Notes: Abstract: The present study was undertaken to explore how transient ischemia in rats alters cerebral metabolic capacity and how postischemic metabolism and blood flow are coupled during intense activation. After 6 h of recovery following transient forebrain ischemia 15 min in duration, bicuculline seizures were induced, and brains were frozen in situ after 0.5 or 5 min of seizure discharge. At these times, levels of labile tissue metabolites were measured, whereas the cerebral metabolic rate for oxygen (CMRO2) and cerebral blood flow (CBF) were measured after 5 min of seizure activity. After 6 h of recovery, and before seizures, animals had a 40–50% reduction in CMRO2, and CBF. However, because CMRO2 rose threefold and CBF fivefold during seizures, CMRO2 and CBF during seizures were similar in control and postischemic rats. Changes in labile metabolites due to the preceding ischemia encompassed an increased phosphocreatine/ creatine ratio, as well as raised glucose and glycogen concentrations. Seizures gave rise to minimal metabolic perturbation, essentially comprising reduced glucose and glycogen contents and raised lactate concentrations. It is concluded that although transient ischemia leads to metabolic depression and a fall in CBF, the metabolic capacity of the tissue is retained, and drug-induced seizures lead to a coupled rise in metabolic rate and blood flow.

Notes: Abstract: The objective of the present study was to explore mechanisms responsible for activation of ion conductances in the initial phases of brain ischemia, particularly for the early release of K+ that precedes massive cell depolarization, and rapid downhill fluxes of K+, Na+, Cl−, and Ca2+. As it has been speculated that a K+ conductance can be activated either by an increase in the free cytosolic calcium concentration (Ca2+i) or by a fall in ATP concentration, the question arises whether the early increase in extracellular K+ concentration (K+e) is preceded by a rise in Ca2+i and/or a fall in ATP content. In the present experiments, ischemia was induced in rats by cardiac arrest, the time courses of the rise in K+e and cellular depolarization were determined by microelectrodes, and the tissue was frozen in situ through the exposed dura for measurements of levels of labile metabolites, including adenine nucleotides and cyclic AMP (cAMP), after ischemic periods of 15, 30, 60, and 120 s. Conversion of phosphorylase b to a was assessed, because it depends, among other things, on changes in Ca2+i. The K+e value rose within a few seconds following induction of ischemia, but massive depolarization (which is accompanied by influx of calcium) did not occur until after ∼65 s. Activation of phosphorylase was observed already after 15 s and before glycogenolysis had begun. At that time, 3′,5′-cAMP concentrations were unchanged, and total 5′-AMP concentrations were only moderately increased. The results demonstrate that a K+ conductance is activated at a time when the overall ATP concentration remains at 95% of control values. If major compartmentation can be excluded, the results fail to demonstrate that an ATP-activated K+ conductance is involved. In view of the early activation of phosphorylase, one may speculate that the triggering event is a rise in Ca2+i.

Notes: Abstract— The objective of the present experiments was to correlate changes in cellular energy metabolism, dissipative ion fluxes, and lipolysis during the first 90 s of ischemia and, hence, to establish whether phospholipase A2or phospholipase C is responsible for the early accumulation of phospholipid hydrolysis products. Ischemia was induced for 15–90 s in rats, extracellular K+ (K+e) was recorded, and neocortex was frozen in situ for measurements of labile tissue metabolites, free fatty acids, and diacylglycerides. Ischemia of 15-and 30-s duration gave rise to a decrease in phosphocreatine concentration and a decline in the ATP/free ADP ratio. Although these changes were accompanied by an activation of K+ conductances, there were no changes in free fatty acids until after 60s, when free arachidonic acid accumulated. An increase in other free fatty acids and in total diacylglyceride content did not occur until after anoxic depolarization. The results demonstrate that the early functional changes, such as activation of K+ conductances, are unrelated to changes in lipids or lipid mediators. They furthermore suggest that the initial lipolysis occurs via both phospholipase A2 and phospholipase C, which are activated when membrane depolarization leads to influx of calcium into cells.

Notes: Abstract: Transient ischemia is known to lead to a long-lastingdepression of cerebral metabolic rate and blood flow and to an attenuatedmetabolic and circulatory response to physiological stimuli. However, thecorresponding responses to induced seizures are retained, demonstratingpreserved metabolic and circulatory capacity. The objective of the presentstudy was to explore how a preceding period of ischemia (15 min) alters therelease of free fatty acids (FFAs) and diacylglycerides (DAGs), the formationof cyclic nucleotides, and the influx/efflux of Ca2+, followingintense neuronal stimulation. For that purpose, seizure activity was inducedwith bicuculline for 30 s or 5 min at 6 h after the ischemia. ExtracellularCa2+ concentration (Ca2+e) was recorded, andthe tissue was frozen in situ for measurements of levels of FFAs, DAGs, andcyclic nucleotides. Six hours after ischemia, the FFA concentrations werenormalized, but there was a lowering of the content of 20:4 in the DAGfraction. Cyclic AMP levels returned to normal values, but cyclic GMP contentwas reduced. Seizures induced in postischemic animals showed similar changesin Ca2+e, as well as in levels of FFAs, DAGs, and cyclicnucleotides, as did seizures induced in nonischemic control animals, with theexception of an attenuated rise in 20:4 content in the DAG fraction. Weconclude that, at least in the neocortex, seizure-induced phospholipidhydrolysis and cyclic cAMP/cyclic GMP formation are not altered by a precedingperiod of ischemia, nor is there a change in the influx/efflux ofCa2+ during seizure discharge or in associated spreadingdepression.

Notes: Abstract— The objective of the present experiments was to study metabolic correlates to the localization of neuronal lesions during sustained seizures. To that end, status epilepticus was induced by i.v. administration of bicuculline in immobilized and artificially ventilated rats, since this model is known to cause neuronal cell damage in cerebral cortex and hippocampus but not in the cerebellum. After 20 or 120 min of continuous seizure activity, brain tissue was frozen in situ through the skull bone, and samples of cerebral cortex, hippocampus, and cerebellum were collected for analysis of glycolytic metabolites, phosphocreatine (PCr), ATP, ADP, AMP, and cyclic nucleotides. After 20 min of seizure activity, the two “vulnerable” structures (cerebral cortex and hippocampus) and the “resistant” one (cerebellum) showed similar changes in cerebral metabolic state, characterized by decreased tissue concentrations of PCr, ATP, and glycogen, and increased lactate concentrations and lactate/ pyruvate ratios. In all structures, though, the adenylate energy charge remained close to control. At the end of a 2-h period of status epilepticus, a clear deterioration of the energy state was observed in the cerebral cortex and the hippocampus, but not in the cerebellum. The reduction in adenylate energy charge in the cortex and hippocampus was associated with a seemingly paradoxical decrease in tissue lactate levels and with failure of glycogen resynthesis (cerebral cortex). Experiments with infusion of glucose during the second hour of a 2-h period of status epilepticus verified that the deterioration of tissue energy state was partly due to reduced substrate supply; however, even in animals with adequate tissue glucose concentrations, the energy charge of the two structures was significantly lowered. The cyclic nucleotides (cAMP and cGMP) behaved differently. Thus, whereas cAMP concentrations were either close to control (hippocampus and cerebellum) or moderately increased (cerebral cortex), the cGMP concentrations remained markedly elevated throughout the seizure period, the largest change being observed in the cerebellum. It is concluded that although the localization of neuronal damage and perturbation of cerebral energy state seem to correlate, the results cannot be taken as. evidence that cellular energy failure is the cause of the damage. Thus, it appears equally probable that the pathologically enhanced neuronal activity (and metabolic rate) underlies both the cell damage and the perturbed metabolic state. The observed changes in cyclic nucleotides do not appear to bear a causal relationship to the mechanisms of damage.

Notes: Abstract: The influence of complete and pronounced incomplete cerebral ischemia on cortical concentrations of reduced (GSH) and oxidized (GSSG) glutathione was studied in lightly anaesthetized (70% N2 O) rats. GSH was extracted with HCl-methanol-perchloric acid and GSSG with trichloroacetic acid in the presence of N-ethylmaleimide and measured fluorometrically, giving normal concentrations in cortical tissue of about 2 and 0.01 μmol.g−1 respectively. Reversible complete ischemia was induced by increasing the intracranial pressure to above the systolic blood pressure by infusing mock CSF into the cisterna magna. Reversible pronounced incomplete ischemia was induced by bilateral carotid artery clamping combined with hypovolemic hypotension. Whether complete or incomplete, a 30-min ischemic period caused a similar decrease in cortical GSH concentration (to about 90% of control) without any concomitant accumulation of GSSG in the tissue (or in CSF). Prolongation of the ischemic period (complete ischemia) to maximally 120 min caused an almost linear decrease of the tissue glutathione concentration to 45% of the preischemic value. During subsequent recirculation following a 30 min period of either complete or pronounced incomplete ischemia, there was a further decrease in cortical GSH concentrations without a reciprocal increase in GSSG concentrations. Lipid peroxidation (verified by determination of malondialdehyde production) induced in brain cortical tissue in vitro caused oxidation of tissue GSH with accumulation of GSSG. As the observed decrease in GSH during brain ischemia in vivo was not accompanied by any reciprocal increase in GSSG the results fail to support the hypothesis that peroxidative damage occurs during or following brain ischemia. The finding of an unchanged GSSG concentration does, however, not exclude the possibility of an increased turnover rate in the glutathione reductase reaction. It is concluded that the observed decrease in tissue GSH concentration mainly reflects a decrease in the glutathione pool size, due to an imbalance between breakdown and synthesis secondary to tissue energy failure.

Notes: Abstract— The levels of ATP, P-creatine, glucose, glycogen, lactate, glutamate and ammonia were measured in mouse brain after administration of the convulsive agent methionine sulphoximine (MSO). No changes were observed in ATP and P-creatine levels either before or during the seizures. Lactate levels were unchanged until the onset of seizures (4–5 hr) at which time the levels increased an average of 65 per cent. Glucose and glycogen levels increased progressively. Just before the onset of seizures the levels had increased 95 and 62 per cent, respectively. During the seizures both substances had increased a total of 130 per cent. Comparable changes were found in cerebral cortex, cerebellum and subcortical forebrain. Through the use of quantitative histochemical methods it was found that the greatest increases in glycogen occurred in layers I and III (layers II and IV were not analysed). Progressively smaller changes were found in layers V and VI and no increase at all was found in the subjacent white matter. Glucose, in contrast to glycogen, increased to about the same degree in all cerebral layers and in subjacent white matter.The increase in glycogen after MSO administration may be related to the fact that MSO also causes an increase in the ratio of brain to serum glucose levels. This would indicate that an increase in intracellular glucose had occurred.Ammonia levels were increased 300–400 per cent in both cerebrum and cerebellum. A time study in cerebellum showed that the increase begins early and reaches maximal levels long before the onset of seizures. Glutamate levels were reduced by small but statistically significant amounts in both cerebrum and cerebellum. Administration of methionine sulphoximine completely prevented seizures and the increase in lactate, but did not prevent the increases in glycogen and glucose. The rise in ammonia was reduced but not prevented.During 20 sec of complete ischaemia (decapitation) ATP, P-creatine and glucose fell somewhat more rapidly than normal in brain of animals undergoing MSO seizures. From the changes it was calculated that the metabolic rate had been increased about 20 per cent by the seizure.A new sensitive and specific enzymic method for determination of tissue ammonia is presented together with evised enzymic procedures for lactate and glutamate.

Notes: Abstract: The objective of the present study was to assess metabolic changes in the neocortex and hippocampus of well-oxygenated or moderately hypoxic rats in which fluorothyl-induced seizures were sustained for 5 or 20 min, or which were allowed recovery periods of 5, 15, or 45 min following cessation of 20-min seizure activity by withdrawal of the convulsant gas. Sustained fluorothyl-induced seizures were found to cause metabolic alterations qualitatively and quantitatively similar to those previously observed with other commonly used convulsants. Thus, although the phosphorylation state of the adenine nucleotide pool remained only moderately perturbed, if at all, there were decreases in tissue concentrations of phosphocreatine and glycogen, and increases in those of cyclic AMP, lactate, and pyruvate, with a calculated fall in intracellular pH of about 0.15 units and a rise in the cytoplasmic NADH/NAD+ ratio. The enhanced metabolic rate was reflected in a marked reduction in the tissue-to-plasma glucose concentration ratio. Induced moderate hypoxia (arterial Po2 40–50 mm Hg) had no metabolic effect after 5 min of seizures but moderately increased lactate concentrations after 20 min (from about 10 to about 15 μmol ± g−1). On cessation of seizure discharge cyclic AMP and phosphocreatine concentrations normalized already within 5 min, whereas glycogen and lactate concentrations normalized more slowly. In the neocortex (but not the hippocampus) postepileptic tissue-to-plasma glucose concentration ratios rose above control, probably reflecting metabolic depression. The results suggest that intracellular pH promptly returned to control, and that postepileptic alkalosis developed. They also suggest that some elevation of the NADH/NAD+ ratio persisted even after 45 min of recovery.