Involvement of the ventral tegmental area (VTA) in morphine-induced memory retention in morphine-sensitized rats.
In the present study, the effects of intra-ventral tegmental area (VTA) injections of morphine on memory retention of a one-trial passive avoidance task have been investigated in morphine-sensitized rats. Retrieval was examined 24h after training and used as memory retention. Sensitization was obtained by subcutaneous (s.c.) injections of morphine, once daily for 3 and 5 days free of the opioid before training. Post-training administration of the both systemic (2.5, 5 and 7.5mg/kg, s.c.) and intra-VTA (5 and 7.5microg/rat) of morphine, dose-dependently decreased memory retention. The response induced by post-training administration of intra-VTA morphine (7.5microg/rat) was significantly reversed in morphine-sensitized rats. The inhibition of morphine-induced amnesia in morphine-sensitized rats was decreased by once daily injections of naloxone (0.5, 1 and 2mg/kg, s.c.), SCH 23390 (0.025, 0.05 and 0.1mg/kg, s.c.) or sulpiride (25, 50 and 100mg/kg, s.c.), during the sensitization. The results suggest that VTA has an important role in morphine-induced amnesia and morphine sensitization affects this process through opioid and dopamine receptors.
Zarrindast
Mohammad-Reza
MR
Department of Pharmacology and Iranian National Center for Addiction Studies, Tehran University of Medical Sciences, P.O. Box 13145-784, Tehran, Iran. zarinmr@ams.ac.ir
Farajzadeh
Zahra
Z
Rostami
Parvin
P
Rezayof
Ameneh
A
Nourjah
Parvaneh
P
D000647:Amnesia / Q000139:chemically induced*; D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance / Q000502:physiology; D008297:Male; D008568:Memory / Q000187:drug effects*; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage*; D009294:Narcotics / Q000008:administration & dosage*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects; D017557:Ventral Tegmental Area / Q000187:drug effects*
D009294:Narcotics; D009020:Morphine