Selective brain hypothermia protects against hypoxic-ischemic injury in newborn rats by reducing hydroxyl radical production.

We hypothesized that selective brain hypothermia (SBHT) decreases production of hydroxyl radicals (*OH) induced by hypoxia-ischemia (H-I) and reperfusion and attenuates neuronal damage in neonatal rat brain. Anesthetized 7-day-old rats were divided into a normothermia (NT) group (n=6) and a SBHT group (n=7) and subjected to 90-min H-I, followed by a 90-min recovery period. Brain temperature (BT) was regulated by a water-cooled metallic plate placed under the head. The BT of the SBHT group was set at 31.0+/-1.0 degrees C during the H-I and recovery period. Microdialysis and the salicylate-trapping method were used to detect *OH in the striatum. Neuronal damage was quantified by counting the surviving neurons at 120 hr after reperfusion. The NT group had significant increases in 2,3-dihydroxybenzoic acid (DHBA) (223+/-166%) and 2,5-DHBA (321+/-153%) above baseline levels. The increases in 2,3-DHBA (127+/-40%) and 2,5-DHBA (133+/-33%) were significantly lower (p < 0.01) in the SBHT group. The number of surviving neurons was decreased significantly in the NT group but not in the SBHT group. We conclude that SBHT reduces *OH production during H-I and reperfusion and has protective effects against neuronal damage.