Involvement of glutamate and cytokine pathways on antinociceptive effect of Pfaffia glomerata in mice

Pfaffia glomerata (Spreng) Pedersen (Amaranthaceae) is a medicinal plant known in Brazil as “Paratudo” and “Brazilian ginseng” and is commonly used as tonic, antidiabetic and to treat gastric disorders. This study evaluates the possible mechanism by which hydroalcoholic extract (HE) of Pfaffia glomerata exerts its antinociceptive effect. The HE was evaluated in acetic acid and glutamate models of pain or by biting behavior following intrathecal (i.t.) administration of agonists of excitatory aminoacids (EAA) receptors glutamate and pro-inflammatory cytokines, IL-1β and TNF-α in mice. Oral administration of HE produced dose-dependent inhibition of acetic acid-induced visceral pain and glutamate-induced pain, with ID 50 of 64.6 (47.7–87.5) mg/kg and ID 50 of 370.8 (253.4–542.7) mg/kg, respectively. The HE (300 mg/kg, p.o.) antinociception, in the acetic acid test, was not affected by i.p. treatment of animals with naloxone. In addition, HE (300 mg/kg, p.o.) inhibited the pain-related behaviors induced by i.t. injection of trans-ACPD and TNF-α, but not by NMDA, AMPA, kainate or IL-1β. Our results suggest that inhibition of glutamatergic metabotropic receptors and TNF-α may account for the antinociceptive action reported for the HE in models of chemical pain used in this study.