Exposure to Nicotine Vapor Produced by an Electronic Nicotine Delivery System Causes Short-Term Increases in Impulsive Choice in Adult Male Rats

Abstract

Introduction: Traditional cigarette use influences cost-benefit decision making by promoting impulsive choice. However, the impact of nicotine exposure via electronic nicotine delivery systems on impulsivity remains unclear. Hence, the present study examined the short- and long-term effects of nicotine vapor on impulsive choice.

Methods: Twenty-four adult male rats were trained in the delay discounting task to choose between small immediate food rewards and large delayed food rewards. After 24 days of training in the task rats were exposed to vapor containing either 0, 12, or 24 mg/mL of nicotine for 10 days. To validate inhalation of nicotine vapor serum cotinine levels were analyzed on exposure days 1, 5, and 10 using enzyme-linked immunosorbent assay. Following vapor exposure, rats were retrained in the discounting task until rats displayed stable responding and the effects of nicotine vapor on choice preference were assessed.

Results: Rats exposed to 12 and 24 mg/mL nicotine vapor displayed higher serum cotinine levels than control rats exposed to 0 mg/mL vapor. There were no differences in impulsive choice between any vapor exposure groups when tested 15 days after exposure, across 6 days of stable responding, suggesting that nicotine vapor does not have long lasting effects on impulsive choice. Interestingly, a subsequent nicotine vapor challenge revealed short-term increases in impulsive choice immediately following a single exposure to 24 mg/mL nicotine vapor, relative to choice preference immediately following exposure to 0 mg/mL vapor.

Conclusions: These results suggest that exposure to nicotine vapor causes immediate, short-term increases in impulsive choice.

Implications: E-cigarette use is increasing at an alarming rate, particularly among adolescents and young adults. This is concerning given the lack of research into the effects of nicotine vapor exposure on the brain and behavior. The present study describes a viable rodent model of human e-cigarette use and suggests that exposure to nicotine vapor produces short-term increases in impulsive choice.

Figure 1.

Blood serum cotinine levels of rats exposed to nicotine or vehicle vapors on exposure days 1, 5, and 10. The rats that were exposed to the 12 mg/mL nicotine vapor (12 mg/mL Nic, green bars) and 24 mg/mL nicotine vapor (24 mg/mL Nic, red bars) displayed an increase in serum cotinine levels when compared with the control rats that were exposed to 0 mg/mL nicotine vapor (0 mg/mL Nic, blue bars). No significant differences were observed between the 12 and 24 mg/mL nicotine treatment groups. Data are presented as mean ± SEM. Asterisk (*) indicates a significant difference between the 0 and 12 or 24 mg/mL nicotine vapor treatment groups. Critical p value is .05.

Figure 2.

Long-term effects of nicotine vapor exposure on average choice preference across 6 days of stable responding. Rats showed no significant long-term effects on impulsive choice 15 days after a 10-day exposure to 0 mg/mL nicotine vapor (0 mg/mL Nic, blue squares), 12 mg/mL nicotine vapor (12 mg/mL Nic, green squares), or 24 mg/mL nicotine vapor (24 mg/mL Nic, red squares). Impulsive choice was averaged across 6 days of stable responding in the delay discounting task (delay discounting days 35–40) and data are presented as mean ± SEM.

Figure 3.

Short-term effects of nicotine vapor challenge on choice preference in rats previously treated with 10 days of (A) 0, (B) 12, or (C) 24 mg/mL of nicotine vapor. Rats previously exposed to 0 and 12 mg/mL nicotine vapor demonstrated increased impulsive choice (decreased choice of the large delayed reward). Data shown include choice preference averaged across delay discounting training days 35–40 (DD 35–40 Ave, white circles), immediately after 0 mg/mL nicotine vapor challenge (0 mg/mL Nic, blue circles), immediately after 24 mg/mL nicotine vapor challenge (24 mg/mL Nic, red circles), and 24 hours after 24 mg/mL nicotine vapor challenge (24 hours post vapor, black circles). Data are presented as mean ± SEM. Plus sign (+) indicates a significant difference in delay discounting between the 0 and 24 mg/mL nicotine vapor challenge days, while asterisk (*) indicates significant difference on delay discounting between the 0 and 24 mg/mL nicotine vapor on identified delay block. Critical p value is .05.