Journal
NAUNYN-SCHMIEDEBERGS ARCHIVES OF PHARMACOLOGY
Volume 361, Issue 6, Pages 584-589Publisher
SPRINGER
DOI: 10.1007/s002100000244
Keywords
mu-opioid receptor; transgenic mice; locomotor activity; self-administration; nose-poke response; morphine; nor-binaltorphimine
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Morphine-induced place preference was demonstrated recently in wild-type mice, whereas this conditioned behaviour was not observed in mu-opioid receptor-deficient mice. In the present study, we investigated locomotor effects of subcutaneously (s.c.) injected morphine as well as intracerebroventricular (i.c.v.) morphine self-administration in mu-opioid receptor-knockout mice. After s.c. morphine injection, locomotor activity significantly increased in wild-type animals. As expected. in the self-administration test the rate of self-administration constantly increased in wild-type mice reflecting reward effects of morphine. This increase was independent of locomotor/motor activity. In contrast, self-administration rates and locomotor/motor activity significantly decreased in the receptor-deficient animals. It was shown that this aversive effect might partly be due to kappa-opioid receptor interaction.
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