Neuroscience Letters 368 (2004) 87–91 Estradiol reduces cytochrome c translocation and minimizes hippocampal damage caused by transient global ischemia in rat Giacinto Bagetta a,b,∗ , Olga Chiappetta a , Diana Amantea a , Michelangelo Iannone c , Domenicantonio Rotiroti c,d , Alfredo Costa b , Giuseppe Nappi b , Maria Tiziana Corasaniti c a Department of Pharmacobiology, University of Calabria,Via Pietro Bucci, 87036 Arcavacata di Rende (CS), Italy b IRCCS C. Mondino, Pavia andExperimental Neurobiology Center, Mondino-Tor Vergata-Santa Lucia, Rome, Italy c CNR Institute of Neurological Sciences, Catanzaro Unit, Catanzaro, Italy d Department of Pharmacobiological Sciences, University Magna Graecia, Catanzaro, Italy Received 17 May 2004; received in revised form 22 June 2004; accepted 24 June 2004 Abstract It is well-established that 17-estradiol (17-E 2 ) confers neuroprotection to male and female rats exposed to focal cerebral ischemia, while less is known about the effects of the hormone under conditions of transient global ischemia. Since translocation of cytochrome c from the mitochondria to the cytosol is a critical step in apoptotic cell death after cerebral ischemia, we have investigated whether 17-E 2 interferes with such mechanism to exert neuroprotection. Global ischemia, induced in male Wistar rats by 5-min 4 vessel occlusion (4VO), resulted in a significant increase of cytosolic cytochrome c (cyt-c) levels as detected by Western blotting at 6h after reperfusion. 17-E 2 (0.2 mg/kg, i.p.) given 1 h before ischemia minimized cytochrome c translocation and the latter effect was partially reversed by tamoxifen (0.25 mg/kg, i.p.). Bilateral cell counting revealed that delayed hippocampal damage typically caused by 4VO was abolished by 17-E 2 and this was partially reversed by tamoxifen in the CA3 subregion, but not in CA1/CA2 or CA4. These findings provide the original observation that 17-E 2 reduces delayed hippocampal damage caused by 4VO in male rats and blocks cytochrome c translocation during the early stages of neuronal death, thus providing an important mechanism involved in estrogen-mediated neuroprotection. © 2004 Elsevier Ireland Ltd. All rights reserved. Keywords: Mechanisms of neuroprotection by 17-estradiol; Cytochrome c translocation; Transient global brain ischemia A large body of evidence has been accumulated demonstrat- ing that 17-estradiol (17-E 2 ) reduces brain damage fol- lowing cerebral ischemia in both male and female rats [8]. Accordingly, both physiological and pharmacological doses of 17-E 2 have been shown to exert neuroprotection when ad- ministered to ovariectomized rodents prior to focal ischemic injury [1,6,25,28]. In addition, the neuroprotective effect of estrogens has also been tested in male rats, since either acute or chronic administration of 17-E 2 has been demonstrated to protect the male rat brain against damage induced by tran- sient middle cerebral artery occlusion (MCAO) [34]. ∗ Corresponding author. Tel.: +39 0984 493 462; fax: +39 0984 493 462. E-mail address: gbagett@tin.it (G. Bagetta). At variance with these data, a few, inconclusive, studies have been carried out to address the question as to whether 17-E 2 may also be neuroprotective under conditions of transient global brain ischemia in rodents. Both intracere- broventricular (i.c.v.) and systemic administration of 17- E 2 have been shown to reduce neuronal loss in the CA1 hippocampal subregion of gerbils after transient forebrain ischemia [4,32], though, under similar experimental condi- tions, negative results with 17-E 2 have also been reported [15]. Furthermore, pre-treatment with physiologically rel- evant plasma levels of 17-E 2 reduced hippocampal neu- ronal loss in a mouse model of global cerebral ischemia [12]. In two rat forebrain ischemia studies neuroprotection was demonstrated by 17-E 2 [22,35], whereas in another study 0304-3940/$ – see front matter © 2004 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2004.06.062