Possible GABA-mediated control of dopamine-dependent behavioural effects from the nucleus accumbens of the rat.

The effect of elevating GABA levels in the region of the nucleus accumbens on various dopamine-dependent behaviours in the rat has been studied. The GABA-transaminase inhibitor, ethanolamine O-sulphate (EOS) was injected bilaterally (through a needle angled at 45 degrees) into the nucleus accumbens. This resulted in a 4-5 fold increase in the GABA concentrations in the mesolimbic areas on day 1, a 2-fold increase on day 3, and a return to normal by day 7. Moderate increases in striatal and cortical GABA levels were also seen on days 1 and 3. At all times animals exhibited normal spontaneous activity and exploratory behaviour in a hold-board apparatus. However, on day 1, when mesolimbic GABA levels were maximal, a low dose of systematically administered amphetamine (0.5 mg/kg) did not induce the increased locomotor activity seen in a control group of animals. Similarly on day 1, the direct injection of dopamine into the nucleus accumbens of rats previously injected with EOS did not evoke the usual hyperactivity response. This response returned to normal on day 7. Apomorphine-induced stereotyped behaviour patterns observed on days 1 and 2 did not significantly differ in those rats previously injected with EOS with animals of a control group. A possible GABA-mediated control of dopaminergic mechanisms in the nucleus accumbens is suggested, and the possible site of interaction discussed.