Neuronal excitability in the medial habenula and ventral tegmental area is differentially modulated by nicotine dosage and menthol in a sex-specific manner.

The medial habenula (MHb) has been identified as the limiting factor for nicotine intake and facilitating nicotine withdrawal. However, few studies have assessed MHb neuronal excitability in response to nicotine and, currently, a gap in knowledge is present for finding behavioral correlates to neuronal excitability in the region. Moreover, no study to date has evaluated sex or nicotine dosage as factors of excitability in the MHb. Here, we utilized an e-vape® self-administration (EVSA) model to determine differences between sexes with different nicotine dosages ± menthol. Following this paradigm, we employed patch-clamp electrophysiology to assess key metrics of MHb neuronal excitability in relation to behavioral endpoints. We observed female mice self-administered significantly more than males, regardless of dosage. We also observed a direct correlation between self-administration behavior and MHb excitability with low-dose nicotine + menthol in males. Conversely, a high dose of nicotine ± menthol yields an inverse correlation between excitability and self-administration behavior in males only. In addition, intrinsic excitability in the ventral tegmental area (VTA) does not track with the amount of nicotine self-administered. Rather, they correlate to the active:inactive discrimination of mice. Using fast-scan cyclic voltammetry, we also observed that dopamine release dynamics are linked to reinforcement-related behavior in males and motivation-related behaviors in females. These results point to a sex-specific difference in the activity of the MHb and VTA leading to distinct differences in self-administration behavior. his could lend evidence to clinical observations of smoking and nicotine-use behavior differing between males and females. Significance Statement Nicotine dependence remains a priority topic due to the fact that hundreds of thousands of individuals die annually due to tobacco-related illnesses. While the mesolimbic reward pathway has been proven to be critical to nicotine's actions, over time other brain areas have been identified to play crucial roles in nicotine reward, reinforcement, and withdrawal. One area, the medial habenula has increasingly been shown to be highly important. Here, our data suggests that the dopamine system of the mesolimbic pathway may be highly important for the learning aspect of nicotine intake while the medial habenula may play a larger role in the amount of nicotine that is taken in a preclinical self-administration model.