Conditioned drug reward enhances subsequent spatial learning and memory in rats.
BACKGROUND
Chronic exposure to drugs of abuse alters neural processes that normally promote learning and memory. A context that is repeatedly paired with reinforcing drugs will acquire secondary reinforcing properties (conditioned reward). However, the effects of conditioned reward on spatial learning are unknown.


OBJECTIVE
Using the conditioned place preference procedure and Morris water maze task, we examined the role of conditioned reward or aversion in spatial learning.


METHODS
Groups of rats acquired morphine (10 mg/kg), cocaine (10 mg/kg), or oral sucrose (15%) conditioned place preference (CPP). Another group of morphine-dependent rats acquired conditioned place aversion (CPA) to a context paired with precipitated opiate withdrawal induced by naloxone injections (1 mg/kg). To examine the role of conditioned reward or aversion in spatial learning, rats were then exposed to the previously morphine-, cocaine-, sucrose- or naloxone-paired context for 10 min before training of spatial learning in the Morris water maze.


RESULTS
Exposure to the morphine- or cocaine-paired but not the sucrose- or the naloxone-paired context decreased the latency to find the platform in the Morris water maze test.


CONCLUSIONS
Our results provide the first evidence that conditioned drug reward promotes spatial learning. We speculate that this enhancement of spatial learning by the drug-paired context may promote contextual-cue-induced relapse to drug taking by facilitating exploratory drug-seeking behaviors.
Zhai
Hai-feng
HF
Department of Neuropharmacology, National Institute on Drug Dependence, Peking University, 38, Xue Yuan Road, HaiDian District, Beijing 100083, China.
Zhang
Zhang-Yin
ZY
Zhao
Mei
M
Qiu
Yi
Y
Ghitza
Udi E
UE
Lu
Lin
L
D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D003042:Cocaine / Q000008:administration & dosage / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects*; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008568:Memory / Q000187:drug effects*; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D009294:Narcotics / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D013037:Spatial Behavior / Q000187:drug effects*
D009292:Narcotic Antagonists; D009294:Narcotics; D009270:Naloxone; D009020:Morphine; D003042:Cocaine