Alterations in nociception after intracisternal administration of prostaglandin D2, E2 or F2α to conscious mice

Abstract The effect of intracisternal administration of three major prostaglandins on nociceptive responses was evaluated in mice. Prostaglandin D 2 had biphasic effects on pain thresholds (hot plate and acetic acid writhing tests) when given in a dosage range of 5 ng to 5 μg per mouse. Lower doses of prostaglandin D 2 (⩽ 15 ng) increased the sensitivity to pain stimulation. Higher doses (⩾50 ng ) caused hypoalgesia, which was completely blocked by intracisternal injection of 500 pg of naloxone. Prostaglandin E 2 (5 ng–5 μg) also had a biphasic effect on pain thresholds, similar to the effect of prostaglandin D 2 . However, the hypoalgesia caused by a higher dose of prostaglandin E 2 (5 μg) was not blocked at all by naloxone doses of up to 500 ng. Prostaglandin F 2α had little effect on pain thresholds. There results indicate that each prostaglandin has a specific effect on the modulation of nociception.