Ontogeny of rapid estrogen-mediated extracellular signal-regulated kinase signaling in the rat cerebellar cortex: Potent nongenomic agonist and endocrine disrupting activity of the xenoestrogen bisphenol A

In addition to regulating estrogen receptor-dependent gene expression, 17 beta-estradiol (E-2) can directly influence intracellular signaling. In primary cultured cerebellar neurons, E-2 was previously shown to regulate growth and oncotic cell death via rapid stimulation of ERK1/2 signaling. Here we show that ERK1/2 signaling in the cerebellum of neonatal and mature rats was rapidly responsive to E-2 and during development to the environmental estrogen bisphenol A (BPA). In vivo dose-response analysis for each estrogenic compound was performed by brief (6-min) intracerebellar injection, followed by rapid fixation and phosphorylation-state-specific immunohistochemistry to quantitatively characterize changes in activated ERK1/2 (pERK) immunopositive cell numbers. Beginning on postnatal d8, E-2 significantly influenced the number of pERK-positive cells in a cell-specific manner that was dependent on concentration and age but not sex. In cerebellar granule cells on postnatal d 10, E-2 or BPA increased pERK-positive cell numbers at low doses (10(-12) to 10(-10) M) and at higher (10(-7) to 10(-6) M) concentrations. Intermediate concentrations of either estrogenic compound did not modify basal ERK signaling. Rapid E-2-induced increases in pERK immunoreactivity were specific to the ERK1/2 pathway as demonstrated by coinjection of the mitogen-activated, ERK-activating kinase (MEK) 1/2 inhibitor U0126. Coadministration of BPA (10(-12) to 10(-10) M) with 10(-10) M E-2 dose-dependently inhibited rapid E-2-induced ERK1/2 activation in developing cerebellar neurons. The ability of BPA to act as a highly potent E-2 mimetic and to also disrupt the rapid actions of E-2 at very low concentrations during cerebellar development highlights the potential low-dose impact of xenoestrogens on the developing brain.