High-frequency stimulation (HFS) of the subthalamic nucleus (STN) alleviates dramatically motor symptoms in Parkinson's disease, and recently it has been suggested that zona incerta (ZI) stimulation might be as beneficial to patients. We used in situ cytochrome oxidase (CoI) mRNA hybridization to investigate and compare the effects of HFS of the STN and the ZI on metabolic activity of the STN, globus pallidus (GP), and substantia nigra reticulata (SNr) in normal rats as well as in rats with 6-hydroxydopamine (6-OHDA) lesion, an animal model of Parkinson's disease. In normal rats, HFS of the STN, as well as of the ZI, induced a significant decrease in CoI mRNA expression within the STN and SNr but an increase within the GP. In 6-OHDA rats, HFS of the STN reversed dopamine denervation-induced changes in the expression of CoI mRNA in the STN, SNr, and GP. Similar results were obtained with HFS of the ZI except for the STN, which showed only a trend toward normalization. These data suggest that the ZI, as well as the STN, are implicated in the functional mechanism of HFS supporting the involvement of GABA transmission for the reduction of neuronal activity in the basal ganglia output structures.