HTR1A and Parkinson disease: In contrast, in PD patients, while buspirone, a partial 5-HT1A agonist, ameliorates dyskinesia (Kleedorfer et al., 1991; Bonifati et al., 1994), sarizotan, another 5-HT1A receptor agonist, failed to improve it compared with placebo (Goetz et al., 2008) and significantly increased off time (Goetz et al., 2007).