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| Paper IPM / Cognitive Sciences / 8820 |
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| Abstract: | |||||||||||
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In the present study, the effects of intra-ventral tegmental area injections
of cholinergic agents on morphine-induced conditioned place preference were
investigated by using an unbiased 3-day schedule of place conditioning design in
rats. The conditioning treatments with subcutaneous injections of morphine (0.5?
7.5 mg/kg) induced a significant dose-dependent conditioned place preference
for the drug-associated place. Intra-ventral tegmental area injection of an
anticholinesterase, physostigmine (2.5 and 5 g/rat) or nicotinic acetylcholine
receptor agonist, nicotine (0.5 and 1 g/rat) with an ineffective dose of morphine
(0.5 mg/kg) elicited a significant conditioned place preference. Furthermore,
intraventral tegmental area administration of muscarinic acetylcholine receptor
antagonist, atropine (1?4 g/rat) or nicotinic acetylcholine receptor antagonist,
mecamylamine (5 and 7.5 g/rat) dose-dependently inhibited the morphine (5
mg/kg)-induced place preference. Atropine or mecamylamine reversed the effect
of physostigmine or nicotine on morphine response respectively. The injection of
physostigmine, but not atropine, nicotine or mecamylamine, into the ventral
tegmental area alone produced a significant place aversion. Moreover, intraventral
tegmental area administration of the higher doses of physostigmine or
atropine, but not nicotine or mecamylamine decreased the locomotor activity.
We conclude that muscarinic and nicotinic acetylcholine receptors in the ventral
tegmental area may critically mediate the rewarding effects of morphine.
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