實驗性小纖維神經病變: 丙烯醯胺對感覺及自主神經之毒性研究

小直徑之感覺及自主神經病變(small-fiber sensory and autonomic neuropathy)是臨床上常見，但一直沒有適當診斷及治療策略的周邊神經疾病，最主要的困難在於這些神經的直徑通常小於1微米，觀察及取樣皆不方便，然而這些神經受傷所引起的後果卻極為嚴重，如因不知疼痛而受傷(pain injury)，但過去也因為技術上的困難，無法研究這些神經，因此許多實驗毒性神經病變(experimental toxic neuropathy)的研究也都認為這些神經可以倖免，然而一些功能的研究，顯示在傳統的大纖維神經病變，可能小纖維也會受傷，丙烯醯胺(acrylamide)即是一例，這些毒性神經病變提供了探討人類周邊神經病變的研究模式。 利用皮膚的免疫化學染色以顯現表皮的神經末稍，以及一般及免疫電子顯微鏡檢查，發現餵食小鼠丙烯醯胺(400ppm)後，表皮神經末梢的分枝在中毒早期會增加而表皮神經末梢有腫脹的現象，在中毒後，表皮神經密度才有明顯地降低。這一研究顯示丙烯醯胺不只是大纖維神經病變，對於小纖維神經亦有神經毒性。其次，這一研究具體呈現了小纖維神經病變的病理進程(pathological progression), 即表皮神經末梢的分枝增加及腫脹為表皮神經退化的早期癥象

Mitochondrial fission augments capsaicin-induced axonal degeneration

Capsaicin, an agonist of transient receptor potential vanilloid receptor 1, induces axonal degeneration of peripheral sensory nerves and is commonly used to treat painful sensory neuropathies. In this study, we investigated the role of mitochondrial dynamics in capsaicin-induced axonal degeneration. In capsaicin-treated rodent sensory axons, axonal swellings, decreased mitochondrial stationary site length and reduced mitochondrial transport preceded axonal degeneration. Increased axoplasmic Ca2+ mediated the alterations in mitochondrial length and transport. While sustaining mitochondrial transport did not reduce axonal swellings in capsaicin-treated axons, preventing mitochondrial fission by overexpression of mutant dynamin-related protein 1 increased mitochondrial length, retained mitochondrial membrane potentials and reduced axonal loss upon capsaicin treatment. These results establish that mitochondrial stationary site size significantly affects axonal integrity and suggest that inhibition of Ca2+-dependent mitochondrial fission facilitates mitochondrial function and axonal survival following activation of axonal cationic channels

Dynamin-2 mutations associated with centronuclear myopathy are hypermorphic and lead to T-tubule fragmentation

Skeletal muscle requires adequate membrane trafficking and remodeling to maintain its normal structure and functions. Consequently, many human myopathies are caused by mutations in membrane trafficking machinery. The large GTPase dynamin-2 (Dyn2) is best known for catalyzing membrane fission during clathrin-mediated endocytosis (CME), which is critical for cell signaling and survival. Despite its ubiquitous expression, mutations of Dyn2 are associated with two tissue-specific congenital disorders: centronuclear myopathy (CNM) and Charcot-Marie-Tooth (CMT) neuropathy. Several disease models for CNM-Dyn2 have been established to study its pathogenic mechanism; yet the cellular and biochemical effects of these mutations are still not fully understood. Here we comprehensively compared the biochemical activities of disease-associated Dyn2 mutations and found that CNM-Dyn2 mutants are hypermorphic with enhanced membrane fission activity, whereas CMT-Dyn2 is hypomorphic. More importantly, we found that the expression of CNM-Dyn2 mutants does not impair CME in myoblast, but leads to T-tubule fragmentation in both C2C12-derived myotubes and Drosophila body wall muscle. Our results demonstrate that CNM-Dyn2 mutants are gain-of-function mutations, and their primary effect in muscle is T-tubule disorganization, which explains the susceptibility of muscle to Dyn2 hyperactivity

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

Sudomotor innervation in transthyretin amyloid neuropathy: Pathology and functional correlates

ObjectiveAutonomic 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. MethodsSkin biopsies were performed on the distal leg of FAP patients with a follow-up duration of 3.81.6 years. Sudomotor innervation was stained with 2 markers: protein gene product 9.5 (PGP 9.5), a general neuronal marker, and vasoactive intestinal peptide (VIP), a sudomotor nerve functional marker, followed by quantitation according to sweat gland innervation index (SGII) for PGP 9.5 (SGIIPGP 9.5) and VIP (SGIIVIP). ResultsThere were 28 patients (25 men) with Ala97Ser transthyretin and late onset (59.9 +/- 6.0 years) disabling neuropathy. Autonomic symptoms were present in 22 patients (78.6%) at the time of skin biopsy. The SGIIPGP 9.5 and SGIIVIP of FAP patients were significantly lower than those of age- and gender-matched controls. The reduction of SGIIVIP was more severe than that of SGIIPGP 9.5 (p=0.002). Patients with orthostatic hypotension or absent sympathetic skin response at palms were associated with lower SGIIPGP 9.5 (p=0.019 and 0.002, respectively). SGIIPGP 9.5 was negatively correlated with the disability grade at the time of skin biopsy (p=0.004), and was positively correlated with the interval from the time of skin biopsy to the time of wheelchair usage (p=0.029). InterpretationThis study documented the pathological evidence of sudomotor denervation in FAP. SGIIPGP 9.5 was functionally correlated with autonomic symptoms, autonomic tests, ambulation status, and progression of disability. Ann Neurol 2015;78:272?28

Skin Denervation in Vasculitic Neuropathy

Background Skin denervation in vasculitic neuropathy has rarely been documented despite frequent manifestations of small-fiber neuropathy including reduced sensitivity and neuropathic pain. Recently, skin biopsy has been established as a new approach to diagnose small-fiber sensory neuropathy. Objectives To investigate the pathologic features of cutaneous nerves and to evaluate inflammatory vasculopathy in the skin of patients with vasculitis. Design Case series. Setting National Taiwan University Hospital , Taipei. Patients Six patients with vasculitic neuropathy . Interventions Patients had 3-mm punch biopsy specimens taken from the distal part of the leg (without active vasculitic lesions) and a sural nerve biopsy specimen was taken in addition to detailed neurologic examinations, laboratory investigations, and nerve conduction studies. Main Outcome Measures Results of nerve conduction studies, epidermal nerve fiber density studies, and immunohistochemistry. Results All 6 patients had combined large- and small-nerve-fiber involvement on the neurologic examinations. Nerve conduction studies showed a pattern of axonal neuropathy or mononeuropathy multiplex. Epidermal nerve fiber densities were significantly reduced in the skin of all patients, consistent with concomitant small-fiber neuropathies. Perivascular infiltration by T cells and macrophages was demonstrated by immunohistochemistry. All patients experienced neurologic improvement in muscle strength and alleviation of sensory symptoms after immunotherapy with corticosteroids, plasma exchange, or cyclophosphamide. Conclusions Small-diameter sensory nerves are affected in vasculitis in addition to the well- known effect of vasculitis on large-diameter nerves. Significant inflammatory vasculopathy is present in the skin despite the absence of clinically active vasculitic lesions

Pathophysiology of Small-Fiber Sensory System in Parkinson's Disease Skin Innervation and Contact Heat Evoked Potential

Sensory symptoms are frequent nonmotor complaints in patients with Parkinson's disease (PD). However, few investigations integrally explored the physiology and pathology of the thermonociceptive pathway in PD. We aim to investigate the involvement of the thermonociceptive pathway in PD. Twenty-eight PD patients (16 men, with a mean age and standard deviation of 65.6 +/- 10.7 years) free of neuropathic symptoms and systemic disorders were recruited for the study and compared to 23 age-and gender-matched control subjects (12 men, with a mean age and standard deviation of 65.1 +/- 9.9 years). We performed skin biopsy, contact heat-evoked potential (CHEP), and quantitative sensory tests (QST) to study the involvement of the thermonociceptive pathway in PD. The duration of PD was 7.1 +/- 3.2 (range 2-17 years) years and the UPDRS part III score was 25.6 +/- 9.7 (range 10-48) during the off period. Compared to control subjects, PD patients had reduced intra-epidermal nerve fiber (IENF) density (2.48 +/- 1.65 vs 6.36 +/- 3.19 fibers/mm, P<0.001) and CHEP amplitude (18.02 +/- 10.23 vs 33.28 +/- 10.48 mu V, P<0.001). Twenty-three patients (82.1%) had abnormal IENF densities and 18 (64.3%) had abnormal CHEP. Nine patients (32.1%) had abnormal thermal thresholds in the feet. In total 27 patients (96.4%) had at least 1 abnormality in IENF, CHEP, or thermal thresholds of the foot, indicating dysfunctions in the small-fiber nerve system. In control subjects, CHEP amplitude linearly correlated with IENF density (P<0.001). In contrast, this relationship disappeared in PD (P = 0.312) and CHEP amplitude was negatively correlated with motor severity of PD independent of age, gender, and anti-PD medication dose (P = 0.036), suggesting the influences of central components on thermonociceptive systems in addition to peripheral small-fiber nerves in PD. The present study suggested impairment of small-fiber sensory system at both peripheral and central levels is an intrinsic feature of PD, and skin biopsy, CHEP, and QST provided an integral approach for assessing such dysfunctions