Treatments (12 and 48 h) with systemic and brain-selective hypothermia techniques after permanent focal cerebral ischemia in rat.

Mild hypothermia lessens brain injury when initiated after the onset of global or focal ischemia. The present study sought to determine whether cooling to approximately 33 degrees 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.