Impact of mild hypothermia on changes of somatosensory evoked potential and synaptophysin mRNA level following traumatic brain injury

Abstract

Objective To investigate effect of mild hypothermia on changes of somatosensory evoked potential (SEP) and synaptophysin mRNA level after traumatic brain injury (TBI) and determine hypothermia-induced neuroprotection.Methods Forty-five SD rats were allocated into mild hypothermia group,TBI group and sham operation group with 15 rats per group according to the random number table.Left-side fluid percussion impact was performed to induce models of TBI.Rats were exposed to hypothermia environment (32-35℃) for 6 hours in mild hypothermia group after TBI.Rats in sham operation group were treated by only drilling on left side of the head,rather than hitting.To evaluate function outcome,modified neurological severity score (mNSS),SEP and synaptophysin mRNA level were measured at 6 hours,24 hours and 7 days postinjury.Results The mNSS in mild hypothermia group lowered compared with TBI group,especially at 24 hours and 7 days (P ＜ 0.05).SEP in mild hypothermia group was significantly shortened at 6 and 24 hours compared with TBI group (P ＜ 0.05),but SEP revealed no significant difference among the 3 groups at 7 days (P ＞ 0.05).Level of synaptophysin mRNA in mild hypothermia group increased at 6 hours postinjury compared with TBI group [(0.08 ± 0.02) vs (0.12 ±0.04)],with further increase at 7 days postinjury[(0.06 ± 0.01) vs (0.33 ± 0.10)] (P ＜0.05).Conclusion The shortage of nerve conduction time of the injured side and promotion of nerve regeneration suggest the neuroprotective role of mild hypothermia following TBI. Key words: Brain injuries ; Evoked potentials, somatosensory ; Hypothermia,induced ; Synaptophysin