The Study Of Mild Hypothermia On The Cerebral Mitochondrial Respiratory Function And Apoptosis-Related Genes MRNA Expression Following Traumatic Brain Injury In Rats

Objective Dysfunction of mitochondria take an important part following traumatic brain injury. This study was designed to investigate the protective effects of Mild hypothermia on cerebral mitochondrial respiratory function such as respiratory control rate (RCR), reactive oxygen species (ROS) generation rate, adenosine 5'-triphophate (ATP) synthesis and the expression of bcl-2,bax after traumatic brain injury in order to probe the possible protective mechanism of Mild hypothermia in traumatic brain injury.Methods Sprague-Dawley rats were subjected to lateral fluid percussion(FP) brain injury of mild severity. Animals were randomly divided into 4 groups: normothermic sham(uninjured) control group, hypothermic sham(uninjured) control group, normothermic TBI group(37℃) and mild hypothermic TBI group(31～32℃2h). The ipsilateral brain was dissected and homogenized brain tissue was extracted to obtain mitochondria by density-centrifugation and speed-centrifugation after TBI 2h,24h,3d,7d. Mitochondrial ultrastructure were studied by electro-microscope. The efficiency of oxidative phosphorylation, ROS generation rate, ATP synthesis, RCR respiratory rate of cerebral mitochondria were observed by bioenergetics. The expression of bcl-2 and bax were measured by real-time PCR.Results:1. Cortical neurons and the mitochondrial ultrastructure of normothemic TBI group were damaged severely, while the hypothermic TBI group were much milder.2. In normothemic TBI group, RCR was decreased at 2h, 24h, and then recovered to normal level at 7d, the capacity of ATP synthesis was decreased at the lowest level at 24h, and recovered at 3d, ROS was increased after injury, recovered at 7d. The hypothermic TBI group was significantly better than the normathermic TBI group.3. The apoptotic response to trauma was regionally distinct. Bax mRNA increased in normothermic TBI group at the right hippocampus, bax expression can be decreased by mild hypothermia; bcl-2 mRNA increased in the normothermic TBI group, it can also be decreased by mild hypothermia at right hippocampus. The other sites were not observed expression differences after injuried 24 hours later.ConclusionsThis study demonstrates that cerebral ultrastructural destroyed, mitochondrial respiratory function and ATP synthesis decreased significantly, ROS production increased during 2h, 24h, 3d and 7d after TBI. Hypothermia can improve these indexes and showed to protect the brain tissue. An effect produced by mild hypothermia was one of cerebroprotective reducing nervous cell apoptosis, mild hypothermia can decrease Bax expression. This may be one of the mechanisms through which hypothermia protect the cerebral cell from traumatic brain injury.