As drug abuse can be viewed as a maladaptive form of neuronal plasticity, attention has focused on defining the synaptic plasticity mechanisms that mediate the long-term effects of these drugs. As Narp is secreted at synaptic sites and binds to the extracellular surface of AMPA receptors, it has been implicated in mediating enduring forms of synaptic plasticity. Accordingly, to assess its potential role in the long-lasting behavioral effects of drugs of abuse, we have investigated the impact of Narp deletion on sustained behavioral responses elicited by repeated morphine administration. Narp knockout mice display normal locomotor sensitization and conditioned place preference, but are markedly resistant to extinction of place preference. Thus, these findings indicate that Narp plays a selective role in extinction, possibly by its effects on AMPA receptor trafficking.

Although long-lasting effects of drug withdrawal are thought to play a key role in motivating continued drug use, the mechanisms mediating this type of drug-induced plasticity are unclear. As Narp is an immediate early gene product that is secreted at synaptic sites and binds to AMPA receptors, it has been implicated in mediating enduring forms of synaptic plasticity. In previous studies, we found that Narp is selectively induced by morphine withdrawal in the extended amygdala, a group of limbic nuclei that mediate aversive behavioral responses. Accordingly, in this study, we evaluated whether long-term aversive effects of morphine withdrawal are altered in Narp KO mice. We found that acute physical signs of morphine withdrawal are unaffected by Narp deletion. However, Narp KO mice acquire and sustain more aversive responses to the environment conditioned with morphine withdrawal than WT controls. Paradoxically, Narp KO mice undergo accelerated extinction of this heightened aversive response. Taken together, these studies suggest that Narp modulates both acquisition and extinction of aversive responses to morphine withdrawal and, therefore, may regulate plasticity processes underlying drug addiction.