Our data support the hypothesis that estrogen enhances an increase in Arc, PSD-95, and SYP expression as well as synaptic
plasticity via activation of ER_. These findings not only support previous studies showing that estrogen increased PSD-95 and SYP expression via ER_ activation in classical genomic pathway [18], but also demonstrate the translocation of cytosolic ER_ to
the nucleus which in turn activates PSD-95 and SYP expression after prolong estrogen treatment. Multiple mechanisms associated
with estrogen-dependent ER_ activation which cause a number of effects at the molecular level at different time course (Fig. 5)
include: (i) estrogen binds to membrane ER_ and activates Arc expression in a rapid time-course non-genomic actions; and (ii)
estrogen activates the internalization of membrane ER_ and the translocation of cytosolic ER_ to the nucleus as well as the PI-
3K pathway after prolong estrogen treatment, indicating classical genomic actions. Therefore, the regulation of receptor localization
is important for both classical genomic and non-genomic actions of estrogen. The non-genomic estrogenic actions of estrogen enhanced PSD-95 and SYP expression require a membrane bound signaling activation after acute estrogen treatment, but the classical genomic actions are associated with the translocation of cytosolic ER to the nucleus. However, the activation of PI-3K pathway after prolong estrogen treatment suggests a crosstalk mechanism between genomic and non-genomic actions of estrogen on synaptic plasticity.