Oral treatment with Berberine reduces peripheral nociception: Possible interaction with different nociceptive pathways activated by different allogeneic substances

Ethnopharmacological relevance: Berberine was identified in extracts of Berberis ruscifolia Lam., a plant used in traditional medicine as an analgesic. Its presence may be involved in the reported pharmacological activity of this species. However, there is still a lack of scientific research concerning its analgesic activity in the peripheral nervous system. Aim of the study: To investigate Berb-induced antinociception in the formalin test and to evaluate several pathways related to its pharmacological antinociceptive effects in chemical models of nociception in mice. Materials and methods: The antinociceptive activity of Berb was assessed by inducing the paw licking in mice with different allodynic agents. In the formalin test, the antiedematous and antithermal effect of Berb was evaluated simultaneously in the same experiment. Other nociceptive behavior produced by endogenous [prostaglandin E2 (PGE2), histamine (His), glutamate (Glu) or bradykinin (BK)] or exogenous [capsaicin (Caps) and cinnamaldehyde (Cin)] chemical stimuli, and activators as protein kinase A (PKA) and C (PKC), were also evaluated.The in vivo doses for p.o. were 3 and 30 mg/kg. Results: Berb, at 30 mg/kg p.o., showed a significant inhibition of the nociceptive action in formalin in both phases being stronger at the inflammatory phase (59 +/- 9%) and more active than Asp (positive control) considering the doses evaluated. Moreover, Berb inhibited the edema (34 +/- 10%), but not the temperature in the formalin test. Regarding the different nociceptive signaling pathways evaluated, the most relevant data were that the administration of p.o. of Berb, at 30 mg/kg, caused significant inhibition of nociception induced by endogenous [His (72 +/- 11%), PGE2 (78 +/- 4%), and BK (51 +/- 7%)], exogenous [Cap (68 +/- 4%) and Cinn (57 +/- 5%)] compounds, and activators of the PKA [(FSK (86 +/- 3%)] and PKC [(PMA(86 +/- 6%)] signaling pathway. Berb did not inhibit the nociceptive effect produced by Glu. Conclusion: The present study demonstrated, for the first time, the potential of Berb in several nociceptive tests, with the compound present in B. ruscifolia contributing to the analgesic effect reported for this species.