Estrogen modulates synaptic plasticity, an important mechanism of memory storage. Previously, we have reported that estrogen rapidly increases the expression of Arc (activity-regulated cytoskeleton associated protein), a key protein for synaptic plasticity, via non-genomic phosphoinositide-3 kinase (PI-3K)-, mitogen-activated protein kinase (MAPK)-, and estrogen receptor (ER)-dependent pathways in SH-SY5Y cells.