Elsevier

Brain Research

Volume 384, Issue 1, 1 October 1986, Pages 145-155
Brain Research

In vivo determination of extracellular concentration of amino acids in the rat hippocampus. A method based on brain dialysis and computerized analysis

https://doi.org/10.1016/0006-8993(86)91230-8Get rights and content

Abstract

Extracellular (EC) concentrations of amino acids were determined in the rat dentate gyrus by means of non-linear regression analysis of ‘in vivo’ brain dialysis data, considering a simple model of diffusion through a dialysis membrane. The apparent diffusion constants (K) of several amino acids were also calculated in the ‘in vivo’ situation. While putative amino acid neurotransmitters (glutamate, aspartate and γ-aminobutyric acid (GABA) were present in the EC fluid at the low micromolar range (0.8–2.9 μM), glutamine was by far the most prominent (193.4 μM). The values of intra/extracellular concentration ratios formed 3 groups: (a) high (>2000) for putative neurotransmitters; (b) low (<100) for serine, glutamine, arginine and α-alanine; and (c) intermediate (about 400) for taurine. The ‘in vivo’ calculatedK values proved useful for estimation of both basal and changing EC concentrations of amino acids in relatively brief perfusions. These data were evaluated in terms of the functional significance of absolute EC concentrations and tissue-EC fluid ratios. Present findings indicate the simultaneous existence of both an inhibitory and an excitatory tonus as well as the utility of high intra/extracellular concentration ratios in determination of the possible neurotransmitter role of specific amino acids.

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    *

    Present address: Instituto de Neurobiologi´a ‘S. Ramo´n y Cajal’, C.S.I.C., Velazquez 144, 28006-Madrid, Spain.

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