臨床經驗顯示電針止痛效果主要取決於是否有”得氣”現象，事實上，此種酸麻脹腫的得氣感也是一種深部組織的痛覺。雖然臨床上此種”得氣”現象對止痛效果的影響已是眾所週知，可是刺激的強度是否要達到傷害性反應(nociceptive response)，才能有止痛效果仍有爭議。我們採用客觀的動物模式，試圖証明是否較強的電刺激(亦即較強的氣感)可獲得較高的止痛效果，也就是說以客觀量化的方式建立得氣感(電刺激強度)與止痛效果的關係。另外，我們也嘗試用大白鼠脊髓背角神經c-fos免疫化學之活性表現來探討電針止痛的效果及其可能機轉。 本次動物實驗中，我們利用Halothane吸入性全身麻醉方式，以避免大白鼠清醒狀態下壓力性止痛作用的干擾。大白鼠共分為：強刺激組、弱刺激組、morphine組與控制組。各組動物之止痛效果則利用閃尾實驗的最大可能效應(MPE :maximal possible effect)來加以分析比較。除此之外，也利用福馬林注射疼痛行為加權評分及大白鼠脊髓背角神經元Fos免疫染色度來評估止痛效果。實驗所得數據則分別接受ANOVA及Dunnett`s post-hoc test分析。各組間P值之差異性若少於0.05，則表示有統計上之差異。 我們的結果顯示：較高的刺激強度對老鼠閃尾反射產生較強的抑制作用,而且和電針穴位刺激強度呈現正向關連，較高的刺激強度對老鼠閃尾反射產生較強的止痛效果。另外，我們數據亦顯示，電針刺激組及morphine組在福馬林注射疼痛加權評分及脊髓背角Fos免疫染色度，相較於控制組皆有明顯的降低。而電針刺激之同側大白鼠背角神經元Fos免疫染色度相較於控制組(沒有電針刺激)並沒明顯增加。此結果也暗喻電針穴位刺激在不超過傷害受体活化的閾值內，其止痛效果與其刺激強度是呈正向關係。; Clinical experience has observed that analgesic effect of electroacupuncture (EA) depends largely on the presence of “De-Qi”, a deep aching sensation evoked by acu-point stimulation. Despite the well-known phenomenon of De-Qi in clinical practice, it remains unclear whether stimulation-evoked nociceptive response is required for EA-induced analgesia. In this animal study, we hypothesized that stronger EA intensity could result in higher analgesic effect, i.e. more De Qi. We also tried to examine the analgesic mechanism of EA by formalin-induced c-fos expression in rat spinal cord dorsal neurons. Animal in this study were anesthetized by halothane inhalation to eliminate the bias from stress-induced analgesia. Maximal possible effect (MPE) of tail flick test was used to compare the analgesic effect between high intensity [20xEAT(electroacupuncture threshold)], low intensity (10xEAT) and morphine (2.5mg/kg s.c., the positive control group). In addition, we also evaluated EA-induced analgesic effect using behavioral parameters (weighted pain score) and neuronal activity marker (Fos-like immunoreactivity (Fos-LI) labeled neurons of spinal dorsal horn of rat) after intraplantar formalin injection. All data were compared by one-way analysis of variance (ANOVA) followed by Dunnetts` post-hoc test performed to compare the mean of tail flick latencies, number of Fos-LI labelled neurons, pain scores at the late phase of formalin test, and pain scores in the whole period between groups. P<0.05 was considered statistically significant. Our results demonstrated that the low frequency EA prolonged the tail flick latency in an intensity-dependent manner, i.e., the higher stimulation intensity the more inhibitory effect on tail withdrawl reflex is produced. We also showed that the equipotent analgesic effect on formalin-induced pain between high intensity EA and morphine group with evidence of decreased pain scores and reduced Fos-LI neurons in spinal level more than control group. However, these strong peripheral electrostimulations did not incur detectable increase in c-fos expression of neurons at sensory receptive field than baseline level. These results implied that the efficacy of EA analgesia could be generated in proportional to its stimulation intensity within the strength not exceeding the threshold of recruiting nociceptor activation.
