BACKGROUND General anesthetics (GAs) may exert harmful effects on the developing brain by disrupting neuronal circuit formation. Anesthetics that act on γ-aminobutyric acid (GABA) receptors can interfere with axonal growth cone guidance, a critical process in the assembly of neuronal circuitry. Here we investigate the mechanism by which isoflurane prevents sensing of the repulsive guidance cue, Semaphorin 3A (Sema3A). METHODS Growth cone sensing was assayed by measuring growth cone collapse in dissociated neocortical cultures exposed to recombinant Sema3A in the presence or absence of isoflurane and/or a panel of reagents with specific actions on components of the GABA receptor and chloride ion systems. RESULTS Isoflurane exposure prevents Sema3A induced growth cone collapse. A GABAA α2 specific agonist replicates this effect (36.83 ± 3.417% vs 70.82 ± 2.941%, in the Sema3A induced control group, p < 0.0001), but an α1-specific agonist does not. Both a Na-K-Cl cotransporter 1 antagonism (bumetanide, BUM) and a chloride ionophore (IONO) prevent isoflurane from disrupting growth cone sensing of Sema3A. (65.67 ± 3.775% in Iso + BUM group vs 67.45 ± 3.624% in Sema3A induced control group, 65.34 ± 1.678% in Iso + IONO group vs 68.71 ± 2.071% in Sema3A induced control group, no significant difference) (n = 96 growth cones per group). CONCLUSION Our data suggest that the effects of isoflurane on growth cone sensing are mediated by the α2 subunit of the GABAA receptor and also that they are dependent on the developmental chloride gradient, in which Cl- exhibits a depolarizing effect. These findings provide a rationale for why immature neurons are particularly susceptible to anesthetic toxicity.

中文翻译：

---

麻醉剂通过对未成熟氯化物梯度介导的 GABAA α2 受体的作用来破坏生长锥引导提示感应。

背景 全身麻醉剂 (GA) 可能通过破坏神经元回路的形成对发育中的大脑产生有害影响。作用于 γ-氨基丁酸 (GABA) 受体的麻醉剂会干扰轴突生长锥引导，这是神经元回路组装的关键过程。在这里，我们研究了异氟醚阻止感知排斥性指导线索信号素 3A (Sema3A) 的机制。方法 通过测量在异氟醚和/或一组对 GABA 受体和氯离子系统的组分具有特定作用的试剂存在或不存在的情况下暴露于重组 Sema3A 的分离的新皮质培养物中的生长锥塌陷来测定生长锥感应。结果 异氟醚暴露可防止 Sema3A 诱导的生长锥塌陷。GABAA α2 特异性激动剂复制了这种效果 (36.83 ± 3. 417% vs 70.82 ± 2.941%，在 Sema3A 诱导的对照组中，p < 0.0001)，但 α1 特异性激动剂没有。Na-K-Cl 协同转运蛋白 1 拮抗剂（布美他尼，BUM）和氯离子载体 (IONO) 均可防止异氟醚破坏 Sema3A 的生长锥感应。（Iso + BUM 组为 65.67 ± 3.775%，Sema3A 诱导对照组为 67.45 ± 3.624%，Iso + IONO 组为 65.34 ± 1.678%，Sema3A 诱导对照组为 68.71 ± 2.071%，无显着差异）（n96）每组锥体）。结论 我们的数据表明异氟醚对生长锥感应的影响是由 GABAA 受体的 α2 亚基介导的，而且它们依赖于发育的氯化物梯度，其中 Cl- 表现出去极化作用。