Intra- and Extraneuronal Changes of Immunofluorescence Staining for TNF- and TNFR1 in the Dorsal Root Ganglia of Rat Peripheral Neuropathic Pain Models

Abstract

1. Several lines of evidence suggest that cytokines and their receptors are initiators of changes in the activity of dorsal root ganglia (DRG) neurons, but their cellular distribution is still very limited or controversial. Therefore, the goal of present study was to investigate immunohistochemical distribution of TNF-alpha and TNF receptor-1 (TNFR1) proteins in the rat DRG following three types of nerve injury. 2. The unilateral sciatic and spinal nerve ligation as well as the sciatic nerve transection were used to induce changes in the distribution of TNF-alpha and TNFR1 proteins. The TNF-alpha and TNFR1 immunofluorescence was assessed in the L4-L5 DRG affected by nerve injury for 1 and 2 weeks, and compared with the contralateral ones and those removed from naive or sham-operated rats. A part of the sections was incubated for simultaneous immunostaining for TNF-alpha and ED-1. The immunofluorescence brightness was measured by image analysis system (LUCIA-G v4.21) to quantify immunostaining for TNF-alpha and TNFR1 in the naive, ipsi- and contralateral DRG following nerve injury. 3. The ipsilateral L4-L5 DRG and their contralateral counterparts of the rats operated for nerve injury displayed an increased immunofluorescence (IF) for TNF-alpha and TNFR1 when compared with DRG harvested from naive or sham-operated rats. The TNFalpha IF was increased bilaterally in the satellite glial cells (SGC) and contralaterally in the neuronal nuclei following sciatic and spinal nerve ligature. The neuronal bodies and their SGC exhibited bilaterally enhanced IF for TNF-alpha after sciatic nerve transection for 1 and 2 weeks. In addition, the affected DRG were invaded by ED-1 positive macrophages which displayed simultaneously TNFalpha IF. The ED-1 positive macrophages were frequently located near the neuronal bodies to occupy a position of the satellites. 4. The sciatic and spinal nerve ligature resulted in an increased TNFR1 IF in the neuronal bodies of both ipsi- and contralateral DRG. The sciatic nerve ligature for 1 week induced a rise in TNFR1 IF in the contralateral DRG neurons and their SGC to a higher level than in the ipsilateral ones. In contrast, the sciatic nerve ligature for 2 weeks caused a similar increase of TNFR1 IF in the neurons and their SGC of both ipsi- and contralateral DRG. The spinal nerve ligature or sciatic nerve transection resulted in an increased TNFR1 IF located at the surface of the ipsilateral DRG neurons, but dispersed IF in the contralateral ones. In addition, the SGC of the contralateral in contrast to ipsilateral DRG displayed a higher TNFR1 IF. 5. Our results suggest more sources of TNF-alpha protein in the ipsilateral and contralateral DRG following unilateral nerve injury including macrophages, SGC and primary sensory neurons. In addition, the SGC and macrophages, which became to be satellites, are well positioned to regulate activity of the DRG neurons by production of TNF-alpha molecules. Moreover, the different cellular distribution of TNFR1 in the ipsi- and contralateral DRG may refle...

CXCL12/CXCR4 axis: an emerging neuromodulator in pathological pain

“…These findings implicate that CXCL12/CXCR4 axis might contribute to the pathogenesis of these complications of peripheral neuropathy. Previously, it was found that unilateral nerve injury excited neurons, activated satellite glia, and initiated macrophage invasion at both ipsilateral and contralateral DRG (Dubový et al, 2006(Dubový et al, , 2007, but the mechanisms underlying these phenomena remain unclear. Recently, it was shown that chronic constriction injury (CCI) operation induced chronic pain, which was associated with the increased expression of CXCR4 in neuron and satellite glia in bilateral lumbar and cervical DRG (Dubovy et al, 2010).…”

An Approach to Identify Nerve Injury-Evoked Changes that Contribute to the Development or Protect Against the Development of Sustained Neuropathic Pain

“…Following nerve injury there is an invasion of immune cells into the nervous system that is promoted largely by the Wallerian degeneration of the injured nerve as well as by damage of the tissue surrounding the nerve (Chung et al, 2007;Dubovy et al, 2007;Hu and McLachlan, 2002). The immune cells alter the neuronal environment in part by changing the level of various cytokines/chemokines produced by the immune cells and by the neurons and glial cells in response to those released by the immune cells (Austin and MoalemTaylor; Brazda et al, 2009;Dubovy et al, 2006;Dubovy et al, 2010a;Dubovy et al, 2010b). Since some of the immune mediators have been shown to contribute to neuropathic pain by altering the excitability of both primary and secondary sensory neurons one approach that has been investigated to treat/prevent chronic pain is to pharmacologically alter their production.…”

Neuroimmune–Glia Interactions in the Sensory Ganglia Account for the Development of Acute Herpetic Neuralgia

“…In addition to the modulation of Kir4.1 expression on SGCs, we could not exclude that a direct action of TNF in the cell body of primary nociceptive neurons might mediate the genesis of herpetic pain. For instance, there are studies showing that TNF is able to sensitize directly the primary sensory nociceptive neurons in vitro (Ohtori et al, 2004;Dubový et al, 2006;Schäfers et al, 2008;Jancálek et al, 2010). TNFR1 is also upregulated in sensory neurons in models of neuropathic and inflammatory pain (Ohtori et al, 2004;Inglis et al, 2005;Dubový et al, 2006;Jancálek et al, 2010).…”

“…For instance, there are studies showing that TNF is able to sensitize directly the primary sensory nociceptive neurons in vitro (Ohtori et al, 2004;Dubový et al, 2006;Schäfers et al, 2008;Jancálek et al, 2010). TNFR1 is also upregulated in sensory neurons in models of neuropathic and inflammatory pain (Ohtori et al, 2004;Inglis et al, 2005;Dubový et al, 2006;Jancálek et al, 2010). The generation of specific TNFR1-deficient conditional mice in primary sensory neurons will unravel this issue.…”