Oral administration of kratom leaf extract alleviates anxiety-like behavior, urinary bladder pain, voiding dysfunction, and bladder hypercontractility via attenuating muscarinic receptor response in male mice exposed to chronic water avoidance stress

organ bath technique, and urinary bladder mast cell infiltration was assessed by toluidine blue staining. Results show that mice receiving WAS had a reduction in the total duration and number of unsupported rearing behaviors, reduced voiding area, and increased bladder pain responses; however, these effects were reversed by treatment with kratom leaf extract (2.5 and 5 mg/kg of mitragynine). Interestingly, the WAS group also exhibited markedly increased tonic contractions in response to carbachol, a muscarinic agonist; these responses were attenuated in mice treated with kratom leaf extract (2.5 and 5 mg/kg) The enhanced tonic contractile response to carbachol was abolished by pre-incubation with ondansetron (a 5-HT₃ antagonist). The WAS group showed an increased total number of mast cells in the urinary bladder, which was reduced by treatment with kratom leaf extract at both 2.5 and 5 mg/kg. Our results indicate that treatment with kratom leaf extract attenuated chronic stress-induced bladder pain responses, voiding abnormalities, and mast cell numbers, and was associated with reduced contractile response to muscarinic stimulation, suggesting a potential modulatory effect on stress-induced bladder dysfunction.