Biomedical subjects

Jean-Pierre Changeux

Publications and source records attributed to Jean-Pierre Changeux.

At least 19 recordsLinked to original sources

PubMed2006

The Ferrier Lecture 1998. The molecular biology of consciousness investigated with genetically modified mice.

The question is raised of the relevance of experimental work with the mouse and some of its genetically modified individuals in the study of consciousness. Even if this species does not go far beyond the level of 'minimal consciousness', it may be a useful animal model to examine the elementary building blocks of consciousness using the methods of molecular biology jointly with investigations at the physiological and behavioural levels. These building blocks which are anticipated to be universally shared by higher organisms (from birds to humans) may include: (i) the access to multiple states of vigilance, like wakefulness, sleep, general anaesthesia, etc.; (ii) the capacity for global integration of several sensory and cognitive functions, together with behavioural flexibility resulting in what is referred to as exploratory behaviour, and possibly a minimal form of intentionality. In addition, the contribution of defined neuronal nicotinic receptors species to some of these processes is demonstrated and the data discussed within the framework of recent neurocomputational models for access to consciousness.

Animals↗

PubMed2006

A prokaryotic proton-gated ion channel from the nicotinic acetylcholine receptor family.

Ligand-gated ion channels (LGICs) mediate excitatory and inhibitory transmission in the nervous system. Among them, the pentameric or 'Cys-loop' receptors (pLGICs) compose a family that until recently was found in only eukaryotes. Yet a recent genome search identified putative homologues of these proteins in several bacterial species. Here we report the cloning, expression and functional identification of one of these putative homologues from the cyanobacterium Gloeobacter violaceus. It was expressed as a homo-oligomer in HEK 293 cells and Xenopus oocytes, generating a transmembrane cationic channel that is opened by extracellular protons and shows slow kinetics of activation, no desensitization and a single channel conductance of 8 pS. Electron microscopy and cross-linking experiments of the protein fused to the maltose-binding protein and expressed in Escherichia coli are consistent with a homo-pentameric organization. Sequence comparison shows that it possesses a compact structure, with the absence of the amino-terminal helix, the canonical disulphide bridge and the large cytoplasmic domain found in eukaryotic pLGICs. Therefore it embodies a minimal structure required for signal transduction. These data establish the prokaryotic origin of the family. Because Gloeobacter violaceus carries out photosynthesis and proton transport at the cytoplasmic membrane, this new proton-gated ion channel might contribute to adaptation to pH change.

Amino Acid Sequence↗

PubMed2006

Nicotine and serotonin in immune regulation and inflammatory processes: a perspective.

Nicotine and serotonin modulate the innate and adaptive immune responses and the inflammatory states. Several nicotinic cholinergic and serotonergic receptor subtypes have been characterized in B and T lymphocytes, monocytes, macrophages, and dendritic cells. The use of knockout mice has allowed a better characterization of nicotinic receptors and their role in anti-inflammatory processes in these cells. Cytokines play a crucial role in controlling inflammatory reactions. Nicotine and serotonin have been reported to regulate cytokine release. Cholinergic mechanisms also play an important role in inflammation through endogenous acetylcholine. Nicotine mimics this effect by activating the cholinergic anti-inflammatory pathways. New concepts of reciprocal interactions between nicotine and serotonin are emerging. The role of nicotine as an anti-inflammatory agent has been established, whereas that of serotonin remains more controversial.

Animals↗

PubMed2006

Implications of the quaternary twist allosteric model for the physiology and pathology of nicotinic acetylcholine receptors.

Nicotinic acetylcholine receptors (nAChR) are pentameric ligand-gated ion channels composed of subunits that consist of an extracellular domain that carries the ligand-binding site and a distinct ion-pore domain. Signal transduction results from the allosteric coupling between the two domains: the distance from the binding site to the gate of the pore domain is 50 A. Normal mode analysis with a C(alpha) Gaussian network of a new structural model of the neuronal alpha7 nAChR showed that the lowest mode involves a global quaternary twist motion that opens the ion pore. A molecular probe analysis, in which the network is modified at each individual amino acid residue, demonstrated that the major effect is to change the frequency, but not the form, of the twist mode. The largest effects were observed for the ligand-binding site and the Cys-loop. Most (24/27) of spontaneous mutations known to cause congenital myasthenia and autosomal dominant nocturnal frontal lobe epilepsy are located either at the interface between subunits or, within a given subunit, at the interface between rigid blocks. These interfaces are modified significantly by the twist mode. The present analysis, thus, supports the quaternary twist model of the nAChR allosteric transition and provides a qualitative interpretation of the effect of the mutations responsible for several receptor pathologies.

Allosteric Regulation↗

PubMed2006

Live imaging of neural structure and function by fibred fluorescence microscopy.

Only a few methods permit researchers to study selected regions of the central and peripheral nervous systems with a spatial and time resolution sufficient to image the function of neural structures. Usually, these methods cannot analyse deep-brain regions and a high-resolution method, which could repeatedly probe dynamic processes in any region of the central and peripheral nervous systems, is much needed. Here, we show that fibred fluorescence microscopy-which uses a small-diameter fibre-optic probe to provide real-time images-has the spatial resolution to image various neural structures in the living animal, the consistency needed for a sequential, quantitative evaluation of axonal degeneration/regeneration of a peripheral nerve, and the sensitivity to detect calcium transients on a sub-second timescale. These unique features should prove useful in many physiological studies requiring the in situ functional imaging of tissues in a living animal.

Animals↗

PubMed2006

Nicotinic modulation of network and synaptic transmission in the immature hippocampus investigated with genetically modified mice.

The hippocampus, a key structure in learning and memory processes, receives a powerful cholinergic innervation from the septum and contains nicotinic acetylcholine receptors (nAChRs). Early in postnatal development, activation of nAChRs by nicotine or endogenous acetylcholine contributes to enhance synaptic signalling. Here, the patch-clamp technique was used to assess the contribution of alpha7 and beta2-containing (alpha7* and beta2*) nAChRs to nicotine-elicited modulation of GABAergic and glutamatergic activity at the network and single-cell level in the immature hippocampus of wild-type (WT), alpha7-/- and beta2-/- mice. We found that alpha7* and beta2* nAChRs were sufficient to modulate nicotine-induced increase in frequency of spontaneously occurring giant depolarizing potentials (GDPs), which are generated at the network level by the synergistic action of glutamate and depolarizing GABA, and thought to play a crucial role in neuronal wiring. However, alpha7* but not beta2* receptors were essential in nicotine-induced increase of interictal discharge frequency recorded after postnatal day 3 in the presence of bicuculline, when GABA shifted from the depolarizing to the hyperpolarizing direction. To correlate these observations with nicotine-elicited changes in synaptic transmission, we recorded spontaneous GABAergic and glutamatergic postsynaptic currents in pyramidal cells and interneurons localized in stratum oriens, stratum pyramidale and stratum radiatum, in slices obtained from WT and knock-out animals. We found that early in postnatal life alpha7* and beta2* nAChRs exert a fine regional modulation of GABAergic and glutamatergic transmission that underlies nicotine-elicited changes in network synchronization.

Acetylcholine↗

PubMed2006

Monitoring protein interactions in the living cell through the fluorescence decays of the cyan fluorescent protein.

Using fluorescence lifetime microspectroscopy and imaging techniques, we have studied the fluorescence of cyan fluorescent protein (CFP) transiently expressed in HEK-293 cells, in the presence or absence of its fluorescence resonance energy transfer (FRET) partner, yellow fluorescent protein (YFP). When the two proteins are attached through a 27-amino-acid linker, a 33 % average efficiency of intramolecular energy transfer is accurately determined inside the cell. Additionally, we observe a systematic quenching of the CFP fluorescence with increasing levels of protein expression. This quenching cannot be accounted for by formation of the previously described dimer of GFP-related proteins, since its magnitude is unchanged when the fluorescent proteins carry the mutation A206K shown to dissociate this dimer in vitro. Even when the intracellular protein concentration largely exceeds the in vitro dissociation constant of the dimer, self-association remains undetectable, either between free proteins or intramolecularly within the CFP-YFP construct. Instead, the detailed concentration effects are satisfactorily accounted for by a model of intermolecular, concentration-dependent energy transfer, arising from molecular proximity and crowding. In the case of CFP alone, we suggest that self-quenching could result from a pseudo-homo FRET mechanism between different, spectrally shifted emissive forms of the protein. These phenomena require careful consideration in intracellular FRET studies.

Bacterial Proteins↗

PubMed2006

Hierarchical control of dopamine neuron-firing patterns by nicotinic receptors.

Nicotine elicits dopamine release by stimulating nicotinic acetylcholine receptors (nAChRs) on dopaminergic neurons. However, a modulation of these neurons by endogenous acetylcholine has not been described. We recorded, in vivo, the spontaneous activity of dopaminergic neurons in the VTA of anaesthetized wt and nAChR knockout mice and their response to nicotine injections. Deleting alpha7 or beta2 subunits modified the spontaneous firing patterns, demonstrating their direct stimulation by endogenous acetylcholine. Quantitative analysis further revealed four principal modes of firing, each depending on the expression of particular nAChR subunits and presenting unique responses to nicotine. The prominent role of the beta2 subunit was further confirmed by its selective lentiviral reexpression in the VTA. These data suggest a hierarchical control of dopaminergic neuron firing patterns by nAChRs: activation of beta2*-nAChR switches cells from a resting to an excited state, whereas activation of alpha7*-nAChRs finely tunes the latter state but only once beta2*-nAChRs have been activated.

Action Potentials↗

PubMed2006

Inhibition of both alpha7* and beta2* nicotinic acetylcholine receptors is necessary to prevent development of sensitization to cocaine-elicited increases in extracellular dopamine levels in the ventral striatum.

RATIONALE: Several studies have suggested that nicotine treatment can modulate the behavioral and neurochemical responses to other psychostimulants, such as cocaine. OBJECTIVES: The current study examined the hypothesis that nicotinic acetylcholine receptor (nAChR) blockade influences the ability of cocaine to elicit increases in extracellular dopamine levels. MATERIALS AND METHODS: Pharmacological studies using nicotinic antagonists as well as genetic inactivation of beta2* nAChRs were used to determine the effect of nAChR blockade on dopamine levels in ventral striatum elicited by acute or repeated administrations of cocaine in mice. RESULTS: Administration of mecamylamine (a general nicotinic antagonist that is not highly selective for individual nAChR subtypes) or co-administration of methyllycaconitine (a more selective antagonist of alpha7* nAChRs) with dihydro-beta-erythroidine (a more selective antagonist of beta2* nAChRs and other heteromeric nAChR subtypes) prevented sensitization of cocaine-elicited increases in extracellular DA levels in the ventral striatum in wild-type mice. In contrast, neither of the more specific antagonists alone was effective in preventing sensitization. Finally, methyllycaconitine administration prevents sensitization in beta2-/- mice but not in beta2+/+ or wild-type mice. CONCLUSIONS: These data indicate that inhibition of both alpha7* and beta2* nAChRs is necessary to prevent development of sensitization of cocaine-elicited increases in extracellular dopamine levels in the ventral striatum of mice.

Aconitine↗

PubMed2006

Conscious, preconscious, and subliminal processing: a testable taxonomy.

Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious and non-conscious visual processing, but their results appear inconsistent. Some support a correlation of conscious perception with early occipital events, others with late parieto-frontal activity. Here we attempt to make sense of these dissenting results. On the basis of the global neuronal workspace hypothesis, we propose a taxonomy that distinguishes between vigilance and access to conscious report, as well as between subliminal, preconscious and conscious processing. We suggest that these distinctions map onto different neural mechanisms, and that conscious perception is systematically associated with surges of parieto-frontal activity causing top-down amplification.

Brain↗

PubMed2006

Reinforcing effects of nicotine microinjections into the ventral tegmental area of mice: dependence on cholinergic nicotinic and dopaminergic D1 receptors.

We used an intracranial self-administration (ICSA) procedure to assess the involvement of the ventral tegmental area (VTA) nicotinic receptors in the rewarding effects of nicotine. We then challenged intra-VTA nicotine self-administration via systemic or local injections of dopamine (DA)-D1 and nicotinic receptor antagonists. C57BL/6J mice were stereotaxically implanted unilaterally with a guide cannula above the VTA. After 1 week of recovery, mice were allowed to discriminate between two arms of a Y-maze over seven daily sessions, one arm being reinforced by intracranial nicotine microinjection. Mice exhibited nicotine self-administration at both doses tested, i.e. 10 ng (21.6 pmol) and 100 ng (216 pmol)/50-nl injection. In contrast, mice receiving a 216-pmol nicotine dose 0.8 mm above VTA performed at chance level. Once the ICSA response was acquired, systemic pretreatment with the DA-D1 receptor antagonist SCH 23390 (25 microg/kg i.p.) or co-infusion of the nAChR antagonist DHbetaE with nicotine disrupted ICSA. Replacement of SCH 23390 by vehicle, or withdrawal of DHbetaE from nicotine/DHbetaE mixed solutions led to recovery of intra-VTA nicotine self-administration. We conclude that nicotinic receptors in the VTA, presumably alpha4beta2 nAChRs are critically to mediate the rewarding effects of nicotine and that DA-D1 receptors are also directly implicated.

Animals↗

PubMed2006

Mechanism of Cl- selection by a glutamate-gated chloride (GluCl) receptor revealed through mutations in the selectivity filter.

To learn about the mechanism of ion charge selectivity by invertebrate glutamate-gated chloride (GluCl) channels, we swapped segments between the GluClbeta receptor of Caenorhabditis elegans and the vertebrate cationic alpha7-acetylcholine receptor and monitored anionic/cationic permeability ratios. Complete conversion of the ion charge selectivity in a set of receptor microchimeras indicates that the selectivity filter of the GluClbeta receptor is created by a sequence connecting the first with the second transmembrane segments. A single substitution of a negatively charged residue within this sequence converted the selectivity of the GluClbeta receptor's pore from anionic to cationic. Unexpectedly, elimination of the charge of each basic residue of the selectivity filter, one at a time or concomitantly, moderately reduced the P(Cl)/P(Na) ratios, but the GluClbeta receptor's mutants retained high capacity to select Cl(-) over Na(+). These results indicate that, unlike the proposed case of anionic Gly- and gamma-aminobutyric acid-gated ion channels, positively charged residues do not play the key role in the selection of ionic charge by the GluClbeta receptor. Taken together with measurements of the effective open pore diameter and with structural modeling, the study presented here collectively indicates that in the most constricted part of the open GluClbeta receptor's channel, Cl(-) interacts with backbone amides, where it undergoes partial dehydration necessary for traversing the pore.

Amino Acid Sequence↗

PubMed2006

Nicotine enhances intracellular nicotinic receptor maturation: a novel mechanism of neural plasticity?

Nicotine addiction, the primary cause of tobacco consumption, is mediated through nicotine binding to brain nicotinic acetylcholine receptor (nAChRs). Upon chronic exposure, nicotine elicits a cascade of events, starting with nAChR activation and desensitization, followed by a long term up-regulation that corresponds to an increase in the number of the high affinity nAChRs, a paradoxical process that occurs in the brain of smokers. Recent investigation of the maturation and trafficking of the major brain alpha4beta2 nAChR demonstrates that up-regulation is initiated in the endoplasmic reticulum soon after protein translation. The data thus far accumulated provide evidence that nicotine elicits up-regulation by promoting maturation of nAChR precursors that would otherwise be degraded. This "maturational enhancer" action of nicotine probably contributes to the long term effect of chronic nicotine, and suggests a novel mechanism of neuronal plasticity through an yet unknown endogenous substance which would modulate the receptor expression under physiological conditions.

Animals↗

PubMed2006

The beta2 but not alpha7 subunit of the nicotinic acetylcholine receptor is required for nicotine-conditioned place preference in mice.

RATIONALE: Tobacco use is implicated in approximately 440,000 deaths per year, making it the leading cause of preventable death in the United States. Although it is generally recognized that tobacco use is correlated with a variety of health-related complications, many smokers are unsuccessful in their efforts to stop smoking using current cessation therapies. OBJECTIVES: Given that nicotine is the addictive component of tobacco, successful smoking cessation therapies must address the various processes, including reward, which contribute to nicotine addiction. As such, determining the nicotinic receptor subtypes involved in nicotine reward is of utmost importance to understanding how nicotine addiction progresses. METHODS: Conditioned place preference (CPP) in three-chamber conditioning boxes was performed. For antagonist studies, drug was given on all conditioning sessions 10 min before nicotine or saline injection and placement in the boxes. RESULTS: We have demonstrated that a pretreatment with the alpha4beta2 subunit of the nicotinic acetylcholine receptor (nAChR) antagonist dihydro-beta-erythroidine (2.0 mg/kg, s.c.) blocked nicotine (0.5 mg/kg, s.c.) CPP in wild-type mice (C57BL/6 mice). In contrast, pretreatment with an antagonist of the alpha7 subunit of the nAChR, methyllycaconitine (MLA, 5.0 or 10.0 mg/kg, s.c.), had no effect on this behavior. Finally, we showed that mice lacking the beta2 subunit of the nAChR did not exhibit nicotine CPP while alpha7 knock-out mice did. CONCLUSION: Taken together, these data suggest that the beta2 subunit of the nAChR is critically involved in nicotine reward as measured by CPP.

Aconitine↗

PubMed2006

A neurocomputational hypothesis for nicotine addiction.

We present a hypothetical neurocomputational model that combines a set of neural circuits at the molecular, cellular, and system levels and accounts for several neurobiological and behavioral processes leading to nicotine addiction. We propose that combining changes in the nicotinic receptor response, expressed by mesolimbic dopaminergic neurons, with dopamine-gated learning in action-selection circuits, suffices to capture the acquisition of nicotine addiction. We show that an opponent process enhanced by persistent nicotine-taking renders self-administration rigid and habitual by inhibiting the learning process, resulting in long-term impairments in the absence of the drug. The model implies distinct thresholds on the dosage and duration for the acquisition and persistence of nicotine addiction. Our hypothesis unites a number of prevalent ideas on nicotine action into a coherent formal network for further understanding of compulsive drug addiction.

Behavior↗

PubMed2006

Attention-deficit/hyperactivity disorder: a plausible mouse model?

UNLABELLED: Attention-deficit/hyperactivity disorder (ADHD) is a multifactorial and heterogeneous disorder, highly prevalent in children and characterized by three main components: inattention, lack of inhibitory control and hyperactivity. Epidemiological evidence reveals that ADHD is associated with nicotine exposure, mostly, with prenatal cigarette smoking. Mice deleted for the beta2-subunit gene of the neuronal nicotinic receptor are proposed as a simple and reliable animal model for ADHD. CONCLUSION: Nicotinic agonists targeting the alpha4beta2 nicotinic receptors alleviate ADHD symptoms and may possibly contribute to an efficient therapy of ADHD children.

Animals↗

PubMed2006

Identification of two critical residues within the Cys-loop sequence that determine fast-gating kinetics in a pentameric ligand-gated ion channel.

Pentameric ligand-gated ion channels (LGICs) are fast-gating receptors, represented by cationic nicotinic acetylcholine (nAChR) and serotonin (5HT3R) receptors, and by anionic GABA and glycine (GlyR) receptors. Because of a highly conserved sequence of 13 amino acids flanked by two canonical cysteine residues shared by all members of the family, these receptors are also known as the Cys-loop family. These receptors are allosteric transmembrane proteins made of five identical (or not) subunits arranged (pseudo) symmetrically around a central ion pore in the membrane. In nAChR, upon ACh binding, the receptor interconverts into discrete allosteric states, with each state corresponding to a different physiological state: resting (closed), active (open), and desensitized (closed).

Amino Acid Sequence↗

PubMed2005

Monoamine oxidase inhibitors allow locomotor and rewarding responses to nicotine.

Although nicotine is generally considered to be the main compound responsible for the addictive properties of tobacco, experimental data indicate that nicotine does not exhibit all the characteristics of other abused substances, such as psychostimulants and opiates. For example, nicotine is only a weak locomotor enhancer in rats and generally fails to induce a locomotor response in mice. This observation contradicts the general consensus that all drugs of abuse release dopamine in the nucleus accumbens, a subcortical structure, and thus increase locomotor activity in rodents. Because tobacco smoke contains monoamine oxidase inhibitors (MAOIs) and decreases MAO activity in smokers, we have combined MAOIs with nicotine to determine whether it is possible to obtain a locomotor response to nicotine in C57Bl6 mice. Among 15 individual or combined MAOIs, including harmane, norharmane, moclobemide, selegiline, pargyline, clorgyline, tranylcypromine and phenelzine, only irreversible inhibitors of both MAO-A and -B (tranylcypromine, phenelzine, and clorgyline+selegiline) allowed a locomotor response to nicotine. The locomotor stimulant interaction of tranylcypromine and nicotine was absent in beta2-nicotinic acetylcholine receptor subunit knockout mice. Finally, it was found that, whereas naïve rats did not readily self-administer nicotine (10 microg/kg/injection), a robust self-administration of nicotine occurred when animals were pretreated with tranylcypromine (3 mg/kg). Our data suggest that MAOIs contained in tobacco and tobacco smoke act in synergy with nicotine to enhance its rewarding effects.

Animals↗