Changes in Responses of Wide Dynamic Range Neurons in the Spinal Dorsal Horn After Dorsal Root or Dorsal Root Ganglion Compression

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Abstract
Study Design The electrophysiologic responses of wide dynamic range neurons in the spinal dorsal horn by compression of the dorsal root or of the dorsal root ganglion were investigated. Objectives This study identified differences between the compression of the dorsal root against the compression of the dorsal root ganglion by examining the responses of wide dynamic range neurons. Summary of Background Data The wide dynamic range neurons studied were known to be excited by primary afferent fibers, not only combined Aδ and C-nociceptive fibers but also low threshold mechanoreceptive Aβ fibers and Aδ fibers of down hairs. Thus, the wide dynamic range neurons are classified as nociceptive neurons. Methods Extracellular activities of 32 wide dynamic range neurons were recorded from the laminae 4-6 of the seventh lumbar cord in anesthetized cats. A microvessel clip (40 g) was applied to compress the dorsal root or the dorsal root ganglion. Results Dorsal root compression produced only an initial burst (about 10-40 seconds). Prolonged repetitive firings were rarely maintained. In contrast, dorsal root ganglion compression resulted in a maintained repetitive firing throughout the period of compression. After release of compression of the dorsal root and the dorsal root ganglion, responses to brushing were facilitated, and the low threshold center of the receptive field expanded. Conclusions These findings are consistent with the previous report that the radicular pain associated with a herniated intervertebral disc initially results from compression of the dorsal root ganglion.