Fig. 3.

Nicotinic receptors subtypes involved in varenicline-induced antinociception in the formalin test. A, blockade of the antinociceptive effect of varenicline in the formalin test by different nicotinic antagonists is shown. Mice were pretreated with various nicotinic antagonists [MEC, 2 mg/kg s.c.; DHβE, 2 mg/kg s.c.; MLA, 10 mg/kg s.c.; α-conotoxin AuIB (α-ctx AuIB), 700 pmol/mouse i.t.] 15 min (5 min for α-conotoxin AuIB) before an active dose of 3 mg/kg varenicline. Fifteen minutes later, mice were injected with formalin (2.5% intraplantary; 20 μl) and then observed for pain behaviors. B, effects of different doses of the α3β4* antagonist α-conotoxin AuIB on varenicline-induced antinociception in the formalin test are shown. Mice were injected intrathecally with different doses of α-conotoxin AuIB (70, 140, and 700 pmol/mouse), and 5 min later they received a dose of 3 mg/kg varenicline. Fifteen minutes later, mice were injected with formalin (2.5% intraplantary; 20 μl) and then observed for pain behaviors. C, antinociceptive effects of vareniciline in the β2 WT and KO mice are shown. Mice received a dose of 3 mg/kg varenicline and 15 min later were tested in the formalin test. Data are expressed as mean ± S.E.M. of licking time. Each group represents the mean ± S.E. of 8 to 12 mice. *, p < 0.05 versus vehicle.