Central effect of histamine on acetic acid-induced visceral nociception in rats

In the present study, the effects of intracerebroventricular (icv) injections of histamine, chlorpheniramine (hrreceptor antagonist) and ranitidine (h2-receptor antagonist) were investigated on visceral nociception induced by an intraperitoneal (ip) injection of acetic acid in rats. the latency time to the beginning of the first abdominal wall contraction (the first writhe) was recorded and the number of writhes was counted for 1 h after the ip injection of acetic acid (1 ml, 1%). all treatments (histamine: 2.5-80 jxg, chlorpheniramine and ranitidine: 5-80 |xg) did not influence the latency time to the beginning of the first writhe significantly except for the 40 |xg dose of histamine, which significantly increased the latency time (p<0.05). doses of histamine of 10 and 40 |xg and doses of chlorpheniramine and ranitidine of 20 and 80 ng significantly decreased the number of writhes (p<0.05). pretreatments with chlorpheniramine or ranitidine at the dose of 80 p.g significantly prevented histamine-induced (40 (ig) antinociception (p<0.05). these results indicate that brain histamine may mediate the perception of visceral antinociception through both central h, and h2 receptors.