We evaluated long-term administration of estrogen after cardiac arrest and cardiopulmonary resuscitation (CA/CPR) on neurohistopathological and behavioral outcome. We also examined the effect of estrogen receptor (ER) stimulation using ER-alpha agonist propyl pyrazole triol (PPT) and ER-beta agonist diarylpropionitrile (DPN) on neuronal survival after CA/CPR to determine whether possible neuroprotective effects of estrogen are ER-mediated. Male C57Bl/6 mice underwent 10 mins of CA/CPR and 3-day survival. In protocol 1, intravenous injection of vehicle (NaCl 0.9%) and 0.5 or 2.5 microg 17beta-estradiol (E2 loading dose) was performed followed by subcutaneous implants containing vehicle (oil) or E2 (12.6 microg), according to a treatment group. In experimental protocol 2, mice were injected (intravenously) with the ER-alpha agonist PPT or ER-beta agonist DPN followed by Alzet pump implants (subcutaneously) containing PPT (200 microg) or DPN (800 microg). Long-term E2 administration reduced neuronal injury in the striatum after administration of either loading dose (41%+/-19%, 35%+/-26% of injured neurons), as compared with vehicle (68%+/-7%, P<0.01), with no effect in the hippocampal CA1 field. In protocol 2, treatment with ER-beta agonist DPN reduced neuronal injury in the striatum (51%+/-13% injured neurons) as compared with ER-alpha agonist PPT (68%+/-10%) and vehicle (69%+/-11%; P<0.01). Estrogen receptor-beta agonist DPN reduced neuronal injury in the hippocampal CA1 field (29%+/-22% injured neurons) as compared with ER-alpha agonist PPT treatment (62%+/-33%; P<0.05). Injury was not different in hippocampal CA1 between vehicle and ER-alpha agonist-treated animals. We conclude that long-term E2 administration after CA/CPR is neuroprotective and that this effect is most likely mediated via ER-beta.