THE TIME-COURSE OF DEVELOPMENTAL CELL-DEATH IN PHENOTYPICALLY DEFINEDDOPAMINERGIC-NEURONS OF THE SUBSTANTIA-NIGRA

We have previously shown that apoptotic natural cell death occurs with in the substantia nigra (SN) pars compacta of the rat postnatally. How ever, the occurrence of natural cell death in phenotypically defined d opaminergic neurons has not previously been identified, nor has its ti me course been defined in pre- or postnatal development. We therefore examined the SN at intervals from E19 to P28 using immunostaining for tyrosine hydroxylase with a Nissl counterstain to identify intranuclea r apoptotic chromatin clumps. We have found that natural cell death in dopaminergic neurons is biphasic. An initial, broad peak begins at E2 0, reaches maximum at P2, and abates by P8. A second peak occurs at P1 4. We conclude that most of the natural cell death in this neuronal po pulation occurs in the early postnatal period.