Motivational properties of opioids: evidence that an activation of delta-receptors mediates reinforcement processes.
The role of central delta-opioid receptors in the mediation of opioid reinforcement and endogenous reward processes was examined using a non-biased place-preference conditioning procedure. Intracerebroventricular (i.c.v.) administration of the selective delta-receptor agonist, [D-Pen2, D-Pen5]-enkephalin (DPDPE, 10.0-25.0 micrograms) produced a significant preference for the drug-associated place and a similar effect was observed following i.c.v. injections of morphine (10.0 micrograms). Administration of the delta-receptor antagonist, ICI 174,864, at doses (1.0-5.0 micrograms, i.c.v.) which had no aversive effects when tested alone, abolished the reinforcing properties of DPDPE. Such treatment did not, however, modify the effect of morphine. These findings demonstrate the involvement delta- as well as mu-receptors in the motivational properties of opioids and suggest that the activation of either receptor type is sufficient for the elicitation of appetitively reinforcing effects.
Shippenberg
T S
TS
Department of Neuropharmacology, Max-Planck-Institut für Psychiatrie, Planegg-Martinsried, F.R.G.
Bals-Kubik
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R
Herz
A
A
D000818:Animals; D001070:Appetitive Behavior / Q000187:drug effects; D001362:Avoidance Learning / Q000187:drug effects; D020881:Enkephalin, D-Penicillamine (2,5)-; D004743:Enkephalin, Leucine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004745:Enkephalins / Q000008:administration & dosage / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009042:Motivation / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D017465:Receptors, Opioid, delta; D012054:Reinforcement, Psychology
D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D004743:Enkephalin, Leucine; D009020:Morphine; D020881:Enkephalin, D-Penicillamine (2,5)-; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine