Nuclear magnetic resonance characterization of secondary mechanisms following traumatic brain injury

Concentration of brain free magnesium following severe brain injury correlates with neurologic motor outcome

Recent studies have shown that brain intracellular free magnesium concentration significantly declines following mild to severe, focal and diffuse traumatic brain injury. However, little is known about how this decline or its attenuation by magnesium salts relates to neurologic outcome. This study uses phosphorus magnetic resonance spectroscopy and rotarod tests to characterise the relationship between brain free magnesium concentration and neurologic motor scores following severe, diffuse traumatic brain injury in rats. An intravenous bolus of MgSO(4) or MgCl(2) (100 mumoles/kg) at 30 min following brain injury significantly attenuated the postinjury brain free magnesium decline. This improved magnesium homeostasis was sustained for the entire postinjury monitoring period (1 week). There was an associated significant improvement in neurologic motor function in magnesium treated rats. Moreover, the brain free magnesium concentration over the one week period was linearly correlated with the neurologic motor function (r=0.70; P < 0.001) as assessed on a daily basis. We propose that brain free magnesium concentration may be used as a prognostic indicator of neurologic motor function after traumatic brain injury.

Substance P antagonists as a therapeutic approach to improving outcome following traumatic brain injury

Although a number of secondary injury factors are known to contribute to the development of morphological injury and functional deficits following traumatic brain injury, accumulating evidence has suggested that neuropeptides, and in particular substance P, may play a critical role. Substance P is released early following acute injury to the CNS as part of a neurogenic inflammatory response. In so doing, it facilitates an increase in the permeability of the blood-brain barrier and the development of vasogenic edema. At the cellular level, substance P has been shown to directly result in neuronal cell death; functionally, substance P has been implicated in learning and memory, mood and anxiety, stress mechanisms, emotion-processing, migraine, emesis, pain, and seizures, all of which may be adversely affected after brain injury. Inhibition of post-traumatic substance P activity, either by preventing release or by antagonism of the neurokinin-1 receptor, has consistently resulted in a profound decrease in development of edema and marked improvements in functional outcome. This review summarizes the current evidence supporting a role for substance P in acute brain injury.

A Substance P Antagonist Increases Brain Intracellular Free Magnesium Concentration after Diffuse Traumatic Brain Injury in Rats

OBJECTIVE

Magnesium (Mg) deficiency has been shown to increase substance P release and induce a pro-inflammatory response that can be attenuated with the administration of a substance P-antagonist. Neurogenic inflammation has also been implicated in traumatic brain injury (TBI), a condition where brain intracellular free magnesium (Mg(f)) decline is known to occur and has been correlated with functional outcome. We therefore examined whether a substance P antagonist restores brain intracellular free magnesium concentration following TBI.

METHODS

Male, adult Sprague-Dawley rats were injured using the Cernak impact acceleration model of diffuse TBI. At 30 min after injury, animals were administered either 0.25 mg/kg i.v. n-acetyl tryptophan or equal volume saline. Prior to and 4 h after induction of injury, phosphorus magnetic resonance spectra were acquired using a 7-tesla magnet interfaced with a Bruker console. Mg(f) was calculated from the chemical shift of the beta ATP. Before injury, Mg(f) was 0.51 +/- 0.05 mM (SEM).

RESULTS

By 4 hr after injury, Mg(f) had significantly declined to 0.27 +/- 0.02 mM in saline treated rats. In contrast, rats treated with n-acetyl tryptophan had a Mg(f) of 0.47 +/- 0.06 mM at 4 h after injury, which was not significantly different from preinjury values. There were no significant differences in pH between the treatment groups.

CONCLUSION

It seems that any beneficial effect of a substance P antagonist on functional outcome following TBI may be related to improvement in brain Mg homeostasis induced by the compound.

The behavioral effects of magnesium therapy on recovery of function following bilateral anterior medial cortex lesions in the rat

Magnesium (Mg(++)) therapy has been shown to be neuroprotective and to facilitate recovery of motor and sensorimotor function in a variety of animal models of traumatic brain injury. However, few studies have investigated the efficacy of Mg(++) therapy on cognitive impairments following injury. The present study evaluated the ability of magnesium chloride (MgCl(2)) to facilitate recovery of function following bilateral anterior medial cortex lesions (bAMC). Rats received electrolytic bAMC lesions or sham surgery and were then treated with 1 mmol/kg, i.p. MgCl(2), 2 mmol/kg, i.p. MgCl(2), or 1.0 ml/kg, i.p. 0.9% saline. Drug treatment was administered 15 min following injury with subsequent injections administered at 24 and 72 h. Rats were tested on a battery of behavioral tests that measured both cognitive (reference and working memory in the Morris Water Maze (MWM) and spatial delayed matching-to-sample (DMTS)) and sensorimotor performance (bilateral tactile adhesive removal). The results indicated that bAMC lesions produced significant cognitive impairments in reference memory and working memory in the MWM, DMTS and sensorimotor impairments compared to shams. Mg(++) therapy exhibited a dose-dependent effect in facilitating recovery of function. Administration of 2mmol of MgCl(2) significantly improved performance on the bilateral adhesive tactile removal test, DMTS and working memory tests. The 1 mmol dose of MgCl(2) reduced the initial deficit on the tactile adhesive removal test and reduced the working memory impairment on the second day of testing. These results suggest Mg(++) therapy improves cognitive performance following injury in a dose-dependent manner.

Magnetic resonance spectroscopy in traumatic brain injury

Magnetic resonance spectroscopy (MRS) offers a unique non-invasive approach for assessing the metabolic status of the brain in vivo and is particularly suited to studying traumatic brain injury (TBI). In particular, MRS provides a noninvasive means for quantifying such neurochemicals as N-acetylaspartate (NAA), creatine, phosphocreatine, choline, lactate, myo-inositol, glutamine, glutamate, adenosine triphosphate (ATP), and inorganic phosphate in humans following TBI and in animal models. Many of these chemicals have been shown to be perturbed following TBI. NAA, a marker of neuronal integrity, has been shown to be reduced following TBI, reflecting diffuse axonal injury or metabolic depression, and concentrations of NAA predict cognitive outcome. Elevation of choline-containing compounds indicates membrane breakdown or inflammation or both. MRS can also detect alterations in high energy phosphates reflecting the energetic abnormalities seen after TBI. Accordingly, MRS may be useful to monitor cellular response to therapeutic interventions in TBI.

Lactate and free fatty acids after subarachnoid hemorrhage

The hypothesis that lactate and free fatty acids (FFA) are elevated in the first minutes after subarachnoid hemorrhage (SAH) is tested. Adult rats were subjected to an endovascular SAH through the right internal carotid artery while under anesthesia. The brains were frozen in-situ at 15, 30, 60 min, and 24 h post-hemorrhage. Regional measures of tissue lactic acid and FFA were made in the hippocampi, ipsilateral cortex, contralateral cortex, and cerebellum. Lactic acid levels were significantly elevated from sham animals in each region within the first hour (p<0.0001 cerebellum, right, and contralateral cortex, p<0.01 hippocampus), but did not change significantly over the first hour. At 24 h post-hemorrhage, there was no significant difference in the lactic acid levels from controls. Similarly, total FFA were significantly higher in each region as compared to sham operated controls within the first hour (p<0.001 cerebellum, p<0.05 hippocampus, p<0.05 contralateral cortex, p<0.0001 ipsilateral cortex). By 24 h, there was no significant difference in FFA levels from shams. The data indicate that aerobic metabolism fails and cellular damage with degradation of cell membranes occurs in the first minutes after SAH, and lasts for at least 1 h. However, this process is stabilized within 24 h in our model. Although the largest effect was seen in the ipsilateral cortex, all areas of the brain were effected.

Improved motor outcome in response to magnesium therapy received up to 24 hours after traumatic diffuse axonal brain injury in rats

OBJECT

The goal of this study was to establish the therapeutic window during which delayed therapy with MgSO4 improves neurological motor outcome in rats that have suffered severe traumatic axonal brain injury.

METHODS

Severe brain injury was induced in male Sprague-Dawley rats by using the impact-acceleration model of severe traumatic diffuse axonal brain injury. Injured animals were subsequently treated with MgSO4 (750 micromol/kg) infused intramuscularly at 30 minutes or at 8, 12, or 24 hours after trauma and were tested for neurological motor outcome during the following week by using the rotarod test. Injured untreated (control) animals demonstrated highly significant (p < 0.001) neurological motor deficits that were sustained over the 1-week assessment period. Animals treated with MgSO4 at 30 minutes or at 8 or 12 hours postinjury demonstrated significantly improved motor outcomes compared with untreated control animals at all time points (0.001 < p < 0.05). Animals treated with MgSO4 at 24 hours had motor scores that were similar to those of untreated control animals early in the week, but demonstrated a significantly more rapid recovery in function and, by the end of the assessment period, they demonstrated significantly improved motor scores (p < 0.01). Repeated administration of MgSO4 over the 1-week observation period did not further improve outcome.

CONCLUSIONS

The present results demonstrate that Mg++ plays a neuroprotective role following severe diffuse traumatic axonal brain injury. Moreover, Mg++ therapy significantly improved motor outcome when administered up to 24 hours after injury, with early treatments providing the most significant benefit. Repeated administration beyond 24 hours postinjury did not provide additional neuroprotection.

Comparison of brain tissue oxygen tension to microdialysis-based measures of cerebral ischemia in fatally head-injured humans

This study investigated the relationship between brain tissue oxygen tension (PbtO2) and cerebral microdialysate concentrations of several compounds in five patients with refractory intracranial hypertension after severe head injury. The following substances were assayed: lactate and glucose; the excitatory amino acids glutamate and aspartate; and the cations potassium, calcium, and magnesium. Glucose concentrations did not correlate with PbtO2, but lactate increased as PbtO2 decreased. The lactate/glucose ratio exhibited a close relationship to PbtO2, increasing sharply only when oxygen tension reached zero. Although glucose and oxygen eventually reached very low levels and zero, respectively, in these fatally head-injured patients, the terminal decrease in PbtO2 slightly preceded that of glucose in four of the five patients. This time lag is the cause of the poor correlation between glucose and PbtO2. Glutamate and aspartate concentrations both demonstrated a close relationship to PbtO2, with sharp increases not occurring until PbtO2 was zero. Concentrations of these amino acids exhibited a similar pattern in response to decreasing glucose concentrations. Potassium concentrations began increasing at a PbtO2 of 35 mm Hg, which is not generally considered indicative of hypoxia. Sharper increases began occurring once PbtO2 dropped below 15 mm Hg, with a slight rise in the minimum potassium concentrations recorded at these low PbtO2 values. Calcium and magnesium concentrations did not vary in response to PbtO2. In summary, the most robust biochemical indicators of cerebral anoxia were elevations in the lactate/glucose ratio and in the concentrations of lactate and of the excitatory amino acids glutamate and aspartate. Furthermore, the fact that glucose concentrations continue to decrease for a short period after oxygen levels reach zero suggests that cells continue to utilize glucose anaerobically for such functions as maintenance of cellular integrity, with collapse of the cell membrane as evidenced by increases of extracellular glutamate and aspartate not occurring until both oxygen and glucose concentrations reach zero.

Blood-free magnesium concentration declines following graded experimental traumatic brain injury

Traumatic brain injury has been shown to result in a decrease in brain-free magnesium concentration that is associated with the development of neurologic motor deficits. Although these changes have been well characterized in the brain, changes in free magnesium homeostasis have not been characterized in other fluid compartments. The current experiments use ion selective electrodes to measure alterations in blood-free magnesium concentration following graded experimental brain injury in rats and to compare these changes with subsequent neurologic outcome. After severe impact-acceleration-induced injury, blood-free magnesium levels significantly declined (p < 0.05) by 25% and remained depressed for at least 4 days after injury. After moderate injury, the decline in blood-free magnesium was less than that observed in the severe injury group with respect to both degree of decline and duration of decline. The post-traumatic blood-free magnesium concentration correlated to observed motor deficits as assessed by rotarod evaluation (p < 0.001). We conclude that blood-free magnesium levels may be a prognostic indicator of outcome following severe traumatic brain injury.

Neuroprotective effects of MgSO4 and MgCl2 in closed head injury: a comparative phosphorus NMR study

Previous studies have shown that free magnesium levels decline after traumatic brain injury and that magnesium salt administration improves posttraumatic outcome. These earlier studies, however, have been limited to models of injury that do not produce a significant degree of diffuse axonal injury and have used either MgSO4 or MgCl2 as the magnesium salt. The present study compares the neuroprotective efficacy of MgSO4 and MgCl2 in a severe model of diffuse axonal injury in rats using phosphorus nuclear magnetic resonance spectroscopy and the rotarod test to monitor effects on metabolism and neurologic outcome, respectively. Both MgSO4 and MgCl2 given as a bolus of 100 micromoles/kg at 30 min after severe, closed head injury significantly improved brain intracellular free magnesium concentration and neurologic outcome. These findings suggest that both salts penetrate the blood-brain barrier after brain trauma, enter injured tissue, and subsequently improve neurologic outcome.

Apparent Mg2+-adenosine 5-triphosphate dissociation constant measured with Mg2+ macroelectrodes under conditions pertinent to 31P NMR ionized magnesium determinations

Using Mg2+ macroelectrodes based on the sensor ETH 7025 and accurate Mg2+-EDTA buffer solutions, the apparent Mg2+-ATP dissociation constant (Kapp) was measured at 25 and 37 degrees C in background solutions mimicking the cationic intracellular milieu of muscle cells. The mean +/- SD (in microM) at 25 degrees C was 157.0 +/- 13 (n = 4), 127.5 +/- 12.0 (n = 11), 101.0 +/- 9.0 (n = 4) and at 37 degrees C was 106.6 +/- 9.6 (n = 4), 87.4 +/- 4.9 (n = 4), 78.1 +/- 2.0 (n = 4) at pH values of 6.7, 7.2, and 7.7, respectively. The dependence of Kapp at 25 degrees C on the ionic strength was also measured, the mean +/- SD (microM) being 61.9 +/- 2.2 (n = 3), 127.5 +/- 12 (n = 11), and 243.0 +/- 11.8 (n = 3) at ionic strengths of 0. 087, 0.156 (normal background), and 0.3 m, respectively. These values are larger than the Kapp values most commonly used in the literature (87.4 microM compared to 38 microM at pH 7.2 and 37 degrees C) to estimate the [Mg2+]i in 31P NMR experiments, attributed to the difficulties in setting the [Mg2+]i without the use of Mg2+ buffer solutions. If these new values are used, the literature values for [Mg2+]i estimated by 31P NMR increase by a factor of around 1.5, making them similar to values obtained by direct Mg2+ microelectrode measurements.

Decrease in cerebral free magnesium concentration following closed head injury and effects of VA-045 in rats

1. We examined the alterations in cerebral free Mg2+ concentration in closed head injury (CHI) in rats and the effects of VA-045, a novel apovincaminic acid derivative, on them with in vivo 31P-NMR. 2. Free Mg2+ decreased by about 30% within 20 min after head impact and, afterward, it gradually decreased further to reach about 60% of the control level after 3 hr. VA-045 inhibited the decrease. 3. In nonimpacted rats, VA-045 did not alter the free Mg2+ level. 4. The decrease in cerebral free Mg2+ following CHI may be a critical factor in the development of irreversible tissue injury, and VA-045 may prevent it.

Blood glucose concentration does not affect outcome in brain trauma: A 31P MRS study

Effects of blood glucose concentration on biochemical and neurologic outcome following lateral fluid percussion-induced traumatic injury of moderate severity (2.8 atm) in rats were studied using radioactive phosphorus (31P) magnetic resonance spectroscopy (MRS) and a battery of tests designed to evaluate posttraumatic neurologic motor function. Prior to injury, male Sprague-Dawley rats (n = 18) were randomly assigned to receive either dextrose, 2 ml 50% (wt/vol), zinc insulin (10 IU/kg) or no treatment, thus dividing the animals into hyperglycemic, hypoglycemic, and normoglycemic groups, respectively. Animals were then injured, monitored for 4 h by 31P MRS before being allowed to recover, and assessed for posttraumatic motor function. Following brain injury, there was no difference in brain intracellular pH between groups over the 4-h posttraumatic MRS monitoring period. Similarly, intracellular free magnesium, cytosolic phosphorylation potential, and neurologic outcome posttrauma were not significantly different between groups. We conclude that, unlike models of ischemia, blood glucose concentration may not be a significant factor affecting outcome in traumatic brain injury.

Traumatic brain axonal injury produces sustained decline in intracellular free magnesium concentration

Decline in brain intracellular free magnesium concentration following experimental traumatic brain injury has been widely reported in a number of studies. However, to date, these studies have been confined to focal models of brain injury and temporally limited to the immediate 8-h period post-trauma. Recently, a new model of impact-acceleration brain injury has been developed which produces nonfocal diffuse axonal injury more typical of severe clinical trauma. The present study has used phosphorus magnetic resonance spectroscopy and the rotarod motor test to characterise magnesium homeostasis and neurologic outcome over a period of 8 days after induction of severe impact-acceleration injury in rats. Severe impact-acceleration induced injury resulted in a highly significant and sustained decline in intracellular free magnesium concentration that was apparent for 4 days post-trauma with recovery to preinjury levels by day six. There were no significant changes in pH or ATP concentration at any time point post-injury. All animals demonstrated a significant neurologic deficit over the assessment period. The extended period of magnesium decline after severe diffuse brain trauma suggests that repeated administration may be required for pharmacotherapies targeted at restoring magnesium homeostasis.

Intrathecal dynorphin-A infusion in rat spinal cord causes energy depletion, edema and neurologic dysfunction

The opioid dynorphin-A (dynA) is thought to contribute to the secondary injury process following spinal cord trauma although little is known about the biochemical mechanisms involved. In the present study, we have used a combination of magnetic resonance imaging (MRI) and spectroscopy (MRS) and hindlimb motor function tests to examine the effects of intrathecal dynA infusion on rat spinal cord. Infusion of 100 nmol of dynA (1-17) caused pronounced edema development as determined by MRI at 24 h after infusion. Infusion of 100 nmol of the dynA (2-17) fragment, which does not have any activity at opiate receptors, also produced profound edema whereas 100 nmol of the low potency kappa opiate receptor ligand dynA (1-8) or artificial CSF (ACSF) did not produce any edema. Both dynA (1-17) and dynA (2-17) produced significant hindlimb motor deficits at 24 h when compared to dynA (1-8) and ACSF (P < 0.05), but the deficits in the dynA (1-17) group were significantly worse than in the dynA (2-17) treated animals (P < 0.05). Similarly, mortality in the dynA (1-17) treated animals was significantly higher than in the other groups (P = 0.002). Phosphorus MRS demonstrated that the dynA (1-17) and dynA (2-17) treated animals also had a pronounced decline in high energy phosphates in the spinal cord 24 h after infusion. We conclude that dynA contributes to spinal cord cell death by causing metabolic failure and edema development.

Effects of acute ethanol intoxication on experimental brain injury in the rat: neurobehavioral and phosphorus-31 nuclear magnetic resonance spectroscopy studies

Using the lateral fluid-percussion model of experimental brain injury in the rat, the authors investigated the effect of acute ethanol (EtOH) intoxication on cardiovascular changes, neurological motor deficits, brain bioenergetics, and mortality associated with traumatic brain injury. Two hours after gastric administration of EtOH (low dose in 20 animals, 1.5 g/kg; high dose in 28, 3.0 g/kg) or saline (equal volume), animals were subjected to a fluid-percussion brain injury centered over the left parietal cortex. These injuries were of either moderate (X = 2.2 atm; 10 animals/treatment) or high severity (X = 3.0 atm; 18 animals/saline, 10 animals/low-dose EtOH, and 18 animals/high-dose EtOH). Neurological motor function was evaluated daily over a 1-week period, while a subset of eight animals receiving high-dose EtOH and subjected to brain injury of high severity were monitored for 4 hours using phosphorus-31 nuclear magnetic resonance spectroscopy to determine intracellular pH, free magnesium, and brain cytosolic phosphorylation potential. A significant (p < 0.05) and prolonged (up to 1 hour) hypotension was observed in animals pretreated with either low- or high-dose EtOH. Neither low-dose (blood-EtOH concentration = 110 +/- 40 mg/dl) nor high-dose (blood-EtOH = 340 +/- 70 mg/dl) EtOH had any effect on survival or neurological motor function after moderate brain injury. Following severe brain injury, animals pretreated with high-dose (blood-EtOH concentration = 352 +/- 65 mg/dl) EtOH showed a significantly increased mortality and markedly worsened neurological deficits at 24 hours postinjury. Following injury, free magnesium and cytosolic phosphorylation potential declined in both groups by approximately 50% to 60%, with no significant differences between groups with respect to these variables. In contrast, brain intracellular pH in the EtOH-treated animals was consistently higher than in the control group after injury. These data suggest that prior exposure to EtOH, particularly at high concentrations, may have detrimental effects on neurobehavioral function and survival in the acute period (up to 24 hours) after severe brain injury, and may be associated with posttraumatic cerebral alkalosis.

Efficacy of competitive vs noncompetitive blockade of the NMDA channel following traumatic brain injury

N-methyl-D-aspartate (NMDA) receptor antagonists have been demonstrated widely to be neuroprotective in cerebral ischemia, hypoxia, and traumatic brain injury. However, although noncompetitive NMDA antagonists have typically proven efficacious under all of these conditions, competitive antagonists have not been shown to be beneficial following moderate traumatic brain injury. The present study has used phosphorus magnetic resonance spectroscopy ([31P]MRS) to examine the effects of the competitive antagonist cis-4-(phosphonomethyl) piperidine-2-carboxylic acid (CGS-19755) and the noncompetitive antagonist dextromethorphan on biochemical outcome following fluid percussion-induced traumatic brain injury in rats. Five minutes prior to induction of moderate (2.8 +/- 0.2 atm) fluid percussion brain injury, animals received either CGS-19755 (10 mg/kg iv), dextromethorphan (10 mg/kg iv), or equal volume saline vehicle. [31P]MRS spectra were then acquired for 4 h post-trauma and intracellular pH, free magnesium concentration, cytosolic phosphorylation potential, and oxidative capacity determined. Both CGS-19755-treated animals and saline treated controls demonstrated significant and sustained declines in intracellular free magnesium concentration and bioenergetic status following trauma. In contrast, administration of dextromethorphan significantly attenuated free magnesium decline and improved bioenergetic state during the post-traumatic monitoring period. These results suggest that the neuroprotective actions of NMDA antagonists following traumatic brain injury are associated with attenuation of free magnesium decline and that such actions seem to be preferentially mediated by noncompetitive blockers.

Inhibition of phospholipase C with neomycin improves metabolic and neurologic outcome following traumatic brain injury

Activation of phospholipase C has been implicated as a factor in the development of irreversible tissue damage following injury to the central nervous system. We have used phosphorus magnetic resonance spectroscopy and a battery of postinjury motor function tests to characterize the role that phospholipase C activity may play in determining biochemical and neurologic outcome following traumatic brain injury in rats. Moderate (2.7 atmospheres) fluid percussion induced lateral brain injury caused a decline in free magnesium concentration, phosphorylation potential, and increased mitochondrial rate of oxidative phosphorylation. Neurologic motor score at 24 h and 1 week posttrauma in these animals was consistent with moderate injury. In contrast, treatment with the phospholipase C inhibitor neomycin B (15 mg/kg i.v.) immediately prior to injury significantly improved free magnesium status, bioenergetic state and neurological outcome (P < 0.01) after injury. We propose that phospholipase C activated second messenger pathways affecting magnesium homeostasis are involved in determining outcome after brain injury.

Dissociation of adenosine levels from bioenergetic state in experimental brain trauma: potential role in secondary injury

Intracellular bioenergetic state and extracellular adenosine levels were monitored in rat brain prior to and following traumatic brain injury (TBI) using phosphorus magnetic resonance spectroscopy and microdialysis, respectively. Fluid percussion-induced TBI (2.6 +/- 0.2 atm) resulted in significant reductions in free cytosolic [Mg2+], cytosolic [ATP]/[ADP] [P(i)], and delta GATP and elevations in cytosolic [ADP] and [5'-AMP]. Intracellular ATP concentration and pH did not change significantly after trauma. Mitochondrial capacity for oxidative phosphorylation (indexed by V/Vmax) increased significantly from approximately 0.45 prior to injury to approximately 0.58 following TBI. All metabolic changes were maximal at 2-3 h post-TBI. Conversely, extracellular adenosine concentrations increased transiently following TBI, with levels peaking at 10 min posttrauma, then declining rapidly to preinjury values by 50 min. Thus, despite pronounced long-term depression in bioenergetic status and a marked rise in [5'-AMP], formation and release of adenosine were elevated only transiently within the first hour following TBI. Since steady-state adenosine levels were essentially unchanged beyond 1 h posttrauma, mooted neuroprotective actions of endogenous adenosine would be minimized. Intracerebroventricular injections of 2-chloroadenosine (0.5 and 2.5 nmol) immediately prior to TBI dose-dependently attenuated metabolic disturbances and improved posttraumatic neurologic outcome (p < 0.05). The observations indicate that (a) TBI results in dissociation of adenosine release from intracellular bioenergetic state, a phenomenon possibly contributing to secondary injury following TBI; and (b) supplementing brain with an adenosine agonist attenuates irreversible injury.

Bioenergetic analysis of oxidative metabolism following traumatic brain injury in rats

Studies of fluid percussion-induced traumatic brain injury have shown that moderate trauma results in ionic imbalances, with resultant increases in energy demand to restore these ion gradients. Because there are also increased rates of glucose metabolism during periods of focal decline in blood flow, it has been suggested that the mitochondria may be incapable of sufficient oxidative metabolism to cope with this increased energy demand after injury and that ATP derived from substrate level phosphorylation must meet this demand. In the present study, we used phosphorus magnetic resonance spectroscopy to determine the mitochondrial capacity for oxidative phosphorylation after moderate brain trauma. Before injury, mean oxidative capacity was 54% +/- 1%. After injury, mean capacity increased significantly (p < 0.001) to a maximum of 61% +/- 1%, indicating that mitochondrial oxidative metabolism was enhanced after trauma. Increased oxidative capacity was accompanied by increases in ADP, AMP, and inorganic phosphate concentrations and was correlated to decreases in cytosolic phosphorylation ratio. We conclude that moderate brain trauma increases mitochondrial rate of ATP synthesis over the first 4 h posttrauma, and that during this time of increased ATP turnover, positive feedback regulation of glycolysis by increased concentrations of ADP, AMP, and inorganic phosphate contributes to maintenance of metabolic steady state.