Mechanisms of halothane action on glycinergic inhibitory synaptic transmission

导读：全麻对抑制性突触传递的作用存在争议，有增强和抑制的报道。这种模糊性是由于在常规实验中获得抑制反应的中间存在兴奋性突触。现在，使用薄片制备，单突触抑制传递是可用的，允许测量全麻的明确作用。方法：取新生大鼠脊髓薄片，用含有2muM CNQX和10^-muM双球茎碱的林格氏液浸泡，95% O2 + 5% CO2泡制。对运动神经元进行全细胞记录（电压固定在-70mV）。视觉识别附近的中间神经元被刺激以唤起运动神经元的单突触抑制反应。将氟烷通过蒸发器（刻度盘设置2%）溶解在超浓生理盐水中，应用10分钟。结果：IPSC（抑制性突触后电流）被“2%”氟烷抑制并恢复。IPSC的振幅为55(]SY.+-。[)23% (n=15), 48(]SY.+-。[)16% (n=8) （mean()）。[)对照分别在氟烷施用5min或10min后的SD值。在一些细胞（15个中的4个）中，在氟烷施用的早期（1-2min）， IPSC略有增加。甘氨酸微灌注诱导向内电流。用2%的氟烷增强甘氨酸诱导电流的振幅和持续时间，水洗后恢复到控制值。结论：氟烷增强了甘氨酸能抑制传递的突触后事件。但使用完全相同的制备方法，我们报道了氟烷抑制了突触前电刺激引起的整体单突触抑制传递。这些结果表明，氟烷在甘氨酸能抑制传递中的主要作用位点是突触前。

Introduction : The action of general anesthetics on the inhibitory synaptic transmission is controversial, both augmentation and suppression are reported. This ambiguity is due to the existence of the excitatory synapse in the middle of the conventional experiment to get the inhibitory response. Now, using the thin slice preparation, monosynaptic inhibitory transmission is available, allowing the measurement of unambiguous action of general anesthetics.Method : Thin slices from the spinal cord of neonatal rats were prepared2, superfused with a Ringer solution containing 2muM CNQX and 10^-muM bicuculline, bubbled with 95% O2 + 5% CO2. Whole cell recordings were made from motoneurons (voltage clamped at -70mV). Nearby interneurons identified visually were stimulated to evoke monosynaptic inhibitory responses in motoneurons. Halothane was dissolved in the superfusing saline through a vaporizer (dial setting 2%) and applied for 10 min.Result : The IPSC (inhibitory Post Synaptic Current) was suppressed by "2%" halothane and recovered. The amplitude of IPSC was 55(]SY.+-。[)23% (n=15), 48(]SY.+-。[)16% (n=8) (mean(]SY.+-。[)SD) of the control after 5 min or 10 min application of halothane, respectively. In some cells (4 out of 15), IPSC was slightly augmented at an early stage (1-2min) of halothane application. Microperfusion of glycine induced an inward current. The amplitude and the duration of this glycine-induced current was enhanced by 2% halothane, and returned to the control value after wash-out.Conclusion : The present study showed that halothane enhances the postsynaptic event in the glycinergic inhibitory transmission. But using exactly the same preparation, we reported that halothane suppressed the overall monosynaptic inhibitory transmission evoked by electrical stimulation of the presynapse. These results indicate that halothane's main site of action in the glycinergic inhibitory transmission is presynapse.