Abstract: Objective To investigate the changes of 5-hydroxytryptamine receptor(5-HTR) mRNA expression during motion adaptation.Methods The rats were exposed to motion stimulation every day and the conterts of 5-HTR_1A, 5-HTR_1B, and 5-HTR_1D mRNA in vestibular nuclei of the rats were determined at the 1^st, 3^rd, 7^th, and 14^th day of the stimulation.Results The expressions of 5-HTR_1A and 5-HTR_1D mRNA increased at the 1^st day of the stimulation, which was 2.32 and 2.71 time higher than that of the control group(P<0.01), and reached to the highest level at the 3^rd day of the stimulation, which was 2.54 and 7.63 time higher than that of the control group(P<0.01).The expression of 5-HTR_1B had no significant change at the 1^st day and significantly increased at the 3^rd day of the motion stimulation, which was 2.72 time higher than that of the control group (P<0.01).The expressions of mRNA of the three of subtypes was down regulated at the 7^th day and reached to the normal level at the 14^th day of the motion stimulation.There was no significant change in 5-HTR_1F mRNA during motion stimulation.Conclusion 5-HTR 1 may play an important role in the development and adaptation of seasickness.