THE EXCITATION AND DEPRESSION OF MAMMALIAN CORTICAL NEURONES BY AMINO ACIDS

Amino acids related to L-glutamic and gamma-amino-n-butyric acid have been administered electrophoretically, and by pressure ejection, into the extraneuronal environment of single neurones in the pericruciate cortex of cats anaesthetized with allobarbitone or allobarbitone-urethane. Acidic amino acids related to glutamic acid, particularly N-methyl-D-aspartic acid, excited cortical neurones. Neutral amino acids related to gamma-amino-n-butyric acid, particularly 3-amino-1-propanesulphonic acid, depressed cortical neurones. Some of the depressants blocked the antidromic invasion of Betz cells by pyramidal volleys. There are no essential differences between the sensitivities of cortical and spinal neurones towards locally administered amino acids. A transmitter function of such amino acids within the mammalian central nervous system is considered unlikely.

METABOLISM OF PROPIONATE BY SHEEP LIVER. INTERRELATIONS OF PROPIONATE AND GLUTAMATE IN AGED MITOCHONDRIA

1. Low concentrations of l-glutamate were slowly and quantitatively converted into aspartate by aged sheep-liver mitochondria with the loss of C-1 of the glutamate. 2. When propionate was present in addition the rate of conversion of glutamate into aspartate was increased slightly, and the presence of glutamate caused a marked stimulation in the rate at which propionate was metabolized. 3. The stimulatory effect of ;sparker' amounts of l-glutamate on propionate metabolism was matched by the effects of alpha-oxoglutarate, pyruvate, citrate and isocitrate, but not by succinate, fumarate, malate or oxaloacetate. Succinate was stimulatory at higher concentrations, whereas oxaloacetate was inhibitory. 4. When propionate was incubated with l-[1-(14)C]glutamate in the presence of a large excess of unlabelled carbon dioxide, some labelling of dicarboxylic acids and aspartate occurred, but this was much less than would have been expected from an obligatory transcarboxylation from C-1 of alpha-oxoglutarate to propionyl-CoA. 5. Possible mechanisms of these effects are discussed.

SEX DIFFERENCES IN THE METABOLISM OF OESTROGENS BY RAT LIVER MICROSOMES

Liver microsomes derived from male rats were shown to convert a higher proportion of [14C]oestrone and [14C]oestradiol to water-soluble products than did similar preparations from female rats. This sex difference became apparent at maturity and could be influenced by castration or treatment with sex hormones. The increased formation of water-soluble material by male rats was accompanied by an increase in the yield of 2-hydroxyoestradiol and other ether-soluble metabolites but no sex difference in oestrogen metabolism was detected in mice or guinea-pigs and the effect was less pronounced with [14C]stilboestrol as substrate. The enzyme system influenced by the hormonal status of the animals was present in the microsomes and showed similarities to the non-specific oxygenases which hydroxylate steroids and a number of drugs.

BACTEROIDES ORALIS, PROPOSED NEW SPECIES ISOLATED FROM THE ORAL CAVITY OF MAN

Loesche, W. J. (Forsyth Dental Center and Harvard School of Dental Medicine, Boston, Mass.), S. S. Socransky, and R. J. Gibbons. Bacteroides oralis, proposed new species isolated from the oral cavity of man. J. Bacteriol. 88:1329-1337. 1964.-Twenty-seven strains of oral bacteroides were characterized and compared with a National Collection of Type Cultures strain of Bacteroides fragilis as well as strains of intestinal bacteroides. A combination of acid end products, gas production, pentose fermentation, and 10% bile tolerance afforded a basis for separation of oral strains from intestinal strains. The oral strains produced succinic, lactic, acetic, and formic acids but no gas. They were inhibited by 10% bile, and did not ferment xylose and arabinose. Intestinal strains consistent with the description for B. fragilis produced succinic, formic, acetic, and propionic acids and gas, with a few strains forming lactic acid. They were stimulated by 10% beef bile, and fermented xylose and arabinose. The oral strains are sufficiently different from intestinal strains of the B. fragilis type, so that they appear to constitute a separate species. It is proposed that they be recognized as B. oralis, sp. n.