Differential effects of selective adenosine A1 and A2A receptor agonists on dopamine receptor agonist-induced behavioural responses in rats.

The effects of the systemic (i.p.) administration of the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the selective adenosine A2A receptor agonist sodium 2-p-carboxyethyl)phenylamino-5'-N-carboxamidoadenosine (CGS 21680) on different dopamine receptor agonist-induced behaviours were studied in the male rat. CGS 21680 (1 micromol/kg), but not CPA, was found to counteract the stereotypies induced by the non-selective dopamine receptor agonist apomorphine (0.25 mg/kg s.c.). Low doses of CGS 21680 (0.1 micromol/kg) and high doses of CPA (3 micromol/kg) counteracted yawning induced by the dopamine D2 selective agonist quinpirole (0.05 mg/kg). On the other hand, low doses of CPA (0.3 micromol/kg) antagonized grooming induced by the selective dopamine D1 receptor-selective agonist SKF 38393 (10 mg/kg i.p.), while CGS 21680 was ineffective. These results are consistent with the proposed existence of a selective antagonistic modulation of dopamine D1 and D2 receptors by adenosine A1 and A2A receptors, respectively. The ability of CGS 21680 to counteract apomorphine-induced stereotypies is weaker compared to its previously reported antagonistic effect of amphetamine-induced motor activity. This supports the hypothesis that adenosine A2A receptor agonists may be potential antipsychotic drugs with a low potential for extrapyramidal side effects.