Biomedical subjects

D Bertrand

Publications and source records attributed to D Bertrand.

At least 37 records · Page 2Linked to original sources

PubMed2003

Limits on diffuse fluxes of high energy extraterrestrial neutrinos with the AMANDA-B10 detector.

Data from the AMANDA-B10 detector taken during the austral winter of 1997 have been searched for a diffuse flux of high energy extraterrestrial muon neutrinos. This search yielded no excess events above those expected from background atmospheric neutrinos, leading to upper limits on the extraterrestrial neutrino flux measured at the earth. For an assumed E-2 spectrum, a 90% classical confidence level upper limit has been placed at a level E2Phi(E)=8.4 x 10(-7) cm(-2) s(-1) sr(-1) GeV (for a predominant neutrino energy range 6-1000 TeV), which is the most restrictive bound placed by any neutrino detector. Some specific predicted model spectra are excluded. Interpreting these limits in terms of the flux from a cosmological distributions of sources requires the incorporation of neutrino oscillations, typically weakening the limits by a factor of 2.

Journal Article↗

PubMed2003

Nicotinic acetylcholine receptors: from structure to brain function.

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels and can be divided into two groups: muscle receptors, which are found at the skeletal neuromuscular junction where they mediate neuromuscular transmission, and neuronal receptors, which are found throughout the peripheral and central nervous system where they are involved in fast synaptic transmission. nAChRs are pentameric structures that are made up of combinations of individual subunits. Twelve neuronal nAChR subunits have been described, alpha2-alpha10 and beta2-beta4; these are differentially expressed throughout the nervous system and combine to form nAChRs with a wide range of physiological and pharmacological profiles. The nAChR has been proposed as a model of an allosteric protein in which effects arising from the binding of a ligand to a site on the protein can lead to changes in another part of the molecule. A great deal is known about the structure of the pentameric receptor. The extracellular domain contains binding sites for numerous ligands, which alter receptor behavior through allosteric mechanisms. Functional studies have revealed that nAChRs contribute to the control of resting membrane potential, modulation of synaptic transmission and mediation of fast excitatory transmission. To date, ten genes have been identified in the human genome coding for the nAChRs. nAChRs have been demonstrated to be involved in cognitive processes such as learning and memory and control of movement in normal subjects. Recent data from knockout animals has extended the understanding of nAChR function. Dysfunction of nAChR has been linked to a number of human diseases such as schizophrenia, Alzheimer's and Parkinson's diseases. nAChRs also play a significant role in nicotine addiction, which is a major public health concern. A genetically transmissible epilepsy, ADNFLE, has been associated with specific mutations in the gene coding for the alpha4 or beta2 subunits, which leads to altered receptor properties.

Animals↗

PubMed2003

Neuromuscular effects of candoxin, a novel toxin from the venom of the Malayan krait (Bungarus candidus).

1 Candoxin (MW 7334.6), a novel toxin isolated from the venom of the Malayan krait Bungarus candidus, belongs to the poorly characterized subfamily of nonconventional three-finger toxins present in Elapid venoms. The current study details the pharmacological effects of candoxin at the neuromuscular junction. 2 Candoxin produces a novel pattern of neuromuscular blockade in isolated nerve-muscle preparations and the tibialis anterior muscle of anaesthetized rats. In contrast to the virtually irreversible postsynaptic neuromuscular blockade produced by curaremimetic alpha-neurotoxins, the neuromuscular blockade produced by candoxin was rapidly and completely reversed by washing or by the addition of the anticholinesterase neostigmine. 3 Candoxin also produced significant train-of-four fade during the onset of and recovery from neuromuscular blockade, both, in vitro and in vivo. The fade phenomenon has been attributed to a blockade of putative presynaptic nicotinic acetylcholine receptors (nAChRs) that mediate a positive feedback mechanism and maintain adequate transmitter release during rapid repetitive stimulation. In this respect, candoxin closely resembles the neuromuscular blocking effects of d-tubocurarine, and differs markedly from curaremimetic alpha-neurotoxins that produce little or no fade. 4 Electrophysiological experiments confirmed that candoxin produced a readily reversible blockade (IC(50) approximately 10 nM) of oocyte-expressed muscle (alphabetagammadelta) nAChRs. Like alpha-conotoxin MI, well known for its preferential binding to the alpha/delta interface of the muscle (alphabetagammadelta) nAChR, candoxin also demonstrated a biphasic concentration-response inhibition curve with a high- (IC(50) approximately 2.2 nM) and a low- (IC(50) approximately 98 nM) affinity component, suggesting that it may exhibit differential affinities for the two binding sites on the muscle (alphabetagammadelta) receptor. In contrast, curaremimetic alpha-neurotoxins have been reported to antagonize both binding sites with equal affinity.

Amino Acid Sequence↗

PubMed2003

Prevalence and risk factors of STDs in rural Haiti: implications for policy and programming in resource-poor settings.

The goals of the current study are to: (1) estimate the prevalence of sexually transmitted diseases (STDs) among women accessing services at a women's health clinic in rural Haiti; and (2) identify risk factors for STDs in this setting. The design is a case control study, comparing risk factors for women who demonstrated positive laboratory results for chlamydia and/or gonorrhoea to women who tested negative for both of these pathogens. The strongest risk factors for chlamydia and/or gonorrhoea were largely economic variables, with work as a domestic servant increasing the risk by four-fold. Working as a market vendor reduced a woman's risk of having an STD by approximately 45%. Given that economic factors are strongly associated with STD risk in this context, one potential mechanism for reducing the risk of STDs, including HIV, would involve increasing economic opportunities for women in rural Haiti.

Adolescent↗

PubMed2003

Regulating the regulators: the role of nicotinic acetylcholine receptors in human epilepsy.

Recent advances in genetic mapping have linked several epilepsies to mutations in genes coding for ion channel proteins. Mutations in genes coding for the alpha(4) and beta(2) subunits of the nicotinic acetylcholine receptor have been found in some families suffering from autosomal dominant nocturnal frontal lobe epilepsy. Expression of mutant alleles in the Xenopus oocyte expression system has allowed functional characterization of these mutant receptors at the cellular level. The challenge is now to design therapeutic strategies based on this knowledge of how receptor function is altered in certain epilepsies.

Animals↗

PubMed2002

Expression of an alpha7 duplicate nicotinic acetylcholine receptor-related protein in human leukocytes.

We examined the potential expression and function of alpha7 nicotinic acetylcholine receptors (nAChRs) in leukocytes. RT-PCR with alpha7 specific primers revealed the presence of the receptor mRNA in leukocytes. Immunoblotting and immunofluorescence experiments demonstrated the expression of a protein that is recognized by alpha7 specific antibodies. However, nicotine and acetylcholine (ACh) failed to elicit current in leukocytes. Binding experiments with alpha-bungarotoxin rhodamine conjugated were negative, illustrating the absence of a high-affinity binding site. RT-PCR analysis revealed the selective expression of the dupalpha7 mRNA. These data indicate that leukocytes express in their membrane the dupalpha7 protein but its physiological role remains to be identified.

Antibody Specificity↗

PubMed2002

Nicotinic cholinergic activation of magnocellular neurons of the hypothalamic paraventricular nucleus.

The aim of the present work was to determine whether paraventricular neurons possess functional acetylcholine nicotinic receptors. Using infrared videomicroscopy and differential interference contrast optics, we performed whole-cell recordings in hypothalamic slices containing the paraventricular nucleus. Acetylcholine, locally applied by pressure microejection in the presence of the muscarinic antagonist atropine, evoked a rapidly rising inward current in paraventricular magnocellular endocrine neurons. This current persisted in the presence of blockers of synaptic transmission. It could be reversibly suppressed by nanomolar concentrations of methyllycaconitine, a selective antagonist of alpha 7-containing nicotinic receptors, but was insensitive to micromolar concentrations of dihydro-beta-erythroidine, an antagonist acting preferentially on non-alpha 7 nicotinic receptors. In addition, the effect of acetylcholine could be mimicked by exo-2-(2-pyridyl)-7-azabicyclo[2.2.1]heptane, a recently synthesized nicotinic agonist specific for alpha 7 receptors. Acetylcholine also desensitized paraventricular nicotinic receptors. Desensitization was pronounced and recovery from desensitization was rapid, consistent with the notion that paraventricular nicotinic receptors contain the alpha 7 subunit. Nicotinic currents could not be evoked in paraventricular parvocellular neurons, suggesting that these neurons are devoid of functional nicotinic receptors. The electrophysiological data were corroborated by light microscopic autoradiography, showing that [(125)I]alpha-bungarotoxin binding sites are present in all the magnocellular divisions of the paraventricular nucleus but are undetectable in other areas of this nucleus. Immunohistochemistry, performed using antibodies directed against vasopressin and oxytocin, indicated that responsiveness to nicotinic agonists was a property of vasopressin as well as of oxytocin magnocellular endocrine neurons, in both the paraventricular and the supraoptic nucleus. We conclude that nicotinic agonists can influence the magnocellular neurosecretory system by directly increasing the excitability of magnocellular neurons. By contrast, they are probably without direct effects on paraventricular parvocellular neurons.

Acetylcholine↗

PubMed2002

Cerebrospinal fluid concentrations of atracurium, laudanosine and vecuronium following clinical subarachnoid hemorrhage.

BACKGROUND: Neuromuscular blocking agents may exert central nervous system effects when they reach the brain. This study assessed the concentrations and the time course of passage of vecuronium, atracurium, and its metabolite laudanosine in the cerebrospinal fluid (CSF) of patients undergoing intracranial aneurysm clipping. METHODS: Twenty-five patients with subarachnoid hemorrhage were randomly allocated to receive an intravenous infusion of vecuronium (n=13) or atracurium (n=12). Arterial blood and lumbar CSF were sampled before and 1, 2, 3, 4 and 8 h after the start of the relaxant infusion. The samples were analyzed by liquid chromatography-electrospray ionization mass spectrometry (vecuronium) and high-pressure liquid chromatography (atracurium and laudanosine). RESULTS: The data of 20 patients (10 in both groups) were analyzed. In 11 CSF samples from five patients atracurium was detected in concentrations from 10 to 50 ng/ml. Laudanosine was retrieved in all CSF samples at 1, 2, 3, 4 and 8 h; the highest CSF concentration of laudanosine occurred at 3 h [38 (18-63) ng/ml: median (range)]. Vecuronium was not found in any CSF sample. CONCLUSION: Significant concentrations of atracurium and laudanosine but not of vecuronium were detected in the CSF of patients during and immediately after intracranial aneurysm surgery.

Adolescent↗

PubMed2002

How mutations in the nAChRs can cause ADNFLE epilepsy.

PURPOSE: The linkage between autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) and neuronal nicotinic acetylcholine receptor has been strongly reinforced by the report of five distinct mutations in the two genes coding for the major brain alpha4beta2 nicotinic acetylcholine (ACh) receptors. As a first step toward understanding the basic mechanisms underlying this genetically transmissible neurologic disorder, we examined the similarities and differences of the functional properties displayed by naturally occurring mutant forms of this ligand-gated channel. METHODS: Functional studies of neuronal nicotinic ACh receptors reconstituted in Xenopus oocytes were designed to analyze the common traits displayed by the different mutations associated with ADNFLE. RESULTS: Coexpression of the control and mutated alleles harboring the alpha4S248F mutation obtained from patient DNAs yielded ACh-evoked currents of amplitude comparable to the control responses but with a higher sensitivity and desensitization to the natural agonist. Alternatively, the other mutants (alpha4L776ins3, alpha4S252L, and beta2V287M) displayed an increased ACh sensitivity without pronounced desensitization. In addition, whereas a reduction of calcium permeability was observed for the mutants (alpha4S248F and alpha4L776ins3), no significant modification of ionic selectivity could be detected in the alpha4S252L mutation. Hence increase in ACh sensitivity is the only common characteristic so far observed between the four naturally occurring mutant receptors investigated. CONCLUSIONS: Analyses of functional properties of four nAChR mutants associated with ADNFLE indicate that a gain of function of these mutant receptors may be at the origin of the neuronal network dysfunction that causes the epileptic seizures. These data are discussed in the context of our latest knowledge of the pyramidal cell function.

Acetylcholine↗

PubMed2001

Neuronal nicotinic receptors: from protein structure to function.

Neuronal nicotinic acetylcholine receptors are a prototype of ligand-gated channels that mediate transmission in the central and peripheral nervous system. Structure-function studies performed at the amino acid level are now unraveling the determinant residues either for the properties of the ligand-binding domain or the ionic pore. In this work we review, in the light of the latest finding, the structure-function relationship of these receptors and their implication in neurological diseases.

Allosteric Site↗

PubMed2001

Observation of high-energy neutrinos using Cerenkov detectors embedded deep in Antarctic ice.

Neutrinos are elementary particles that carry no electric charge and have little mass. As they interact only weakly with other particles, they can penetrate enormous amounts of matter, and therefore have the potential to directly convey astrophysical information from the edge of the Universe and from deep inside the most cataclysmic high-energy regions. The neutrino's great penetrating power, however, also makes this particle difficult to detect. Underground detectors have observed low-energy neutrinos from the Sun and a nearby supernova, as well as neutrinos generated in the Earth's atmosphere. But the very low fluxes of high-energy neutrinos from cosmic sources can be observed only by much larger, expandable detectors in, for example, deep water or ice. Here we report the detection of upwardly propagating atmospheric neutrinos by the ice-based Antarctic muon and neutrino detector array (AMANDA). These results establish a technology with which to build a kilometre-scale neutrino observatory necessary for astrophysical observations.

Journal Article↗

PubMed2001

Chronic exposure to nicotine upregulates the human (alpha)4((beta)2 nicotinic acetylcholine receptor function.

Widely expressed in the brain, the alpha4beta2 nicotinic acetylcholine receptor (nAChR) is proposed to play a major role in the mechanisms that lead to and maintain nicotine addiction. Using the patch-clamp technique and pharmacological protocols, we examined the consequences of long-term exposure to 0.1-10 micrometer nicotine in K-177 cells expressing the major human brain alpha4beta2 receptor. The acetylcholine dose-response curves are biphasic and revealed both a high- and a low-affinity component with apparent EC(50) values of 1.6 and 62 micrometer. Ratios of receptors in the high- and low-affinity components are 25 and 75%, respectively. Chronic exposure to nicotine or nicotinic antagonists [dihydro-beta-erytroidine (DHbetaE) or methyllycaconitine (MLA)] increases the fraction of high-affinity receptors up to 70%. Upregulated acetylcholine-evoked currents increase by twofold or more and are less sensitive to desensitization. Functional upregulation is independent of protein synthesis as shown by the lack of effect of 20 micrometer cycloheximide. Single-channel currents recorded with 100 nm acetylcholine show predominantly high conductances (38.8 and 43.4 pS), whereas additional smaller conductances (16.7 and 23.5 pS) were observed with 30 micrometer acetylcholine. In addition, long-term exposure to dihydro-beta-erytroidine increases up to three times the frequency of channel openings. These data indicate, in contrast to previous studies, that human alpha4beta2 nAChRs are functionally upregulated by chronic nicotine exposure.

Acetylcholine↗

PubMed2001

Desensitization of neuronal nicotinic acetylcholine receptors conferred by N-terminal segments of the beta 2 subunit.

Desensitization is a general property of ligand-gated ion channels. Because of a wide array of available subunit combinations, it generates different time constants for channel closure, thereby modulating the processing of information in the brain. Within the family of neuronal nicotinic acetylcholine receptors (nAChRs), alpha 3 beta 2 and alpha 3 beta 4 receptors display contrasting properties of desensitization. When measured using two-electrode voltage-clamp in Xenopus oocytes, desensitization results in current decreases 2 s after initiation of acetylcholine application by 94% for alpha 3 beta 2 receptors, but only by 6% in the case of alpha 3 beta 4 receptors. Desensitization was analyzed by inserting different portions of the beta2 into the beta 4 subunit. Residues 1--212 of the beta2 subunit were able to confer 78% desensitization in 2 s, while smaller chimeras revealed desensitization in 2 s conferred by residues 1--42 alone to a level of 50%, by residues 72--89 to a level of 74%, and by residues 96--212 to a level of 77%. Some long-term (25 min) effects of desensitization driven by acetylcholine were found to rely partially on the same elements, including an enhancement mediated by residues 1--95 and 96--212 of the beta 2 subunit individually. Our results reveal that desensitization relies independently on diverse portions of the extracellular domain of the beta 2 subunit. Phenotype of alpha 3 beta 4 involves, in contrast, complex structural requirements involving residues dispersed throughout the entire N-terminal domain of the beta 4 subunit.

Acetylcholine↗

PubMed2001

"Weak toxin" from Naja kaouthia is a nontoxic antagonist of alpha 7 and muscle-type nicotinic acetylcholine receptors.

A novel "weak toxin" (WTX) from Naja kaouthia snake venom competes with [(125)I]alpha-bungarotoxin for binding to the membrane-bound Torpedo californica acetylcholine receptor (AChR), with an IC(50) of approximately 2.2 microm. In this respect, it is approximately 300 times less potent than neurotoxin II from Naja oxiana and alpha-cobratoxin from N. kaouthia, representing short-type and long-type alpha-neurotoxins, respectively. WTX and alpha-cobratoxin displaced [(125)I]alpha-bungarotoxin from the Escherichia coli-expressed fusion protein containing the rat alpha7 AChR N-terminal domain 1-208 preceded by glutathione S-transferase with IC(50) values of 4.3 and 9.1 microm, respectively, whereas for neurotoxin II the IC(50) value was >100 microm. Micromolar concentrations of WTX inhibited acetylcholine-activated currents in Xenopus oocyte-expressed rat muscle AChR and human and rat alpha7 AChRs, inhibiting the latter most efficiently (IC(50) of approximately 8.3 microm). Thus, a virtually nontoxic "three-fingered" protein WTX, although differing from alpha-neurotoxins by an additional disulfide in the N-terminal loop, can be classified as a weak alpha-neurotoxin. It differs from the short chain alpha-neurotoxins, which potently block the muscle-type but not the alpha7 AChRs, and is closer to the long alpha-neurotoxins, which have comparable potency against the above-mentioned AChR types.

Amino Acid Sequence↗

PubMed2001

Role of neuronal nicotinic receptors in the transmission and processing of information in neurons of the central nervous system.

The properties of nicotinic acetylcholine receptors (nAChRs) were studied following exogenous expression in a host system or using whole-cell recordings in brain slices, autoradiography and immunohistochemistry. When expressed in HEK-293 cells, alpha 4 beta 2 nAChRs displayed both a high and a low affinity component. The ratio of these two states was modified by chronic nicotine exposure, resulting in an enhanced sensitivity and a marked reduction in desensitization. Mutations in the gene coding for the alpha 4 subunit are responsible for a particular form of nocturnal epilepsy. When expressed in Xenopus oocytes, alpha 4 beta 2 nAChRs containing these mutations displayed distinct alterations in agonist affinity, desensitization and calcium permeability. Magnocellular endocrine neurons in the supraoptic (SO) nucleus of the hypothalamus were found to express functional alpha 7-containing nAChRs, which could play a role in regulating neurohypophysial peptide secretion. Facial (VII), hypoglossal (XII) and vagal (X) motoneurons of young rats responded to ACh by a fast inward current. The nAChRs present in VII and XII nuclei were of the non-alpha 7-containing type, whereas those present in the X nucleus contained the alpha 7 subunit. In Bcl-2 transgenic mice, facial nerve axotomy caused nAChRs downregulation by interfering negatively with the expression of the alpha 4 subunit. Binding sites corresponding to alpha 7-containing nAChRs were also detected in spinal motor nuclei and axotomy provoked a reduction of the binding. Together, these data indicate that long-term exposure to nicotine can promote neuroadaptive changes in nAChRs and that genetic alterations of neuronal nAChRs can result in transmissible neurological diseases. They also suggest that these receptors probably play a role in the central regulation of autonomic functions, as well as in motor control.

Animals↗

PubMed2001

Ion channel variation causes epilepsies.

The discovery of genetically transmissible form of epilepsy associated with a mutation in a gene that codes for a subunit of a ligand-gated channel shined a new light in this field of neurological diseases. Because this gene (CHRNA4) codes for a neuronal nicotinic acetylcholine receptor subunit, functional studies could be designed to evaluate the alterations caused by this mutation. Since this initial observation, five mutations were identified and determination of their functional properties initiated. These experiments were extended to pairwise expression of the control and mutated allele to mimic the heterozygote human genotype. The first common functional trait identified so far, in four of these mutants, is an increased sensitivity to the acetylcholine, suggesting that these mutations may cause a gain of function. An alternative possibility that cannot be excluded is that conditions in the brain are such that these higher responding receptors may be more prone to desensitization. The importance of ionic channels as cause of epilepsies was further demonstrated with the identification of the association between the benign neonatal epilepsy and mutations in genes coding for potassium channel subunits (KCNQ2, KCNQ3). Additional evidences were brought by the identification of mutations in voltage-dependent sodium channels (SCN1A, SCN1B) in a form of generalized epilepsy with febrile seizures.

Acetylcholine↗

PubMed2001

Neurotoxicity of channel mutations in heterologously expressed alpha7-nicotinic acetylcholine receptors.

Nicotinic acetylcholine receptors (nAChR) composed of chick alpha7 subunits mutated to threonine at amino acid valine-251 in the putative channel-lining M2 domain were expressed heterologously in several neuron-like and non-neuronal mammalian cell lines. Expression of mutant alpha7-nAChR is toxic to neuron-like cells of the human neuroblastoma cell lines SH-SY5Y and IMR-32, but not to several other cell types. Growth in the presence of the alpha7-nAChR antagonist methyllycaconitine (MLA) protects against neurotoxicity, as does gradual downregulation of functional, mutant alpha7-nAChR in surviving transfected SH-SY5Y cells. Relative to wild-type alpha7-nAChR, functional alpha7-nAChR mutants show a higher affinity for agonists, slower rates of desensitization, and sensitivity to dihydro-beta-erythroidine (DHbetaE) as an agonist, but they retain sensitivity to MLA as a competitive antagonist. These findings demonstrate that expression of hyperfunctional, mutant forms of Ca2+-permeable alpha7-nAChR is toxic to neuron-like cells.

Aconitine↗

PubMed2001

Neuronal nicotinic receptors: from structure to function.

Molecular identification of the genes and resulting protein sequences for a large number of nicotinic acetylcholine receptor (nAChR) subunits has stimulated numerous studies highlighting their role in several human behaviors including neurological disorders and nicotine addiction. This receptor gene family is likely to be involved in release of multiple neurotransmitters in both brain and periphery that mediate sensitivity and tolerance to nicotine. Recent findings also suggest that alterations in these receptors may lead to neurological diseases, some associated with increased incidence of smoking. This review addresses current knowledge of nicotinic receptor structure, regulation of expression, and function, in both normal and psychiatric subjects.

Brain↗