Synthetic cooling agents enhance nicotine reinforcement and mesolimbic dopamine signaling

Flavor additives in electronic delivery systems (ENDS) have been shown to enhance nicotine reinforcement. Although some states and cities have pursued implementation of menthol bans, synthetic coolants such as WS-3 and WS-23 have emerged as substitutes. In this study, we investigated the impact of WS-3 and WS-23 on nicotine self-administration behavior and dopamine (DA) release in the nucleus accumbens (NAc) core. To model nicotine reinforcement, we used an E-Vape® self-administration (EVSA) assay and observed that male and female mice exposed to nicotine plus WS-3 and WS-23 exhibited enhanced self-administration behavior when compared to mice exposed to nicotine alone or PGVG (control treatment). We also observed that the enhancement in nicotine self-administration is similar to what is observed with menthol. To measure changes in dopamine release, we used fast-scan cyclic voltammetry (FSCV) and fiber photometry. Here, we observed that WS-3 and WS-23 increased the amount of dopamine released in the NAc under both tonic (5 Hz) and phasic (60 Hz) stimulation conditions when compared with nicotine-alone. Fiber photometry recordings showed that the WS-3 and WS-23 enhanced nicotine-stimulated dopamine release in the NAc core. Using electrophysiology and microscopy assays, we observed that synthetic coolants enhance the intrinsic excitability of ventral tegmental area (VTA) dopamine neurons and enhance nicotine-induced upregulation of nicotinic acetylcholine receptors (nAChRs). In both FSCV and photometry assays, synthetic coolants produced enhancements in dopamine signaling that were comparable in magnitude to those observed with menthol. These findings demonstrate that synthetic cooling agents enhance nicotine reinforcement and are associated with increased mesolimbic dopamine signaling, enhanced VTA dopamine neuron excitability, and increased nicotine-induced nAChR upregulation.