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01 March 2005 : Letter/Correspondence  

A word on Glutamate uptake by rat brain astroglia incubated in human cerebrospinal fluid

Tadaomi Alfonso Miyamoto

Med Sci Monit 2005; 11(3): LE1-1 :: ID: 15403

Abstract

Dear Editor,
Colombo J [1] is to be congratulated for the elegant study demonstrating that cultured astrocytes display signifi - cant glutamate uptake. Which is increased if the potassium concentration is elevated from 3.45 to 12.0 mM in culture medium supplemented with calf serum, but not in the presence of cerebrospinal fl uid (CSF) instead of calf serum. However, the implication is somewhat contradicting to the house-cleaning function attributed to glial cells, for
one would expect increased glutamate uptake under the
environment leading to high K+ in in-vivo conditions with normal CSF. The author departed from the premise that CSF composition is similar to the extracelullar medium, and made the laudable effort in using human CSF as a mean to mimic the physiological extracelullar medium. However, is it really
physiological to use CSF from hydrocephalic patients?
The effect of subtle composition differences from those of a normal CSF could not be ruled out and might explain the observed differences. Although the author did not entertain such possibility, an alternate explanation could be the differences
in the content of various other aminoacids that may
affect the glutamate uptake of the astroglia. Specifi cally, was taurine concentration measured in the so-called physiological CSF? Taurine cortical content in hydrocephalic H-Tx rats is substantially decreased [2] and I would think its concentration in the CSF would also be reduced. Normal CSF taurine content is only one tenth of that of plasma [3] and that from hydrocephalic patients might be much lower than
that. It is known that CSF taurine content vary dynamically with the underlying pathology and brain functional status at the time it was obtained, and could account for the observed difference that seems somewhat contradictory to the anticipated effect.
It is suggested that while the taurine content of Basal Medium supplemented with calf serum most likely is suffi - cient, that of the BM-hydrocephalic CSF’s might be inadequateto support the astroglial glutamate uptake displayed when incubated with adequate amounts of taurine. Taurine is known to attenuate neuronal NMDA release [4,5], but might conceivably play an equally important role in
astroglial glutamate uptake, though still to be demonstrated is not unlikely for the inhibitory and protective effects of taurine could very well involve both actions. Our experimental work with systemically administered taurine indicates that it has dose dependent effects on production (larger doses) and uptake (small doses) of other aminoacids and peptides at the systemic level, suggesting it should also
have similar effects at local level, especially regarding uptake. It is unfortunate that incubation media taurine was not determined. Had it been measured the role taurine played would have been suggested.
References:
1. Colombo J: Glutamate uptake by rat brain astroglia incubated in human cerebrospinal fl uid. Med Sci Monit, 2005; 11(1): BR13–BR17
2. Jones HC, Harris NG, Rocca JR, Andersohn RW: Progressive changes in cortical metabolites at three stages of infantile hydrocephalus studied by in vitro NMR spectroscopy. J Neurotrauma, 1997; 14(9):
587–602
3. Laterra J, Keep R, Betz AL, Goldstein GW: Blood-Brain-Cerebrospinal Fluid Barriers. In: Basic Neurochemistry. Molecular, Cellular and Medical Aspects. Eds: Agranoff BW, Albers RW, Fisher SK, Uhler
MD. Lippincot-Raven, Philadelphia-New York, 1999; p. 671–89
4. Anderzhanova E, Oja SS, Saransaari P, Albrecht J: Changes in the striatal extracellular levels of dopamine and dihydroxyphenylacetic acid evoked by ammonia and N-methyl-D-aspartate: modulation by
taurine. Brain Res, 2003; 11; 977(2): 290–93
5. Hilgier W, Anderzhanova E, Oja SS et al: Taurine reduces ammonia- and N-methyl-D-aspartate-induced accumulation of cyclic GMP and hydroxyl radicals in microdialysates of the rat striatum. Eur J Pharmacol.
2003; 468(1): 21–25

Keywords: Taurine - chemistry, Astrocytes - metabolism, Brain - cytology, Cerebrospinal Fluid - physiology, Culture Media - chemistry, Dose-Response Relationship, Drug, Glutamic Acid - metabolism, Hydrocephalus - physiopathology, Taurine - pharmacology

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