title: D-amphetamine-like stimulus properties are produced by morphine injections into the ventral tegmental area but not into the nucleus accumbens.
abstract: We investigated whether injections of morphine into the ventral tegmental area (VTA) or the nucleus accumbens (NAS) could produce amphetamine-like stimulus properties and locomotor stimulant effects. Rats were trained to discriminate 1.0 mg/kg D-amphetamine from saline using both VI-30 and FR-16 reinforcement schedules and they were then tested following bilateral injections of morphine sulfate (2.5, 5.0 and 10.0 micrograms/side) either into the VTA or the NAS. Intra-VTA injections of morphine produced significant increases in amphetamine-lever responding that were comparable to increases observed following intra-NAS D-amphetamine (2.5, 5.0 and 10.0 micrograms/side). Such increases were not observed, however, following intra-NAS injections of morphine. Tests for the effects of intracerebral morphine and D-amphetamine on locomotor activity produced a similar pattern of results. Locomotor activity was increased following intra-VTA morphine and intra-NAS D-amphetamine injections, but not after intra-NAS morphine injections. Together, these findings indicate that activation of opioid receptors within the VTA, but not the NAS, can produce a behavioral state which mimics to some degree the state produced by systemic and intra-NAS injections of D-amphetamine.
authors.affiliation: Department of Psychology, Concordia University, Montreal, Que., Canada.
authors.forename: J P
authors.initials: JP
authors.lastname: Druhan
authors.forename: S E
authors.initials: SE
authors.lastname: Deschamps
authors.forename: J
authors.initials: J
authors.lastname: Stewart
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D003463:Cues; D003913:Dextroamphetamine / Q000494:pharmacology*; D004193:Discrimination Learning / Q000187:drug effects / Q000502:physiology; D004192:Discrimination, Psychological / Q000187:drug effects; D004298:Dopamine / Q000378:metabolism / Q000502:physiology; D005795:Generalization, Stimulus / Q000187:drug effects; D007267:Injections; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000502:physiology; D009714:Nucleus Accumbens / Q000502:physiology*; D051381:Rats; D017450:Receptors, Opioid, mu / Q000378:metabolism; D012055:Reinforcement Schedule; D017557:Ventral Tegmental Area / Q000502:physiology*
chemical_list: D017450:Receptors, Opioid, mu; D009270:Naloxone; D009020:Morphine; D001058:Apomorphine; D003913:Dextroamphetamine; D004298:Dopamine