Stevens C W, Pezalla P D
Life Sci. 1983 Nov 21;33(21):2097-103. doi: 10.1016/0024-3205(83)90333-8.
The application of acetic acid to the hind leg of a frog will induce a spinally mediated wiping reflex only if the acetic acid concentration is above a certain threshold. By using this reflex as the basis of a test for nociception, we show that morphine sulfate is a potent analgesic in the frog when injected into the lumbar area of the spinal cord. Significant analgesia is induced within 5 min after injection of as little as 0.0316 microgram of morphine sulfate. Low doses of morphine sulfate (0.0316 or 0.1 microgram) induce analgesia which dissipates within 1 h while for higher doses (0.316, 1.0 or 3.16 micrograms) the analgesia persists for at least 3 h. The analgesic effect of 0.316 micrograms of morphine sulfate is completely blocked by naloxone HCl at either 0.158 or 0.316 micrograms. Animals receiving naloxone alone (0.316 micrograms) appear to be slightly hyperalgesic compared to saline injected controls but this effect is not significant.
仅当醋酸浓度高于某一阈值时，将其涂抹于青蛙后腿才会诱发脊髓介导的擦拭反射。以该反射作为伤害感受测试的基础，我们发现，将硫酸吗啡注入青蛙脊髓腰段时，它是一种强效镇痛药。注射低至0.0316微克硫酸吗啡后5分钟内即可产生显著的镇痛效果。低剂量硫酸吗啡（0.0316或0.1微克）引起的镇痛作用在1小时内消散，而高剂量（0.316、1.0或3.16微克）的镇痛作用至少持续3小时。0.316微克硫酸吗啡的镇痛效果可被0.158或0.316微克盐酸纳洛酮完全阻断。与注射生理盐水的对照组相比，单独接受纳洛酮（0.316微克）的动物似乎有轻微的痛觉过敏，但这种效应并不显著。
