Glutamate–glutamine cycle: https://en.wikipedia.org/wiki/Glutamate%E2%80%93glutamine_cy...
"Multiple Mechanistically Distinct Modes of Endoc annabinoid Mobilization at Central Amygdala Glutamatergic Synapses" (2014) https://www.cell.com/neuron/fulltext/S0896-6273(14)00017-8
Glutamine https://en.wikipedia.org/wiki/Glutamine :
> Glutamine is synthesized by the enzyme glutamine synthetase from glutamate and ammonia. The most relevant glutamine-producing tissue is the muscle mass, accounting for about 90% of all glutamine synthesized. Glutamine is also released, in small amounts, by the lungs and brain. [20] Although the liver is capable of relevant glutamine synthesis, its role in glutamine metabolism is more regulatory than producing, since the liver takes up large amounts of glutamine derived from the gut. [7]
"Glutamine-to-glutamate ratio in the nucleus accumbens predicts effort-based motivated performance in humans" (2020) https://www.nature.com/articles/s41386-020-0760-6
> High glutamine-to-glutamate ratio predicts the ability to sustain motivation: The researchers found that individuals with a higher glutamine-to-glutamate ratio had a higher success rate and a lower perception of effort. https://neuroscienceschool.com/2020/10/11/how-to-sustain-mot...