Adenosine receptor mediates nicotine-induced antinociception in formalin test.

In this study, the effect of adenosine receptor agents on nicotine induced antinociception, in formalin test, has been investigated. Intraperitoneal (i.p.) administration of different doses of nicotine (0.1, 1, 10 and 100 microgkg(-1)) induced a dose-dependent antinociception in mice, in the both first and second phases of the test. Adenosine receptor antagonist, theophylline (5, 10, 20 and 80 mgkg(-1), i.p.) also induced antinociception in the both phases, while a dose of the drug (40 mgkg(-1), i.p.) did not induce any response. Theophylline reduced antinociception induced by nicotine in both phases of formalin test. The A(2) receptor agonist, 5'-N-ethylcarboxamide adenosine (NECA; 1 and 5 microgkg(-1), i.p.) also produced antinociception, which was reversed with different doses of theophylline (5, 10, 20 and 40 mgkg(-1), i.p.). But administration of the adenosine receptor agonist, NECA did not potentiate the response of nicotine. It is concluded that adenosine system may be involved in modulation of antinociception induced by nicotine.