GABA-producing <i>Lactococcus lactis</i> alleviates gut dysfunction and neurobehavioral abnormalities associated with irritable bowel syndrome

<b>Aim:</b> This study aimed to screen <i>Lactococcus lactis</i> strains with varying gamma-aminobutyric acid (GABA) production and evaluate their effects on intestinal dysfunction and neurobehavioral abnormalities in an irritable bowel syndrome (IBS) mouse model, with a focus on GABAergic signaling and dose-dependent mechanisms. <b>Methods:</b> Three <i>Lactococcus lactis</i> strains were selected based on GABA yield and genetic analysis. IBS was induced in mice via <i>Citrobacter rodentium</i> infection and water avoidance stress. Intestinal integrity, inflammation, histopathology, and behavior were assessed. GABA levels in the colon and serum were measured by liquid chromatography-mass spectrometry (LC-MS). GABA receptor subunit expression in the colon, hippocampus, and amygdala was analyzed via quantitative real-time polymerase chain reaction and Western blotting. <b>Results:</b> GABA-producing strains alleviated intestinal dysfunction in IBS mice by reducing <i>IL-6</i> gene expression and iNOS activity, upregulating <i>CLDN2</i>, and improving tissue integrity. Anxiety-like behaviors and cognitive deficits were also attenuated. Colonic GABA levels, <i>GABRA13</i> mRNA, and GABRA3 protein expression increased in a dose-dependent manner, whereas TRPV1 mRNA and TRPV1 protein levels were downregulated. Serum GABA remained unchanged. In the central nervous system, the expression of hippocampal GABA_A and GABA_B receptors was elevated, with both <i>GABRA13</i> mRNA and GABRA3 protein levels positively correlating with colonic GABA concentrations. <i>GABRA15</i> expression was upregulated in the amygdala. <b>Conclusion:</b> GABA-producing <i>Lactococcus lactis</i> effectively alleviates IBS-related intestinal dysfunction and neurobehavioral abnormalities by coordinately modulating GABAergic signaling in both the gut and the central nervous system, exhibiting a clear dose-dependent effect across multiple key phenotypes.