Antinociception induced by central administration of histamine in the formalin test in rats

In the present study, effects of intracerebroventricular (icv) administration of histamine, mepyramine (H1-receptor antagonist) and famotidine (H2-receptor antagonist) have been investigated on the formalin test in rats. Subcutaneous injection of formalin (50 microl, 1%) into the ventral surface of the left hind paw produced a marked biphasic pain response (first phase: 0-5 min and second phase: 15-45 min). All the performed treatments did not significantly influence the first phase of pain. Histamine at the doses of 10 and 40 microg and mepyramine and famotidine at the same doses of 20 and 80 microg, significantly (P < 0.05) decreased the late phase of formalin-induced pain. Pretreatments with mepyramine and famotidine at the same dose of 80 microg, significantly (P < 0.05) prevented the histamine (40 microg)-induced antinociception. These results indicate that brain histamine produces antinociception, and both central H1 and H2 receptors may involve in the histamine-induced antinociception in the formalin test in rats.