Gonadal steroids and the maturation of the species-specific gonadotropin-releasing hormone system in brain and pituitary of the male African catfish (Clarias gariepinus)

The effect of testosterone (T), 11-ketotestosterone (KT) and estradiol (E-2 ) On the development of the catfish gonadotropin-releasing hormone system ( cfGnRH) of male African catfish (Clarias gariepinus), at the onset of puber ty (between 10 and 12 weeks post hatching (ph)l was investigated. The cfGnR H neurons, located in the ventral forebrain, were visualized by immunofluor escence and their numbers were determined and the amounts of cfGnRH-associa ted peptide (cfGAP) in the pituitary were measured by RIA. Steroid treatmen ts did not significantly alter the numbers of immunoreactive GnRH neurons. However, T and E-2 caused an increase in the amount of GnRH, demonstrated b y the intensity of the immunostaining of GnRH neurons and fibers in the bra in and the amount of cfGAP in the pituitary. Treatment with KT, the main ci rculating androgen in adult male catfish, neither changed the number of cfG nRH neurons, nor elevated the cfGnRH content in the pituitary. In previous experiments with younger, prepubertal fish (2-6 weeks ph), T caused an elev ation of the number of cfGnRH neurons to the same level as present in puber tal fish of 12-14 weeks. We conclude that the onset of puberty in the male African catfish coincides with the completion of the steroid-dependent stru ctural maturation of the cfGnRH system in the brain. T and/or E-2, however, are still able to exert a positive influence on the amounts of cfGnRH duri ng the later stages of pubertal development, thus still playing a role in t he control of the cfGnRH system. (C) 2001 Elsevier Science Inc. All rights reserved.