Mice given intraperitoneal injections of methionine sulfoximine (MSO) (100 mg/kg body weight) showed tonic-clonic seizures 7 to 8 h later. The protein synthesis inhibitors actinomycin D and cycloheximide, when combined with MSO delayed the onset of seizures. Methionine completely abolished the convulsions and metyrapone delayed them for some hours. Twenty-four h after the administration of the convulsant, the activity of the gluconeogenic enzyme, fructose-1, 6-biphosphatase (FBPase), and the glycogen content were determined in different areas of the brain. MSO induced an increase in both FBPase activity and glycogen content. These effects were antagonized by the inhibitors of protein synthesis. Metyrapone partly inhibited MSO-induced increases of FBPase activity and glycogen content whereas methionine completely abolished them. MSO decreased glycogen content in liver but had no effect on blood glucose level 24 h after its administration. These findings suggested that in MSO epileptogenic brain, glycogen accumulation may proceed from an enhanced gluconeogenesis.

Kinetics for transport of adenosine into guinea-pig neocortex synaptosomes were studied by incubating them with [14C]adenosine for up to 30 s. The apparent Km value of the high-affinity transport system for adenosine was 21.1 microM and the Vmax value was 257.3 pmol/min/mg protein. The transport system was inhibited by both compounds structurally related (compounds 554 and 555) and unrelated (dipyridamole) to adenosine. Because electrically stimulated synaptosomes release up to 1.5% of the adenosine derivative content per min, the physiological significance of adenosine uptake is discussed as a possible mechanism to compensate for the loss of adenine nucleotides from synaptosomal preparations.

No abstract

Numerous methods used for the isolation of brain microvessels involve procedures which disturb the structural integrity of the cells and their organelles. In the present study, analysis of the adenylate energy charge and content as well as the incorporation of adenosine derivatives in isolated rat brain microvessels indicated a lesion of the mechanisms of energy production. The results show that experiments on isolated microvessels prepared by a mechanical homogenization exerting shear forces should be interpreted with caution when the rate of energy metabolism is a significant factor in the study.

Abstract— The experiments reported here confirm that glutamate can penetrate the inner membrane of isolated rat brain non‐synaptosomal mitochondria, either on a glutamate‐hydroxyl antiporter or on a glutamate‐aspartate antiporter. An inhibition of respiratory activity of mitochondria with glutamate as substrate was obtained in the presence of avenaciolide or N‐ethylmaleimide. Swelling of the mitochondria in iso‐osmotic NH4+‐l‐glutamate was inhibited in the presence of avenaciolide and N‐ethylmaleimide, but mersalyl, kainic acid, glisoxepide and amino‐oxyacetic acid had no effect on the glutamate‐hydroxyl exchange. Glutamate induced the reduction of intramitochondrial NAD(P), as estimated by double‐beam spectrophotometry, and this reduction was inhibited on the one hand by N‐ethylmaleimide, avenaciolide or fuscine, on the other hand by aminooxyacetic acid. A direct estimation of the penetration of l‐[14C]glutamate into brain mitochondria was performed by using the centrifugation‐stop procedure. This penetration followed saturation kinetics, with a mean apparent Km of 1.56 MM at pH 7.4 and at 20°C, the value of Knax was 4.34 nmol per min per mg protein in the same conditions. IV‐Ethylmaleimide slowed down the initial rate of glutamate penetration, and this inhibition appeared to be non‐competitive with a Ki of 0.7 Mm ‐at pH 7.4 and at 20°C. The entry of glutamate was pH‐dependent and it increased 2‐fold in the pH range of 7.4 to 6.4. A temperature‐dependence of glutamate transport was also shown between 2 and 25°C; the Arrhenius plot was a straight line, with a calculated EA of 12.8 kCal per mol of glutamate and a Q10 of 2.16. The activity of γ‐glutamyl transpeptidase was practically absent in these rat brain mitochondria. Oxidation of extramitochondrial NADH by the‘malate‐aspartate shuttle’reconstituted in vitro was followed in rat brain non‐synaptosomal mitochondria. In the absence of extramitochondrial malate or glutamate the ‘shuttle’ did not function, and in the absence of extramitochondrial aspartate the rate of NADH oxidation was low. Glutamine or γ‐aminobutyrate did not replace glutamate efficiently. A high inhibition of the‘malate‐aspartate shuttle’occurred in the presence of avenaciolide or mersalyl, and a moderate one in the presence of n‐ethylmaleimide, glisoxepide or n‐butylmalonate. Glutaminase activity in intact brain mitochondria was inhibited in the presence of extramitochondrial glutamate.