Developing rat cerebellum: Glutamine and glutamate influx correlated to the cellular distribution of glutamine synthetase

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Abstract
Glutamate has been suggested to be the neurotransmitter of the granule cells in cerebellar cortex. Autoradiographic studies using very low concentrations (1μM range) of 2-3-[ 3 H] l -glutamate or 2-3-[ 3 H] l -glutamine have shown that both amino acids were preferentially taken up in the molecular layer of the cerebellar cortex of adult rats, but [ 3 H]Glu accumulated essentially in glial cells, while Gln did not show a cellular preference (de Barry et al ., Neuroscience 7,1289–1297,1982). In this paper we show that during development the preferential accumulation of [ 3 H]Glu and [ 3 H]Gln are the same as in the adult but, in addition, at young ages (7–10 days) [ 3 H]Gln accumulated in replicating cells of the external granular layer (EGL). The absence of glutamine synthetase in the EGL cells suggests that this accumulation of exogenous Gln might be used for the synthesis of purines and pyrimidines required for the active multiplication of these cells and is not correlated to neurotransmission. The metabolism of [ 3 H]Gln was slow at young ages and changed during development. The metabolism of the Glu taken up was constant throughout development which is consistent with the hypothesis that high affinity Glu uptake is mainly a glial cell property and that the increasing accumulation rate during development reflects glial maturation.