To-Jung Tseng

Cutaneous innervation in chronic inflammatory demyelinating polyneuropathy

Abstract—The authors evaluated epidermal nerve density (END) and thermal thresholds in 18 patients with chronic inflammatory demyelinating polyneuropathy (CIDP). END of patients with CIDP were lower than those of controls (4.5 ± 2.9 vs 10.5 ± 3.9 fibers/mm, p < 0.001). Reduced END were associated with autonomic symptoms. Thermal thresholds of patients with CIDP were elevated (88.2% for warm stimuli and 70.6% for cold stimuli). Patients with CIDP have small-fiber sensory and autonomic neuropathies.

Cutaneous Nerve Terminal Degeneration in Painful Mononeuropathy

Nociceptive nerves innervate the skin and play an important role in the generation of neuropathic pain. However, it remains elusive whether and how nociceptive nerve terminals degenerate in neuropathic pain conditions. To address this issue, we investigated cutaneous innervation in a model of painful mononeuropathy, the chronic constriction injury (CCI). The hind paws of rats were immunocytochemically stained with a pan-axonal marker, protein gene product 9.5 (PGP 9.5). Within 2 days after CCI, rats exhibited thermal hyperalgesia, and there was a partial depletion of epidermal nerves. The extent of reduction in epidermal nerves after CCI was variable with an epidermal nerve density of 3.65 +/- 1.97 fibers/mm (compared to 15.39 +/- 1.58 fibers/mm on the control side, P < 0.02). There was a mild but concomitant increase in PGP 9.5 (+) Langerhans cells in the epidermis of the skin with CCI (10.19 +/- 1.99 vs 7.75 +/- 1.36 cells/mm, P < 0.05). In the skin denervated by tight ligation of the sciatic nerve, epidermal nerves were completely depleted (0 fibers/mm vs. 12.26 +/- 1.44 fibers/mm on the control side, P < 0.001). Animals with tight ligation of the sciatic nerve exhibited thermal anesthesia. These findings suggest that the epidermis is partially denervated in CCI, and that a partial injury of nerves is correlated with the development of neuropathic pain.

Enhancement of cutaneous nerve regeneration by 4-methylcatechol in resiniferatoxin-induced neuropathy.

To generate an experimental neuropathy model in which small-diameter sensory nerves are specifically affected and to test a potential treatment, adult mice were given a single injection (50 &mgr;g/kg, i.p.) of the capsaicin analog resiniferatoxin (RTX). On Day 7 after RTX treatment, there was a 53% reduction in unmyelinated nerve density in the medial plantar nerve (p = 0.0067) and a 66% reduction in epidermal nerve density of hind paw skin (p = 0.0004) compared with vehicle-treated controls. Substance P-immunoreactive dorsal root ganglion neurons were also markedly depleted (p = 0.0001). These effects were associated with the functional deficit of prolonged withdrawal latencies to heat stimuli (p = 0.0007) on a hot plate test. The potential therapeutic effects of 4-methylcatechol (4MC) on this neuropathy were then tested by daily injections of 4MC (10 &mgr;g/kg, i.p.) from Days 7 to 35 after neuropathy induction. On Day 35, 4MC-treated mice had an increase in unmyelinated (p = 0.014) and epidermal nerve (p = 0.0013) densities and a reduction in thermal withdrawal latency (p = 0.0091) compared with RTX-only controls. These results indicate that 4MC promoted regeneration of unmyelinated nerves in experimental RTX-induced neuropathy and enhanced function.

Effects of decompression on neuropathic pain behaviors and skin reinnervation in chronic constriction injury.

Decompression is an important therapeutic strategy to relieve neuropathic pain clinically; there is, however, lack of animal models to study its temporal course of neuropathic pain behaviors and its influence on nerve regeneration to sensory targets. To address these issues, we established a model of decompression on rats with chronic constriction injury (CCI) and investigated the effect on skin reinnervation. Animals were divided into a decompression group, in which the ligatures were removed, and a CCI group, in which the ligatures remained at postoperative week 4 (POW 4). At this time point, the skin innervation indexes of protein gene product 9.5 (PGP 9.5), substance P (SP), and calcitonin gene-related peptide (CGRP) were reduced in both groups to similar degrees. Beginning from POW 6, the decompression group exhibited significant reductions of thermal hyperalgesia and mechanical allodynia compared to the CCI group (p<0.001). At POW 8, neuropathic pain behaviors had completely disappeared in the decompression group, and the decompression group had a higher skin innervation index of SP than the CCI group (0.45+/-0.05 vs. 0.16+/-0.03, p<0.001). These indexes were similar in both groups for PGP 9.5 (0.32+/-0.09 vs. 0.14+/-0.04, p=0.11) and CGRP (0.38+/-0.06 vs. 0.21+/-0.07, p=0.09). These findings demonstrate the temporal changes in the disappearance of neuropathic pain behaviors after decompression and suggest that decompression causes different patterns of skin reinnervation for different markers of skin innervation.

Reversal of ERK activation in the dorsal horn after decompression in chronic constriction injury.

Injury-induced neuropathic pain is related to changes in the central terminals of dorsal root ganglia neurons, i.e., dorsal horn plasticity. We investigated the influences of decompression by removing ligatures producing chronic constriction injury (CCI) in Sprague-Dawley rats at postoperative week (POW) 4, the decompression group; for comparison, all ligatures remained through the experimental period in the CCI group. The effect was evaluated with extracellular signal-regulated kinase (ERK) activation in the dorsal horn, i.e., number of phosphorylated ERK (+) cells in the dorsal horn. At POW 1, the dorsal horn indexes had increased to a similar degree in both groups (2.40+/-0.58 vs. 2.27+/-0.36, p=0.73). At POW 8, thermal hyperalgesia and mechanical allodynia had completely disappeared with a normalization of dorsal horn index (1.17+/-0.11 vs. 1.02+/-0.12 at POW 0, p=0.07) in the decompression group; in contrast, the dorsal horn index remained elevated in the CCI group (2.48+/-0.30, p<0.001) with persistent neuropathic pain behaviors at POW 8. This report suggests that ERK activation in the dorsal horn is correlated with neuropathic pain behaviors and its normalization reflects the reversal of neuropathic pain behaviors after decompression.

Depletion of peptidergic innervation in the gastric mucosa of streptozotocin-induced diabetic rats

Autonomic neuropathy affecting the gastrointestinal system is a major presentation of diabetic neuropathy. Changes in the innervation of gastric mucosa or muscle layers can contribute to gastrointestinal symptoms. The present study investigated this issue by quantitatively analyzing the immunohistochemical patterns of the gastric innervation in rats with streptozotocin (STZ)-induced diabetes. In control rats, calcitonin gene-related peptide (CGRP) and substance P (SP) (+) nerve fibers appeared in the gastric mucosa and muscle layers. Double immunohistochemical staining showed that immunoreactivities for SP and CGRP were co-localized with a pan-neuronal marker protein gene product 9.5. Both SP (+) nerve fibers (p<0.001) and CGRP (+) nerve fibers (p<0.005) were decreased in the gastric mucosa within 4 weeks of diabetes; the reduction persisted throughout 24 weeks. Diabetic rats treated with insulin did not show decrease of SP or CGRP (+) fibers in the mucosa 4 weeks after STZ injection (p>0.05). There was no significant change in SP (+) nerve fibers (p>0.05) or CGRP (+) nerve fibers (p>0.05) of the gastric muscle layers. Reverse transcription-polymerase chain reaction (RT-PCR) showed that the expression levels of SP and CGRP mRNA in the thoracic dorsal root ganglia were similar between diabetic and control animals (p>0.05). Qualitative and quantitative ultrastructural examinations on the gastric mucosa documented unmyelinated nerve degeneration. These results suggest the existence of gastric sensory neuropathy in STZ-induced diabetes, and this pathology provides a foundation for understanding diabetic gastropathy.

Peptidergic intraepidermal nerve fibers in the skin contribute to the neuropathic pain in paclitaxel-induced peripheral neuropathy.

Paclitaxel in chemotherapy-induced peripheral neuropathy (CIPN) is predominantly with a dose-limiting effect on neuropathic pain in clinical strategy. In the present study, the relationship between the neuropathic pain and nerve degeneration in paclitaxel CIPN was investigated. Adult male Sprague-Dawley (SD) rats were divided into three paclitaxel groups (0.5, 1.0, 2.0mg/kg) and a vehicle group with four intraperitoneal (i.p.) injections on alternating days. Our results demonstrated that the paclitaxel groups significantly exhibited the reductions of thermal hyperalgesia and mechanical allodynia. The neurotoxicity of paclitaxel conveyed the degeneration of intraepidermal nerve fibers (IENFs) in hindpaw glabrous skin. Nevertheless, the influence of paclitaxel to the peptidergic IENFs are even unknown. The skin innervation of protein gene product 9.5 (PGP 9.5)-immunoreactive (IR) IENFs in paclitaxel groups revealed the decreasing levels of density (73.54±0.72%, 63.17±1.77%, 61.79±2.68%, respectively; vs. vehicle group, p<0.05) throughout the entire experimental period. Additionally, the diminishing levels of density for peptidergic substance P (SP)-IR IENFs in paclitaxel groups were significantly shown (48.84±1.74%, 30.02±1.69%, 30.14±0.37%, respectively; vs. vehicle group, p<0.05). On the contrary, the density for peptidergic calcitonin gene-related peptide (CGRP)-IR IENFs in paclitaxel groups were revealed the similar decreasing levels (82.75±0.91%, 84.34±3.20%, 81.99±0.25%, respectively; vs. vehicle group, p<0.05). Linear regression analyses exhibited that densities of IENFs for PGP 9.5, SP, CGRP were correlated with withdrawal latencies (r(2)=0.77, p<0.0001; r(2)=0.75, p<0.0001; r(2)=0.28, p=0.0001, respectively) and mechanical thresholds (r(2)=0.43, p<0.0001; r(2)=0.73, p<0.0001; r(2)=0.40, p<0.0001, respectively). Therefore, the present results suggested that the development of neuropathic pain following paclitaxel injection induced the progressive degeneration of IENFs in skin and gave the evidence that the peptidergic IENFs may play an important role in therapeutic strategy of paclitaxe CIPN.

Influences of surgical decompression on the dorsal horn after chronic constriction injury: Changes in peptidergic and δ-opioid receptor (+) nerve terminals

To understand plastic changes in the dorsal horn related to neuropathic pain, we developed a model of decompression in rats with chronic constriction injury (CCI) and investigated corresponding changes in the dorsal horn. At postoperative week 4 (POW 4) of CCI, rats were divided into a decompression group, in which ligatures were removed, and a CCI group, in which ligatures remained. Spinal cords were immunostained for substance P (SP), the delta-opioid receptor (DOR), and calcitonin gene-related peptide (CGRP). Areas of immunoreactive nerve terminals in the dorsal horn were quantified and expressed as the dorsal horn index (immunoreactive areas of the operated side compared with those of the contralateral side). At POW 4, dorsal horn indexes of all of these molecules were significantly reduced in both groups to similar degrees (0.36-0.43). At POW 8, neuropathic pain behaviors had completely disappeared in the decompression group with significant reversal of the dorsal horn indexes compared with the CCI group (0.81+/-0.02 vs. 0.58+/-0.09, P < 0.001 for SP and 0.75+/-0.04 vs. 0.55+/-0.03, P < 0.001 for DOR). In the CCI group, neuropathic pain behaviors became normalized at POW 12 with corresponding changes in dorsal horn indexes for both SP and DOR similar to those of the decompression group. In contrast, changes in the dorsal horn indexes of CGRP were similar in both the CCI and decompression groups throughout the experimental period. These findings suggest that CCI and decompression cause different patterns in peptidergic and DOR (+) nerve terminals in the dorsal horn.

Determinants of nerve conduction recovery after nerve injuries: Compression duration and nerve fiber types

Introduction: The aims of this study were to determine the influences of: (1) timing of nerve decompression; and (2) nerve fiber types on the patterns of nerve conduction studies (NCS) after nerve injury. Methods: Nerve conduction studies (NCS) were performed on 3 models of nerve injury: (1) crush injury due to transient nerve compression (crush group); (2) chronic constriction injury (CCI), or permanent compression (CCI group); and (3) CCI with removal of ligatures, or delayed nerve decompression (De‐CCI group). Results: There were distinct patterns of NCS recovery. The crush and De‐CCI groups achieved similar motor nerve recovery, better than that of the CCI group. In contrast, recovery of sensory nerves was limited in the CCI and De‐CCI groups and was lower than in the crush group. Conclusions: Immediate relief of compression resulted in the best recovery of motor and sensory nerve conduction. In contrast, delayed decompression restored only motor nerve conduction. Muscle Nerve 52: 107–112, 2015

Redistribution of voltage-gated sodium channels after nerve decompression contributes to relieve neuropathic pain in chronic constriction injury

Nerve decompression is an important therapeutic strategy to relieve neuropathic pain and promote the peripheral nerve regeneration. To address these issues, we investigated the effects of nerve decompression on relief of neuropathic pain behaviors, redistribution of voltage-gated sodium channels (VGSCs), and skin reinnervation with chronic constriction injury (CCI). At post-operative week (POW) 4, animals were divided into a decompression group, in which the ligatures were removed, and a CCI group, in which the ligatures remained. Thermal hyperalgesia and mechanical allodynia at POW 8 had distinct reductions in decompression group compared to CCI group. At that time in CCI group, morphological evidence of pan VGSCs (Pan Nav) and isoforms of VGSCs (Nav1.6, Nav1.9, except for Nav1.8) were shown the widely distribution along the injured sciatic nerve. All of the VGSCs in decompression group became clustering around the node of Ranvier, similar to the pattern of control sciatic nerve at POW 8. Skin reinnervation was demonstrated by epidermal nerve density (END) for protein gene product 9.5 (PGP 9.5)-immunoreactive (IR) nerve fibers and a significant difference between groups only at POW 24 (p=0.01). Growth-associated protein 43 (GAP-43) is participated in the nerve fiber growth and sprouting, a difference in END for GAP-43-IR nerve fibers at POW 24 between groups were also significant (p=0.02). These observations demonstrated that nerve decompression was accompanied with the disappearance of neuropathic pain behaviors after CCI. Morphological studies provided the evidence that redistribution of VGSCs along the injured sciatic nerve but still with an incomplete skin reinnervation. These significant findings demonstrated a role of VGSCs in the pathogenesis of neuropathic pain, and gave an approaching in pharmacological basis of therapeutics.