Glutamine is an important precursor for transmitter glutamate

In cultured neurons three different glutamine carriers that mediate glutamine uptake have been identified (Tamarappoo et al., 1997), but so far they have not been cloned, and the 

Glutaminase may become of special importance after cell damage, e.g. as caused by trauma or hypoxia, when the enzyme leaks out of neurons and into the extracellular space. Here it may convert extracellular glutamine into Glu, thus contributing to a continuous and excitotoxic glutamatergic stimulation of neurons. Such a mechanism has been demonstrated 

NEURONS CAN ALSO CARBOXYLATE PYRUVATE AND ARE THEREEORE NOT COMPLETELY DEPENDENT ON GLUTAMINE AS A PRECURSOR FOR TRANSMITTER GLUTAMATE 

The finding that neurons, or at least subpopulations of neurons, seem to have the ability to replenish their TCA cycle by carboxylating pyruvate (Hassel and Brathe, 2000a,b) may explain why some glutamatergic pathways have a low level of glutaminase, whereas others have high levels as detected by immunocytochemistry (Laake et al., 1999 Fig. 6E), and it explains how transmitter Glu may be formed from neuronal precursors. 

HANDLING OF TRANSMITTER GLUTAMATE AFTER RELEASE EORMATION OF GLUTAMINE OR PYRUVATE 

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