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

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.

Glutamine synthetase expression in rat oligodendrocytes in culture: Regulation by hormones and growth factors

“…Thus, GS is involved in the detoxification of ammonia in the brain and also plays an important role in aminoacid neurotransmitter metabolism (Berl, 1971;Schousboe et al, 1977;Hertz, 1979;Shank and Aprison, 1981;Caldani et al, 1982;Tardy et al, 1984;Patel and Hunt, 1985). Although it is generally assumed that GS in vivo is present only in astrocytes and their processes (Martinez-Hernandez et al, 1977;Norenberg and Martinez-Hernandez, 1979;de Barry et al, 1983;Tholey et al, 1987b), various laboratories…”

Immunohistochemical localization of glutamine synthetase in mesencephalon and telencephalon of the lizard Gallotia galloti during ontogeny

“…There is one example of such a functional specialization of astrocytes in rodent cerebellum: Bergman glia, present in the cerebellar molecular layer where the glutamatergic neurotransmission network is dense, takes up glutamate by a very highaffinity system; this is not the case for astrocytes located in the cerebellar granular layer (de Barry et al, 1983). In the case of Gallotiagalloti, there is no information on glutamatergic neurotransmission in lizard CNS, and a mapping of glutamatergic neurons would be necessary.…”

“…The different expression of astrocytic markers in astrocytes in different anatomical sites or in different subcellular compartments may have functional implications; for example, in view of the fact that the enzymatic activity of astrocytic GS is essential for the glutamatergic neurotransmission in mammals (Hamberger et al, 1979), astrocytes near glutamatergic circuits might be the richest in GS. There is one example of such a functional specialization of astrocytes in rodent cerebellum: Bergman glia, present in the cerebellar molecular layer where the glutamatergic neurotransmission network is dense, takes up glutamate by a very highaffinity system; this is not the case for astrocytes located in the cerebellar granular layer (de Barry et al, 1983). In the case of Gallotiagalloti, there is no information on glutamatergic neurotransmission in lizard CNS, and a mapping of glutamatergic neurons would be necessary.…”