Baclofen Analgesia in Mice: Possible Mechanism

BALERIO GRACIELA N., RUBIO MODESTO C.

Montreal, Quebec, Canadá

Congreso; XII International Congress of Pharmacology; 1994

BACLOFEN ANALGESIA IN MICE: POSSIBLE MECHANISM. G. N. Balerio and M. C. Rubio. Cátedra de Farmacología. Fac. de Farmacia y Bioquímica (UBA) e ININFA (CONICET), Junín 956 5º piso, 1113, Buenos Aires, República Argentina.    In previous reports we have demonstrated a dose-related antinociceptive effect of baclofen (BAC) by hot plate (H P) and Acetic acid-induced writhing (A W). The ED50 value of BAC for analgesia was found to be 1.94 mg/kg i.p. (H P) and 0.1 mg/kg i.p.(A W). To confirm the analgesic effect produced by BAC cannot be due to motor incordination or sedation, we measured the number of falls and turns occurring within 5 min with BAC (1 and 3 mg/kg i.p., 1 h post administration) and it was not found significantly different from the control (6.0 + 0.4 and 4.0 + 1.7). We also studied the analgesic effect of GABA (50 and 100 mg/kg i.p.) and the percentage of the maximum possible effect (MPE) was 30 and 70 % respectively (H P), while impairment of rotating-rod performance was not altered. The analgesic effect of BAC was sensitive to reversal by naloxone 3 mg/kg i.p., 10 min before BAC 2 mg/kg i.p. administration by H P and BAC 0.1 mg/kg by A W.  H P: (%MEP) BAC control: 44 + 3; naloxone + BAC: 15 + 2, p< 0.01. A W: (% writhing inhibition) BAC control: 48 + 4; naloxone + BAC: 12 + 5, p< 0.01. These results suggest a possible interaction between GABAergic and opioidergic systems in the production of analgesic.