Regional levels of lactate and norepinephrine after experimental brain injury

The recently developed controlled cortical impact model of brain injury in rats may be an excellent tool by which to attempt to understand the neurochemical mechanisms mediating the pathophysiology of traumatic brain injury. In this study, rats were subjected to lateral controlled cortical impact brain injury of low grade severity; their brains were frozen in situ at various times after injury to measure regional levels of lactate, high energy phosphates, and norepinephrine. Tissue lactate concentration in the injury site left cortex was increased in injured animals by sixfold at 30 min and twofold at 2.5 h and 24 h after injury (p < 0.05). At all postinjury times, lactate concentration was also increased in injured animals by about twofold in the cortex and hippocampus adjacent to the injury site (p < 0.05). No significant changes occurred in the levels of ATP and phosphocreatine in most of the brain regions of injured animals. However, in the primary site of injury (left cortex), phosphocreatine concentration was decreased by 40% in injured animals at 30 min after injury (p < 0.05). The norepinephrine concentration was decreased in the injury site left cortex of injured animals by 38% at 30 min, 29% at 2.5 h, and 30% at 24 h after injury (p < 0.05). The level of norepinephrine was also reduced by ~20% in the cortex adjacent to the injury site in injured animals. The present results suggest that controlled cortical impact brain injury produces disorder in the neuronal oxidative and norepinephrine metabolism.