Cell death of motoneurons in the chick embryo spinal cord. VI. Reduction of naturally occurring cell death in the thoracolumbar column of Terni by nerve growth factor.

A discrete preganglionic cell column (column of Terni, CT) in the caudal thoracolumbar (segments 21-23) spinal cord is first discernible in a avian embryos on day 8 when it contains approximately 9,300 visceral motoneurons. By day 10 there are about 6,900 motoneurons in the thoracolumbar (sympathetic) CT and this number remains constant until at least day 15. Daily injections of nerve growth factor (NGF) (1-20 micrograms) on the chorioallantoic membrane from day 3 to day 9 produced a dose-dependent increase in both the volume of the caudal thoracolumbar sympathetic ganglia and the number of motoneurons in the corresponding CT on day 10. The number and size of the neurons in the paravertebral sympathetic ganglia was also increased by NGF. Nerve growth factor decreased the number of pyknotic (dying) neurons in both the thoracolumbar sympathetic ganglia and the corresponding CT on days 8 and 10. The increased number of neurons in both the thoracolumbar sympathetic ganglia and the corresponding CT following chronic administration of NGF is the result of decreased cell death. The highest dose of NGF reduced naturally occurring cell death in the thoracolumbar CT by more than 60%. Daily injections of cytochrome C (20 micrograms) from day 3 to day 9 had no effect on either the volume of the sympathetic ganglia or the number of motoneurons in the Ct on day 10. Daily injections of NGF (10-20 micrograms) from day 10 until day 14 increased the volume of (and the number of neurons in) the caudal thoracic sympathetic ganglia on day 15 but no effect on the number of motoneurons in the corresponding CT. Nerve growth factor also had no effect on the number of motoneurons in either the somatic lateral motor column, the sacral (parasympathetic) CT, or the "abortive" visceral efferent column at the cervical level. Daily administration of NGF produced a similar increase in the volume of the dorsal root ganglia at the cervical, thoracic, and sacral levels. The reduction of cell death in the thoracolumbar CT by NGF is the result of neither a direct effect on spinal motoneurons nor an indirect effect of increased sensory innervation. Naturally occurring cell death of sympathetic preganglionic neurons is regulated by the size of their innervation field.