The dopamine-gamma aminobutyric acid interaction in the striatum of the rat is differently regulated by dopamine D-1 and D-2 types of receptor: evidence obtained with rotational behavioural experiments.

The effects of GABA antagonists on apomorphine- and pergolide-induced rotational behaviour were studied with models combining intracerebral and systemic pharmacological treatments. Whether given systemically or intrastriatally to 6-hydroxydopamine-lesioned rats, the GABA antagonist picrotoxin inhibited the rotational responses produced by s.c. administration of the dopamine (DA) D-1/D-2 agonist apomorphine while it enhanced the rotational behaviour produced by the DA D-2 agonist pergolide. Following unilateral injection of picrotoxin or bicuculline into the striatum of naive rats, apomorphine produced ispsilateral rotation, while pergolide produced contralateral rotation. These contrasting effects are compared to the behavioural responses produced by intracerebral administration of GABAergic drugs alone. Intrapallidal injection of picrotoxin produced contralateral rotational behaviour which was independent of pallido-nigral pathways. Contralateral rotation was also produced by GABA agonists, but only following intranigral injections. The results are discussed in terms of differences in the localization of DA D-1 and DA D-2 receptors on striatal GABAergic neurons. The DA D-2 receptor agonist pergolide may induce inhibition of striato-pallidal GABAergic neurons, as well as of a local GABAergic circuit exerting inhibition on a striato--pallidal enkephalinergic pathway. However, the DA D-1/D-2 receptor agonist apomorphine may inhibit striatal interneurons exerting inhibition on a striato-nigral GABAergic projection. Such a neuronal arrangement may explain that striatal DA stimulation increases GABA release from the striato-nigral terminals.