Unit: Receptors and Cognition
Director: CHANGEUX Jean-Pierre
During 2005, the main scientific achievements are : the proposal of a model of conformational transitions of the nicotinic receptor by a quaternary twist of the whole oligomer ; the construction of a chimera between the molluscan acetylcholine binding protein and an ion channel able to undergo allosteric transitions ; the experimental demonstration that the opening of the ion channel results from a rigid tilt of the 5 pore lining segments and its linkage with the ligand binding domain through amino acid residues from the cys-loop and the M1-M3 loop ; the up-regulation by nicotine of its own receptor through enhanced intracellular maturation ; the restoration of cognitive behaviour and nicotine reinforcement by re-expression of nicotinic receptor β2-subunit in a knock-out mouse by targeted injection of a lentiviral vector in the ventral tegmental area ; the deficits in breathing caused by perinatal exposure to nicotine as a mouse model of Sudden Infant Death Syndrome ; the modeling of a neuronal network able to learn through reward-dependant synapse selection and to perform a delayed - matching - to - sample task as well as the theoretical proposal of a role of ongoing spontaneous activity on the control of access to consciousness.
The activity of the " Receptors and Cognition CNRS 2182 " Unit is centered on the study of the nicotinic acetylcholine receptor, an " allosteric " membrane protein involved in the tranduction of chemical neurotransmitter signals into electrical responses at the level of the postsynaptic membrane of the neuromuscular junction and of the central nicotinic synapses.
The five main objectives are :
1) identification, at the amino acid level, of the elementary structures engaged in the recognition of nicotinic ligands, in ionic selectivity and transport and in their diverse modes of " allosteric " coupling (activation, desensitization) and in " up regulation " caused by chronic exposure to nicotine.
2) the regulatory mechanisms of gene expression involved in the focal distribution of nicotinic receptors in muscle endplate postsynaptic membrane (in the course of development and in the adult) and in the differential distribution of nicotinic receptors in the brain.
3) the neural processes taking place in the dendritic vs. axonal compartments of central neurons and involved in learning and reward mechanisms associated with nicotine addiction and various brain pathologies
4) the demonstration of causal relationships between the molecular properties of neuronal nicotinic receptors and their distribution with brain physiology and behavior.
5) the theoretical modeling of neuronal networks establishing bottom up and top-down links between the molecular and cognitive level and its plausible applications to human behavior and pathologies.
The methods used to attain the first objective include crystallization of the purified protein (or specific fragments) and analysis of the three-dimensional fonctional organization by site-directed mutagenesis, stopped-flow with fluorescent ligands in wild type and mutant brain nicotinic receptors. To attain objectives 2 and 3, the most recent advances in recombinant DNA technologies, cloning and sequencing of cDNAs in situ hybridization, promoter analyses, in vivo and in vitro transfection experiments, conditional homologous recombination in vivo and stereotaxic injection of lentiviral vectors are being exploited, along with cell biology methods such as confocal microscopy, cell imaging, small animal fMRI and optic fiber imaging in vivo.
Ongoing applications of the current work to medicine include ; (1) the pharmacology of peripheral and central nicotinic synapses in relation with the effect of nicotine in addiction, cognitive enhancement, anagesia, anesthesia, and neuroprotection.
(2) the pathology of the innervated skeletal muscle and after denervation, the pathology of myasthenia gravis.
(3) brain defects resulting from (or associated with) alterations of nicotinic receptors such as frontal lobe, epilepsy, Alzheimer's ans Parkinson's disease, analgesia, aging and nicotine addiction.
Among the original works published in 2005, one may mention :
1) The proposal of a model of conformational transitions of the nicotinic receptor ion channel gating mechanism based upon normal mode analysis and postulating a quaternar twist of the whole oligomer (Taly et al 2005).
2) The construction of a chimera between the molluscan acetylcholine binding protein and a cationic/anionic ion channel able to undergo allosteric transitions which spontaneously stabilizes in a desensitized form (Grutter at al 2005)
3) The experimental demonstration that the opening of the ion channel results from a rigid tilt of the 5 pore lining segments (Paas et al 2005) linked with the ligand binding domain through amino acid residues from the cys-loop and the M1-M3 loop (Grutter et al 2005).
4) Nicotine up-regulate its own receptor through enhanced intracellular maturation (Salette et al 2005).
5) The re-expression of nicotinic receptor β2-subunit in a knock-out mouse by targeted injection of a lentiviral vector in the ventral tegmental area restores altogether cognitive behaviour and nicotine reinforcement (Maskos et al 2005).
6) Perinatal exposure to nicotine in a mouse model causes instable breathing, impaired arousal and catecholamine biosynthesis associated with a phenotypic loss of nicotinic receptor functions (Cohen et al 2005).
7) The map of visual space in the superior colliculus is altered in β2-subunit knock-out mice lacking early retinal waves (Mrsic-Flogel et al 2005).
8) Nicotinic receptors regulate lymphocytes development (Skok et al 2005-1) and lymphocyte B activation and immune response (Skok et al 2005-2).
9) The modelisation of a neuronal network able to learn through reward dependant synapse selection and to perform a delayed - matching - to - sample task (Gisinger et al 2005).
10) The theoretical proposal of a role of ongoing spontaneous activity on the control of access to consciousness and of a neuronal model for inattentional blindness (Dehaene and Changeux 2005).
Targeted expression of the nicotinic receptor β2-subunit by stereotaxic injection of a lentiviral vector in the ventral tegmental area.
Keywords: nicotinic acetylcholine receptors, allosteric protein, learning, knockout mice, nicotine addiction