Description_x000D_ Biochem/physiol Actions_x000D_ Azasetron (Y-25130) is an orally active, potent and selective 5-HT3 receptor antagonist (binding Ki = 0.33 nM against [3H]granisetron/rat small intestine, 2.9 nM against [3H]quipazine/rat cortex; little or no affinity toward H1,d5-HT1A/2, Dopamine D1/2, α1/α2 adrenoceptor, muscarinic receptors) with in vivo antiemetic efficacy (0.1-0.3 mg/kg i.v. & 0.1-1 mg/kg p.o.; dogs, ferrets). Y-25130 inhibits 5-HT-induced bradycardia in anesthetized rats (ED50 = 820 ng/kg i.v.), while concurrent intrahippocampal infusion (1.0 μg/side) prevents memory function impairment caused by muscarinic acetylcholine receptor antagonist scopolamine (3.2 μg/side), but not NMDA receptor antagonist CPP (32 ng/side).