The Goldfish as a Model for Studying Neuroestrogen Synthesis, Localization, and Action in the Brain and Visual System

Abstract

Organizational and activational effects of estrogen (E) in the central nervous system (CNS) are exerted directly by circulating E and indirectly after aromatization of circulating androgen to E in the brain itself. Understanding an environmental chemical's ability to disrupt E-dependent neural processes, therefore, requires attention to both pathways. Because aromatase (Aro) is highly expressed in teleost brain, when compared to mammals and other vertebrates, fish are technically advantageous for localization and regulation studies and may also provide a model in which the functional consequences of brain-derived (neuro-)E synthesis are exaggerated. Recently, Aro was immunolocalized in cell bodies and fiber projections of second-and third-order neurons of the goldfish retina and in central visual processing areas. Authentic Aro enzyme activity was verified biochemically, suggesting a heretofore unrecognized role of sex steroids in the visual system. Initial studies show that in vivo treatment with aromatizable androgen or E increases calmodulin synthesis and calmodulin protein in retina and also affects retinal protein and DNA. Whether there are related changes in the processing of visual information that is essential for seasonal reproduction or in the generative and regenerative capacity of the goldfish visual system requires further investigation. -Environ Health Perspect 103(Suppl 7): 51-57 (1995)

Brain steroid contents in the catfish Heteropneustes fossilis: sex and gonad stage-specific changes

“…Teleost fishes are known to exhibit a high brain aromatase activity mainly due to the expression of cyp19a1b gene that encodes aromatase B (Callard et al 1995;Pellegrini et al 2005;Forlano et al 2006;Kah et al 2009). Recent studies based on both in situ hybridization and immunohistochemistry have demonstrated that the enzyme is restricted to radial glial cells and mostly abundant in the forebrain such as olfactory bulb, telencephalon, preoptic area, mediobasal hypothalamus, and pituitary (proximal pars distalis and neurohypophysis) (Robel and Baulieu 1994;Kah et al 2009;Halm et al 2003;Sakamoto et al 2001).…”

“…Fish brain has an exceptionally high level of aromatase activity; for example, 1,300 versus 1-5 fmol/mg protein/h in the hypothalamic/preoptic area of goldfish versus rat, mouse, rabbit, or hamster, respectively (Callard and Pasmanik 1987). Callard et al (1995) reported goldfish brain as a source of neuroestrogen and other steroids. Recently, it has been demonstrated that pregnenolone (P 5 ) and 17a-hydroxypregnenolone (17a-OH-P 5 ) were identified as cholesterol metabolites in the brain and pituitary gland of lacustrine sockeye salmon (Onchorhynchus nerka) during sexual maturation (Matsumoto et al 2003).…”

Ovarian steroidogenesis and the role of sex steroid hormones on ovarian growth and maturation of the Japanese eel

“…2). Gaining a better understanding of the regulation of E2 synthesis is reliant on studies on extragonadal metabolism of androgens and estrogens, and molecular characterization of multiple forms of 17␤-HSD in fish, although such reports [31,44,[49][50][51][52] have been restricted to date.…”

Surflan™ and oryzalin impair reproduction in the teleost medaka (Oryzias latipes)

“…Bjerselius et al (2001) showed that a relatively brief exposure to estradiol (24-28 d) negatively impacted a number of courtship parameters in treated male goldfish paired with an unexposed, artificially-induced spawning female.Therefore, for males in particular, but also potentially for females, decreased fertility may be due to effects of treatment with estrogenic substances on reproductive behavior. Although certain data indicate that exogenous estrogen may impact brain p450arom activity, a causal link between altered p450aromatase activity and behavior have not been established (Callard et al, 1995;Melo and Ramsdell, 2001).…”