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Adult green anoles, Anolis carolinensis, exhibit numerous sex differences resulting from divergent strategies for maximizing reproductive success. I focused on the ontogeny of sex differences in behavior in juveniles, in relation to adult sex differences, by documenting the behavior of free-ranging juveniles, examining the structure and use of headbobbing displays, and determining the role of the androgen testosterone (T) in producing behavioral sex differences. Field observations indicated that juvenile males eat and forage actively more often than juvenile females. This divergent feeding behavior may result from sexual selection, given that body size is a major factor in determining the reproductive success of males. Analyses of headbobbing displays, used by adults in aggressive and sexual interactions, revealed that juvenile males and females each give the same three A, B, and C display types described for adults. However, there may be a maturational component to display structure, as juvenile displays differ from those of adults in within-display temporal structure, and are not as stereotyped. Concerning display use, social context affects neither the types of display interactions observed nor the rates of displays and related behaviors. However, size affects nearly every aspect of display behavior. Both juvenile males and females show increased display rates and probabilities of expressing display-related behaviors with increasing body size, although in the largest juveniles, male display rates become higher than those of females. These results, like those from analyses of display structure, suggest a maturational component to display use, perhaps mediated by changes in the underlying motivational states of juveniles. Consistent with the divergence in display rates in large juveniles, males of approximately 30 d of age and older have higher plasma T concentrations than females. Furthermore, juvenile males and females that have been given T implants each respond with increased behavior levels, approaching those of breeding adult males. These analyses indicate that sexual dimorphisms in behavior in adults likely arise through underlying physiological differences between males and females that mediate the expression of behavior, rather than through fundamental sex differences in the ability to perform these behaviors. / Ph. D.

L'arrivée des souris transgéniques a ouvert une ère nouvelle pour la physiologie intégrative permettant d’étudier la fonction d'un gène au sein d'un organisme vivant. Ces techniques ont permis la découverte du rôle de l'os sur le métabolisme énergétique et la fertilité. Contrôle neurologique de la masse osseuse. La leptine agit dans le tronc cérébral en freinant les neurones sérotoninergiques qui projettent sur l'hypothalamus pour contrôler la masse osseuse (VMH) et l'appétit (noyau arqué). La sérotonine cérébrale freine le tonus sympathique et stimule la masse osseuse. Régulation osseuse du métabolisme énergétique. L’ostéocalcine est une hormone protéique sécrétée par l'ostéoblaste, qui stimule la production d'insuline par le pancréas et diminue l'insulinorésistance périphérique. Nous rapportons la démonstration directe chez l'homme de l'action de l’ostéocalcine sur la glycémie. Ici l’ostéome ostéoïde est un adénome bénin sécrétant de l’ostéocalcine. Dans une large étude, l’ostéocalcine est négativement corrélée à la glycémie, au syndrome métabolique et à l'existence de calcifications aortiques abdominales. Steroides sexuels et os. Le traitement adjuvant du cancer du sein par anti-aromatase induit une perte osseuse sévère. Par ailleurs, nous avons identifié un patient avec une oligospermie, un syndrome métabolique et une mutation F464Y du récepteur de l'ostéocalcine GPRC6A. Nous présentons un nouvel axe « pancréas-os-testicule » qui régule la fertilité. / Transgenic mice offers powerful tools to study integrative physiology especially to study a specific gene function in a whole organism. Using transgenic mice revealed the role of the skeleton on fertility and energy metabolism.Central control of bone mass. Leptin acts on brain stem and decrease serotonin neuron (SN) activity. SN project on hypothalamus to control bone mass (VMH nucleus) and appetite (arcuate nucleus). Brain serotonin reduces sympathetic tone and increases bone mass.Bone regulates energy metabolism. Osteocalcin is a new hormone secreted by osteoblast which stimulates insulin secretion and reduces insulin resistance. We show here for the first time that the action of osteocalcin on blood glucose is conserved in humans. Osteoid osteoma can be considered as a benign tumor secreting osteocalcin. In a large cohort of elderly males, osteocalcin is negatively associated to blood glucose, metabolic syndrome and abdominal aortic calcifications. Sex steroids and bone. First we show aromatase inhibitor induces bone loss after one year of adjuvant therapy in breast cancer. Second we identified a patient presenting severe oligospermia, metabolic syndrome and a F464Y mutation of the GPRC6A osteocalcin receptor. We identified a new independent pancreas- bone – testis axis to regulate fertility.

O presente estudo avaliou a possibilidade de extração e dosagem de esteroides sexuais em amostras de gordura de carcaças e biópsias de baleia jubarte. A progesterona (P4), testosterona (T) e estradiol (E2) puderam ser dosados em todas as amostras pela técnica de enzimaimunoensaio. Amostras de carcaças foram utilizadas para validação da colheita. Uma série de experimentos foi realizada a fim de se avaliar: se o estado de decomposição da amostra altera os níveis hormonais; se os níveis de hormônios são diferentes em diferentes locais amostrados; se a profundidade de colheita (camadas externa, média e interna) altera os níveis hormonais; e finalmente o efeito do tamanho da amostra sobre as dosagens de hormônio. Todos estes elementos podem influenciar de maneira significativa a dosagem final. Também foram realizadas colheitas por meio de biópsias em 2011 e 2012 em área de reprodução no Atlântico Sul o Parque Nacional Marinho de Abrolhos e seu entorno; e em área de alimentação em 2011 e 2012 no Pacífico Sul o Parque Marino Francisco Coloane e seu entorno - localizado na Patagônia chilena. Como esperado, fêmeas apresentaram médias mais elevadas de P4 e E2 que machos, e machos apresentaram médias mais elevadas de T que fêmeas. Também foi observada sazonalidade reprodutiva com níveis mais elevados T em machos adultos em área de reprodução, especialmente nos meses de setembro e outubro. Os níveis de E2 em áreas de alimentação foram mais elevados que em área de reprodução tanto em machos quanto em fêmeas. Esta aparente inversão dos níveis de E2 com relação ao estado reprodutivo deve-se provavelmente ao tempo de metabolização deste hormônio na gordura. Algumas fêmeas adultas acompanhadas e desacompanhadas de filhotes apresentaram nível de P4 compatível com níveis de prenhez em outras espécies de cetáceos. Alguns dos animais biopsados tiveram seu comprimento corporal estimado através de fotogrametria. A menor fêmea acompanhada de filhote mediu 10.21 metros. Machos e fêmeas não apresentaram comprimentos corporais diferentes entre si, 12.96 e 12.04 metros, respectivamente. O tecido adiposo mostrou-se como uma matriz viável para dosagens de esteroides sexuais e estudos acerca da fisiologia reprodutiva de baleias de vida livre. A dosagem de hormônio da camada de gordura tem o potencial de indicar variações sazonais, estados de prenhez, picos de testosterona em machos, e diferenças entre machos e fêmeas. Quando combinada com comprimento corporal e história de vida, a dosagem hormonal pode promover informações ainda mais robustas acerca do estado reprodutivo dos indivíduos de determinada população. / The current study evaluated the possibility of extracting and measuring steroid hormones from the blubber of carcasses and living animals. Progesterone (P4), testosterone (T) and estradiol (E2) were successfully measured trough enzimaimunoassay technique. Stranded animals were sampled to validate the blubber collection. A set of experiments were performed: whether the state of decomposition of fat affects hormone levels; whether the body region from which samples were collected affects the levels of P4, E2, and T; whether the depth of the layer selected (outer, middle, inner) affects hormone levels; and finally the size of sample effect on hormone levels. All of these four elements can potentially alter the measurement final results. Also, biopsy sampling were done at a South Atlantic breeding Area, National Marine Park Abrolhos in 2011 and 2012; and in one feeding area, the Marine Park Francisco Coloane, locate at Chilean Patagonia. As expected females had higher P4 and E2 means compared to males, and males exhibited higher means of T than females. Also a reproductive seasonality was detected in E2 and T levels. T levels were higher in adult males during breeding season, especially in September and October. E2 were higher in both females and males during feeding season. This apparent inversion of E2 level to the reproductive condition is probably a result of the lag of the hormone from blood to blubber and the time for its metabolism to occur. Part of the adult females with calves and without calves had P4 levels similar to some pregnant cetacean species. Some of the biopsied animals had their body length estimated. The smallest female with calf had 10.21 meters. Males and females did not differ in total body length: 12.96 and 12.04 respectively. The bubbler showed to be a feasible biological matrix to measure sex hormones from free ranging humpback whales, and can indicate differences among sexes and reproductive states. When combined with total body length and life history, the hormone measurements can provide robust information on reproductive state of individuals.

Dans le cadre de la production de nouvelles espèces aquacoles, le sandre, Sander lucioperca, est devenu, depuis plusieurs années, une espèce d’intérêt piscicole en raison de sa valeur économique potentielle. Pour développer et pérenniser sa production aquacole, il est nécessaire de comprendre et maîtriser son cycle de reproduction ainsi que les mécanismes physiologiques mis en jeu afin d’obtenir des œufs et des juvéniles viables tout au long de l’année. Dans cet optique d’optimisation du contrôle du cycle, la dopamine apparaît, chez de nombreux téléostéens dont certains perciformes, comme un inhibiteur de l’axe gonadotrope, via les récepteurs de la famille D2, en bloquant le pulse ovulatoire de LH et l’ovulation. Chez le sandre, le rôle de la dopamine et de ses récepteurs, notamment les récepteurs de la famille D1, est inconnu. L’objet de cette thèse est de déterminer le rôle du système dopaminergique lors des phases finales de l’ovogénèse chez le sandre à travers trois axes principaux : (1) déterminer l’effet du blocage des récepteurs de la dopamine, D1 ou D2, sur la régulation de l’axe gonadotrope et l’induction de l’ovulation en absence et en présence d’une molécule de sGnRHa, (2) définir le répertoire et le profil d’expression des récepteurs dopaminergiques par l’étude du transcriptome cérébral du sandre en période pré-ovulatoire et (3) établir le rôle de la dopamine et de ses différents récepteurs (familles D1 et D2) dans la régulation directe et locale de l’axe gonadotrope aux niveaux cérébral et ovarien. La première partie de ce travail a permis pour la première fois, par l’utilisation d’antagonistes spécifiques des familles de récepteurs D1 et D2, de mettre en évidence un rôle potentiel de la dopamine sur la sécrétion de certains stéroïdes sexuels en période pré-ovulatoire chez le sandre par l’intermédiaire des récepteurs de la famille D1. L’identification de l’ensemble des récepteurs de la dopamine existant chez le sandre nous a permis de confirmer leur expression à tous les niveaux de l’axe gonadotrope (cerveau, hypophyse et ovaires) étayant l’hypothèse d’un rôle de la dopamine dans la reproduction du sandre. Enfin, la dernière partie de ce projet a permis de montrer un rôle régulateur du système dopaminergique, directement au niveau ovarien, sur la production de testostérone par l’intermédiaire des deux familles de récepteurs de la dopamine. L’implication des deux familles de récepteurs a également été mise en évidence dans la production ovarienne de la 17β-estradiol. Au niveau cérébral, seule la famille des récepteurs D2 a été montrée impliquée dans la régulation de l’expression du gène de la GnRH-3. De façon générale, cette étude a permis de mettre en évidence l’implication des récepteurs de la dopamine dans la régulation de l’axe gonadotrope lors des phases finales de l’ovogenèse. Toutefois, des travaux ultérieurs devront être menés pour approfondir les mécanismes physiologiques mis en jeu. D’un point de vue aquacole, les traitements hormonaux à base d’antagonistes des récepteurs de la dopamine ont été inefficaces pour améliorer les performances de reproduction du sandre ce qui n’est pas en faveur de leur utilisation future pour induire l’ovulation chez cette espèce. Ainsi, la mise au point d’autres méthodes d’optimisation sera nécessaire pour continuer à développer la production aquacole du sandre / Pikeperch, Sander lucioperca, is a potential valuable economic fish, making it a species of interest for aquaculture diversification. In the domestication process, controlling and understanding the reproductive cycle is a crucial step in order to produce viable offspring in a synchronous and predictable way. In many teleosts including some perciforms, dopamine inhibits the ovulatory pulse of LH and the ovulation step through D2 dopamine receptors family. In pikeperch, the roles of dopamine and its receptors, especially those belonging to the D1 receptors family, are unknown. For the purpose of the optimization of pikeperch reproduction, we investigated the role of the dopaminergic system during the final stages of oogenesis in this species: (1) by determining the effects of D1 or D2 receptor antagonists alone or in association with sGnRHa on the regulation of the reproductive axis and on the induction of ovulation, (2) by determining the repertoire and the expression profile of the dopamine receptors using a brain transcriptome analysis during the pre-ovulatory period and (3) by evaluating the role of dopamine and its receptors (D1 and D2 families) in the direct and local regulation of the gonadotropic axis at the brain and ovarian levels. For the first time, we showed that the dopamine/D1 receptors complex regulates the sex-steroids release during the pre-ovulatory period, suggesting that dopamine is involved in pikeperch reproduction. Also, we support its involvement thanks to the identification of the dopamine receptors gene expression at the brain, pituitary and ovarian levels. Finally, we showed that the dopaminergic system directly regulates the ovarian testosterone production, through both D1 and D2 receptor families. The involvement of both dopamine receptor families was also highlighted on ovarian 17β-estradiol production. Only the D2 receptor family was shown to be involved on the brain GnRH-3 gene expression. In conclusion, we point out a dopamine receptors implication on the gonadotropic axis regulation during the final stages of oogenesis in pikeperch. However, further studies should be performed to pinpoint the physiological mechanisms behind this phenomenon. From an aquaculture point of view, hormonal treatments with dopamine receptor antagonists appear to be ineffective to improve pikeperch reproductive performances. Therefore, their use to induce pikeperch ovulation should be put into question and the development of alternative methods is necessary to further promote pikeperch production

O presente estudo avaliou a possibilidade de extração e dosagem de esteroides sexuais em amostras de gordura de carcaças e biópsias de baleia jubarte. A progesterona (P4), testosterona (T) e estradiol (E2) puderam ser dosados em todas as amostras pela técnica de enzimaimunoensaio. Amostras de carcaças foram utilizadas para validação da colheita. Uma série de experimentos foi realizada a fim de se avaliar: se o estado de decomposição da amostra altera os níveis hormonais; se os níveis de hormônios são diferentes em diferentes locais amostrados; se a profundidade de colheita (camadas externa, média e interna) altera os níveis hormonais; e finalmente o efeito do tamanho da amostra sobre as dosagens de hormônio. Todos estes elementos podem influenciar de maneira significativa a dosagem final. Também foram realizadas colheitas por meio de biópsias em 2011 e 2012 em área de reprodução no Atlântico Sul o Parque Nacional Marinho de Abrolhos e seu entorno; e em área de alimentação em 2011 e 2012 no Pacífico Sul o Parque Marino Francisco Coloane e seu entorno - localizado na Patagônia chilena. Como esperado, fêmeas apresentaram médias mais elevadas de P4 e E2 que machos, e machos apresentaram médias mais elevadas de T que fêmeas. Também foi observada sazonalidade reprodutiva com níveis mais elevados T em machos adultos em área de reprodução, especialmente nos meses de setembro e outubro. Os níveis de E2 em áreas de alimentação foram mais elevados que em área de reprodução tanto em machos quanto em fêmeas. Esta aparente inversão dos níveis de E2 com relação ao estado reprodutivo deve-se provavelmente ao tempo de metabolização deste hormônio na gordura. Algumas fêmeas adultas acompanhadas e desacompanhadas de filhotes apresentaram nível de P4 compatível com níveis de prenhez em outras espécies de cetáceos. Alguns dos animais biopsados tiveram seu comprimento corporal estimado através de fotogrametria. A menor fêmea acompanhada de filhote mediu 10.21 metros. Machos e fêmeas não apresentaram comprimentos corporais diferentes entre si, 12.96 e 12.04 metros, respectivamente. O tecido adiposo mostrou-se como uma matriz viável para dosagens de esteroides sexuais e estudos acerca da fisiologia reprodutiva de baleias de vida livre. A dosagem de hormônio da camada de gordura tem o potencial de indicar variações sazonais, estados de prenhez, picos de testosterona em machos, e diferenças entre machos e fêmeas. Quando combinada com comprimento corporal e história de vida, a dosagem hormonal pode promover informações ainda mais robustas acerca do estado reprodutivo dos indivíduos de determinada população. / The current study evaluated the possibility of extracting and measuring steroid hormones from the blubber of carcasses and living animals. Progesterone (P4), testosterone (T) and estradiol (E2) were successfully measured trough enzimaimunoassay technique. Stranded animals were sampled to validate the blubber collection. A set of experiments were performed: whether the state of decomposition of fat affects hormone levels; whether the body region from which samples were collected affects the levels of P4, E2, and T; whether the depth of the layer selected (outer, middle, inner) affects hormone levels; and finally the size of sample effect on hormone levels. All of these four elements can potentially alter the measurement final results. Also, biopsy sampling were done at a South Atlantic breeding Area, National Marine Park Abrolhos in 2011 and 2012; and in one feeding area, the Marine Park Francisco Coloane, locate at Chilean Patagonia. As expected females had higher P4 and E2 means compared to males, and males exhibited higher means of T than females. Also a reproductive seasonality was detected in E2 and T levels. T levels were higher in adult males during breeding season, especially in September and October. E2 were higher in both females and males during feeding season. This apparent inversion of E2 level to the reproductive condition is probably a result of the lag of the hormone from blood to blubber and the time for its metabolism to occur. Part of the adult females with calves and without calves had P4 levels similar to some pregnant cetacean species. Some of the biopsied animals had their body length estimated. The smallest female with calf had 10.21 meters. Males and females did not differ in total body length: 12.96 and 12.04 respectively. The bubbler showed to be a feasible biological matrix to measure sex hormones from free ranging humpback whales, and can indicate differences among sexes and reproductive states. When combined with total body length and life history, the hormone measurements can provide robust information on reproductive state of individuals.

Neurotransmitters are widely distributed in the central nervous system of tilapia during development. In the present study, the effects of gonadal steroids, temperature, and neurotransmitters on the development of central neurotransmitter systems in tilapia, Oreochromis mossambicus, were investigated. Exogenous E2 before 10 days posthatching resulted in an inhibitory effect on the activity of central 5-HT system via decreasing TPH activity and increasing MAO activity, a decrease of the gene expression of brain aromatase and ERa, which is involved in the feminization. The masculinizing actions of 17a-methyltestosterone (MT) are most potent later at up to day 20 of age, and may depend on MT-induction of aromatase activity, aromatase mRNA gene expression and estrogen receptor-b mRNA gene expression. The development of central neurotransmitter systems is influenced by aquatic temperature during its respective restricted period. The influence of both lower and elevated temperatures on the neurotransmitter activity, either increasing or suppressing, is dependent on its developing stage. Neurotransmitters have an effect to influence the development of central neurotransmitter and this effect may mediated by the neural proliferation.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 156-171). Available also in a digital version from Dissertation Abstracts.

Orientador : Irani Quagio-Grassiotto / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-07T07:43:09Z (GMT). No. of bitstreams: 1 Antoneli_FernandaNatalia_D.pdf: 38673941 bytes, checksum: b5d1b651382a852a4a58b296f16a2d96 (MD5) Previous issue date: 2006 / Resumo: Os peixes teleósteos exibem vários padrões sexuais durante sua ontogenia, nos quais as gõnadas se transformam em ovários ou testículos funcionais. Nas distintas Ordens podem ser encontradas espécies gonocóricas, assim como hermafroditas, tanto simultâneas quanto seqüenciais ou consecutivas. No hermafroditismo seqüencial (protândrico ou protogínico), a mudança de sexo nos indivíduos adultos envolve a degeneração do tecido gonadal do primeiro sexo e o crescimento e maturação do tecido do sexo oposto, passando por uma fase de intersexo. Nas espécies hermafroditas protogínicas, mais frequentemente observada nos teleósteos, os individuos desenvolvem-se como fêmeas e, posteriormente, na vida adulta, seus ovários funcionais são substituídos por testículos, transformando-as em machos reprodutivamente ativos. Fatores internos e externos (ambientais) parecem controlar a mudança de sexo nas espécies hermafroditas seqüenciais. Nos vertebrados, o funcionamento do sistema reprodutor envolve o sistema nervoso e complexas vias de feedback hormonais, ambos integrados no chamado eixo hipotalâmico-hipofisário-gonadal. Nos peixes teleósteos, os esteróides sexuais, assim como os hormônios hipotalâmicos e adenohipofisários são considerados os principais fatores que controlam o desenvolvimento sexual gonadal, e podem estar envolvidos na inversão de sexo em espécies hermafroditas. Synbranchus marmoratus é um peixe hermafrodita protogínico diândrico e, na busca das possíveis correlações entre as alterações morfológicas gonadais e variações plasmáticas dos esteróides sexuais, observou-se que, na dependência do grau de decréscimo da oogênese e aumento da atividade do tecido masculino, o processo de inversão de sexo foi dividido em três fases: inicial, intermediária e final. A gõnada transicional de S. marmoratusfoi caracterizada pela a) desorganização da estrutura típica ovariana; b) massiva degeneração de células germinativas femininas; c) surgimento das células germinativas masculinas iniciais nas bordas das lamelas ovigeras, em associação com prováveis células de Sertoli; d) intensa proliferação e migração de células mióides; e) intensa atividade macrofágica, com a presença de melanomacrófagos e centros melanomacrofágicos; e f) aparecimento de grupos de células de Leydig no compartimento intersticial. As células de Leydig constituíram estruturas masculinas pioneiras a surgirem no ovário, então considerada gônada transicional inicial. Assim, estas células foram consideradas marcadores mortológicos e funcionais do processo de inversão sexual nesta espécie. As células de Leydig apresentaram as típicas características ultraestruturais associadas à esteroidogênese, bem como alta atividade esteroidogênica (3j3-HSD),provavelmente, produzindo andrógenos necessários ao desenvolvimento do tecido masculino gonadal e à espermatogênese. Na fase intermediária, a arquitetura masculina gonadal começa a ser definida, com a proliferação de numerosos cistos com células germinativas em diferentes fases de desenvolvimento. Nas gônadas transicionais finais, apenas poucos oócitos em degeneração e centros melanomacrofágicos permanecem. A mortologia da gônada transicional nesta fase é caracterizada pela completa formação das "lamelas testiculares" e dos túbulos seminíferos, os quais podem ser classificados como do tipo lobular irrestrito. Em nível hormonal, o início da transição sexual está associado à diminuição dos níveis plasmáticos de 17'beta'-estradiol, e o aumento da testosterona circulante, sugerindo a implicação destas circunstâncias para dar início à inversão de sexo natural em S. marmoratus. Os níveis plasmáticos de 11-cetotestosterona apenas sofrem baixas variações durante o início e progresso do referido processo, indicando um papel secundário deste andrógeno na inversão de sexo em S. marmoratus. A identificação das células adenohípofisárias de S. marmoratus durante a inversão de sexo não mostra qualquer alteração no padrão de imunomarcação das células produtoras dos diferentes hormônios ao longo do processo, excetuando-se as células gonadotrópicas, cuja atividade de síntese foi bastante alta nos intersexos iniciais. Provavelmente, estas células ofereçam suporte hormonal para a inversão de sexo nessa espécie. Assim, a inversão de sexo em S. marmoratus parece ocorrer sob controle do eixo hipotalâmico-hipofisário-gonadal. Por sua vez, as alterações morto lógicas necessárias à efetivação do processo propriamente dito - desestruturação do tecido gonadal feminino e desenvolvimento do tecido do sexo oposto - são gradualmente promovidas, seja pela falta ou escassez de estrógenos, e/ou pelo aumento dos níveis de andrógenos. Por conseguinte, S. marmoratus constitui um excelente modelo para o estudo dos eventos morto-funcionais da inversão de sexo / Abstract: Teleost fishes exhibit several sexual patterns during their ontogeny, in which the gonads change into functional ovaries or testes. In distinct Orders, both gonochoristic and hermaphrodite species, simultaneous as well as sequential or consecutive, can be found. In sequential hermaphroditism (protandrous or protogynous), sex change in adult individuais involves the degeneration of the primary sex gonadal tissue and the growth and maturation of the opposite sex, passing through an intersex phase. In protogynous hermaphrodite species, most frequently observed in teleosts, individuais first develop into females and later, at adulthood, their functional ovaries are gradually replaced by testes, becoming them into active reproductively males. Internal and external (environmenta) factors seem to control the sex change in sequential hermaphrodite species. In vertebrates, the dynamic of reproductive system involves the nervous system and complex hormonal biosynthetic pathways, all of them integrated in the called brain-pituitary-gonad axis. In teleost fish, sex steroids, as well as brain and pituitary hormones, are considered to be the main factors controlling gonadal sex development, and may be involved in sex reversal in hermaphrodite species. Synbranchus marmoratus is a protogynous diandric fish. Depending on the degree of female gametogenesis decrease and male tissue activity increase, the sex reversal process was divided into three phases: early, intermediate, and final. S. marmoratus transitional gonad was characterized by the: a) disorganization of the typical ovarian structure; b) massive degeneration of the female germ cells; c) appearance of initial male germ cells . at the border of ovigerous lamellae in association with putative Sertoli cells; d) intense proliferation and migration of myoid cells; e) intense macrophage activity with the presence of melanomacrophages and melanomacrophage centers; and f) appearance of clusters of Leydig cells in the interstitial compartment. Leydig cells constitute the pioneer male structures to arise in the ovary, considered the early transitional gonad at this point. Thus, these cells were considered morphological and functional markers of the sex reversal process in this species. Leydig cells presented the typical fine structures associated to steroidogenesis, such as high steroidogenic activity (3'beta'-HSD), probably, producing androgens necessary to development of gonadal male tissue, and spermatogenesis. In the intermediate phase, the male gonadal architecture begins to be defined, with the proliferation of numerous spermatocysts containing germ cells at different developmental stages. In final transitional gonads, only few degenerating oocytes and melanomacrophage centers remain. The morphology of transitional gonad at this phase is characterized by the complete formation of the testicular lamellae and the seminiferous lobules, which can be classified as unrestricted lobular type. At hormonal level, the beginning of the sexual transition is associated with the decrease of plasma estradiol-17 'beta' levels and the increase of circulating testosterone, suggesting the implication of such circumstances to trigger the natural sex change in S. marmoratus. Plasma 11-ketotestosterone levels onlysuffered weak variations during the initiation and progress of such process, which may indicate the secondary role of this androgen in S. marmoratus sex reversal. The identification of the adenohypophyseal cells of Synbranchus marmoratus during sex reversal does not show any alteration in the immunomarcation pattern of secretory cells of different hormones during the process, except for gonadotropin-producing oolls, which synthesis activity was very high in the initial intersexes. Probably, these cells offer hormonal support for sex reversal in this species. Therefore, sex reversal in S. marmoratus seems to occur under hypothalamic-hypophyseal-gonadal axis control. Morphological alterations necessary to sex reversal process accomplishment - disorganization of female gonadal tissue and development of the tissue of opposite sex - are gradually promoted by the estrogens privation, and/or by the androgens levels increase. Therefore, S. marmoratus constitutes an excellent model for the studying of morpho-functional eventsof sex change / Doutorado / Biologia Celular / Doutor em Biologia Celular e Estrutural