Abstract
The effects of intraventricularly (i.c.v.) administered divalent cations, cation chelators and an ionophore (A23187) on antinociception produced by i.c.v. administration of morphine or dibutyryl guanosine 3':5'-cyclic monophosphate (db c-GMP) were quantitated in the mouse tail-flick procedure. Ca++ pretreatment produced a dose-related potentiation (> 10-fold) of db c-GMP and a dose-related antagonism (> 20-fold) of morphine antinociception. Mg++ pretreatment antagonized db c-GMP, whereas morphine antinociception was unaffected. Ba++ and Sr++ were observed to possess intrinsic antinociceptive activity. Administration of Ba++ or Sr++ had greater than additive effects on db c-GMP and morphine antinociception. EDTA pretreatment did not affect db c-GMP or morphine antinociception. Ethylene glycol bis(beta-aminoethyl ether)N,N-tetraacetic acid had no effect on db c-GMP but potentiated the morphine response. The ionophore A23187 had no effect on db c-GMP or morphine in the tail-flick test. However, A23187 potentiated the effect of high doses of Ca++ on db c-GMP and increased the antagonistic effect of a low dose of Ca++ on morphine antinociception. The results provide further evidence that the mechanism of db c-GMP antinociception is different from that of morphine.
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|