Morphine induced alterations in NMDA receptor subunit expression

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DESCRIPTION (provided by applicant): Opioids are a mainstay of modern pain therapy, yet opioid abuse has a significant negative impact on the abuser and society. It is estimated that 21% of currently incarcerated individuals are in prison because of drug related crimes. The cost to incarcerate these individuals is tens of billions of dollars per year. Since only a small percentage of opioid use results in abuse it is likely that there are some distinguishing molecular factors that may predispose an individual to opioid abuse. This project will investigate morphine induced alterations in N-methyl-D-aspartate (NMDA) receptors as one potential mechanism for predisposition to opioid abuse. NMDA receptors are intimately entwined in the processes of tolerance, withdrawal and addiction to opioids. NMDA antagonists can suppress these adverse effects of opioids. However, a single dose of an opioid is insufficient to induce significant tolerance, withdrawal or addiction indicating that time is required for some change in the NMDA receptors or neuronal circuitry to occur in order to observe these sequelae. We have found that the NR1 and NR2 subunits of NMDA receptors are highly susceptible to alterations as a result of changes in neuronal activity and that these changes in NMDA receptors may persist for an extended period of time. The altered NMDA receptors have a profound effect on behavior. Thus we hypothesize that there are changes in the splicing of NR1 subunits and changes in NR2 subunits that are induced in various regions of the CNS by morphine or morphine withdrawal. We further hypothesize that some individuals may retain these altered or "disease state" NMDA receptors long after withdrawal of the opioid, which may result in prolonged tolerance or withdrawal signs and increased susceptibility to opioid abuse. In this project we will evaluate the effects of morphine and morphine withdrawal on NR1 splice variants and NR2 subunits in various regions of the rat CNS. We will also determine if these changes persist for up to 16 weeks following the withdrawal of morphine. The NR1 and NR2 proteins will be evaluated by western blots and two-dimensional western blots and the data will be correlated to behavior in two nociceptive assays. If the data indicate that some individuals retain the disease state NMDA receptors techniques could be devised to reverse the NMDA receptor changes in an attempt to reduce the abuse susceptibility of these individuals. PUBLIC HEALTH RELEVANCE: N-methyl-D-aspartate (NMDA) receptor antagonists suppress tolerance and addiction to opioids. This project will determine if morphine treatment alters NMDA receptor subunit expression within the CNS and determine if these changes persist in a subgroup of rats. These data could provide clues to novel treatments or novel methods to prevent opioid abuse.