Our gut microorganisms produce other essential neurotransmitters too. Lactobacillus and Bifidobacterium create gamma-aminobutyric acid (GABA), an important inhibitory chemical, as we saw in Chapter 2. Escherichia coli, Bacillus, and Saccharomyces produce norepinephrine, which is important for alertness; Bacillus and Serratia produce dopamine. Bifidobacterium infantis increases levels of tryptophan, an important precursor to serotonin, melatonin, and vitamin B3. Lactobacillus acidophilus increases the expression of the natural cannabinoid and opioid receptors in the brain, affecting appetite,
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