Naloxone precipitated morphine withdrawal and clock genes expression in striatum: A comparative study in three different protocols for the development of morphine dependence

The present study has been designed to do a comparative study on the morphine treatment protocols for the development of morphine dependence. We have selected three different previously reported chronic morphine treatment protocols where mice were treated with different doses of morphine for different time intervals of varied number of days to develop morphine dependence. At first, animals were divided into four groups: control or saline treated and three morphine treated groups. Then we determined the differences in naloxone precipitated withdrawal behaviors and checked the expression level of the circadian clock genes in striatum. In addition we examined the level of pERK in brain tissues from cortex, hippocampus and striatum regions. Our studies showed differences in the severity of naloxone precipitated withdrawal behaviors in the three protocols. A significant increase of Period 2 gene was found in one of the morphine treated group which was absent in the animals subjected to other morphine dose regimen. Increased pERK was observed in the hippocampus of two morphine treated groups. These results support that the differences in the level of morphine dependence may not only reflect in somatic withdrawal behaviors but also have an impact on both naloxone precipitated ERK phosphorylation and clock gene expressions. Hence it can be stated that choice of chronic morphine treatment protocol may influence the research outcomes.