Comparison of the behavioral effects of adenosine agonists and dopamine antagonists in mice

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Abstract
The adenosine agonists 5′-N-ethylcarboxamidea-denosine (NECA), 2-chloroadenosine (2-CLA), N6-cyclohexyladenosine (CHA), N6-cyclopentyladenosine (CPA), 2-(phenylamino)adenosine (CV-1808) and R and S isomers of N6-phenylisopropyladenosine (R-PIA and S-PIA) decreased spontaneous locomotor activity in mice and, except for CPA, did so at doses that did not impair motor coordination, a profile shared by dopamine antagonists. CV-1808, the only agent with higher affinity for A2 as compared with A1 adenosine receptors, displayed the largest separation between locomotor inhibitory and ataxic potency. Like dopamine antagonists, NECA and CV-1808 also decreased hyperactivity caused by d-amphetamine at doses that did not cause ataxia whereas A1-selective adenosine agonists reduced amphetamine's effects only at ataxic doses. Unlike dopamine antagonists, adenosine agonists inhibited apomorphine-induced cage climbing only at doses that caused ataxia. Involvement of central adenosine receptors in these effects was suggested by the significant correlation obtained between potency for locomotor inhibition after IP and ICV administration. Affinity for A1 but not A2 adenosine receptors was significantly correlated with potency for inducing ataxia. These results suggest that the behavioral profile of adenosine agonists in mice is related to their affinity for A1 and A2 adenosine receptors and indicate that adenosine agonists produce certain behavioral effects that are similar to those seen with dopamine antagonists.