Effect of the endogenous kappa opioid agonist dynorphin A(1-17) on cocaine-evoked increases in striatal dopamine levels and cocaine-induced place preference in C57BL/6J mice.
BACKGROUND
Effects of synthetic kappa opioid receptor agonists on cocaine-induced reward have been studied extensively in rats but relatively few studies have used the endogenous kappa agonist dynorphin A(1-17).


OBJECTIVE
Three studies were conducted to examine the effect of the natural sequence dynorphin on cocaine-induced increases in dopamine, on the formation of conditioned place preference and on increases in locomotor activity in C57BL/6 J mice.


METHODS
After implantation of guide cannulae into the caudate putamen, mice were allowed 4-5 days to recover from surgery. In the first study, dynorphin A (0, 1, 2, 4.4 nmol) was infused into the caudate putamen and dopamine levels were measured by in vivo microdialysis in that brain region. Then, the effect of dynorphin A (4.4 nmol) on increases in dopamine levels induced by 15 mg/kg cocaine i.p. was also measured with in vivo microdialysis. The third experiment examined the effect of dynorphin A (4.4 nmol) on conditioned place preference and locomotion induced by 15 mg/kg cocaine.


RESULTS
Dynorphin A significantly decreased basal dopamine levels in a dose-dependent manner by more than 60% at the highest dose, and this effect was completely blocked by pre-injection of the kappa-opioid receptor antagonist nor-BNI (10 mg/kg). The highest dose of dynorphin (4.4 nmol) blocked increases in dopamine levels, the formation of conditioned place preference and attenuated locomotion induced by 15 mg/kg cocaine.


CONCLUSIONS
The blockade of the cocaine-induced rise in striatal dopamine may contribute to both dynorphin's ability to prevent the development of cocaine-induced conditioned place preference and to attenuate the increase in locomotor activity.
Zhang
Yong
Y
The Laboratory of the Biology of Addictive Diseases, The Rockefeller University, 1230 York Avenue, Box 171, New York, NY 10021, USA. zhangyo@rockvax.rockefeller.edu
Butelman
Eduardo R
ER
Schlussman
Stefan D
SD
Ho
Ann
A
Kreek
Mary Jeanne
MJ
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003042:Cocaine / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects*; D004298:Dopamine / Q000378:metabolism*; D004399:Dynorphins / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D017551:Microdialysis; D009043:Motor Activity / Q000187:drug effects*; D017072:Neostriatum / Q000378:metabolism*; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D012201:Reward
D017473:Receptors, Opioid, kappa; D004399:Dynorphins; D003042:Cocaine; D004298:Dopamine