Department of Anesthesiology, Weill Cornell Medicine, New York, NY 10065.
Department of Pharmacology, Weill Cornell Medicine, New York, NY 10065.
eNeuro. 2019 Jan 24;6(1). doi: 10.1523/ENEURO.0278-18.2018. eCollection 2019 Jan-Feb.
Volatile anesthetics affect neuronal signaling by poorly understood mechanisms. Activation of central dopaminergic pathways has been implicated in emergence from general anesthesia. The volatile anesthetic isoflurane differentially inhibits glutamatergic and GABAergic synaptic vesicle (SV) exocytosis by reducing presynaptic Ca influx without affecting the Ca-exocytosis relationship, but its effects on dopaminergic exocytosis are unclear. We tested the hypothesis that isoflurane inhibits exocytosis in dopaminergic neurons. We used electrical stimulation or depolarization by elevated extracellular KCl to evoke exocytosis measured by quantitative live-cell fluorescence imaging in cultured rat ventral tegmental area neurons. Using trains of electrically evoked action potentials (APs), isoflurane inhibited exocytosis in dopaminergic neurons to a greater extent (30 ± 4% inhibition; < 0.0001) than in non-dopaminergic neurons (15 ± 5% inhibition; = 0.014). Isoflurane also inhibited exocytosis evoked by elevated KCl in dopaminergic neurons (35 ± 6% inhibition; = 0.0007), but not in non-dopaminergic neurons (2 ± 4% inhibition). Pharmacological isolation of presynaptic Ca channel subtypes showed that isoflurane inhibited KCl-evoked exocytosis mediated exclusively by either Ca2.1 (P/Q-type Ca channels; 30 ± 5% inhibition; = 0.0002) or by Ca2.2 (N-type Ca channels; 35 ± 11% inhibition; = 0.015). Additionally, isoflurane inhibited single AP-evoked Ca influx by 41 ± 3% and single AP-evoked exocytosis by 34 ± 6%. Comparable reductions in exocytosis and Ca influx were produced by lowering extracellular [Ca]. Thus, isoflurane inhibits exocytosis from dopaminergic neurons by a mechanism distinct from that in non-dopaminergic neurons involving reduced Ca entry through Ca2.1 and/or Ca2.2.
挥发性麻醉剂通过尚未完全了解的机制影响神经元信号传递。中枢多巴胺能通路的激活被认为与全身麻醉的苏醒有关。挥发性麻醉剂异氟醚通过减少突触前 Ca 内流来抑制谷氨酸能和 GABA 能突触小泡（SV）的胞吐作用，而不影响 Ca-胞吐关系，但对多巴胺能胞吐作用的影响尚不清楚。我们测试了异氟醚抑制多巴胺能神经元胞吐作用的假设。我们使用电刺激或升高细胞外 KCl 来引发去极化，以通过培养的大鼠腹侧被盖区神经元的定量活细胞荧光成像来测量胞吐作用。使用电诱发动作电位（AP）的串，异氟醚对多巴胺能神经元的胞吐作用抑制作用更大（30±4%抑制；<0.0001），而非多巴胺能神经元（15±5%抑制；=0.014）。异氟醚还抑制多巴胺能神经元中由升高的 KCl 引起的胞吐作用（35±6%抑制；=0.0007），但不抑制非多巴胺能神经元（2±4%抑制）。突触前 Ca 通道亚型的药理学分离表明，异氟醚抑制由 Ca2.1（P/Q 型 Ca 通道；30±5%抑制；=0.0002）或 Ca2.2（N 型 Ca 通道；35±11%抑制；=0.015）介导的 KCl 诱发的胞吐作用。此外，异氟醚抑制单 AP 诱发的 Ca 内流 41±3%，单 AP 诱发的胞吐作用 34±6%。降低细胞外[Ca]也会产生类似的胞吐作用和 Ca 内流减少。因此，异氟醚通过一种与非多巴胺能神经元不同的机制抑制多巴胺能神经元的胞吐作用，该机制涉及通过 Ca2.1 和/或 Ca2.2 减少 Ca 内流。
