Interactions between nerve growth factor binding and estradiol in early development of the zebra finch telencephalon

The zebra finch telencephalon exhibits rapid and substantial development in the first few weeks after hatching. In parallel, the rate of estradiol syn thesis is very high in the zebra finch forebrain, and estradiol can have po tent neurotrophic effects in specific telencephalic regions, including thos e that control the learning and production of song, In an attempt to elucid ate mechanisms regulating telencephalic development, potentially including a role for the large capacity for estrogen production, I-125-nerve growth f actor (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 h igh-affinity I-125-NGF binding sites was observed in 3-day-old finches, Usi ng an aromatase inhibitor, Fadrozole, to reduce estradiol levels in 1 to 4- day-old zebra finches significantly decreased both high- and low-affinity I -125-NGF binding sites. Conversely, treating adult or 8 to 14-day-old hatch lings with estradiol increased high-affinity I-125-NGF binding sites. These results are consistent with the hypothesis that estradiol influences the l evel of NGF receptors, and suggest one mechanism through which the steroid could affect brain development. The data also indicate that estradiol and N GF activity may be important for very early development of the telencephalo n. (C) 1999 John Wiley & Sons, Inc.