Repeated morphine treatment influences operant and spatial learning differentially.
OBJECTIVE
To investigate whether repeated morphine exposure or prolonged withdrawal could influence operant and spatial learning differentially.


METHODS
Animals were chronically treated with morphine or subjected to morphine withdrawal. Then, they were subjected to two kinds of learning: operant conditioning and spatial learning.


RESULTS
The acquisition of both simple appetitive and cued operant learning was impaired after repeated morphine treatment. Withdrawal for 5 weeks alleviated the impairments. Single morphine exposure disrupted the retrieval of operant memory but had no effect on rats after 5-week withdrawal. Contrarily, neither chronic morphine exposure nor 5-week withdrawal influenced spatial learning task of the Morris water maze. Nevertheless, the retrieval of spatial memory was impaired by repeated morphine exposure but not by 5-week withdrawal.


CONCLUSIONS
These observations suggest that repeated morphine exposure can influence different types of learning at different aspects, implicating that the formation of opiate addiction may usurp memory mechanisms differentially.
Wang
Mei-Na
MN
Key Laboratory of Animal Models and Human Disease Mechanisms, Laboratory of Learning and Memory, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, and Graduate School of Chinese Academy of Sciences, Beijing 100039, China.
Dong
Zhi-Fang
ZF
Cao
Jun
J
Xu
Lin
L