THE INVOLVEMENT OF HISTAMINE H-2-RECEPTORS IN RESTRAINT-INDUCED ANTINOCICEPTION IN MALE-MICE

Restraint for 1 h induced significant antinociceptive activity in male mice assessed by the hot-plate test at 55-degrees-C. The antinociceptive activity was significant throughout the 1-h period of observation. Prior administration of the histamine H-2-receptor agonist dimaprit further enhanced the antinociceptive activity. Furthermore, the induction of antinociception by restraint was antagonized by prior administration of the histamine H-2-receptor blocker cimetidine. Similar findings were obtained with another histamine H-2-receptor blocker, zolantidine, which supposedly crosses the blood-brain barrier. On the other hand, prior administration of 2-pyridylethylamine, a histamine H-1-receptor agonist, or mepyramine, a histamine H-1-receptor antagonist, did not affect the development of antinociceptive activity induced by restraint. The doses of histamine receptor agonists and antagonists used in the present study had no effect on the hot-plate response of non-restraint control animals. These results suggest that histamine H-2-receptors may be involved in the restraint-induced antinociceptive activity in mice.