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Coupling of the HPA and HPG Axes University of New Orleans ScholarWorks@UNO University of New Orleans Theses and Dissertations Dissertations and Theses Fall 12-20-2013 Coupling of the HPA and HPG Axes Andrew Dismukes University of New Orleans, [email protected] Follow this and additional works at: https://scholarworks.uno.edu/td Part of the Biological Psychology Commons Recommended Citation Dismukes, Andrew, "Coupling of the HPA and HPG Axes" (2013). University of New Orleans Theses and Dissertations. 1732. https://scholarworks.uno.edu/td/1732 This Thesis is protected by copyright and/or related rights. It has been brought to you by ScholarWorks@UNO with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights- holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/or on the work itself. This Thesis has been accepted for inclusion in University of New Orleans Theses and Dissertations by an authorized administrator of ScholarWorks@UNO. For more information, please contact [email protected]. Coupling of the HPA and HPG Axes A Thesis Submitted to the Graduate Faculty of the University of New Orleans in partial fulfillment of the requirements for the degree of Master of Science in Psychology by Andrew Dismukes B.S. Auburn University December, 2013 Table of Contents Table of Figures ............................................................................................................................................................ ii Abstract ......................................................................................................................................................................... iii Introduction ................................................................................................................................................................... 1 Stress, Hormones, and Development ........................................................................................................................ 3 The HPA and HPG Axes ............................................................................................................................................. 6 Parallel Structure and Architecture .................................................................................................................................... 8 Top-down Processes: Neural regulation of the HPA and HPG axis ....................................................................... 9 Bottom-up Processes: HPA & HPG .................................................................................................................................. 15 Mechanistic Concerns: How do the HPA and HPG Axis talk to one another? ................................................. 19 Standing on the shoulders of giants: What does the existing literature say about coupling? ....................... 22 Adolescence: A period when the HPA and HPG axes are both excited. ........................................................ 24 Stress Revisited: Context for the Current Proposal ............................................................................................ 27 Stress Reactivity: The Skydiving Study ............................................................................................................................. 28 Short-term Stress Exposure: The MRI/SPIT Project ................................................................................................... 29 Long-term Stress Exposure: The Mendota Project ...................................................................................................... 30 Methods ....................................................................................................................................................................... 31 Stress Reactivity: The Skydiving Study ............................................................................................................................. 31 Short-Term Stress Exposure: The MRI/SPIT Project .................................................................................................. 33 Long-Term Stress Exposure: The Mendota Project ..................................................................................................... 34 Analytic Strategy ...................................................................................................................................................................... 36 Results .......................................................................................................................................................................... 39 Stress Reactivity: The Skydiving Study ............................................................................................................................. 39 Short-Term Stress Exposure: The MRI/SPIT Project .................................................................................................. 41 Long-Term Stress Exposure: The Mendota Project ..................................................................................................... 46 Discussion .................................................................................................................................................................. 52 Stress Reactivity: The Skydiving Project ......................................................................................................................... 52 Short-Term Stress Exposure: The MRI/SPIT Project .................................................................................................. 55 Long-Term Stress Exposure: The Mendota Project ..................................................................................................... 56 Limitations and Future Directions ......................................................................................................................... 61 Conclusion .................................................................................................................................................................. 64 References ................................................................................................................................................................... 64 Vita ............................................................................................................................................................................... 71 i Table of Figures Figure 1: Stress Exposure Influences the HPA and HPG Axes……………………………………………3 Figure 2: The Limbic-HPA Loop………………………………………………………………………………………7 Figure 3: Suppressive Cross-Axis Communication……………………………………………………………22 Figure 4: Organization of the Study………………………………………………………………………………..28 Figure 5: Analytic Summary……………………………………………………………………………………………38 Figure 6: Coupling in the Skydiving Study……………………………………………………………………….40 Table 1: Bivariate coupling of cortisol with Testosterone and DHEA…………………41 Table 2: Trivariate coupling of Cortisol, Testosterone and DHEA in Skydiving………………....41 Table 3: Bivariate Coupling in the MRI/SPIT Data set………………………………….45 Figure 7: Short-term coupling of cortisol and testosterone……………………………..45 Table 4: Descriptive Statistics for Mendota Stress Variables…………………………..48 Figure 8: Abuse and predicted cortisol levels…………………………………………………………………..50 Table 5: Coupling in the context of long-term stress…………………………………………….………….50 Table 6: Trivariate Coupling of Cortisol, Testosterone and DHEA…………………………………....51 ii Abstract The Hypothalamic-Pituitary-Adrenal (HPA) and –Gonadal (HPG) axes have been considered mutually inhibitory; however, emerging evidence supports the proposition that this might not necessarily be the case. This idea is termed “coupling,” in which the HPA-HPG axis are mutually activated or deactivated. Coupling is examined across three data sets with different time-courses of stress exposure, and results demonstrate HPA- HPG co-activation occurs. Furthermore, stress exposure influences this relationship. The discussion shows how it is physiologically possible to have positive coupling or co- activation between these axes according to complex regulatory feedback systems and overlapping neural structures. Findings are interpreted developmentally, because adolescence may be a critical time for this co-activation to occur. Finally, the discussion emphasizes an individual difference perspective because each individual differs in the duration and type of stress they experience, and these exerted individualized effects on HPA-HPG coupling. KEYWORDS: Stress; HPA; HPG; Coupling; Cortisol; Testosterone iii Introduction The current project examines the manner in which Hypothalamic-Pituitary- Adrenal and –Gonadal axes fluctuate with one another. The interplay between adrenal and gonadal axes will be examined across three data sets, which include repeated hormone assessment of both axes. Historically, hormone axes have been examined in isolation, but an emerging perspective suggests that it is worthwhile to analyze them in conjunction with one another – to look at the manner in which axes are ‘coupled’ together. Coupling makes sense from the point of view of functional interconnections between the HPA and HPG axes, and from a developmental point of view. Furthermore, it is likely that stress exposure would influence the degree of coupling between the HPA in HPG axes, magnifying the
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