Naturally Occurring Cell Death during Postnatal Development of the Substantia Nigra Pars Compacta of Rat

We have quantified degenerating cells during the postnatal development of the substantia nigra pars compacta (SNpc) of normal rat. The cells are identified at the light microscope level by the characteristic morphologic appearance of large, rounded clumps of chromatin, stained intensely with both Nissl and silver stains. These cells were most numerous on Postnatal Day (PND) 2 and rapidly declined in number by PND 12. However, on PND 14, there was a second peak in the number of pyknotic cells. Their number again rapidly diminished to very few by PND 28. Many of these cells appear neuronal in origin. We conclude that naturally occurring cell death is a prominent feature of normal nigra development, and we hypothesize that the magnitude of this regressive event may be regulated by target (striatal)-derived trophic support.