Neuroendocrine and behavioral implications of endocrine disrupting chemicals in quail

Studies in our laboratory have focused on endocrine, neuroendocrine, and be havioral components of reproduction in the Japanese quail. These studies co nsidered various stages in the life cycle, including embryonic development, sexual maturation, adult reproductive function, and aging. A major focus o f our research has been the role of neuroendocrine systems that appear to s ynchronize both endocrine and behavioral responses. These studies provide t he basis for our more recent research on the impact of endocrine disrupting chemicals (EDCs) on reproductive function in the Japanese quail. These end ocrine active chemicals include pesticides, herbicides, industrial products , and plant phytoestrogens. Many of these chemicals appear to mimic vertebr ate steroids, often by interacting with steroid receptors. However, most ED Cs have relatively weak biological activity compared to native steroid horm ones. Therefore, it becomes important to understand the mode and mechanism of action of classes of these chemicals and sensitive stages in the life hi story of various species. Precocial birds, such as the Japanese quail, are likely to be sensitive to EDC effects during embryonic development, because sexual differentiation occurs during this period. Accordingly, adult quail may be less impacted by EDC exposure. Because there are a great many data available on normal development and reproductive function in this species, the Japanese quail provides an excellent model for examining the effects of EDCs. Thus, we have begun studies using a Japanese quail model system to s tudy the effects of EDCs on reproductive endocrine and behavioral responses . In this review, we have two goals: first, to provide a summary of reprodu ctive development and sexual differentiation in intact Japanese quail embry os, including ontogenetic patterns in steroid hormones in the embryonic and maturing quail. Second, we discuss some recent data from experiments in ou r laboratory in which EDCs have been tested in Japanese quail. The Japanese quail provides an excellent avian model for testing EDCs because this spec ies has well-characterized reproductive endocrine and behavioral responses. Considerable research has been conducted in quail in which the effects of embryonic steroid exposure have been studied relative to reproductive behav ior. Moreover, developmental processes have been studied extensively and in clude investigations of the reproductive axis, thyroid system, and stress a nd immune responses. We have conducted a number of studies, which have cons idered long-term neuroendocrine consequences as well as behavioral response s to steroids. Some of these studies have specifically tested the effects o f embryonic steroid exposure on later reproductive function in a multigener ational context. A multigenerational exposure provides a basis for understa nding potential exposure scenarios in the field. In addition, potential rou tes of exposure to EDCs for avian species are being considered, as well as differential effects due to stage of the life cycle at exposure to an EDC. The studies in our laboratory have used both diet and egg injection as mode s of exposure for Japanese quail. In this way, birds were exposed to a spec ific dose of an EDC at a selected stage in development by injection. Altern atively, dietary exposure appears to be a primary route of exposure; theref ore experimental exposure through the diet mimics potential field situation s. Thus, experiments should consider a number of aspects of exposure when a ttempting to replicate field exposures to EDCs. (C) 2001 Academic Press.