High and low concentration of 17α-estradiol protect cerebellar granule neurons in different time windows.

17α-estradiol is a hormonally inactive isomer of 17β-estradiol, but with similar potency as neuroprotector. However, we have previously reported that pretreatment with high concentration (10 μM) of both estrogens abolishes their neuroprotection in rat cerebellar granule neurons. Here, we have examined neuroprotective properties of 17α-estradiol against glutamate-induced excitotoxicity in chicken cerebellar granule neurons using low (1 nM) and high concentration.17α-Estradiol, 1 nM, was neuroprotective when glutamate was administered after a pretreatment period of 24 h, but not when coadministered with glutamate. In contrast, 10 μM was protective when coadministered with glutamate, but was not efficient when glutamate was administered after a pretreatment period. The difference in protection was linked to a stronger calcium response during glutamate exposure in the non-protective treatments. In addition, the pretreatment period with 10 μM was accompanied by increased protein level of the N-methyl-d-aspartate receptor subunit NR2B and reduced glutathione level. Thus, 17α-estradiol has a concentration and time dependent protective effect against glutamate-induced cell death.