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. Thus, there is a critical need to determine the mechanisms by which stress systems enhance withdrawal severity in females versus males, and the influence of ovarian hormones on these measures in adult females. If this knowledge gap is not filled, then the challenges of reducing nicotine use and developing specialized medications for females will remain largely insurmountable. The long-term goal of our research program is to identify the mechanisms that mediate nicotine use among different clinical populations that are uniquely susceptible to this problem. The objective of this application is to determine the mechanisms that promote withdrawal from chronic nicotine vapor inhalation. Our central hypothesis is that sex differences in withdrawal are modulated in the local circuits of the IPN, where stress and ovarian hormones modulate withdrawal severity in females. The rationale for the proposed research is that its successful completion is likely to contribute to a mechanistic framework for the development of new cessation strategies, particularly for women. Guided by strong preliminary data, the following specific aims were designed to: 1) identify the mechanisms by which the IPN controls nicotine withdrawal in females and males and 2) determine the effects of ovarian hormones on IPN-modulated nicotine withdrawal in females. The proposed studies constitute a multi-disciplinary approach involving tract tracing, behavior, immunocytochemistry, neurochemistry, and gene-transfer technology to compare sex differences (Aim 1) and the influence of ovarian hormones (Aim 2) on withdrawal severity and inhibitory tone in the IPN. Supplement, Graduate Student, Nicotine, Neuroscience, Training