Chronic nicotine exposure in preadolescence enhances later spontaneous recovery of fear memory

Abstract

Preadolescent mice have been shown to be differentially susceptible to the effects of both acute and chronic nicotine exposure on contextual fear learning relative to adults. For this study, we tested the effects of chronic nicotine exposure in preadolescence on adulthood extinction and spontaneous recovery of fear memory in a model in which contextual fear acquisition occurred prior to nicotine exposure. Preadolescent (postnatal day 23) and adult (postnatal day 53) male C57BL/6J mice underwent contextual fear conditioning and were then exposed to chronic nicotine at 12.6 mg/kg/day for 12 days via osmotic minipump. Eighteen days following the removal of nicotine, both groups of mice underwent fear extinction, followed by a spontaneous recovery session a week later. History of chronic nicotine did not affect later extinction of fear memory in adult-trained mice, whereas adolescent-trained mice exhibited a global impairment in retention of fear memory that precluded detection of effects of early nicotine on later fear extinction. However, it was found that adult spontaneous recovery of fear memory was impaired in mice exposed to nicotine as adults and enhanced in mice exposed to nicotine as preadolescents. These results may indicate greater vulnerability to recurrence of traumatic memory as well as compromised inhibitory control in young smokers. (PsycINFO Database Record

Figure 1

Schematic representation of experimental design.

Figure 2

Top panel PND23 percent freezing during test day, extinction, and spontaneous recovery trials; Bottom panel: PND53 percent freezing during test day, extinction, and spontaneous recovery trials. * denotes significance at p < .025

Figure 3

Within-trial extinction in PND23-conditioned mice as a function of percent freezing between first and third 100-second time bins. * denotes significance at p < .01