GABAergic influences on defensive fighting in rats.

The involvement of GABAergic mechanisms in shock-induced defensive fighting in rats was investigated in a series of three experiments. In Experiment 1, sodium n-dipropylacetate (100-200 mg/kg) failed to produce significant behavioural change whilst gamma-vinyl-GABA (100-200 mg/kg) induced a selective and dose-dependent reduction in fighting. In Experiment 2, although inconsistent behavioural effects were obtained with (+)-bicuculline (0.25-4 mg/kg), a biphasic influence on defensive fighting was observed with picrotoxin (0.125-2 mg/kg). The inhibitory effect on fighting, induced by the highest dose of picrotoxin, was related to motor impairment. In Experiment 3, muscimol reduced fighting at doses above 0.25 mg/kg with motor disruption evident only at the highest dose used (1 mg/kg). A dose-dependent inhibition of defensive fighting was observed with 1-baclofen (0.15-1.2 mg/kg) which, at the highest dose tested, also impaired motor coordination. None of the compounds tested significantly altered shock thresholds. Results are discussed in relation to the hypothesized inhibitory role of GABA in the mediation of aggressive behaviours.