Papers of the Week

Aripiprazole is an antipsychotic drug used to treat schizophrenia and bipolar disorder. Recently, its peripheral analgesic component was evaluated, however, the mechanism involved in this effect is not fully established. Therefore, the aim of the study was to obtain pharmacological evidence for the involvement of the nitric oxide system in the peripheral antinociceptive effect induced by aripiprazole. The hyperalgesia was induced via intraplantar injection of prostaglandin E in mice and the nociceptive thresholds evaluated using the paw pressure test. All drugs were injected locally into the right hind paw. The PI3K inhibitor (AS605240), but not rapamycin (mTOR kinase inhibitor), reversed the peripheral antinociceptive effect induced by Aripiprazole. Antinociception was antagonized by the non-selective inhibitor of the nitric oxide synthase (L-NOarg). The same response was observed using the selective iNOS, but not with the selective nNOS inhibitors. The selective guanylyl cyclase enzyme inhibitor (ODQ) and the non-selective potassium channel blocker tetraethylammonium were able to reverse the antinociceptive effect of aripiprazole. The same was seen using glibenclamide, an ATP-dependent K channel blocker. However, calcium-activated potassium channel blockers of small and high conductance, dequalinium chloride and paxilline respectively, did not reverse this effect. The injection of cGMP-specific phosphodiesterase type 5 inhibitor zaprinast, potentiated the antinociceptive effect induced by a low dose of aripiprazole. The results provide evidence that aripiprazole induces peripheral antinociceptive effects via PI3K/NO/cGMP/K pathway activation.