The effect of intracerebroventricular injection of histamine in visceral nociception induced by acetic acid in rats.

OBJECTIVE: This study was designed to investigate the role of brain histamine and H1 and H2 receptors in mediating the central perception of visceral pain in rats. MATERIALS AND METHODS: In conscious rats implanted with a lateral brain ventricle cannula, the effect of intracerebroventricular (i.c.v.) injection of histamine (2.5, 10, and 40 µg), and chlorpheniramine and ranitidine at the same doses of 5, 20, and 80 µg were investigated on visceral pain. Visceral nociception induced by intraperitoneal (i.p.) injection of acetic acid (1 mL, 1%), and the number of complete abdominal wall muscle contractions accompanied with stretching of hind limbs (writhes) were counted for 1 h. RESULTS: Histamine at doses of 10 and 40 µg and chlorpheniramine and ranitidine at the same doses of 20 and 80 µg, significantly decreased the numbers of writhes (P < 0.05). Pretreatment with chlorpheniramine and ranitidine at the same dose of 80 µg, significantly prevented histamine (40 µg)-induced antinociception (P < 0.05). CONCLUSION: The results of this study suggest that brain histamine may be involved in modulation of visceral antinociception through both central H(1)and H(2)receptors.

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.