Antiparkinson potential of delta-opioid receptor agonists

delta-Opioid receptors, present in very high concentrations in striatum and overlying cortex, are thought to be involved in a number of processes, inc luding analgesia, mood, reward, modulation of neuronal excitability, and al terations in neurotransmitter release. Given the localization of the recept ors in motor circuits in brain, we thought it of interest to study the anti parkinson potential of delta-opioid receptor agonists. Rats were given unil ateral 6-hydroxydopamine lesions of the nigrostriatal tract, and following recovery, were tested for rotational activity. Tonazocine mesylate is a non peptide, partial delta-opioid receptor agonist with mu-receptor antagonist properties. Tonazocine (0.1-10 mg/kg) evoked a dose-related, ipsilateral ro tation, consistent with augmentation of dopaminergic function on the unlesi oned side. The rotation evoked by tonazocine was blocked by the selective d elta-opioid receptor antagonist naltrindole, suggesting that the effect was mediated by delta-opioid receptors. The full delta-opioid receptor agonist (+)-4-[9-alpha-R)-alpha-(2S,5RO-4-allyl-2,5-dimethyl-1-piperaziny-1)-3- me thoxybenzyl]-N,N-diethylbenzamide (SNC-80) produced both contralateral and ipsilateral rotation. Tonazocine additionally augmented the effects of L-3, 4 dihydroxyphenylalanine (L-DOPA) on reserpine-induced suppression of motor activity. Binding affinities and efficacies of tonazocine and SNC-80 again st mu-, kappa-, and delta-opioid receptors were also confirmed and compared to standards. These data suggest therapeutic potential of agents interacti ng with delta-opioid receptors, and indicate some differences in the activi ties of tonazocine and SNC-80. (C) 2000 Elsevier Science B.V. All rights re served.