In this study, mice in the ROT group showed a significant reduction in serum levels of 5-HT (Figure 2F, p < 0.05) and mRNA expression levels of 5-HTR4 in the striatum and colon (Figure 2G,H, p < 0.01), suggesting that the 5-HT signaling system may be an important mediator of ROT-induced dyskinesia and constipation symptoms in PD. Here, HTR5A is linked to Parkinson disease.