Dopaminergic involvement in adenosine A(1) receptor-mediated antinociception in the tail flick latency model in mice

The interaction between the adenosinergic and dopaminergic systems in nocic eption was assessed in the tail flick latency (TFL) test in mice. Adenosine exhibited qualitatively different responses depending on the dose: Adenosi ne 10 and 100 mg/kg i.p. caused antinociception as evidenced by an increase in TFL while the middle dose of 30 mg/kg decreased TFL. On the other hand, the specific adenosine A(1) receptor agonist N-6-cyclopentyladenosine (CPA ) at doses of 0.05, 0.1, 0.25 and 0.5 mg/kg (i.p.) resulted in dose-depende nt antinociception. The antinociceptive effect of CPA was reversed by class ical albeit nonspecific adenosine receptor antagonist theophylline (5 mg/kg ) at a dose which had no effect on TFL per se. A low dose (1 mg/kg i.p.) of the dopaminergic agonist apomorphine caused an early mild hyperalgesic res ponse while the high dose (10 mg/kg i.p) had no significant effect on TFL. the antinociceptive effect of CPA was attenuated by pretreatment with low d ose apomorphine while pretreatment with the high dose caused mild but insig nificant potentiation. Theophylline, when administered prior to apomorphine failed to modify the nociceptive response. The results suggest that an int eraction between adenosine and dopamine may be involved in nociception. (C) 2000 Prous Science. All rights reserved.