Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.
Mol Pain. 2020 Jan-Dec;16:1744806920938237. doi: 10.1177/1744806920938237.
The Merkel disc is a main type of tactile end organs formed by Merkel cells and Aβ-afferent endings as first tactile sensory synapses. They are highly abundant in fingertips, touch domes, and whisker hair follicles of mammals and are essential for sensory tasks including social interaction, environmental exploration, and tactile discrimination. We have recently shown that Merkel discs use serotonin to transmit tactile signals from Merkel cells to Aβ-afferent endings to drive slowly adapting type 1 impulses on the Aβ-afferent nerves. This raises a question as whether the serotoninergic transmission at Merkel discs may be regulated by serotonin transporters and whether serotonin transporter inhibitors may affect the tactile transmission. Here, we made recordings from whisker afferent nerves of mouse whisker hair follicles and tested the effects of monoamine transporter inhibitors on slowly adapting type 1 impulses. We show that methamphetamine, a monoamine releasing facilitator and reuptake inhibitor, elicited spontaneous impulses as well as increased the numbers of slowly adapting type 1 impulses elicited by whisker hair deflections. S-duloxetine, a potent inhibitor of transporters of serotonin and norepinephrine, and fluoxetine, a selective inhibitor of serotonin transporters, both also increased the numbers of slowly adapting type 1 impulses. Prolonged treatment of whisker hair follicles with methamphetamine abolished most of slowly adapting type 1 impulses. Furthermore, the treatment of whisker hair follicles with methamphetamine resulted in serotonin release from whisker hair follicles. Taken together, our results suggest that serotonin transporters play a role in regulating tactile transmission at Merkel discs.
Merkel 盘是由 Merkel 细胞和 Aβ传入末梢形成的主要触觉终末器官，作为第一触觉感觉突触。它们在哺乳动物的指尖、触觉穹窿和触须毛囊中高度丰富，对于包括社交互动、环境探索和触觉辨别在内的感觉任务至关重要。我们最近表明，Merkel 盘利用 5-羟色胺将来自 Merkel 细胞的触觉信号传递到 Aβ传入末梢，以驱动 Aβ传入神经上的缓慢适应型 1 冲动。这就提出了一个问题，即 Merkel 盘的 5-羟色胺能传递是否可能受到 5-羟色胺转运体的调节，以及 5-羟色胺转运体抑制剂是否会影响触觉传递。在这里，我们从老鼠触须毛囊的触须传入神经中进行了记录，并测试了单胺转运体抑制剂对缓慢适应型 1 冲动的影响。我们表明，苯丙胺是一种单胺释放促进剂和再摄取抑制剂，可引起自发性冲动，并增加由触须毛发偏转而引起的缓慢适应型 1 冲动的数量。S-度洛西汀，一种强效的 5-羟色胺和去甲肾上腺素转运体抑制剂，以及氟西汀，一种选择性的 5-羟色胺转运体抑制剂，都能增加缓慢适应型 1 冲动的数量。用苯丙胺长时间处理触须毛囊会消除大部分缓慢适应型 1 冲动。此外，用苯丙胺处理触须毛囊会导致触须毛囊中 5-羟色胺的释放。总之，我们的结果表明，5-羟色胺转运体在调节 Merkel 盘的触觉传递中起作用。
