CXCL12 and CXCR4 proteins and mRNAs were monitored in the dorsal root ganglia (DRGs) of lumbar (L4-L5) and cervical (C7-C8) spinal segments of naïve rats, rats subjected to sham operation, and those undergoing unilateral complete sciatic nerve transection (CSNT) on post-operation day 7 (POD7). Immunohistochemical, Western blot, and RT-PCR analyses revealed bilaterally increased levels of CXCR4 protein and mRNA in both lumbar and cervical DRG neurons after CSNT. Similarly, CXCL12 protein levels increased, and CXCL12 mRNA was upregulated primarily in lumbar DRGs ipsilateral to the nerve lesion. Intrathecal application of the CXCR4 inhibitor AMD3100 following CSNT reduced CXCL12 and CXCR4 protein levels in cervical DRG neurons, as well as the length of afferent axons regenerated distal to the ulnar nerve crush. Furthermore, treatment with the CXCR4 inhibitor decreased levels of activated Signal Transducer and Activator of Transcription 3 (STAT3), a critical transforming factor in the neuronal regeneration program. Administration of IL-6 increased CXCR4 levels, whereas the JAK2-dependent STAT3 phosphorylation inhibitor (AG490) conversely decreased CXCR4 levels. This indicates a link between the CXCL12/CXCR4 signaling axis and IL-6-induced activation of STAT3 in the sciatic nerve injury-induced pro-regenerative state of cervical DRG neurons. The role of CXCR4 signaling in the axon-promoting state of DRG neurons was confirmed through in vitro cultivation of primary sensory neurons in a medium supplemented with CXCL12, with or without AMD3100. The potential involvement of conditioned cervical DRG neurons in the induction of neuropathic pain is discussed.

• Keywords
• AMD3100, IL-6, STAT3, axon regeneration, pre-conditioning, sciatic nerve, transection,
• MeSH
• Benzylamines MeSH
• Chemokine CXCL12 metabolism   genetics   MeSH
• Cyclams MeSH
• Interleukin-6 metabolism   pharmacology   MeSH
• Rats MeSH
• Sciatic Neuropathy * metabolism   MeSH
• Sensory Receptor Cells * metabolism   MeSH
• Sciatic Nerve * injuries   metabolism   MeSH
• Rats, Sprague-Dawley MeSH
• Receptors, CXCR4 * metabolism   genetics   MeSH
• Nerve Regeneration * MeSH
• Signal Transduction * MeSH
• Ganglia, Spinal metabolism   MeSH
• STAT3 Transcription Factor metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Benzylamines MeSH
• Chemokine CXCL12 MeSH
• CXCL12 protein, rat MeSH Browser
• Cxcr4 protein, rat MeSH Browser
• Cyclams MeSH
• Interleukin-6 MeSH
• plerixafor MeSH Browser
• Receptors, CXCR4 * MeSH
• Stat3 protein, rat MeSH Browser
• STAT3 Transcription Factor MeSH

Glial cells activated by peripheral nerve injury contribute to the induction and maintenance of neuropathic pain by releasing neuromodulating cytokines and chemokines. We investigated the activation of microglia and astrocytes as well as the cellular distribution of the chemokine CCL2 and its receptor CCR2 in the trigeminal subnucleus caudalis (TSC) ipsilateral and contralateral to infraorbital nerve ligature (IONL). The left infraorbital nerve was ligated under aseptic conditions, and sham controls were operated without nerve ligature. Tactile hypersensitivity was significantly increased bilaterally in vibrissal pads of both sham- and IONL-operated animals from day 1 to 7 and tended to normalize in sham controls surviving for 14 days. Activated microglial cells significantly increased bilaterally in the TSC of both sham- and IONL-operated animals with a marked but gradual increase in the ipsilateral TSC from 1 to 7 days followed by a decrease by day 14. In contrast, robust activation of astrocytes was found bilaterally in the TSC of IONL-operated rats from 3 to 14 days with a transient activation in the ipsilateral TSC of sham-operated animals. Cellular distribution of CCL2 varied with survival time. CCL2 immunofluorescence was detected in neurons within 3 days and in astrocytes at later time points. In contrast, CCR2 was found only in astrocytes at all time points with CCR2 intensity being dominant in the ipsilateral TSC. In summary, our results reveal bilateral activation of microglial cells and astrocytes as well as changes in the cellular distribution of CCL2 and its receptor CCR2 in the TSC during the development and maintenance of orofacial neuropathic pain.

• Keywords
• Astrocytes, Infraorbital nerve, Microglia, Unilateral nerve injury,
• MeSH
• Chemokine CCL2 metabolism   MeSH
• Rats MeSH
• Disease Models, Animal MeSH
• Neuralgia metabolism   MeSH
• Neuroglia metabolism   MeSH
• Rats, Wistar MeSH
• Receptors, CCR2 metabolism   MeSH
• Substantia Gelatinosa metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chemokine CCL2 MeSH
• Receptors, CCR2 MeSH

BACKGROUND: IL-6 is a typical injury-induced mediator. Together with its receptors, IL-6 contributes to both induction and maintenance of neuropathic pain deriving from changes in activity of primary sensory neurons in dorsal root ganglia (DRG). We used in situ hybridization to provide evidence of IL-6 and IL-6 receptors (IL-6R and gp130) synthesis in DRG along the neuraxis after unilateral chronic constriction injury (CCI) of the sciatic nerve as an experimental model of neuropathic pain. RESULTS: All rats operated upon to create unilateral CCI displayed mechanical allodynia and thermal hyperalgesia in ipsilateral hind paws. Contralateral hind paws and forepaws of both sides exhibited only temporal and nonsignificant changes of sensitivity. Very low levels of IL-6 and IL-6R mRNAs were detected in naïve DRG. IL-6 mRNA was bilaterally increased not only in DRG neurons but also in satellite glial cells (SGC) activated by unilateral CCI. In addition to IL-6 mRNA, substantial increase of IL-6R mRNA expression occurred in DRG neurons and SGC following CCI, while the level of gp130 mRNA remained similar to that of DRG from naïve rats. CONCLUSIONS: Here we evidence for the first time increased synthesis of IL-6 and IL-6R in remote cervical DRG nonassociated with the nerve injury. Our results suggest that unilateral CCI of the sciatic nerve induced not only bilateral elevation of IL-6 and IL-6R mRNAs in L4-L5 DRG but also their propagation along the neuraxis to remote cervical DRG as a general neuroinflammatory reaction of the nervous system to local nerve injury without correlation with signs of neuropathic pain. Possible functional involvement of IL-6 signaling is discussed.

• MeSH
• In Situ Hybridization MeSH
• Interleukin-6 genetics   MeSH
• Rats MeSH
• RNA, Messenger metabolism   MeSH
• Disease Models, Animal MeSH
• Sciatic Neuropathy genetics   MeSH
• Neuralgia genetics   MeSH
• Neuroglia metabolism   MeSH
• Rats, Wistar MeSH
• Receptors, Interleukin-6 genetics   MeSH
• Ganglia, Spinal metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Interleukin-6 MeSH
• RNA, Messenger MeSH
• Receptors, Interleukin-6 MeSH

Cannabinoid receptor type 2 (CB2R) plays a critical role in nociception. In contrast to cannabinoid receptor type 1 ligands, CB2R agonists do not produce undesirable central nervous system effects and thus promise to treat neuropathic pain that is often resistant to medical therapy. In the study presented here, we evaluated the bilateral distribution of the CB2R protein and messenger RNA (mRNA) in rat dorsal root ganglia (DRG) after unilateral peripheral nerve injury using immunohistochemistry, western blot, and in situ hybridization analysis. Unilateral chronic constriction injury (CCI) of the sciatic nerve induced neuropathic pain behavior and bilateral elevation of both CB2R protein and mRNA in lumbar L4-L5 as well as cervical C7-C8 DRG when compared with naive animals. CB2R protein and mRNA were increased not only in DRG neurons but also in satellite glial cells. The fact that changes appear bilaterally and (albeit at a lower level) even in the remote cervical DRG can be related to propagation of neuroinflammation alongside the neuraxis and to the neuroprotective effects of CB2R.

• Keywords
• remote neuroinflammation, satellite glial cells, unilateral nerve injury,
• MeSH
• Behavior, Animal MeSH
• Rats MeSH
• RNA, Messenger genetics   metabolism   MeSH
• Disease Models, Animal MeSH
• Sciatic Nerve injuries   MeSH
• Neuralgia genetics   metabolism   pathology   MeSH
• Rats, Wistar MeSH
• Receptor, Cannabinoid, CB2 genetics   metabolism   MeSH
• Gene Expression Regulation * MeSH
• Ganglia, Spinal metabolism   pathology   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• RNA, Messenger MeSH
• Receptor, Cannabinoid, CB2 MeSH

BACKGROUND: Current research implicates interleukin (IL)-6 as a key component of the nervous-system response to injury with various effects. METHODS: We used unilateral chronic constriction injury (CCI) of rat sciatic nerve as a model for neuropathic pain. Immunofluorescence, ELISA, western blotting and in situ hybridization were used to investigate bilateral changes in IL-6 protein and mRNA in both lumbar (L4-L5) and cervical (C7-C8) dorsal root ganglia (DRG) following CCI. The operated (CCI) and sham-operated (sham) rats were assessed after 1, 3, 7, and 14 days. Withdrawal thresholds for mechanical hyperalgesia and latencies for thermal hyperalgesia were measured in both ipsilateral and contralateral hind and fore paws. RESULTS: The ipsilateral hind paws of all CCI rats displayed a decreased threshold of mechanical hyperalgesia and withdrawal latency of thermal hyperalgesia, while the contralateral hind and fore paws of both sides exhibited no significant changes in mechanical or thermal sensitivity. No significant behavioral changes were found in the hind and fore paws on either side of the sham rats, except for thermal hypersensitivity, which was present bilaterally at 3 days. Unilateral CCI of the sciatic nerve induced a bilateral increase in IL-6 immunostaining in the neuronal bodies and satellite glial cells (SGC) surrounding neurons of both lumbar and cervical DRG, compared with those of naive control rats. This bilateral increase in IL-6 protein levels was confirmed by ELISA and western blotting. More intense staining for IL-6 mRNA was detected in lumbar and cervical DRG from both sides of rats following CCI. The DRG removed from sham rats displayed a similar pattern of staining for IL-6 protein and mRNA as found in naive DRG, but there was a higher staining intensity in SGC. CONCLUSIONS: Bilateral elevation of IL-6 protein and mRNA is not limited to DRG homonymous to the injured nerve, but also extended to DRG that are heteronymous to the injured nerve. The results for IL-6 suggest that the neuroinflammatory reaction of DRG to nerve injury is propagated alongside the neuroaxis from the lumbar to the remote cervical segments. This is probably related to conditioning of cervical DRG neurons to injury.

• MeSH
• Enzyme-Linked Immunosorbent Assay MeSH
• Functional Laterality physiology   MeSH
• Physical Stimulation MeSH
• In Situ Hybridization MeSH
• Hyperalgesia metabolism   MeSH
• Immunohistochemistry MeSH
• Interleukin-6 biosynthesis   genetics   MeSH
• Cervical Vertebrae MeSH
• Rats MeSH
• Lumbosacral Region MeSH
• Pain Measurement MeSH
• RNA, Messenger biosynthesis   genetics   MeSH
• Sciatic Neuropathy metabolism   MeSH
• Neuralgia metabolism   MeSH
• Image Processing, Computer-Assisted MeSH
• Rats, Wistar MeSH
• Receptors, Interleukin-6 biosynthesis   genetics   MeSH
• Ganglia, Spinal metabolism   MeSH
• Constriction, Pathologic MeSH
• Nerve Compression Syndromes metabolism   MeSH
• Hot Temperature MeSH
• Blotting, Western MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Interleukin-6 MeSH
• RNA, Messenger MeSH
• Receptors, Interleukin-6 MeSH