitary complex of the medulla oblongata.

The present study was carried out to elucidate the influence of catecholamines on swallowing, a polysynaptic reflex organized by an interneuronal network localized mainly within the lateral solitary complex (LSC) of the medulla oblongata. The effects of catecholaminergic agents were investigated in the rat, on rhythmic swallowing elicited by repetitive stimulation of the superior laryngeal nerve (SLN). Catecholaminergic agents were microinjected by pressure application, through multibarrelled glass micropipettes, into the LSC including the tractus solitarius, the swallowing region of the nucleus of the solitary tract and the adjacent reticular formation. Microinjections of noradrenaline (NA, 0.1-5 nmol, 50 nl) induced a significant decrease of the number and the amplitude of the rhythmic swallows elicited by stimulation of the ipsilateral SLN. This inhibitory effect was dose-related. Microinjections of clonidine (2.5 nmol, 50 nl), dopamine (0.25-2.5 nmol, 50 nl) and apomorphine (0.5 nmol, 50 nl), also inhibited swallowing. No significant modification of swallowing was induced by control injections of the vehicle (50 nl) within the active sites. Moreover the NA-induced inhibition of swallowing, was significantly antagonized by pretreatment with the alpha-adrenergic blocker phentolamine applied locally in the LSC. Furthermore neither blood pressure, nor respiratory rhythm were consistently modified by the catecholaminergic microinjections, indicating that the catecholamine-induced inhibition of swallowing was not a secondary side effect originating from alteration of these functions. It can therefore be concluded that the present results demonstrate the existence within the LSC of a catecholaminergic inhibition of the swallowing reflex. This inhibitory effect likely arises from activation of specific catecholaminergic receptors and affects the swallowing structures localized within the LSC, i.e., the laryngeal swallowing afferents running in the solitary tract and/or the swallowing interneurons within the nucleus of the solitary tract.

Animals↗
PubMed1986

Inhibitory influence of monoamines and brainstem monoaminergic regions on the medullary swallowing reflex.

Swallowing is a polysynaptic reflex organized by a neuronal network localized mainly within the lateral region of the nucleus tractus solitarius (NTS). Monoamine microinjections (serotonin, noradrenaline; 1 nmol, 50 nl) within the swallowing region of the NTS produced a significant decrease in the number of swallows elicited by repetitive stimulation of the superior laryngeal nerve. Stimulation, with concentric bipolar electrodes, of several brainstem structures overlapping monoaminergic regions such as the nucleus raphe magnus, the nucleus raphe pallidus, the lemniscus medialis, the ventrolateral reticular formation, the locus coeruleus and the nucleus commissuralis, induced an inhibition of the laryngeal-initiated swallowing. These results indicate the existence, within the NTS, of a monoaminergic inhibition of the swallowing reflex which might originate from monoaminergic brainstem regions.

Animals↗
PubMed1986

Scanning electron microscope study of the predentin-pulpal border zone in human dentin.

Fragments of sound human molars were prepared for the scanning electron microscope (SEM) using modified fixative procedures and the carbon dioxide critical-point method to study the predentin-pulpal border zone. This technique minimizes the usual artifacts related to SEM procedures. The elongated odontoblast bodies are closely related to each other at the predentin level. For the first time in SEM procedures, the cell processes almost completely fill the predentinal tubules. Fibers measuring 0.3 to 0.5 micron in diameter are visible between the odontoblasts and fan out into the predentin. They correspond to the so-called Korff's fibers. Others, measuring less than 0.2 micron in diameter, are visible on the predentinal surface and follow the cell processes into the predentinal tubules. They correspond to nerve fibers. This study demonstrates that the proper use of improved SEM fixative techniques and the carbon dioxide critical-point method provides data on the relation between the different components of the predentin-pulpal border zone, which are in agreement with transmission electron microscope data.

Dental Pulp↗
PubMed1986

cDNA clones for liver cytochrome P-450s from individual aroclor-treated rats: constitutive expression of a new P-450 gene related to phenobarbital-inducible forms.

Differential hybridization and screening with cloned inserts was used to identify two families of cytochrome P-450 cDNA clones in libraries prepared from total liver poly(A)+RNA of individual Aroclor-treated rats. One family has cDNA inserts for the major phenobarbital-inducible P-450s, P-450b and P-450e. Two types of P-450e inserts were identified. In addition, irregular inserts were characterized from two clones (PB23 and PB24) of this group. The other family has cDNA inserts for the major 3-methylcholanthrene-inducible species, P-450c and P-450d. No coding sequence restriction site variants were detected among 26 P-450d and P-450c inserts analyzed. The restriction map of the irregular 2.2-kb PB23 insert has a P-450b-like portion, followed by a 3' extension that hybridizes to RNAs of 2.7 and 4.8 kb, which are also detectable with a classical P-450b probe. The PB23 insert and the 2.7- and 4.8-kb RNAs presumably represent 3' extensions of P-450b/P-450e mRNAs, polyadenylated at downstream sites. The 858-bp sequence of the PB24 insert encodes the carboxy-terminal portion of a P-450b/P-450e-like protein. There is approximately 20% divergence at the polypeptide level between the PB24 and P-450b/P-450e sequences; nevertheless, they share many essential features. A PB24-specific probe hybridizes to a 1.9-kb RNA species which is present in the liver of untreated rats and which is not appreciably induced by phenobarbital or Aroclor. The PB24 cDNA most likely represents a constitutive cytochrome P-450, related to phenobarbital-inducible forms.

Amino Acid Sequence↗
PubMed1985

Inhibition of the swallowing reflex by local application of serotonergic agents into the nucleus of the solitary tract.

Swallowing is a medullary polysynaptic reflex organized by an interneuronal network localized mainly within the nucleus of the solitary tract (NST). The existence of several putative neurotransmitters within the NST has been well demonstrated. The presence of serotonin (5-HT) in nerve terminals and fibers has been particularly well-documented. This study was therefore designed to determine the role of 5-HT in the swallowing reflex. The effects of serotonergic agents were investigated in the rat, on rhythmic swallowing elicited by long repetitive stimulation of the superior laryngeal nerve (SLN). The agents were microinjected by pressure application, within the swallowing region of the NST. Microinjections of 5-HT (0.3-5 nmol, 30-50 nl) significantly decreased the number and the amplitude of swallows elicited by stimulation of the ipsilateral SLN without changing the swallowing reflex induced by contralateral SLN stimulation. The decrease induced by 5-HT microinjections was dose-related. No significant modification of swallowing was induced by control injections of the vehicle within the active sites. Moreover, the effect of 5-HT microinjections was significantly antagonized by pretreatment with metitepine (0.4 nmol) applied locally in the NST and microinjections of quipazine (2.5 nmol) also decreased the number of swallows. It can therefore be concluded that the present findings suggest the existence within the NST of a serotonergic inhibition of the swallowing reflex elicited by laryngeal afferents.

Animals↗
PubMed1985

Identification of the medullary swallowing regions in the rat.

The aim of the present study was to identify the central structures involved in the organization of the swallowing reflex in the rat. Using concentric bipolar electrodes, the medulla and pons were systematically explored in order to determine which central areas responded to stimulation by inducing swallowing. These areas, which were located in the dorsal medulla oblongata, were the solitary tract, the nucleus of the solitary tract (NST) and the adjacent reticular formation. Stimulation of the ventral ponto-medullary regions was ineffective with regard to the initiation of the swallowing reflex. The activity of medullary swallowing neurons was recorded using extracellular microelectrodes. These swallowing neurons responded with a burst of spikes (swallowing activity) which was closely linked to the swallowing reflex elicited by stimulation of the superior laryngeal nerve (SLN). Under SLN stimulation, the activity of some of the swallowing neurons furthermore showed an initial response consisting of 1 or 2 spikes after a brief latency. According to their location and the latency of their initial response, swallowing neurons were divided into two groups. Group I neurons were located in a dorsal area of the medulla oblongata corresponding to the NST and the adjacent reticular formation. All these neurons exhibited an initial response with a very short latency (1 to 4 ms), the swallowing activity of most of these neurons started before the onset of the swallowing motor sequence. Group II neurons were located either in a ventral area corresponding to the nucleus ambiguus and the surrounding reticular formation or in a dorsal and medial area corresponding to the hypoglossal nucleus and its vicinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Radioautographic study of serotoninergic axon terminals in the rat trigeminal motor nucleus.

Serotonin (5-HT) axon terminals were demonstrated in the rat trigeminal motor nucleus (VmN) using radioautography following local injection of tritiated 5-HT. The light microscope radioautographs of the VmN showed silver grain aggregates typical of axonal varicosities having taken up the exogenous 5-HT. In electron microscope radioautographs, labeled 5-HT axon terminals took the form of unmyelinated enlargements, 0.3-2 micron in diameter (average 0.9 micron) containing small clear and large granular vesicles. Out of 182 labeled 5-HT profiles, only 4.9% showed a clear synaptic junction with dendritic branches, indicating the existence of non-synaptic as well as synaptic mechanisms for the 5-HT terminals within the VmN. An estimate of the density of 5-HT varicosities within the VmN was performed on histological radioautographs: the concentration of labeled terminals was evaluated at (1.8 +/- 0.38) X 10(6) per mm3.

Animals↗