Chemical Control of Sensory Ganglia during a Critical Period of Development

Abstract

Two populations of cells appear during differentiation of sensory ganglia in the chick embryo, These have been designated as ventro-lateral (V-L) and median-dorsal (M-D)^1–3. Changing the field of innervation, by either implantation or extirpation of limb buds, produces morphologic alterations solely in the V-L cells. The nerve growth-promoting protein (NGF), described and partially characterized by Levi-Montalcini and Cohen^4–6, produces hyperplasia and hypertrophy of embryonic M-D sensory cells as well as sympathetic nerve cells. Although the growth-promoting effects of NGF on sympathetic cells persist into adulthood in various species, its stimulatory effect on sensory cells is restricted to the embryonic period of development⁵. It was the purpose of this investigation to delineate further the critical period during development when sensory ganglia exhibit a morphological response to purified NGF and to explore some of the mechanisms controlling the reactive sequence.