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 antinocicept ive activity was significant throughout the 1-h period of observation. Prior administration of the histamine H-2-receptor agonist dimaprit f urther enhanced the antinociceptive activity. Furthermore, the inducti on of antinociception by restraint was antagonized by prior administra tion of the histamine H-2-receptor blocker cimetidine. Similar finding s were obtained with another histamine H-2-receptor blocker, zolantidi ne, which supposedly crosses the blood-brain barrier. On the other han d, prior administration of 2-pyridylethylamine, a histamine H-1-recept or agonist, or mepyramine, a histamine H-1-receptor antagonist, did no t affect the development of antinociceptive activity induced by restra int. The doses of histamine receptor agonists and antagonists used in the present study had no effect on the hot-plate response of non-restr aint control animals. These results suggest that histamine H-2-recepto rs may be involved in the restraint-induced antinociceptive activity i n mice.