HTR1A and major depressive disorder: Further implicating the 5-HT1A autoreceptor and the 5-HTTLPR in SSRI response, antidepressant effects were boosted by the 5-HT1A antagonist, pindolol, specifically in MDD patients with the short allele serotonin transporter genotype (see below in this section) (Zanardi et al., 2001).