RESUMEN

Early adverse experiences disrupt brain development and behavior, but little is known about how such experiences impact on the development of the peripheral nervous system. Recently, we found alterations in the electrophysiological and histological characteristics of the sensory sural (SU) nerve in maternally deprived, artificially reared (AR) adult male rats, as compared with maternally reared (MR) control rats. In the present study, our aim was to characterize the ontogeny of these alterations. Thus, male pups of four postnatal days (PND) were (1) AR group, (2) AR and received daily tactile stimulation to the body and anogenital region (AR-Tactile group); or (3) reared by their mother (MR group). At PND 7, 14, or 21, electrophysiological properties and histological characteristics of the SU nerves were assessed. At PND 7, the electrophysiological properties and most histological parameters of the SU nerve did not differ among MR, AR, and AR-Tactile groups. By contrast, at PND 14 and/or 21, the SU nerve of AR rats showed a lower CAP amplitude and area, and a significant reduction in myelin area and myelin thickness, which were accompanied by a reduction in axon area (day 21 only) compared to the nerves of MR rats. Tactile stimulation (AR-Tactile group) partially prevented most of these alterations. These results suggest that sensory cues from the mother and/or littermates during the first 7-14 PND are relevant for the proper development and function of the adult SU nerve. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 351-362, 2018.

Asunto(s)

Privación Materna , Células Receptoras Sensoriales/citología , Células Receptoras Sensoriales/fisiología , Nervio Sural/citología , Nervio Sural/crecimiento & desarrollo , Tacto/fisiología , Animales , Masculino , Vaina de Mielina/patología , Vaina de Mielina/fisiología , Estimulación Física , Distribución Aleatoria , Ratas Wistar , Células Receptoras Sensoriales/patología , Nervio Sural/patología , Nervio Sural/fisiología

RESUMEN

BACKGROUND: The morphometric analysis of myelinated nerve fibers of peripheral nerves in cross-sectional optical microscopic images is valuable. Several automated methods for nerve fiber identification and segmentation have been reported. This paper presents a new method that uses a deep learning model of a convolutional neural network (CNN). We tested it for human sural nerve biopsy images. METHODS: The method comprises four steps: normalization, clustering segmentation, myelinated nerve fiber identification, and clump splitting. A normalized sample image was separated into individual objects with clustering segmentation. Each object was applied to a CNN deep learning model that labeled myelinated nerve fibers as positive and other structures as negative. Only positives proceeded to the next step. For pretraining the model, 70,000 positive and negative data each from 39 samples were used. The accuracy of the proposed algorithm was evaluated using 10 samples that were not part of the training set. A P-value of <0.05 was considered statistically significant. RESULTS: The total true-positive rate (TPR) for the detection of myelinated fibers was 0.982, and the total false-positive rate was 0.016. The defined total area similarity (AS) and area overlap error of segmented myelin sheaths were 0.967 and 0.068, respectively. In all but one sample, there were no significant differences in estimated morphometric parameters obtained from our method and manual segmentation. COMPARISON WITH EXISTING METHODS: The TPR and AS were higher than those obtained using previous methods. CONCLUSIONS: High-performance automated identification and segmentation of myelinated nerve fibers were achieved using a deep learning model.

Asunto(s)

Procesamiento de Imagen Asistido por Computador/métodos , Aprendizaje Automático , Microscopía/métodos , Fibras Nerviosas Mielínicas , Reconocimiento de Normas Patrones Automatizadas/métodos , Adolescente , Adulto , Anciano , Biopsia , Femenino , Humanos , Masculino , Persona de Mediana Edad , Fibras Nerviosas Mielínicas/patología , Nervio Sural/citología , Nervio Sural/patología

RESUMEN

The transplantation of rodent Schwann cells (SCs) provides anatomical and functional restitution in a variety of spinal cord injury (SCI) models, supporting the recent translation of SCs to phase 1 clinical trials for human SCI. Whereas human (Hu)SCs have been examined experimentally in a complete SCI transection paradigm, to date the reported behavior of SCs when transplanted after a clinically relevant contusive SCI has been restricted to the use of rodent SCs. Here, in a xenotransplant, contusive SCI paradigm, the survival, biodistribution, proliferation and tumorgenicity as well as host responses to HuSCs, cultured according to a protocol analogous to that developed for clinical application, were investigated. HuSCs persisted within the contused nude rat spinal cord through 6 months after transplantation (longest time examined), exhibited low cell proliferation, displayed no evidence of tumorigenicity and showed a restricted biodistribution to the lesion. Neuropathological examination of the CNS revealed no adverse effects of HuSCs. Animals exhibiting higher numbers of surviving HuSCs within the lesion showed greater volumes of preserved white matter and host rat SC and astrocyte ingress as well as axon ingrowth and myelination. These results demonstrate the safety of HuSCs when employed in a clinically relevant experimental SCI paradigm. Further, signs of a potentially positive influence of HuSC transplants on host tissue pathology were observed. These findings show that HuSCs exhibit a favorable toxicity profile for up to 6 months after transplantation into the contused rat spinal cord, an important outcome for FDA consideration of their use in human clinical trials.

Asunto(s)

Regeneración Nerviosa/fisiología , Células de Schwann/fisiología , Células de Schwann/trasplante , Traumatismos de la Médula Espinal/cirugía , Adulto , Factores de Edad , Animales , Antígenos Nucleares/metabolismo , Proteínas de Ciclo Celular , Proliferación Celular/fisiología , Supervivencia Celular , Células Cultivadas , Modelos Animales de Enfermedad , Femenino , Humanos , Masculino , Persona de Mediana Edad , Proteínas del Tejido Nervioso/metabolismo , Proteínas Asociadas a Matriz Nuclear/metabolismo , Ratas , Ratas Desnudas , Receptor de Factor de Crecimiento Nervioso/metabolismo , Traumatismos de la Médula Espinal/mortalidad , Nervio Sural/citología , Factores de Tiempo , Adulto Joven

RESUMEN

Entropy analysis of images are usually performed using Shannon entropy, which calculates the probability of occurrency of each gray level on the image. However, not only the pixel gray level but also the spatial distribution of pixels might be important for image analysis. On the other hand, sample entropy (SampEn) is an important tool for estimation of irregularity in time series, which calculates the probability of pattern occurrence within the series. Therefore, we propose here an extension of SampEn to a two-dimensional case, namely SampEn2D, as an entropy method for extracting features from images that accounts for the spatial distribution of pixels. SampEn2D was applied to histological segments of sural nerve obtained from young (30 days) and elderly (720 days) rats. Morphometric indexes, such as the total number of myelinated fibers and the average myelinated fibers area and perimeter were also calculated. Results show that SampEn2D can extract useful information from histological nerve images, classifying elderly rat image as more regular than young rat. As SampEn2D is related to irregularity/unpredictability, we can conclude that the proposed method is complementary to morphometric indexes. Further studies are being built to validate SampEn2D.

Asunto(s)

Envejecimiento/fisiología , Entropía , Procesamiento de Imagen Asistido por Computador/métodos , Nervio Sural/fisiología , Animales , Vaina de Mielina/fisiología , Probabilidad , Ratas Wistar , Nervio Sural/citología

RESUMEN

BACKGROUND: Recently, vagus nerve preservation or reconstruction of vagus has received increasing attention. The present study aimed to investigate the feasibility of reconstructing the severed vagal trunk using an autologous sural nerve graft. METHODS: Ten adult Beagle dogs were randomly assigned to two groups of five, the nerve grafting group (TG) and the vagal resection group (VG). The gastric secretion and emptying functions in both groups were assessed using Hollander insulin and acetaminophen tests before surgery and three months after surgery. All dogs underwent laparotomy under general anesthesia. In TG group, latency and conduction velocity of the action potential in a vagal trunk were measured, and then nerves of 4 cm long were cut from the abdominal anterior and posterior vagal trunks. Two segments of autologous sural nerve were collected for performing end-to-end anastomoses with the cut ends of vagal trunk (8-0 nylon suture, 3 sutures for each anastomosis). Dogs in VG group only underwent partial resections of the anterior and posterior vagal trunks. Laparotomy was performed in dogs of TG group, and latency and conduction velocity of the action potential in their vagal trunks were measured. The grafted nerve segment was removed, and stained with anti-neurofilament protein and toluidine blue. RESULTS: Latency of the action potential in the vagal trunk was longer after surgery than before surgery in TG group, while the conduction velocity was lower after surgery. The gastric secretion and emptying functions were weaker after surgery in dogs of both groups, but in TG group they were significantly better than in VG group. Anti-neurofilament protein staining and toluidine blue staining showed there were nerve fibers crossing the anastomosis of the vagus and sural nerves in dogs of TG group. CONCLUSION: Reconstruction of the vagus nerve using the sural nerve is technically feasible.

Asunto(s)

Abdomen/inervación , Nervio Sural/cirugía , Nervio Vago/cirugía , Abdomen/fisiología , Potenciales de Acción , Animales , Perros , Vaciamiento Gástrico/fisiología , Nervio Sural/citología , Nervio Sural/fisiología , Trasplantes , Nervio Vago/citología , Nervio Vago/fisiología

RESUMEN

Spontaneously Diabetic Torii (SDT) rat is a hereditary model of diabetes. Although the SDT rat shows severe diabetic complications, the onset of hyperglycemia is late. SDT fatty rat, established by introducing the fa allele of the Zucker fatty rat to SDT rat, develops diabetes much faster than SDT rat. In the present study, diabetic peripheral neuropathy (DPN) was evaluated to show the further usefulness of this animal model. Motor nerve conduction velocity (MNCV) was delayed, and the number of sural nerve fibers was decreased in SDT fatty rat. Treatment of pioglitazone lowered blood glucose level and prevented delay of MNCV in SDT fatty rats. SDT fatty rat is a useful animal model for studies of DPN in type 2 diabetes.

Asunto(s)

Diabetes Mellitus Tipo 2/fisiopatología , Neuropatías Diabéticas/fisiopatología , Modelos Animales de Enfermedad , Neuronas Motoras/fisiología , Conducción Nerviosa/fisiología , Animales , Glucemia/efectos de los fármacos , Peso Corporal , Diabetes Mellitus Tipo 2/complicaciones , Insulina/sangre , Masculino , Pioglitazona , Ratas , Ratas Sprague-Dawley , Ratas Zucker , Nervio Sural/citología , Tiazolidinedionas/farmacología

RESUMEN

In mammalian peripheral nerves, unmyelinated C-fibers usually outnumber myelinated A-fibers. By using transmission electron microscopy, we recently showed that the saphenous nerve of the naked mole-rat (Heterocephalus glaber) has a C-fiber deficit manifested as a substantially lower C:A-fiber ratio compared with other mammals. Here we determined the uniqueness of this C-fiber deficit by performing a quantitative anatomical analysis of several peripheral nerves in five further members of the Bathyergidae mole-rat family: silvery (Heliophobius argenteocinereus), giant (Fukomys mechowii), Damaraland (Fukomys damarensis), Mashona (Fukomys darlingi), and Natal (Cryptomys hottentotus natalensis) mole-rats. In the largely cutaneous saphenous and sural nerves, the naked mole-rat had the lowest C:A-fiber ratio (∼1.5:1 compared with ∼3:1), whereas, in nerves innervating both skin and muscle (common peroneal and tibial) or just muscle (lateral/medial gastrocnemius), this pattern was mostly absent. We asked whether lack of hair follicles alone accounts for the C-fiber paucity by using as a model a mouse that loses virtually all its hair as a consequence of conditional deletion of the ß-catenin gene in the skin. These ß-catenin loss-of function mice (ß-cat LOF mice) displayed only a mild decrease in C:A-fiber ratio compared with wild-type mice (4.42 compared with 3.81). We suggest that the selective cutaneous C-fiber deficit in the cutaneous nerves of naked mole-rats is unlikely to be due primarily to lack of skin hair follicles. Possible mechanisms contributing to this unique peripheral nerve anatomy are discussed.

Asunto(s)

Enfermedades Desmielinizantes , Ratas Topo/anatomía & histología , Fibras Nerviosas Amielínicas/fisiología , Nervio Peroneo/citología , Piel/inervación , Nervio Sural/citología , África , Animales , Enfermedades Desmielinizantes/genética , Femenino , Folículo Piloso/citología , Folículo Piloso/inervación , Folículo Piloso/fisiología , Masculino , Ratas Topo/clasificación , Fibras Nerviosas Amielínicas/clasificación , Nervio Peroneo/química , Nervio Peroneo/fisiología , Piel/citología , Especificidad de la Especie , Nervio Sural/química , Nervio Sural/fisiología

RESUMEN

We hypothesized that cutaneous afferent myelinated fibers (A-fibers) and afferent unmyelinated fibers (C-fibers) respond to the same natural stimuli applied to their axons as to their terminals in the skin. In anesthetized rats, activity was recorded from afferent axons in strands isolated proximally from the sural nerve. Mechanical, cold or heat stimuli were applied to the skin or along a 15-mm length of the distal sural nerve. One-hundred and eighteen A-fibers and 109 C-fibers were characterized by their conduction velocity and/or shape of their action potentials, and by their responses to natural stimulation of the skin. Then, these fibers were tested for their responses to the same stimuli applied to the nerve. In some cases, the nerve was crushed distally after the nerve fibers had been characterized by their responses to physiological stimulation of the skin, and the responses to stimuli applied to the nerve proximal to the lesion were tested again. Almost all non-nociceptive cold-sensitive (type 1) C-fibers (97%) could be activated by cold stimuli applied to the nerve. Of nociceptive cold-sensitive (type 2) C-fibers, 39% were activated by cold stimuli applied to the nerve. Furthermore, 34% of heat-sensitive C-fibers could be activated by heating the nerve. In contrast, only 2-4% of mechanosensitive A-fibers and C-fibers responded to mechanical stimuli applied to the nerve. In conclusion, cold and heat sensitivity of cutaneous afferent neurons is not restricted to their terminals in the skin, but often extends along the axons in the nerve. Mechanosensitivity is restricted to the afferent endings in the skin.

Asunto(s)

Axones/fisiología , Mecanorreceptores/fisiología , Fibras Nerviosas Mielínicas/fisiología , Fibras Nerviosas Amielínicas/fisiología , Neuronas Aferentes/fisiología , Termorreceptores/fisiología , Sensación Térmica/fisiología , Animales , Frío , Electrofisiología , Calor , Masculino , Neuronas Aferentes/citología , Estimulación Física , Ratas , Ratas Wistar , Piel/inervación , Nervio Sural/citología , Nervio Sural/fisiología

RESUMEN

BACKGROUND: In the present study, the labeling efficacy of tracers Fluoro-ruby (FR), Fluoro-emerald (FE), True Blue (TB), Fluoro-Gold (FG), Diamidino Yellow (DY) and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) to retrogradely label the cutaneous afferent neurons in the rat was examined. METHODS: The proximal stump of the transected sural nerve was exposed for 1 hour either to one of the examined dyes (FR, FE, TB, FG, DY and DiI group) in single labeling experiments, or to mixtures of two dyes (TB-FG, FG-DiI, TB-DY and TB-DiI group) in double labeling experiments (n=5 for each group). After 10 days, dorsal root ganglia (DRGs) L3-S1 were harvested, cut to 20 microm thick longitudinal sections and all labeled neurons were counted. RESULTS: The average numbers of labeled DRG neurons in FR group (1063+/-158; mean+/-SD) and FE group (1067+/-203) were statistically significantly lower than those in TB group (2831+/-379), FG group (2802+/-134), DY group (2888+/-262) or DiI group (2900+/-278) (p<0.05). In double labeling experiments, the average number of double labeled neurons in TB-DY group (2208+/-207) was statistically significantly lower than those in TB-FG group (2775+/-316), FG-DiI group (2921+/-419), or TB-DiI group (2805+/-179) (p<0.05). CONCLUSIONS: Among examined tracers, TB, FG, DY and DiI, have the highest and similar labeling efficacy for retrograde labeling of cutaneous afferent neurons in the rat. The tracers TB, DiI and FG effectively label the same neuronal population in double labeling, therefore, their combinations are most suitable for double retrograde labeling studies of cutaneous afferent neurons in the rat.

Asunto(s)

Colorantes Fluorescentes/farmacocinética , Ganglios Espinales/citología , Técnicas de Trazados de Vías Neuroanatómicas/métodos , Trazadores del Tracto Neuronal/farmacocinética , Células Receptoras Sensoriales/citología , Coloración y Etiquetado/métodos , Vías Aferentes/citología , Vías Aferentes/fisiología , Animales , Transporte Axonal/fisiología , Recuento de Células/métodos , Disección/métodos , Ganglios Espinales/fisiología , Masculino , Procedimientos Neuroquirúrgicos/métodos , Ratas , Ratas Wistar , Células Receptoras Sensoriales/fisiología , Nervio Sural/citología , Nervio Sural/fisiología , Nervio Sural/cirugía

RESUMEN

Sprouting of uninjured nociceptive axons was examined in young adult, middle aged and aged rats. Axon sprouting from the spared sural nerve, both into adjacent denervated skin and into end-to-side coapted nerve graft, was significantly higher in young rats than in aged rats. Cross-transplantations of the end-to-side coapted nerve grafts between young and aged rats demonstrated that axon sprouting from young recipient nerves into aged donor nerve grafts was significantly deteriorated, whereas the axon sprouting from aged recipient nerves into young donor nerve grafts was not statistically significantly affected. The levels of laminin polypeptides in peripheral nerves were 50-100% higher in young adult than in aged rats. However, the levels of peripherin, NGF isoforms and TrkA in skin, peripheral nerves and DRG, respectively, were not significantly reduced in aged rats. Therefore, impaired sprouting of nociceptive axons in aged rats is due rather to the alterations in peripheral neural pathways, than to the limited sprouting capacity of aged sensory neurons. Decreased levels of extracellular matrix components might be important in this respect.

Asunto(s)

Envejecimiento/fisiología , Axones/fisiología , Regeneración Nerviosa/fisiología , Nociceptores/fisiología , Nervio Sural/fisiología , Animales , Ganglios Espinales/metabolismo , Proteínas de Filamentos Intermediarios/metabolismo , Laminina/metabolismo , Masculino , Glicoproteínas de Membrana/metabolismo , Fibras Nerviosas Mielínicas/fisiología , Factor de Crecimiento Nervioso/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Vías Nerviosas/fisiología , Nociceptores/citología , Dolor/fisiopatología , Dolor/cirugía , Nervios Periféricos/fisiología , Nervios Periféricos/trasplante , Periferinas , Isoformas de Proteínas/metabolismo , Ratas , Ratas Wistar , Receptor trkA/metabolismo , Recuperación de la Función/fisiología , Piel/inervación , Piel/metabolismo , Nervio Sural/citología

RESUMEN

Aging affects peripheral nerve function and regeneration in experimental models but few literature reports deal with animals aged more than one year. We investigated morphological and morphometric aspects of the sural nerve in aging rats. Female Wistar rats 360, 640 and 720 days old were killed, proximal and distal segments of the right and left sural nerves were prepared for light microscopy and computerized morphometry. No morphometric differences between proximal and distal segments or between right and left sides at the same levels were found in all experimental groups. No increase in fiber and axon sizes was observed from 360 to 720 days. Likewise, no difference in total myelinated fiber number was observed between groups. Myelinated fiber population distribution was bimodal, being the 720-days old animals' distribution shifted to the left, indicating a reduction of the fiber diameters. The g ratio distribution of the 720-days old animals' myelinated fiber was also shifted to the left, which suggests axonal atrophy. Morphological alterations due to aging were observed, mainly related to the myelin sheath, which suggests demyelination. Large fibers were more affected than the smaller ones. Axon abnormalities were not as common or as obvious as the myelin changes and Wallerian degeneration was rarely found. These alterations were observed in all experimental groups but were much less pronounced in rats 360 days old and their severity increased with aging. In conclusion, the present study indicates that the aging neuropathy present in the sural nerve of female rats is both axonal and demyelinating.

Asunto(s)

Envejecimiento/fisiología , Vaina de Mielina/ultraestructura , Nervio Sural/citología , Factores de Edad , Animales , Peso Corporal/fisiología , Femenino , Fibras Nerviosas Mielínicas/ultraestructura , Ratas , Ratas Wistar

RESUMEN

Enhancement of membrane K(+) conductance may reduce the abnormal excitability of primary afferent nociceptive neurons in neuropathic pain. It has been shown that retigabine, a novel anticonvulsant, activates Kv7 (KCNQ/M) channels in the axonal/nodal membrane of peripheral myelinated axons. In this study, we have tested the effects of retigabine on excitability parameters of C-type nerve fibers in isolated fascicles of human sural nerve. Application of retigabine (3-10 microM) produced an increase in membrane threshold. This effect was pronounced in depolarized axons and small in hyperpolarized axons. This finding indicates that retigabine produces a membrane hyperpolarization which is limited by the K(+) equilibrium potential. The retigabine-induced reduction in excitability was accompanied by modifications of the post-spike recovery cycle. Most notable is the development of a late subexcitability at 250-400 ms following a short burst of action potentials. All effects of retigabine were blocked in the presence of XE991 (10 microM). The data show that Kv7 channels are present on axons of unmyelinated, including nociceptive, peripheral human nerve fibers. It is likely that activation of these channels by retigabine may reduce the ectopic generation of action potentials in neuropathic pain.

Asunto(s)

Anticonvulsivantes/farmacología , Axones/efectos de los fármacos , Carbamatos/farmacología , Fibras Nerviosas Amielínicas/efectos de los fármacos , Nervios Periféricos/citología , Nervios Periféricos/efectos de los fármacos , Fenilendiaminas/farmacología , Potenciales de Acción/efectos de los fármacos , Anciano , Anciano de 80 o más Años , Antracenos/farmacología , Electrofisiología , Femenino , Humanos , Técnicas In Vitro , Masculino , Persona de Mediana Edad , Fibras Nerviosas Amielínicas/fisiología , Técnicas de Placa-Clamp , Nervio Sural/citología , Nervio Sural/efectos de los fármacos , Nervio Sural/fisiología , Taquifilaxis/fisiología

RESUMEN

OBJECTIVE: Autologous nerve grafts are used to treat severe peripheral nerve injury, but recovery of nerve function after grafting is rarely complete. Exogenous application of neurotrophic factors may enhance regeneration, but thus far the application of neurotrophic factors has been hampered by fast degradation after local application and unwanted side effects after systemic application. These problems may be overcome with the use of lentiviral (LV) vectors that direct sustained local transgene expression in cells. METHODS: Human sural nerve segments were either submerged in or injected with LV vectors encoding green fluorescent protein and cultured in vitro. Production of nerve growth factor (NGF) by nerve segments after injection of LV-NGF was quantified. The effect of NGF produced by LV-transduced fibroblasts derived from human sural nerve segments was assessed on neurite outgrowth in vitro. RESULTS: The injection of vector into nerve segments is a more effective way to deliver the vector than submersion of the nerve in vector-containing medium, leading to large numbers of transduced fibroblasts over a significant extent inside the nerve. The injection of LV-NGF leads to a gradual increase of NGF production, reaching a plateau after 4 days. LV-NGF-transduced human fibroblasts promote neurite outgrowth in vitro. CONCLUSION: We have developed a method to transduce cells in human sural nerve segments with LV vector. This approach holds promise as a powerful novel adjuvant therapy for peripheral nerve surgery and can be performed without changing the routine practice of nerve grafting.

Asunto(s)

Vectores Genéticos/fisiología , Lentivirus/fisiología , Factor de Crecimiento Nervioso/metabolismo , Nervio Sural/fisiología , Transducción Genética/métodos , Proteínas Fluorescentes Verdes/metabolismo , Humanos , Técnicas In Vitro , Neuritas/fisiología , Nervio Sural/citología , Factores de Tiempo

RESUMEN

Recording of action potentials from single unmyelinated nerve fibers by microneurography is an important tool to investigate peripheral neural functions in human neuropathies. However, the interpretation of microneurography recordings can be difficult because axonal membrane potential is not revealed by this method. We tested the hypothesis that the recovery cycle of excitability after a single action potential is correlated with changes in the axonal membrane potential. To this end, we used the threshold tracking technique to study how different chemical mediators, with known effects on the membrane potential, influence the post-spike superexcitability of C-fiber compound action potentials in isolated rat sural and vagus nerves. We found that: (1) some chemical mediators (e.g., adenosine 5'-triphosphate) produce a reduction or loss of superexcitability together with increased axonal excitability, indicating membrane depolarization; (2) blockade of axonal hyperpolarization-activated (Ih) currents produces an enhancement of superexcitability together with a decreased excitability, indicating membrane hyperpolarization; and (3) application of calcium produces an increase in membrane threshold without an alteration in superexcitability, indicating a non-specific increase in surface charge and a change in the voltage-dependent activation of sodium channels. In addition, we demonstrated that membrane depolarization and hyperpolarization induce opposite post-spike latency shifts (changes in supernormality) in rat and human nerve segments. Thus, recordings of post-spike excitability and shifts in latency are sensitive techniques for detection of various types of neuromodulation, which are correlated with changes in membrane potential of unmyelinated peripheral axons and may help to understand observations obtained by microneurography in peripheral human neuropathies.

Asunto(s)

Potenciales de la Membrana/fisiología , Fibras Nerviosas Amielínicas/fisiología , Acetilcolina/farmacología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Adenosina Trifosfato/análogos & derivados , Adenosina Trifosfato/farmacología , Marcadores de Afinidad , Animales , Cesio/farmacología , Relación Dosis-Respuesta en la Radiación , Estimulación Eléctrica/métodos , Humanos , Técnicas In Vitro , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/efectos de la radiación , Ratas , Ratas Wistar , Tiempo de Reacción/fisiología , Tiempo de Reacción/efectos de la radiación , Nervio Sural/citología , Nervio Vago/citología

RESUMEN

Previous results from our group and others showed that skin and muscle afferents are equipped with tetrodotoxin-resistant (TTX-r) channels. The great majority of the TTX-r fibres are unmyelinated (C or group IV) and are assumed to have nociceptive functions. Therefore, a block of the TTX-sensitive (TTX-s) fibres offers the possibility to study reactions of central nervous neurones to a purely nociceptive input. The present study compared spinal synaptic field potentials (SFPs) evoked by electrical stimulation of TTX-r afferent fibres from skin and muscle at various depths of the spinal segments L4 and L5 in the rat. Cutaneous input was produced by stimulation of the sural nerve (SU), input from muscle by stimulation of the gastrocnemius-soleus nerves (GS). To block the (non-nociceptive) TTX-s afferents, a pool containing TTX (concentration 1microM) was built around the dorsal roots L3-L6. As a measure of synaptic activity, the area of averaged SFPs was determined. After TTX application, the SFPs of fast conducting myelinated afferent fibres vanished completely. Simultaneously, the size of the potentials evoked by electrical stimulation of slowly conducting TTX-r skin and muscle afferents increased significantly. The field potentials of TTX-r GS afferents had a maximum in laminae IV-VI of the dorsal horn, whereas the SFPs induced by SU stimulation were more evenly distributed over all laminae. The results are a further indication that nociceptive input from skin and muscle is differently processed at the spinal level.

Asunto(s)

Músculo Esquelético/inervación , Neuronas Aferentes/efectos de los fármacos , Piel/inervación , Médula Espinal/fisiología , Sinapsis/fisiología , Tetrodotoxina/farmacología , Animales , Resistencia a Medicamentos , Estimulación Eléctrica , Potenciales Evocados/efectos de los fármacos , Masculino , Potenciales de la Membrana/fisiología , Fibras Nerviosas/efectos de los fármacos , Nociceptores/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Médula Espinal/citología , Médula Espinal/efectos de los fármacos , Nervio Sural/citología , Nervio Sural/efectos de los fármacos

RESUMEN

Morphometry has an important role in the interpretation of sural nerve biopsies. It is used for early detection of structural abnormalities in peripheral neuropathies. This application requires a comparison with data of normal population. However, most data in the literature were of Western subjects with a small number of samples. In this study the authors reported the morphometric data of sural nerve harvested within 24 hours after death from 78 Thai subjects without known causes of neuropathy. The samples were transversely sectioned and analyzed for the number and area of fascicles, the total number of myelinated axons, myelinated fiber diameter; myelinated axon diameter, myelin sheath thickness, g ratio and myelinated axon density. Results were discordant in some measurement parameters compared to previous reports. These data are valuable for the early recognition of peripheral nerve diseases from biopsied sural nerve of Thai subjects.

Asunto(s)

Recolección de Datos , Nervio Sural/anatomía & histología , Nervio Sural/citología , Adulto , Biopsia , Cadáver , Femenino , Humanos , Masculino , Microscopía/métodos , Tailandia

RESUMEN

Morphometry has an important role in the assessment of sural nerve biopsies as a part of early detection of structural abnormalities in peripheral nerve. Various sampling methods have been used to reduce time and effort needed in the analysis of total nerve fibers but their accuracy remains controversial. We examined the accuracy of three-window sampling method in the morphometric evaluation of human sural nerve biopsies by comparing with the total fiber quantification. Three windows (0.012 mm(2) each) were placed in every possible fascicle in the sections and data from all windows were pooled and analyzed for the number of myelinated axons, myelinated fiber diameter, axon diameter, myelin thickness, g ratio as well as myelinated fiber density. Means and ranges of the data from the two techniques were similar and the agreement was further confirmed by intraclass correlation analysis. These findings indicate that the three-window sampling method can be used to evaluate human sural nerve with accuracy.

Asunto(s)

Recolección de Datos/métodos , Nervio Sural/citología , Adulto , Axones , Biopsia , Cadáver , Femenino , Humanos , Masculino , Persona de Mediana Edad , Fibras Nerviosas , Estadísticas no Paramétricas

RESUMEN

Increased prevalence of impaired glucose tolerance (IGT) has been recently detected in patients with painful sensory neuropathy. To determine whether nerve abnormalities are present in IGT we investigated IGT subjects without clinical neuropathy. Nerve conduction studies (NCS) were performed in 12 subjects with IGT without symptoms and signs of neuropathy. The results were compared with those obtained from 12 patients with type 2 diabetes (DM) without clinical neuropathy and 12 healthy controls. Sensory NCS of the sural nerve were performed on different segments, the distal-leg (10 cm proximal to the lateral malleolus) and the proximal-leg segment (10 cm more proximal). The distal conduction velocity of the sural nerve was increased in IGT subjects, compared both to healthy controls and DM patients. No difference was found among the groups with respect to the sensory conduction velocity of the sural nerve fibers in the proximal-leg segment. A reduction of both distal and proximal amplitudes of the sural nerve action potentials was detected in DM patients compared with IGT subjects and controls. The abnormal conduction velocity in the distal segment of the sural nerve, observed in IGT subjects without clinical neuropathy, suggests that the myelin dysfunction of the distal sensory fibers represents the earliest detectable nerve response to the hyperglycemia. The reduced amplitude of the sural nerve action potential in asymptomatic patients with DM arises from the axonal degeneration and represents a more advanced stage of nerve disease.

Asunto(s)

Neuropatías Diabéticas/diagnóstico , Neuropatías Diabéticas/fisiopatología , Intolerancia a la Glucosa/complicaciones , Diagnóstico Precoz , Femenino , Humanos , Hiperglucemia/complicaciones , Masculino , Persona de Mediana Edad , Fibras Nerviosas/fisiología , Conducción Nerviosa , Neuronas Aferentes/fisiología , Neuronas Aferentes/ultraestructura , Nervio Sural/citología , Nervio Sural/fisiopatología

RESUMEN

The authors investigated whether T cells have a role in the pathogenesis of axonal polyneuropathy and monoclonal gammopathy by comparing the presence of T cells in sural nerves of 23 patients with axonal polyneuropathy and monoclonal gammopathy (12 IgM, 11 IgG), of 15 patients with chronic idiopathic axonal polyneuropathy, and of 10 autopsy cases. Seven patients with an increased T-cell density had a progressive disease course, and four of these patients were treated with prednisone with a good response, suggesting that vasculitis plays a role in the pathogenesis.

Asunto(s)

Paraproteinemias/inmunología , Polineuropatías/inmunología , Nervio Sural/inmunología , Linfocitos T/citología , Axones/patología , Progresión de la Enfermedad , Humanos , Recuento de Linfocitos , Polineuropatías/patología , Nervio Sural/citología , Nervio Sural/patología

RESUMEN

The relation between neurofilament expression and/or phosphorylation in the proximal versus distal components of the sensory peripheral neuraxis was studied and related to disorders in structure and function of the distal axon of streptozocin (STZ)-induced diabetic rats studied for 14 weeks. The ability of neurotrophin-3 (NT-3) to prevent abnormalities in neurofilament biology was also investigated. Compared with age-matched controls, neurofilament heavy (NF-H) (3.3-fold) and neurofilament medium (NF-M) (2.5-fold), but not neurofilament light (NF-L), subunits accumulated in the proximal axon of sensory neurons of the lumbar dorsal root ganglia (DRG) in untreated diabetic rats. Neurofilament accumulation was prevented by NT-3. Small- and large-diameter sensory neurons exhibited elevated levels of NF-H protein accumulation and phosphorylation in the DRG of untreated diabetic rats, levels that were ameliorated by NT-3. The sural nerve of untreated diabetic rats showed a 50% decrease in the levels of NF-H and NF-M, but not NF-L, subunits; NT-3 only partially normalized the defect in NF-M expression. These observations were associated with significant lowering of motor and sensory nerve conduction velocity but no alteration in the mean axonal diameter of myelinated axons in the sural nerve in untreated diabetic rats. It is proposed that the accumulation of NF-H and NF-M subunits in the proximal axon is an etiologic factor in the distal axon degeneration observed in diabetes.

Asunto(s)

Diabetes Mellitus Experimental/metabolismo , Proteínas de Neurofilamentos/metabolismo , Neuronas Aferentes/metabolismo , Neurotrofina 3/metabolismo , Animales , Neuropatías Diabéticas/metabolismo , Masculino , Proteína Quinasa 8 Activada por Mitógenos , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Fosforilación , Ratas , Ratas Wistar , Nervio Sural/citología , Nervio Sural/metabolismo , Proteínas Quinasas p38 Activadas por Mitógenos