Passive cigarette smoke exposure induces dose-dependent conditioned place preference in mice

Nicotine reward is a key driver of tobacco dependence; however, the mechanisms underlying reward induced by cigarette smoke, particularly under passive exposure conditions, remain incompletely understood. In the present study, we established an adjustable cigarette smoke exposure system to generate controlled smoke concentrations (0.5, 1.0, and 2.0 g/m³) and investigated the behavioral and molecular consequences of repeated smoke exposure in mice. Animals were exposed to cigarette smoke or air for 2 h daily for 14 or 28 days. Serum nicotine levels were quantified by UPLC-MS/MS, reward-related behavior was evaluated using a conditioned place preference (CPP) paradigm, and the expression of reward-associated signaling proteins in the nucleus accumbens (NAc) was assessed by Western blotting. Cigarette smoke exposure produced a dose-dependent increase in serum nicotine concentrations. No significant CPP was observed after 14 days of exposure; however, after 28 days, mice exhibited a significant and dose-dependent increase in preference for the smoke-paired compartment, accompanied by elevated preference index values. At the molecular level, repeated smoke exposure induced dose-dependent increases in p-ERK, p-CaMKII, and c-Fos expression in the NAc. Furthermore, administration of the nicotinic acetylcholine receptor antagonist mecamylamine significantly attenuated both CPP behavior and the activation of these signaling pathways. These findings demonstrate that repeated cigarette smoke exposure induces nicotine-dependent reward behavior through activation of NAc-associated signaling pathways. This model provides a reproducible and physiologically relevant platform for investigating the neurobiological mechanisms of smoke-induced nicotine reward under passive exposure conditions and may facilitate the development of therapeutic strategies for tobacco dependence.