Estrogens are among important contributing factors to many sex differences in neuroendocrine regulation of energy homeostasis induced by stress. Research in this field is warranted since chronic stress-related psychiatric and metabolic disturbances continue to be top health concerns, and sex differences are witnessed in these aspects. For example, chronic stress disrupts energy homeostasis, leading to negative consequences in the regulation of emotion and metabolism. Females are known to be more vulnerable to the psychological consequences of stress, such as depression and anxiety, whereas males are more vulnerable to the metabolic consequences of stress. Sex differences that exist in the susceptibility to various stress-induced disorders have led researchers to hypothesize that gonadal hormones are regulatory factors that should be considered in stress studies. Further, estrogens are heavily recognized for their protective effects on metabolic dysregulation, such as anti-obesogenic and glucose-sensing effects. Perturbations to energy homeostasis using laboratory rodents, such as physiological stress or over-/under- feeding dietary regimen prevalent in today’s society, offer hints to the underlying mechanisms of estrogenic actions. Metabolic effects of estrogens primarily work through estrogen receptor α (ERα), which is differentially expressed between the sexes in hypothalamic nuclei regulating energy metabolism and in extrahypothalamic limbic regions that are not typically associated with energy homeostasis. In this review, we discuss estrogenic actions implicated in stress-induced sex-distinct metabolic disorders.

Chronic pain is highly prevalent in the pediatric population. Many factors are involved in the transition from acute to chronic pain. Currently, there are conceptual models proposed, but they lack a mechanistically sound integrated theory considering the stages of child development. Objective biomarkers are critically needed for the diagnosis, risk stratification, and prognosis of the pathological stages of pain chronification. In this article, we summarize the current evidence on mechanisms and biomarkers of acute to chronic pain transitions in infants and children through the developmental lens. The goal is to identify gaps and outline future directions for basic and clinical research toward a developmentally informed theory of pain chronification in the pediatric population. At the outset, the importance of objective biomarkers for chronification of pain in children is outlined, followed by a summary of the current evidence on the mechanisms of acute to chronic pain transition in adults, in order to contrast with the developmental mechanisms of pain chronification in the pediatric population. Evidence is presented to show that chronic pain may have its origin from insults early in life, which prime the child for the development of chronic pain in later life. Furthermore, available genetic, epigenetic, psychophysical, electrophysiological, neuroimaging, neuroimmune, and sex mechanisms are described in infants and older children. In conclusion, future directions are discussed with a focus on research gaps, translational and clinical implications. Utilization of developmental mechanisms framework to inform clinical decision-making and strategies for prevention and management of acute to chronic pain transitions in children, is highlighted.

Stress during adolescence clearly impacts brain development and function. Sex differences in adolescent stress-induced or exacerbated emotional and metabolic vulnerabilities could be due to sex-distinct gene expression in hypothalamic, limbic, and prefrontal brain regions. However, adolescent stress-induced whole-genome expression changes in key subregions of these brain regions were unclear. In this study, female and male adolescent Sprague Dawley rats received one-hour restraint stress daily from postnatal day (PD) 32 to PD44. Corticosterone levels, body weights, food intake, body composition, and circulating adiposity and sex hormones were measured. On PD44, brain and blood samples were collected. Using RNA-sequencing, sex-specific differences in stress-induced differentially expressed (DE) genes were identified in subregions of the hypothalamus, limbic system, and prefrontal cortex. Canonical pathways reflected well-known sex-distinct maladies and diseases, substantiating the therapeutic potential of the DE genes found in the current study. Thus, we proposed specific sex distinct, adolescent stress-induced transcriptional changes found in the current study as examples of the molecular bases for sex differences witnessed in stress induced or exacerbated emotional and metabolic disorders. Future behavioral studies and single-cell studies are warranted to test the implications of the DE genes identified in this study in sex-distinct stress-induced susceptibilities.

Introduction: Mu opioid receptor gene (OPRM1) variant rs1799971 introduces a CpG site, which may influence DNA methylation (DNAm) and opioid/pain outcomes. Objectives: In this nested analysis, we investigated both OPRM1 A118G genotype and promoter/immediate downstream blood DNAm sequencing data for associations with opioid effects and chronic postsurgical pain (CPSP) in a surgical cohort. Methods: Prospectively recruited opioid naïve patients undergoing Nuss procedure or spinal fusion with rs1799971 genotypes (Illumina arrays), DNAm (next generation enzymatic methylation sequencing at Chr6:154,039,209-154,039,803) and outcomes—opioid analgesia (integrated opioid use + pain over postoperative days 0 and 1 normalized to surgery type), safety—respiratory depression (RD) in high opioid use groups, and CPSP (Numerical Rating Scale >3/10 2-12 months postsurgery)—were included. Linear and logistic regression were performed to test genetic and epigenetic associations, adjusted for sociodemographics, cell types, and analgesics. Results: In this cohort (N = 112; 15.3 ± 2.0 years, 50% female, 83% White, 55% had CPSP, 13% had RD), DNAm at Chr6:154039216-154039217 was associated with CPSP (odds ratio [OR], 1.26; 95% confidence interval [CI], 1.00-1.57; P = 0.03), Chr6:154039661-154039662 with acute integrated pain (β = −20.9, 95% CI, −40.70 to −1.10, P = 0.04), Chr6:154039520-154039521 (OR, 1.49; 95% CI, 1.09-2.03; P = 0.01), and Chr6:154039571-154039572 (OR, 1.47; 95% CI, 1.08-2.01; P = 0.02) with RD. Significant CpG sites were located in Repressed Polycomb chromatin states. Genotype was not associated with DNAm or outcomes. Conclusion: Our analyses support OPRM1 DNAm as predictors of acute and chronic pain/opioid outcomes in children after painful surgery. Study limitations included absent GG genotype, low sequencing coverage, and lack of correction for multiple testing.