HTR1A and depressive disorder: Moreover, since desensitization of 5-HT1A autoreceptors presumably plays a key role in the therapeutic action of SSRIs (Piñeyro and Blier, 1999), whereas their upregulation could be related to core symptoms of depression (Stockmeier et al., 1998), we checked the functional integrity of the serotonergic transmission in HDC-/- mice also by using the hypothermic response to the 5-HT1A agonist 8-OH-DPAT.