Modulation of the mTOR pathway in male Lewis rats after morphine self-administration and subsequent extinction training

Addiction is a chronic disorder with an elevated risk of relapse, even after long periods of abstinence. Some of the neural mechanisms mediating addictions require protein synthesis, which could be relevant for the development of more effective treatments. The mTOR signaling pathway regulates protein synthesis processes that have recently been linked to the development of drug addiction. Thus, we have assessed the effects of morphine self-administration and its subsequent extinction on the expression of several genes that act in this pathway, and on the levels of some phosphoproteins in three brain areas related to reward learning and extinction: the amygdala, the nucleus accumbens, and the prefrontal cortex. We found an increase in Raptor and Eif4ebp2 gene expression in the amygdala of rats that self-administered morphine, and this persisted beyond the extinction period. The expression of Insr in the amygdala of control animals decreased over time while the opposite effect was seen in the rats that self-administered morphine. We also found a strong correlation between some of the biochemical variables measured and behavioral traits, suggesting a significant role for the genes and phosphoproteins identified, mostly in the amygdala, in the behavioral effects of morphine.