Chronic Nicotine Treatment During Adolescence Attenuates the Effects of Acute Nicotine in Adult Contextual Fear Learning.

INTRODUCTION: Adolescent onset of nicotine abuse is correlated with worse chances at successful abstinence in adulthood. One reason for this may be due to enduring learning deficits resulting from nicotine use during adolescence. Previous work has indicated that chronic nicotine administration beginning in late adolescence (PND38) caused learning deficits in contextual fear when tested in adulthood. The purpose of this study was to determine if chronic nicotine treatment during adolescence would alter sensitivity to nicotine's cognitive enhancing properties in adulthood.

METHODS: C57BL/6J mice received saline or chronic nicotine (12.6mg/kg/day) during adolescence (postnatal day 38) or adulthood (postnatal day 54) for a period of 12 days. Following a 30-day protracted abstinence, mice received either an acute injection of saline or nicotine (0.045, 0.18, and 0.36mg/kg) prior to training and testing a mouse model of contextual fear.

RESULTS: It was found that chronic nicotine administration in adult mice did not alter sensitivity to acute nicotine following a protracted abstinence. In adolescent mice, chronic nicotine administration disrupted adult learning and decreased sensitivity to acute nicotine in adulthood as only the highest dose tested (0.36mg/kg) was able to enhance contextual fear learning.

CONCLUSIONS: These results suggest that adolescent nicotine exposure impairs learning in adulthood, which could increase the risk for continued nicotine use in adulthood by requiring administration of higher doses of nicotine to reverse learning impairments caused by adolescent nicotine exposure.

IMPLICATIONS: Results from this study add to the growing body of literature suggesting chronic nicotine exposure during adolescence leads to impaired learning in adulthood and demonstrates that nicotine exposure during adolescence attenuates the cognitive enhancing effects of acute nicotine in adulthood, which suggests altered cholinergic function.