Chen Shao-Rui, Pan Hui-Lin
Department of Anesthesiology, Penn State University College of Medicine, 500 University Drive, Hershey, PA 17033-0850, USA.
J Pharmacol Exp Ther. 2003 Nov;307(2):676-81. doi: 10.1124/jpet.103.055905. Epub 2003 Sep 9.
Spinally administered muscarinic receptor agonists or acetylcholinesterase inhibitors produce effective pain relief. Intrathecal injection of a small dose of neostigmine produces a profound antiallodynic effect in rats with diabetic neuropathy. However, the mechanisms of increased antinociceptive effect of cholinergic agents on diabetic neuropathic pain are not clear. In the present study, we tested the hypothesis that spinal muscarinic receptors are up-regulated in diabetes. The withdrawal threshold of the hindpaw in response to noxious heat and pressure stimuli was determined in streptozotocin-induced diabetic and age-matched normal rats. Muscarine-stimulated guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding was used to assess the change of functional muscarinic receptors in the spinal cord in diabetes. The [3H]AF-DX 384 membrane binding was performed to determine the number and affinity of spinal cord M2 muscarinic receptors in normal and diabetic rats. We found that the antinociceptive effect of intrathecal 2 to 12 mug muscarine in diabetic animals was potentiated significantly compared with that in normal animals. The maximal muscarine-stimulated [35S]GTPgammaS binding was 112.5 +/- 8.3% in normal rats and 168.8 +/- 12.1% (P < 0.05) in diabetic rats. Although the KD value (2.9 nM) was similar in both groups, the Bmax of [3H]AF-DX 384 membrane binding was significantly higher in diabetic than in normal rats (255.2 +/- 5.9 versus 165.9 +/- 3.5 fmol/mg protein, P < 0.05). Collectively, these data strongly suggest that the muscarinic receptor is up-regulated in the dorsal spinal cord in diabetic rats. This finding probably accounts for the increased efficacy of the antinociceptive effect of intrathecal muscarinic agonists in diabetic neuropathic pain.
脊髓给予毒蕈碱受体激动剂或乙酰胆碱酯酶抑制剂可有效缓解疼痛。鞘内注射小剂量新斯的明对糖尿病性神经病变大鼠具有显著的抗痛觉过敏作用。然而，胆碱能药物对糖尿病性神经病理性疼痛镇痛作用增强的机制尚不清楚。在本研究中，我们检验了糖尿病时脊髓毒蕈碱受体上调的假说。测定链脲佐菌素诱导的糖尿病大鼠和年龄匹配的正常大鼠后爪对有害热刺激和压力刺激的撤足阈值。用毒蕈碱刺激的鸟苷5'-O-(3-[35S]硫代)三磷酸([35S]GTPγS)结合来评估糖尿病时脊髓中功能性毒蕈碱受体的变化。进行[3H]AF-DX 384膜结合实验以确定正常和糖尿病大鼠脊髓M2毒蕈碱受体的数量和亲和力。我们发现，与正常动物相比，鞘内注射2至12μg毒蕈碱对糖尿病动物的镇痛作用显著增强。正常大鼠中毒蕈碱刺激的最大[35S]GTPγS结合率为112.5±8.3%，糖尿病大鼠为168.8±12.1%（P<0.05）。虽然两组的KD值（2.9 nM）相似，但糖尿病大鼠[3H]AF-DX 384膜结合的Bmax显著高于正常大鼠（255.2±5.9对165.9±3.5 fmol/mg蛋白，P<0.05）。总体而言，这些数据强烈表明糖尿病大鼠脊髓背角毒蕈碱受体上调。这一发现可能解释了鞘内毒蕈碱激动剂对糖尿病性神经病理性疼痛镇痛作用增强的原因。
