The neuroleptic-like peptide desenkephalin-gamma-endorphin does not antagonize the dopamine receptor agonist-induced inhibition of the release of [3H]dopamine from rat nucleus accumbens slices in vitro.
In rats, the non-opioid beta-endorphin (beta E) fragment desenkephalin-gamma-endorphin (DE gamma E, beta E6-17) antagonizes the hypomotility induced by a small dose of dopamine (DA) receptor agonists. It has been suggested that DE gamma E might act in this respect by a direct or indirect blockade of presynaptically located DA receptors in the nucleus accumbens, thereby causing an increase of DA release. Therefore in the present study the effect of DE gamma E was examined on DA receptor agonist-induced inhibition of the electrically evoked release of previously accumulated [3H]DA from rat nucleus accumbens slices in vitro. The DA receptor agonists apomorphine, LY 171555 and n,n-di-n-propyl-7-hydroxy-2-aminotetralin (DP-7-AT) inhibited in a concentration-dependent manner the electrically evoked release of [3H]DA. The selective D2 receptor antagonist (-)-sulpiride blocked the effects of apomorphine, corroborating that the DA receptor involved is of a D2 type. DE gamma E was tested at several concentrations (10(-9)-10(-6) M) and under various experimental conditions. DE gamma E, by itself, did not affect either the electrically stimulated or the basal release of [3H]DA. The inhibiting effect of DA receptor agonists was slightly reduced by DE gamma E, but this effect was present in some experiments only. It is concluded that DE gamma E does not function as an antagonist for the DA receptor mediating DA release and that the interaction observed in behavioural experiments between DA agonists and DE gamma E does not occur at the level of this receptor.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D004873:Ergolines / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009714:Nucleus Accumbens / Q000187:drug effects / Q000502:physiology*; D019257:Quinpirole; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects / Q000502:physiology*; D012686:Septal Nuclei / Q000502:physiology*; D014316:Tritium; D001615:beta-Endorphin / Q000494:pharmacology*
D004873:Ergolines; D011954:Receptors, Dopamine; D014316:Tritium; D019257:Quinpirole; D001615:beta-Endorphin; C033558:des-enkephalin-gamma-endorphin; D001058:Apomorphine; D004298:Dopamine