NEUROPEPTIDE-Y IN THE DEVELOPING AND ADULT BRAIN OF THE SOUTH-AFRICANCLAWED TOAD XENOPUS-LAEVIS

To get more insight into developmental aspects of neuropeptide Y (NPY) -containing neuronal structures in the brain of amphibians and their p ossible involvement in background adaption, we have studied immunohist ochemically the distribution of this. neuropeptide in embryos, larvae and adults of Xenopus laevis. Antisera against NPY revealed that alrea dy at early embryonic stages NPY immunoreactive cell bodies are presen t in the ventral thalamus and rhombencephalic tegmentum. Slightly late r, cell bodies appear in the olfactory bulb, the basal forebrain inclu ding the lateral and medial amygdala, the preoptic area, the ventral a nd dorsal thalamus, the suprachiasmatic region, the anteroventral tegm ental nucleus and the solitary tract area. At late embryonic stages, t he NPY cell groups not only show an increase in number of cells, but a lso stain more intensely. Around the time of hatching, a dramatic decr ease in the number of immunodetectable cells occurs, particularly in t he basal forebrain and in the rhombencephalic tegmentum. At the same t ime, however, new eel groups appear in telencephalic pallial regions a nd in the torus semicircularis. By the end of the premetamorphic stage s, the distribution of NPY-immunoreactive cell bodies and fibers resem bles closely the pattern observed in adult Xenopus brains. When compar ed with the development of catecholamine systems, it is clear that the NPY neurotransmitter system develops earlier. However, the expression of NPY- and dopamine-immunoreactivity in the suprachiasmatic nucleus occurs at about the same time (around stage 40) and coincides with sev eral other events related to background adaptation, suggesting that th is nucleus plays a key role in this complex neuroendocrine mechanism.