Influence of dopamine D2-type receptors on motor behaviors in the green tree frog, Hyla cinerea

• A D2 receptor agonist and an antagonist influence motor performance in an amphibian.
• Quinpirole increased while haloperidol decreased time to exit water in the test arena.
• Behaviors associated with exiting the water improved with repeated trials.
• Results support a conserved role for D2 receptors in motor behaviors in vertebrates.

Dopamine modulates a range of behaviors that include motor processes, learning, and incentive motivation. Research supports anatomical conservation of dopaminergic populations in the midbrain across vertebrate species, however, less evidence is available for dopamine receptor distributions. In order to test the behavioral role of dopamine in an anatomically conserved dopaminergic system, the effects of D2-type receptor manipulation on motor behaviors were examined in the anuran amphibian green tree frog, Hyla cinerea. In two different within-subject experiments, frogs were treated with a control treatment, and a high and low dose of either a D2 receptor-specific agonist, quinpirole, or antagonist, haloperidol, then exposed to a testing session to measure changes in swimming and climbing motor behaviors. No treatments resulted in complete immobility or catalepsy, however treatment-specific effects on certain motor behaviors were present. The high quinpirole dose (1 mg/kg bw) generally inhibited motor behaviors associated with exiting water and jumping, while both haloperidol treatments (0.12 mg/kg bw and 1.2 mg/kg bw) generally stimulated motor behaviors associated with exiting water, as predicted based on receptor mechanisms. Performance improvement also appeared in frogs in each experiment, suggesting that the D2 receptor is not involved in the motor learning mechanism in this species. Overall, the results support general conservation of D2 receptors in motor processes in vertebrate species.