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| Paper IPM / Cognitive / 12171 |
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| Abstract: | |||||||
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In the present study, the effects of morphine treatment upon reduction of memory consolidation by posttraining
administration of the non-selective cannabinoid CB1/CB2 receptor agonist, WIN55,212-2, into
the dorsal hippocampus (intra-CA1) have been investigated in rats. Step-through inhibitory avoidance
apparatus was used to test memory retrieval, which was made of two white and dark compartments. In
training day, electric shocks were delivered to the grid floor of the dark compartment. On the test day, the
animal was placed in the white compartment and allowed to enter the dark compartment. The latency
with which the animal crossed into the dark compartment was recorded as memory retrieval. Morphine
was injected subcutaneously (S.C.), once daily for three days, followed by a five day morphine-free period
before training. Bilateral post-training intra-CA1 infusions of WIN55,212-2 (0.25 and 0.5g/rat) shortened
the step-through latency, which suggested impaired memory consolidation. The deleterious effect
of WIN55,212-2 (0.5g/rat) was prevented in rats previously injected with morphine (10 mg/kg/day�3
days, S.C.). Prevention of the WIN55,212-2-induced amnesic-like effect was counteracted by the mureceptor
antagonist, naloxone, and the dopamine D2 receptor antagonist, sulpiride, but not by the D1
receptor antagonist, SCH 23390, when administered prior to each morphine injection. The results have
suggested that subchronic morphine treatment may cause mu-opioid and D2 receptor sensitization,
which in turn prevents impairment of memory consolidation induced by WIN55,212-2.
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