Early life nicotine vapor exposure increases nicotine vapor seeking in adult male rats.

RATIONALE: The ongoing epidemic of nicotine vaping use in adolescents and young adults presents a significant health concern, yet the long-term effects of nicotine vaping remain largely unknown.

OBJECTIVE

The present study aimed to investigate how nicotine vapor intake early in life influences reward-seeking behavior immediately after exposure and later in adulthood.

METHODS

Experiment 1 was completed in 3 phases. In Phase 1, 24 male adolescent Sprague-Dawley rats (PND = 58) were passively exposed to vehicle (propylene glycol/vegetable glycerin, 50/50) or nicotine (24 mg/mL) vapor and immediately tested in a Progressive Ratio (PR) task that utilized food pellet delivery as reinforcement for 10 consecutive days. In Phase 2, the PR testing was replicated in early adulthood (PND = 140), with groups further divided into four groups: No exposure, adolescent exposure, early adulthood exposure, and both adolescent and early adulthood exposure. Lastly, in Phase 3, during late adulthood (PND = 341), all four vapor groups underwent nicotine vapor self-administration (NVSA) testing (6 mg/mL). For Experiment 2, 16 male young adult Wistar rats received vehicle or nicotine vapor deliveries during the PR task. Rats were given access to increasing concentrations of nicotine (1, 3, 6, 12, 24 mg/mL) for two days at each concentration. After the PR tests, the rats were given two additional days of NVSA (24 mg/mL) on a Fixed Ratio 1 (FR1) schedule of reinforcement.

RESULTS

Experiment 1 revealed that adolescent but not adult exposure to 24 mg/mL of nicotine vapor, resulted in an increase in both active and inactive lever presses relative to controls. Notably, rats in the adolescent and early adulthood exposure groups displayed significant increases in active but not inactive port nosepokes later in life, when compared to rats that were not previously exposed to nicotine vapor. Experiment 2 revealed no group differences in responding for vapor deliveries in the PR task when testing young adult rats. However, there was more active port nosepoking compared to vehicle vapor controls, when testing using an FR1 schedule of reinforcement.

CONCLUSIONS

These results demonstrate that exposure to nicotine vapor early in life may increase nicotine seeking behavior in adulthood, suggesting that restricting early e-cigarette use may reduce future nicotine intake and the negative health consequences associated with its use.