HTR1A and depressive disorder: Despite no direct interaction between antidepressants used in this study (SSRI or SNRI) and 5-HT1A receptors, indirect influences of these drugs on the receptors via enhanced stimulation by 5-HT would be more appropriately identified by analyzing 18F-MPPF binding before and after the initiation of the antidepressant therapy, although the performance of PET in untreated cases with depression might cause a delay in the commencement of the therapy.