Post-ischemic modest hypothermia (358C) combined with intravenous magnesium is more effective at reducing CA1 neuronal death than either treatment used alone following global cerebral ischemia in rats Hongdong Zhu a , Bruno P. Meloni a, T , Christina Bojarski a , Michael W. Knuckey b , Neville W. Knuckey a a Department of Neurosurgery, Sir Charles Gairdner Hospital, Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Australian Neuromuscular Research Institute, Australia b Faculty of Engineering, Computing and Mathematics, University of Western Australia, Australia Received 20 October 2004; revised 31 December 2004; accepted 28 January 2005 Available online 8 March 2005 Abstract In this study, we investigated the efficacy of pre- and 2 h post-ischemic magnesium treatment with different durations of modest hypothermia (358C) induced immediately or 2 h following global cerebral ischemia in rats. In experimental group 1, rats received an intravenous loading dose (LD) of 360 Amol/kg MgSO 4 immediately before ischemia followed by a 48 h intravenous infusion (IVI) at 120 Amol/kg/h. Immediately post-ischemia, body temperature was lowered to 358C for 6 h or maintained at 378C. In experimental group 2, 2 h after ischemia, rats received the MgSO 4 LD/IVI and/or had their body temperature lowered to 358C for 6, 12 or 24 h. In experimental group 1, ischemic rats receiving 6 h of modest hypothermia demonstrated 9.4% CA1 neuronal survival, whereas rats treated with magnesium alone or magnesium and 6 h of modest hypothermia demonstrated 5.1% and 37.9% neuronal survival, respectively. In experimental group 2, ischemic rats receiving 6, 12 or 24 h of modest hypothermia demonstrated 6.1, 5 and 43% CA1 neuronal survival, respectively. Rats treated with magnesium and 6, 12 or 24 h of modest hypothermia demonstrated 8.1, 9 and 76% neuronal survival, respectively. Our findings demonstrate that post-ischemic treatment with a 24 h duration of modest hypothermia and magnesium is more effective than either treatment used alone. D 2005 Elsevier Inc. All rights reserved. Keywords: Global cerebral ischemia; Magnesium; Modest hypothermia; Neuroprotection; CA1 neurons; Combination therapy; Stroke Introduction In the recently completed Intravenous Magnesium Efficacy in Stroke trial (IMAGES), magnesium treatment was found to be largely ineffective (IMAGES Study, 2004). In addition, the neuroprotective efficacy of magnesium in animal global and focal cerebral ischemia models has been inconsistent (Miles et al., 2001; Zhu et al., 2004a,b). To this end, we have recently shown that intravenous magnesium treatment following global and focal cerebral ischemia does not reduce brain damage in normothermic animals (Zhu et al., 2004a,b). We hypothesized and subsequently showed in our transient global ischemia model that magnesium is only neuroprotective following cerebral ischemia when com- bined with hypothermia (Zhu et al., 2004a). Despite the knowledge post-ischemic hypothermia can act synergistically to unmask or boost a neuroprotective effect of an agent, relatively few studies have taken advantage of this phenomenon (Coimbra et al., 1996; Dietrich et al., 1995, 1999; Liu et al., 2004; Schmid- Elsaesser et al., 1999; Zausinger et al., 2003a,b). With respect to post-ischemic hypothermia, experimental and clinical studies have shown efficacy when cooling depth is V348C and prolonged (12–24 h) (Bernard et al., 2002; 0014-4886/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.expneurol.2005.01.022 * Corresponding author. Australian Neuromuscular Research Institute, A Block, 4th Floor, QEII Medical Centre, Nedlands, Western Australia 6009, Australia. Fax: +61 8 9346 3487. E-mail address: meloni@cyllene.uwa.edu.au (B.P. Meloni). Experimental Neurology 193 (2005) 361 – 368 www.elsevier.com/locate/yexnr