Whei-Min Lin

Degeneration of nociceptive nerve terminals in human peripheral neuropathy

Patients with peripheral neuropathy have symptoms involving small-diameter nociceptive nerves and elevated thermal thresholds. Nociceptive nerves terminate in the epidermis of the skin and are readily demonstrated with the neuronal marker, protein gene product 9.5 (PGP 9.5). To investigate the pathological characteristics of elevated thermal thresholds, we performed PGP 9.5 immunocytochemistry on 3 mm punch skin biopsies (the forearm and the leg) from 55 normal subjects and 35 neuropathic patients. Skin innervation was evaluated by quantifying epidermal nerve densities. Epidermal nerve densities were reduced in neuropathic patients compared to normal subjects. Epidermal nerve densities were variably correlated with thermal thresholds. The proportion of neuropathic patients with reduced epidermal nerve densities was larger than the proportion of neuropathic patients with elevated thermal thresholds. These results indicated that degeneration of epidermal nerve terminals preceded the elevation of thermal thresholds. Skin biopsy together with immunocytochemical demonstration of epidermal innervation offers a new approach to evaluate small-fiber sensory neuropathy.

Effects of aging on human skin innervation

To understand the effect of aging on human skin innervation, we investigated intraepidermal nerve fiber (IENF) density of skin biopsies. IENF densities of the distal leg were lower in elderly (≥ 60 years of age) than in young adults (19–39 years of age; 7.80 ± 0.79 vs 13.55 ± 0.85 fibers/mm, p < 0.01). A similar trend was also observed in the distal forearm (11.67 ± 1.55 vs 19.39 ± 1.60 fibers/mm, p < 0.001). IENF densities were negatively correlated with age according to multiple linear regression analysis on the entire study population (age range: 19–78 years) with standardized coefficients of −0.462 (p < 0.001) in the distal leg and −0.335 (p = 0.005) in the distal forearm. These findings suggest a significant reduction in IENF densities with age.

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.

Ultrastructural localization and regulation of protein gene product 9.5.

PROTEIN gene product 9.5 (PGP), a ubiquitin hydrolase, is abundant in the nervous system. To investigate the ultrastructural localization of PGP and the regulation of its expression, we performed electron microscopic immunocytochemistry and reverse transcription-polymerase chain reaction (RT-PCR) on normal and transected rat sciatic nerves. In normal nerves, strong PGP-immunoreactivity was localized in the myelinated and unmyelinated axons with virtually no staining in the Schwann cells. After nerve degeneration, denervated Schwann cells exhibited intense staining for PGP, corroborated with up-regulation of PGP transcripts by RT-PCR. The present data suggest that the pattern of expression of PGP is more complicated than was expected previously, and reflects the integrity of nerves and status of axon—Schwann cell interactions.

Sudomotor innervation in transthyretin amyloid neuropathy: Pathology and functional correlates

Autonomic neuropathy is a major component of familial amyloid polyneuropathy (FAP) due to mutated transthyretin, with sudomotor failure as a common manifestation. This study aimed to investigate the pathology and clinical significance of sudomotor denervation.

Glycemic control is related to the severity of impaired thermal sensations in type 2 diabetes

Small‐fibre sensory neuropathy of diabetes presenting as impaired thermal sensations is associated with ominous consequences, such as foot ulcer and amputation, but there is a lack of systematic studies on its occurrence in large cohorts. We investigated (1) the impact of glycemic control on thermal thresholds, (2) the frequencies and patterns of sensory deficits, and (3) the contribution of sensory nerve abnormalities to neuropathic symptoms.

Skin innervation and its effects on the epidermis

Sensory innervation of the skin subserves protective sensations for the body to prevent thermal and noxious injuries. Neurophysiologically, they belong to the categories of Adelta and C fibers, usually with caliber less than one micro m in diameter. Morphological demonstration of the terminals of these nerves in the epidermis has been recognized recently by sensitive immunocytochemistry and an axonal marker, the protein gene product 9.5 (PGP). PGP is a ubiquitin C-terminal hydrolase, which is abundantly present in the nervous system, and particularly enriched in the unmyelinated nerves. Sensory nerves positive for PGP arise from the dorsal root ganglion, pass through the dermis, parallel the epidermis-dermis border, penetrate the basement membrane, move vertically and upwards in the epidermis with tortuous course and knobby appearance, and finally terminate at the granular layers of the epidermis. In rodents, denervation of the skin results in degeneration of epidermal nerves within 48 h of nerve transection, and thinning of the epidermis. In humans, application of this technique to evaluate disorders of the peripheral nervous system makes study of the degeneration of sensory nerve terminals possible. Patients with sensory neuropathy had fewer epidermal nerves than normal subjects, consistent with the notion of distal axonopathy. This approach has the potential to evaluate human sensory neuropathy in temporal and spatial domains. In addition, the influences of epidermal denervation open a new field to explore the interactions between sensory nerves and keratinocytes.

Skin Denervation and Its Clinical Significance in Late-Stage Chronic Kidney Disease

OBJECTIVE To investigate the skin innervation and its clinical significance in late-stage chronic kidney disease (CKD). DESIGN Case series. SETTING National Taiwan University Hospital, Taipei, Taiwan. PATIENTS Forty consecutive nondiabetic patients with late-stage CKD (14 female and 26 male; mean [SD] age, 60.7 [12.3] years), including 2 cases with stage 3 CKD, 6 with stage 4 CKD, and 32 with stage 5 CKD, ie, end-stage kidney disease. INTERVENTIONS Clinical evaluation of neurological deficits, nerve conduction study, autonomic function tests, and a 3-mm-diameter skin biopsy specimen taken from the distal leg. MAIN OUTCOME MEASURES Quantitation of epidermal innervation, parameters of nerve conduction study, R-R interval variability, and sympathetic skin response. RESULTS Clinically, 21 patients (52.5%) were symptomatic with paresthesia over the limbs or autonomic symptoms. The intraepidermal nerve fiber (IENF) density was markedly reduced in patients with CKD compared with age- and sex-matched controls (mean [SD], 2.8 [2.0] vs 8.6 [2.8] fibers/mm; P < .001). Skin denervation was observed in 27 patients (67.5%). Fifteen patients (37.5%) had abnormalities on nerve conduction studies, and 29 patients (72.5%) had abnormal results on autonomic function tests. By analysis with multiple regression models, the IENF density was negatively correlated with the duration of renal disease (P = .02). Additionally, the R-R interval variability at rest was linearly correlated with the IENF density (P = .02) and the absence of sympathetic skin responses at the soles was associated with reduced IENF density (P = .03). CONCLUSIONS Small-fiber sensory and autonomic neuropathies constitute the major form of neuropathy in late-stage CKD. Furthermore, skin denervation was associated with the duration of renal disease.

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.

Patterns of target tissue reinnervation and trophic factor expression after nerve grafting.

Background: Reinnervation of target tissues determines functional outcomes after nerve grafting, which is important in traumatic injury caused by accidents or consequences resulting from surgical removal of tumors. Previous studies documented the influences of nerve repair mainly based on nerve morphometry but rarely compared the final outcomes according to target reinnervation patterns by nerve fibers of different categories. Methods: In a mouse model of nerve grafting, the authors analyzed the innervation indexes of different target tissues after transection-reimplantation on the sciatic nerve, which were defined as a parameter on the operated side normalized to that on the control side. Results: Muscle reinnervation appeared to be the best compared with skin reinnervation (p < 0.0001) and sweat gland reinnervation (p < 0.0001) at postoperative month 3. The sudomotor reinnervation was relatively higher than the cutaneous reinnervation (p = 0.014). The abundance of trophin transcripts for brain-derived neurotrophic factor (BDNF), glial cell line–derived neurotrophic factor (GDNF), and neurotrophin 3 (NT3) was higher in plantar muscles on the operated side than those on the control side. In contrast, transcripts of BDNF, GDNF, nerve growth factor, and NT3 were all similar in the footpad skin between the operated and control sides. Conclusions: The results suggested that, compared with the skin, muscles achieved the best reinnervation after nerve grafting, which was related to higher expression of BDNF, GDNF, and NT3 in muscles than in the skin.