The Journal of Neuroscience, March 1, 2002, 22(5):2005-2011
Deletion of CCK2 Receptor in Mice Results in an
Upregulation of the Endogenous Opioid System
Blandine
Pommier1,
Françoise
Beslot1,
Axelle
Simon1,
Matthieu
Pophillat1,
Toshimitsu
Matsui2,
Valérie
Dauge1,
Bernard P.
Roques1, and
Florence
Noble1
1 Département de Pharmacochimie Moléculaire
et Structurale, Institut National de la Santé et de la Recherche
Médicale U266-Centre National de la Recherche Scientifique
Unité Mixte de Recherche 8600, Unité de Formation et de
Recherche des Sciences Pharmaceutiques et Biologiques, 75270 Paris
Cedex 06, France, and 2 Third Division Department of
Medecine, Kobe University School of Medecine, Chuo-ku Kobe 650-0017, Japan
Stimulation of the brain CCK2 receptor by the
C-terminal octapeptide CCK8 of cholecystokinin (CCK)
negatively modulates opioid responses. This suggests the existence of
physiologically relevant interactions between endogenous CCK and opioid
peptides, opening new perspectives particularly in the treatment of
pain or drug addiction. CCK2 receptor-deficient mice were
used to analyze the incidence of this gene invalidation on opioid
system. Compared with wild-type mice, mutants exhibited the following:
(1) a hypersensitivity to the locomotor activity induced by inhibitors
of enkephalin catabolism or by morphine; (2) a spontaneous hyperalgesia
to thermal nociceptive stimulus, which was reversed by previous
administration of the NMDA antagonist MK-801
[(+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine
maleate], and a large reduction in analgesic effects of
endogenous or exogenous opioids; and (3) a more severe withdrawal
syndrome after chronic morphine treatment. As expected, stimulation of
µ,
, and D2 receptors on brain tissue of
wild-type animals induced a dose-dependent decrease in adenylate cyclase activity, whereas a striking mirror effect was observed in
mutants. All of these results suggest that the absence, in knock-out
mice, of the negative feedback control on the opioid system, normally
performed out by CCK2 receptor stimulation, results in an
upregulation of this system. These biochemical and pharmacological results demonstrate the critical role played by CCK2
receptors in opioid-dependent responses.
Key words:
cholecystokinin; opioid; mutant mice; adenylyl cyclase; binding; behavior
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