Receptor crosstalk:: Characterization of mice deficient in dopamine D1 and adenosine A2A receptors

Here we report the development of D1A(2A) receptor knockout mice to investigate whether interactions between dopamine D-1 and adenosine A(2A) receptors participate in reward-related behavior. The combined deletion of D-1 and A(2A) receptors resulted in mice with decreased weight and appetitive processes, reduced rearing and exploratory behaviors, increased anxiety, and a significantly poorer performance on the rotarod, compared to wild-type littermates. D1A(2A) receptor knockout mice shared phenotypic similarities with mice deficient in D-1 receptors, while also paralleling behavioral deficits seen in A(2A) receptor knockout mice, indicating individual components of the behavioral phenotype of the D1A(2A) receptor knockout attributable to the loss of both receptors. In contrast, ethanol and saccharin preference in D1A(2A) receptor knockout mice were distinctly different from that observed in derivative D-1 or A(2A) receptor-deficient mice. Compared to wild types, preference and consumption of ethanol were decreased in D1A(2A) receptor knockout mice, the reduction in ethanol consumption greater even than that seen in D-1 receptor-deficient mice. Preference and consumption of saccharin were also reduced in D1A(2A) receptor knockout mice, whereas saccharin preference was similar in wild-type, D-1, and A(2A) receptor knockout mice. These data suggest an interaction of D-1 and A(2A) receptors in the reinforcement processes underlying the intake of rewarding substances, whereby the A(2A) receptor seems involved in goal-directed behavior and the motor functions underlying the expression of such behaviors, and the D-1 receptor is confirmed as essential in mediating motivational processes related to the repeated intake of novel substances and drugs.