The present study assessed the possible antinociceptive action of the hydroalcoholic extract, fractions and pure compounds obtained from the aerial parts of Baccharis illinita DC (Asteraceae) in behavioural models of chemical nociception in mice. The hydroalcoholic extract and fractions (
hexane and aqueous but not EtOAc fraction) obtained from B. illinita (30-1000 mg/kg orally) produced a dose-related inhibition of the
acetic acid-induced nociceptive response. However, the
hexane fraction was more potent than the hydroalcoholic extract and the aqueous fraction. The
hexane fraction derivatives
baurenol,
alpha-spinasterol and
oleanolic acid (0.00001-10 mg/kg intraperitoneally) also caused potent inhibition of
acetic acid-induced
pain. The
hexane fraction (300-1000 mg/kg orally) produced inhibition of both phases of
formalin-induced
pain. Moreover, the
hexane fraction (30-600 mg/kg orally) also caused a dose-dependent inhibition of
glutamate-induced
pain. Nevertheless, the
hexane fraction only at the dose of 300 mg/kg orally, produced partial inhibition of the paw oedema caused by
carrageenan. Furthermore, the
hexane fraction (300 mg/kg orally) caused inhibition of the nociceptive response induced by
intrathecal injection of
N-methyl-d-aspartic acid,
alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, tumour
necrosis factor-alpha and
interleukin-1beta. In contrast, the
hexane fraction did not affect the biting response induced by the metabotropic or ionotropic glutamatergic receptor agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic
acid and
kainate, respectively. In addition, the antinociception caused by the
hexane fraction (300 mg/kg orally) in the
acetic acid test was not affected by intraperitoneal treatment of mice with
naloxone (a non-selective
opioid receptor antagonist). The precise mechanism responsible for the antinociceptive effect of the
hexane fraction remains unclear, but appears to be partly associated with an inhibition of glutamatergic transmission and an inhibition of pathways dependent on pro-inflammatory
cytokines. Finally,
baurenol,
alpha-spinasterol and
oleanolic acid have an important role in the antinociceptive effects of the
hexane fraction. Moreover, the antinociceptive action demonstrated in the present study supports the ethnomedical uses of this plant.