Interactions Between Nerve Growth Factor Binding and Estradiol in Early Development of the

ABSTRACT: The zebra finch telencephalon exhib-its rapid and substantial development in the first few weeks after hatching. In parallel, the rate of estradiol synthesis is very high in the zebra finch forebrain, and estradiol can have potent neurotrophic effects in specific telencephalic regions, including those that control the learning and production of song. In an attempt to elu-cidate mechanisms regulating telencephalic develop-ment, potentially including a role for the large capacity for estrogen production, 125I–nerve growth factor (NGF) binding was measured in homogenates of telencephalon from zebra finches age 3, 15, 30, 60, and 120 days. The highest density of low- and high-affinity 125I-NGF bind-ing sites was observed in 3-day-old finches. Using an aromatase inhibitor, Fadrozole, to reduce estradiol lev-els in 1 to 4-day-old zebra finches significantly decreased both high- and low-affinity 125I-NGF binding sites. Con-versely, treating adult or 8 to 14-day-old hatchlings with estradiol increased high-affinity 125I-NGF binding sites. These results are consistent with the hypothesis that estradiol influences the level of NGF receptors, and sug-gest one mechanism through which the steroid could affect brain development. The data also indicate that estradiol and NGF activity may be important for very early development of the telencephalon. © 1999 John Wile