Unit: Receptors and Cognition - CNRS URA 2182
Director: Jean-Pierre Changeux
During 2003, our unity has crystallized in 3D the nicotinic receptor protein ; demonstrated the occurrence of a critical H-bond in the activation of the ion channel by acetylcholine ; shown the consequences of phosphorylation of GABP in the transcriptional activation of the receptor genes ; revealed the activation by nicotine of immature " silent " connections in the developing hippocampus ; investigated the respective contribution of α 4, α 6, α 7 and α 2 in the mouse dopaminergic system and on the cognitive behavior of the mouse ; and proposed a model of the conscious workspace which links subjective reports and objective physiological data.
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 three 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 and in " up regulation " to 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 from both the theoretical and experimental point of views.
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, cloning of transcription factors and conditional homologous recombination in vivo are being exploited, along with cell biology methods such as confocal microscopy.
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 epilepsy, Alzheimer's ans Parkinson'disease, analgesia, aging and nicotine addiction.
Among the original works published in 2003, one may mention :
1) the 3D crystallization of the nicotinic receptor protein in structured lipid-detergent matrices (Pass et al 2003).
2) the demonstration of a critical H-bond between residues from different loops of the acetylcholine binding site in the activation mechanism (Grutter et al 2003).
3) the phosphorylation elicited quaternary changes of the transcription factors GABP in transcriptional activation of acetylcholine receptor genes (Sunesen et al 2003).
4) the activation by nicotine of immature " silent " connections in the developing hippocampus (Maggi et al 2003).
5) the localization of nicotine, cytisine, epibatidine and α -bungarotoxin binding sites in the brain of the macaque revealing a more important contribution of α 2 and α 7 subunits than
in the rodent brain (Han et al 2003).
6) the analysis of the subunit composition of the nicotinic receptor oligomers on dopaminergic neurons using knock-out mice demonstrating the contribution of α 6 α 2 receptors in the axon terminals and of [non α 6] α 4 α 2 oligomers in the somatodendritic compartment (Champtiaux et al 2003).
7) a model of neuronal network linking subjective reports and objective physiological data during conscious perception (Dehaene et al 2003).
8) the compared quantitative automated analysis of the locomotor sequential behavior and social interaction of wild type and α 2 ko mice revealing a deficit in executive functions which resemble the rigid and asocial behavior found in autism and attention deficit hyperactivity disorder (Granon et al 2003).
Keywords: nicotinic acetylcholine receptors , allosteric proteins , learning , knockout mice , nicotine addiction