Abstract The goal of the Border Biomedical Research Center (BBRC) is to provide an infrastructure to study the factors that promote cancer-related health disparities, including nicotine use. The proposed administrative supplement will enhance research capacity by integrating a team of scientists that are focused on the mechanisms by which stress promotes nicotine use and subsequent increased risk of cancer. Recently, we discovered important new insights into the mechanisms by which stress systems in the habenula-interpeduncular nucleus (Hb-IPN) pathway modulate sex differences in nicotine withdrawal. Specifically, we found that withdrawal severity is closely associated with the activation of interneurons in the IPN that release the inhibitory neurotransmitter, gamma aminobutyric acid (GABA). This work established that inhibitory tone in the IPN plays a key role in the behavioral effects of nicotine withdrawal. The primary objective of this application is to vertically extend our prior work by determining the mechanisms by which stress systems in the IPN modulate withdrawal from chronic nicotine vapor inhalation. Our central hypothesis is that stress enhances anxiety-like behavior during withdrawal to a larger extent in females versus males, and this effect is due to greater inhibitory tone in the IPN. We expect that the proposed work will lead to a stronger mechanistic foundation for understanding how stress systems are anatomically positioned to increase inhibitory tone in the IPN during withdrawal in female versus male rats. A secondary objective is to assess changes in plasma biomarkers levels from rats that were included in the mechanistic studies of Aim 1. We will assess the relationship between stress, nicotine use, and subsequent biomarkers of allostatic load. We hypothesize that stress and high levels of nicotine intake in females will increase the biomarkers of allostatic overload versus males. The successful completion of the proposed work is likely to contribute to a mechanistic framework for the development of new nicotine use cessation strategies, particularly for women. The proposed work capitalizes upon BBRC core facilities to attain our objectives in two specific aims. Aim 1 will elucidate the mechanisms that modulate sex differences in nicotine withdrawal. Our working hypothesis is that exposure to a variable stress regimen will enhance nicotine withdrawal severity in females via greater inhibitory tone in the IPN as compared to males. Aim 2 will examine the relationship between chronic stress and nicotine exposure on allostatic overload and subsequent changes in the biomarkers of cancer risk. Our working hypothesis is that stress and nicotine exposure in females will produce greater allostatic overload as compared to males. At the completion of the proposed work, our expected outcomes are to have 1) defined the mechanisms of sex differences in nicotine withdrawal and 2) explored sex differences in the influence of chronic stress...