Effects of mild hypothermia on cerebral blood flow-independent changes in cortical extracellular levels of amino acids following contusion trauma in the rat

In this present study, the effects of mild hypothermia on the changes in cortical extracellular amino acids and cerebral blood flow (CBF) caused by cerebral contusion created in the rat parietal cortex were investigated. CBF in both normothermia (37°C) and hypothrmia (32°C) groups, which was monitored using the hydrogen clearance technique, decreased significantly after contusion, but never fell below the threshold for ischemia. Cortical levels of glutamate and aspartate, which were measured by intracerebral microdialysis, were significantly increased after contusion in each group. However these increases were greater in the hypothermic than in the normothermic rats. Normal plasma amino acid levels were high, and autoradiography following intravenous injection of ^<14>C-labeled glutamate revealed marked extravasation of [^<14>C]glutamate at the site of cortical impact. These results suggest that the post-traumatic increase in extracellular amino acids occurs independently of CBF reduction, and that extravasation of amino acids from the vascular compartment partly contributes to this increase. Hypothermic cerebroprotection in TBI is thus likely to occur through a mechanism other than reduction in interstitial excitatory amino acids. In TBI, it is postulated that the postsynaptic effects of hypothermia may be more important than the presynaptic effects, when CBF is kept above the ischemic threshold.

重傷頭部外傷

低体温療法

興奮性アミノ酸

本文データは山口大学医学会の許諾に基づきCiNiiから複製したものである