Behavioral and neurochemical alterations induced by long-term exposure to tobacco heating system emissions in rats

Tobacco heating systems (THSs) are increasingly being used as alternatives to conventional cigarettes (CIGs). In this study, we compared the effects of mainstream THS emissions and CIG smoke on the affective, locomotor, and cognitive behaviors in rats.

Forty-five male Wistar rats were randomized into three groups (n = 15 each): control (normal air), CIG (mainstream smoke from a common cigarette brand), and THS (emissions from IQOS ILUMA and TEREA Smartcore Sticks™, Philip Morris International). Rats underwent whole-body exposure to emissions/smoke (two sticks/day, ∼4 min/stick, morning and evening) for 60 days. The toxicants were quantified in emissions/smoke. Post-exposure assessments included the actophotometer (locomotor activity), forced swim test (FST) (affective behavior), and novel object recognition test (NORT) (recognition memory). Blood was analyzed for hemoglobin (Hb), leukocyte count, serum nicotine, and serum cotinine. Brain dopamine levels and histopathological changes in the hippocampus and cerebral cortex were evaluated.

THS emissions exhibited significantly lower nicotine-free dry particulate matter (NFDPM), particulate matter, and toxicants (e.g., nitrogen/sulfur oxides, ammonia, hydrogen cyanide, and arsenic) than CIG smoke (p < 0.001). Behavioral analyses revealed that both exposure groups showed elevated locomotor activity and reduced immobility time in the FST compared to the controls, suggesting increased central arousal and reduced depressive-like behavior. The THS group demonstrated a higher discrimination index in the NORT, indicating relatively preserved recognition memory compared with that of the CIG group. Despite lower serum nicotine and brain dopamine levels, THS-exposed rats exhibited milder histopathological changes without apparent neurotoxicity, whereas CIG exposure induced marked hippocampal and cortical toxicity. CIG rats also showed elevated leukocyte counts and Hb relative to THS and control rats (p < 0.05).

The observed behavioral effects likely reflect improved affective and locomotor regulation, with evidence of relatively preserved cognitive function in THS-exposed rats. These findings highlight the need for further mechanistic investigations to delineate the long-term neurobehavioral safety profile of THS exposure.