Effects of nerve growth factor on autonomic neurons in the chick embryo: A stereological study

Quantitative effects of nerve growth factor (NGF) on the sympathetic, Remak and ciliary ganglia in chicken embryos were investigated. Purified mouse beta NGF was injected (80 micrograms per day for three or four consecutive days) into the yolk sac at different stages (starting on days 6, 8, 10 and 13) of embryonic development. Ganglia were taken for fixation and embedding one day after the last NGF injection. The number of neurons belonging to the different size classes was determined by a computer aided stereological method based on unfolding of cell diameter frequencies. The volume of sympathetic ganglia was increased at all stages with a maximum of 8-fold occurring on day 10. The ganglion of Remak showed a 3-fold volume increase up to embryonic days 10 and 12. Ciliary ganglia did not exhibit any differences in volume or neuron size between the controls and the embryos injected with NGF. The number of neurons was increased in younger sympathetic and Remak ganglia in response to NGF, as was the recruitment of neurons to the larger size classes.