INVOLVEMENT OF GABA(B) RECEPTORS IN THE ANTINOCICEPTION INDUCED BY BACLOFEN IN THE FORMALIN TEST

1. The effect of GABA receptor antagonists on baclofen-induced antinoc iception was examined in rats using the formalin test. Intraperitoneal (IP) administration of different doses of baclofen (2.5-10 mg kg(-1)) to rats induced antinociception in both phases of the test. 2. The re sponse was dose-dependent and the maximum response was observed with 1 0 mg kg(-1) of the drug. Intracerebroventricular (ICV) injection of ba clofen (0.5-20 mu g/rat) also induced dose-dependent antinociception i n the second phase of the formalin test. 3. The GABA(B) antagonist, ph aclofen (1 mg kg(-1), IP) but not the GABA(A) antagonists picrotoxin ( 1 mg kg(-1), IP) and bicuculline (1.5 mg kg(-1), IP), decreased the an tinociception induced by both ICV and IP administration of baclofen. 4 . It is concluded that baclofen antinociception in the formalin test i s mediated through GABA(B) receptor activation. (C) 1997 Elsevier Scie nce Inc.