Title: Antidepressant-like effects of P2 purinergic antagonist PPADS is dependent on serotonergic and noradrenergic integrity. Authors:

Depression is a common mental disorder affecting around 350 million of individuals globally. The available antidepressant drug monotherapy is far from ideal since it has an efficiency of approximately 60% and takes around 3-4 week to achieve clinical improvement. Attention has been paid to the purinergic signaling regarding neuropathological mechanisms, since it might be involved in psychiatric disorders, such as depression. In fact, blockade of purinergic P2X receptors induces antidepressant-like effects in preclinical models. However, the mechanisms involved in this effect are not yet completely understood. The present work investigated the interplay between a P2X receptor antagonist (PPADS) and clinically used antidepressant drugs on the forced swimming test, an animal model predictive of antidepressant effect. We observed significant synergistic effect of PPADS combined with sub-effective doses of fluoxetine or reboxetine in the FST. Moreover, depletion of serotonergic or noradrenergic systems, with PCPA and DSP-4 treatment, respectively, blocked the antidepressant-like effect of PPADS. No increase in locomotion, a possible source of confusion on FST data, was detected in any of the treated groups. Our results indicate the antidepressant-like effect of PPADS depends on the integrity of serotonergic and noradrenergic transmission.