Body Temperature and Discriminative Stimulus Effects of Nicotine and Menthol Aerosols in Male Rats: Role of α4β2 Nicotinic Acetylcholine Receptors.

Abstract

Menthol, a prevalent additive in tobacco and electronic cigarette products, has been reported to interact with nicotine at both neuropharmacological and behavioral levels. Although menthol alone is not reinforcing, converging evidence suggests that it may modulate the pharmacological and behavioral effects of nicotine through nicotinic acetylcholine receptor (nAChR) mechanisms. Using an inhalation-based rodent model that mimics human exposure to electronic nicotine delivery systems, we examined how menthol aerosol influences nicotine-induced hypothermia, discriminative stimulus effects, and the potential involvement of α4β2* nAChRs in male rats. Plasma nicotine, cotinine, and trans-3'-hydroxycotinine (3'-OH-cotinine) concentrations were also measured to assess pharmacokinetic interactions. Menthol aerosol prolonged and potentiated nicotine-induced hypothermia, and this effect was attenuated by the α4β2* receptor antagonist dihydro-β-erythroidine (DHβE). In drug discrimination (DD) assays, coinhalation of menthol enhanced nicotine-appropriate responding, suggesting facilitation of nicotine's interoceptive stimulus properties. These effects were also attenuated by DHβE, consistent with involvement of α4β2* nAChR-mediated mechanisms. In addition, the behavioral effects were accompanied by alterations in nicotine pharmacokinetics, including increased levels of nicotine metabolites. Collectively, these findings suggest that menthol modulates nicotine's pharmacological and behavioral effects, potentially through α4β2* nAChR-dependent mechanisms. By prolonging nicotine's physiological and interoceptive effects, menthol may increase the salience of nicotine-related cues during inhalation exposure. These interactions could contribute to enhanced abuse liability associated with menthol-containing nicotine products, although further studies are required to establish causal mechanisms. This study provides mechanistic insight into menthol-nicotine interactions and highlights considerations relevant to mentholated e-cigarette products.