Effects of GABAergic system on naloxone-induced jumping in morphine-dependent mice.

The effect of GABA (gamma-aminobutyric acid system) receptor agonists and antagonists on naloxone-induced jumping in morphine-dependent mice was examined. Intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) injection of different doses of the GABA(B) receptor agonist, baclofen (2.5, 5 and 10 mg/kg), reduced naloxone-induced jumping in morphine-dependent mice. The i.p. administration of the GABA(B) receptor antagonist, CGP35348 (P-[3-aminopropyl]-p-diethoxymethyl-phosphinic acid), but not the i.c.v. injection of the drug, increased naloxone-induced jumping. The antagonist also decreased the baclofen response. Administration of the GABA(A) receptor agonist, muscimol, but not the GABA(A) receptor antagonists bicuculline and picrotoxin, decreased the naloxone response in morphine-dependent animals. It is concluded that both GABA(A) and GABA(B) receptor subtypes may have an inhibitory influence on naloxone-induced withdrawal jumping in mice.