Published in Pain. 2014 Jun 28. pii: S0304-3959(14)00308-X. doi: 10.1016/j.pain.2014.06.019
Authors: Crosby ND et al
Cervical facet joint injury induces persistent pain and central sensitization. Preventing the peripheral neuronal signals that initiate sensitization attenuates neuropathic pain. Yet, there is no clear relationship among facet joint afferent activity, development of central sensitization, and pain, which may be hindering effective treatments for this pain syndrome.
This study investigates how afferent activity from the injured cervical facet joint affects induction of behavioral sensitivity and central sensitization. Intra-articular bupivacaine was administered to transiently suppress afferent activity immediately or 4 days after facet injury.
Mechanical hyperalgesia was monitored after injury, and spinal neuronal hyperexcitability and spinal expression of proteins that promote neuronal excitability were measured on day 7. Facet injury with saline vehicle treatment induced significant mechanical hyperalgesia (P less than .027), dorsal horn neuronal hyperexcitability (P less than .026), upregulation of pERK1/2, pNR1, mGluR5, GLAST, and GFAP, and downregulation of GLT1 (P less than .032).
However, intra-articular bupivacaine immediately after injury significantly attenuated hyperalgesia (P less than .0001), neuronal hyperexcitability (P less than .004), and dysregulation of excitatory signaling proteins (P less than .049).
In contrast, intra-articular bupivacaine at day 4 had no effect on these outcomes. Silencing afferent activity during the development of neuronal hyperexcitability (4hours, 8hours, 1day) attenuated hyperalgesia and neuronal hyperexcitability (P less than .045) only for the treatment given 4hours after injury.
This study suggests that early afferent activity from the injured facet induces development of spinal sensitization via spinal excitatory glutamatergic signaling. Peripheral intervention blocking afferent activity is effective only over a short period of time early after injury and before spinal modifications develop, and is independent of modulating spinal glial activation.