TABLE 1. Studies investigating the effect of a lack of microbiota on neurotransmitter systems.

5-HIAA: 5-Hydroxyindoleacetic Acid; 5-HT: 5-Hydroxytryptamine; BDNF: Brain-Derived Neurotrophic Factor; GABA: Gamma-Aminobutyric Acid; GF: Germ-Free; HPA: Hypothalamic-Pituitary-Adrenal; PSD-95: Postsynaptic Density Protein 95; SLC6A4: Serotonin Transporter; SPF: Specific Pathogen Free; TPH-1: Tryptophan Hydroxylase 1.

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