Astroglial cells in the brain can actively import the amino acid glutamate from the synaptic cleft, convert it to the amino acid glutamine, and release the glutamine into the cleft to be subsequently taken up by the presynaptic neurons. The neurons then convert it back to glutamate. Why is this function of glial cells important?

A) Because it competes with and replaces the direct uptake of glutamate by the neurons and thus regulates neuronal function.
B) Because neurons cannot produce the amino acids glutamine and glutamate and rely on the glial cells for their supply.
C) Because glutamate cannot be taken up directly by the neurons.
D) Because glutamate is an excitatory neurotransmitter and should be cleared from the synaptic cleft rapidly after its release.
E) Because glutamate import through glutamate-Na⁺ symporters in the glial cells is required for the maintenance of Na⁺ concentration in the synaptic cleft.