The effect of nerve growth factor on developing primary sensory neurons of the trigeminal nerve in chick embryos.

The response to nerve growth factor (NGF) of two sensory neuron populations of the trigeminal nerve was studied in chick embryos. NGF promoted neuronal survival and cellular hypertrophy in the Gasserian ganglia with minimal effect on the neuron population of the mesencephalic trigeminal nucleus. NGF induced prolific neurite outgrowth from cultured Gasserian ganglia, in contrast, cultured mesencephalic trigeminal neurons remained refractory to NGF treatment. The apparent lack of response of mesencephalic trigeminal neurons to NGF may be explained either by their derivation from placodal material rather than from the neural crest, or their lost sensitivity to NGF due to interaction with the local environment in the central nervous system.