The GPR88 receptor agonist 2-PCCA does not alter the behavioral effects of methamphetamine in rats

GPR88 is a novel orphan G protein-coupled receptor that is primarily located at the striatum. Genetic knockout studies reveal phenotypes of increased dopamine D₂ receptor sensitivity in mice, suggesting that GPR88 receptors may be involved in the modulation of dopaminergic system. However, there is no study that examines the pharmacological effects of GPR88 receptor ligands in in vivo preparations. This study examined the effects of a GPR88 receptor agonist, (1R, 2R)-2-pyridin-2-yl-cyclopropane carboxylic acid ((2S, 3S)-2-amino-3-methyl-pentyl)-(4′-propylbiphenyl-4-yl)-amide (2-PCCA), on the motor activity in rats and on methamphetamine-induced hyperactivity and discriminative stimulus effects. 2-PCCA (0.1-3.2 mg/kg) dose-dependently decreased the locomotor activity in rats and, when studied in combination with 1.0 mg/kg methamphetamine, also dose-dependently decreased methamphetamine- induced hyperactivity. However, the dose of 2-PCCA that significantly attenuated methamphetamine-induced hyperactivity was also the dose that by itself markedly decreased the baseline locomotor activity. In rats discriminating 0.32 mg/kg methamphetamine, 2-PCCA (1-3.2 mg/kg) itself did not produce methamphetamine-like discriminative stimulus effects and, when studied in combination, did not alter the discriminative stimulus effects of methamphetamine. Together, these data have provided the first line of evidence that activation of GPR88 receptors does not alter the behavioral effects of methamphetamine. The potential implications of these findings are also discussed.