Background: Emerging evidence demonstrates that diet-induced obesity disrupts corticolimbic circuits underlying emotional regulation. Studies directed at understanding how obesity alters brain and behavior are easily confounded by a myriad of complications related to obesity. This study investigated the early neurobiological stress response triggered by an obesogenic diet. Furthermore, this study directly determined the combined impact of a short-term obesogenic diet and adolescence on critical behavioral and molecular substrates implicated in emotion regulation and stress. Methods: Adolescent (postnatal day 31) or adult (postnatal day 81) Lewis rats were fed for 1 week with an experimental Western-like high-saturated fat diet (WD, 41% kcal from fat) or a matched control diet (CD, 13% kcal from fat). We used the acoustic fearpotentiated startle (FPS) paradigm to determine the effects of the WD on cued fear conditioning and fear extinction. We used c-Fos mapping to determine the functional influence of the diet and stress on corticolimbic circuits. Results: We report that 1-week WD consumption was sufficient to induce fear extinction deficits in adolescent rats, but not in adult rats. We identify fear-induced alterations in corticolimbic neuronal activation and demonstrate increased prefrontal cortex CRHR1 messenger RNA (mRNA) levels in the rats that consumed the WD. Conclusion: Our findings demonstrate that short-term consumption of an obesogenic diet during adolescence heightens behavioral and molecular vulnerabilities associated with risk for anxiety and stress-related disorders. Given that fear extinction promotes resilience and that fear extinction principles are the foundation of psychological treatments for posttraumatic stress disorder (PTSD), understanding how obesogenic environments interact with the adolescent period to affect the acquisition and expression of fear extinction memories is of tremendous clinical relevance.

Background: Anxiety and stress-related disorders are strongly linked with obesity and the consumption of obesogenic diets. Paralleling clinical findings, we showed that the consumption of an obesogenic diet during adolescence disrupts the structural integrity of amygdalar and prefrontal cortex circuits underlying emotional responses to stress. These abnormalities were associated with a PTSD-like phenotype, including heightened stress reactivity to predator odor trauma, anxietylike behaviors, and profound learning deficits. The present follow-up study investigates how an obesogenic diet alters aversion-related associative memories across adolescence. Methods: Adolescent Lewis rats were fed for eight weeks with an experimentalWestern-like high-saturated fat/high-sugar diet (WD, 41% kcal from fat) or a matched control diet (CD, 13% kcal from fat). Acoustic fear-potentiated startle (FPS) responses were assessed longitudinally at weeks 1, 4, and 8 after commencing the diets to determine the effects of the WD on cued fear conditioning, fear extinction learning, and fear extinction retention. Results:We found that the rats that consumed the WD exhibited substantial attenuation of fear extinction and fear extinction retention when remote memory was tested. One-week WD consumption was sufficient to induce impairments in fear extinction learning. This phenotype was associated with reduced dopamine receptor 1 mRNA levels in the prefrontal cortex. Interestingly, our reconditioning paradigm revealed that early-acquired fear memories were resistant to the disruptive effects of chronic WD consumption on cued fear learning. Vega-Torres et. al., 3Conclusions: Our findings demonstrate that consumption of an obesogenic WD during adolescence heightens behavioral vulnerabilities associated with risk for anxiety and stress-related disorders. Given that fear extinction promotes resilience and that fear extinction principles are the foundation of psychological treatments for PTSD, understanding how obesity and obesogenic diets affect the acquisition and expression of fear extinction memories is of tremendous clinical relevance. HIGHLIGHTS• Acute WD consumption impairs cued fear extinction learning in a fearpotentiated startle paradigm.• WD consumption attenuates fear extinction memory retention • WD consumption during adolescence increases acoustic startle responsivity over time • Chronic WD consumption decreases dopamine receptor D1 mRNA levels in the prefrontal cortex.

Background: Emerging evidence demonstrates that diet-induced obesity disrupts corticolimbic circuits underlying emotional regulation. Studies directed at understanding how obesity alters brain and behavior are easily confounded by a myriad of complications related to obesity. This study investigated the early neurobiological stress response triggered by an obesogenic diet. Furthermore, this study directly determined the combined impact of a short-term obesogenic diet and adolescence on critical behavioral and molecular substrates implicated in emotion regulation and stress.Methods: Adolescent (postnatal day 31) or adult (postnatal day 81) Lewis rats were fed for one week with an experimental Western-like high-saturated fat diet (WD, 41% kcal from fat) or a matched control diet (CD, 13% kcal from fat). We used the acoustic fear-potentiated startle (FPS) paradigm to determine the effects of the WD on cued fear conditioning and fear extinction. We used c-Fos mapping to determine the functional influence of the diet and stress on corticolimbic circuits. Results:We report that one-week WD consumption was sufficient to induce fear extinction deficits in adolescent rats, but not in adult rats. We identify fear-induced alterations in corticolimbic neuronal activation and demonstrate increased prefrontal cortex CRHR1 mRNA levels in the rats that consumed the WD. Conclusions:Our findings demonstrate that short-term consumption of an obesogenic diet during adolescence heightens behavioral and molecular vulnerabilities associated with risk for anxiety and stress-related disorders. Given that fear extinction promotes resilience, and that fear extinction principles are the Vega-Torres et. al., 3 foundation of psychological treatments for PTSD, understanding how obesogenic environments interact with the adolescent period to affect the acquisition and expression of fear extinction memories is of tremendous clinical relevance. KEYWORDS PTSD, diet-induced obesity, adolescence, anxiety, fear-potentiated startle, CRHR1 HIGHLIGHTS • Short-term WD consumption during adolescence impairs cued fear extinction memory retention in a fear-potentiated startle paradigm.• Short-term WD consumption during adolescence attenuates neuronal activation to electric footshock stress in the basomedial nuclei of the amygdala.• Short-term WD consumption increases CRHR1 mRNA levels in the medial prefrontal cortex.• Adult LEW rats exhibit increased basal HPA axis tone and heightened emotional reactivity to footshock stress relative to adolescent rats.

Cardiovascular disease (CVD) is the leading cause of death and disability worldwide. Stress is a major risk factor for CVD. However, little is known about how stress leads to pathological changes over time, contributing to the development and progression of CVD. Enhancing our understanding of the molecular and cellular mechanisms that are affected following the activation of the hypothalamic‐pituitary‐adrenal (HPA) axis may provide mechanistic links connecting stress and CVD risk. Endothelin‐1 (ET‐1) is one of the most potent vasoconstrictors and it is produced by vascular endothelial cells. Recent evidence indicates that its expression is elevated following stress. However, how ET‐1 expression increases following stress is unknown. This study investigated molecular links connecting stress‐responsive hormonal signals to ET‐1 expression in endothelial cells. We found elevated ET‐1 mRNA and protein levels in heart tissue from Lewis rats exposed to mild psychogenic stressor (1.9 fold ± 0.7 relative to unexposed controls, p<0.05, n=12 rats/group). ET‐1 expression and corticosterone levels were significantly correlated in rats exposed to mild psychogenic stress (r = 0.4770, p < 0.0129; n=12). In vitro studies using the human endothelial cell line EA.hy926 revealed that hydrocortisone significantly increased ET‐1protein levels in a dose response manner (1.8 fold ± 0.4 relative to vehicle treatment, p<0.01,n=4). We found that this effect was abolished when cells were pre‐treated with the glucocorticoid receptor (GR) antagonist mifepristone (p<0.0001). Furthermore, FKBP5 gene knockdown experiments demonstrated that FKBP5 is essential for the production of ET‐1 following GR activation. Our data identifies a novel pathway for GR‐mediated ET‐1 induction, which may provide fundamental understanding of the mechanistic links connecting stress and CVD. Support or Funding Information This study was partly supported by the NIH (P20MD006988 and 2R25 GM060507), the Loma Linda University School of Medicine Seed Grant, GRASP Funds to JDF and by the Abbvie Research Fellowship 34254. EA‐hy926 cells exhibited increased (A) FKBP5 and (B) Edn mRNA levels in a hydrocortisone dose‐specific manner. One‐way ANOVA: relative to control: p<0.05, p<0.01, p<0.001, p<0.0001; n=4. (C‐D) We study 10nM and 100nM of hydrocortisone exposure EA‐hy926 cells for 24 hours with and without Mifepristone. This attenuates hydrocortisone effects on FKBP5 (C) and Edn (D) mRNA levels. Two‐way ANOVA: p<0.05, p<0.01, p<0.001, p<0.0001; n=4. (E) Mifepristone reduces ET‐1 protein levels in EA‐hy926 cells. FKBP5 is required for the induction of endothelin 1 expression by cortisol. (A) FKBP5 mRNA levels were markedly reduced by FKBP5 siRNA treatment. (B) FKBP5 siRNA treatment blunted the induction of Edn by cortisol. (C) FKBP5 siRNA treatment reduced ET‐1 levels even in the presence high hydrocortisone levels. Two‐way ANOVA: p<0.05, p<0.01, p<0.001, p<0.0001; n=4.