Tatsuro Kawamata

Dynamic changes in local cerebral glucose utilization following cerebral concussion in rats: evidence of a hyper- and subsequent hypometabolic state

Following cerebral concussion, in which there is no evidence of direct morphological damage, cells are exposed to an increase in extracellular potassium as well as an accumulation of calcium. This concussion-induced ionic flux most likely alters the cellular energy demands thereby modifying metabolic processes. To investigate the metabolic changes after cerebral concussion, local cerebral metabolic rates for glucose (lCMRglc) utilizing [14C]2-deoxy-D-glucose were studied in rats (n = 98; 250-300 g) immediately, 30 min, 6 h, 1, 2, 3, 5 and 10 days following a unilateral frontoparietal fluid percussion (F-P) injury (3.7-4.3 atm). Compared to sham controls, animals exhibited bilateral hypermetabolism immediately following brain injury. However, this effect was more pronounced in structures ipsilateral to the site of F-P and was especially marked for the cerebral cortex (46.6-30.1% higher than control) and hippocampus (90.1-84.4% higher than control). By 30 min post-trauma many ipsilateral regions still showed evidence of hypermetabolism, although their lCMRglc had subsided. Beginning as early as 6 h following injury many regions within the ipsilateral cortex and hippocampus went into a state of metabolic depression (16.4-33.7% of control) which lasted for as long as 5 days. These results indicate that, although not mechanically damaged from the insult, cells exposed to concussive injury dramatically alter their metabolic functioning. This period of post-concussive metabolic dysfunction may delineate a period of time, following injury, during which cells are functionally compromised.

Diffuse prolonged depression of cerebral oxidative metabolism following concussive brain injury in the rat : a cytochrome oxidase histochemistry study

Utilizing a lateral fluid percussion injury as a model of cerebral concussion, rats were studied histochemically measuring the degree of cytochrome oxidase activity present within different structures at different times following injury. After concussion, the cerebral cortex ipsilateral to the site of injury exhibited a diffuse decrease in its level of chromotome oxidase (CO) activity beginning at as soon as one day and lasting for up to 10 days after the insult. The ipsilateral dorsal hippocampus also exhibited an injury-induced decrease in CO activity, however, it was not as severe as in the cortex. These results indicate that oxidative metabolism is depressed primarily within the cerebral cortex and hippocampus for several days following a cerebral concussion. We propose that this period of metabolic depression may delineate a period of time during which the injured brain is unable to function normally and thus would be vulnerable to a second insult.

Administration of Excitatory Amino Acid Antagonists via Microdialysis Attenuates the Increase in Glucose Utilization Seen following Concussive Brain Injury

Immediately following concussive brain injury, cells exhibit an increase of energy demand represented by the activation of glucose utilization. We have proposed that this trauma-induced hypermetabolism reflects the effort of cells to restore normal ionic balance disrupted by massive ionic fluxes through transmitter-gated ion channels. In the present study, changes in local CMRglc following fluid-percussion concussive injury were determined using [14C]2-deoxy-d-glucose autoradiography, and the effects of in situ administration (via microdialysis) of excitatory amino acid (EAA) antagonists [kynurenic acid (KYN), 2-amino-5-phosphonovaleric acid (APV; 100 μM, 1 mM, and 10 mM), and 6-cyano-7-nitroquinoxaline-2,3-dine (CNQX; 300 μM, 1 mM, and 10 mM] on glucose utilization were investigated. Animals that did not receive dialysis showed a remarkable increase (up to 181% of normal control) in cortical glucose utilization following injury. In contrast, this high demand for glucose was reduced in areas infiltrated with KYN, APV, and CNQX. These results indicate that EAA-activated ion channels are involved in the posttraumatic increase in glucose utilization, reflecting the energy demand of cells required to drive pumping mechanisms against an ionic perturbation seen immediately following the concussive injury. The effects of KYN, APV, and CNQX suggest that although all subtypes of the glutamate receptor appear to be involved in this phenomenon, N-methyl-d-aspartate-activated channels may play a major role.

Lactate accumulation following concussive brain injury: the role of ionic fluxes induced by excitatory amino acids

During the first few minutes following traumatic brain injury, cells are exposed to an indiscriminate release of glutamate from nerve terminals resulting in a massive ionic flux (e.g., K+ efflux) via stimulation of excitatory amino acid (EAA)-coupled ion channels. The present study was undertaken to elucidate the causal relationship between these ionic shifts and lactate accumulation in the injured brain, by examining the effects of ouabain (an inhibitor of Na+/K+-ATPase), Ba2+ (an inhibitor or non-energy-dependent glial K+ uptake) and kynurenic acid (KYN; a broad-spectrum EAA antagonist) on lactate accumulation. Two microdialysis probes were placed bilaterally in the rat parietal cortex. One was perfused with a test drug (1.0 mM ouabain, 2.0 mM Ba2+ or 10 mM KYN) and the other with Ringers solution (control) for 30 min prior to injury. Following a 2.2-2.7 atm fluid-percussion injury, lactate levels in the dialysate increased (up to 116.6% above baseline) for the first 16 min and returned to baseline levels within 20 min after injury. This lactate accumulation was attenuated by preinjury administration of ouabain and KYN and was prolonged by Ba2+ administration. These findings indicate that lactate accumulations following concussive brain injury is a result of increased glycolysis which supports ion-pumping mechanisms, thereby, restoring the ionic balance which was disrupted by stimulation of EAA-coupled ion channels.

Calcium-dependent glutamate release concomitant with massive potassium flux during cerebral ischemia in vivo

The changes in extracellular glutamate ([Glu]e) and potassium ([K+]e) in the rat hippocampus during cerebral ischemia were determined simultaneously by microdialysis in vivo. Biphasic increases in [Glu]e, i.e. an earlier rapid increase concomitant with an abrupt increase in [K+]e followed by a later slow increase, were observed. Dialysis with Ca(2+)-free perfusate containing Co2+ blocked the earlier rapid increase completely but the later slow increase only partially. These findings suggest that Ca(2+)-dependent exocytotic release from the presynaptic nerve terminals is involved predominantly in the earlier rapid increase in [Glu]d. The later slow increase in [Glu]d may be due in part to a breakdown of membrane function resulting from several causes, including a loss of the electrogenic component of the glutamate gradients across the plasma membrane, and a loss of function of the glutamate uptake system.

Hippocampal CA3 Lesion Prevents Postconcussive Metabolic Dysfunction in CA1

Immediately following fluid-percussion (F-P) brain injury, the hippocampus exhibits a marked increase in its local CMRglc (LCMRglc; μmol/100 g/min) as determined using [14C]2-deoxy-d-glucose autoradiography. This injury-induced increase in metabolism is followed in 6 h by a subsequent decrease in LCMRglc. These two postinjury metabolic states may be the result of ionic disruptions following trauma via stimulation of glutamategated ion channels. To determine if endogenous glutamate innervation to the CA1 region of the hippocampus can provide an anatomical basis for this proposed mechanism, it was removed by kainic-acid–induced destruction of CA3, and the effect on CA1 metabolism following concussive injury was studied. Five days before a lateral F-P injury (3.5–4.5 atm), kainic acid (0.5 μg) or vehicle was stereotaxically injected into the left ventricle of 65 rats. Histological inspection indicated that kainic acid produced severe cell loss primarily in the CA3 region of the hippocampus ipsilateral to the injection. The metabolic results indicated that immediately following injury, animals with an intact hippocampus exhibited an increase in LCMRglc to 84.6 ± 5 within the CA1 region, representing a 81.5% increase over controls. However, in the CA3-lesioned animals, CA1 showed no evidence of an injury-induced hypermetabolism, with LCMRglc remaining at control levels (51.4 ± 3.9). At 6 h postinjury, the intact hippocampus exhibited a reduction of LCMRglc to rates of 40.7 ± 4.7 within the CA1 region, representing a 17.9% reduction compared with controls. In contrast, CA3-lesioned animals exhibited less of an injury-induced decrease in LCMRglc within the CA1 region, exhibiting a mean rate of 43.4 ± 4.5, representing only a 12.5% reduction compared with controls. These results indicate that the removal of the CA3 projection to CA1 protects the CA1 cells from the metabolic dysfunction typically seen following injury. This supports our previous work indicating the important role glutamate plays in the ionic flux and subsequent metabolic changes that follow traumatic brain injury.

The Increase in Local Cerebral Glucose Utilization Following Fluid Percussion Brain Injury is Prevented with Kynurenic Acid and is Associated with an Increase in Calcium

Immediately following a lateral fluid percussion brain injury, the cerebral cortex and hippocampus ipsilateral to the percussion show a marked accumulation of calcium and a pronounced increase in glucose metabolism. To determine if this increase in glucose metabolism was related to the indiscriminate release of the excitatory amino acid (EAA) glutamate, kynurenic acid (an EAA antagonist) was perfused into the cerebral cortex through a microdialysis probe for 30 min prior to injury. The results show that adding kynurenic acid to the extracellular space prior to trauma prevents the injury-induced increase in glucose utilization. These results indicate that calcium contributes to the ionic fluxes that are typically seen following brain injury and supports the concept of an increased energy demand upon cells to drive pumping mechanisms in order to restore membrane ionic balance.

Concussive Brain Injury Produces a State of Vulnerability for Intracranial Pressure Perturbation in the Absence of Morphological Damage

Following a fluid percussion (F-P) brain injury the cells in the brain go into a state of vulnerability during which, if they sustain a second, typically nonlethal insult, they die. This has been previously described in the rat [3] where a F-P injury was followed in 1 hour by a 6 min forebrain ischemic insult. Cells within the CAl region of the hippocampus that normally survive both insults independently, now die when the insults are administered in close temporal proximity.

Pre-Or Postsynaptic Blocking of Glutamatergic Functioning Prevents the Increase in Glucose Utilization Following Concussive Brain Injury

During the first few minutes following an experimental concussive brain injury in the rat, the cerebral cortex and underlying hippocampus are exposed to an increase in extracellular potassium (1). In addition to this ionic flux, these same regions exhibit an increase in glucose metabolism using [14C]2-deoxy-o-glucose (2DG) autoradiography(2). It has been proposed that any ionic flux due to an traumatic brain injury would result in a stimulation of glycolysis, presumably due to the energy demand of cells to activate ionic pumping mechanisms in their effort to restore ionic balance(3).

Impaired Synaptic Plasticity and Dendritic Damage of Hippocampal CA1 Pyramidal Cells in Chronic Hydrocephalus

The long-term potentiation (LTP) of the Schaffer collateral/CA1 pyramidal cell system of the rat hippocampus was investigated at various periods after induction of hydrocephalus by cisternal kaolin injection. There was a progressive decrease in LTP during the initial 3 weeks, and LTP remained decreased thereafter following the induction of hydrocephalus. Since the intraventricular pressure reached its maximum level within 2 weeks after kaolin injection, the continuous presence of hydrocephalus appeared to be necessary for producing the deficit in LTP induction. Dendritic dysfunction was apparently important for this functional change, since in a previous study by electron microscopy, we revealed a number of swollen dendrites in the CA1 region, while the changes in the axons, synaptic structures, and soma were far less pronounced. In agreement with this interpretation, a swelling of the dendrites of the CA1 pyramidal cells and irregularity of their arrangement was demonstrated by microtubule-associated protein 2-immunohistochemistry to be associated with the decreased LTP. Since LTP is likely to reflect the hippocampal function related to memory retention, functional changes underlying the impaired LTP might be responsible for memory deficit in hydrocephalus.