The cell surface receptor for beta-nerve growth factor was used as a probe to study the development of embryonic chick sensory ganglia. The ganglia were shown to lose their responsiveness to nerve growth factor in vitro between 14 and 16 days of embryonic age. This loss occurred by a decrease in the magnitude of the maximum biological response, not by a shifting of the response to higher concentrations. Binding assays for the beta-nerve growth factor receptor, using 125I-radiolabelled beta-nerve growth factor, were performed with cells from sensory ganglia 8, 12, 14, 16, 18, and 21 days of age. The assays revealed a twofold increase in the number of receptor sites per ganglion between 8 and 14 days and a sixfold drop between 14 and 16 days of embryonic life. Neither increase nor decrease was accompanied by a large change in the affinity of the receptor for the protein. Together with the results of the bioassay, the data show that the loss of biological responsiveness is correlated with and may be due to a loss of the cells' ability to bind beta-nerve growth factor. Correlation of the results of the binding assays with the known ontogeny of the chick embryo provides a hint at the role of nerve growth factor in normal development.

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