Effects of serotonin on caudal raphe neurons: Activation of an inwardly rectifying potassium conductance
Effects of serotonin on caudal raphe neurons: Activation of an inwardly rectifying potassium conductance
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DOI：
10.1152/jn.1997.77.3.1349
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发表时间：
1997-03-01
影响因子：
2.5
通讯作者：
Talley, EM
中科院分区：
文献类型：
--
作者：
Bayliss, DA;Li, YW;Talley, EM
我们在新生大鼠脑干切片中使用全细胞电流和电压钳记录来表征发射特性和血清素 (5-HT) 对中缝苍白 (RPa) 和中缝暗 (ROb) 神经元 (n = 225) 的影响。在免疫组织化学处理检测色氨酸羟化酶 (TPH) 后回收的 51 个充满荧光黄的神经元样本中，发现 34 个具有 TPH 免疫反应性（即，血清素能）。血清素能神经元具有长时间的动作电位，并以低频（类似于 1 Hz）以通常不规则的模式自发放电；在较高的发射频率下，放电变得更加规则。这些神经元表现出尖峰频率适应，最大稳态放电率< 4 Hz。绝大多数已识别的血清素能神经元因浴液施加 5-HT 而超极化（94%；n = 32 of 34）；相反，该样本中大多数被 5-HT 超极化的细胞都是血清素能细胞（78%；n = 41 中的 32）。 TPH 免疫阴性神经元分为两个群体。其中一组的特性与中缝尾部的血清素能神经元没有什么区别。另一组确实与众不同。这些神经元具有更多超极化的静息膜电位，不自发活动，具有较短持续时间的动作电位，并且被 5-HT 去极化。尾中缝神经元对 5-HT (1-5 μM) 作出反应，电流钳中膜超极化 (-13.4 +/- 1.1 mV，平均值 +/- SE) 或电压钳中外向电流 (16.0 +/- 1.4 pA)。 5-HT 诱导的电流是内向整流的，与峰值电导的增加相关，并且对 K+ 具有高度选择性。它被 0.2 mM Ba2+ 完全阻断，但不能被 ATP 敏感 K+ 通道抑制剂格列本脲阻断。 5-HT的作用是剂量依赖性的，EC(50)为0.1-0.3μM。5-HT1A激动剂8-OH-DPAT模拟5-HT1A拮抗剂(+)WAY 100135和NAN 190，阻断5-HT的作用。 5-HT2A/C拮抗剂酮色林不抑制5-HT的作用。与未暴露于百日咳毒素的相邻对照切片（类似于 85%）相比，在急性暴露于百日咳毒素的切片中遇到的 5-HT 反应神经元较少（类似于 13%）。此外，在用含有 GTP gamma S (0.1 mM) 的移液管记录的神经元中，5-HT 诱导了内向整流电流，该电流在清洗时不会反转。在用 GTP gamma S 记录的许多细胞中，在没有激动剂的情况下产生的电流与 5-HT 敏感电流具有相同的特性；当长时间跟踪时，不依赖激动剂的 GTP gamma S 诱导的电导变得不敏感，以类似于 18 分钟的时间常数返回到对照水平。这些结果共同表明，ROb 和 RPa 的血清素能神经元在新生大鼠脑干切片制剂中自发活跃，并且这些神经元通过 5-HT1A 受体刺激而超极化是由于百日咳毒素敏感的 G 蛋白介导的内向整流 K+ 电导激活。此外，我们还发现了一组非血清素能髓缝神经元，它们具有独特的电生理特性，并且可以被 5-HT 去极化。
We used whole cell current- and voltage-clamp recording in neonatal rat brain stem slices to characterize firing properties and effects of serotonin (5-HT) on neurons (n = 225) in raphe pallidus (RPa) and raphe obscurus (ROb). Of a sample of 51 Lucifer yellow-filled neurons recovered after immunohistochemical processing to detect tryptophan hydroxylase (TPH), 34 were found to be TPH immunoreactive (i.e., serotonergic). Serotonergic neurons had long-duration action potentials and fired spontaneously at low frequency (similar to 1 Hz) in a pattern that was often irregular; at higher firing frequencies the discharge became more regular. These neurons displayed spike frequency adaptation, with maximal steady-state firing rates of < 4 Hz. The overwhelming majority of identified serotonergic neurons was hyperpolarized by bath-applied 5-HT (94%; n = 32 of 34); conversely, most cells in this sample that were hyperpolarized by 5-HT were serotonergic (78%; n = 32 of 41). TPH-immunonegative neurons were separated into two populations. One group had properties that were indistinguishable from those of serotonergic caudal raphe neurons. The other group was truly distinct; those neurons had more hyperpolarized resting membrane potentials, were not spontaneously active, had shorter-duration action potentials, and were depolarized by 5-HT. Caudal raphe neurons responded to 5-HT (1-5 mu M) with membrane hyperpolarization in current clamp (-13.4 +/- 1.1 mV, mean +/- SE) or with outward current in voltage clamp (16.0 +/- 1.4 pA). The current induced by 5-HT was inwardly rectifying and associated with an increase in peak conductance and was highly selective for K+. It was completely blocked by 0.2 mM Ba2+ but not by glibenclamide, an inhibitor of ATP-sensitive K+ channels. Effects of 5-HT were dose dependent, with an EC(50) of 0.1-0.3 mu M. The 5-HT1A agonist 8-OH-DPAT mimicked, and the 5-HT1A antagonists (+)WAY 100135 and NAN 190 blocked, effects of 5-HT. The 5-HT2A/C antagonist ketanserin did not inhibit the effects of 5-HT. Fewer 5-HT-responsive neurons were encountered in slices exposed acutely to pertussis toxin (similar to 13%) than in adjacent control slices not exposed to pertussis toxin (similar to 85%). In addition, in neurons recorded with pipettes containing GTP gamma S (0.1 mM), 5-HT induced an inwardly rectifying current that did not reverse on washing. In many cells recorded with GTP gamma S, a current developed in the absence of agonist that had properties identical to those of the 5-HT-sensitive current; when followed for extended periods, the agonist-independent GTP gamma S-induced conductance desensitized, returning toward control levels with a time constant of similar to 18 min. Together these results indicate that serotonergic neurons of ROb and RPa are spontaneously active in a neonatal rat brain stem slice preparation and that hyperpolarization of those neurons by 5-HT1A receptor stimulation is due to pertussis toxin-sensitive G protein-mediated activation of an inwardly rectifying K+ conductance. In addition, we identified a group of nonserotonergic medullary raphe neurons that had distinct electrophysiological properties and that was depolarized by 5-HT.