Repeated administration of dopaminergic agents in the nucleus accumbens and morphine-induced place preference.
In the present study, the effects of repeated intra nucleus accumbens (intra-NAc) injections of dopamine receptor agents on morphine-induced conditioned place preference (CPP) in rats were investigated by using an unbiased 3-days schedule of place conditioning design. The animals receiving once daily subcutaneous (s.c.) injections of morphine (0.5-7.5mg/kg) or saline (1.0 ml/kg, s.c.) showed a significant place preference in a dose-dependent manner. The maximum response was observed with 5mg/kg of the opioid. Three days intra-NAc injections of apomorphine (0.5 and 1 microg/rat) followed by 5 days free of the drug, increased or decreased, respectively CPP induced by the lower dose of morphine (0.5mg/kg, s.c.). Morphine-induced CPP was also significantly increased in the animals that had previously received the 3-days intra-NAc injections of SKF 38393 (4 and 8 microg/rat) or quinpirole (2 and 4 microg/rat, intra-NAc). The CPP induced by a higher dose of morphine (5mg/kg, s.c.) was significantly decreased in the animals that had previously received the 3-days SCH 23390 (0.005 and 0.01 microg/rat; intra-NAc). On the other hand, the CPP induced by morphine (5mg/kg, s.c.) was significantly increased in the animals that had previously received the 3-days sulpiride administration (5 microg/rat, intra-NAc). The 3-days administration of apomorphine, SKF 38393 or quinpirole, but not SCH 23390 and sulpiride reduced the locomotor activity in the test session. It is concluded that repeated injections of dopamine receptors agents followed by 5 days free of the drugs in the NAc can affect morphine reward.
Department of Pharmacology and Iranian National Center for Addiction Studies, School of Medicine, Tehran University of Medical Sciences, PO Box 13145-784, Tehran, Iran. zarinmr@ams.ac.ir
Mohammad-Reza
MR
Zarrindast
Bibi-Nasrin
BN
Azami
Parvin
P
Rostami
Ameneh
A
Rezayof
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003216:Conditioning, Operant / Q000187:drug effects* / Q000502:physiology; D015259:Dopamine Agents / Q000008:administration & dosage*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004347:Drug Interactions; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009294:Narcotics / Q000494:pharmacology*; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012054:Reinforcement, Psychology
D015259:Dopamine Agents; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D009294:Narcotics; D009020:Morphine