Biochemical effects of the anticonvulsants trimethadione, ethosuximide and chlordiazepoxide in rat brain

Cerebral energy metabolism in rats with genetic absence epilepsy is not correlated with the pharmacological increase or suppression of spike-wave discharges

The quantitative [14C]2-deoxyglucose (2-DG) autoradiographic method was applied to measure the effects of pharmacological agents on local cerebral metabolic rates of glucose (LCMRglcs) in a selected strain of Genetic Absence Epilepsy Rats from Strasbourg (GAERS). In a previous study, we have shown that GAERS display an overall significant increase of LCMRglc compared to non-epileptic rats from a selected strain. To further characterize the metabolic responses in GAERS, we measured the effects of drugs aggravating or suppressing absences. The animals were divided into 4 groups, i.e. 2 non-epileptic control groups and 2 GAERS groups. Ten min before the initiation of the 2-DG procedure, both non-epileptic control and epileptic rats received an injection of the same amount of the pharmacological agent, either haloperidol (2 mg/kg) or ethosuximide (200 mg/kg). In the presence of haloperidol, GAERS exhibited almost continuous spike-wave discharges; however, the difference in energy metabolism between GAERS and non-epileptic control rats was abolished and LCMRglcs were similar in all structures of both groups of animals. In GAERS treated with ethosuximide, spike-wave discharges were totally suppressed, whereas rates of energy metabolism remained higher by 31-72% in all structures of epileptic rats compared to their corresponding non-epileptic controls. These data demonstrate a lack of correlation between the occurrence of spike-wave discharges and LCMRglcs and are in favor of normal or decreased ictal metabolism and of increased interictal glucose utilization by the brain in rats with absence epilepsy.

Chronic ketosis and cerebral metabolism

The effects of chronic ketosis on cerebral metabolism were determined in adult rats maintained on a high-fat diet for approximately three weeks and compared to a control group of animals. The fat-fed rats had statistically significantly lower blood glucose concentrations and higher blood beta-hydroxybutyrate and acetoacetate concentrations; higher brain concentrations of bound glucose, glucose 6-phosphate, pyruvate, lactate, beta-hydroxybutyrate, citrate, alpha-ketoglutarate, alanine, and adenosine triphosphate (ATP); lower brain concentrations of fructose 1,6-diphosphate, aspartate, adenosine diphosphate (ADP), creatine, cyclic nucleotides, succinyl coenzyme A (CoA), acid-insoluble CoA, and total CoA; and similar brain concentrations of glucose, malate, calculated oxaloacetate, glutamate, glutamine, adenosine monophosphate, phosphocreatine, reduced CoA, acetyl CoA, sodium, potassium, chloride, and water content. The metabolite data in the chronically ketotic rats demonstrate an increase in the cerebral energy reserve and energy charge. These data also suggest negative modification of the enzymes phosphofructokinase, pyruvic dehydrogenase, and alpha-ketoglutaric dehydrogenase; positive modification of glycogen synthase; and possible augmentation of the hexose transport system. There was no demonstrable difference in brain pH, water content, or electrolytes in the two groups of animals. We speculate that the increased brain ATP/ADP ratio is central to most, if not all, the observed metabolic perturbations and may account for the increased neuronal stability that accompanies chronic ketosis.

Effects of anticonvulsant and convulsant drugs on the ATPase activities of synaptosomes and their components

1. The effects of anticonvulsants, and other drugs on the Na+, K+-adenosine triphosphatase (ATPase) (ouabain-sensitive) and Mg++-ATPase activities of synaptosomes and their components have been determined. 2. The Mg++-ATPase activity of synaptosomes was not affected by the drugs but the Na+, K+-ATPase activity was inhibited by phenytoin (diphenylhydantoin), ethosuximide and diazepam. 3. Fractions containing mainly membranes, mitochondria or synaptic vesicles, were prepared from synaptosomes by osmotic shock and subsequent density gradient centrifugation. Inhibition of Na+, K+-ATPase activity by phenytoin, ethosuximide and diazepam was apparent only in the membrane fraction. 4. The fraction containing synaptic vesicles exhibited pronounced Md++-ATPase but no Na+, K+-ATPase activity. In contrast to the enzymes of the membranes and mitochondria, the Mg++-ATPase of the vesicles was inhibited by diazepam and all of the anticonvulsants tested.

The estimation of rates of utilization of glucose and ketone bodies in the brain of the suckling rat using compartmental analysis of isotopic data

The brains of 18-day-old rats utilize glucose and ketone bodies. The rates of acetyl-CoA formation from these substrates and of glycolysis were determined in vivo from the labelling of intermediary metabolites after intraperitoneal injection of d-[2-(14)C]glucose, l(+)-[3-(14)C]- and l(+)-[U-(14)C]-lactate and d(-)-3-hydroxy[(14)C]butyrate. Compartmental analysis was used in calculating rates to allow for the rapid exchange of blood and brain lactate, the presence in brain of at least two pools each of glucose and lactate, and the incomplete equilibration of oxaloacetate with aspartate and of 2-oxoglutarate with glutamate. Results were as follows. 1. Glucose and ketone bodies labelled identical pools of tricarboxylate-cycle metabolites, and were in every way alternative substrates. 2. The combined rate of oxidation of acetyl-CoA derived from pyruvate (and hence glucose) and ketone bodies was 1.05mumol/min per g. 3. Ketone bodies contributed 0.11-0.53mumol/min per g in proportion to their concentration in blood, with a mean rate of 0.30mumol/min per g at 1.24mm. 4. Pyruvate and ketone bodies were converted into lipid at 0.018 and 0.008mumol/min per g respectively. 5. Glycolysis, at 0.48mumol/min per g, was more rapid in most rats than pyruvate utilization by oxidation and lipid synthesis, resulting in a net output of lactate from brain to blood. 6. Rates of formation of brain glutamate, glutamine and aspartate were also measured. Further information on the derivation of the models has been deposited as Supplementary Publication SUP 50034 (18 pages) at the British Library, Lending Division (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7QB, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973) 131, 5.