依托咪酯对成年大鼠脊髓胶状质局部突触传递的作用

Effects of etomidate on local synaptic transmission in substantia gelatinosa neurons of the adult rat spinal cord

应用盲插全细胞膜片钳技术,在成年大鼠脊髓薄片上观察依托咪酯(etomidate,ET)对脊髓胶状质局部突触传递的影响。实验结果显示,在钳制电压为-70mV时,500μmol/L的ET对微小兴奋性突触后电流(mEPSC)的持续时间、频率和幅度都无明显的作用。在钳制电压为0mV时,50μmol/L的ET使GABA能微小抑制性突触后电流(mIPSC)的持续时间延长45.57±12.46%(P<0.05),但对其频率和幅度无影响。同样在钳制电压为0mV的情况下,50μmol/L的ET对甘氨酸能mIPSC的持续时间、频率及幅度均无作用。以上结果表明,在成年大鼠的脊髓胶状质,ET主要通过延长GABA能mIPSC的持续时间,即延长受体通道的开放时间发挥作用,ET对于兴奋性的突触传递没有直接的作用。

By using blind spinal slice whole-cell patch-clamp technique, we observed the influence of etomidate (ET) on synaptic transmission in substantia gelatinosa neurons of the adult rat spinal cord. Male adult Sprague-Dawley rats (7～8 weeks old) were anaesthetized with urethane (1.2 g/kg, i.p.), and then lumbosacral laminectomy was performed. The lumbosacral spinal cord (L1～S3) was removed and placed in preoxygenated Krebs solution at 1～3℃. After cutting all of the ventral and dorsal roots, the pia-arachnoid membrane was removed. The spinal cord was mounted on a vibrating microslicer and then a 500 μm thick transverse slice was cut. The slice was placed on a nylon mesh in the recording chamber, and then perfused at a rate of 15～20 ml/min with Kreds solution saturated with 95% O_2 and 5% CO_2,and maintained at 36 ±1℃. Substantia gelatinosa neurons were identified by their location. Under a binocular microscope and with transmitted illumination, the substantia gelatinosa was clearly discernible as a relatively translucent band across the dorsal horn. The resistance of patch clamp electrodes was 8～12 MΩ. Signals were gained by using an Axopatch 200B amplifier With low-passfiltered at 5 kHz, and digitized at 333 kHz with an A/ D converter.The results are as follows. (1) To see whether or not ET has any effects on the local miniature excitatory postsynaptic currents (mEPSC), the holding potential was set up at-70 mV. Under such a condition extracelluar superfusion was made with 1 μmol/L TTX for 2 min first, which was followed by consisten application of 500 μmol/L ET and 1 μmol/L TTX for 1 min. It was shown that ET did not influence the decay time, frequency and amplitude of mEPSC, when compared to the control. (2) To see whether or not ET has any effects on the local miniature inhibitory postsynaptic currents (mIPSC) mediated by GABA_A receptor, the holding potential was set up at 0 mV. Under this condition extracellular superfusion was made with 1 μmol/L TTX and 1μmol/L strychinin, an antagonist of glycine receptor, for 2 min, and then with consistent application of 50 μmol/L ET, 1μmol/L TTX and 1μmol/L strychnine for 1 min. ET prolonged the decay time of GABAergic mIPSC by 45.57±12.46% (P<0.05), but did not influence the frequency and amplitude of GABAergic mIPSC, when compared with the control. (3) To see whether or not ET has any effects on the local mIPSC mediated by glycine receptor,the holding potential was also set up at 0 mV, and under this condition extracellular superfusion was made with 1 μmol/L TTX and 10μmol/L biculline, an anagonist of GABA_A receptor, for 2 min, and then with consistent application of 50μmol/L ET, 1μmol/L TTX and 10μmol/L bicuculline for 1 min. ET had no effects on decay time, frequency and amplitude of glycinergic mIPSC. The above-mentioned results show that ET plays anesthetic or analgesic roles by modulating the decay time of GABAergic mIPSC, i.e. by prolonging the mean open time of GABA_A receptors, however, ET has no direct effect on local excitatory synaptic transmission in substantia gelatinosa neurons of the adult rat spinal cord.