THE NOVEL DELTA OPIOID RECEPTOR AGONIST UFP-512 DUALLY MODULATES MOTOR ACTIVITY IN HEMIPARKINSONIAN RATS VIA CONTROL OF THE NIGRO-THALAMIC PATHWAY O. S. MABROUK, a,b M. MARTI, a,b S. SALVADORI c AND M. MORARI a,b * a Department of Experimental and Clinical Medicine, Section of Pharma- cology, University of Ferrara, via Fossato di Mortara 17-19, 44100 Fer- rara, Italy b National Institute of Neuroscience and Neuroscience Center, University of Ferrara, via Fossato di Mortara 17-19, 44100 Ferrara, Italy c Department of Pharmaceutical Sciences and Biotechnology Center, Uni- versity of Ferrara, via Fossato di Mortara 17-19, 44100 Ferrara, Italy Abstract—The present study aimed to characterize the ability of the novel delta opioid peptide (DOP) receptor agonist H-Dmt- Tic-NH-CH(CH 2 –COOH)-Bid (UFP-512) to attenuate motor defi- cits in 6-hydroxydopamine (6-OHDA) hemilesioned rats. Lower doses (0.1–10 g/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 g/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 g/kg) de- creased 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 g/kg) of UFP- 512 increased pallidal GABA, simultaneously producing a de- crease in GABA and an increase in nigral GLU release. More- over, 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 re- ceptor 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. © 2009 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: delta opioid, microdialysis, naltrindole, 6-OHDA, Parkinson’s disease, UFP-512. Opioid transmitter systems have long been studied for their involvement in a number of physiological functions ranging from nociception to mood and movement. The localization of opioid receptors and their endogenous ligands within the basal ganglia, a set of midbrain structures critical to motor programming and execution, has also led investigators to study their contribution to neurodegenerative diseases such as Parkinson’s disease (PD; for a review see Samadi et al., 2006). Previous studies were encouraged by the finding that loss of dopamine (DA) cells in the substantia nigra (SN) compacta (SNc), a hallmark of PD, results in alterations of opioid signaling throughout the basal ganglia (Rinne et al., 1983; Llorens-Cortes et al., 1984; Gerfen et al., 1990). For example, the pathogenic rise in striato–pallidal GABA release which follows the loss of striatal D2 receptor stimulation (Ma- neuf et al., 1994; Stanford and Cooper, 1999) is compen- sated for by an upregulation of striatal preproenkephalin-A mRNA (Bezard et al., 2001) which is presumed to cause excessive release in globus pallidus (GP). Indeed, delta opi- oid peptide (DOP) receptor stimulation was shown to reduce pallidal GABA release in vitro (Dewar et al., 1987; Maneuf et al., 1994) as well as in vivo (Mabrouk et al., 2008). To confirm the compensatory nature of such changes in DOP receptor transmission, the selective nonpeptide DOP receptor agonist ()-4-[(R)--(2S,5R)-allyl-2,5-dimethyl-1-piperazinyl)-3-me- thoxy-benzyl]-N–N-diethylbenzamide (SNC-80; Bilsky et al., 1995) caused pronounced reversal of motor deficits in 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine treated marmo- sets and reserpinized or 6-hydroxydopamine (6-OHDA) hemilesioned (hemiparkinsonian) rats (Manueuf et al., 1994; Pinna and Di Chiara, 1998; Hill et al., 2000; Hille et al., 2001). We recently confirmed these findings in hemipar- kinsonian rats (Mabrouk et al., 2008), showing that, in contrast with the commonly accepted belief, the site of the antiparkinsonian action of SNC-80 was the SN reticulata (SNr) rather than GP. Indeed, the antiakinetic effect and the accompanied reduction in pallidal GABA release elicited by SNC-80 were prevented by intranigral but not intrapal- lidal perfusion of the DOP receptor antagonist naltrindole (NTD). Moreover, injections of SNC-80 into SNr but not GP replicated the antiparkinsonian effects of systemic SNC- 80. These findings prompted us to further evaluate the circuitry underlying the antiparkinsonian effect of DOP re- ceptor agonists. In particular, the impact of DOP receptor stimulation on nigro–thalamic transmission was investi- *Corresponding author. Tel: 39-0532-455210; fax: 39-0532-455205. E-mail address: m.morari@unife.it (M. Morari). Abbreviations: ANOVA, analysis of variance; AP, antero–posterior; DA, dopamine; DOP, delta opioid peptide; DV, dorso–ventral; ENK, enkephalins; GLU, glutamate; GP, globus pallidus; ML, medio–lateral; NTD, naltrindole; PD, Parkinson’s disease; RM, repeated measure; SNC-80, ()-4-[(R)--(2S,5R)-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxy- benzyl]-N–N-diethylbenzamide; SNr, substantia nigra reticulata; UFP-512, H-Dmt-tic-NH-CH(CH 2 –COOH)-Bid; VMTh, ventromedial thalamus; 6-OHDA, 6-hydroxydopamine. Neuroscience 164 (2009) 360 –369 0306-4522/09 $ - see front matter © 2009 IBRO. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.neuroscience.2009.08.058 360