Medaka (Oryzias latipes) for use in evaluating developmental effects of endocrine active chemicals with special reference to gonadal intersex (testis-ova).

Japanese medaka (Oryzias latipes) has been widely used for the evaluation of the toxicity of endocrine active chemicals (EACs) and other chemicals as well as for monitoring the adverse effects of effluent discharges in relation to sexual development and function. It is useful for these evaluations for many reasons including the following: 1) it has a short life cycle facilitating studies extending over long phases of development and over multigenerations, 2) it is easy to rear, 3) male and female phenotypes can easily be distinguished on the basis of secondary sex characteristics, and 4) a genetic marker (DMY) is available for identifying the true genotypic sex. Several biomarkers have been found to be useful for identifying the effects of exposure to estrogenic and androgenic chemicals in medaka and they include increased levels of hepatic vitellogenin (VTG) and testis-ova induction in males for exposure to estrogenic chemicals, and decreased levels of hepatic VTG in females and an altered morphology of dorsal and anal fins and formation of papillae for androgenic chemicals. In this paper, we present a critical analysis of the use of medaka as a test species for studies of endocrine disruption and report on the use of sex-related genetic markers and alterations in gonadal development, including the induction of testis-ova formation, for assessing the disruptive effects of EACs. In this paper, we focus on some of the more recent studies and findings.

A general structured model for a sequential hermaphrodite population.

This paper introduces and analyzes a model of sequential hermaphroditism in the framework of continuously structured population models with sexual reproduction. The model is general in the sense that the birth, transition (from one sex to the other) and death processes of the population are given by arbitrary functions according to a biological meaningful hypotheses. The system is reduced to a single equation introducing the intrinsic sex-ratio subspace. The steady states are analyzed and illustrated for several cases. In particular, neglecting the competition for resources we have explicitly found a unique non-trivial equilibrium which is unstable.

Androgen imprinting of the brain in animal models and humans with intersex disorders: review and recommendations.

PURPOSE: Psychosexual development, gender assignment and surgical treatment in patients with intersex are controversial issues in the medical literature. Some groups are of the opinion that gender identity and sexual orientation are determined prenatally secondary to the fetal hormonal environment causing irreversible development of the nervous system. We reviewed the evidence in animal and human studies to determine the possible role of early postnatal androgen production in gender development. MATERIALS AND METHODS: An extensive literature review was performed of data from animal experiments and human studies. RESULTS Many animal studies show that adding or removing hormonal stimulus in early postnatal life can profoundly alter gender behavior of the adult animal. Human case studies show that late intervention is unable to reverse gender orientation from male to female. Most studies have not permitted testing of whether early gender assignment and treatment as female with suppression/ablation of postnatal androgen production leads to improved concordance of the gender identity and sex of rearing. CONCLUSIONS: Animal studies support a role for postnatal androgens in brain/behavior development with human studies neither completely supportive nor antagonistic. Therefore, gender assignment in infants with intersex should be made with the possibility in mind that postnatal testicular hormones at ages 1 to 6 months may affect gender identity. A case-control study is required to test the hypothesis that postnatal androgen exposure may convert ambisexual brain functions to committed male behavior patterns.

Proliferation zones in the adult brain of a sequential hermaphrodite teleost species (Sparus aurata).

Teleost sex change is an important model to understand general principles of sexual differentiation and plasticity in the adult brain. The present study is the first to examine the proliferation zones in the adult brain of males, females and sex-changing individuals of a protandrous teleost species (Sparus aurata), by means of 5-bromo-2-deoxyuridine immunocytochemistry. Postnatal neurogenesis in the marine teleost brain was found in ventricular and subventricular areas of the brain that in most cases coincided with the embryonic proliferation zones. The molecular layer of corpus and valvula cerebelli exhibited the highest mitotic activity in the adult brain. High mitotic activity was observed in the hypothalamic, thalamic and telencephalic ventricular areas, as well as the dorsal and ventral rim of the optic tectum. Most of the labeled cells were elongated, indicating the initiation of migratory activity. There were no qualitative differences in the distribution of proliferation zones between the sex phases studied with the exception of the ventricular region of the dorsal hypothalamic area. Volume fraction analysis of the area occupied by the labeled cells suggested that this region included higher densities of newborn cells in the female animals. The proliferation pattern in the adult gilthead sea bream brain is in agreement with the hypothesis of the continuous generation of new cells in the teleost brain. Moreover, our data propose that cell proliferation differences possibly existing in the ventricular region of the dorsal hypothalamus between sexual phases, might be involved in central mechanisms of sexual plasticity in protandrous hermaphrodite teleosts.

Relationships between sex and the size and number of forebrain gonadotropin-releasing hormone-immunoreactive neurones in the ballan wrasse (Labrus berggylta), a protogynous hermaphrodite.

This study is the first to examine the brain gonadotropin-releasing hormone (GnRH) cell population phenotype in a protogynous and monandric sequentially hermaphroditic fish. Male ballan wrasse (Labrus berggylta) had on average higher numbers of GnRH-immunoreactive (GnRH-ir) cells within the brain preoptic area (POA) than females, a difference not found in GnRH-ir cells in other brain regions. Furthermore, in males, but not females, the number of these POA GnRH-ir cells correlated with body size. Maturational state (prespawning or postspawning) had marked effects on mean profile sizes (but not numbers) of both GnRH-ir cell bodies and cell nuclei, even when existing differences in body size and allometric relationships had been taken into account. Postspawning males tended to have larger GnRH-ir profiles in all brain regions relative to both prespawning males and females. Moreover, the GnRH-ir cell number in POA, and the cell body profile size in both POA and at the level of the anterior commissure, correlated with gonad size in spermiated prespawning males, indicating a relationship between both size and number of GnRH cells and male gonadal development. These results suggest that temporary changes in the size of brain GnRH-ir neurones are coupled to the male spawning cycle, and that permanent POA GnRH-ir cell number changes are involved in the process of sex change in sequential hermaphrodites. However, smaller males had no more preoptic GnRH-ir cells than equally sized females, which may argue against a proximate inducing role of GnRH cell number changes in naturally occurring sex reversal.

Number of preoptic GnRH-immunoreactive cells correlates with sexual phase in a protandrously hermaphroditic fish, the dusky anemonefish (Amphiprion melanopus).

The populations of gonadotropin-releasing hormone (GnRH)-producing cells within the preoptic area (POA) and terminal nerve (TN) of the brain have been suggested as the neuronal systems mediating social control of sex and gonadogenesis in sequentially hermaphroditic teleosts. In the present study, the number and soma size of GnRH-immunoreactive (GnRH-ir) cells in the POA and TN were studied in male, female and juvenile individuals of the dusky anemonefish (Amphiprion melanopus), a species which displays both male to female sex change and socially controlled sexual maturation. The results showed that the number of POA (but not TN) GnRH-ir cells differ significantly between sexual phases, with males displaying higher cell numbers than both females and juveniles. Soma sizes of POA and TN GnRH-ir cells were larger in females than in males and juveniles. However, this relationship was fully explained by differences in body size. The results indicate that high POA GnRH cell numbers are part of a masculinizing mechanism and support the hypothesis that the POA GnRH cell population plays a central role in initiating or mediating the process of socially induced gonadal and/or behavioural transformations in sequential hermaphrodites.

Changes in plasma and gonadal steroid hormones in relation to the reproductive cycle and the sex inversion process in the protandrous seabass, Lates calcarifer.

Plasma and gonadal levels of several gonadal steroids (testosterone, 11-ketotestosterone, androstenedione, 11 beta-hydroxyandrostenedione, 17 beta-estradiol, and estrone) were measured by RIA in the protandrous seabass, Lates calcarifer, throughout an annual reproductive cycle. Twenty to 25 fish were killed every month for gonadal and plasma sampling. Very low plasma levels of 11-ketotestosterone in females (monthly means always less than 75 pg/ml), and of 17 beta-estradiol (means always less than 68 pg/ml) and estrone (means always less than 42 pg/ml) in males did not fluctuate significantly during the cycle. Conversely, plasma concentrations of testosterone, estrone, and 17 beta-estradiol peaked during vitellogenesis in females (highest mean: 182 +/- 121, 182 +/- 32 and 598 +/- 369 pg/ml, respectively) and testosterone and 11-ketotestosterone peaked during spermiation in males (highest mean: 189 +/- 91 and 223 +/- 94 pg/ml, respectively). When sex type are compared over the whole cycle, females displayed higher 17 beta-estradiol (172 +/- 233.5 pg/ml) and estrone (79.5 +/- 72 pg/ml) levels than males (57 +/- 7.5 and 44 +/- 62.5 pg/ml, respectively), while males had higher 11-ketotestosterone levels (153 +/- 88 pg/ml) and, to a lesser extent, higher testosterone levels (128 +/- 82 pg/ml) than females (51.5 +/- 28 and 91.5 +/- 60 pg/ml, respectively). Transitional fish always exhibit low plasma levels for these four steroids (testosterone 56.5 +/- 12.5 pg/ml, 11-ketotestosterone 59 +/- 23.5 pg/ml, 17 beta-estradiol 65.6 +/- 36 pg/ml, and estrone 61 +/- 47.5 pg/ml). Among gonadal androgens, 11 beta-hydroxyandrostenedione predominated in testes (3.95 +/- 3 ng/g), except during spermiation (0.8 +/- 0.5 ng/g), and remained low in ovaries (1.05 +/- 1.4 ng/g). No differences were detected in gonads, for testosterone and 11-ketotestosterone whatever the sex type, but their concentrations were higher in vitellogenic and atretic ovaries. Androstenedione levels were slightly higher in testes (2.21 +/- 2 ng/g) than in ovaries (1.53 +/- 1.32 ng/g). Transitional gonads always showed low concentrations for these four androgens (testosterone 0.66 +/- 1.77 ng/g, 11-ketotestosterone 0.14 +/- 0.05 ng/g, androstenedione 0.3 +/- 0.34 ng/g, and 11 beta-hydroxyandrostenedione 0.2 +/- 0.23 ng/g). Gonadal 17 beta-estradiol was nearly undetectable in testes (0.06 +/- 0.07 ng/g), low in ovaries (0.42 +/- 0.46 ng/g), and strikingly high in transitional gonads (2.89 +/- 1.64 ng/g) even at the very beginning of sex inversion. This suggests an important role for this estrogen in the protandrous sex inversion process in the seabass L. calcarifer.