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. Author manuscript; available in PMC: 2025 Mar 15.
Published in final edited form as: Horm Behav. 2025 Feb 8;169:105697. doi: 10.1016/j.yhbeh.2025.105697

Cognitive effects of early life exposure to PCBs in rats: Sex-specific behavioral, hormonal and neuromolecular mechanisms involving the brain dopamine system

Emily N Hilz 1, Cameron Schnurer 1, Swati Bhamidipati 1, Jahnabi Deka 1, Lindsay M Thompson 1, Andrea C Gore 1,*
PMCID: PMC11908942  NIHMSID: NIHMS2057597  PMID: 39923265

Abstract

Endocrine-disrupting chemicals (EDCs) are environmental toxicants that disrupt hormonal and neurodevelopmental processes. Among these chemicals, polychlorinated biphenyls (PCBs) are particularly concerning due to their resistance to biodegradation and tendency to bioaccumulate. PCBs affect neurodevelopmental function and disrupt the brain’s dopamine (DA) system, which is crucial for attentional, affective, and reward processing. These disruptions may contribute to the rising prevalence of DA-mediated neuropsychiatric disorders such as ADHD, depression, and substance use disorders. Notably, these behaviors are sexually dimorphic in part due to differences in sex hormones and their receptors, which are targets of estrogenic PCBs. Therefore, this study determined effects of early life PCB exposure on behaviors and neurochemistry related to potential disruption of dopaminergic signaling. Male and female Sprague Dawley rats were exposed to the PCB mixture Aroclor 1221 (A1221) or vehicle perinatally and then underwent a series of behavioral tests in adulthood, including the sucrose preference test to measure anhedonia, conditioned orienting to assess incentive-motivational phenotype, and attentional set-shifting to evaluate cognitive flexibility and response latency. Following these tests, rats were euthanized, and serum estradiol (E2), DA cells in the midbrain ventral tegmental area (VTA) and substantia nigra (SN), and gene expression from those combined midbrain nuclei were measured. Female rats exposed perinatally to A1221 exhibited decreased sucrose preference, and both male and female A1221 rats had reduced response latency in the attentional set-shifting task compared to vehicle counterparts. Conditioned orienting and serum estradiol (E2)were not affected in either sex; however, A1221-exposed rats of both sexes displayed higher TH+ cell numbers in the VTA and increased expression of dopamine receptor 1 (Drd1) in the combined midbrain nuclei. Additionally, E2 uniquely predicted behavioral outcomes and VTA DAergic cell numbers in A1221-exposed female rats, whereas DA signaling genes were predictive of behavioral outcomes in males. These data highlight sex-specific effects of A1221 on neuromolecular and behavioral phenotypes.

Keywords: PCBs, Endocrine disruption, Dopamine, Attention, Reward, Neuromolecular, Endocrine-disrupting chemical (EDC)

1. Introduction

Environmental endocrine-disrupting chemicals (EDCs) are linked to a range of adverse health outcomes in humans and wildlife (Darbre, 2019; Gore et al., 2015; Heindel, 2019; Streifer and Gore, 2021). The developing brain is an especially sensitive target of EDCs (Gore et al., 2015), due to their influences on neurodevelopmental processes that are sculpted by steroid hormones (McCarthy, 2020). Among EDCs, perinatal exposures to polychlorinated biphenyls (PCBs) affect the developing brain’s neuroendocrine systems, with associated behavioral, protein, and gene expression changes observed in the brain of adults (Gillette et al., 2017; Gore et al., 2022; Krishnan et al., 2018). Although banned in the 1970s, PCBs remain environmentally relevant due to resistance to biodegradation and accumulation up the food chain (Borja et al., 2005; Burreau et al., 2004); humans and wildlife throughout the world have detectable PCB body burdens in present times (van den Berg et al., 2017). Epidemiological data suggest PCBs increase the risk of attention-deficit/hyperactivity disorder (ADHD) and associated cognitive disruptions in children and adults (Behforooz et al., 2017; Eubig et al., 2010; Lenters et al., 2019). Despite increasing knowledge about PCB effects on the neuroendocrine system, there are substantial gaps in knowledge on behaviors and brain systems involved in disorders of attention and hyperactivity related to ADHD, reward-seeking behaviors, and affect.

In the United States, the diagnosis of ADHD has steadily increased in adults and children since the 1990s (Chung et al., 2019; Fairman et al., 2020; Sclar et al., 2012a; Sclar et al., 2012b). The presentation of ADHD is often co-morbid with psychiatric conditions such as mood and substance use disorders, among others (Biederman et al., 2008; Capusan et al., 2019; Chen et al., 2018; Mochrie et al., 2020). The reason for this comorbidity is not well understood but may reflect at least in part shared neurological circuitry that, when disrupted, results in broad changes to behavioral and cognitive function and the presentation of comorbid psychiatric disorders.

Disruption of the brain dopamine (DA) system is a likely candidate to which ADHD and comorbid psychiatric conditions can be attributed: DA synthesis is disrupted in ADHD, higher availability of the DA transporter is observed in ADHD, and the first-choice drugs in treatment for ADHD are DAergic psychostimulants (Faraone, 2018; Krause, 2008; Volkow et al., 2012). DA is an important component of the brain reward system, and it is near dogma that brain DA contributes not only to the hedonic (i. e., pleasurable) aspects of rewarding stimuli, but also and perhaps more importantly to learning and motivation around rewarding experiences (Alikaya et al., 2018; Robinson et al., 2005; Schultz, 2013; Volkow et al., 2009). Anhedonia, or reduced ability to experience pleasure from rewarding stimuli, is a common factor in ADHD, mood disorders (e.g., major depression disorder), and substance use disorder (Der-Avakian and Markou, 2012; Sternat and Katzman, 2016). DA contributes to multiple endophenotypes present in comorbid ADHD including impulsivity, risky decision making, and “bottom-up” executive control wherein self-regulatory processes are heavily informed by subcortical structures (Klein et al., 2019; Volkow et al., 2017).

The DA system develops in early life under the partial influence of estrogens (Ivanova and Beyer, 2003; Kipp et al., 2006; Varshney et al., 2017), making it a candidate for estrogenic EDC-mediated disruption during periods of DA system development and refinement (e.g., gestation through adolescence). Exposure to EDCs that affect estrogen signaling pathways during these periods may have implications for the development of the DA system and the emergence of associated cognitive pathologies like ADHD. Therefore, in the present experiment, we explored the role of exposure to PCBs during these sensitive neurodevelopmental windows on hormone and DA-mediated behavioral and physiological endpoints.

2. Methods

All procedures conducted on experimental subjects were approved by the Institutional Animal Care and Use Committee at The University of Texas at Austin in accordance with NIH guidelines.

2.1. Subjects

Sexually naive male and female Sprague-Dawley rats (n = 20/sex) used for breeding were purchased at ~60 days of age from Envigo (Envigo, Indianapolis, IN, USA). Rats were given 1 week to acclimate to the colony room and were housed under 12:12 h dark:light conditions with lights off at 11:00 AM; the rats had ad libitum access to water and a low phytoestrogen diet (Teklad 2019: Envigo, Indianapolis, IN, USA) unless otherwise noted.

On the day of proestrus, each female was checked for sexual receptivity and then paired overnight with one of the males. The following morning dams were vaginally lavaged; if sperm was present the dams were singly housed, and this was considered embryonic day 0 (E0). From E8 – E18, dams were fed a piece of ‘Nilla wafer cookie treated with either vehicle (Veh; 3 % DMSO in sesame oil, Sigma-Aldrich, Cat. # D4540 and S3547, respectively) or the PCB mixture Aroclor 1221 (A1221, 1 mg/kg, AccuStandard, Cat # C-221N-50MG), a dose and treatment route selected to represent human exposures and because it is a weakly estrogenic EDC in use in the lab for years (Dickerson et al., 2011; Gillette et al., 2022; Reilly et al., 2015). Treatments occurred each morning 2 h prior to lights out at 11:00 AM. Treatments ceased from E19 until birth. On postnatal day 1 (P1), the day after birth, pups (F1) were culled to 6 males and 6 females based on median anogenital index (AGI). Treatments resumed from P1–P21 through continued feeding of the wafer cookies to the dams. Pups were weaned at P21, after which treatment was discontinued, and littermates were housed in same-sex dyads with weekly handling until behaviors occurred in adulthood (P60). Two F1 male and female pups from each litter were used for behavioral testing (n = 40/sex).

2.2. Apparatus

Sucrose preference testing was conducted in standard polystyrene housing cages measuring 21.5 cm W, 43.5 cm L, and 20 cm H. Steel cage toppers were attached to each cage; two polycarbonate plastic bottles were inserted into the cage topper on either the left or right side, and low phytoestrogen diet was provided ad libitum in the center. The bottles contained either tap water or 0.08 % sucrose solution.

Pavlovian light-food conditioning and attentional set-shifting were performed in standard conditioning chambers with dimensions of 30.5 cm W, 25.5 cm L, and 30.5 cm H (Coulbourn Instruments, Whitehall, PA). The chambers featured clear acrylic walls at the front and back, steel-rod flooring, and aluminum sides and ceiling. Food pellets (45 mg TestDiet, Richmond, IN) acted as an unconditioned stimulus (US) and were dispensed into a food cup on the right wall via an external magazine. Entries into the food cup were measured via infrared beam at the cup’s opening. A 2-watt bulb positioned 20 cm above the food cup served as the conditioned stimulus (CS) when illuminated. Five open ports were located on the left side of the chamber; for Pavlovian conditioning, the ports were inactive and covered. For attentional set-shifting the outer left, right, and center ports were blocked and were not used during the procedure. Nose-pokes into the ports were measured via infrared beam at the opening of each port. The chambers were housed in sound- and light-attenuating enclosures (Coulbourn Instruments, Whitehall, PA). Digital video cameras (KT&C USA, Fairfield, NJ), mounted inside the enclosures but outside the chambers, were used to record orienting activity during Pavlovian food-light conditioning.

2.3. Behavioral procedures

2.3.1. Sucrose preference testing

Prior to the procedure, sucrose and tap water bottles were weighed. Rats were placed individually into a clean standard housing cage, and then both sucrose and tap water bottles were inserted into the cage topper with the location of the bottles (left or right) semi randomized. The procedure began at 08:00 AM and lasted 24 h; at the 12-hour timepoint, the location of the sucrose and tap bottle was switched to account for potential side biases. The following day, rats were removed from the test cages at 08:00 AM and bottles were weighed. The difference in weight (g) from beginning to end of the procedure was used to generate sucrose preference scores by dividing the amount of sucrose solution consumed by the total liquid (sucrose and tap) consumed over the 24-hour period.

2.3.2. Pavlovian conditioning

Prior to Pavlovian conditioning, rats were food restricted for 5 days to reach 90 % body weight. Food restriction was maintained throughout the Pavlovian conditioning and attentional set-shifting procedures, and both procedures were conducted under red light beginning 1 h after lights out (12:00 PM).

On the first day of Pavlovian conditioning, rats underwent training to retrieve food pellets from the foodcup where 30 food unconditioned stimuli (USs) were delivered on a 60-second fixed inter-trial interval (ITI) with no light conditioned stimulus (CS). The following day, rats underwent habituation to the light CS. For the first 8 trials, the light CS was presented for 10 s without delivery of the food US; for the second 8 trials, the 10-second light CS preceded delivery of 1 food US. Habituation occurred over ~35 min with a variable ITI of 120 s ± 60 s. The subsequent conditioning sessions occurred over the following 3 days and consisted of 16 CS-US presentations on the same ITI schedule. Each session video recording was scored by a blind and independent observer. A conditioned orienting response (OR) was defined as vertical rearing of the rat wherein the front paws leave the floor, excluding grooming behavior (Hilz et al., 2019a; Hilz et al., 2019b; Hilz et al., 2021). Because the light CS is diffuse in the conditioning chamber, ORs were counted regardless of if the body was oriented towards or away from the CS. Each CS presentation was divided into 3 5-second (s) intervals: pre-CS: 5 s prior to CS illumination (a baseline measure of OR), CS1: the first 5 s of the CS, and CS2: the second 5 s of the CS. ORs were scored every 1.25 s, allowing for up to 4 OR scores in each CS. Pre-CS OR scores were subtracted from CS1 and CS2 OR scores, providing a final OR score adjusted for any unconditioned ORs occurring prior to the CS illumination.

2.3.3. Attentional set-shifting

Attentional set-shifting procedures were adapted from (Hilz et al., 2021). On the first day of attentional set-shifting, rats were trained to nose-poke into one of two open ports on the left side of the conditioning chamber. Each trial was signaled by illumination of the house light; after 3 s, one of the two open ports was illuminated with red light and the rat was required to make a nose-poke into the illuminated port within 10 s to receive 1 food pellet. This training lasted until the rats made 50 successful nose-pokes within a 30-minute period, which was completed for all rats in one training session. The location of the illuminated port was semi-randomized such that half of the rats were trained beginning with the left port and half of the rats were trained beginning with the right port.

The following day, rats underwent the set-shifting procedure. The procedure was counter-balanced such that half of the rats began with the response discrimination task, and half began with the visual discrimination task. For both tasks, the beginning of a trial was signaled with a 3-second illumination of the house light and subsequently one of the two open ports would illuminate for up to 10 s. Trials were presented on a variable 20-second ITI, and ports were illuminated semi-randomly such that neither port illuminated >3 times consecutively.

For the spatial discrimination task, rats were required to nose-poke one of the two ports (left or right) regardless of whether the port was illuminated. Half of the rats were required to nose-poke the left port, and half of the rats were required to nose-poke the right port. A nose-poke to the correct port resulted in delivery of 1 food pellet and darkening of the port and house light. Nose-poking to the incorrect port or failing to nose-poke to either port within 10 s (counted as omissions) resulted in darkening of the house light and port, and no food pellet delivery. The test lasted for up to 2 h and was considered completed after the rat met a criterion of 10 correct responses in a row. Most rats completed the task within one session, but those that did not were required to undergo the task again the following day until the criterion was met. After reaching criterion, rats that began testing with the spatial discrimination task underwent the visual discrimination task on the following day.

For the visual discrimination task, rats were required to nose-poke the illuminated port regardless of its location in space (left or right). Otherwise, the experimental parameters were identical to the response discrimination task. After reaching the criterion of 10 correct consecutive responses, rats that began testing with the visual discrimination task underwent the spatial discrimination task on the following day.

2.4. Euthanasia and collection of biological specimens

Rats were allowed to eat ad libitum and regain body weight for one week prior to euthanasia. At ~P80 rats were euthanized by either rapid decapitation or perfusion; females were euthanized during proestrus based on cytological examination of cells collected via vaginal lavage. For the subset of rats that were rapidly decapitated (n = 20/sex), brains were snap-frozen in isopentane, and trunk blood was collected, allowed to clot, and centrifuged to separate out serum. Both brains and serum were stored at −80 °C until use. For the subset of rats that were perfused (n = 20/sex), the rats were overdosed with an intraperitoneal injection of ketamine (100 mg/kg) and xylazine (40 mg/kg). Once anesthetized, cardiac blood was collected, allowed to clot, centrifuged to separate out serum, and stored at −80 °C. The rats were then perfused for 1 min with 1 % paraformaldehyde (PFA) in phosphate buffered saline (PBS), and then for 8 min with 4 % PFA in PBS. Brains were stored for 24 h at 4 °C in 4 % PFA-PBS, and then underwent 3 days of gentle agitation in increasing sucrose solution concentrations (10 %, 15 %, and 30 %) until finally being stored at −20 °C in cryoprotectant.

2.5. Serum estradiol radioimmunoassay

Circulating serum estradiol (E2) from all behaviorally characterized rats was quantified using radioimmunoassay (RIA) according to the manufacturer’s protocol (Beckman Coulter, DSL4800). The RIA was conducted in a single cohort and samples were analyzed in duplicate; the sensitivity of the assay was 2.2 pg/mL with an intra-assay CV of 5.67 %.

2.6. Tissue processing and dopamine immunohistochemistry

Perfused brains (n = 20/sex; 40 total) were sliced coronally into 6 series at 30 μm on a vibrating microtome (Leica VT 1000S). The samples were stored at −20 °C in cryoprotectant until immunohistochemical (IHC) processing. One series containing the substantia nigra and ventral tegmental areas of the midbrain was processed using IHC for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis that is commonly used to identify DAergic cells in DA-producing regions of the brain. Briefly, tissues were washed in PBS followed by 0.3 % H2O2 in PBS; tissues were gently agitated for 1 h in blocking buffer (6 % normal goat serum in 0.3 % PBS-Triton) and then underwent primary incubation with TH antibody (1:2500; 22941, ImmunoStar, Hudson, WI) in blocking buffer (3 % NGS in 0.15 % PBS-T), gently agitated overnight at 4 °C. Tissues were washed, incubated in secondary biotinylated goat anti-mouse IgG (1:250; Vector Laboratories) for 1 h, and then VECTASTAIN Elite ABC-HRP Kit (Vector) was used and tissue was stained with 3′3 diaminobenzidine (Vector). The tissue was mounted onto Superfrost Plus slides (Thermo Fisher Scientific, Carlsbad, CA, USA), allowed to dry overnight, dipped in a series of increasing EtOH concentrations followed by xylene, and cover-slipped using DPX mounting media (Fisher).

Midbrain nuclei samples were imaged at 20× magnification using an Olympus BX61 bright field microscope. Each sample was imaged bilaterally; for the substantia nigra (SN), images were captured at −4.80 mm, −4.92 mm, and −5.04 mm from bregma (Paxinos and Watson, 1986) and two images were taken at each level. For the ventral tegmental area (VTA), images were captured at −5.04 mm from bregma and one image was taken at this level. The number of TH+ cells for each image was quantified by an observer blinded to the experimental condition.

2.7. Tissue processing and qPCR

Fresh frozen brains (n = 20/sex; 40 total) were sliced coronally on an NX50 cryostat (Fisher) at 400 μm. SN and VTA regions were immediately punched bilaterally at 0.75 mm using a Palkovits punch (Stoelting, Wood Dale, IL, USA). The SN and VTA punches were combined in a chilled microfuge tube and stored at −80 °C. RNA was extracted using AllPrep DNA/RNA/miRNA Universal Kit (80224; Qiagen, Germantown, MD) according to the manufacturer’s protocol with an added 15-minute incubation of 10 μL DNase and 70 μL RDD buffer (79256; Qiagen). The concentration of RNA was confirmed by a nanodrop. RNA was concentrated via vacuum centrifugation, resuspended in nuclease free water, and diluted to 20 ng/μl for cDNA conversion (High Capacity cDNA Reverse Transcription Kit, Thermo Fisher Scientific). Real-time PCR was performed with TaqMan Gene Expression Master Mix (Thermo Fisher Scientific) using ViiA7 and QuantStudio 7 Real-time PCR Systems (Applied Biosystems, Carlsbad, CA, USA) at 50 °C (2 min), 95 °C (10 min), and 42 cycles of 95 °C (15 s) and 60 °C (1 min). Primers and probes were purchased from Thermo Fisher Scientific for estrogen receptor alpha (Esr1), estrogen receptor beta (Esr2), dopamine receptor 1 (Drd1), dopamine receptor 2 (Drd2), dopamine transport gene Slc6a3, and tyrosine hydroxylase coding gene Th. The primers and probes were duplexed to the housekeeping gene Gapdh, and relative gene expression was determined using the comparative Ct method wherein samples were normalized to Gapdh and calibrated to the median delta-cycle threshold of Veh controls (ΔΔCt). Fold changes in gene expression were calculated using the formula: 2^− (ΔΔCt).

2.8. Statistical analysis

All statistical analyses were performed in R studio version 4.3.1 (R Core Team, 2023). Unless otherwise noted, outcome variables were analyzed using within-subjects 2 × 2 ANOVAs for repeated measures data or between-subjects 2 × 2 ANOVAs for non-repeated measures data using the common factor “Treatment” (i.e., Veh or A1221) and “Sex” (i. e., Female or Male). Normality and homogeneity of variance in the data were first confirmed using Shapiro-Wilk’s test of normality and Bartlett’s test of homogeneity of variance; data that violated assumptions were transformed using optimized Box-Cox power transformations. Pairwise post hoc comparisons were applied to significant main or interaction effects using estimated marginal means with Bonferroni adjustment to explore differences between treatment groups by sex. A measure of effect size, partial eta squared (n2p), was provided for significant comparisons; 0.01 is considered a small effect size, 0.06 is medium, and 0.14 is large (Lakens, 2013).

2.8.1. Behavioral analyses

For the sucrose preference test, the factor “Solution” indicated the amount of tap water or sucrose solution consumed in grams, and “Preference” indicated the percentage of sucrose solution consumed relative to total liquid consumed. For Pavlovian conditioning, the factor “Block” indicated acquisition of ORs over time (i.e., blocks of 8 trials, 4 days) and the first block, which represented unpaired CS-US presentations, was excluded from analysis. For the attentional set-shifting task, the factor “Condition” indicated the initial attentional “set” building task (i.e., spatial or visual discrimination task, counterbalanced) and the subsequent “shift” to the new requirement task (i.e., spatial or visual discrimination task, counter-balanced). “Counterbalance” indicated the order in which rats underwent the tasks (i.e., spatial- to-visual or visual-to-spatial), and the response variables analyzed were nose pokes into the correct or incorrect port, and latency to respond.

2.8.2. Biological measures

E2 concentration, the number of TH+ cells quantified in the SN and VTA, and expression of target genes were analyzed with factorial ANOVAs using the factors “E2” (i.e., mean serum E2 concentration from sample duplicates), “DA” (i.e., mean number of TH+ cells from samples quantified), or factors relative to the target gene (i.e., mean of fold gene expression for Esr1, Esr2, Drd1, Drd2, Slc6a3, and Th).

2.8.3. Regression analyses

Regression models were generated for each sex separately using the ‘lm’ function from the ‘stats’ package in R. For each, the dependent variable matched factors described in behavioral analyses; E2 (all rats, n = 20/treatment/sex; 80 total), DA cells in either SN or VTA (from the subset of perfused rats, n = 10/treatment/sex; 40 total), and each of the target genes from SN and VTA combined (from the subset of rats that were rapidly decapitated, n = 10/treatment/sex; 40 total) acted as independent variables, and treatment group was included as an interaction term in each model. Data were converted to z-scores prior to analysis. The overall model was considered significant if p < 0.05; beta coefficient (β), standard error (SE), t-value, and p-value were reported for significant main effects and/or interaction terms.

3. Results

3.1. Behavioral outcomes

3.1.1. Sucrose preference test

All rats consumed more sucrose solution than tap water (Fig. 1A), indicated by a main effect of Solution (F(1,76) = 347.83, p < 0.001, n2p = 0.82; post hoc adjusted p < 0.001). A significant interaction between Treatment, Sex, and Solution (F(176) = 5.91, p = 0.02, n2p = 0.07) indicated that A1221 and Veh rats of both sexes consumed more sucrose than tap water solution (post hoc adjusted p < 0.001 for all comparisons) and there was no significant difference in the amount of sucrose solution consumed in either sex (post hoc adjusted p > 0.1 for both). Males consumed similar amounts of tap water (post hoc adjusted p > 0.1); however, A1221 females had a non-significant increase in tap water consumed compared to Veh controls (post hoc adjusted p = 0.07). No main effects of Treatment or Sex were observed on preference for sucrose solution; however, a significant interaction between Treatment and Sex (F(1,76) = 6.05, p = 0.02, n2p = 0.07; Fig. 1B) indicated that A1221 female rats had a significantly lower preference for the sucrose solution compared to Veh females (post hoc adjusted p = 0.05). No such difference was detected between male treatment groups (post hoc adjusted p > 0.1)

Fig. 1.

Fig. 1.

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Sucrose preference test results. Points indicate values for individual rats, N = 20/sex/treatment. A. Mean tap water or sucrose solution consumed in grams (g) ± SEM. Female rats with A1221 exposure drank a non-significantly higher amount of tap water (left panel) compared to Veh controls (p = 0.07). There was no difference in sucrose solution consumption between treatment groups in either sex. B. Mean percent (%) preference for sucrose solution ± SEM. The dashed line indicates the 50 % preference point, above which rats exhibit increased preference for the sucrose solution. Female rats with A1221 exposure had a significantly lower preference for sucrose solution compared to Veh controls (p = 0.05). Male sucrose preference was not different between treatment groups.

3.1.2. Conditioned orienting

We previously found that OR behavior was consistently higher in CS1 and foodcup (FC) behavior was higher in CS2 (Hilz et al., 2019a; Hilz et al., 2019b; Hilz et al., 2021; Olshavsky et al., 2014). The current results mirrored our previous findings: OR and FC behavior showed significant acquisition over the course of Pavlovian conditioning in CS1 and CS2 respectively.

For OR behavior, there were significant effects of CS (F(1,978) = 32.32, p < 0.001, n2p = 0.10) and Block (F(6,978) = 5.95, p < 0.001, n2p = 0.09), as well as a CS by Block interaction (F(6,978) = 15.54, p < 0.001, n2p = 0.09; Fig. 2A). A significant CS by Sex interaction (F(1,978) = 10.35, p = 0.001, n2p = 0.01) indicated differential patterns of OR behavior between males and females, with males exhibiting larger differences between CS1 and CS2 across blocks. Post hoc comparisons revealed significant increases in ORs for CS1 compared to CS2 in males during later blocks (e.g., Block 7: p < 0.001; Block 8: p < 0.001), while females showed smaller, but still significant, differences in these blocks (e.g., Block 7: p = 0.005; Block 8: p < 0.001). There were no main nor interaction effects involving Treatment on acquisition of conditioned orienting (p > 0.1 for all; Fig. 3C).

Fig. 2.

Fig. 2.

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Orienting response (OR) and foodcup (FC) scores over Pavlovian conditioning, N = 20/sex/treatment. A. Mean OR scores over conditioning in CS1 and CS2 ± SEM. In both female (left panel) and male rats (right panel), OR scores were higher at the end of conditioning (block 8) in CS1 compared to CS2 (p < 0.001 for both). B. Mean FC scores over conditioning in CS1 and CS2 ± SEM. In both sexes, FC scores were higher at the end of conditioning (block 8) in CS2 compared to CS1 (p < 0.001 for both). C. Mean CS1 OR scores over conditioning ± SEM between treatment groups. There were no effects of treatment in either sex on acquisition of ORs in CS1. D. Mean CS2 FC scores over conditioning ± SEM. There were no effects of treatment in either sex on acquisition of FC behavior in CS2.

Fig. 3.

Fig. 3.

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Response measures in the attentional set-shifting task. Points indicate values for individual rats, shape indicates counterbalanced order of response requirements. N = 20/sex/treatment. A. Mean total trials to criterion ± SEM. In both female and male rats, the total trials required to reach criterion did not differ between treatment groups in the attentional set task (left panel) nor after the shift in response requirements (right panel). B. Mean errors before criterion ± SEM. In both female and male rats, erroneous responses prior to reaching criterion did not differ between treatment groups in the attentional set task (left panel) nor after the shift in response requirements (right panel). C. Mean latency to respond in seconds (s) ± SEM. A1221 exposure decreased response latency compared to Veh controls (p = 0.01).

For FC behavior, there were also significant effects of CS (F(1,988) = 318.97, p < 0.001, n2p = 0.24) and Block (F(6,988) = 120.55, p < 0.001, n2p = 0.42), along with a CS × Block interaction (F(6,988) = 20.28, p < 0.001, n2p = 0.11; Fig. 2B). Post hoc analyses showed significant increases in FC responses for CS2 over CS1 across blocks, with the magnitude of the differences increasing in later blocks for both sexes. By Block 8, females showed a large and significant difference in FC behavior in CS2 compared to CS1 (p < 0.001), as did males (p < 0.001). There were no significant main nor interaction effects with Treatment on acquisition of foodcup behavior (p > 0.1 for all; Fig. 2D).

3.1.3. Attentional set-shifting

A significant main effect of Condition (F(1,71) = 29.37, p < 0.001, n2p = 0.29; Fig. 3A) indicated that the total number of trials required to reach criterion was significantly higher after the shift in response requirements (post hoc adjusted p < 0.001). There were no main nor interaction effects of Treatment with any other variables (p > 0.1 for all comparisons); however, the order of tests influenced overall trials required to reach criterion indicated by an interaction between Condition, Counterbalance, and Sex (F(1,71) = 5.70, p < 0.02, n2p = 0.07). Males in the spatial-visual counterbalance required more trials to reach criterion after the shift in response requirements (post hoc adjusted p < 0.001); females showed a similar but non-significant pattern (post hoc adjusted p = 0.07), and all other comparisons were non-significant (post hoc adjusted p > 0.1). Incorrect responses followed a similar pattern: a significant main effect of Condition indicated that all rats made more incorrect responses before reaching criterion after the shift in response requirements (F(1,71) = 41.86, p < 0.001, n2p = 0.38; post hoc adjusted p < 0.001; Fig. 3B). There were no effects nor interactions of Treatment on incorrect responses in either sex (p > 0.1 for all comparisons); however, an interaction between Condition and Counterbalance (F(1,71) = 15.11, p < 0.001, n2p = 0.18) indicated that all rats in the spatial-to-visual test order group required significantly more trials to reach criterion after shifting response requirements than rats in the visual-to-spatial group (post hoc adjusted p < 0.001).

An effect of Treatment was observed in the latency to make a response. After the shift in response requirements, latency to respond was lower in A1221-exposed rats (F(1,72) = 10.19, p = 0.002, n2p = 0.12; post hoc adjusted p = 0.05; Fig. 3C) compared to Veh controls. The order of test presentation was a significant factor (F(1,72) = 21.77, p < 0.001, n2p = 0.23), such that response latency was higher in the visual-to-spatial test order group for both sexes. The order of tests did not interact with Treatment to affect response latency (p > 0.1 for all), and there were no main nor interaction effects with Sex (p > 0.1 all).

3.2. Physiological measures

3.2.1. Serum estradiol

The analysis of serum estradiol (E2) levels revealed a significant main effect of Sex (F(1,76) = 49.28, p < 0.001, n2p = 0.39; Fig. 4A), with females exhibiting higher E2 levels compared to males (post hoc adjusted p < 0.001). There were no significant main nor interaction effects with Treatment (p > 0.1 for all).

Fig. 4.

Fig. 4.

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Serum estradiol (E2; N = 20/sex/treatment) and tyrosine hydroxylase positive (TH+; N = 10/sex/treatment) cells in the midbrain Ventral Tegmental Area and Substantia Nigra. Points indicate values for each individual. A. Mean serum E2 (pg/ml) ± SEM. In all behaviorally characterized female and male rats (n = 20/sex/treatment), serum E2 did not differ between treatment groups. B. Mean TH+ cells in the Ventral Tegmental Area (VTA) ± SEM. In the subset of rats used for immunohistochemistry (n = 10/sex/treatment), TH+ cell numbers were significantly higher in the A1221 treatment group compared to Veh controls (p = 0.05). C. Mean TH+ cells in the Substantia Nigra (SN) ± SEM. In the subset of rats used for immunohistochemistry (n = 10/sex/treatment), TH+ cell numbers did not differ between treatment groups.

3.2.2. Midbrain dopamine cell numbers

In the VTA, a main effect of Treatment (F(1,36) = 4.24, p = 0.05, n2p = 0.11; Fig. 4B) indicated that A1221-treated rats had more TH+ cells compared to Veh controls (post hoc adjusted p = 0.05). No interaction effects between Treatment and Sex were observed in the VTA (p > 0.1). In the SN, no significant effects of Treatment, Sex, or their interaction were found on TH+ cell counts (p > 0.1 for all; Fig. 4C). Representative micrographs of TH+ neurons are provided in Fig. 5.

Fig. 5.

Fig. 5.

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Representative micrographs of tyrosine hydroxylase (TH) immunohistochemical labeling of cell bodies and processes, with arrows indicating a TH+ cell body in each region. Scale bar (black) = 25 μm. A. TH+cells in the Ventral Tegmental Area (VTA). ST = stria terminalis, used as a biological landmark for VTA imaging. B. TH+ cells in the Substantia Nigra.

3.3. Gene expression analyses

The analysis of gene expression levels in the combined VTA and SN for estrogen receptors (Esr1 and Esr2), dopamine transporters (Slc6a3), and related markers revealed limited treatment effects, apart from Drd1. For Esr1 and Esr2, there were no significant main effects of treatment or sex, nor interactions between the two (p > 0.1 for all; Fig. 6A, B). Similarly, expression of Drd2 (dopamine receptor D2; Fig. 6D), Slc6a3 (dopamine transporter; Fig. 6E) and Th (Fig. 6F) did not show significant differences across treatment or sex, nor their interaction (p > 0.1 for all).

Fig. 6.

Fig. 6.

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Expression of target genes in the midbrain (substantia nigra and ventral tegmental area combined). Points indicate individual scores. N = 10/sex/treatment. A. Mean fold change in estrogen receptor alpha (Esr1) ± SEM. Esr1 expression did not differ between treatment groups. B. Mean fold change in estrogen receptor beta (Esr2) ± SEM. Esr2 expression did not differ between treatment groups. C. Mean fold change in dopamine receptor 1 (Drd1) ± SEM. A1221 exposure increased Drd1 expression relative to Veh controls (p = 0.03). Note: For A1221, 2 datapoints (1 per sex) were above the y-axis cutoff and are not shown. D. Mean fold change in dopamine receptor 2 (Drd2) ± SEM. In female and male rats, Drd2 expression did not differ between treatment groups. E. Mean fold change in dopamine transport gene Slc6a3 ± SEM. Slc6a3 expression did not differ between treatment groups. F. Mean fold change in tyrosine hydroxylase encoding gene Th ± SEM. Th expression did not differ between treatment groups.

In contrast, Drd1 expression (dopamine receptor 1) showed a significant main effect of treatment (F(1,36) = 5.33, p = 0.03, ηp2 = 0.13; Fig. 6C), with post hoc comparisons indicating higher Drd1 expression in the A1221 treatment group compared to the vehicle group (post hoc adjusted p = 0.03). There was no effect of Sex nor interaction between Treatment and Sex.

3.4. Regression analyses

3.4.1. Estradiol and behavior

In females, serum E2 predicted the total number of responses required to reach criterion in the set-shifting task after the response requirement shift differently between treatment groups (Fig. 7A). The omnibus model, accounting for both main effects and interactions, explained 24.2 % of the variation in the data with an adjusted R2 of 17.9 % (F(3,36) = 3.84, p = 0.02). The overall relationship between E2 and total responses was positive (β = 0.30, STE = 0.14, t = 2.11, p = 0.04). However, there was a significant negative interaction between E2 and Treatment on total responses (β = −0.55, STE = 0.18, t = −3.12, p = 0.004). This indicates that while E2 positively correlated with performance in the Veh control reference group, this effect was significantly attenuated or reversed in A1221-exposed females. A similar model showed a predictive relationship between serum E2 and incorrect responses after the requirement shift in female rats (Fig. 7B). The omnibus model explained 24.6 % of the variation in the data, with an adjusted R2 of 18.4 % (F(3,36) = 3.93, p = 0.02). The overall relationship between E2 and incorrect responses was positive (β = −0.29, STE = 0.13, t = 2.23, p = 0.03). However, a significant negative interaction between E2 and Treatment on incorrect responses (β = −0.52, STE = 0.16, t = −3.21, p = 0.003) indicated that the positive correlation between E2 and incorrect responses in Veh controls was significantly attenuated or reversed in A1221-exposed females. E2 did not predict behavioral outcomes in male rats (all models p > 0.1).

Fig. 7.

Fig. 7.

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Scatterplots with regression lines showing significant relationships between outcomes variables. Points indicate individual scores, and lines indicate trends within treatment groups; all data are standardized to z-scores. R2 and p-values are from the omnibus regression analysis, accounting for both main and interaction effects, are shown. A. Serum estradiol (E2; N = 20/treatment) explained 17.9 % (R2) of the variation in the trials required to reach criterion after the response requirement shift in female rats (p = 0.02). The slope of the regression lines was significantly different between A1221 females and Veh controls. B. Serum estradiol (E2) explained 24.6 % (R2) of the variation in errors before reaching criterion after the response requirement shift in female rats (p = 0.02). The slope of the regression lines was significantly different between A1221 females and Veh controls. C. In the subset of female rats used for IHC (N = 10/treatment group), serum estradiol (E2) explained 24.6 % (R2) of the variation in Ventral Tegmental Area (VTA) dopamine (DA) cells (i.e., TH+ cells; p = 0.02). The slope of the regression lines was significantly different between A1221 females and Veh controls. D. In the subset of male rats used for PCR (N = 10/treatment group), expression of dopamine receptor 1 (Drd1) from the combined midbrain regions explained 39.1 % (R2) of the variation in preference for sucrose solution (p = 0.01). The slope of the regression lines was significantly different between A1221 males and Veh controls. The arrow indicates a potential outlier point in the regression model; when removed, the model and interaction term remained significant (p = 0.02 and p = 0.01, respectively; not shown). E. Expression of dopamine receptor 2 (Drd2) explained 39.1 % (R2) of the variation in response latency after the requirement shift in the attentional set-shifting task (p = 0.02). The slope of the regression lines was significantly different between A1221 males and Veh controls. F. Expression of dopamine transport gene Slc6a3 explained 24.6 % (R2) of the variation in response latency after the requirement shift in the attentional set-shifting task (p = 0.05). The slope of the regression lines was significantly different between A1221 males and Veh controls. F. Expression of dopamine transport gene Slc6a3 explained 24.6 % (R2) of the variation in response latency after the requirement shift in the attentional set-shifting task (p = 0.05). The slope of the regression lines was significantly different between A1221 males and Veh controls.

3.4.2. Estradiol and dopamine cells

In the subset of females used for IHC, serum E2 was predictive of the number of dopamine cells (DA; i.e., mean TH+ cells) in the VTA in a manner that interacted with Treatment group (Fig. 7C). The omnibus model explained 38.7 % of the variation in the data, with an adjusted R2 of 27.3 % (F(3,16) = 3.39, p = 0.04). The overall relationship between E2 and VTA DA was positive (β = 0.40, STE = 0.33, t = 1.19, p = 0.03). However, a significant negative interaction between E2 and Treatment on VTA DA (β = −0.97, STE = 0.42, t = −2.31, p = 0.03) indicated that the positive correlation between E2 and VTA DA in Veh controls was significantly attenuated or reversed in A1221-exposed females. This relationship was unique to VTA in females: in the SN, the overall regression model between E2 and DA was not significant (p > 0.1), and E2 did not predict DA cell numbers in male rats (p > 0.1 for both VTA and SN).

3.4.3. Estradiol and gene expression

There were no significant predictive relationships in females or males between E2 and expression of the target genes (all models p > 0.1).

3.4.4. Dopamine cells and behavior

There were no significant predictive relationships in females or males between VTA and SN DA cells and behavioral outcomes (all models p > 0.1).

3.4.5. Gene expression and behavior

Of the target genes, Drd1, Drd2, and Slc6a3 varied with behavioral outcomes in a manner that differed between treatment groups only in male rats (all other gene-behavior models p > 0.1). Drd1 predicted preference for sucrose solution between male treatment groups (Fig. 7D): the omnibus model explained 48.8 % of the variation in the data, with an adjusted R2 of 39.1 % (F(3,16) = 5.08, p = 0.01). The overall relationship between Drd1 and sucrose preference was positive (β = 13.97, STE = 4.49, t = 3.11, p = 0.007). However, a significant negative interaction between Drd1 and Treatment on sucrose preference (β = −13.87, STE = 4.50, t = −3.09, p = 0.007) indicated that the positive correlation between Drd1 and sucrose preference in Veh controls was significantly attenuated or reversed in A1221-exposed males. Notably, the effect of Drd1 on sucrose preference was not driven by a single data point: when a potential outlier was removed, the model (F (3,15) = 4.47, p = 0.02; adjusted R2 = 36.6 %) and interaction effect (β = −7.78, STE = 2.65, t = −2.94, p = 0.01) remained significant.

Drd2 and Slc6a3 both predicted latency to respond in the attentional set-shifting task between male treatment groups (Fig. 7E, F). For Drd2, the omnibus model explained 44.6 % of the variation in the data, with an adjusted R2 of 34.3 % (F(3,16) = 4.30, p = 0.02). The overall relationship between Drd2 and response latency was positive (β = 0.62, STE = 0.21, t = 3.03, p = 0.008). However, a significant negative interaction between Drd2 and Treatment on response latency (β = −0.69, STE = 0.28, t = −2.58, p = 0.02) indicated that the positive correlation between Drd2 and response latency in Veh controls was significantly attenuated or reversed in A1221-exposed males. Similarly for Slc6a3, the omnibus model explained 36.5 % of the variation in the data, with an adjusted R2 of 24.6 % (F(3,16) = 3.07, p = 0.05). The overall relationship between Slc6a3 and response latency was positive (β = 0.53, STE = 0.22, t = 2.43, p = 0.03). However, a significant negative interaction between Slc6a3 and Treatment on response latency (β = −0.61, STE = 0.29, t = −2.04, p = 0.05) indicated that the positive correlation between Slc6a3 and response latency in Veh controls was significantly attenuated or reversed in A1221-exposed males.

4. Discussion

The presented data demonstrate that perinatal exposure to the PCB mixture A1221 has sex-specific effects on DA-mediated behavior and gene expression in DA-producing regions of the midbrain. Moreover, the data suggest that different mechanisms may drive these responses in male and female rats. Female rats exposed to A1221 perinatally showed broader behavioral effects including reduced preference for sucrose solution accompanied with decreased response latency in the set-shifting task. Behavioral effects in males were limited to reduced response latency. In females, E2 was a modest predictor of behavioral responses and DAergic cells in the midbrain. In males, expression of multiple DAergic genes in the midbrain predicted behavioral responses. Taken together, these results provide potential evidence that behavioral disruptions associated with perinatal A1221 exposure may rely partially on hormonal mechanisms in female rats and on neuromolecular mechanisms in male rats.

4.1. Depressive-like behavior, dopamine, and estradiol

Anhedonia, or the reduced ability to experience pleasure, is a key aspect of major depression disorder (First, 2013). Reductions in preference for sucrose solution are considered a proxy of anhedonic behavior in rodents (Primo et al., 2023). In this experiment, female rats exposed perinatally to A1221 showed a modest reduction in preference for sucrose solution. Sucrose preference is modulated in part by DAergic activity and the DA-producing regions of the midbrain: in rodents, DA depletion in the SN or in the VTA reduce sucrose preference (Martínez-Hernández et al., 2006; Santiago et al., 2014; Shibata et al., 2009). DA receptors 1 and 2 (D1 and D2, respectively) also impact sucrose preference: antagonists of either receptor decrease preference for lower concentrations of sucrose (Muscat and Willner, 1989), and D1-deficient mice show reduced motivation for sucrose reward (El-Ghundi et al., 2003). Rats exposed to A1221 in this experiment showed a broad increase in Drd1 expression and DAergic cells in the VTA across sex, although only female rats exhibited a concurrent decrease in sucrose preference.

Additionally, E2 has known antidepressive effects in rodents (Carrier et al., 2015; Romano-Torres and Fernández-Guasti, 2010). We used the weakly estrogenic PCB mixture A1221, which we have previously shown increases serum E2 levels in developing but not adult female rats (Streifer et al., 2024), and increases Drd1 in the hypothalamus of male rats (Liberman et al., 2020). A1221 did not affect overall E2 levels in the current experiment; however, female E2 levels in adulthood correlated with DAergic cell numbers in the VTA differently between A1221-exposed females and controls. Because DAergic cell numbers are established during development, this correlation likely reflects the influence of unidentified mediating variables between E2 and DA cell numbers. A similar relationship was observed between E2 and performance on the set-shifting task, suggesting that female rats exposed to A1221 may utilize E2 differently than controls. Interestingly, we did not observe any differences in expression of estrogen receptors, nor any relationships between estrogen receptor gene expression and behavior. E2 exerts tonic inhibition on D2 receptors to stimulate sucrose intake (Bâ et al., 2018); it is possible that A1221 exposure changes the way E2 interacts with DAergic targets in the midbrain, thereby impacting functionality of these cells and affecting behavior without changing the overall measurement of these targets. In males, we did not see rote effects of A1221 on sucrose preference; however, the positive relationship between Drd1 and sucrose preference in A1221 males may suggest that A1221 increases functional activity of DA receptor 1 – which is associated with higher sucrose preference (Muscat and Willner, 1989).

4.2. Response latency and dopamine

PCB mixtures reduce DA transporter levels, synaptosomal DA content, and induce DAergic cell death in adult exposure models (Bemis and Seegal, 2004; Caudle et al., 2006; Lee et al., 2012). In the current study, both female and male rats exposed perinatally to A1221 exhibited reduced response latency in the set-shifting task. A1221 exposure increased expression of Drd1 in the midbrain DA-producing regions. DA signaling genes Drd1 and Slc6a3 have known roles in affective and attentional processing, and DA transporter genes are targets of PCBs in adult exposure models (Andersen and Teicher, 2000; El-Ghundi et al., 2003; Krause, 2008; Richardson and Miller, 2004). Drd2 and Slc6a3 had negative relationships with response latency in the A1221 males; higher D2 is associated with lower response inhibition in humans and rodents (Beste et al., 2016; Eagle et al., 2011; Robertson et al., 2015), and antagonism of this receptor increases response latency in the attentional set-shifting task (Haluk and Floresco, 2009).

Increased response latency is considered a measure of cognitive decline in aging rodents and may be reflective of higher cognitive effort in complex tasks (Young et al., 2010), but the inverse of this – decreased response latency – is more difficult to interpret. It is possible that A1221 improves performance in the set-shifting task; although uncommon, some PCBs (i.e., PCB 77) have been shown to improve specific behavioral outcomes like reducing response errors in a working memory task (Schantz et al., 1996). However, reduced response latency without a concurrent improvement in cognitive flexibility (i.e., ability to shift response requirements) may also be suggestive of a hyperactive or disinhibited response type (Bari and Robbins, 2013; Puumala et al., 1996). D2 receptor and dopamine transporter genes are implicated in the etiology of ADHD (DiMaio et al., 2003; Swanson et al., 2000; Volkow et al., 2009), and D2 specifically is implicated in hyperactivity (Fan et al., 2010). The relationship observed here – higher Drd2 and Slc6a3 correlated with decreased response latency in A1221 males – provides potential evidence for ADHD-like symptomology in these animals. However, identifying whether this represents a hyperactive phenotype, one of behavioral disinhibition, or even broad improvements in cognitive processing speed requires more nuanced testing using appropriate paradigms, such as the 5-choice serial reaction time or Go/No-Go tests (Loos et al., 2010).

4.3. The brain reward system in broader context

While our study focused on the behavioral effects of EDC exposure in the context of midbrain DAergic producing regions, it is important to consider the broader DA circuits that mediate the behaviors assessed. The prefrontal cortex (PFC) and ventral striatum are key regions where DA signaling plays a critical role in reward processing and cognitive flexibility (Block et al., 2007; Floresco et al., 2008; Tzschentke, 2000). DAergic projections from the midbrain to the ventral striatum are essential for encoding reward value and motivating behavior (Ikemoto, 2007), while DA inputs to the PFC guide executive functions, including cognitive flexibility and reward information processing (Floresco, 2013; Tzschentke, 2000). These interconnected regions create the basis for the brain reward learning system, which develops under partial control of estrogens in early life (Ivanova and Beyer, 2003; Kipp et al., 2006; Varshney et al., 2017) and are refined through adolescence (Kalsbeek et al., 1988; Voorn et al., 1988) – the periods captured by our exposure paradigm. Exposure to estrogenic A1221 may cause disruptions in the development or later activity of these circuits, which could contribute to the observed behavioral phenotypes described in this study and represent an important area for further research regarding the implications of EDC exposure on DA-mediated brain and behavioral processes.

4.4. A note on conditioned orienting

A core inspiration for this research was to determine if disrupted hormonal processes in early developmental life may have an impact on DAergic behaviors and neuromolecular function. Of the selected behaviors, conditioned orienting is a DA-mediated behavior with a sex-specific presentation that does not rely on availability of E2 in adults (Hilz et al., 2022, 2021; Lee et al., 2011). We hypothesized that sex differences in conditioned orienting may be organized in early life, and that exposure to A1221 in this period may impact the development of the orienting phenotype. Our results did not support this hypothesis. In separate analyses not shown here, we examined the relationships between OR phenotype (i.e., OR level at the end of conditioning, classified as Orienters or Nonorienters using the methods from Hilz et al., 2019a) and various behavioral outcomes. We found strong associations across multiple endpoints, including a positive correlation with DA cell numbers in the midbrain and impaired performance in attentional set- shifting tasks. However, the experiment was not powered to consider both OR phenotype and exposure to A1221 in concert. The results taken as they are suggest that A1221 in the perinatal window did not target processes involved in the development of the orienting phenotype – and the limited cognitive-attentional effects in general suggest that perinatal exposure to A1221 may not be a candidate for the development of ADHD-like behavior in rodents. Other exposure models, such as inter- and transgenerational models, or the use of chemical mixtures that have different impacts on hormonal processes like anti-androgenic compounds or complex EDC mixtures (Gore et al., 2022), may help elucidate the mechanisms that organize attentional phenotypes.

4.5. Conclusion

Taken together, the current data provide new evidence that exposure to A1221 during the perinatal period affects developmental processes that influence behavioral function in adulthood, and that the mechanisms via which this occurs may differ between male and female rats. These results are consistent with previous work from our lab on EDCs reporting that they 1) have broader behavioral effects in female rats compared to males (Gillette et al., 2022; Gore et al., 2022); 2) cause hormonally mediated behavioral disruptions in females (Reilly et al., 2015); and 3) involve neuromolecular-mediated disruptions, more so in male rats (Gore et al., 2022, 2021). To fully understand the implications of EDC exposure on attentional function and the increasing comorbidities between neuropsychiatric disorders, it is crucial to assess impacts in models that approximate real-world scenarios. Understanding the mechanisms that drive behavioral effects of EDCs can help design better interventions in a world with an increasing burden of EDC exposure.

Acknowledgements

We would like to thank Dr. Hongjoo J. Lee at the University of Texas at Austin for the use of her conditioning chambers in this research.

Grant support

This research was supported by the National Institute of Environmental Health Sciences F32 ES034257 (ENH) and R35 ES035024 (ACG).

Footnotes

Declaration of competing interest

ACG is a consultant on a legal case related to PCBs. There are no other disclosures.

CRediT authorship contribution statement

Emily N. Hilz: Writing – review & editing, Writing – original draft, Visualization, Validation, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Cameron Schnurer: Data curation. Swati Bhamidipati: Data curation. Jahnabi Deka: Data curation. Lindsay M. Thompson: Project administration. Andrea C. Gore: Writing – review & editing, Resources, Funding acquisition, Conceptualization.

Data availability

Data will be made available on request.

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