title: Assessing effects of environmental chemicals on neuroendocrine systems: potential mechanisms and functional outcomes.
abstract: Environmental pollutants encompass a vast array of compounds. Most studies in birds have focused on toxicological effects, with little attention to non-lethal effects. Consequently, it has proven difficult to assess potential risk associated with exposure to endocrine disrupting chemicals (EDCs). Assessing potential adverse effects due to exposure is further complicated by the great variation that occurs across avian species. These include variations in reproductive strategies, life span, sexual differentiation, and migration. Differences in reproductive strategies, particularly in the developmental patterns and mechanisms for precocial and altricial chicks, predispose birds to wide variations in response to steroids and steroid-like EDCs. We have investigated the effects of EDCs in precocial birds including Japanese quail (Coturnix japonica) and mallard ducks (Anas platyrhynchos) as well as in wild altricial songbirds. Studies in Japanese quail characterized endogenous steroid hormone changes during development and have demonstrated that the developing embryo uses the yolk as a 'steroid hormone depot'. It appears that actual embryonic exposure is quantitatively lower than indicated by the treatment in egg injections and that the true amount of compound necessary for bioactivity may be quite low relative to the actual dosage delivered. Additionally, embryonic exposure to specific EDCs adversely affected sexual differentiation in quail, especially impacting male sexual behavior as well as neural systems, immune response, and thyroid hormones. Many of these studies considered single compounds; however, wild birds are exposed to complex mixtures and multiple compounds. We tested complex mixtures of polychlorinated biphenyls (PCBs) at concentrations that bracketed those found in eggs in contaminated regions. Results indicated that the predictive value of the toxic equivalency (TEQ), based on comparative activation of the aryl hydrocarbon receptor (AhR) relative to dioxin was not as accurate as expected. We discuss the potential of developing an endocrine disruption index (EDI) to bridge the inconsistencies observed between responses predicted by the TEQ and those observed in vivo following exposure to EDCs. Further, we will discuss how an EDI would complement the adverse outcome pathways analyses to consider the range of effects of endocrine disruptors in birds.
authors.affiliation: Department of Animal and Avian Sciences, University of Maryland, College Park, MD 20742, USA. maotting@umd.edu
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Ottinger
authors.forename: Tiffany
authors.initials: T
authors.lastname: Carro
authors.forename: Meredith
authors.initials: M
authors.lastname: Bohannon
authors.forename: Leah
authors.initials: L
authors.lastname: Baltos
authors.forename: Allegra M
authors.initials: AM
authors.lastname: Marcell
authors.forename: Moira
authors.initials: M
authors.lastname: McKernan
authors.forename: Karen M
authors.initials: KM
authors.lastname: Dean
authors.forename: Emma
authors.initials: E
authors.lastname: Lavoie
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Abdelnabi
mesh_terms: D000818:Animals; D001717:Birds / Q000378:metabolism; D052244:Endocrine Disruptors / Q000633:toxicity*; D004785:Environmental Pollutants / Q000633:toxicity*; D008297:Male; D009490:Neurosecretory Systems / Q000187:drug effects* / Q000378:metabolism*; D011784:Quail / Q000378:metabolism; D012098:Reproduction / Q000187:drug effects; D012733:Sex Differentiation / Q000502:physiology; D012726:Sexual Behavior, Animal / Q000502:physiology
chemical_list: D052244:Endocrine Disruptors; D004785:Environmental Pollutants
keywords: Avian reproduction; Endocrine disrupting chemicals; Japanese quail; Male sexual behavior; Neuroendocrine systems; Sexual differentiation