HTR1A and depressive symptom measurement: Mechanistically, decreased serotonergic signaling and increased nitric oxide (NO) transmission in the hippocampus transduced Tert deficiency into depression as evidenced by our observation that the infusion of a pharmacological agonist for serotonin receptor 1a (5-HTR1A) and a selective antagonist for neuronal NO synthase into the hippocampus successfully normalized the depressive behavior of Tert−/− mice.