Keep in mind the possibility of microbial involvement or the processing of glutamate to GABA might be a more sophisticated way the body handles this regulatory process.
serotonin and microbiota connection may be of particular interest given the evidence that the strain of Bifidobacterium infantis 35624 can increase plasma concentrations of serotonin precursortryptophan (20). Apart from serotonin, microbiota can influence the enteric nervous system by producing other locally acting neurotransmitters, such as GABA, melatonin, histamine and acetylcholine and by generating active forms of catecholamines in the gut lumen
GABAâproducing Bifidobacterium dentium modulates visceral sensitivity in the intestine
The probiotic Bifidobacterium infantis 35624 displays visceral antinociceptive effects in the rat
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2982.2010.01520.x
GABA-PRODUCING CULTURABLE BACTERIA DERIVED FROM THE HUMAN
GASTROINTESTINAL TRACT