GONADOTROPIN-RELEASING-HORMONE NEUROBLASTS FROM ONE OLFACTORY PLACODECAN BE PRESENT IN BOTH HEMISPHERES IN THE CLAWED TOAD XENOPUS-LAEVIS

Ontogenetic differentiation of the GnRH-immunoreactive (GnRHir) neuron system was studied in the clawed toad Xenopus laevis by immunocytoche mistry employing polyclonal antibodies against mammalian GnRH and chic ken type II GnRH, and monoclonal antibodies against GnRH exhibiting wi de cross-reactivity over animal classes. Toads at different stages of differentiation as well as postmetamorphic toads subjected to uni- or bilateral ablation of the olfactory placode (OPX) between developmenta l stages 25 and 30 were studied. GnRHir neurons and nerve fibers could not be detected before metamorphosis. Following metamorphosis, at sta ge 65-66, hemi-OPX toads did not exhibit any side differences in the n umber and overall distribution of the GnRHir neuronal structures; howe ver, the total number of GnRHir neurons was approximately 50% of that counted in intact controls at the same developmental stages. These fin dings indicate that GnRHir neuroblasts differentiating on one side in the olfactory placode can appear on both sides of the brain in the cou rse of their migration.