The gonadotropin-releasing hormone (GnRH) neuron system of the clawed toad Xenopus laevis.

The GnRH immunoreactive (GnRH-ir) neuronal system of the Clawed toad Xenopus laevis was studied and compared with the GnRH-ir system of the frog Rana esculenta. Polyclonal antibodies against mammalian (mGnRH) and chicken type-II GnRH (cGnRH-II), and monoclonal antibodies against mGnRH were used in the study. In the Xenopus laevis, most of the immunopositive neuronal cell bodies were located in telencephalic (35-50 per cent) and diencephalic areas (50-65 per cent). About 15-20 per cent of the GnRH perikarya appeared in mesencephalic tegmental regions. Besides the larger GnRH fiber tracts present also in mammals, the toad has rich mGnRH immunopositive axon population in the mesencephalon and in the upper part of the medulla. A similar distribution of the GnRH-ir neuronal elements exists in Rana esculenta, but the number of stained cells and fibers was less. Specificity of the staining of cGnRH-IIir structures located in the lower brainstem could not be proved and therefore the study is only restricted to the findings with mGnRH-antibodies.