In the present study, we investigated the effects of pre-treatment with morphine on impairment of spatial memory acquisition induced by intra dorsal hippocampus (intra-CA1) administration of the non-selectivecannabinoid CB1/CB2 receptor agonist, WIN55,212-2 in adult male rats. 2-day version of Morris water maze task has been used for the assessment of spatial memory. On the training day, rats were trained by a single training session of eight trials and 24h later a probe trial test consist of 60 s free swim period without a platform and the visible test was administered. Rats received pre-treatment subcutaneous (s.c.) injections of morphine, once daily for three days followed by five days drug-free treatment before training trials. The results indicated that bilateral pre-training intra-CA1 infusions of WIN55,212-2 (0.25 and 0.5μg/rat) impaired acquisition of spatial memory on the training and test day. The amnesic effect of WIN55, 212-2 (0.5μg/rat) was prevented in rats previously injected with morphine (20mg/kg/day×3 days, S.C.). Improvement in spatial memory acquisition in morphine-pretreated rats was inhibited by once daily administration of naloxone (1 and 2mg/kg, s.c.) 15min prior to injection of morphine for three days. The results suggest that sub-chronic morphine treatment may produced sensitization to cannabinoids, which in turn reversed the impairment of spatial memory acquisition induced by WIN55,212-2 and mu- opioid receptors may play an important role in this effect.
Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

PMID:

 

23912031

 

[PubMed – as supplied by publisher]