Nicotinic regulation of neurotransmission in the CNS

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The transmission of information between neurons in the brain is governed by the release of chemicals called "neurotranmitters" which bind to ion channels located on the surface of neurons. The binding of neurotransmitters to ion channels transduces changes in electrical activity of the neuron via the flux of ions across the membrane. The present study focuses on a class of ligand-gated ion channels called nicotinic acetylcholine receptors. alpha4beta2 is the most prevalent nicotinic receptor subtype in the CNS. Our long term goal is to examine the basic function of nicotinic receptors in modulating neurotransmission in the CNS. To address this issue we have produced three lines of knock-in mice, whereby a nicotinic receptor subunit (alpha4) was mutated to contain a fluorescent tag allowing us to localize the receptor in the CNS with exquisite detail. One of the mouse lines also contains a gain-of-function mutation rendering nicotinic receptors with several fold larger nicotinic currents and 50 fold greater affinity to nicotine. This mouse line will allow us to specifically target the receptor with very low concentrations of nicotinic agonist to unambiguously ascertain the receptor's function in physiology and behavioral experiments. We plan to achieve our overall goal firstly by imaging the localization and quantifying nicotinic receptors in specific neurons in various brain regions by exploiting the alpha4 fluorescent mouse lines. To our knowledge, these mice are the first knock-ins to express fluorescently tagged ion channels. After mapping the location and quantifying the receptor we can then precisely target specific neurons for electrophysiological recordings and design intelligently the experiments to ascertain the function of the receptor in influencing neuronal excitability. By knowing the precise quantity and subcellular localization and function of nicotinic receptors in specific neurons and circuits in the brain, we can then predict and test the role of the nicotinic receptor in modulating certain behaviors, such as reward, cognition and pain. We are also interested in understanding the function of other nicotinic receptor subtypes and we will produce fluorescently tagged alpha7 nicotinic receptors as a first step in this endeavor.