Bunin M A, Prioleau C, Mailman R B, Wightman R M
Department of Chemistry, University of North Carolina, Chapel Hill 27599-1108, USA.
J Neurochem. 1998 Mar;70(3):1077-87. doi: 10.1046/j.1471-4159.1998.70031077.x.
Fast scan cyclic voltammetry with carbon fiber electrodes has been used to investigate the dynamics of the neurotransmitter 5-hydroxytryptamine (5-HT) in the extracellular fluid of two brain regions: the dorsal raphe and the substantia nigra reticulata. The method used previously was shown to be optimized to allow the time course of 5-HT concentration changes to be measured rapidly. Measurements were made in slices prepared from the brains of rats with the carbon fiber electrode inserted into the tissue and a bipolar stimulating electrode placed on the slice surface. Identification of 5-HT as the detected substance in both regions was based on voltammetric, anatomical, physiological, and pharmacological evidence. Autoradiography using [3H]paroxetine revealed highest 5-HT transporter binding densities in the regions in which voltammetric measurements were made. Evaluation of the pharmacological actions of tetrodotoxin and tetrabenazine, as well as the effects of calcium removal, suggested that 5-HT storage was vesicular and that the release process was exocytotic. The effects of fluoxetine (0.5 microM) were typical of a competitive uptake inhibitor, changing Km with little effect on Vmax. Release of 5-HT was found to be maximal with wide (2-ms) stimulus pulses in both regions, as expected for release from small unmyelinated processes, and to increase linearly with the number of pulses when high frequencies (100 Hz) were used. At lower frequencies, the concentration observed was a function of both release and uptake. Kinetic simulations of the data revealed that the major difference in 5-HT neurotransmission between the two regions was that release and uptake rates are twice as large in the dorsal raphe ([5-HT] per pulse = 100 +/- 20 nM, Vmax = 1,300 +/- 20 nM/s for dorsal raphe; [5-HT] per pulse = 55 +/- 7 nM, Vmax = 570 +/- 70 nM/s for substantia nigra reticulata). When normalized to tissue content, uptake rates in both regions were identical and similar to rates previously reported for dopamine in dopamine terminal regions. Nonetheless, compared with dopaminergic transmission in terminal regions such as the striatum, the absolute clearance rates in the substantia nigra reticulata and dorsal raphe were lower, resulting in a longer lifetime of 5-HT in the extracellular fluid and allowing long-range interactions.
利用碳纤维电极进行的快速扫描循环伏安法，已被用于研究两个脑区——中缝背核和黑质网状部细胞外液中神经递质5-羟色胺（5-HT）的动态变化。先前使用的方法已被证明经过优化，能够快速测量5-HT浓度变化的时间进程。测量是在从大鼠大脑制备的脑片中进行的，将碳纤维电极插入组织中，并在脑片表面放置一个双极刺激电极。基于伏安法、解剖学、生理学和药理学证据，确定5-HT为这两个区域中检测到的物质。使用[3H]帕罗西汀进行的放射自显影显示，在进行伏安测量的区域中，5-HT转运体结合密度最高。对河豚毒素和丁苯那嗪的药理作用以及钙去除的影响进行评估后表明，5-HT的储存是囊泡性的，释放过程是胞吐性的。氟西汀（0.5微摩尔）的作用是典型的竞争性摄取抑制剂，改变米氏常数（Km），对最大反应速度（Vmax）影响很小。正如从小的无髓鞘突起释放所预期的那样，在两个区域中，发现宽（2毫秒）刺激脉冲时5-HT的释放最大，并且当使用高频（100赫兹）时，释放量随脉冲数线性增加。在较低频率下，观察到的浓度是释放和摄取的函数。对数据的动力学模拟表明，这两个区域之间5-HT神经传递的主要差异在于，中缝背核中的释放和摄取速率是黑质网状部的两倍（中缝背核每脉冲[5-HT] = 100±20纳摩尔，Vmax = 1300±20纳摩尔/秒；黑质网状部每脉冲[5-HT] = 55±7纳摩尔，Vmax = 570±70纳摩尔/秒）。当根据组织含量进行归一化时，两个区域的摄取速率相同，并且与先前报道的多巴胺终末区域中多巴胺的摄取速率相似。尽管如此，与纹状体等终末区域的多巴胺能传递相比，黑质网状部和中缝背核中的绝对清除率较低，导致5-HT在细胞外液中的寿命更长，从而允许进行远距离相互作用。
