Search

Additional file 1: Supplementary Figures and Tables.

In cranial and spinal nerve ganglia, both axotomized primary sensory neurons without regeneration (axotomy-nonregenerative neurons) and spared intact primary sensory neurons adjacent to axotomized neurons (axotomy-spared neurons) have been definitely shown to participate in pain transmission in peripheral neuropathic pain states. However, whether axotomized primary sensory neurons with regeneration (axotomy-regenerative neurons) would be integral components of neural circuits underlying peripheral neuropathic pain states remains controversial. In the present study, we utilized an adult rat sciatic nerve crush model to systematically analyze pain behaviors on the glabrous plantar surface of the hindpaw sural nerve skin territories. To the best of our knowledge, our results for the first time showed that heat hyperalgesia, cold allodynia, mechanical allodynia, and mechanical hyperalgesia emerged and persisted on the glabrous sural nerve skin areas after adult rat sciatic nerve crush. Interestingly, mechanical hyperalgesia was sexually dimorphic. Moreover, with our optimized immunofluorescence staining protocol of free-floating thick skin sections for wide-field epifluorescence microscopic imaging, changes in purely regenerative reinnervation on the same skin areas by axotomized primary sensory afferents were shown to be paralleled by those pathological pain behaviors. To our surprise, Protein Gene Product 9.5-immunoreactive nerve fibers with regular and large varicosities ectopically emigrated into the upper dermis of the glabrous sural nerve skin territories after adult rat sciatic nerve crush. Our results indicated that axotomy-regenerative primary sensory neurons could be critical elements in neural circuits underlying peripheral neuropathic pain states. Besides, our results implied that peripheral neuropathic pain transmitted by axotomy-regenerative primary sensory neurons alone might be a new dimension in the clinical therapy of peripheral nerve trauma beyond regeneration.

Background Antigen-specific and MHCII-restricted CD4+ αβ T cells have been shown or suggested to play an important role in the transition from acute to chronic mechanical allodynia after peripheral nerve injuries. However, it is still largely unknown where these T cells infiltrate along the somatosensory pathways transmitting mechanical allodynia to initiate the development of chronic mechanical allodynia after nerve injuries. Therefore, the purpose of this study was to ascertain the definite neuroimmune interface for these T cells to initiate the development of chronic mechanical allodynia after peripheral nerve injuries. Methods First, we utilized both chromogenic and fluorescent immunohistochemistry (IHC) to map αβ T cells along the somatosensory pathways for the transmission of mechanical allodynia after modified spared nerve injuries (mSNIs), i.e., tibial nerve injuries, in adult male Sprague-Dawley rats. We further characterized the molecular identity of these αβ T cells selectively infiltrating into the leptomeninges of L4 dorsal roots (DRs). Second, we identified the specific origins in lumbar lymph nodes (LLNs) for CD4+ αβ T cells selectively present in the leptomeninges of L4 DRs by two experiments: (1) chromogenic IHC in these lymph nodes for CD4+ αβ T cell responses after mSNIs and (2) fluorescent IHC for temporal dynamics of CD4+ αβ T cell infiltration into the L4 DR leptomeninges after mSNIs in prior lymphadenectomized or sham-operated animals to LLNs. Finally, following mSNIs, we evaluated the effects of region-specific targeting of these T cells through prior lymphadenectomy to LLNs and chronic intrathecal application of the suppressive anti-αβTCR antibodies on the development of mechanical allodynia by von Frey hair test and spinal glial or neuronal activation by fluorescent IHC. Results Our results showed that during the sub-acute phase after mSNIs, αβ T cells selectively infiltrate into the leptomeninges of the lumbar DRs along the somatosensory pathways responsible for transmitting mechanical allodynia. Almost all these αβ T cells are CD4 positive. Moreover, the temporal dynamics of CD4+ αβ T cell infiltration into the lumbar DR leptomeninges are specifically determined by LLNs after mSNIs. Prior lymphadenectomy to LLNs specifically reduces the development of mSNI-induced chronic mechanical allodynia. More importantly, intrathecal application of the suppressive anti-αβTCR antibodies reduces the development of mSNI-induced chronic mechanical allodynia. In addition, prior lymphadenectomy to LLNs attenuates mSNI-induced spinal activation of glial cells and PKCγ+ excitatory interneurons. Conclusions The noteworthy results here provide the first evidence that CD4+ αβ T cells selectively infiltrate into the DR leptomeninges of the somatosensory pathways transmitting mechanical allodynia and contribute to the transition from acute to chronic mechanical allodynia after peripheral nerve injuries. Electronic supplementary material The online version of this article (10.1186/s12974-018-1115-7) contains supplementary material, which is available to authorized users.

To determine the effect of early systemic administration of IL-10 on peripheral neuropathic pain induced by tibial nerve permanent transection [modified spared nerve injury (mSNI)]in adult rats.Male adult Sprague-Dawley (SD) rats (ten-week old, 250-300 g) with mSNI were randomly divided into mSNI, sham-operated, IL-10 intervention (intraperitoneal injection), PBS intervention (intraperitoneal injection) groups, each containing six rats. Intraperitoneally injections (IL-10 or PBS) were given immediately after surgeries for a single regime with a dosage of 500 uL (0.1 mg/mL). Plantar test, von Frey hairs test, pinprick test and acetone test were performed before and after tibial nerve injuries (0 d, 4/5 d, 7/8 d, 14/15 d) to evaluate region-specific pain responses of the rats on the plantar sural and saphenous skin territories of ipsilateral and contralateral hindpaws. The hindpaw position (on 8 d) of six additional rats with standard SNI was compared with those with mSNI.The rats with standard SNI showed an eversion posture of hindpaws, more prominent than those with mSNI. Region-specific pathological pain evoked by mechanical and thermal stimuli on the sural and saphenous skin territories of the plantar surfaces of rat hindpaws was demonstrated on the ipsilateral rather than contralateral hindpaws. This effect was shown in the rats with mSNI but not in those with sham operations. Compared with PBS, early intraperitoneal injection of IL-10 significantly and persistently attenuated either allodynia or hyperalgesia in the rats with mSNI.Tibial nerve permanent transection models of adult rats can be used as a simple but useful rodent model of peripheral neuropathic pain. Early systemic administration of IL-10 impairs the pathogenesis of neuropathic pain induced by tibial nerve injuries.