To get more insight into developmental aspects of neuropeptide Y (NPY)-containing
neuronal structures in the brain of amphibians and their possible involvement in background
adaption, we have studied immunohistochemically the distribution of this neuropeptide
in embryos, larvae and adults of Xenopus laevis. Antisera against NPY revealed that
already at early embryonic stages NPY immunoreactive cell bodies are present in the
ventral thalamus and rhombencephalic tegmentum. Slightly later, cell bodies appear
in the olfactory bulb, the basal forebrain including the lateral and medial amygdala,
the preoptic area, the ventral and dorsal thalamus, the suprachiasmatic region, the
anteroventral tegmental nucleus and the solitary tract area. At late embryonic stages,
the NPY cell groups not only show an increase in number of cells, but also stain more
intensely. Around the time of hatching, a dramatic decrease in the number of immunodetectable
cells occurs, particularly in the basal forebrain and in the rhombencephalic tegmentum.
At the same time, however, new cell groups appear in telencephalic pallial regions
and in the torus semicircularis. By the end of the premetamorphic stages, the distribution
of NPY-immunoreactive cell bodies and fibers resembles closely the pattern observed
in adult Xenopus brains. When compared 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 several other events related to
background adaptation, suggesting that this nucleus plays a key role in this complex
neuroendocrine mechanism.