Larson A A
Brain Res. 1983 Apr 11;265(1):109-17. doi: 10.1016/0006-8993(83)91339-2.
Tryptamine was applied directly into the spinal subarachnoid space of rats via permanently indwelling cannulas. Changes in pain-perception were measured by changes in the latency of the tail-flick in response to a radiant heat source of low intensity. While an intrathecal injection of serotonin has been previously shown to be analgesic, exogenous tryptamine produced dual effects on the pain-threshold, depending on the dose of tryptamine injected. Low doses of tryptamine (100 and 200 micrograms/rat) injected intrathecally onto the sacral area of the spinal cord appeared to be hyperalgesic by significantly decreasing the average tail-flick latency by 5 min after injection. Administration of the serotonin antagonist methysergide alone was without effect on the average tail-flick reaction time when injected either intrathecally or subcutaneously. However, pretreatment with either methysergide or cinanserin not only failed to inhibit tryptamine's potentiation of nociception, but actually enhanced the hyperalgesia produced by tryptamine. In contrast, a dose of 400 micrograms of tryptamine significantly increased the average tail-flick latency, suggesting an analgesic effect at this higher dose. This analgesic effect of 400 micrograms of tryptamine was completely inhibited by subcutaneously administered methysergide, while intrathecally injected methysergide produced even greater decreases in the tail-flick latencies after this high dose of tryptamine. These results suggest that tryptamine, although it differs from serotonin by only one hydroxyl group, may play a role in nociception which is opposite that played by serotonin.
色胺通过永久性留置套管直接注入大鼠脊髓蛛网膜下腔。通过对低强度辐射热源做出反应时甩尾潜伏期的变化来测量痛觉的改变。虽然先前已证明鞘内注射血清素具有镇痛作用，但外源性色胺对痛阈产生双重影响，这取决于所注射色胺的剂量。鞘内注射到脊髓骶部区域的低剂量色胺（100和200微克/大鼠），在注射后5分钟显著缩短平均甩尾潜伏期，似乎具有痛觉过敏作用。单独鞘内或皮下注射血清素拮抗剂美西麦角对平均甩尾反应时间没有影响。然而，用美西麦角或辛那色林预处理不仅未能抑制色胺对伤害感受的增强作用，实际上还增强了色胺产生的痛觉过敏。相比之下，400微克色胺的剂量显著增加了平均甩尾潜伏期，表明在这个较高剂量下具有镇痛作用。皮下注射美西麦角完全抑制了400微克色胺的这种镇痛作用，而鞘内注射美西麦角在给予高剂量色胺后使甩尾潜伏期缩短得更多。这些结果表明，色胺虽然与血清素仅相差一个羟基，但在伤害感受中可能发挥与血清素相反的作用。
