Presynaptic supperssion by an inhalation anesthetic

简介：全麻对突触前的作用存在争议，有无作用和抑制的报道。这种模糊是由于难以从突触前直接记录。本研究采用两种方法直接观察麻醉药的突触前作用。一种是使用电压敏感染料，另一种是对MNTB （Medial Nucleus of the梯形体）花萼的大突触前末端进行膜片钳。方法：(1)取2周龄大鼠脊髓400μ切片，用电压敏感吸收染料RH-482染色，灌注95% 02 + 5% CO2充氧的林格液。对背根进行刺激，测量背角的光吸收变化。通过添加AP-5和CNQX分离突触前改变。(2)取2周龄大鼠脑桥300μ切片，灌注95% 02 + 5% CO2充氧的林格液。膜片夹紧MNTB花萼突触前末端，记录全细胞记录。结果：(1)氟烷对突触前电位变化具有剂量依赖性和可逆性。含钡、镉、双青碱、士的宁的溶液也有这种抑制作用。(2)氟烷对EPSC具有剂量依赖性和可逆抑制作用。氟烷对突触前Ca电流、突触前Na电流和突触前动作电位均无抑制作用。但是氟烷使突触前超极化。结论：本研究表明氟烷抑制和超极化突触前。但确切的机制在很大程度上仍然未知。

Introduction : The action of general anestheticson the presynapse is controversial, both no action and suppression are reported. This ambiguity is due to the difficulty of direct recording from the presynapse. In the present study, we used two methodsto observe the anesthetic' s presynaptic action directly. One is to use the voltage sensitive dye, and another is to patch-clamp the large presynaptic terminal of the calyx of MNTB (Medial Nucleus of the trapezoid body).Method : (1) Slice preparations of 400μ from the spinal cord of the rat (Ca 2 weeks old) was stained with a voltage-sensitive absorption dye RH-482, and perfused with Ringer solution oxygenated with 95% 02 + 5% CO2.The dorsal root was stimulated and the light absorption changein the dorsal horn was measured.The presynaptic change was isolated by adding AP-5 and CNQX.(2) Slice preparations of 300μ from the pons of the rat (Ca 2 weeks old) was perfused with Ringer solution oxygenated with 95% 02 + 5% CO2.The presynaptic terminal of the calyx of MNTB was patch clamped and whole cell recordings were made Halothane was dissolved in the perfusing Ringer solution.Result : (1) The presynaptic potential change was dose-dependently and reversibly suppressed by halothane. This suppression was also observed with the solution containing Ba, Cd, bicuculline, strychnine. (2) The EPSC was dose-dependently and reversibly suppressed by halothane.Halothane did not suppress the presynaptic Ca current, nor presynaptic Na current, nor presynaptic action potential. But halothane hyperpolarized the presynapse.Conclusion : The present study showed that halothane suppress and hyperpolarize the presynapse. But the precise mechanism is still largely unknown.