Genetic reconstruction of dopamine D1 receptor signaling in the nucleus accumbens facilitates natural and drug reward responses

Abstract

The dopamine D1 receptor (D1R) facilitates reward acquisition and its alteration leads to profound learning deficits. However, its minimal functional circuit requirement is unknown. Using conditional reconstruction of functional D1R signaling in D1R knock-out mice, we define distinct requirements of D1R in subregions of the nucleus accumbens (NAc) for specific dimensions of reward. We demonstrate that D1R expression in the core region of the NAc (NAc(Core)), but not the shell (NAc(Shell)), enhances selectively a unique form of pavlovian conditioned approach and mediates D1R-dependent cocaine sensitization. However, D1R expression in either the NAc(Core) or the NAc(Shell) improves instrumental responding for reward. In contrast, neither NAc(Core) nor NAc(Shell) D1R is sufficient to promote motivation to work for reward in a progressive ratio task or for motor learning. These results highlight dissociated circuit requirements of D1R for dopamine-dependent behaviors.

Figure 1.

Conditional viral restoration of D1R expression in either the NAc^Core or the NAc^Shell. A, Schematic representation of Drd1a^Cre allele and AAV-FLEX-D1RGFP construct. B, Left, D1R protein expression is highly enriched in the striatum. Right, mouse brain atlas, bregma +1.34 (Franklin and Paxinos, 2007). C, Higher magnification of NAc^Core region from B. D1R is completely absent in D1R mutants, but selectively expressed in the NAc^Core with AAV-FLEX-D1RGFP. D, Higher magnification of NAc^Shell region from B. D1R is completely absent in D1R mutants, but selectively expressed in the NAc^Shell with AAV-FLEX-D1RGFP. E, F, Tracing of bilateral D1RGFP expression in D1R-NAc^Core (n = 7) and D1R-NAc^Shell (n = 9) mice. Scale bars: B, 500 μm; C, D, 100 μm. ac, Anterior commissure. Data are shown as means ± SEM.

Figure 2.

D1R in either the NAc^Core or the NAc^Shell restores behavioral responsiveness and functional D1R signaling. A, B, Locomotor response to the D1 agonist SKF-81297 in NAc^Core and NAc^Shell mice (NAc^Core: Het-GFP, n = 7; Het-D1R, n = 8; Mut-GFP, n = 7; Mut-D1R, n = 7; NAc^Shell: Het-GFP, n = 12; Het-D1R, n = 13; Mut-GFP, n = 7; Mut-D1R, n = 9). C, D, SKF-81297 induced c-Fos expression (red) in D1R-NAc^Core (Mut-D1R) and control mice and D1R-NAc^Shell (Mut-D1R) and control mice. Brain sections were counterstained with Hoechst (blue). E, F, Quantification of c-Fos-positive cells in NAc^Core and NAc^Shell mice (NAc^Core: saline controls, all genotypes, n = 8; Het-GFP, n = 5; Het-D1R, n = 5; Mut-GFP, n = 6; Mut-D1R, n = 6; NAc^Shell: saline controls, all genotypes, n = 9; Het-GFP, n = 10; Het-D1R, n = 10; Mut-GFP, n = 6; Mut-D1R, n = 7). A, B, Bonferroni's multiple-comparison test, *p < 0.05, **p < 0.01 for D1R-NAc^Core or D1R-NAc^Shell mice versus D1R mutants, respectively. E, F, Tukey's multiple-comparison test, **p < 0.01, ***p < 0.001 for D1R mutants versus all other groups. Scale bars, 100 μm. Data are shown as means ± SEM.

Figure 3.

D1R in the NAc^Core, but not the NAc^Shell, facilitates pavlovian conditioned approach behavior. A, B, Pavlovian conditioned approach score, [(CS head entry rate) − (intertrial interval head entry rate)] for NAc^Core and NAc^Core mice (NAc^Core: Het-GFP, n = 8; Het-D1R, n = 8; Mut-GFP, n = 7; Mut-D1R, n = 7; NAc^Shell: Het-GFP, n = 13; Het-D1R, n = 13; Mut-GFP, n = 7; Mut-D1R, n = 9). C, D, Track tracing from last trial of day 7 for D1R mutant and D1R-NAc^Core mice and D1R mutant and D1R-NAc^Shell mice illustrating conditioned approach to the lever and receptacle in D1R-NAc^Core mice, but not in the mutant control groups or D1R-NAc^Shell mice. E, F, Quantification of conditioned approach behavior for NAc^Core and NAc^Shell mice from A, B. E, F, Tukey's multiple-comparison test, **p < 0.01, ***p < 0.001. Data are shown as means ± SEM.

Figure 4.

D1R in either the NAc^Core or the NAc^Shell promotes instrumental conditioning. A, B, Interpress interval during instrumental conditioning over 4 d for NAc^Core and NAc^Shell mice (NAc^Core: Het-GFP, n = 8; Het-D1R, n = 8; Mut-GFP, n = 7; Mut-D1R, n = 7; NAc^Shell: Het-GFP, n = 13; Het-D1R, n = 13; Mut-GFP, n = 7; Mut-D1R, n = 9). C, D, Cumulative lever presses on day 4 for NAc^Core and NAc^Shell mice from A, B. E, F, Progressive ratio breakpoint analysis for NAc^Core and NAc^Shell mice (NAc^Core: Het-GFP, n = 4; Het-D1R, n = 4; Mut-GFP, n = 4; Mut-D1R, n = 4; NAc^Shell: Het-GFP, n = 13; Het-D1R, n = 13; Mut-GFP, n = 7; Mut-D1R, n = 9). A–D, Bonferroni's multiple-comparison test, *p < 0.05, **p < 0.01, ****p < 0.0001 for D1R-NAc^Core or D1R-NAc^Shell mice versus D1R mutants, respectively. E, F, Tukey's multiple-comparison test, *p < 0.05, ***p < 0.001 for D1R mutants versus all other groups. Data are shown as means ± SEM.

Figure 5.

D1R in neither the NAc^Core nor the NAc^Shell improves rotarod performance. A, B, Average latency to fall during 3 trials/d of rotarod testing over 5 d. Neither D1R-NAc^Core nor D1R-NAc^Shell mice demonstrated significant improvement relative to mutant control groups (NAc^Core: Het-GFP, n = 8; Het-D1R, n = 8; Mut-GFP, n = 7; Mut-D1R, n = 7; NAc^Shell: Het-GFP, n = 13; Het-D1R, n = 13; Mut-GFP, n = 7; Mut-D1R, n = 9). Data are shown as means ± SEM.

Figure 6.

D1R in the NAc^Core, but not the NAc^Shell, is sufficient for locomotor sensitization to cocaine. A, B, Locomotor response to cocaine on day 1 for NAc^Core and NAc^Shell mice (NAc^Core: Het-GFP, n = 7; Het-D1R, n = 8; Mut-GFP, n = 7; Mut-D1R, n = 7; NAc^Shell: Het-GFP, n = 12; Het-D1R, n = 13; Mut-GFP, n = 7; Mut-D1R, n = 9). C, D, Sensitized locomotor response to cocaine on day 5 for D1R-NAc^Core, but not D1R-NAc^Shell, mice. E, F, Normalized cumulative locomotor activity, [90 min postinjection period] − [90 min baseline preinjection period] for saline (S) and 5 d of cocaine. C, E, Bonferroni's multiple-comparison test, **p < 0.01, ****p < 0.0001 for D1R-NAc^Core or D1R-NAc^Shell mice versus D1R mutants. Data are shown as means ± SEM.