Hamilton RT, Rettberg JR, Mao Z, To J, Zhao L, Appt SE, Register TC, Kaplan JR, Brinton RD. Hippocampal responsiveness to 17ß-estradiol and equol after long-term ovariectomy: implication for a therapeutic window of opportunity. Brain Res. 2011 Mar 16; 1379:11-22.