Loss of β-arrestin2 in D2 cells alters neuronal excitability in the nucleus accumbens and behavioral responses to psychostimulants and opioids

Psychostimulants and opioids increase dopamine (DA) neurotransmission, activating D1 and D2 G protein-coupled receptors. β-arrestin2 (βarr2) desensitizes and internalizes these receptors and initiates G protein-independent signaling. Previous work revealed that mice with a global or cell-specific knockout of βarr2 have altered responses to certain drugs; however, the effects of βarr2 on the excitability of medium spiny neurons (MSNs) and its role in mediating the rewarding effects of drugs of abuse are unknown. D1-Cre and D2-Cre transgenic mice were crossed with floxed βarr2 mice to eliminate βarr2 specifically in cells containing either D1 (D1βarr2-KO) or D2 (D2βarr2-KO) receptors. We used slice electrophysiology to characterize the role of βarr2 in modulating D1 and D2 nucleus accumbens MSN intrinsic excitability in response to DA and tested the locomotor-activating and rewarding effects of cocaine and morphine in these mice. We found that eliminating βarr2 attenuated the ability of DA to inhibit D2-MSNs but had little effect on the DA response of D1-MSNs. While D1βarr2-KO mice had mostly normal drug responses, D2βarr2-KO mice showed dose-dependent reductions in acute locomotor responses to cocaine and morphine, attenuated locomotor sensitization to cocaine, and blunted cocaine reward measured with conditioned place preference. Both D2βarr2-KO and D1βarr2-KO mice displayed an enhanced conditioned place preference for the highest dose of morphine. These results indicate that D2-derived βarr2 functionally contributes to the ability of DA to inhibit D2-MSNs and multiple behavioral responses to psychostimulants and opioids, while loss of βarr2 in D1 neurons has little impact on D1-MSN excitability or drug-induced behaviors.