Abstract
The orphan receptor GPR88 is highly expressed in D1R- and D2R-medium spiny neurons (MSNs) and has been associated to striatum-dependent functions in rodents. The total deletion of Gpr88 in mice was shown to decrease anxiety-like behaviors, increase stereotypies and locomotion, and impair motor coordination and motor learning. Knowing the opposing role of D1R- and D2R-MSNs, we here investigated the respective roles of GPR88 in the two MSN subtypes for these behaviors. To do so, we compared effects of a conditional Gpr88 gene knockout (KO) in D1R-MSNs (D1R-Gpr88 mice) or D2R-MSNs (A2AR-Gpr88 mice) with effects of the total Gpr88 KO (CMV-Gpr88 mice). Overall, most phenotypes of CMV-Gpr88 mice were recapitulated in A2AR-Gpr88 mice, including reduced marble burying, increased social interactions, increased locomotor activity and stereotypies in the open field, and reduced motor coordination in the rotarod. Exceptions were the reduced habituation to the open field and reduced motor skill learning, which were observed in CMV-Gpr88 and D1R-Gpr88 mice, but not in A2AR-Gpr88 mice. D1R-Gpr88 mice otherwise showed no other phenotype in this study. Our data together show that GPR88 modulates the function of both D1R- and D2R-MSNs, and that GPR88 activity in these two neuron populations has very different and dissociable impacts on behavior. We suggest that GPR88 in D2R-MSNs shapes defensive and social behavior and contributes in maintaining the inhibition of basal ganglia outputs to control locomotion, stereotypies and motor coordination, while GPR88 in D1R-MSNs promotes novelty habituation and motor learning.
Significance Statement GPR88, an orphan G-protein-coupled receptor, has been implicated in the regulation of striatum-dependent behaviors. In the striatum, GPR88 is most abundant in both medium spiny neurons expressing dopamine D1 and D2 receptors. We compared effects of a conditional Gpr88 gene knockout in D1R-MSNs or D2R-MSNs with effects of the total Gpr88 deletion. Our data suggest that GPR88 in D2R-MSNs shapes defensive and social behavior and contributes in maintaining the inhibition of basal ganglia outputs to control locomotion, stereotypies and motor coordination, while GPR88 in D1R-MSNs promotes novelty habituation and motor learning. Gpr88 therefore plays very distinct roles in modulating D1R- and D2R-type neurons function and the related behaviors.
Footnotes
Authors report no conflict of interest.
This work was also supported by the National Institute of Health (National Institute of Drug Abuse Grant No. 05010 to BLK), the National Institute on Alcohol Abuse and Alcoholism (Grant No. 16658 to BLK), the Canada Fund for Innovation and the Canada Research Chairs to BLK, FRS–FNRS (Belgium) to AKE, and Fondation Simone et Pierre Clerdent (Belgium) (AKE). A.C.M. acknowledges doctoral fellowship from Fondation Française pour la Recherche Médicale (FRM: FDT20140930830). AKE is a Research Director of the FRS–FNRS (Belgium) and a WELBIO investigator (Belgium).
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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