Long term dietary methoxychlor exposure in rats increases sodium solution consumption but has few effects on other sexually dimorphic behaviors

Developmental Exposure to Low Levels of Ethinylestradiol Affects Play Behavior in Juvenile Female Rats

Juvenile social play contributes to the development of adult social and emotional skills in humans and non-human animals, and is therefore a useful endpoint to study the effects of endocrine disrupters on behavior in animal models. Ethinylestradiol (EE₂) is a widely produced, powerful synthetic estrogen that is widespread in the environment mainly because is a component of the contraceptive pill. In addition, fetuses may be exposed to EE2 when pregnancy is undetected during contraceptive treatment. To understand whether exposure to EE₂ during gestation or lactation affects social play, we exposed 72 female Sprague-Dawley rats to EE₂ or vehicle either during gestation (gestation day (GD) 5 through GD 20) or during lactation (from postnatal day (PND) 1 through PND 21). Two doses of EE₂ were used to treat the dams: a lower dose in the range of possible environmental exposure (4 ng/kg/day) and a higher dose equivalent to that received during contraceptive treatment (400 ng/kg/day). Behavioral testing was carried out between PND 40 and 45. A principal component analysis of frequencies of behavioral items observed during play sessions identified three main components: defensive-like play, aggressive-like play, and exploration. Aggressive-like play was significantly increased by both doses of EE₂, and the gestational administration was in general more effective than the lactational one. Defensive-like play and exploration were not significantly affected by treatment. This research showed that low and very low doses of EE₂ that mimic clinical or environmental exposure during development can affect important aspects of social behavior even during restricted time windows.

Developmental treatment with ethinyl estradiol, but not bisphenol A, causes alterations in sexually dimorphic behaviors in male and female Sprague Dawley rats

The developing central nervous system may be particularly sensitive to bisphenol A (BPA)-induced alterations. Here, pregnant Sprague Dawley rats (n = 11-12/group) were gavaged daily with vehicle, 2.5 or 25.0 μg/kg BPA, or 5.0 or 10.0 μg/kg ethinyl estradiol (EE2) on gestational days 6-21. The BPA doses were selected to be below the no-observed-adverse-effect level (NOAEL) of 5 mg/kg/day. On postnatal days 1-21, all offspring/litter were orally treated with the same dose. A naïve control group was not gavaged. Body weight, pubertal age, estrous cyclicity, and adult serum hormone levels were measured. Adolescent play, running wheel activity, flavored solution intake, female sex behavior, and manually elicited lordosis were assessed. No significant differences existed between the vehicle and naïve control groups. Vehicle controls exhibited significant sexual dimorphism for most behaviors, indicating these evaluations were sensitive to sex differences. However, only EE2 treatment caused significant effects. Relative to female controls, EE2-treated females were heavier, exhibited delayed vaginal opening, aberrant estrous cyclicity, increased play behavior, decreased running wheel activity, and increased aggression toward the stimulus male during sexual behavior assessments. Relative to male controls, EE2-treated males were older at testes descent and preputial separation and had lower testosterone levels. These results suggest EE2-induced masculinization/defeminization of females and are consistent with increased volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) at weaning in female siblings of these subjects (He, Z., Paule, M. G. and Ferguson, S. A. (2012) Low oral doses of bisphenol A increase volume of the sexually dimorphic nucleus of the preoptic area in male, but not female, rats at postnatal day 21. Neurotoxicol. Teratol. 34, 331-337). Although EE2 treatment caused pubertal delays and decreased testosterone levels in males, their behaviors were within the range of control males. Conversely, BPA treatment did not alter any measured endpoint. Similar to our previous reports (Ferguson, S. A., Law, C. D. Jr and Abshire, J. S. (2011) Developmental treatment with bisphenol A or ethinyl estradiol causes few alterations on early preweaning measures. Toxicol. Sci. 124, 149-160; Ferguson, S. A., Law, C. D. and Abshire, J. S. (2012) Developmental treatment with bisphenol A causes few alterations on measures of postweaning activity and learning. Neurotoxicol. Teratol. 34, 598-606), the BPA doses and design used here produced few alterations.

A multi-generational study on low-dose BPA exposure in Wistar rats: effects on maternal behavior, flavor intake and development

Bisphenol A (BPA) is a common endocrine disruptor found as an environmental and food contaminant. It exerts both developmental and behavioral effects, mainly when exposure occurs in early life. The aim of this study was to determine the multi-generational effects of chronic, human-relevant low-dose exposure to BPA on development, maternal behavior and flavor preference in Wistar rats. BPA was orally administered at a daily dose of 5 μg/kg body weight to F0 pregnant dams from the first day of gestation (GD 1) until the last day of lactation (LD 21), and then to F1 offspring from weaning (PND 21) to adulthood (PND 100). F2 offspring were not exposed. Development and clinical signs of toxicity were assessed daily. Maternal behavior was evaluated by observing nursing and pup-caring actions, as well as "non-maternal" behaviors in F0 and F1 dams from parturition until LD 8. The flavor preferences of F1 and F2 offspring were evaluated based on the intake of sweet, salt and fat solutions using the two-bottle choice test on PND 21-34 and PND 86-99. BPA exposure: 1) decreased maternal behavior in F1 dams, 2) caused developmental defects in both F1 and F2 offspring, with a noticeable decrease in anogenital distance in male rats, and 3) did not affect flavored solution intake in F1, but induced changes in sweet preference in F2 juveniles and in salt and fat solution intakes in F2 adults, and 4) induced a body weight increase in the F2 generation only, whereas food intake and water consumption did not change. Taken as a whole, our findings showed that both gestational (F0) and lifelong (F1) exposures to a human-relevant dose of BPA could induce multi-generational effects on both development and behavior. These results suggest possible selective neuroendocrine defects and/or epigenetic changes caused by BPA exposure.

Perinatal xenohormone exposure impacts sweet preference and submandibular development in male rats

OBJECTIVE

To determine the effect of perinatal exposure to low doses of genistein and/or vinclozolin on submandibular salivary gland (SSG) development in juvenile and adult male rats and to establish a link with sweet preference.

MATERIAL AND METHODS

Female rats received orally (1 mg kg(-1) body weight/day) genistein and vinclozolin, alone or in combination, from the first gestational day up to weaning. Sweet preference was assessed at weaning and in adulthood in male offspring; submandibular glands were then collected to study the morphogenesis and mRNA expression of steroid receptors, growth factors and taste related proteins.

RESULTS

Exposure to genistein and/or vinclozolin resulted in a higher saccharin intake on postnatal day 25 (P < 0.05) linked to a higher number of pro-acinar cells (P < 0.01) and mRNA expression of progesterone receptor, growth factors and gustine (P < 0.01). These increases disappeared in adulthood, but mRNA expressions of sex hormone receptors and growth factors were strongly repressed in all treated groups (P < 0.01).

CONCLUSION

Our findings confirm that the SSG are target for xenohormones and provide evidence that perinatal exposure to low doses of genistein and/or vinclozolin could simultaneously disrupt not only the salivary gland prepubertal development and sweet intake but also endocrine gene mRNA expression later in life.

Pesticide exposure and neurodevelopmental outcomes: review of the epidemiologic and animal studies

Assessment of whether pesticide exposure is associated with neurodevelopmental outcomes in children can best be addressed with a systematic review of both the human and animal peer-reviewed literature. This review analyzed epidemiologic studies testing the hypothesis that exposure to pesticides during pregnancy and/or early childhood is associated with neurodevelopmental outcomes in children. Studies that directly queried pesticide exposure (e.g., via questionnaire or interview) or measured pesticide or metabolite levels in biological specimens from study participants (e.g., blood, urine, etc.) or their immediate environment (e.g., personal air monitoring, home dust samples, etc.) were eligible for inclusion. Consistency, strength of association, and dose response were key elements of the framework utilized for evaluating epidemiologic studies. As a whole, the epidemiologic studies did not strongly implicate any particular pesticide as being causally related to adverse neurodevelopmental outcomes in infants and children. A few associations were unique for a health outcome and specific pesticide, and alternative hypotheses could not be ruled out. Our survey of the in vivo peer-reviewed published mammalian literature focused on effects of the specific active ingredient of pesticides on functional neurodevelopmental endpoints (i.e., behavior, neuropharmacology and neuropathology). In most cases, effects were noted at dose levels within the same order of magnitude or higher compared to the point of departure used for chronic risk assessments in the United States. Thus, although the published animal studies may have characterized potential neurodevelopmental outcomes using endpoints not required by guideline studies, the effects were generally observed at or above effect levels measured in repeated-dose toxicology studies submitted to the U.S. Environmental Protection Agency (EPA). Suggestions for improved exposure assessment in epidemiology studies and more effective and tiered approaches in animal testing are discussed.

Environmental levels of atrazine decrease spatial aggregation in the freshwater mussel, Elliptio complanata

The commonly used herbicide atrazine (ATR), may cause estrogen-like alterations and, like other xenoestrogens, may alter behavior. Here effects on animal aggregation were tested in freshwater mussels exposed short-term to ecologically relevant ATR concentrations between 1.5 and 150microg/L. The aggregation index (AI), the fraction of mussels in the most densely populated tank section, was evaluated and showed higher AI at later times in both 6- and 72-h trials (p<0.001). After 72h, there was also less aggregation in estradiol- and mid-ATR-treated animals, 26% and 24% less than control, respectively (p<0.04). These data suggest that freshwater mussels tend to aggregate, that 72-h exposure to ecologically relevant ATR concentrations decreases aggregation, and that estradiol exposure has a similar effect. Given that bivalve aggregation may be related to reproduction, the results suggest that low concentrations of ATR may have ecological consequences on animal populations in this species.