PRENATAL-DEVELOPMENT AND POSTNATAL-DEVELOPMENT OF DOPAMINERGIC NEURONNUMBERS IN THE MALE AND FEMALE MOUSE MIDBRAIN

Quantitative information about dopaminergic neuron numbers in the mese ncephalon is needed to assess the significance of physiological cell d eath in the regulation of the development of this neural system. There fore, stereological techniques were applied to determine absolute numb ers of mesencephalic neurons immunoreactive to tyrosine hydroxylase du ring the ontogenetic period between embryonic day (E) 13 and postnatal day (P) 90. Male and female CBA/J mice were examined separately. The most rapid development with a 2.5-fold increase of total counts of imm unostained cells per midbrain took place in the prenatal period. Begin ning at E21, immunostained cells were counted separately in their thre e main locations, substantia nigra (SN), ventral tegmental area (VTA), and retrorubral field (RRF). Neuron numbers in RRF and VTA reached ad ult levels perinatally. In contrast, counts of immunostained cells in SN continued to increase postnatally. The only sign of cell loss was a transient decrease in VTA cell numbers (but not in total numbers of i mmunostained midbrain neurons) between E21 and P14. There were no stat istically significant sex differences in cell numbers at any time poin t investigated. It is concluded that physiological cell death is not a major factor in the developmental regulation of dopaminergic cell num bers in the mouse midbrain.