Lateralized dendritic correlates of enhanced conditioned fear retrieval following cessation from chronic nicotine exposure in adolescent and adult rats




Bergstrom, Hadley C.

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Cigarette smoking is often associated with anxiety disorders. Evidence has accumulated to indicate that smokers may be at a greater risk for the development of an anxiety disorder. A neural basis has not been established for the transition between smoking and anxiety-related behavior. To address this question, rats at postnatal day (P) 32 (adolescent) and P61 (adult) were administered subcutaneous injections of nicotine (0.5 mg/kg; free base) or saline control three times per week (Mon., Wed., Fri.) for two weeks (6 total injections). Seventeen days following nicotine cessation, rats were tested for fear conditioning and fear extinction. Rats dosed with nicotine during adolescence exhibited no alterations in later fear conditioning and fear extinction. In contrast, adult nicotine exposure enhanced conditioned fear retrieval, but had no lasting effect on fear extinction. Twenty-four hours following behavioral testing, brains were extracted for Golgi-cox staining and dendrites of principal neurons from the basolateral amygdala complex (BLA) and pyramidal neurons from the infralimbic cortex (IL) were digitally reconstructed for morphometric analysis. In the adult group, enhanced fear retrieval was accompanied by increased complexity of basilar dendrites in the BLA. In the adolescent group, nicotine was found to reduce apical dendritic arbors. Dendritic remodeling was lateralized in the BLA for both age groups. Dendrites were unaffected by nicotine in the IL, indicating region-specific dendritic alteration in response to nicotine. Together, these data implicate dendritic reorganization in the amygdala as a factor in development of anxiety-related behavior following cessation from chronic nicotine exposure.



Nicotine, Adolescence, Amygoala, Dendritic morphology, Lateralization, Fear conditioning