Characterizing the neural substrates of irritability in women: an experimental neuroendocrine model

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Irritability, defined as a predisposition to exhibit anger, is a prominent, defining symptom of perinatal depression (PND) and many other neuropsychiatric disorders. Despite the near ubiquity of irritability across disorders, the neural dysfunction underlying the vulnerability to, onset of, and exacerbation of irritability is understudied and poorly understood. The proposed study involves experimentally manipulating reproductive hormones in nonpregnant, euthymic women to create a scaled down version of the changes that occur during pregnancy and the postpartum period. This endocrine manipulation paradigm, which we have shown provokes irritability in past studies, will be used to examine the neurocircuitry underlying irritability under baseline and hormone challenge conditions among women who are hormone sensitive (HS+; n=15) and non-hormone sensitive (HS-; n=15). The long-term goal of this research is to advance our understanding of the neural systems underlying both the triggering of and susceptibility to irritability in women. The objective of the current project is to examine whether HS+ show differences in the behavioral activation system relative to HS- under baseline and hormone challenge conditions using functional magnetic resonance imaging (fMRI) and behavioral tests. Our central hypothesis is that reproductive hormone changes are associated with dysregulated threat and reward processing and consequent irritability in HS+. The rationale for the proposed study is that employing a scaled down model of puerperal hormonal events permits the identification of a group of individuals homogeneous for hormone sensitivity (HS+), hence creating the best opportunity for disentangling the specific changes in brain function due to reproductive hormones (i.e., HS-) from those accompanying reproductive hormone-precipitated affective dysfunction (i.e., HS+). Because women will act as their own controls across time, this study design also allows for a powerful evaluation of state and trait variables that may contribute to irritability, including both threat and reward processing. Identifying both state and trait markers of irritability, and disentangling them from the effects of reproductive hormones on brain and behavior, will allow for the identification of neural substrates of irritability susceptibility that can be investigated across neuropsychiatric disorders. We plan to accomplish the objectives of this application by pursuing the following specific aims: to determine the extent to which irritability is characterized by 1) dysfunctional threat processing and 2) dysfunctional reward processing during reproductive hormone challenge relative to baseline in HS+ and HS-. We expect that, relative to baseline, HS+ women will show greater behavioral approach during threat and frustration as well as dysregulation in brain regions responsible for threat and reward processing during hormone challenge, relative to baseline, compared with HS-. The expected outcome of this research is the identification of neural circuits underlying both the susceptibility to and mediation of irritability.