Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology
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Neuropsychopharmacology · Feb 2003
Enhanced morphine preference following prolonged abstinence: association with increased Fos expression in the extended amygdala.
We previously found that chronically morphine-pretreated, abstinent rats show stronger preferences for morphine-associated environments than placebo-pretreated rats. Here we show that this increased preference persisted for at least 5 weeks after withdrawal of chronic morphine. To determine brain regions involved in this behavior, we examined neural activation (as indexed by Fos-like proteins) induced by a morphine-conditioned place preference test. ⋯ Chronically morphine-pretreated (M) rats that exhibited enhanced morphine preference 5 weeks after morphine withdrawal showed significantly greater Fos in all the same areas except the BNST-DL relative to conditioned P or nonconditioned M rats. Place preference measures and Fos expression were positively correlated in the Cg and ABL, for conditioned P animals, and in the Cg, ABL and BNST-VL for conditioned M animals. These results indicate a relationship between place preference behavior and neural indices of activation in the forebrain in response to morphine-conditioned cues that may be chronically modulated by prior morphine exposure.