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Testosterone accelerates the development of the catfish GnRH system in the brain of immature African catfish (Clarias gariepinus).

The effects of two endogenous steroids on the maturation of the catfish GnRH and the chicken GnRH-II system in the African catfish were investigated. Immature fish (2 weeks of age, which is before sexual differentiation; thus male and female genotypes present) were fed with food pellets containing either testosterone (T), 11beta-hydroxyandrostenedione (OHA) or no steroid (control). After 2 and 4 weeks of treatment, the effects on the two GnRH systems were investigated immunocytochemically, using specific antibodies against the respective GnRH-associated peptides. By means of fluorescence microscopy the number of GnRH perikarya and the cell surfaces were determined. Confocal laser scanning microscopy was applied to verify spatial distribution and staining intensity. After 2 weeks of treatment no difference in any of the parameters between the groups was observed. However, 4 weeks T treatment resulted in significantly more cfGnRH-ir perikarya in the brain compared to the OHA and control groups. In addition, in the T group the number of immunoreactive fibers was markedly higher and the staining of the perikarya and axons was more intense. The distribution of cfGnRH-ir neurons over the ventral forebrain differed between the two age groups: in 4-week-old fish, the largest concentration of neurons was localized in the ventral telencephalon, while 2 weeks later the number of neurons in the supraoptic area had markedly increased, suggesting that the cfGnRH system is still undergoing developmental changes during this period. In 6-week-old fish the average volume of the cfGnRH perikarya (expressed as surface size in the microscopical sections) in both the OHA and the T group was significantly bigger than that in the control group. The cGnRH-II-ir neurons in the midbrain tegmentum showed strong immunoreactivity in all groups, both treated and nontreated. In contrast to the cfGnRH neurons, the staining intensity and the number of cGnRH-II neurons did not change after steroid treatment. The results of this study show that T is able to accelerate the development of the cfGnRH system, whereas OHA has only minimal effects; the cGnRH-II system develops independent from these steroids.