Intermittent and chronic morphine treatment induces long-lasting changes in δ-opioid receptor-regulated acetylcholine release in rat striatum and nucleus accumbens

Guno H.K. Tjon, Taco J. De Vries, Patrizia Nestby, George Wardeh, Arie H. Mulder, Anton N.M. Schoffelmeer*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Intermittent treatment of rats with morphine (10 mg/kg s.c., once daily) caused an increase (of about 30%) of the electrically evoked release of [14C]acetylcholine from cholinergic interneurons of superfused striatal slices 1-21 days after morphine withdrawal. Similarly, chronic treatment with escalating doses of morphine (5-50 mg/kg s.c., 3 times daily), causing physical dependence (unlike intermittent treatment), resulted in an enduring enhanced response of these neurons towards depolarization. Following chronic morphine treatment this adaptive increase of acetylcholine release was associated with a slight but long-lasting decrease of the (δ-opioid receptor-mediated) maximal inhibitory effect of [Met5]enkephalin, whereas upon intermittent drug treatment δ-opioid receptor desensitization was observed 1 day after opiate withdrawal only. Also in slices of the nucleus accumbens both intermittent as well as chronic morphine administration caused a long-lasting increase of the electrically evoked [14C]acetylcholine release. Therefore, we hypothesize that an enhanced (re)activity of striatal and accumbal cholinergic neurons, which are regulated by dopaminergic neurons of the ventral mesencephalon, may represent a long-lasting neuroadaptive effect of morphine (and possibly other drugs of abuse) playing a crucial role in behavioral sensitization associated with enhanced vulnerability to drugs of abuse.

Original languageEnglish
Pages (from-to)169-176
Number of pages8
JournalEuropean Journal of Pharmacology
Issue number1-3
Publication statusPublished - 5 Sep 1995

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