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Involvement of the ventral tegmental area (VTA) in morphine-induced memory retention in morphine-sensitized rats.

Zarrindast MR, Farajzadeh Z, Rostami P, Rezayof A, Nourjah P

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

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.

Published 18 July 2005 in Behav Brain Res, 163(1): 100-6.
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