The molecular mechanisms of morphine addiction.

Addiction to opiates such as morphine is a major public health concern. A more thorough understanding of the molecular mechanisms of opiate addiction can lead to better treatment options in the future. Many of the changes in neuronal activity that occur upon morphine exposure have been known for some time, but until recently, little was known about the changes in gene expression that underlie these effects. Recent advances in molecular biology such as microarray analysis and quantitative (real time) PCR have allowed us to examine the gene expression changes that occur in response to morphine treatments and during morphine withdrawal. This review summarizes many of the known molecular and cellular actions of morphine, and some of the important gene expression changes that occur in response to morphine treatment. Many of these gene expression changes underlie the alterations in neuronal excitability, cell morphology and cell birth or death responsible for producing morphine's rewarding effects, the development of dependence, and withdrawal symptoms after treatment ends.