FREE AMINO ACIDS AND RELATED COMPOUNDS IN FIVE REGIONS OF BIOPSIED CAT BRAIN

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Abstract
Abstract— Contents (μmol/g wet wt.) of 34 free amino acids and related compounds were measured in grey matter from three areas of cerebral cortex, from the cerebellum, and from the caudate nucleus in unanaesthetized cats with classical cerveau isolé preparations. Brain specimens were frozen in liquid nitrogen within 10 s of removal; thus, the values found were expected to approximate those which occur in living cat brain. Levels of most of the compounds measured were lower than those previously reported for the cat. In the case of GABA, alanine, and ethanolamine, the lower values found seemed attributable to the rapid freezing of brain tissue, and may more closely approximate levels occurring in living cat brain. On the other hand, the relatively low levels of aspartic and glutamic acids found may have resulted from use of the cerveau isolé preparation. Little difference in levels of amino compounds was found among the three cerebral cortical areas examined. However, there were significant differences in the contents of a number of amino acids between cerebral cortex and the cerebellum or caudate nucleus. These differences resembled those previously observed in autopsied human brain. The content of GABA was two‐fold higher in biopsied cat cortex than in biopsied human cortex, whereas the content of cystathionine was only 10 per cent of that in human cortex. Homocarnosine and α‐(γ‐aminobutyryl)‐lysine, two GABA‐containing dipeptides found in relatively large amounts in human brain, were not detectable in cat brain. Living cat brain contained two amino acids not previously reported for this species:putreanine and ɛ‐N‐methyllysine.