No / In the present study, we investigated the effect of 5-hydroxytryptamine (5-HT) and 5-HT receptor agonists and antagonists on motion sickness in Suncus murinus, and the possibility that the emetic stimulus of 5-HT can alter the sensitivity of the animals to the different emetic stimulus of motion sickness. 5-HT (1.0, 2.0, 4.0 and 8.0 mg/kg ip) induced emesis and that was antagonised by methysergide (1.0 mg/kg ip), the 5-HT4receptor antagonist sulphamate[1-[2-[(methylsulphonyl)amino]ethyl]-4-piperidinyl]methyl-5-fluoro-2-methoxy-1H-indole-3-carboxylate (GR125487D; 1.0 mg/kg ip) and granisetron (0.5 mg/kg ip). Pretreatment with 5-HT caused a dose-related attenuation of the emetic response induced by a subsequent motion stimulus, which was not significantly modified by methysergide, granisetron or GR125487D pretreatment. (+)-1-(2,5-Dimethoxy-4-iodophenyl)-2-amino-propane (DOI; 0.5 and 1.0 mg/kg ip), 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT; 0.1 mg/kg ip) but not methysergide, GR125487D or granisetron, attenuated motion-induced emesis, and that was not affected by pretreatment with ketanserin (2.0 mg/kg, ip) or N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl)cyclohexanecarboxamide trihydrocholoride (WAY-100635; 1.0 mg/kg ip), respectively. Indeed, ketanserin alone (0.1, 0.3, 1.0 and 2.0 mg/kg ip) attenuated motion sickness. These data indicate that 5-HT1/2, 5-HT3 and 5-HT4 receptors are involved in the induction of 5-HT-induced emesis. However, agonist action at the 5-HT1A/7 and 5-HT2 receptors, and antagonist action at the 5-HT2A receptors can attenuate motion sickness in S. murinus.