Transmitter self-regulation by extracellular glutamate in fresh human cortical slices

In human brain tissue samples, the ratio of glutamate to glutamine outside cells stays near 1:2 even when processes that release or clear glutamate are altered, showing a consistent metabolic balance between neurons and glial cells.

Blocking a specific transporter that removes glutamate from brain tissue increases glutamate levels outside cells but does not change glutamine levels, showing that glutamine release does not require glutamate to be taken back up by this transporter.

Glutamine is broken down in cells to produce alpha-ketoglutarate, which supports energy generation in mitochondria, and glutamate, which is used to make neurotransmitters.

In human brain tissue samples, glutamate is about 20 times more abundant than GABA at rest, and activating sodium channels reduces this difference.

In human brain tissue samples, opening sodium channels increases glutamate outside neurons, and closing sodium channels decreases glutamate outside neurons, showing that electrical activation of neurons directly causes glutamate release.

In human brain tissue slices, the amount of glutamate outside nerve cells controls how much glutamine glial cells release through SN1 transporters, creating a regulatory loop where glutamate levels determine the rate of its own removal.