PRESYNAPTIC ASPECTS OF NICOTINE ADDICTION

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A major obstacle to understanding the CNS effects of nicotine has been the lack of information on the role of neuronal nicotinic acetylcholine receptors (nAChRs) in CNS synaptic transmission. Although nAChRs were discovered more than 100 years ago, with Langley's paintbrush application of nicotine to neural tissue, fundamental aspects of CNS nAChR function have only just emerged from molecular biological and biophysical analyses. This proposal examines the functional role and molecular composition of presynaptic nicotinic acetylcholine receptors in the CNS. The proposed experiments are motivated by the hypothesis that the behavioral and addictive effects of nicotine may involve activation of presynaptic nicotinic AChRs that control transmitter release at CNS synapses. The preliminary studies that are the groundwork of this proposal, reveal that nicotine profoundly alters the release of glutamate at specific nerve- nerve synapses both in vitro and in semi-intact preparations (CNS slice). Specifically, we propose to examine the presynaptic actions of nicotine on glutamatergic transmission by experiments that: (1) characterize the synaptic facilitation and depression mediated by nAChRs at an identified CNS synapse (2) determine the distribution of presynaptic nAChRs as well as the nAChR channel subtype(s) underlying these phenomena using biophysical, and molecular biological techniques and (3) examine changes in transmission induced by chronic as well as by acute nicotine exposure. Nicotine dependence is accompanied by CSF nicotine levels in the submicromolar range as well as changes in high affinity nicotine binding sites in specific brain regions. This IRPG examines the effects of low level nicotine exposure on the activation of presynaptic nAChRs that regulate release (this proposal) and its effects on altering the relationship between activated and inactivated states of nAChRs (collaborative IRPG proposal; Dr J. Dani). Detailed study of both of these aspects of chronic, low level nicotine exposure are likely to be fundamental to dissecting the molecular mechanisms of nicotine addiction. Finally, in view of the prominence of glutamatergic transmission in cognitive and affective behaviors that are altered by nicotine, the studies. of nAChR-mediated regulation of glutamatergic transmission that are the basis of this proposal may elucidate mechanisms underlying the short term behavioral effects of nicotine.