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摘要：
目的 探讨激活γ-氨基丁酸B（γ-aminobutyric acid B, GABAB）受体对糖尿病神经痛大鼠脊髓背角谷氨酸能神经元递质释放中的影响。方法 30只（4周龄，150 g~170 g）雄性Sprague-Dawley(SD)大鼠，采用随机数字表法随机分为2组（每组15只）：正常对照组（N组）、糖尿病神经痛组（D组）。D组通过腹腔注射链脲佐菌素（streptozotocin , STZ）50 mg/kg制备糖尿病神经痛模型，N组腹腔给予等量生理盐水，两组分别于腹腔注射后第3~4周测定空腹血糖、机械缩足阈值（paw withdrawal mechanical threshold, PWMT）；然后处死大鼠取腰1~5脊髓，制备脊髓薄片，采用全细胞膜片钳技术，记录脊髓II板层单突触神经元谷氨酸能诱发兴奋性突触后电流（evoked excitatory postsynaptic currents, eEPSCs）。细胞封接后稳定5 min开始记录，灌流液中加入终浓度为1、10、20、50 μmol/L的Baclofen（GABAB受体特异性激动剂），于给药前对照、给予上述浓度药后各时点及洗脱后5 min，记录上述各时点eEPSCs的波幅变化，比较Baclofen对两组大鼠eEPSCs波幅的抑制率，并观察CGP55845（GABAB受体特异性阻断剂，1 μmol/L）对Baclofen（50 μmol/L）eEPSCs作用的影响。 结果 与N组比较，D组大鼠血糖显著增高，PWT明显降低（P﹤0.05）。电生理共记录30个神经元（每组15个），1 μmol/L~50 μmol/L的Baclofen均以剂量依赖方式降低两组大鼠eEPSCs波幅（P﹤0.05），N、D两组在1、10、20、50 μmol/L Baclofen时点波幅抑制率均明显下降（P﹤0.05），两组上述时点比较，D组显著低于N组（P﹤0.05），分别为：(47±7)vs(21±7),(55±6)vs(50±6),(92±6)vs(72±9),(95±8)vs(88±8)，1 μmol/LCGP55845可完全去除50 μmol/L Baclofen对两组神经元(每组12个)eEPSCs的作用。结论 激活GABAB受体可明显抑制脊髓背角神经元谷氨酸递质释放，但对糖尿病神经痛大鼠其抑制作用减弱。
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Abstract: Objective To explore the effect of activation of γ-aminobutyric acid B (GABAB) receptors on glutamate release in spinal dorsal horn neurons in rats with diabetic neuropathyic pain(DNP). Methods Thirty Sprague-Dawley(SD) male rats(aged 4weeks, weighing 150 g -170 g) were randomly divided into 2 groups (n=15): Normal rats group (N group), DN rats group (D group). DNP were induced by single intraperitoneal(IP) injection of streptozotocin(STZ, 50 mg/kg), and rats in C group received the equal volume saline injection. At 3-4 weeks after STZ or saline intraperitoneal injection, blood glucose level and paw withdraw threshold(PWT) were measured, and the rats were then killed, the lumbar segment of spinal cord(L1-5) was removed for slices preparations. Monosynaptic glutamatergic evoked excitatory postsynaptic currents (eEPSCs) of lamina II neurons were recorded by using whole-cell voltage-clamp patch. Bath baclofen(1, 10, 20, 50 μmol/L) was applicated, monosynaptic eEPSCs was recorded before application of baclofen, at 1, 10, 20, 50 μmol/L and wash out 5 min, the inhibitory rate(%) of eEPSCs was compared between two groups(n=15), the effect of CGP55845(1 μmol/L) on eEPSCs of 50 μmol/L baclofen was analyzed in two groups(n=12). Results The mean blood glucose level was significantly higher in D group than in N group, while PWT in D group was significantly lower than that in N group(P<0.05). eEPSCs in totally 30 glutamatergic neurons was recorded by electrophysiological recording. (1, 10, 20, 50 μmol/L) baclofen dose-dependently decreased the amplitude of eEPSCs both in two groups, the significant decrease of the amplitude inhibitory rate(%) of eEPSCs was observed at 1, 10, 20, 50 μmol/L baclofen both in two groups(P<0.05), its in D group were significantly decreased compared with N group at above times(P<0.05) respectively: (47±7)vs(21±7),(55±6)vs(50±6),(92±6)vs(72±9),(95±8)vs(88±8). CGP55845 was completely abolished the inhibitory effect of 50 umol/L baclofen on the amplitude of monosynaptic eEPSCs in lamina II neurons both two groups. Conclusions Activation of GABAB receptors effectively inhibits the glutemate neurotransmitter release in the spinal cord dorsal horn neurons, while it’s inhibitory role may decrease in rats with diabetic neuropathy.
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