Experimental Fluid-percussion Brain Injury Research Articles

Gender as a Moderator of Cognitive and Affective Outcome After Traumatic Brain Injury

Gender as a Moderator of Cognitive and Affective Outcome After Traumatic Brain Injury

Alterations in ionized and total blood magnesium after experimental traumatic brain injury: relationship to neurobehavioral outcome and neuroprotective efficacy of magnesium chloride.

Experimental evidence suggests that magnesium plays a role in the pathophysiological sequelae of brain injury. The present study examined the variation of blood ionized and total magnesium, as well as potassium, sodium, and ionized calcium, after experimental fluid percussion brain injury in rats. Blood ionized magnesium concentration significantly declined from 0.45 +/- 0.02 to 0.32 +/- 0.02 mM by 30 min postinjury and stayed depressed for the 24-h study period in vehicle-treated rats. Blood total magnesium concentration was 0.59 +/- 0.01 mM and remained stable over time in brain-injured vehicle-treated animals. When magnesium chloride (125 micromol/rat) was administered 1 h postinjury, ionized magnesium levels were restored by 2 h postinjury and remained at normal values up to 24 h following brain trauma. Magnesium treatment also significantly reduced posttraumatic neuromotor impairments 1 and 2 weeks after the insult, but failed to attenuate spatial learning deficits. A significant positive and linear correlation could be established between ionized magnesium levels measured 24 h postinjury and neuromotor outcome at 1 and 2 weeks. We conclude that acute ionized magnesium measurement may be a predictor of long-term neurobehavioral outcome following head injury and that delayed administration of magnesium chloride can restore blood magnesium concentration and attenuate neurological motor deficits in brain-injured rats.

The effect of postinjury administration of polyethylene glycol-conjugated superoxide dismutase (pegorgotein, Dismutec) or lidocaine on behavioral function following fluid-percussion brain injury in rats.

Previous studies in our laboratory have shown that polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) or lidocaine treatment before experimental fluid-percussion brain injury in rats reduces the cortical hypoperfusion normally found in the early posttraumatic period. The purpose of the current study was to determine if posttreatment with PEG-SOD or lidocaine is also associated with changes in the trauma-induced suppression of motor and cognitive function that occurs following traumatic brain injury (TBI). Twenty-four hours after surgical preparation, rats were randomly assigned to a saline or drug posttreatment group, PEG-SOD (pegorgotein, Dismutec 10,000 IU/kg) or lidocaine (2 mg/kg), which was injected iv 30 min after moderate injury. PEG-SOD completely prevented beam walk deficits on days 1-5 postinjury while lidocaine similarly prevented beam walk deficits on days 2 through 5 postinjury. Both drugs produced a statistically insignificant trend for a decrease in beam balance duration deficits on days 1-5 postinjury and had no effect on cognitive function, as assessed by the Morris water maze, on days 11 through 15 postinjury. The mechanism by which PEG-SOD and lidocaine reduce posttraumatic motor deficits may be related to their free radical scavenging effect or previously reported effects on posttraumatic cerebral blood flow. To our knowledge, this is the first report of the effectiveness of these two agents in laboratory animals when administered after traumatic injury.

The Effect of Acute Cocaine or Lidocaine on Behavioral Function following Fluid Percussion Brain Injury in Rats

One of the goals of our laboratory is to examine how the presence of drugs of abuse will influence traumatic brain injury. Previous studies in our laboratory have shown that cocaine or lidocaine treatment before experimental fluid percussion brain injury in rats reduces the cortical hypoperfusion normally found in the early posttraumatic period. The purpose of the current study was to determine if pretreatment with cocaine or lidocaine is also associated with changes in trauma-induced suppression of reflexes and motor and cognitive dysfunction that occurs following traumatic brain injury (TBI). Twenty-four hours after surgical preparation, rats were randomly assigned to a saline or drug pretreatment group, cocaine (0.5, 2, or 5 mg/kg) or lidocaine (2 mg/kg), which was injected via the tail vein. None of the drug pretreatments worsened injury. Lidocaine and cocaine decreased the duration of suppression of some neurological reflexes and reduced posttraumatic body weight losses. Lidocaine and cocaine both decreased postinjury motor deficits. Lidocaine and cocaine did not affect cognitive function on days 11-15 postinjury. The mechanism by which lidocaine improves acute neurological and motor function following brain injury is unknown, but may involve improved posttraumatic cortical blood flow, as seen in our previous study. Our results, along with other studies showing lidocaine to be neuroprotective in animal models of ischemia, suggest that studies of the effect of posttraumatic administration of lidocaine are warranted.

Central and systemic kappa-opioid agonists exacerbate neurobehavioral response to brain injury in rats.

The endogenous opioid peptide dynorphin has been implicated in the pathophysiology of secondary tissue injury after central nervous system (CNS) trauma. The detrimental effects of dynorphin appear to be mediated through both opioid receptors (probably kappa-receptors) and nonopioid mechanisms. However, both kappa-opioid agonists and antagonists have been reported to improve outcome in models of CNS trauma. To attempt to clarify this controversy, we examined the effects of centrally or systemically administered kappa-opioid agonists on neurological recovery after experimental fluid-percussion brain injury in the rat. Agonists included dynorphin A-(1-17) [Dyn A-(1-17)], which has actions at both kappa 1- and kappa 2-sites, and the selective kappa 1-agonists U-50,488H and U-69,593. des-Tyr-dynorphin A-(2-17) [Dyn A-(2-17)], which is inactive at opioid receptors, was also used. Microinjection of Dyn A-(1-17), but not Dyn A-(2-17) or U-50,488H, into the lateral ventricle 15 min before brain injury significantly worsened motor deficits over a 2-wk period. However, systemic administration of high doses of the kappa-agonists U-50,488H and U-69,593 also significantly worsened neurological outcome. These results fail to demonstrate any protective actions of kappa 1-agonists in this model of experimental traumatic brain injury and suggest that the opioid-related pathophysiological actions of dynorphin may be mediated by kappa 2-opioid receptors.

Evaluation of a novel calcium channel blocker, (S)-emopamil, on regional cerebral edema and neurobehavioral function after experimental brain injury.

The authors investigated the effects of a novel calcium channel blocker, (S)-emopamil, on cerebral edema and neurobehavioral and memory function following experimental fluid-percussion brain injury in the rat. Two independent experiments were performed to evaluate the effects of this compound on cardiovascular variables and postinjury cerebral edema (increases in tissue water content), and on cognitive deficits and neurological motor function following brain injury. Treatment with (S)-emopamil significantly reduced focal brain edema at 48 hours after brain injury. Profound memory dysfunction induced by brain injury was significantly attenuated following (S)-emopamil treatment. In addition, (S)-emopamil also attenuated the deficits in motor function that were observed over a 2-week period following brain injury. These results suggest that changes in calcium homeostasis may play an important role in the pathogenesis of trauma to the central nervous system and that the calcium channel blocker (S)-emopamil might be a useful compound for the treatment of traumatic brain injury.

Development of prolonged focal cerebral edema and regional cation changes following experimental brain injury in the rat.

The present study examined the formation of regional cerebral edema in adult rats subjected to lateral (parasagittal) experimental fluid-percussion brain injury. Animals receiving fluid-percussion brain injury of moderate severity over the left parietal cortex were assayed for brain water content at 6 h, 24 h, and 2, 3, 5, and 7 days post injury. Regional sodium and potassium concentrations were measured in a separate group of animals at 10 min, 1 h, 6 h, and 24 h following fluid-percussion injury. Injured parietal cortex demonstrated significant edema, beginning at 6 h post injury (p less than 0.05) and persisting up to 5 days post injury. In the hippocampus ipsilateral to the site of cortical injury, significant edema occurred as early as 1 h post injury (p less than 0.05), with resolution of water accumulation beginning at 3 days. Sodium concentrations significantly increased in both injured cortex (1 h post injury, p less than 0.05) and injured hippocampus (10 min post injury, p less than 0.05). Potassium concentrations fell significantly 1 h post injury within the injured cortex (p less than 0.05), whereas significant decreases were not observed until 24 h post injury within the injured hippocampus. Cation alterations persisted throughout the 24-h post injury period. These results demonstrate that regional brain edema and cation deregulation occur in rats subjected to lateral fluid-percussion brain injury and that these changes may persist for a prolonged period after brain injury.

Restoration of cerebrovascular responsiveness to hyperventilation by the oxygen radical scavenger n-acetylcysteine following experimental traumatic brain injury

Previous experiments have shown that, following experimental fluid-percussion brain injury, cyclo-oxygenase-dependent formation of oxygen radicals prevents arteriolar vasoconstriction in response to hyperventilation. The oxygen radical scavengers superoxide dismutase and catalase restore normal reactivity; however, they are not routinely available for clinical use. The present study tested whether n-acetylcysteine (Mucomyst), an agent currently available for acetaminophen toxicity, could be used as a radical scavenger to restore reactivity after brain injury. N-acetylcysteine (163 mg/kg) was given intraperitoneally prior to or 30 minutes after fluid-percussion brain injury (2.6 atm) in cats, and reactivity to hyperventilation was tested 1 hour after injury. The authors found either that pre- or postinjury administration led to normal reactivity. Additional experiments supported the hypothesis that n-acetylcysteine is an oxygen radical scavenger, since it reduced or prevented the free radical-dependent cerebral arteriolar dilation normally induced by the topical application of arachidonic acid or bradykinin. The mechanism by which n-acetylcysteine is effective in trauma may involve direct scavenging of radicals or stimulation of glutathione peroxidase activity. The results suggest that n-acetylcysteine may be useful for treatment of oxygen free radical-mediated brain injury.

Effect of Noncompetitive Blockade of N‐Methyl‐d‐Aspartate Receptors on the Neurochemical Sequelae of Experimental Brain Injury

Pharmacological inhibition of excitatory neurotransmission attenuates cell death in models of global and focal ischemia and hypoglycemia, and improves neurological outcome after experimental spinal cord injury. The present study examined the effects of the noncompetitive N-methyl-D-aspartate receptor blocker MK-801 on neurochemical sequelae following experimental fluid-percussion brain injury in the rat. Fifteen minutes after fluid-percussion brain injury (2.8 atmospheres), animals received either MK-801 (1 mg/kg, i.v.) or saline. MK-801 treatment significantly attenuated the development of focal brain edema at the site of injury 48 h after brain injury, significantly reduced the increase in tissue sodium, and prevented the localized decline in total tissue magnesium that was observed in injured tissue of saline-treated animals. Using phosphorus nuclear magnetic resonance spectroscopy, we also observed that MK-801 treatment improved brain metabolic status and promoted a significant recovery of intracellular free magnesium concentrations that fell precipitously after brain injury. These results suggest that excitatory amino acid neurotransmitters may be involved in the pathophysiological sequelae of traumatic brain injury and that noncompetitive N-methyl-D-aspartate receptor antagonists may effectively attenuate some of the potentially deleterious neurochemical sequelae of brain injury.

Combined effect of respirator-induced ventilation and superoxide dismutase in experimental brain injury.

The function-specific enzyme superoxide dismutase (SOD) was tested for its protective effect in severe experimental fluid-percussion brain injury (4.45 +/- 0.10 atm) in 30 of 60 randomly selected male Sprague-Dawley rats. A respirator was used only in the event of need. The number of animals with permanent resumption of spontaneous breathing (Type I respiratory response) remained essentially the same in each group. However, when Type II apnea (cannot maintain recovery) and Type III apnea (never recovers from the initial apnea) were terminated with a respirator, all rats with Type II responses from each group were successfully converted to a state of sustained spontaneous breathing. In contrast, only five (41.7%) of the 12 rats with Type III response were salvaged in the control group while five (83.3%) of six Type III rats in the SOD-treated group were saved. The results reveal the nature of the therapeutic effectiveness of superoxide radical scavengers in the overall outcome of head injury in this animal model. While SOD alone did not increase the number of spontaneous survivors, the drug shifted a number of animals from the critically injured rats with Type III respiratory response to the less critical Type II condition. Whereas induced respiration as the sole therapy in the control group lowered the mortality rate to 23.3%, respiratory assistance together with SOD treatment reduced the "mortality" to a single animal with Type III apnea (3.3%) which was alive but still required the respirator after 2 hours (p less than 0.001). The results show that respiratory assistance alone accounted for a 33% decrease in mortality rate and that SOD, given in addition to induced ventilation, further decreased mortality by 20%. Since SOD enzymes are reactively specific for superoxide, the increased survival rate of the brain-injured rat must have been due either to preventing or to minimizing pathophysiological changes, probably in the brain stem, caused by oxygen free radicals.

Experimental fluid percussion brain injury: vascular disruption and neuronal and glial alterations

Because of the potential relationship between vascular disturbances and secondary tissue damage, we identified areas of brain which exhibited hemorrhage and leakage of protein during the acute stage after experimental brain injury and subsequently studied the development of pathologic changes, including cavity formation, neuronal necrosis, and gliosis within these regions. The development of pathologic changes was evaluated at 1, 6, and 24 h and 1, 2, and 4 weeks after lateral, fluid percussion (FP) brain injury of moderate severity in the rat. Vascular disruption in the acute stages, as evidenced by hemorrhage and leakage of Evans blue albumin, was most prominent 6 h postinjury and was maximal in the parieto-occipital cortex. From 1 to 24 h after injury, regions of the injured hemisphere, including the cortex and hippocampus, exhibited abnormal neurons which stained with acid fuchsin and Alizarin red, histochemical markers for injured neurons and calcium, respectively. These same regions suffered significant neuronal cell loss from 1 to 4 weeks after injury. The distribution of reactive astrocytes was also evaluated by immunocytochemical localization of glial fibrillary acidic protein (GFAP). By 2 weeks postinjury, a prominent cavity was present in the frontopariental and occipital cortices. Although astrogliosis was most pronounced in the cortex surrounding the cavity, prominent reactive astrocytes were widely distributed throughout the injured hemisphere. This study characterized the pathological changes which occur after experimental traumatic brain injury. In particular, we propose that neuronal cell injury in the hippocampus serves as a useful ‘window’ to assess beneficial efficacy of pharmacological intervention in the treatment of brain injury.

Increased Plasma PGE2, 6-Keto-PGF1α, and 12-HETE Levels Following Experimental Concussive Brain Injury

Previous investigations have shown that brain prostaglandin levels are transiently elevated following experimental fluid percussion brain injury. Associated with these increased prostaglandin levels there is free radical production and abnormalities in cerebral arteriolar function. The purpose of this study was to determine whether experimental fluid percussion brain injury in cats is associated with increased systemic levels of prostaglandins and the lipoxygenase product, 12-HETE. Blood samples were collected before and at various periods of time after 2.7 atm of fluid percussion brain injury was produced in adult cats. Prostaglandin and 12-HETE analysis was performed by radioimmunoassay after extraction of the plasma samples. The control levels for 6-keto-PGF1 alpha, PGE2, and 12-HETE were 477 +/- 42, 2,372 +/- 431, and 13,328 +/- 1,769 pg/ml, respectively. Following injury all three eicosanoids reached peak plasma levels by 1-5 min after injury. The percentile increases for all eicosanoids were similar and increased from 70 to 110%. The increases were sustained at up to 30 min postinjury and by 1 h after injury were at control levels. As in previous studies, hypertension following injury was maximal by 1 min postinjury and blood pressure had returned to near normal levels by 5 min postinjury. These studies demonstrate prolonged systemic increases in eicosanoids following injury. Since free radical production and vascular damage occur concomitantly with eicosanoid production, the prolonged increases in these products suggest that there is an attainable therapeutic window following injury during which administration of free radical scavengers may decrease radical damage and reduce the consequences of injury.

Superoxide production in experimental brain injury.

The appearance of superoxide anion radicals in cerebral extracellular space during and after experimental fluid-percussion brain injury was investigated in anesthetized cats equipped with cranial windows. Superoxide was detected by demonstrating the presence of superoxide dismutase (SOD)-inhibitable reduction of nitroblue tetrazolium (NBT). The SOD-inhibitable rate of reduction of NBT was 3.52 +/- 0.72 nM/min/sq cm during brain injury and 4.11 +/- 0.74 nM/min/sq cm 1 hour after injury. No significant superoxide production was detected in control animals. The sustained arteriolar dilation and reduced responsiveness to the vasoconstrictor effects of arterial hypocapnia observed 30 minutes after brain injury were eliminated by after-treatment with topical SOD (60 U/ml) and catalase (40 U/ml). The results show that experimental brain injury causes the generation and appearance in extracellular fluid space of superoxide. Superoxide production continues for at least 1 hour following injury. The sustained dilation and abnormal responsiveness of cerebral arterioles after injury are due to the continued generation of superoxide and other radicals derived from it. These functional changes can be reversed by after-treatment with appropriate scavenging agents.

Oxygen radicals in brain injury.

Experimental fluid percussion brain injury in anesthetized cats causes vascular injury characterized by sustained arteriolar dilation, abnormal reactivity to vasoconstrictor and vasodilator interventions, focal endothelial lesions, and reduction of the oxygen consumption of the vessel wall. These abnormalities are minimized or completely inhibited by pretreatment with cyclooxygenase inhibitors or with oxygen radical scavengers. They were therefore ascribed to oxygen radicals generated in the course of accelerated arachidonate metabolism via cyclooxygenase. Following this type of brain injury, there is an increase in the activity of phospholipase c in the brain and a transient increase in brain concentration of prostaglandins. Superoxide anion radical was detected in the extracellular space of the brain both immediately following brain injury as well as one hour afterwards as the superoxide dismutase inhibitable portion of nitroblue tetrazolium reduction. The sustained dilation and abnormal reactivity of cerebral arterioles following brain injury were also reversed by superoxide dismutase and catalase applied on the brain surface 30 minutes after injury. These results suggest that treatment with oxygen radical scavengers might be effective in inhibiting or reversing some of the effects of brain injury, even though the intervention with the therapeutic agents occurs sometime after the injury has taken place.

Increased phospholipase C activity after experimental brain injury.

Phospholipase C activity was measured in 1000 X G centrifuged cellular fractions isolated from cerebral cortical homogenates obtained from either control cats or cats subjected to experimental fluid-percussion brain injury. Phospholipase C activity was determined directly by measuring the Ca++-dependent conversion of membrane-bound, labeled phosphatidate to diacylglycerol or indirectly by measuring the diacylglycerol-dependent (brain diacylglycerol content) formation of phosphatidylcholine in the presence of labeled cytidine diphosphate (CDP) choline. Phospholipase C activity determined by either method was about two time greater in cell fractions isolated from animals subjected to brain injury than in controls (p less than 0.01). The brain injury-induced rise in phospholipase C activity may be responsible, at least in part, for generating diacylglycerol that may be a source of free arachidonic acid that stimulates prostaglandin synthesis. These changes may account for the rise in brain prostaglandin levels that has been demonstrated earlier to occur after this type of brain injury.

Cyclooxygenase products of arachidonic acid metabolism in cat cerebral cortex after experimental concussive brain injury.

Previous studies have suggested that following experimental fluid percussion brain injury, increased prostaglandin (PG) synthesis, with its concomitant production of oxygen free radicals, causes functional and morphological abnormalities of the cerebral arterioles. The purpose of this study was to chemically determine if PGs are altered following this injury. To facilitate interpretation of neurochemical measurements the cats were ventilated, blood pressure was measured, and a cranial window, for microscopic observation of pial arteriolar diameter was inserted. PG levels were determined in quick-frozen cortical tissue removed from control and 3 groups of injured cats at 1.5, 8,0, and 60 min after injury. Analysis of PGE2, PGF2 alpha, and 6-keto-PGF1 alpha was performed by HPLC and GC/MS. The control levels of PGE2, PGF2 alpha, and 6-keto-PGF1 alpha were 216 +/- 44, 210 +/- 48, and 48 +/- 12 ng/g wet weight, respectively. Following injury, produced by a 22 ms increase in intracranial pressure, the pial arterioles dilated irreversibly and a transient hypertensive response occurred, thereby producing hyperemia. During the maximum hyperemic response, the total PGs were 75% of control. At 8 min after injury, when blood pressure returned to control level, the PGs were 158% of control and PGs fell to 111% of control at 60 min. These experiments supported our previous studies implicating increased PG synthesis in te genesis of the physiologic and morphologic sequelae of experimental concussive brain injury.