Tobacco use remains a major public health concern in the United States and abroad where it is a major factor in the initiation of illnesses leading to preventable death. Yet, despite such adverse consequences, the number of smokers continues to increase worldwide. Although considerable progress has been made in elucidating the neuronal mechanisms underlying several of the effects of nicotine, the active component of tobacco, the knowledge accumulated to date falls short of what is necessary to intervene successfully to reduce tobacco use. The experiments proposed in this program project will use a multi-disciplinary approach to assess the impact of repeated exposure to nicotine on nicotinic acetylcholine receptors (nAChRs), neuronal excitability and behavior. They have in common the goal of ultimately understanding how nicotine acts to initiate self-administration behaviors and how repeated exposure to nicotine produces changes that promote the continued expression of these behaviors. Nicotine produces its effects on motivated behavior by activating brain nAChRs. The ability of nicotine to up regulate these receptors can thus have a substantial impact on the ability of this drug to initiate such behaviors in animals subsequently re-exposed to it. Project 1 will aim to identify the molecular mechanisms underlying nicotine-induced up regulation of nAChRs and characterize this phenomenon in different brain regions of nicotine-exposed rats. As with other drugs of abuse, nicotine use relies in large part on its ability to increase midbrain dopamine transmission. Project 2 will characterize the effect of previous exposure to nicotine on the functional properties of nAChRs with access to these dopamine systems and assess their contribution to long-term potentiation of synapses onto dopamine cells. Repeated exposure to nicotine is known to lead to locomotor sensitization, yet little is known about how this effect is produced. Project 3 will identify the brain nAChR fields involved, characterize their role in the induction of sensitization of dopamine neuron reactivity and determine whether their repeated activation leads to increased motivation to self-administer nicotine.