Presynaptic supperssion by an inhalation anesthetic

前言：全麻药对突触前的作用一直存在争议，无作用和抑制作用均有报道。这种模糊性是由于直接从突触前记录的困难造成的。本研究采用两种方法直接观察麻醉剂S的突触前活动。方法：(1)取大鼠(2周龄)脊髓4 0 0μ切片，用压敏吸收染料RH-482染色，用含95%O2+5%CO2的Ringer液灌流刺激大鼠背根，观察背角光吸收的变化，加入AP-5和CNQX分离突触前改变。(2)用95%02+5%CO2充氧的Ringer液灌流大鼠脑片(30 0μ)，膜片钳MNTB的突触前末端，全细胞记录氟烷溶解于灌流液中。含有BA、Cd、荷包牡丹碱、士的宁的溶液也能观察到这种抑制作用。(2)氟烷对EPSC的抑制呈剂量依赖性和可逆性，氟烷对突触前钙电流、突触前钠电流和突触前动作电位均无抑制作用。但氟烷使前突触超极化。结论：本研究表明氟烷抑制和超极化前突触。但确切的机制在很大程度上仍不清楚。

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.