D1-D2 dopamine receptor interaction: an in vivo single unit electrophysiological study.

After intrastriatal administration of selective dopamine receptor agonists only a small percentage of substantia nigra pars reticulata single units showed changes in firing rate (23% after SKF38393 and 17% after quinpirole). After their intrastriatal co-administration, however, or after the application of the non-selective dopamine receptor agonist apomorphine, 72% and 69% of units responded, respectively. This result confirms the participation of the striatum in the phenomenon of D1-D2 receptor interaction, and show that co-activation of both receptor subtypes produced a maximal effect on basal ganglia output nuclei.