Do rapid systemic changes of brain temperature have an influence on the brain?

Summary.

 Background: The purpose of the present study was to examine the influence of cooling and rewarming conditions using an accurate brain temperature control system.

 Method: The brain temperature of animals was measured with a thermometer while feedback regulation was achieved with a cold (4^°C) and hot (50^°C) water on-off flow system. Brain temperature was well controlled throughout the experiment by using both cold water and hot water simultaneously. Three groups were studied, as follows: 1) the standard group (cooled to 24^°C for 1 hour, kept at 24^°C for 2 hours and rewarmed to 37^°C for 1 hour), 2) the rapid-cooling group (cooled to 24^°C for 30 min, kept at 24^°C for 2 h, and rewarmed to 37^°C for 1 h), 3) the rapid-rewarming group (cooled to 24^°C for 1 h, kept at 24^°C for 2 h, and rewarmed to 37^°C for 30 min) and the normal-control group.

 Findings: An increase of MAP-2 immunoreactivity of the CA1 neurons in the dorsal hippocampus was observed one week but not one month after hypothermia in the rapid-rewarming group. There was also a significant increase in the glutamate and lactate value at the end of rewarming compared with the baseline in the rapid-rewarming group (p<0.01).

 Interpretation: Our results suggest that rapid rewarming after hypothermia triggered an uncoupling of cerebral circulation and metabolism, inducing an increase of extracellular glutamate and lactate, consequently reversible neuronal cell damage.