CEREBRAL METABOLIC CHANGES DURING PROLONGED EPILEPTIC SEIZURES IN RATS

Abstract

Abstract— Sustained epileptic seizures were induced in paralysed, artificially ventilated and anaesthetized (70% N 2 O) rats by means of intravenous bicuculline (1.2mgkg−1), and cerebral cortical tissue was frozen in situ after periods varying between 10 s and 2 h for analyses of labile phosphates, glycolytic metabolites, citric acid cycle intermediates, and associated amino acids and ammonia, using enzymic fluorometric techniques. Body temperature was kept at 37°C, and arterial hypotension, arterial hypoxaemia and hypoglycaemia were prevented. Cortical glycogen concentrations fell progressively (to 23% of control levels) between 1 and 20 min after seizure onset but returned to control concentrations after 120 min of seizure activity. Cortical glucose concentration fell to 30% of control after 1 min of seizure activity, remained close to 50% of control for 1 h, and fell again to 30% after 2 h of seizure activity. Cortical lactate concentration was doubled in brains frozen 10 s after bicuculline injection. It rose over the following 20 min, reaching a steady concentration of about 10μmolg−1 wet wt. The changes in lactate and glucose concentration indicated a 34‐fold increase in the rate of glycolysis during the first minute of seizure. Phosphocreatine concentration was reduced by nearly 50% after 10 and 30 s of seizure activity, and subsequently stabilized at a concentration 2/3 of normal. ATP concentration was maximally reduced (by 7%) after 30 s and remained close to normal thereafter. Larger, initial reductions occurred in ATP/ADP and ATP/ AMP ratios, as well as in the adenylate energy charge. All these parameters remained significantly reduced for the rest of the 2 h seizure period. However, the changes were moderate since the energy charge was maintained within 2% of control. Changes in citric acid cycle intermediates included initial reductions in α‐ketoglutarate and oxaloacetate (calculated) and progressive increases in fumarate, malate and citrate. After long periods of seizures all citric acid cycle intermediates except oxaloacetate were increased in concentration. Ammonia increased during the first min to reach steady state values of 200% of control. Alanine increased progressively during the first 20 min, to stabilize at 200% of control thereafter. GABA increased at 5 min and subsequently rose to almost twice the control value (120 min). At 20 min and onwards there were progressive decreases in glutamate and aspartate, and a progressive increase in glutamine. The sum of amino acids measured increased significantly and the sum of ammonia equivalents rose substantially. Intracellular pH calculated from the creatine kinase equilibrium decreased by 0.25 units during the first minute. However, since the pH calculated from P co, and cellular buffer base changes remained close to normal during this period, it is concluded that the components of the creatine kinase reaction were not in equilibrium, and the pH values calculated from this equilibrium were incorrect. Tentative calculations of NADH/NAD+ ratios indicated that redox changes of opposite direction occurred in cytoplasm (reduction) and mitochondria (oxidation).