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Biomedical subjects

L Leger

Publications and source records attributed to L Leger.

At least 19 recordsLinked to original sources
PubMed2004

Brainstem structures responsible for paradoxical sleep onset and maintenance.

This paper is dedicated to our mentor, Michel Jouvet who inspired our career and transmitted to us his passion for the study of the mechanisms responsible for paradoxical sleep genesis and also that of its still mysterious functions. We expose in the following the progresses in the knowledge in this field brought during 40 years by Michel Jouvet and his team and more recently by the members of a new CNRS laboratory in which we aim to pursue in the path opened by Michel Jouvet.

Animals↗
PubMed2001

Anatomical distribution of serotonin-containing neurons and axons in the central nervous system of the cat.

By using a monoclonal antibody to serotonin (5-HT), an immunohistochemical study was undertaken to provide a comprehensive description of the 5-HT-containing neurons and of the distribution of their axonal processes in the cat brain and spinal cord. The localization of cell bodies was comparable to that previously reported in studies using formaldehyde-induced fluorescence and other 5-HT antibodies, with a large proportion of labeled neurons in the raphe nuclei and a minor, yet not negligible number, in the ventral, lateral, and dorsal reticular formation. The ascending efferent non-varicose axons were best visualized in sagittal sections and mainly seen taking a rostroventral direction through the tegmentum. The varicose axons could be grossly classified into thin and large fibers, according to the size and shape of the immunoreactive varicosities, which were elongated (up to 2 microm in length and 1 microm in width) or round (2-4 microm in diameter). Varicose axonal arborizations invaded almost every region of the gray matter and avoided large myelinated bundles except in the spinal cord. Variations in the density of the plexuses of immunoreactive fibers generally followed the anatomical divisions and were also observed within nuclei, especially in laminated structures. Only the superior olivary complex could be regarded as devoid of 5-HT-containing axons. A few areas contained extremely rich fiber plexuses. These were the olfactory tubercle, nucleus accumbens, ventral mesencephalon, periventricular gray from the hypothalamus to the pons, facial nucleus, subdivisions of the inferior olive, and the intermediolateral nucleus in the spinal cord. Varicose axons formed tight pericellular arrays in the neocortex, mainly the ectosylvian gyrus, and in the lateral septum and medullar magnocellular nucleus. These data, combined with those of the literature concerning the synaptic versus non-synaptic mode of termination of the 5-HT-immunoreactive varicosities and the high number of distinct receptors, are indicative of the multiple possible actions of serotonin in the central nervous system.

Animals↗
PubMed2000

Direct experimental evidence of slip in hexadecane: solid interfaces

The boundary condition for the flow velocity of a Newtonian fluid near a solid wall has been probed experimentally with a novel setup using total internal reflection-fluorescence recovery after photobleaching leading to a resolution from the wall of the order of 80 nm. For hexadecane flowing on a hydrocarbon/lyophobic smooth surface, we give what we think to be the first direct experimental evidence of noticeable slip at the wall. We show that the surface roughness and the strength of the fluid-surface interactions both act on wall slip, in antagonist ways.

Journal Article↗
PubMed1999

Nitric oxide and sleep in the rat: a puzzling relationship.

To date, only a few studies indicate that nitric oxide may play a role in the regulation of the sleep-wake cycle. However, data reported are controversial and the part played by nitric oxide in sleep-wake cycle regulation still remains uncertain. In the present report, we studied the effects on sleep amounts of two different nitric oxide synthase inhibitors: N-nitro-L-arginine methyl ester, a non-selective nitric oxide synthase inhibitor, and 7-nitro-indazole, a specific inhibitor of neuronal nitric oxide synthase. The above compounds were administered via two routes, i.e. intraperitoneally or locally in the dorsal raphe nucleus, a structure involved in sleep regulation. In order to evaluate their efficiency to inhibit nitric oxide synthesis in the rat brain, they were first administered intraperitoneally to a group of animals, and the cortical release of nitric oxide was determined by means of voltammetric measurements. N-Nitro-L-arginine methyl ester (100 mg/kg, i.p.) did not affect the cortical release of nitric oxide, whereas it increased both slow-wave sleep and paradoxical sleep durations. On the contrary, 7-nitro-indazole (40 mg/kg, i.p.) significantly decreased the cortical release of nitric oxide (-25%) and paradoxical sleep duration. Furthermore, following microinjection of either N-nitro-L-arginine methyl ester or 7-nitro-indazole at 100 ng/0.20 microl into the nitric oxidergic cell area of the dorsal raphe nucleus, decreases in paradoxical sleep duration were obtained (-32.8% and -25.3%, respectively). The results obtained support the existence of a duality in the sleep regulation modalities exerted by nitric oxide, i.e. a peripheral inhibiting influence and a central facilitating role for the nitric oxide-serotoninergic neurons of the dorsal raphe nucleus.

Animals↗
PubMed1995

Sleep permissive components within the dorsal raphe nucleus in the rat.

Two peptides known for their hypnogenic properties, CLIP (corticotropin-like intermediate lobe peptide or ACTH 18-39) or VIP (vasoactive intestinal polypeptide), were injected locally into the nucleus raphe dorsalis (nRD) of rats pretreated with p-chlorophenylalanine (PCPA). During the dark period, the PCPA insomnia was primarily associated with a reduction in paradoxical sleep (PS), whereas both slow wave sleep (SWS) and PS were decreased during the light period. Immunohistochemistry of serotonin in PCPA-pretreated animals indicated a clear disappearance of 5-HT fibers in the basal hypothalamus and the nRD as compared to control animals. Local injections of CLIP or VIP in the nRD restored PS and SWS. The positive injection sites corresponded to the anatomical distribution of either CLIP or VIP fibers, i.e., the entire nRD for VIP and the antero-dorsal part of this nucleus for CLIP. The sleep effects obtained in PCPA-pretreated rats involve a non-5-HT sleep permissive component within the nRD upon which these injected peptides act.

Adrenocorticotropic Hormone↗
PubMed1995

[3H]Nisoxetine binding sites in the cat brain: an autoradiographic study.

The binding of [3H]nisoxetine, a selective inhibitor of the high-affinity noradrenaline uptake sites, was studied on frontal frozen sections of the cat brain. The highest densities in autoradiographic signal were observed in the nucleus locus coeruleus and its ascending pathways, in the area postrema and in the dorsal part of the inferior olive, the pontine nuclei, the raphe nuclei, the colliculi, the periventricular and lateral areas of the hypothalamus, the suprachiasmatic nucleus, the nucleus accumbens and the olfactory bulb. A moderately high concentration of binding sites was observed in the hippocampal formation, especially in the molecular layer of Ammon's horn, in the superficial layers of the entorhinal cortex and in the indusium griseum. Binding sites were visualized in all the subdivisions of the neocortex. The highest density of binding was generally detected in the outer edge of the superficial layer I. In some cortical areas, especially in the visual cortex, labeling with a prevalent laminar distribution in the superficial layers I-III and in the deep layers V-VI was clearly observed. Moderate to low densities of binding sites were seen in most other areas of the brain except in the white matter, the caudate nucleus and putamen, which were devoid of labeling. Overall these findings indicate a good correlation between the distribution of [3H]nisoxetine binding sites and the noradrenergic systems. Furthermore, data suggest that in several areas, high-affinity noradrenaline reuptake mechanisms could play an important role in local interactions between the noradrenergic system and the other monoaminergic systems.

Animals↗
PubMed1994

Is the nucleus raphe dorsalis a target for the peptides possessing hypnogenic properties?

Several peptides exhibiting hypnogenic properties when administered i.p., i.v. or i.c.v. are now known. No data, however, are available concerning their targets in the brain. In the present work we hypothesize that the nucleus raphe dorsalis (nRD) may be one such target since it contains 2 sleep permissive components that must be influenced for sleep to occur. One of these components is serotoninergic in nature and gates the occurrence of ponto-geniculo-occipital (PGO) waves. The other, of unknown nature, influences tonic sleep phenomena. For hypnogenic peptides, a putative mechanism permitting the triggering and maintenance of sleep might consist of influencing both the above components. In the present work, 3 hypnogenic substances, CLIP (corticotropin-Like intermediate lobe peptide), VIP (vasoactive intestinal polypeptide) and DSIP (delta sleep inducing peptide), were injected into the nRD in order to determine whether these compounds still induce sleep by local administration. To verify that such local injections do not spread outside the nRD, radiolabelled CLIP and VIP were also injected. Autoradiograms obtained with either labeled CLIP or VIP indicate that these compounds, injected in a 0.2 microliter volume, do not spread outside the nRD. The sleep data obtained confirm that CLIP, at a dose of 10 ng, induces an increase in duration of paradoxical sleep (PS); this effect is observed only for injection sites located in the dorsolateral part of the nRD, an area where CLIP immunoreactive (IR) fibers are present. VIP, at a dose of 100 ng, also increases PS duration, whereas at 10 ng, only slow wave sleep duration is increased. In this case, the positive injection sites are scattered throughout the entire nRD as are the VIP-IR fibers. With DSIP, no sleep effect was found whatever the dose used or the site injected; in the same manner, no DSIP-IR fibers have been located in this structure. These data suggest that the nRD is a target for the expression of the hypnogenic properties of CLIP and VIP, but not for DSIP. The nature of the possible mechanisms permitting such expression are discussed.

Adrenocorticotropic Hormone↗
PubMed1993

Chromatographic analysis of the enkephalin immunoreactivity in the nucleus locus coeruleus of the cat after local colchicine administration.

Cell bodies immunoreactive for methionine- and leucine-enkephalin are found in the area of the locus coeruleus (dorsolateral pons) of the cat after injection of colchicine in the ascending projections of the nucleus. Using radioimmunoassay procedures, it is shown that colchicine induces a significant increase in methionine- and leucine-enkephalin-immunoreactive material in this area of the brain. High pressure liquid chromatography analysis demonstrated that the immunoreactive materials were authentic methionine- and leucine-enkephalin. The methionine- and leucine-enkephalin patterns were identical in the colchicine injected and non-injected sides of the dorsolateral pons. It is suggested that, in this area of the brain, colchicine (i) does not significantly modify the processing of proenkephalin to form the pentapeptides methionine- and leucine-enkephalin, and (ii) does not induce the appearance of new substances reactive to the enkephalin antisera employed.

Animals↗
PubMed1990

The proenkephalin-A-derivative Met-enkephalin-Arg-Gly-Leu is not present in the feline species.

No opioid octapeptide Met-enkephalin-Arg-Gly-Leu was detected either in the brain or in the adrenal gland of the cat using a specific radioimmunoassay. Whereas it was possible to determine the Met-enkephalin and Leu-enkephalin contents. The Met-enkephalin versus Leu-enkephalin concentration ratio was around five in each area of the brain assayed. The presence of authentic Met-enkephalin and Leu-enkephalin was confirmed by high performance liquid chromatography analysis. All in all, these data seem to indicate that the cat proenkephalin is partly different from that previously analysed in mammalian species including humans, rats and cows.

Amino Acid Sequence↗
PubMed1987

Mapping of neuropeptide Y-like immunoreactivity in the feline hypothalamus and hypophysis.

The distribution of neuropeptide Y (NPY) in the cat hypothalamus and hypophysis was studied with the indirect immunofluorescence technique of Coons and co-workers (Coons, Leduc, and Connolly: J. Exp. Med. 102:49-60, 1955), which provided a detailed map of NPY-like immunoreactive neurons. The immunolabelling was detected in cell bodies, fibers, and terminallike structures widely distributed throughout the whole hypothalamus. A large population of medium-sized NPY-like immunoreactive cell bodies was localized in the area of arcuate nucleus. The number of immunoreactive cell bodies visualized was dramatically increased after intracerebroventricular injections of colchicine. Numerous immunolabelled cell bodies were also visible in the median eminence and scattered in the lateral hypothalamic area. Dense plexuses of NPY-immunoreactive fibers were observed in the arcuate nucleus, internal layer of median eminence, periventricular zone, and paraventricular nucleus. Other regions of hypothalamus displaying numerous NPY-like immunoreactive fibers included dorsal and ventrolateral hypothalamic areas. In contrast, certain hypothalamic areas were almost devoid of NPY-like immunoreactive fibers-namely, the mammillary bodies and suprachiasmatic nucleus. Finally, in neurohypophysis, bright immunofluorescent fibers were observed along the pituitary stalk and penetrating the neural lobe. These results suggest the widespread distribution of the NPY-containing neuronal systems in the cat hypothalamus and hypophysis.

Animals↗
PubMed1986

Hormone and metabolite response to weight-lifting training sessions.

Eleven weight-trained athletes (age X +/- SD = 33 +/- 5 yrs, weight = 72 +/- 10 kg) with a maximal performance in bench press at the beginning of the study (116 +/- 19 kg) were studied at rest, after a standardized submaximal training session, and after a maximal session once a month for 4 months to study the blood metabolites and hormonal changes during weight lifting. The submaximal load was six series of eight bench presses at 70% of maximal performance presses, and the maximal load was the maximal number of repetitions at the same work load. The levels of several metabolites (lactate, glycerol, triglycerides, beta-OH-butyrate) and hormones (norepinephrine and epinephrine) increased (P less than 0.05) after submaximal work and more after maximal work. Glucose, FFA, acetoacetate, insulin, testosterone, and cortisol did not change significantly or consistently. Lactate after maximal work was higher after the 4th training month (P less than 0.05). Other variables did not change much with training while the maximal number of repetitions in the last series increased slightly (P less than 0.05). In general, the changes observed were smaller than the ones reported for endurance or interval running, which use larger muscle groups. Nevertheless, weight lifting induced changes in blood metabolites which reflect a mobilization of both carbohydrates and lipids stores for energy.

Adult↗