Troy A. Roepke

Organophosphate flame retardants (OPFRs) are ubiquitous flame-retardant additives with endocrine-disrupting properties. Despite increasing evidence that OPFRs impact neurodevelopment, their effects on the neuroendocrine stress response remain poorly understood. To examine their long-term impact on stress regulation, we treated pregnant C57Bl/6J dams to a mixture of tris(1,3-dichloro-2-propyl) phosphate (TDCPP), triphenyl phosphate (TPP), and tricresyl phosphate (TCP; 1 mg/kg each) from gestational day (GD) 7 through postnatal day (PND) 14. Adult offspring (8-9 weeks of age) were then challenged with acute stressors, including 1 h restraint or a 6-day acute variable stress (AVS) paradigm. Perinatal OPFR exposure produced persistent, sex-specific alterations in the hypothalamic–pituitary–adrenal (HPA) axis and stress-related neurocircuitry. Following 1 h restraint, OPFR-treated females showed heightened serum corticosterone. In addition, gene expression analysis revealed sex-dependent disruptions in key stress-regulatory pathways after OPFR treatment and 1 h restraint in the hypothalamus (Crhr1, Crhr2, Ptpn5) and pituitary (Crhr1, Pomc, Nr3c1). Females demonstrated more differences in adrenal gene expression related to steroidogenesis (Mc2r, Cyp11b2) and catecholamine biosynthesis (Dbh, Pnmt), with OPFR-treated groups having blunted responses. OPFR AVS females displayed reduced corticosterone and Crh mRNA in the hypothalamus, and downregulated Pacap/Pac1r expression in the bed nucleus of the stria terminalis (BNST), accompanied by increased behavioral avoidance and immobility. In males, OPFR exposure led to increased BNST Pacap and Pac1r, expression, along with hyperactivity and avoidance behaviors. Together, these findings demonstrate that early-life OPFR exposure induces lasting, sex-specific dysregulation of the HPA axis and associated stress circuits, highlighting OPFRs as developmental neuroendocrine disruptors with implications for mood and stress-related disorders.

Developmental exposure to organophosphate flame retardants (OPFRs) is a public health concern due to their endocrine-disrupting potential. We examined perinatal exposure to tris(1,3-dichloro-2-propyl) phosphate, triphenyl phosphate, and tricresyl phosphate in mice. Adult male and female offspring were assessed for memory and anxiety-like behavior. Dopamine and norepinephrine were quantified in the hippocampus and prefrontal cortex (PFC), and bulk RNA sequencing was conducted for the hippocampus. OPFR-treated females in high ovarian hormone states spent less time in the open field test (OFT) center, the Y-maze unknown arm, and with the displaced object in spatial object recognition (SOR) indicating increased anxiety-like behavior and impaired spatial memory. These females also illustrated improved memory on the short-term Barnes maze, and a trending improvement in the novel object recognition test. Females in low ovarian hormone states, demonstrated a trend in center OFT exploration. OPFR-treated males displayed disruption in memory in the SOR and the short- and long-term Barnes maze. Perinatal OPFR reduced hippocampal dopamine in males and altered prefrontal dopamine in females in a hormone-dependent manner. OPFR-treated females in high ovarian hormones states demonstrated a trending decrease in PFC norepinephrine. Perinatal OPFR treatment caused differential gene expression in 121 individual genes and alteration to functional modules related to RNA processing, cellular metabolism, and extracellular organization. Hormone status also affected gene OPFR-induced altered expression, with similarity between males and high ovarian hormone state females. Our findings suggest that perinatal OPFR exposure causes widespread, sex specific, and hormone dependent disruptions in behavior, neurochemistry, and gene expression in adulthood. Highlights: Anxiety-like behavior in OPFR-treated females varied with ovarian hormone status High ovarian hormone OPFR females showed task-dependent changes in memory Males displayed impaired spatial memory following perinatal OPFR treatment Perinatal OPFR modifies hippocampal and prefrontal dopamine and norepinephrine OPFR treatment altered individual gene and functional gene module expression

Organophosphate flame retardants (OPFRs) are ubiquitous flame-retardant additives with endocrine-disrupting properties. Despite increasing evidence that OPFRs impact neurodevelopment, their effects on the neuroendocrine stress response remain poorly understood. To examine their long-term impact on stress regulation, we treated pregnant C57Bl/6J dams to a mixture of tris(1,3-dichloro-2-propyl) phosphate (TDCPP), triphenyl phosphate (TPP), and tricresyl phosphate (TCP; 1 mg/kg each) from gestational day (GD) 7 through postnatal day (PND) 14. Adult offspring (8-9 weeks of age) were then challenged with acute stressors, including 1 h restraint or a 6-day acute variable stress (AVS) paradigm. Perinatal OPFR exposure produced persistent, sex-specific alterations in the hypothalamic–pituitary–adrenal (HPA) axis and stress-related neurocircuitry. Following 1 h restraint, OPFR-treated females showed heightened serum corticosterone. In addition, gene expression analysis revealed sex-dependent disruptions in key stress-regulatory pathways after OPFR treatment and 1 h restraint in the hypothalamus ( Crhr1, Crhr2, Ptpn5 ) and pituitary ( Crhr1, Pomc, Nr3c1 ). Females demonstrated more differences in adrenal gene expression related to steroidogenesis ( Mc2r, Cyp11b2 ) and catecholamine biosynthesis ( Dbh, Pnmt ), with OPFR-treated groups having blunted responses. OPFR AVS females displayed reduced corticosterone and Crh mRNA in the hypothalamus, and downregulated Pacap/Pac1r expression in the bed nucleus of the stria terminalis (BNST), accompanied by increased behavioral avoidance and immobility. In males, OPFR exposure led to increased BNST Pacap and Pac1r , expression, along with hyperactivity and avoidance behaviors. Together, these findings demonstrate that early-life OPFR exposure induces lasting, sex-specific dysregulation of the HPA axis and associated stress circuits, highlighting OPFRs as developmental neuroendocrine disruptors with implications for mood and stress-related disorders.

The maternal–fetal environment is influenced by multiple factors, including nutrition and environmental contaminants, which can impact long-term development. Perinatal exposure to organophosphate flame retardants (OPFRs) disrupts energy homeostasis and causes maladaptive behaviors in mice. Maternal obesity affects development by impairing blood–brain barrier (BBB) formation, influencing brain regions involved in energy regulation and behavior. This study examined the combined effects of maternal obesity and perinatal OPFR treatment on offspring development. Female mice were fed either a low-fat (LFD) or a high-fat diet (HFD) for 8 weeks, mated, and treated with either sesame oil or an OPFR mixture (tris(1,3-dichloro-2-propyl)phosphate, tricresyl phosphate, and triphenyl phosphate, 1 mg/kg each) from gestational day 7 to postnatal day 14. Results showed that both maternal diet and OPFR treatment disrupted blood–brain barrier integrity, energy balance, and reproductive gene expression in the hypothalamus of neonates. The expression of hepatic genes related to lipid and xenobiotic metabolism was also altered. In adulthood, LFD OPFR-treated female offspring exhibited increased avoidance behavior, while HFD OPFR-treated females demonstrated memory impairments. Metabolic assessments revealed decreased energy expenditure and nighttime activity in LFD OPFR-treated females. These findings suggest that maternal diet and OPFR treatment alter hypothalamic and liver gene expression in neonates, potentially leading to long-term metabolic and behavioral changes.

Chronic stress is a physiological state marked by dysregulation of the hypothalamic–pituitary–adrenal axis and high circulating levels of stress hormones, such as corticosterone in mice or cortisol in humans. This dysregulated state may result in the development of mood disorders, but the process by which this occurs is still unknown. The bed nucleus of the stria terminalis (BNST) serves as an integration center for stress signaling and is therefore likely an important area for the development of mood disorders. This project utilized a chronic variable mild stress (CVMS) paradigm to persistently stress mice for 6 weeks, followed by RNA‐Sequencing of the anterodorsal (ad) BNST and electrophysiology of corticotropin‐releasing hormone‐expressing cells in the adBNST. Our results show significant sex biases in the transcriptome of the adBNST as well as effects of CVMS on the transcriptome of the adBNST specifically in males. Female‐biased genes are related to synaptic transmission, while male‐biased genes are related to RNA processing. Stress‐sensitive genes in males are related to synaptic transmission and synapse formation. Additionally, electrophysiology data showed that CVMS suppressed the M‐current in males but not females. However, CVMS increased the strength of excitatory post‐synaptic currents in females but not males. This suggests significant differences in how males and females process chronic stress. It also suggests that the BNST is more sensitive to chronic stress in males than in females.

Flame retardants have been used extensively to reduce flammability in household and industrial materials raising significant concerns due to their toxicological effects, particularly on neurodevelopment and cognition. These chemicals, including legacy compounds such as polybrominated diphenyl ethers and newer organophosphate flame retardant, exhibit endocrine-disrupting properties that interfere with hormonal pathways, neurotransmission, and synaptic plasticity. Epidemiological studies have linked flame retardant exposure to adverse developmental outcomes, including anxiety and cognitive deficits. Mechanistic research reveals that flame retardants disrupt neurogenesis, synaptogenesis, and neurotransmitter pathways, often mediated through oxidative stress, mitochondrial dysfunction, and nuclear receptor modulation. Animal studies corroborate these findings, showing impaired spatial memory, altered anxiety-like behaviors, and disrupted neurochemical homeostasis following perinatal and postnatal exposure to flame retardants. Emerging organophosphate flame retardants, such as bis(2-ethylhexyl) phenyl phosphate, demonstrate comparable or increased toxicity, further emphasizing the need for regulatory scrutiny and safer alternatives. This review synthesizes current knowledge on the neurotoxic mechanisms of flame retardants, highlighting their impact on anxiety and cognition across developmental stages. Understanding these pathways is essential to mitigating the long-term environmental and human health effects of flame retardant exposure.

Stress can be broken down into systemic and processive stressors with processive stressors requiring higher limbic processing. These are also often called social stressors as they require an understanding of social dynamics as opposed to physical based stressors. This differing of processing necessitates we study both phenomena. Additionally, sex is an important aspect of stress research as men and women show differing responses to stress and mood disorder development. To study this, we used a chronic social instability stress (CSIS) paradigm to stress male and female mice. This paradigm is approximately 7-weeks long and involves changing the cage mates of a mouse every 3 days so stable social dynamics cannot form. Afterwards, one cohort was used for avoidance behavior testing using the open field test, the elevated plus maze, the light/dark box emergence test, and the novelty suppressed feeding test. A second cohort was used for bulk RNA-Sequencing of the anterodorsal bed nucleus of the stria terminalis which is a limbic structure known to be related to chronic stress signaling. In the behavior assays, CSIS caused the females to be less avoidant, while the males became more avoidant. Additionally, we found that a low estrogen state in the females caused them to be less avoidant than in a high estrogen state. In the transcriptome, we found major differences between the males and females with the males expressing more genes related to transcription whereas the females expressed more genes related to synaptic transmission. We also found that the transcriptome in the males is more sensitive to the stress than the females. In summary, we have found how social stress is differentially regulated between males and females and how this may be related to the development of stress-related behavioral changes.