Pirenperone Ketanserin Morphine Ketamine

and 120 min after injections by measuring the time that it took each vat to remove its tail from a 52C water bath. Pirenperone, at 0.08,0.16. and 0.24 mg/kg (SC) attenuated morphine-induced antinociception. In contrast, only the high ID mg/kg (SC) dose of ketanserin attenuated the effect of morphine. Because pirenperone easily enters the central nervous system whereas ketanserin does not, these results indicate the involvement of central S, receptors in morphine-induced antinociception. The 10mg/kg, dose or ketanserin. however, did not attenuate the antinociception produced by 100rmg/kg f ketamine. Thus, the antianalgesic effect of s ± receptor blockers may be specific to opioid-mediated analgesia