Estrogen regulates the development of brain-derived neurotrophic factor mRNA and protein in the rat hippocampus

During development, estrogen has a variety of effects on morphological and electrophysiological properties of hippocampal neurons. Brain-derived neurotrophic factor (BDNF) also plays an important role in the survival and differentiation of neurons during development. We examined the effects of gonadectomy with and without estrogen replacement on the mRNA and protein of BDNF and its receptor, trkB, during early postnatal development of the rat hippocampus. We used immunocytochemistry to demonstrate that estrogen receptor alpha (ERalpha) and BDNF were localized to the same cells within the developing hippocampus. BDNF and ERalpha were colocalized in pyramidal cells of the CA3 subregion and to a lesser extent in CA1. To determine whether BDNF mRNA was regulated by estrogen during development, we gonadectomized male rat pups at postnatal day 0 (P0) and examined mRNA and protein levels from P0 to P25 using real-time reverse transcription-PCR and Western blot analysis. After gonadectomy, BDNF mRNA levels are significantly reduced on P7, but after treatment of gonadectomized animals with estradiol benzoate on P0, levels at all ages were similar to those in intact animals. BDNF mRNA changes after gonadectomy are accompanied by an increase in the levels of BDNF protein, which were reduced by estrogen treatment at P0. We also examined the effect of postnatal estrogen treatment on trkB. There were no significant changes in trkB mRNA or protein in gonadectomized or estrogen-replaced animals. These results suggest that a direct interaction may exist between ERalpha and BDNF to alter hippocampal physiology during development in the rat.