Profile of amino acid synthesis in rat hippocampus during push-pull perfusion of ethanol or morphine

In the unanesthetized rat, the effect of ethanol or morphine on the new synthesis of six amino acids, gamma-aminobutyrate, glutamate, alanine, aspartate, glycine and glutamine, was determined at circumscribed sites in the hippocampus. In the fasted animal, 5.0 microCi of [U-14C]glucose was microinjected in a volume of 1.0 microliter into a discrete region of the hippocampus through a permanently implanted guide tube. After 10-15 min, the tip of a concentric push-pull cannula assembly was lowered through the guide tube to the labelled site, and an isotonic artificial cerebrospinal fluid was continuously perfused at a rate of 25 microliters/min. Samples of perfusate were collected every 5.0 min in a total volume of 125 microliters. During the fourth perfusion, either ethanol (94 or 471 mM) or morphine (0.1 or 1.0 microgram/microliter) was added to the push-pull perfusate. Amino acids and glucose contained in each sample of perfusate were separated by means of a two-dimensional, thin-layer chromatographic procedure. The results show that the 94 mM dose of ethanol acted only to significantly suppress the new synthesis of alanine. Conversely, the higher 471 mM dose of ethanol significantly increased the new synthesis of both glycine and glutamine from the glucose precursor. The effect of the 0.1 microgram/microliter morphine dose on amino acid synthesis paralleled that of the lower dose of ethanol since it evoked a similar decrease in the synthesis of alanine; however, the higher dose of 1.0 microgram/microliter morphine produced no effect. None of the other amino acids in the hippocampus were affected by either of the CNS depressants. Thus, whereas ethanol seems to exert significant stimulating activity on hippocampal synthesis of glycine and glutamine, morphine and ethanol possess the same inhibitory effect on alanine synthesis in this subcortical structure.