Protein receptor for activated C kinase 1 is involved in morphine reward in mice.

Opiate addiction is associated with upregulation of cAMP signaling in the brain. cAMP-responsive element binding protein (CREB), a nuclear transcription factor, is a downstream component of the extracellular signal-regulated protein kinase (ERK) pathway, which has been shown to regulate different physiological and psychological responses of drug addiction. RACK1, the protein receptor for activated C kinase 1, is a multifunctional scaffolding protein known to be a key regulator of various signaling cascades in the CNS. RACK1 functions specifically in integrin mediated activation of ERK cascade and targets active ERK. We examined if RACK1 is involved in the mechanism of drug addiction by regulating CREB in mouse hippocampus and prefrontal cortex. Several expressions were observed. Chronic administration of morphine made the expression of RACK1 and CREB mRNA increase in hippocampus and prefrontal cortex. The expression of RACK1 and CREB protein was strongly positive in CA1, CA3 and dentate gyrus (DG) of the hippocampus of morphine-treated mice brain, especially the pyramidal neurons in the DG of the hippocampus. Using the small interfering RNA technology, we determined that the expression of CREB mRNA was decreased in hippocampus and prefrontal cortex of morphine-treated mice. The expression of RACK1 and CREB protein was negative in CA1, CA3 and DG of hippocampus. These findings suggest that morphine reward can influence the expression of RACK1 in mouse hippocampus and prefrontal cortex through regulating CREB transcription.