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| Paper IPM / Cognitive Sciences / 8959 |
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| Abstract: | |||||||
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In the present study, the effects of bilateral intra-ventral tegmental area (intra-
VTA) injections of an anticholinesterase, physostigmine and/or muscarinic
acetylcholine receptor antagonist, atropine on memory retention and morphine
state-dependent learning were examined in adult male Wistar rats. As a model of
learning, a step-through passive avoidance task was used. Post-training
subcutaneous administration of morphine (0.5, 2.5 and 5 mg/kg) dosedependently
impaired memory retrieval on the test day. Pre-test administration of
morphine (2.5 and 5 mg/kg) induced state-dependent retrieval of the memory
acquired under post-training morphine influence. Pre-test intra-VTA
microinjection of physostigmine (0.5, 1 and 2 μg/ rat) or atropine (1, 2 and 3
μg/rat) alone cannot affect memory retention. Interestingly, pre-test intra-VTA
administration of physostigmine (1 and 2 μg/rat) reversed post-training morphine
(5 mg/kg, s.c.)-induced retrieval impairment. Furthermore, pre-test intra-VTA
microinjection of physostigmine (1 and 2 μg/rat) with an ineffective dose of
morphine (0.5 mg/kg), synergistically improved memory performance impaired by
post-training morphine. On the other hand, pre-test intra-VTA microinjection of
atropine (2 and 3 μg/rat) 5 min before the administration of morphine (5 mg/kg,
s.c.) dose-dependently inhibited morphine statedependent memory. Pre-test
atropine microinjection also reversed the influence of physostigmine on morphine
response. It may be concluded that the muscarinic acetylcholine receptors of the
VTA play an important role in morphine-induced recovery of memory, on the test
day.
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