title: Delayed occurrence of enhanced striatal preprodynorphin gene expression in behaviorally sensitized rats: differential long-term effects of intermittent and chronic morphine administration.
abstract: Protracted changes in basal "steady-state" opioid peptide gene expression in the brain may represent adaptations underlying the behavioral effects of drugs of abuse, observed long after drug exposure. Here, we have studied the long-term effects of two distinct regimens of morphine administration ("intermittent" vs "chronic" morphine treatment) on behavioral sensitization and "steady-state" striatal preprodynorphin and preproenkephalin gene expression in rats. Opioid peptide gene expression was investigated using in situ hybridization at three rostrocaudal levels (rostral, intermediate and caudal) of the caudate-putamen and the nucleus accumbens. Behavioral studies showed that the intermittent morphine treatment resulted in a significantly greater enhancement of morphine-induced locomotion than the chronic morphine treatment three weeks after cessation of opiate exposure. The intermittent morphine treatment resulted in an initial decrease of preprodynorphin gene expression of about 5-10% in the caudate-putamen and the nucleus accumbens at the rostral and intermediate levels one day after the last morphine administration. In contrast, a protracted increase of preprodynorphin gene expression of about 20% throughout the caudate-putamen and of about 6% in intermediate sections of the nucleus accumbens was observed 21 days after cessation of intermittent morphine treatment. Although the chronic morphine treatment induced a decrease of preprodynorphin messenger RNA levels one day after the last administration, no significant changes were observed three weeks after cessation of chronic morphine treatment. No long-term changes were observed in preproenkephalin gene expression after either morphine treatment. Since the intermittent morphine administration induced long-term behavioral sensitization much more effectively than the chronic morphine treatment, we tentatively suggest that the protracted increase of preprodynorphin gene expression may play a facilitative role in the long-term character of opiate-induced behavioral sensitization.
authors.affiliation: Research Institute Neurosciences Vrije Universiteit, Faculty of Medicine, Department of Pharmacology, Free University, Amsterdam, The Netherlands.
authors.forename: G H
authors.initials: GH
authors.lastname: Tjon
authors.forename: P
authors.initials: P
authors.lastname: Voorn
authors.forename: L J
authors.initials: LJ
authors.lastname: Vanderschuren
authors.forename: T J
authors.initials: TJ
authors.lastname: de Vries
authors.forename: N H
authors.initials: NH
authors.lastname: Michiels
authors.forename: A J
authors.initials: AJ
authors.lastname: Jonker
authors.forename: H
authors.initials: H
authors.lastname: Klop
authors.forename: P
authors.initials: P
authors.lastname: Nestby
authors.forename: A H
authors.initials: AH
authors.lastname: Mulder
authors.forename: A N
authors.initials: AN
authors.lastname: Schoffelmeer
mesh_terms: D000818:Animals; D001345:Autoradiography; D001522:Behavior, Animal / Q000187:drug effects*; D003342:Corpus Striatum / Q000502:physiology*; D004399:Dynorphins / Q000235:genetics*; D004745:Enkephalins / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects*; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology; D009043:Motor Activity / Q000187:drug effects; D009294:Narcotics / Q000008:administration & dosage* / Q000494:pharmacology; D011498:Protein Precursors / Q000235:genetics*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D004745:Enkephalins; D009294:Narcotics; D011498:Protein Precursors; C036448:pre-prodynorphin; D004399:Dynorphins; D009020:Morphine; C033660:preproenkephalin