Remote Activation of Microglia and Pro-Inflammatory Cytokines Predict the Onset and Severity of Below-Level Neuropathic Pain After Spinal Cord Injury In Rats (original) (raw)
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Role of spinal microglia in rat models of peripheral nerve injury and inflammation
European Journal of Pain, 2007
Mounting evidence supports the hypothesis that spinal microglia modulate the development and maintenance of some chronic pain states. Here we examined the role of spinal microglia following both peripheral inflammatory insult and peripheral nerve injury. We observed significant ipsilateral dorsal horn microglia activation 2 weeks after injury and bilateral activation 50 days following nerve injury as well as 24 h following intraplantar zymosan but not intraplantar complete Freund's adjuvant (CFA). Ipsilateral but not contralateral microglia activation was associated with hind paw mechanical hyperalgesia. Spinal injection of the glial metabolic inactivator fluorocitrate attenuated ipsilateral hyperalgesia and bilateral spinal microglia activation after peripheral nerve injury. Intrathecal fluorocitrate reversed hyperalgesia after intraplantar zymosan and produced no reversal of CFA-induced hyperalgesia. These data suggest a role for spinal glia in the persistence of mechanical hyperalgesia following peripheral nerve injury. However, activation of spinal microglia contralaterally did not correlate to nociception. Furthermore, it would appear that the time course of microglia activation and their contribution to inflammatory pain is dependent on the inflammatory stimulus administered.
European Journal of Pharmacology, 2009
The pharmacological attenuation of glial activation represents a novel approach for controlling neuropathic pain, but the role of microglial and astroglial cells is not well established. To better understand the potential role of two types of glial cells, microglia and astrocytes, in the pathogenesis of neuropathic pain, we examined markers associated with them by quantitative RT-PCR, western blot and immunohistochemical analyses in the dorsal horn of the lumbar spinal cord 7 days after chronic constriction injury (CCI) to the sciatic nerve in mice. The mRNA and protein of microglial cells were labeled with C1q and OX42(CD11b/c), respectively. The mRNA and protein of astrocytes were labeled with GFAP. The RT-PCR results indicated an increase in C1q mRNA that was more pronounced than the increased expression of GFAP mRNA ipsilateral to the injury in the dorsal spinal cord. Similarly, western blot and immunohistochemical analyses demonstrated an ipsilateral upregulation of OX42-positive cells (72 and 20%, respectively) and no or little (8% upregulation) change in GFAP-positive cells in the ipsilateral dorsal lumbar spinal cord. We also found that chronic intraperitoneal injection of the minocycline (microglial inhibitor) and pentoxifylline (cytokine inhibitor) attenuated CCI-induced activation of microglia, and both, but not fluorocitrate (astroglial inhibitor), diminished neuropathic pain symptoms and tactile and cold sensitivity. Our findings indicate that spinal microglia are more activated than astrocytes in peripheral injury-induced neuropathic pain. These findings implicate a glial regulation of the pain response and suggest that pharmacologically targeting microglia could effectively prevent clinical pain syndromes in programmed and/or anticipated injury.
Microglial activation in different models of peripheral nerve injury of the rat
Journal of Molecular Histology, 2007
Pain and pain modulation has been viewed as being mediated entirely by neurons. However, new research implicates spinal cord glia as key players in the creation and maintenance of pathological pain. Sciatic nerve lesions are one of the most commonly studied painrelated injuries. In our study we aimed to characterize changes in microglial activation in the rat spinal cord after axotomy and chronic constriction injury of the sciatic nerve and to evaluate this activation in regard to pain behavior in injured and control groups of rats. Microglial activation was observed at ipsilateral side of lumbar spinal cord in all experimental groups. There were slight differences in the level and extent of microglial activation between nerve injury models used, however, differences were clear between nerve-injured and sham animals in accordance with different level of pain behavior in these groups. It is known that activated microglia release various chemical mediators that can excite pain-responsive neurons. Robust microglial activation observed in present study could therefore contribute to pathological pain states observed following nerve injury.
Upregulation of Inflammatory Mediators in a Model of Chronic Pain after Spinal Cord Injury
Neurochemical Research, 2011
Chronic neuropathic pain is a disabling condition observed in large number of individuals following spinal cord injury (SCI). Recent progress points to an important role of neuroinflammation in the pathogenesis of central neuropathic pain. The focus of the present study is to investigate the role of proinflammatory molecules IL-1β, TNF-α, MCP-1, MMP-9 and TIMP-1 in chronic neuropathic pain in a rodent model of SCI. Rats were subjected to spinal cord contusion using a controlled linear motor device with an injury epicenter at T10. The SCI rats had severe impairment in locomotor function at 7 days post-injury as assessed by the BBB score. The locomotor scores showed significant improvement starting at day 14 and thereafter showed no further improvement. The Hargreaves' test was used to assess thermal hyperalgesia for hindpaw, forepaw and tail. A significant reduction in withdrawal latency was observed for forepaw and tail of SCI rats at days 21 and 28, indicating the appearance of thermal hyperalgesia. Changes in expression of mRNAs for IL-1β, TNF-α, MCP-1, MMP-9 and TIMP-1 were assessed using realtime polymerase chain reaction in spinal cord including the injury epicenter along with regions above and below the level of lesion at day 28 post-injury. A significant increase was observed in
Nature communications, 2016
Microglia and peripheral monocytes contribute to hypersensitivity in rodent models of neuropathic pain. However, the precise respective function of microglia and peripheral monocytes has not been investigated in these models. To address this question, here we combined transgenic mice and pharmacological tools to specifically and temporally control the depletion of microglia and monocytes in a mouse model of spinal nerve transection (SNT). We found that although microglia and monocytes are required during the initiation of mechanical allodynia or thermal hyperalgesia, these cells may not be as important for the maintenance of hypersensitivity. Moreover, we demonstrated that either resident microglia or peripheral monocytes are sufficient in gating neuropathic pain after SNT. We propose that resident microglia and peripheral monocytes act synergistically to initiate hypersensitivity and promote the transition from acute to chronic pain after peripheral nerve injury.
Cell reports, 2016
Peripheral nerve injury causes neuropathic pain accompanied by remarkable microgliosis in the spinal cord dorsal horn. However, it is still debated whether infiltrated monocytes contribute to injury-induced expansion of the microglial population. Here, we found that spinal microgliosis predominantly results from local proliferation of resident microglia but not from infiltrating monocytes after spinal nerve transection (SNT) by using two genetic mouse models (CCR2(RFP/+):CX3CR1(GFP/+) and CX3CR1(creER/+):R26(tdTomato/+) mice) as well as specific staining of microglia and macrophages. Pharmacological inhibition of SNT-induced microglial proliferation correlated with attenuated neuropathic pain hypersensitivities. Microglial proliferation is partially controlled by purinergic and fractalkine signaling, as CX3CR1(-/-) and P2Y12(-/-) mice show reduced spinal microglial proliferation and neuropathic pain. These results suggest that local microglial proliferation is the sole source of spi...
Neurochemistry International, 2004
Activated spinal glial cells have been strongly implicated in the development and maintenance of persistent pain states following a variety of stimuli including traumatic nerve injury. The present study was conducted to characterize the time course of surface markers indicative of microglial and astrocytic activation at the transcriptional level following an L5 nerve transection that results in behavioral hypersensitivity. Male Sprague-Dawley rats were divided into a normal group, a sham surgery group with an L5 spinal nerve exposure and an L5 spinal nerve transected group. Mechanical allodynia (heightened response to a non-noxious stimulus) of the ipsilateral hind paw was assessed throughout the study. Spinal lumbar mRNA levels of glial fibrillary acidic protein (GFAP), integrin alpha M (ITGAM), toll-like receptor 4 (TLR4) and cluster determinant 14 (CD14) were assayed using real-time reverse transcription polymerase chain reaction (RT-PCR) at 4 h, 1, 4, 7, 14 and 28 days post surgery. The spinal lumbar mRNA expression of ITGAM, TLR4, and CD14 was upregulated at 4 h post surgery, CD14 peaked 4 days after spinal nerve transection while ITGAM and TLR4 continued to increase until day 14 and returned to almost normal levels by postoperative day 28. In contrast, spinal GFAP mRNA did not significantly increase until postoperative day 4 and then continued to increase over the duration of the study. Our optimized real-time RT-PCR method was highly sensitive, specific and reproducible at a wide dynamic range. This study demonstrates that peripheral nerve injury induces an early spinal microglial activation that precedes astrocytic activation using mRNA for surface marker expression; the delayed but sustained expression of mRNA coding for GFAP implicates astrocytes in the maintenance phase of persistent pain states. In summary, these data demonstrate a distinct spinal glial response following nerve injury using real-time RT-PCR.
Clinical and Experimental Pharmacology and Physiology, 2015
It is believed that neuropathic pain results from aberrant neuronal discharges although some evidence suggests that the activation of glia cells contributes to pain after an injury to the nervous system. This study aimed to evaluate the role of microglial activation on the hyper-responsiveness of wide dynamic range neurons (WDR) and Toll-like receptor 4 (TLR4) expressions in a chronic constriction injury (CCI) model of neuropathic pain in rats. Adult male Wistar rats (230 AE 30 g) underwent surgery for induction of CCI neuropathy. Six days after surgery, administration of minocycline (10, 20, and 40 mg/kg, i.p.) was initiated and continued until day 14. After administration of the last dose of minocycline or saline, a behavioral test was conducted, then animals were sacrificed and lumbar segments of the spinal cord were collected for Western blot analysis of TLR4 expression. The electrophysiological properties of WDR neurons were investigated by single unit recordings in separate groups. The findings showed that after CCI, in parallel with thermal hyperalgesia, the expression of TLR4 in the spinal cord and the evoked response of the WDR neurons to electrical, mechanical, and thermal stimulation significantly increased. Post-injury administration of minocycline effectively decreased thermal hyperalgesia, TLR4 expression, and hyperresponsiveness of WDR neurons in CCI rats. The results of this study indicate that post-injury, repeated administration of minocycline attenuated neuropathic pain by suppressing microglia activation and reducing WDR neuron hyperresponsiveness. This study confirms that post-injury modulation of microglial activity is a new strategy for treating neuropathic pain.
Spinal Microglia Contribute to Sustained Inflammatory Pain via Amplifying Neuronal Activity
SUMMARYMicroglia are highly dynamic immune cells of the central nervous system (CNS). Microglial processes interact with neuronal elements constantly on the order of minutes. The functional significance of this acute microglia-neuron interaction and its potential role in the context of pain is still largely unknown. Here, we found that spinal microglia increased their process motility and electrophysiological reactivity within an hour after the insult in a mouse model of formalin-induced acute, sustained, inflammatory pain. Using an ablation strategy to specifically deplete resident microglia in the CNS, we demonstrate that microglia participate in formalin-induced acute sustained pain behaviors by amplifying neuronal activity in the spinal dorsal horn. Moreover, we identified that the P2Y12 receptor, which is specifically expressed in microglia in the CNS, was required for microglial function in formalin-induced pain. Taken together, our study provides a novel insight into the cont...