The present study aimed to characterize the ability of the novel delta opioid peptide (DOP) receptor agonist H-Dmt-Tic-NH-CH(CH2-COOH)-Bid (UFP-512) to attenuate motor deficits in 6-hydroxydopamine (6-OHDA) hemilesioned rats. Lower doses (0.1-10 microg/kg) of UFP-512 administered systemically (i.p.) stimulated stepping activity in the drag test and overall gait abilities in the rotarod test whereas higher doses (100-1000 microg/kg) were ineffective or even worsened Parkinsonism. Microdialysis coupled to an akinesia test (bar test) was then used to determine the circuitry involved in the motor actions of UFP-512. An antiakinetic dose of UFP-512 (10 microg/kg) decreased GABA in globus pallidus (GP) as well as GABA and glutamate (GLU) release in substantia nigra reticulata (SNr). On the other hand, a pro-akinetic dose (1000 microg/kg) of UFP-512 increased pallidal GABA, simultaneously producing a decrease in GABA and an increase in nigral GLU release. Moreover, to test the hypothesis that changes in motor behavior were associated with changes in nigro-thalamic transmission, amino acid release in ventromedial thalamus (VMTh, a target of nigro-thalamic GABAergic projections) was also measured. The anti-akinetic dose of UFP-512 reduced GABA and increased thalamic GLU release while the pro-akinetic dose increased GABA without affecting thalamic GLU release. Finally, regional microinjections were performed to investigate the brain areas involved in motor actions of UFP-512. UFP-512 microinjections into GP increased akinesia whereas UFP-512 microinjections into SNr reduced akinesia. Furthermore, the selective DOP receptor antagonist naltrindole (NTD) increased akinesia when injected into either area, GP being more sensitive. We conclude that UFP-512, depending on dose, improves or worsens motor activity in hemiparkinsonian rats by acting differentially as a DOP receptor agonist in SNr and a DOP receptor antagonist in GP, ultimately decreasing or increasing the activity of nigro-thalamic GABAergc output neurons, respectively.