Beta-Arrestin 1 Regulation Of Rewardmotivated Behaviors And Glutamatergic Function

The two highly homologous non-visual arrestins, beta-arrestin 1 and 2, are ubiquitously expressed in the central nervous system, yet knowledge of their disparate roles is limited. While beta-arrestin 2 (beta arr2) has been implicated in several aspects of reward-related learning and behavior, very little is known about the behavioral function of beta-arrestin 1 (beta arr1). Using mice lacking beta arr1, we focused on the role of this scaffolding and signal transduction protein in reward-motivated behaviors and in striatal glutamatergic function. We found that beta arr1 KO mice were both slower in acquiring cocaine self-administration and in extinguishing this behavior. They also showed deficits in learning tasks supported by a natural food reward, suggesting a general alteration in reward processing. We then examined glutamatergic synaptic strength in WT and KO medium spiny neurons (MSNs) of the Nucleus Accumbens (NAc) shell in naive animals, and from those that underwent cocaine selfadministration. An increase in the AMPA/NMDA (A/N) ratio and a relative lack of GluN2Benriched NMDARs was found in naive KO vs WT MSNs. Applying Lim Domain Kinase (LIMK1), the kinase that phosphorylates and inactivates cofilin, to these cells, showed that both beta arr1 and LIMK regulate the A/N ratio and GluN2B-NMDARs. Cocaine self-administration increased the A/N ratio and GluN2B-NMDARs in WT MSNs and, although the A/N ratio also increased in KO MSNs, this was accompanied by fewer GluN2B-NMDARs and an appearance of calcium-permeable AMPARs. Finally, to examine the consequences of reduced basal GluN2B-NMDARs in reward-processing seen in KO mice, we chronically infused ifenprodil, a GluN2B antagonist, into the NAc shell of WT mice. This intervention substantially reduced food-motivated behavior. Together these findings identify a previously unknown role of beta arr1 in regulating specific reward-motivated behaviors and glutamatergic function.