The novel delta opioid receptor agonist UFP-512 dually modulates motor activity in hemiparkinsonian rats via control of the nigro-thalamic pathway.
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.
Mabrouk
O S
OS
Department of Experimental and Clinical Medicine, Section of Pharmacology, University of Ferrara, via Fossato di Mortara 17-19, 44100 Ferrara, Italy.
Marti
M
M
Salvadori
S
S
Morari
M
M
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D000978:Antiparkinson Agents / Q000008:administration & dosage / Q000494:pharmacology*; D001562:Benzimidazoles / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005917:Globus Pallidus / Q000187:drug effects / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009434:Neural Pathways / Q000187:drug effects / Q000378:metabolism; D009842:Oligopeptides / Q000008:administration & dosage / Q000494:pharmacology*; D016627:Oxidopamine; D020734:Parkinsonian Disorders / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017465:Receptors, Opioid, delta / Q000819:agonists / Q000037:antagonists & inhibitors; D013378:Substantia Nigra / Q000187:drug effects* / Q000378:metabolism; D013788:Thalamus / Q000187:drug effects* / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
C526539:2',6'-dimethyltyrosyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (1H-benzimidazol-2-yl)(carboxymethyl)methylamide; D000596:Amino Acids; D000978:Antiparkinson Agents; D001562:Benzimidazoles; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D009271:Naltrexone; D016627:Oxidopamine; C055382:naltrindole