ABSTRACT
The effect of the nerve growth factor (NGF) on chick embryo spinal ganglia was studied in the hanging-drop bioassay system by comparison with parallel development in vivo.
The well-differentiated ventrolateral neuroblasts, which in vivo increase 1·33 times in size during the culture period, did not increase in size at all in vitro. Only 65–72% survived to the end of the culture period regardless of the NGF concentration.
The less-differentiated mediodorsal (M-D) neuroblasts, which in vivo increase .1-31 times in size during the culture period, were found to increase equally in vitro if sufficient NGF was present. Such a quantity was greater than that which evoked maximum outgrowth of neurites.
Survival of M-D neuroblasts was also related to NGF concentration but did not equal the in vivo condition even at the highest concentration. The hyperchromatic type of degeneration prevented by high NGF concentrations is that which results in vivo from insufficient peripheral field.
From this and other reports it would appear that the response to NGF seen in vitro is due only to the M-D neuroblasts, and that all biochemical and cytological observations which have been reported would therefore represent conditions within those cells only.
