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Despite intense scrutiny over the past 20 years, the reasons for the high addictive liability of nicotine and extreme rates of relapse in smokers have remained elusive. One factor that contributes to the development and maintenance of nicotine addiction is the ability of nicotine to produce long-lasting modifications of behavior, yet little is known about the mechanisms by which nicotine alters the underlying synaptic plasticity responsible for behavioral changes. This study is the first to explore how nicotine interacts with learning to alter gene transcription, which is a process necessary for long-term memory consolidation. Transcriptional upregulation of hippocampal jun-N terminal kinase 1 (JNK1) mRNA was found in mice that learned contextual fear conditioning (FC) in the presence of nicotine, whereas neither learning alone nor nicotine administration alone exerted an effect. Furthermore, the upregulation of JNK1 was absent in β2 nicotinic receptor subunit knockout mice, which are mice that do not show enhanced learning by nicotine. Finally, hippocampal JNK activation was increased in mice that were administered nicotine before conditioning, and the inhibition of JNK during consolidation prevented the nicotine-induced enhancement of contextual FC. These data suggest that nicotine and learning interact to alter hippocampal JNK1 gene expression and related signaling processes, thus resulting in strengthened contextual memories. [ABSTRACT FROM AUTHOR]

Abstract: A predominant symptom of nicotine withdrawal is cognitive deficits, yet understanding of the neural basis for these deficits is limited. Withdrawal from chronic nicotine disrupts contextual learning in mice and this deficit is mediated by direct effects of nicotine in the hippocampus. Chronic nicotine treatment upregulates nicotinic acetylcholine receptors (nAChR); however, it is unknown whether upregulation is related to the observed withdrawal-induced cognitive deficits. If a relationship between altered learning and nAChR levels exists, changes in nAChR levels after cessation of nicotine treatment should match the duration of learning deficits. To test this hypothesis, mice were chronically administered 6.3mg/kg/day (freebase) nicotine for 12 days and trained in contextual fear conditioning on day 11 or between 1 to 16 days after withdrawal of treatment. Changes in [125I]-epibatidine binding at cytisine-sensitive and cytisine-resistant nAChRs and chronic nicotine-related changes in α4, α7, and β2 nAChR subunit mRNA expression were assessed. Chronic nicotine had no behavioral effect but withdrawal produced deficits in contextual fear conditioning that lasted 4 days. Nicotine withdrawal did not disrupt cued fear conditioning. Chronic nicotine upregulated hippocampal cytisine-sensitive nAChR binding; upregulation continued after cessation of nicotine administration and the duration of upregulation during withdrawal paralleled the duration of behavioral changes. Changes in binding in cortex and cerebellum did not match behavioral changes. No changes in α4, α7, and β2 subunit mRNA expression were seen with chronic nicotine. Thus, nicotine withdrawal-related deficits in contextual learning are time-limited changes that are associated with temporal changes in upregulation of high-affinity nAChR binding. [Copyright &y& Elsevier]