Forskolin enhancement of opioid currents in rat locus coeruleus neurons
Forskolin enhancement of opioid currents in rat locus coeruleus neurons
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DOI：
10.1152/jn.1996.76.3.1559
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发表时间：
1996-09-01
影响因子：
2.5
通讯作者：
Williams, JT
中科院分区：
文献类型：
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作者：
Osborne, PB;Williams, JT
1. 已知阿片样物质使蓝斑核（LC）中的所有神经元超极化，并抑制腺苷酸环化酶。最近的研究表明，用福斯克林激活腺苷酸环化酶增加了LC细胞中阿片样物质超极化的振幅。本研究的目的是确定这种增强超极化的机制。使用细胞内和全细胞记录研究脑切片LC细胞中的激动剂诱导电流。Forskolin增加了-阿片样物质和α(2)-肾上腺素受体介导电流的幅度，其幅度与-60 mV下测量的对照组的30%相似。福斯克林的这种作用依赖于浓度的阈值与1 μ M相似，峰值效应与30 μ M相似。双氧福斯克林（30 μ M）引起阿片电流振幅的小幅下降（-52 +/- 28 pA，平均+/- SE）。当从水平平面切片记录的细胞中进行记录时，Forskolin在-140和-50 mV之间的整个电位范围内增加了向外的激动剂电流。这种增强的电流使表面逆转电位向更负的值移动。通过冠状面切片、增加细胞外钾浓度、卡贝诺酮处理片等方法改善空间钳，降低了福斯克林对阿片电流的增强，也降低了阿片电流本身。此外，福斯克林没有改变阿片电流的反转电位。当以百分比变化表示时，福斯克林对卡贝诺洛酮中的阿片电流没有显著影响（-13 +/- 13%），但对高细胞外钾（15 +/- 4%）和冠状片（31 +/- 12%）产生了小的增强。我们测试了两种模型来解释福斯克林的作用，一种是通过福斯克林敏感电导（偶联细胞模型）电致耦合细胞，另一种是阿片类药物介导对福斯克林诱导的阳离子电导的抑制（2电导模型）。实验结果仅适用于偶联细胞模型，该模型预测阿片/forskolin相互作用是间接的，主要发生在forskolin增加LC神经元之间电紧张偶联程度的反应中。增加耦合的结果将是增加核内的同步活动。
1. Opioids are known to hyperpolarize all neurons in the nucleus locus coeruleus (LC) and to inhibit adenylyl cyclase. Recent work has shown that activation of adenylyl cyclase with forskolin increased the amplitude of the opioid hyperpolarization in LC cells. The aim of the present study was to determine the mechanism of this augmented hyperpolarization.2. Agonist-induced currents were studied in LC cells in brain slices using both intracellular and whole cell recordings. Forskolin increased the amplitude of mu-opioid- and alpha(2)-adrenoceptor-mediated currents by similar to 30% of control measured at -60 mV. This effect of forskolin was dependent on the concentration having a threshold of similar to 1 mu M and a peak effect at similar to 30 mu M. Dideoxyforskolin (30 mu M) caused a small reduction (-52 +/- 28 pA, mean +/- SE) in the amplitude of the opioid current.3. Forskolin increased the agonist current in the outward direction over the entire potential range between -140 and -50 mV when recordings were made from neurons in cells recorded from slices cut in the horizontal plane. This augmented current produced a shift of the apparent reversal potential to more negative values.4. Both the forskolin augmentation of the opioid current and the opoid current itself were reduced when the space clamp was imrpoved by cutting the slice in the coronal plane, increasing the extracellular potassium concentration, and treating the slice with carbenoxolone. In addition, forskolin did not change the reversal potential of the opoid current. When expressed as a percentage change from control forskolin had no significant effect on the opioid current in carbenoxolone (-13 +/- 13%) but produced a small augmentation in high extracellular potassium (15 +/- 4%) and coronoal slices (31 +/- 12%).5. Two models were tested to explain the action of forskolin, one where cells are coupled electrotonically by a forskolin-sensitive conductance (coupled-cell model) and a second where opioids mediate an inhibition of a forskolin-induced cation conductance (2-conductance model). The experimental results were fit well only by the coupled-cell model, which predicted that the opioid/forskolin interaction is indirect and occurs primarily in response to forskolin increasing the degree of electrotonic coupling between LC neurons. The consequence of increased coupling would be to augment synchronous activity within the nucleus.