NEURONAL NICOTINIC RECEPTORS-EXPRESSION AND REGULATION

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DESCRIPTION (From applicant's abstract): Nicotinic acetylcholine receptors containing the alpha7 gene product (alpha7-nACHRs) are among the most abundant in the nervous system and have been implicated in a wide variety of higher brain functions and neurodegenerative diseases. Because of their high calcium permeability and diverse locations, the receptors can influence many cellular events. The present renewal application is based on three new discoveries: the receptors can be concentrated on somatic spines by cytoskeletal interactions for synaptic signaling; receptor function may be constrained substantially by negative regulation in vivo; and the receptors can influence gene expression in novel ways. These findings shape the four specific aims proposed. (1) Identify components that tether alpha7-nAChRs at synaptic sites. (2) Analyze mechanisms controlling the responsiveness of alpha7-nAChRs. (3) Assess the significance of alpha7-nAChR signaling for gene expression. (4) Test CNS models of postsynaptic alpha7-nAChRs. The initial work will be carried out with chick ciliary ganglion neurons because they provide the richest known source of the receptors. The neurons will be examined both in vivo and in cell culture to identify cell-cell interactions and receptor-associated molecules that govern somatic spine formation and alpha7-nAChR clustering. Exogenous components that dramatically increase the whole-cell alpha7-nAChR response will be examined for molecular mechanism and for in vivo relevance. The conditions and mechanisms enabling alpha7-nAChR receptors to influence gene expression will also be examined, and the gene families affected will be identified in order to test hypotheses about the physiological relevance of the effect. CNS neurons enriched in alpha7-nAChRs will then be used to determine which of the regulatory principles governing ciliary ganglion receptors can be extended broadly across systems having different physiological assignments. The experimental approaches will utilize fluorescence imaging, 3-D tomographic EM reconstruction, and whole-cell patch clamp recording in situ and in cell culture. These will be combined with biochemical and molecular biological approaches to identify and examine molecules influencing receptor function and location, and to determine which gene families are most affected by the receptors. The information obtained will indicate how a major nicotinic receptor in brain is controlled and how it, in turn, exerts long-term control through gene regulation. The biomedical relevance is substantial because of the enormous health-related consequences of tobacco usage and nicotine addiction and because of growing evidence that alpha7-nAChRs in particular are involved in neurodegenerative diseases such as Alzheimer's with a devastating toll on the public.