Motoneuronal death during human fetal development.

The total number of ventral horn motoneurons throughout the spinal cord was determined for 19 human fetuses ranging in age from 11 to 32 menstrual weeks. There was a significant (approximately 35%) decline in motoneuron number between wks 11 and 25 of gestation, but no further decline from wks 25-32. Counts of pyknotic cells indicated a peak of motoneuronal degeneration between about wks 12 and 16 of age. The normal period of motoneuronal death observed here overlaps with the initiation of functional neuromuscular contact as well as the period of androgen production by the human fetal testes. As in rats, androgen may influence final motoneuron number in the human spinal cord by attenuating cell death in sexually dimorphic motor nuclei.