HTR1A and Spinocerebellar ataxia type 3: Moreover, decreased 5-HT1A receptor binding affinity was observed in 12-week-old R6/2 huntingtin (HD model) mice [117], which may explain why inhibition of the 5-HT transporter by citalopram is more effective than 5-HT receptor activation using vabicaserin in SCA3 animal models [16].