RESUMO

It has been traditionally accepted that the gonadotropins (GtHs), follicle stimulating hormone (FSH) and luteinizing hormone (LH), are synthesized and secreted only by the pituitary. However, the presence of theses hormones in extrapituitary tissues has been demonstrated in mammals, and more recently also in fish. In this study, we cloned the cDNAs and characterized the expression of FSH-ß, LH-ß, and glycoprotein hormone α (GPH-α) subunits from brain and gonads of male and female pejerrey Odontesthes bonariensis at different stages of gonadal maturation. In situ hybridization revealed that, in addition to their classical location in pituitary cells, the three GtH transcripts were also located in the gonads. FSH-ß and GPH-α subunits were found in the cytoplasm of oogonia, previtellogenic and vitellogenic oocytes in ovaries. LH-ß expression was detected in previtellogenic and vitellogenic oocytes but not in oogonia. In males, the three subunits were expressed in spermatogonia and to a lesser extent in spermatocytes. Exposure of fish to high water temperatures that impair pejerrey reproduction also induced a decrease of extrahypophyseal expression of GtH subunits.

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RESUMO

Pejerrey is a teleost fish presenting a strong temperature-dependent sex determination. This study was conducted to clone pejerrey amh cDNA, analyze its expression profile during thermal and endocrine manipulation of gonadal differentiation, and compare its expression with that of gonadal aromatase (cyp19a1). Amh displayed higher expression at masculinizing than at feminizing temperatures during the gonadal differentiation period. Its expression at an intermediate temperature (females 1:1 males), was high in half of the larvae and low in the other half. Cyp19a1 showed a reciprocal expression pattern to that of amh both individually- and temperature-wise. Increased cyp19a1 and amh expression was observed before morphological gonadal differentiation. Amh expression in larvae feminized by administration of estradiol or masculinized by the administration of an aromatase inhibitor was down- and up-regulated, respectively. These results show that amh plays a critical role in testicular differentiation and it is apparently modulated by estrogens in this species.

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RESUMO

Starved larvae of the silversides O. hatcheri (2- and 5-days-old) and Odontesthes bonariensis (5-days-old) were used to compare the oxygen consumption rates at 0, 5, 10, 20 and 30 ppt salinity. Oxygen consumption of O. hatcheri and O. bonariensis was minimal at 0 and 10 ppt, respectively, salinities close to those encountered in areas inhabited by these fishes. In both species, oxygen consumption rates thereafter increased with increasing salinity, and then abruptly decreased at 30 ppt. Lower consumption at extreme salinities might be a result of reduced activity, which in itself was salinity-modulated. Differences in activity may explain the fact that oxygen consumption rates of 5-day-old larvae were higher than 2-day-old larvae, which still possess yolk-sac. In this case, starved larvae incurred in higher metabolic demand due to the continuous swimming in the search for food.

As larvas em inanição de peixe-rei O. hatcheri (2 e 5 dias de idade) e Odontesthes bonariensis (5 dias de idade) foram usadas para comparar as taxas de consumo de oxigênio em salinidades de 0, 5, 10, 20 e 30 ppt. As taxas de consumo de oxigênio de O. hatcheri e O. bonariensis foram mínimas a 0 e 10 ppt, respectivamente, salinidades próximas aquelas encontradas nas áreas onde estes peixes habitam. Em seguida, em ambas as espécies, as taxas de consumo de oxigênio aumentaram com o incremento da salinidade, e abruptamente caíram a 30 ppt. As taxas de consumo mais baixas em salinidades extremas podem ser resultado da atividade reduzida, sendo portanto modulada pela salinidade. Diferenças na atividade possivelmente explicam o fato das taxas de consumo de oxigênio de larvas de 5 dias de idade serem maiores em comparação a larvas de 2 dias, ainda com saco vitelínico. Neste caso, larvas em inanição impõem um maior gasto metabólico devido a natação contínua em busca de alimento.

RESUMO

The development of gonadotropin-releasing hormone (GnRH) neurons was studied in relation to the sensitive period of thermolabile sex determination in the pejerrey Odontesthes bonariensis, an atherinid fish from South America. Fish were raised from hatching at three different temperatures: 17 degrees C (100% females), 24 degrees C (70% females), and 29 degrees C (100% males). Three groups of immunoreactive GnRH (ir-GnRH) neurons were identified at the terminal nerve ganglion (TNG), the midbrain tegmentum (MT), and the preoptic area (POA). Immunoreactive GnRH (ir-GnRH) neurons were identified in the TNG at hatching (day 0) and in the MT at day 3 at all the experimental temperatures. In the POA ir-GnRH neurons were identified in the nucleus preopticus periventricularis simultaneously with the first appearance of ir-GnRH fibers in the pituitary on days 11, 14, and 17 for larvae kept at 29, 24, and 17 degrees C, respectively. The number of ir-GnRH neurons in the TNG did not show any statistical difference between temperatures. The number of ir-GnRH neurons in the MT increased in number during the experiment for larvae kept at 17 and 24 degrees C but decreased between days 17 and 31 in larvae kept at 29 degrees C. The number of ir-GnRH neurons in the POA increased during development with a peak at day 28 for all temperatures studied and the magnitude of this peak showed a correlation with incubation temperature. These results reinforce the notion that the hypothalamus-pituitary-gonadal axis is active during sex determination in pejerrey suggesting a possible role of the central nervous system and GnRH in this process. It is also suggested that GnRH neurons located in the preoptic area might be the physiological transducers of temperature during the temperature sensitive period in this species.

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