Mol Pain
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Neuropathic pain can be generated by chronic compression of dorsal root ganglion (CCD). Stimulation of primary motor cortex can disrupt the nociceptive sensory signal at dorsal root ganglion level and reduce pain behaviors. But the mechanism behind it is still implicit. ⋯ In vivo extracellular recording of the ventral posterolateral thalamus, viral expression in the primary motor cortex, and protein kinase C gamma expression in dorsal root ganglion were investigated. So, optical cortico-thalamic inhibition by motor cortex stimulation can improve neuropathic pain behaviors in CCD animal, and knocking down of protein kinase C gamma plays a conducive role in the process. This study provides feasibility for in vivo optogenetic stimulation on primary motor cortex of dorsal root ganglion-initiated neuropathic pain.
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An electrophysiological technique that can record nerve impulses from a single nerve fiber is indispensable for studying modality-specific sensory receptors such as low threshold mechanoreceptors, thermal receptors, and nociceptors. The teased-fiber single-unit recording technique has long been used to resolve impulses that are likely to be from a single nerve fiber. The teased-fiber single-unit recording technique involves tedious nerve separation procedures, causes nerve fiber impairment, and is not a true single-fiber recording method. ⋯ This new approach can record impulses from rapidly adapting mechanoreceptors (RA), slowly adapting type 1 mechanoreceptors (SA1), and slowly adapting type 2 mechanoreceptors (SA2) in these tissue preparations. We have also applied the pressure-clamped single-fiber recordings to record impulses on Aβ-fibers, Aδ-fibers, and C-fibers. The pressure-clamped single-fiber recording technique provides a new tool for sensory physiology and pain research.
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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. ⋯ 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.