Effects of serotonin on caudal raphe neurons: Inhibition of N- and P/Q-type calcium channels and the afterhyperpolarization
Effects of serotonin on caudal raphe neurons: Inhibition of N- and P/Q-type calcium channels and the afterhyperpolarization
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DOI：
10.1152/jn.1997.77.3.1362
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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
本研究采用全细胞钙通道钡电流技术，观察了5-羟色胺（5-HT）对新生大鼠中缝尾侧核神经元钙通道电流和放电行为的影响。色氨酸羟化酶（TPH），5-羟色胺合成酶（n = 21）染色后恢复记录的神经元的亚群，这些细胞中，86%的TPH免疫反应，这表明大多数记录的神经元是多巴胺能。在中缝尾侧神经元中，钙通道电流在约-40 mV时开始激活，并在-10 mV时显示出952.2 +/- 144.2（SE）pA的峰值幅度。还观察到小的低电压激活电流（类似于22 pA）。在大多数测试细胞中，浴用5-HT对钙通道电流产生了强烈抑制（与90%相似）。5-HT抑制钙电流的EC（50）为0.1 μ M;饱和浓度（1.0 μ M）阻断了从-70 mV的保持电位在0 mV诱发的电流的49%（n = 101）。电流抑制与激活动力学的减慢和电流-电压关系的峰值的偏移相关，并且通过强去极化部分缓解。5-HT对电流的抑制作用可被5-HT 1A特异性激动剂8-OH-DPAT所模拟，并可被5-HT 1A拮抗剂NAN 190和（+）WAY 100135所阻断，但不受5-HT 2A/C拮抗剂酮色林的影响。ω-芋螺毒素GVIA（ω-CgTx）-敏感的N-型通道和ω-龙舌兰毒素IVA（ω-AgaIVA）-敏感的P/Q-型通道一起占钙电流的大部分（分别为36%和37%）。尼莫地平对钙电流没有影响，表明中缝尾侧神经元不表达二氢吡啶敏感的L型电流。应用omega-CgTx、omega-AgaIVA和尼莫地平后仍有大量残余电流（27%）。大部分5-HT敏感性钙电流被omega-CgTx和omega-AgaIVA阻断; 5-HT对残余电流影响不大。当用GTP γ S（一种不可水解的5 ′-三磷酸鸟苷（GTP）类似物）代替吸管中的GTP时，5-HT对钙电流的抑制是不可逆的。用百日咳毒素（PTX）预处理切片可阻断5-HT的作用。总之，这些数据表明，N-和P/Q-型钙电流的抑制在多巴胺能尾中缝神经元介导的5-HT 1A受体通过PTX敏感的G蛋白。在电流钳下，钙通道毒素（ω-CgTx和ω-AgaIVA）和5-HT各自引起尖峰后超极化的减少，并增强对注入电流的重复放电反应。5-HT和钙通道毒素对放电行为的相似作用表明5-HT的这些作用是次要的，对N型和P/Q型钙通道的抑制。
We characterized whole cell barium currents through calcium channels and investigated the effects of serotonin (5-HT) on calcium channel currents and firing behavior in visualized caudal raphe neurons of the neonatal rat in brain stem slices (n = 201). A subpopulation of recorded neurons was recovered after staining for tryptophan hydroxylase (TPH), the 5-HT synthesizing enzyme (n = 21); of those cells, 86% were TPH immunoreactive, suggesting that the majority of recorded neurons was serotonergic. Calcium channel currents began to activate at about -40 mV in caudal raphe neurons and showed a peak amplitude of 952.2 +/- 144.2 (SE) pA at -10 mV. A small low-voltage-activated current was also observed (similar to 22 pA). Calcium channel currents were potently inhibited by bath-applied 5-HT in most cells tested (similar to 90%). The EC(50) for inhibition of calcium current by 5-HT was 0.1 mu M; a saturating concentration (1.0 mu M) blocked similar to 49% of the current evoked at 0 mV from a holding potential of -70 mV (n = 101). Current inhibition was associated with a slowing of activation kinetics and a shift in the peak of the current-voltage relationship, and was partially relieved by strong depolarizations. Current inhibition by 5-HT was mimicked by 8-OH-DPAT, a specific 5-HT1A agonist, and blocked by the 5-HT1A antagonists NAN 190 and (+)WAY 100135, but was unaffected by ketanserin, a 5-HT2A/C antagonist. omega-Conotoxin GVIA (omega-CgTx)-sensitive N-type channels and omega-agatoxin IVA (omega-AgaIVA)-sensitive P/Q-type channels together accounted for most of the calcium current (36 and 37%, respectively). Nimodipine had no effect on calcium current, indicating that caudal raphe neurons do not express dihydropyridine-sensitive L-type currents. A substantial residual current (27%) remained after application of omega-CgTx, omega-AgaIVA, and nimodipine. Most of the 5-HT-sensitive calcium current was blocked by omega-CgTx and omega-AgaIVA; 5-HT had little effect on the residual current. Inhibition of calcium current by 5-HT was irreversible when GTP gamma S, a nonhydrolyzable guanosine 5'-triphosphate (GTP) analogue, was substituted for GTP in the pipette. In addition the effects of 5-HT were blocked by pretreating slices with pertussis toxin (PTX). Together these data indicate that inhibition of N- and P/Q-type calcium current in serotonergic caudal raphe neurons is mediated by a 5-HT1A receptor via PTX-sensitive G proteins. Under current clamp, calcium channel toxins (omega-CgTx and omega-AgaIVA) and 5-HT each caused a decrease in the spike afterhyperpolarization and enhanced the repetitive firing response to injected current. The similar effects of 5-HT and the calcium channel toxins on firing behavior suggest that those effects of 5-HT were secondary to inhibition of N- and P/Q-type calcium channels.