Tobacco use remains a major public health and economic concern, particularly in women who are more susceptible to the long-term consequences of nicotine exposure. Clinical evidence has revealed that stress produced by nicotine withdrawal can be intensified by fluctuations in gonadal hormones in women, although the underlying mechanisms remain obscure. There is a critical need to determine how stress systems enhance withdrawal severity and inhibitory tone in the IPN of females versus males, and the influence of ovarian hormones on these measures in adult females. Our long-term goal is to contribute to the development of more clinically effective, evidence-based interventions for nicotine cessation, particularly useful for susceptible populations. The overall objective for this application is to vertically extend what has been learned under current funding by determining how the IPN modulates withdrawal from chronic nicotine vapor inhalation using an approach in rats that mimics nicotine use patterns in humans. Our central hypothesis is that females experience more anxiety-like behavior during withdrawal from chronic nicotine inhalation than males due to greater inhibitory tone in IPN. In females, it is also hypothesized that the magnitude of withdrawal severity and inhibitory tone in the IPN is regulated by the ovarian hormones, estradiol (E2) and progesterone. The rationale for the proposed research is that its successful completion is likely to contribute to a mechanistic framework for the development of new nicotine use cessation strategies, particularly for women. Guided by strong preliminary data, the following two specific aims will be pursued 1) Identify the mechanisms whereby the IPN controls nicotine withdrawal in females versus males and 2) Determine the effects of ovarian hormones on IPN-modulated nicotine withdrawal in females.