Chronic constipation is a common gastrointestinal disorder characterized by impaired intestinal motility and dysbiosis of the gut microbiota. This study evaluated the therapeutic potential of the probiotic yeastvar.(HO12) on loperamide-induced constipation in rats. We assessed fecal parameters, intestinal transit, histological alterations, neurotransmitter levels, and short-chain fatty acid (SCFA) production. HO12 administration effectively alleviated constipation symptoms in a dose-dependent manner. It significantly increased fecal number, weight, water content, and improved gastrointestinal transit, indicating enhanced intestinal motility. HO12 also restored serotonin levels and the expression of serotonin-related genes, key regulators of enteric neurotransmission. Furthermore, HO12 increased the production of acetic acid and total SCFAs, contributing to a favorable intestinal environment. Histological analysis demonstrated that HO12 restored mucosal thickness, crypt cell distribution, and interstitial cells of Cajal, thereby supporting intestinal functional recovery. In conclusion, our results demonstrate that HO12 alleviates loperamide-induced constipation by modulating intestinal neurotransmitters, enhancing intestinal motility, and increasing SCFA production. These findings suggest thatHO12 has strong potential as a therapeutic probiotic for constipation management. Saccharomyces cerevisiae boulardii S. boulardii
