Developmentally regulated induction of neurite outgrowth from immature chick sensory neurons (DRG) by homogenates of avian or mammalian heart, liver and brain.

Neurite outgrowth is elicited from whole explants or dissociated neurons of 8--10-day-old chick embryo sensory, dorsal root ganglia when cultured in the presence of a high speed supernatant fraction (105,000 g) from homogenates of chick or rat heart, liver or brain. The neurite promoting activity is not identical to mouse nerve growth factor (NGF) and is non-dialyzable. Expression of this neurogenic factor would appear to be developmentally regulated as its activity is barely detectable in organs from 6--9-day-old embryos but specific activity rises dramatically in homogenates of organs from embryos of greater than 11 days incubation. Greatest activity is found in chick heart and rat brain with only trace levels in lung or kidney and none in spinal cord.