The increase in extracellular potassium concentration in the ischemic brain in relation to the preischemic functional activity and cerebral metabolic rate

Relationships among ATP synthesis, K+ gradients, and neurotransmitter amino acid levels in isolated rat brain synaptosomes

Correlations were made among ATP synthesis, transmembrane K+ gradients, and leakage of three amino acid neurotransmitters, gamma-aminobutyric acid (GABA), aspartate, and glutamate, in rat brain synaptosomes incubated under normoxic and respiration-limited conditions. Even under normoxic conditions, a substantial proportion of total ATP synthesis (8%) was provided by glycolysis. Limitation of respiration by approximately 30% through addition of amobarbital (Amytal) caused a twofold decrease in the creatine phosphate/creatine ([CrP]/[Cr]) ratio, and consequently the [ATP]/[ADP] ratio, and a threefold increase in lactate production. There was a detectable decrease in intracellular [K+] and small rises in external GABA, aspartate, and glutamate concentrations. More severe limitations in ATP synthesis caused larger declines in the [CrP]/[Cr] ratio and progressive leakage of K+ and neurotransmitter amino acids. A comparison of delta GATP and delta GNa, K showed the former to be larger by 6 kcal, which indicates that the plasma membrane Na+/K+ pump operates at far from equilibrium. Under respiration-limited conditions, even when total ATP synthesis decreased by approximately 80% and [ATP] declined to less than 0.4 mM, delta GATP was still larger than delta GNa,K. It is suggested that during hypoxia and ischemia, the activity of the plasma membrane Na+/K+ pump in brain becomes limited by [ATP], which falls below the Km value for the low-affinity regulatory site on the enzyme. This failure of the pump and consequent collapse of the ion gradients may contribute to the leakage of neurotransmitter amino acids that occurs in these pathological states.

The post-injury responses in trauma and ischemia: secondary injury or protective mechanisms?

Transient injuries to the central nervous system, whether due to trauma or ischemia, often produce long lasting metabolic derangements, lipid peroxidation, edema, and falls in blood flow at the lesion site. Because these post-injury responses are believed to be causes of secondary injury, much research effort has been devoted to developing therapies that prevent them. Recent studies suggest that excessive Ca entry into injured cells instigates these post-injury responses. A new theory is proposed to explain these post-injury responses. This theory posits that Ca ions entering dying cells activate phospholipases that break down membranes to release phosphates. The phosphates then bind and precipitate Ca ions, producing the profound and prolonged decreases in extracellular Ca activity that have been observed in traumatized spinal cords and ischemic brains. The phospholipase activity also facilitates release of lipid peroxides which enhance edema and reduce blood flow. Both of these in turn decrease Ca diffusion to the lesion site and slow the recovery of extracellular Ca activity, giving the tissue time to recover and avoiding the consequences of rapid restoration of extracellular Ca activity. The theory suggests that central nervous tissues evolved these Ca-activated responses as a general mechanism to protect neurons against excessive Ca entry. Brain and spinal cord tissues contain very high concentrations of phosphates, many times greater than is necessary to bind all the Ca ions in the tissues. This excessive Ca buffering capacity enables the tissue to sacrifice a small proportion of severely injured cells to reduce Ca entry into less severely injured neurons. This process will also rapidly eliminate moribund cells that may otherwise linger and consume oxygen and metabolic substrates better utilized by the remaining cells. If confirmed, this theory raises serious questions concerning the current experimental therapeutic approaches to CNS trauma and stroke. Therapy should perhaps be designed to optimize rather than to abort the post-injury responses.

An evaluation of the effect of lidocaine in experimental focal cerebral ischemia

In order to determine the effect of lidocaine in focal cerebral ischemia, the left middle cerebral artery was transorbitally occluded in twenty cats. Eleven received lidocaine hydrochloride intravenously. The infusion was begun half an hour prior to clip occlusion and the rate was adjusted to maintain an isoelectric EEG. Nine cats served as controls, receiving an equivalent volume of 5% dextrose 0.2% saline. Thirteen animals (7 lidocaine-treated and 6 control) were sacrificed after six hours of left middle cerebral artery occlusion without reperfusion. In the remaining seven cats, the vessel was occluded for four hours prior to sacrifice. Ischemic neuronal alteration was assessed by both histochemical (2'3'5' triphenyl-2H-tetrazolium hydrochloride reaction) and histological examination. With both durations of ischemia, there was no significant difference in the extent and severity of neuronal alterations between the lidocaine-treated and control groups of animals.

Effect of pharmacological doses of 3-0-methyl-D-glucose and 2-deoxy-D-glucose on rat brain glucose and lactate

The present investigation examined the effects of two glucose analogues, 3-0-methyl-D-glucose (30MG) and 2-deoxy-D-glucose (2DOG) on basal levels of rat brain glucose and lactate. The results showed that pretreatment (iv) with 30MG up to 2 g/kg caused a transient drop in brain glucose levels to 42% of control value within 2.5 min and a drop in lactate levels to 75% of control value by 5 min. 2DOG administration (2 g/kg) affected glucose in a biphasic response with an initial drop to 46% of control value seen by 2.5 min, followed by a progressive increase to 290% of the control value by 40 min. This elevated level of glucose was sustained for approximately 40 min. Lactate levels responded to 2DOG administration by a decrease to 37% of control value within 10 min post-injection and returned to near basal levels by 160 min. A dose response was also examined for both compounds. Behaviorally 30MG had no apparent effects. However, the response to 2DOG was a reduction in voluntary movements, piloerection, irregular clonic jerks, splayed limbs and fits of wild running. These experiments were designed to evaluate the potential of 30MG or 2DOG for attenuating the well documented rise in brain lactate levels following an ischemic insult. Our results suggest that under certain experimental conditions either 30MG or 2DOG could prevent brain lactate rise and might have beneficial effects in minimizing the neuropathological consequences of ischemic damage that could be related to increases in brain lactate.

Management of a glomus jugulare tumour with internal carotid artery involvement

A previously healthy 40-year-old female presented for surgical resection of a large glomus jugulare tumour with extensive involvement of the carotid siphon and intracranial extension. Conduct of anaesthesia with specific reference to cerebral protection is discussed. A combination of induced hypothermia, barbiturate therapy, normotension, normocarbia and prior clamping of the distal internal carotid artery was chosen. The role of barbiturates as a therapeutic intervention is debated.

Brain anoxia releases striatal dopamine in rats

Immediately following death resulting from discontinuance of artificial respiration in anesthetized rats, a large increase in electrochemically reactive materials in the extracellular fluid was detected by in vivo voltammetry with an electrode in the striatum. The use of in vivo brain dialysis permitted identification of the reactive material as dopamine. The release of dopamine occurred about 6 minutes after cessation of artificial respiration and death. A similar release of dopamine was found after intrastriatal ouabain administration. A large release of dopamine might result in irreversible tissue damage in certain pathological conditions such as stroke or anoxia.

Ion and membrane changes in the brain during anoxia

Anoxia has two main effects on the brain, a rapid, reversible loss of function and permanent damage when the period of anoxia exceeds a critical length of time. The initial loss of function is related to a K+-conductance increase of the nerve membrane, leading to reduction of membrane resistance and hyperpolarization. After a few minutes, a non-selective increase of membrane permeability mediates rapid transfer of ions between the intra- and extracellular spaces. The subsequent rise of intracellular Ca2+ concentration may be responsible for the nerve cell death.

Correlation between brain surface potassium and glucose utilization after bilateral cerebral ischemia in the gerbil

The correlation between cerebral glucose utilization and brain surface potassium concentration (BS-K+) was studied during reperfusion following bilateral cerebral ischemia in the gerbil. Cerebral glucose utilization rate was measured by the 14C-2-deoxyglucose method and BS-K+ was continuously monitored by a potassium sensitive membrane electrode. BS-K+ increased from 3.0 +/- 0.6 mM (mean +/- S.D.) before ischemia to 58.7 +/- 17.3 mM 30 minutes after the occlusion of both common carotid arteries. The rate of decline of BS-K+ after release of occlusion differed between animals. Glucose utilization rate in the cerebral cortex immediately under the potassium electrode was low but homogeneous in 7 animals while in 5 animals the metabolic pattern was heterogeneous with areas of both low and high glucose metabolism. The former animals exhibited a fast recovery of potassium flux while the latter animals showed a slow recovery. Glucose utilization rate and potassium half recovery time were linearly correlated. These studies suggest that the reason that potassium flux may not recover rapidly in postischemic brain tissue is due to the lack of sufficient energy for a rapid re-establishment of the ion gradient across the cell due to the inefficient energy production of anaerobic glycolysis.

Release of pentobarbital-induced depression of metabolic rate during bilateral ischemia in the gerbil brain

Treatment of gerbils with 40 mg/kg of pentobarbital (i.p.) reduced the metabolic rate in the hippocampus and cerebral cortex by approximately 60%. However, the depression of metabolic rate was lost within 40 s of ischemia and further, pentobarbital delayed but did not prevent the depletion of energy metabolites observed in the ischemic brain.

Extracellular pH, potassium, and calcium activities in progressive ischaemia of rat cortex

We measured the relationships between changes in extracellular pH (pHe), potassium (Ke), and calcium (Cae) activities and DC potential (DCe) in progressive ischaemia of rat cerebral cortex. pHe and Ke, or Cae and Ke, were measured at the same point simultaneously, using triple-barrelled, double-ion-sensitive microelectrodes. Ischaemia was produced using bilateral carotid artery occlusion and hypotension in rats under 50% N2O-0.4% halothane anaesthesia. Unilateral carotid artery occlusion did not affect blood flow, but bilateral occlusion reduced flow to approximately 40% of normal. Autoregulation of blood pressure (BP) changes was lost after bilateral occlusion, and so progressive hypotension produced a linear decrease in flow. pHe began to decrease at high levels of flow (30-35 ml 100 g-1 min-1) and showed stepwise acidotic shifts with reductions in BP. Ke was affected at flows of approximately 15 ml 100 g-1 min-1, during which time it was critically dependent on BP. When Ke reached 6 mM, it increased rapidly to 40 mM and was associated with a negative shift in DCe. When Ke reached approximately 10 mM, Cae decreased rapidly to approximately 0.1 mM. pHe had reached 6.87 when Ke increased rapidly and showed a transient alkalotic shift of approximately 0.14 units at that time. Possible mechanisms for the sequence of ion changes described are discussed.

Brain free fatty acids, edema, and mortality in gerbils subjected to transient, bilateral ischemia, and effect of barbiturate anesthesia

Brain free fatty acids (FFAs) and brain water content were measured in gerbils subjected to transient, bilateral cerebral ischemia under brief halothane anesthesia (nontreated group) and pentobarbital anesthesia (treated group). Mortality in the two groups was also evaluated. In nontreated animals, both saturated and mono- and polyunsaturated FFAs increased approximately 12-fold in total at the end of a 30-min period of ischemia; during recirculation, the level of free arachidonic acid dropped rapidly, while other FFAs gradually decreased to their preischemic levels in 90 min. In treated animals, the levels of total FFAs were lower than the nontreated group during ischemia, but higher at 90 min of reflow, and the decrease in the rate of free arachidonic acid was slower in the early period of reflow. Water content increased progressively during ischemia and recirculation with no extravasation of serum protein, but the values were consistently lower in the treated group. None of the nontreated animals survived for 2 weeks; in contrast, survival was 37.5% in the treated group. It is suggested that barbiturate protection from transient cerebral ischemia may be mediated by the attenuation of both membrane phospholipid hydrolysis during ischemia and postischemic peroxidation of accumulated free arachidonic acid.

A model of focal cortical contusion in gerbils

An experimental model of focal laceration and contusion in gerbils is described. Associated with this injury are systemic changes which are neurogenically mediated and result in an immediate reduction in blood pressure, bradycardia, and generalized reduction in cerebral blood flow. There is generalized edema, as judged by a decreased specific gravity in the brain, probably related to reduced blood flow; superimposed on this, there is an edema gradient which is maximal close to the injury. This, in turn, affects the local capillary bed and prevents any local increase in flow. A separate group studied over a longer time period (6 hours) did not reveal egress of Evans blue into the surrounding tissue and this is in contrast to reports from cold-injury studies.

Brain hypoxia: the turning-point in the genesis of the migraine attack?

The hypothesis postulates that a brief episode of focal cerebral hypoxia occurs in every attack of migraine. Clinical biochemical and technical (EEG and CT scans) evidence is summarized suggesting that cerebral hypoxia is seen as the turning-point in the pathogenesis of the attack. It may be provoked by different mechanisms in different patients; the potential role of decreased oxygen supply and of increased oxygen need are reviewed and excess sympathetic drive is considered a potential key mechanism in a majority of patients. Whether or not focal hypoxia leads to a genuine migraine attack, depends largely upon the quality of the whirlpool of biochemical, vascular and hematological changes that follow the hypoxic episode. These changes are discussed and it is concluded that those which have been reported to occur during migraine attacks could be due to a preceding hypoxic event. Finally, the hypoxia viewpoint is confronted with some popular theories about the pathogenesis of migraine. It is found that the other points of view are compatible with the hypoxia hypothesis.

Energy-requiring cell functions in the ischemic brain. Their critical supply and possible inhibition in protective therapy

✓ The energy-requiring cell functions in the brain are described. The role of specific inhibition of these functions, and their critical low-supply levels of blood flow and oxygen are reviewed in relation to clinical management of focal and complete global cerebral ischemia.

Extracellular ion concentrations during spreading depression and ischemia in the rat brain cortex

We compared interstitial ion concentrations in rat brain cortex during two conditions where pronounced changes are observed: spreading depression and ischemia. Initially, during the two phenomena, an increase of [K+]e from 3 to approximately 10 mM were observed, but only small changes of the other ion concentrations. Hereafter, [K+]e exhibited a rapid increase (2-3 s) to 55 mM, whereas [Na+]e rapidly decreased to 60 mM, [Cl-]e to 75 mM, and [Ca++]e to 0.08 mM. The changes were accompanied by a rapid negative shift in the local electrical potential. However, there were differences in the ionic events during the two phenomena. In spreading depression, the initial [K+]e increase took place in 5-10 s, but in ischemia it lasted 1-2 min. The ionic perturbations were spontaneously reverted in SD, but in ischemia they proceeded further and reached after 5 min (mM): [K+]e 75, [Na+]e 50, [Cl-]e 72, and [Ca++]e 0.06. The similar chain of ionic events during spreading depression and ischemia suggests a common mechanism for the ionic changes, probably involving changes of ionic permeability of brain cells.

Oxygen and glucose consumption related to Na+-K+ transport in canine brain

This study examines the relation between Na+-K+ transport and metabolism in the canine brain. Cerebral oxygen and glucose consumption was measured by the sagittal sinus outflow technique. Synaptic transmission and related metabolism was blocked by pentobarbital 40 mg/kg (EEG flat). Lidocaine blocked an additional 15-20%, presumable by restricting Na+-K+ leak fluxes and reducing the demand for Na+-K+ transport. Ouabain blocked an additional 20-25% of metabolism. Ouabain also inhibited the Na+-K+ sensitive ATPase associated transport and caused a net efflux of K+ from the cellular compartment as evidenced by an increasing extracellular K+ concentration in the cortex. Accordingly, a total of 40% of metabolism in te EEG-arrested barbiturate inhibited brain could be related to Na+-K+ leak fluxes and associated transport. The remaining 60% are related to processes unidentified by this study. It is concluded that cerebral metabolism may be reduced below the hitherto described barbiturate minimum.

Changes in extracellular potassium concentration in cortex and brain stem during the acute phase of experimental closed head injury

A high potassium concentration ([K+]o) in brain tissue impedes neuronal activity, as observed in spreading cortical depression. Experimental studies were performed on mice and rats to determine the role of changes of [K+]o in cerebral concussion. In the first experiment, a 600 gm-cm impact was delivered to the vertex of the mouse skull. This impact induced arrest of spontaneous movement for 465 +/- 55.9 seconds (mean +/- SD), accompanied by apnea, bradycardia, and low-voltage electroencephalographic recordings (EEG). The injury was also frequently followed immediately by epilepsy. This impact induced an increase of cortical [K+]o from the control level of 4.1 +/- 1.8 mM to 20-30 mM, with gradual recovery within 30 minutes to the control level. In the second experiment, an impact of 9000 gm-cm was delivered to the midline parieto-occipital area of the rat and produced concussion-like phenomena similar to those elicited in mice. This level of trauma induced a significant increase of cortical [K+]o from the control level of 4.2 +/- 0.8 mM to 20-50 mM in all of the rats, and also a significant increase of brain-stem [K+]o from 3.9 +/- 0.6 to 20-30 mM in 73% of the rats. In these latter rats, the impact also induced apnea and a transient elevation of blood pressure, and resulted in low-voltage EEG recordings. In 23% of the rats in which [K+]o changes in the brain stem were not significant, the impact caused a transient reduction of blood pressure. The present study disclosed that an increase of [K+]o in the cerebral cortex and also in the brain stem is an important element in the phenomenon of concussion.