Adult consequences of repeated nicotine and Δ 9 -tetrahydrocannabinol (THC) vapor inhalation in adolescent rats

Rationale Use of electronic drug delivery systems (EDDS, “e-cigarettes”) to ingest nicotine and Δ 9 -tetrahydrocannabinol (THC) has surged in adolescents in the USA; five times as many high-school seniors vape nicotine daily using tobacco. At the same time, 19.5% of seniors use cannabis at least monthly, with 12% using EDDS to deliver it. Objectives This study was conducted to examine the impact of repeated adolescent vapor inhalation of nicotine and THC in rats. Methods Female Sprague–Dawley rats were exposed to 30-min sessions of vapor inhalation, twice daily, from post-natal day (PND) 31 to PND 40. Conditions included vapor from the propylene glycol (PG) vehicle, nicotine (60 mg/mL in the PG), THC (100 mg/mL in the PG), or the combination of nicotine (60 mg/mL) and THC (100 mg/mL). Rats were assessed on wheel activity, heroin anti-nociception and nicotine and heroin vapor volitional exposure during adulthood. Results Nicotine-exposed rats exhibited few differences as adults, but were less sensitive to anti-nociceptive effects of heroin (1 mg/kg, s.c.). THC- and THC + nicotine–exposed rats were less spontaneously active, and obtained fewer nicotine vapor deliveries as adults. In contrast, THC-exposed rats obtained volitional heroin vapor at rates indistinguishable from the non-THC-exposed groups. Repeated THC exposure also caused tolerance to temperature-disrupting effects of THC (5 mg/kg, i.p.). Conclusions These studies further confirm that the effects of repeated vapor exposure to THC in adolescence last into early to middle adulthood, including decreased volitional consumption of nicotine. Effects of repeated nicotine in adolescence were comparatively minor.