Ondansetron acts by:
Ondansetron blocks the depolarizing action of serotonin through 5-HT3 receptors on vagal afferents in the gut as well as in NTS and CTZ. It donot block dopamine receptors or ACH receptors.( ref KDT 6/e p646)
Action on CTZ
5-HT3 antagonism
D1 and D2 receptor antagonism
Increasing GIT motility
Gastrointestinal tract