Author's personal copy Treatments (12 and 48 h) with systemic and brain-selective hypothermia techniques after permanent focal cerebral ischemia in rat Darren L. Clark, Mark Penner, Shannon Wowk, Ian Orellana-Jordan, Frederick Colbourne ⁎ Department of Psychology and Centre for Neuroscience, University of Alberta, Edmonton, AB, Canada abstract article info Article history: Received 16 July 2009 Revised 21 September 2009 Accepted 3 October 2009 Available online 13 October 2009 Keywords: Stroke Ischemia Temperature Therapeutic hypothermia Neuroprotection Rodent Recovery Behavior Mild hypothermia lessens brain injury when initiated after the onset of global or focal ischemia. The present study sought to determine whether cooling to ∼ 33 °C provides enduring benefit when initiated 1 h after permanent middle cerebral artery occlusion (pMCAO, via electrocautery) in adult rats and whether protection depends upon treatment duration and cooling technique. In the first experiment, systemic cooling was induced in non-anesthetized rats through a whole-body exposure technique that used fans and water mist. In comparison to normothermic controls, 12- and 48-h bouts of hypothermia significantly lessened functional impairment, such as skilled reaching ability, and lesion volume out to a 1-month survival. In the second experiment, brain-selective cooling was induced in awake rats via a water-cooled metal strip implanted underneath the temporalis muscle overlying the ischemic territory. Use of a 48-h cooling treatment significantly mitigated injury and behavioral impairment whereas a 12-h treatment did not. These findings show that while systemic and focal techniques are effective when initiated after the onset of pMCAO, they differ in efficacy depending upon the treatment duration. A direct and uncomplicated comparison between methods is problematic, however, due to unknown gradients in brain temperature and the use of two separate experiments. In summary, prolonged cooling, even when delayed after onset of pMCAO, provides enduring behavioral and histological protection sufficient to suggest that it will be clinically effective. Nonetheless, further pre-clinical work is needed to improve treatment protocols, such as identifying the optimal depth of cooling, and how these factors interact with cooling method. © 2009 Elsevier Inc. All rights reserved. Introduction Mild hypothermia, in the range of 32 to 35 °C, is the most extensively studied therapy for ischemic brain injury. Based upon many animal studies (reviewed in MacLellan et al., 2009; Polderman, 2008; van der Worp et al., 2007), hypothermia was successfully translated to the clinic where it has been proven to reduce morbidity and mortality after cardiac arrest (Bernard et al., 2002; The Hypothermia After Cardiac Arrest Study Group, 2002) and to improve outcome in infants suffering from a hypoxic-ischemic event (Gluck- man et al., 2005; Shankaran et al., 2005). Despite these successes and encouraging animal data, hypothermia has not yet been clinically proven to lessen the devastation of a focal cerebral ischemic insult (stroke) in adults. Nonetheless, initial clinical findings are encourag- ing, such as the use of cooling to lessen raised intracranial pressure, and further study is underway to test the ability of hypothermia to improve functional outcome (Polderman, 2008). In most adult patients, systemic hypothermia is used. This is induced and maintained through surface-cooling blankets and adhesive pads, the use of an endovascular cooling system and sometimes cold intravenous fluids initially (Polderman, 2008; Polder- man and Callaghan, 2006). These more advanced systems allow for a rapid induction and steady control of hypothermia, which are improvements over older methods. Nonetheless, inducing systemic hypothermia carries considerable risk, including arrhythmias, dehy- dration and increased infection rates, which become more trouble- some at temperatures below 32 °C and with more prolonged treatment (Polderman, 2008; Schubert, 1995). Thus, several methods, including cooling helmets, epidural cooling pads and intranasal cooling systems, have been devised to selectively cool the brain thereby avoiding systemic side effects altogether. While the safety and effectiveness of such methods have yet to be fully determined, animal studies are promising (Covaciu et al., 2008; Wagner and Zuccarello, 2005). Although, not all agree that a significant amount and duration of selective brain cooling is truly possible in humans, at least not without some drop in core temperature. As in humans, one may induce either systemic or brain-selective hypothermia in rodents. Most methods to systemically cool, such as use of cooling pads, require anesthesia and are appropriate for cooling periods shorter than 6 h. The use of cold rooms or exposure techniques, including our fan and water spray system (Colbourne et al., 1996), are effective for inducing more prolonged cooling in awake Experimental Neurology 220 (2009) 391–399 ⁎ Corresponding author. Department of Psychology, P217 Biological Sciences Building, University of Alberta, Edmonton, AB, Canada T6G 2E9. Fax: +1 780 492 1768. E-mail address: fcolbour@ualberta.ca (F. Colbourne). 0014-4886/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.expneurol.2009.10.002 Contents lists available at ScienceDirect Experimental Neurology journal homepage: www.elsevier.com/locate/yexnr