Our objectives are to assess the pharmacology and regulation of the diverse heteromeric neuronal nicotinic cholinergic receptor (nAChR) subtypes in the mammalian central nervous system (CNS). These receptors are widely distributed in the CNS, where they modulate release of several neurotransmitters in important neuronal pathways. Thus, they influence a wide range of functions, and they have been clearly implicated in nicotine addiction. In addition, these receptors are thought to play an important role in a wide range of other CNS disorders including Parkinson's disease, Alzheimer's disease, Tourette's syndrome and neuropathic pain. Nicotinic receptors are also crucial for normal functioning of the autonomic nervous system, and thus they influence virtually all organ systems in the body. These receptors are pentameric structures assembled from 11 subunits representing 2 classes, alpha and beta. The subunit composition of a receptor defines its subtype and determines its pharmacological and biophysical properties, which vary subtly, or not so subtly, among the particular subtypes. Two nAChR subtypes seem to form the main templates for several other heteromeric receptors found in the CNS and autonomic nervous systems. Receptors based on the alpha4beta2 subtype predominate in most areas of the CNS;whereas, the alpha3beta4 subtype provides the main template autonomic ganglia.
The specific aims of the studies described in this proposal are: 1) To quantify the alpha4beta2alpha5 subtype in brain areas and determine the influence of the alpha5 subunit on the regulation of these receptors by nicotine;2) To study the subunit composition, pharmacology and regulation of nAChRs containing alpha6 subunits;and 3) To use a powerful new method, expression of concatameric receptors consisting of all five subunits fused into a single defined receptor, to determine the properties of mixed heteromeric nAChRs of known subunit composition, stoichiometry, and subunit order. The studies described in this proposal will lead to a better understanding of important differences in the pharmacology and regulation among these different receptor subtypes and help us to understand how nicotine regulates CNS nAChRs.
Nicotine is a drug of abuse that acts by binding to neuronal cell-surface proteins in the brain called nicotinic acetylcholine receptors. In addition to being involved in drug abuse, these receptors are thought to play an important role in a wide range of other disorders of the nervous system including Parkinson's disease, Alzheimer's disease, Tourette's syndrome and neuropathic pain. These nicotinic acetylcholine receptors normally are involved in transmitting information in the brain from neuron to neuron via the neurotransmitter acetylcholine. These receptors, when bound to acetylcholine or nicotine, open a channel in the membrane of the cell and allow ions such as sodium, potassium, and calcium to pass, and by so doing cause marked changes in the activity of the cells. These receptors are complexes of five separate proteins, called subunits, which come together by mutual attraction to form the functional receptor. There are two categories of receptor subunit proteins, called alpha and beta. Each of these categories has several distinct subunit proteins (e.g. alpha2 through alpha6 and beta2 through beta4) and a functional receptor can be generated when two copies of a specific alpha protein associates with three copies of a specific beta protein to form what is known as a heteromeric nicotinic receptor. Because there are several different alpha and beta subunits, the number of possible combinations is large. We, and others, have developed methods to determine which subunits actually assemble with which other subunits to form functional receptors in various brain regions. Depending on which subunits form the receptor, the pharmacological and biophysical properties are different. Aims 1 and 2 of this proposal are directed at a more complete understanding of which types of subunits assemble with each other to form nicotinic receptors. Because the properties of the most complex receptors containing more than one type of alpha and/or more than one type of beta subunit are unknown, in Aim 3 of this proposal we have developed a method with which we can generate receptors of known subunit composition and order and then study their functional and pharmacological properties. The studies described in this proposal will lead to a better understanding of important differences in the pharmacology, physiology, and regulation among these different receptor subtypes and help us to understand how nicotine regulates its receptors in the central nervous system.
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