Early Exposure to Common Plastic Chemical Linked to Increased Anxiety in Adult Male Rats

CHICAGO, Illinois – New research presented at ENDO 2026, the Endocrine Society’s annual meeting, has unveiled a concerning link between early-life exposure to a widely used plastic chemical and elevated anxiety levels in adult male rats. The findings, originating from the University of Buenos Aires School of Medicine, suggest that developmental exposure to di-(2-ethylhexyl) phthalate (DEHP), a ubiquitous plasticizer, can induce long-lasting behavioral changes, raising potential implications for human health.

The study, led by Osvaldo Juan Ponzo, M.D., Ph.D., a professor of physiology, demonstrated that male rats exposed to DEHP during critical prenatal and immediate postnatal developmental stages exhibited significantly higher anxiety behaviors as adults, even in the absence of continued exposure. This research underscores the vulnerability of developing systems to endocrine-disrupting chemicals (EDCs) and highlights the potential for lasting neurobehavioral consequences.

Understanding Di-(2-ethylhexyl) Phthalate (DEHP)

DEHP is a phthalate ester commonly incorporated into plastics to enhance their flexibility and durability. Its widespread application means it is found in a vast array of consumer and medical products. From the flexible tubing of intravenous medical devices and blood bags to children’s toys, shower curtains, and protective outerwear like raincoats, DEHP’s presence in daily life is extensive.

The chemical’s pervasive nature has prompted significant scientific scrutiny. Previous research has established that DEHP and its metabolic byproducts can interfere with the endocrine system and exert adverse effects on multiple organ systems in both animal models and humans. Notably, the reproductive and nervous systems have been identified as key targets of DEHP’s disruptive potential. Building upon this established body of knowledge, the University of Buenos Aires researchers specifically sought to investigate DEHP’s impact on anxiety-related behaviors in adult male rats. A critical component of their investigation was to determine whether the neurotransmitter gamma-aminobutyric acid (GABA), known for its inhibitory role in the central nervous system, or the hormone testosterone, played a mediating role in these observed behavioral changes.

The Experimental Design: A Chronological Approach to Exposure

The study’s methodology was carefully designed to simulate early-life exposure scenarios. Pregnant female rats were administered daily oral doses of DEHP. This exposure commenced on the very first day of gestation and continued throughout the entire period of lactation, ensuring that the developing pups were exposed to the chemical during their most formative developmental windows – the prenatal period and the immediate postnatal period. This controlled exposure strategy allowed researchers to isolate the effects of early-life DEHP contact.

Once the male offspring reached a mature adult stage, specifically at 70 days of age, their anxiety-related behaviors were rigorously assessed. The primary tool employed for this evaluation was the elevated plus maze (EPM). This widely recognized behavioral paradigm in rodent research capitalizes on the innate aversion of rodents to open, elevated spaces. The maze is configured in a cross shape, featuring two enclosed arms and two open arms. The fundamental principle is that anxious animals will tend to spend more time in the safer, enclosed areas and less time exploring the exposed, potentially threatening open arms.

Researchers meticulously quantified several behavioral parameters during the EPM test. These included the frequency with which the rats entered each type of arm (open versus enclosed), the total duration of time spent in each arm, and the duration of immobility, a behavior often referred to as "freezing." Freezing is a common indicator of fear and anxiety in rodents, reflecting a state of heightened vigilance and avoidance of perceived threats. By analyzing these metrics, the researchers could objectively measure the degree of anxiety exhibited by the adult male rats that had been exposed to DEHP during their development.

Reversing the Effects: The Role of GABA and Testosterone

The study then introduced a crucial intervention phase to explore potential countermeasures to DEHP-induced anxiety. Ninety minutes prior to their scheduled EPM testing, some of the DEHP-exposed rats received therapeutic treatments. One group was administered GABA agonists, which are compounds designed to mimic the action of GABA by binding to and activating its receptors. This intervention aimed to enhance the inhibitory signaling within the brain, potentially counteracting anxiety-promoting pathways. Another group of DEHP-exposed rats received testosterone. This hormonal treatment was administered every 48 hours for a period of 14 days leading up to the behavioral testing, investigating the potential influence of androgen signaling on DEHP-related behavioral modifications.

The results of these interventions provided compelling insights. Male rats that had been exposed to DEHP during development and received no further treatment exhibited clear and significant signs of heightened anxiety. They demonstrated a marked reluctance to explore the open arms of the elevated plus maze, opting instead to remain predominantly within the enclosed arms. Furthermore, these rats displayed longer periods of freezing behavior, indicating a state of increased fearfulness and avoidance.

In stark contrast, the DEHP-exposed rats that were subsequently treated with either GABA agonists or testosterone showed a notable reversal of these anxiety-related behaviors. Their patterns of exploration in the EPM shifted, with a greater willingness to enter and spend time in the open arms. The increased freezing behavior also diminished, suggesting that these treatments effectively counteracted the behavioral alterations induced by early DEHP exposure.

Expert Commentary and Scientific Significance

Dr. Ponzo elaborated on the significance of these findings, stating, "This work demonstrates that contact with DEHP in the early stages of life could modify behavior with regard to anxiety, even in the absence of DEHP exposure in adulthood. These neuroendocrine changes can be reversed by treating with GABA agonists or testosterone." This statement emphasizes the lasting imprinting effect of early developmental exposure to EDCs and points to specific neurobiological mechanisms that may be involved.

The presentation of this research at ENDO 2026, the Endocrine Society’s premier annual scientific conference, signifies its importance within the endocrinology and broader scientific community. The Endocrine Society is a global organization representing professionals dedicated to understanding and treating endocrine disorders, making it a key platform for disseminating cutting-edge research on hormone action and chemical disruption of the endocrine system. The annual meeting serves as a critical forum for researchers to share their latest findings, engage in scientific discourse, and foster collaborations.

Broader Implications and Future Research Directions

While the study was conducted in a rodent model, the implications for human health are a significant consideration. The developmental trajectories of rats and humans share fundamental similarities, particularly concerning the critical windows of organogenesis and neural development. The widespread presence of DEHP in products used by pregnant women and infants raises concerns about potential human exposure during these vulnerable periods.

The observed link between early DEHP exposure and increased anxiety in adult rats suggests that similar long-term behavioral changes could occur in humans. Endocrine-disrupting chemicals, by their very nature, interfere with the body’s hormonal signaling, which plays a crucial role in the development and function of the brain. The nervous system and the endocrine system are intricately linked, and disruptions during development can have profound and enduring consequences on mood, behavior, and cognitive function.

The findings that GABA agonists and testosterone could reverse these effects provide promising avenues for further investigation. GABA is the primary inhibitory neurotransmitter in the mammalian brain, and its dysregulation has been implicated in various anxiety disorders. Testosterone, an androgen hormone, also plays a role in brain development and function, including in areas related to mood and behavior. Understanding the precise mechanisms by which DEHP disrupts GABAergic and androgenic signaling during development is a critical next step.

Further research could focus on:

• Human Epidemiological Studies: Investigating whether similar correlations exist in human populations, particularly by examining exposure levels during pregnancy and childhood and correlating them with anxiety disorders later in life.
• Mechanistic Studies: Delving deeper into the molecular and cellular pathways affected by DEHP during critical developmental periods, focusing on its impact on neurogenesis, synaptic plasticity, and the development of neural circuits involved in anxiety regulation.
• Dose-Response Relationships: Determining the specific doses of DEHP that elicit these behavioral changes and assessing whether there are critical periods of exposure during development that are particularly sensitive.
• Intervention Strategies: Exploring the efficacy of similar interventions (e.g., GABAergic agents, hormonal therapies) in mitigating DEHP-induced behavioral alterations in more complex animal models or, if ethically and scientifically justifiable, in human populations.
• Cumulative Effects of EDCs: Investigating how DEHP exposure interacts with other common environmental chemicals that may also act as EDCs, as human exposure typically involves a complex mixture of substances.

The research presented at ENDO 2026 serves as a critical reminder of the potential health impacts of widespread chemical exposures during vulnerable developmental stages. It underscores the need for continued vigilance in evaluating the safety of widely used chemicals and for robust scientific inquiry into their long-term effects on neurobehavioral development. The findings from the University of Buenos Aires provide a compelling foundation for future research aimed at protecting public health from the insidious effects of endocrine disruption.