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.

Digital morphometry of rat cerebellar climbing fibers reveals distinct branch and bouton types.

Cerebellar climbing fibers (CFs) provide powerful excitatory input to Purkinje cells (PCs), which represent the sole output of the cerebellar cortex. Recent discoveries suggest that CFs have information-rich signaling properties important for cerebellar function, beyond eliciting the well known all-or-none PC complex spike. CF morphology has not been quantitatively analyzed at the same level of detail as its biophysical properties. Because morphology can greatly influence function, including the capacity for information processing, it is important to understand CF branching structure in detail, as well as its variability across and within arbors. We have digitally reconstructed 68 rat CFs labeled using biotinylated dextran amine injected into the inferior olive and comprehensively quantified their morphology. CF structure was considerably diverse even within the same anatomical regions. Distinctly identifiable primary, tendril, and distal branches could be operationally differentiated by the relative size of the subtrees at their initial bifurcations. Additionally, primary branches were more directed toward the cortical surface and had fewer and less pronounced synaptic boutons, suggesting they prioritize efficient and reliable signal propagation. Tendril and distal branches were spatially segregated and bouton dense, indicating specialization in signal transmission. Furthermore, CFs systematically targeted molecular layer interneuron cell bodies, especially at terminal boutons, potentially instantiating feedforward inhibition on PCs. This study offers the most detailed and comprehensive characterization of CF morphology to date. The reconstruction files and metadata are publicly distributed at NeuroMorpho.org.

Diagnostic strategy for diabetic polyneuropathy: Focus on nerve fiber type and magnetic resonance neurography.

Recently, various neurological tests for evaluating small-fiber neuropathy have been developed. Magnetic resonance neurography has also developed as a novel method to visualize diabetic neuropathy. The current status of diabetic polyneuropathy diagnosis focusing on the types of nerve fiber and magnetic resonance neurography is summarized.

Spinocerebellar projections from the cervical and lumbosacral enlargements in the chicken spinal cord.

In birds, spinocerebellar (SC) projections to the cerebellar cortex have not been understood well. We examined SC fiber terminal fields originating from the cervical and lumbosacral enlargements (CE and LSE, respectively) in the chicken. SC fiber terminals show parasagittal bands in the granular layer. Labeled terminals from the CE were distributed primarily in folia II-V and IX. Parasagittal bands of labeled terminals from the CE were not clearly separated in folia II and III but were clearly separated in folia IV and V. In folium IX, labeled terminals were diffusely distributed in all subfolia with no evidence of banding. The numbers of bands were 5 in folium II, 12 in folium III and 7 in folia IV and V at maximum. Labeled terminals from the LSE were distributed primarily in folia II-VI and IX. Labeled terminals from the LSE were arranged in 4 bands in folium II and in 8 bands in folium III at maximum. Parasagittal bands from the LSE in folia IV and V were not clearly separated. In folium VI, the numbers of parasagittal bands was 6 at maximum. In folium IX, labeled terminals were mainly found in subfolium IXc forming 6-8 parasagittal bands. There were more parasagittal bands of labeled terminals from the CE than from the LSE. The topography of SC fiber terminals from the CE was different from that of SC fiber terminals from the LSE.

Microanatomical and immunohistochemical study of the human lateral antebrachial cutaneous nerve of forearm at the antecubital fossa and its clinical implications.

Changes in the intraneural anatomy with age can cause poor prognosis of nerve repair in patients after nerve injury. The occurrence of Complex Regional Pain Syndrome-Type II, secondary to peripheral nerve injury, is common. The purpose of this study is to asses changes in cross-sectional anatomy of the lateral antebrachial cutaneous nerve of forearm (LCNF) at the antecubital fossa in the fascicular, nonfascicular components (adipose and nonadipose tissue), and sympathetic fibers area with respect to age. For the purpose of the study, 32 human (37-88 years) fresh cadaveric LCNF were collected from left-antecubital fossae and processed for histological, morphometric analysis [total cross-sectional (Asc), fascicular (Af), and nonfascicular area (Anonf)], and immunohistochemical method (tyrosine hydroxylase) for sympathetic fibers. The LCNF's average total cross-sectional area was 3.024 mm(2), and fascicular area was 0.582 mm(2). The average number of fascicles per mm(2) was 3.09. The cross-sectional area in the nerve was mainly occupied by nonfascicular connective tissue (80.75%). There was increased adipose tissue deposition (48.48% of Asc) and decreased collagen fibers (32.24% of Asc) in interfascicular domains without any definite relationship with age. The average sympathetic fiber area was 0.026 mm(2) within the nerve fascicular area without any correlation with age. In LCNF, there was more adipose tissue and less collagen fibers deposition in the interfascicular domains of all age cases, and this may act as an obstacle for nerve fiber regeneration on using LCNF as an interpositional nerve graft.

Rich innervation of deep infiltrating endometriosis.

BACKGROUND: Deep infiltrating endometriosis (DIE) is a specific type of endometriosis, which can be associated with more severe pelvic pain than other forms of endometriotic lesions. However, the mechanisms by which pain is generated are not well understood. METHODS: DIE (n = 31) and peritoneal endometriotic (n = 40) lesions were sectioned and stained immunohistochemically with antibodies against protein gene product 9.5, neurofilament, nerve growth factor (NGF), NGF receptors tyrosine kinase receptor-A (Trk-A) and p75, substance P, calcitonin gene-related peptide, vesicular acetylcholine transporter, neuropeptide Y, vasoactive intestinal peptide and tyrosine hydroxylase to demonstrate myelinated, unmyelinated, sensory and autonomic nerve fibres. RESULTS: There were significantly more nerve fibres in DIE (67.6 +/- 65.1/mm(2)) than in peritoneal endometriotic lesions (16.3 +/- 10.0/mm(2)) (P < 0.01). DIE was innervated abundantly by sensory Adelta, sensory C, cholinergic and adrenergic nerve fibres; NGF, Trk-A and p75 were strongly expressed in endometriotic glands and stroma of DIE. CONCLUSIONS: The rich innervation of DIE may help to explain why patients with this type of lesion have severe pelvic pain.

The sweet taste quality is linked to a cluster of taste fibers in primates: lactisole diminishes preference and responses to sweet in S fibers (sweet best) chorda tympani fibers of M. fascicularis monkey.

BACKGROUND: Psychophysically, sweet and bitter have long been considered separate taste qualities, evident already to the newborn human. The identification of different receptors for sweet and bitter located on separate cells of the taste buds substantiated this separation. However, this finding leads to the next question: is bitter and sweet also kept separated in the next link from the taste buds, the fibers of the taste nerves? Previous studies in non-human primates, P. troglodytes, C. aethiops, M. mulatta, M. fascicularis and C. jacchus, suggest that the sweet and bitter taste qualities are linked to specific groups of fibers called S and Q fibers. In this study we apply a new sweet taste modifier, lactisole, commercially available as a suppressor of the sweetness of sugars on the human tongue, to test our hypothesis that sweet taste is conveyed in S fibers. RESULTS: We first ascertained that lactisole exerted similar suppression of sweetness in M. fascicularis, as reported in humans, by recording their preference of sweeteners and non- sweeteners with and without lactisole in two-bottle tests. The addition of lactisole significantly diminished the preference for all sweeteners but had no effect on the intake of non-sweet compounds or the intake of water. We then recorded the response to the same taste stimuli in 40 single chorda tympani nerve fibers. Comparison between single fiber nerve responses to stimuli with and without lactisole showed that lactisole only suppressed the responses to sweeteners in S fibers. It had no effect on the responses to any other stimuli in all other taste fibers. CONCLUSION: In M. fascicularis, lactisole diminishes the attractiveness of compounds, which taste sweet to humans. This behavior is linked to activity of fibers in the S-cluster. Assuming that lactisole blocks the T1R3 monomer of the sweet taste receptor T1R2/R3, these results present further support for the hypothesis that S fibers convey taste from T1R2/R3 receptors, while the impulse activity in non-S fibers originates from other kinds of receptors. The absence of the effect of lactisole on the faint responses in some S fibers to other stimuli as well as the responses to sweet and non-sweet stimuli in non-S fibers suggest that these responses originate from other taste receptors.

The classification and identification of human somatic and parasympathetic nerve fibres including urinary bladder afferents and efferents is preserved following spinal cord injury.

UNLABELLED: Single-fibre extracellular action potentials were recorded with 2 pairs of wire electrodes from lower human sacral nerve roots during surgery. The roots from which was recorded from were used for morphometry. Nerve fibre groups were identified by conduction velocity distribution histograms of single afferent and efferent fibres and partly by nerve fibre diameter distribution histograms. The values of group conduction velocity and group nerve fibre diameter measured in the paraplegics were very similar to those obtained from brain-dead humans and patients with no spinal cord injury. Thus the classification and identification of nerve fibre groups remained preserved following spinal cord injury. Upon retrograde bladder filling the urinary bladder stretch and tension receptor afferent activities were increased; on two occasions they even fired when the bladder was empty. Two reasons are brought forward for a too small storage volume of the urinary bladder in paraplegics: too high afferent activity of the bladder due to changed receptor field transduction mechanisms and too low compliance. SUMMARY: 1. Single nerve fibre action potentials (APs) of lower sacral nerve roots were recorded extracellularly with 2 pairs of wire electrodes during an operation for implanting an anterior root stimulator for bladder control in 9 humans with a spinal cord injury and a dyssynergia of the urinary bladder. Roots that were not saved and that were used to record from were later used for morphometry. 2. Nerve fibre groups were identified by conduction velocity distribution histograms of single afferent and efferent fibres and partly by nerve fibre diameter distribution histograms, and correlation analysis was performed. Group conduction velocity values were obtained additionally from compound action potentials (CAPs) evoked by electrical stimulation of nerve roots and the urinary bladder. 3. The group conduction velocities and group nerve fibre diameters had the following pair-values at 35.5 degrees C: Spindle afferents: SP1 (65 m/s / 13.1 microm), SP2 (51/12.1); touch afferents: T1 (47/11.1), T2 (39/10.1), T3 (27/9.1), T4 (19/8.1); urinary bladder afferents: S1 (41 m/s / -), ST (35/-); alpha-motoneurons: alpha 13 (-/14.4), alpha 12 (65 m/s /13.1 microm), alpha 11 (60?/12.1)[FF], alpha 2 (51/10.3)[FR], alpha 3 (41/8.2)[S]; gamma-motoneurons: gamma(beta) (27/7.1), gamma 1 (21/6.6), gamma 21 (16/5.8), gamma 22 (14/5.1); preganglionic parasympathetic motoneurons: (10 m/s / 3.7 microm). 4. The values of group conduction velocity and group nerve fibre diameter measured in the paraplegics were very similar to those obtained earlier from brain-dead humans and patients with no spinal cord injury. Also, the axon number and the axon density of myelinated fibres of lower sacral nerve roots remain unchanged following spinal cord injury. Thus the classification and identification of nerve fibre groups remained preservedfollowing spinal cord injury. A direct comparison can thus be made of natural impulse patterns of afferent and efferent nerve fibres between paraplegics (pathologic) and brain-dead humans (supraspinal destroyed CNS, in many respects physiologic). 5. When changing the root temperature from 32 degrees C to 35.5 degrees C, the group conduction velocities changed in the following way in one case: SP2: 40 m/s (32 degrees C) to 50 m/s (35.5%), S1: 31.3 to 40, ST: 25 to 33.8, M: 12.5 to 13.8; alpha 2: 40 to 50, alpha 3: 33 to 40. The group conduction velocities showed different temperature dependence apart from SP2 fibres and alpha 2-motoneurons. 6. Upon retrograde bladder filling the urinary bladder stretch (S1) and tension receptor afferent (ST) activity levels were undulating and increased. As compared to activity levels detected in a brain-dead human, S1 (designates afferents, not cord segment) and ST afferents fired even when the bladder was empty, with an activity level similar to those observed in a brain-dead human with the bladder half filled. Two reasons are brought forward for an too small storage volume of the urinary bladder in paraplegics: too high afferent activity of the bladder due to changed receptor field signal transduction mechanisms and too low compliance. 7. With the newly developed 'coordination dynamics therapy', applied early after spinal cord injury, such complications of bladder functioning can be avoided; the bladder can causally be cured in severe spinal cord injury.

Intraburst and interburst signaling by climbing fibers.

Although cerebellar Purkinje cell complex spikes occur at low frequency (approximately 1/s), each complex spike is often associated with a high-frequency burst (approximately 500/s) of climbing fiber spikes. We examined the possibility that signals are present within the climbing fiber bursts. By intracellularly recording from depolarized, nonspiking Purkinje cells in anesthetized pigmented rabbits, climbing fiber burst patterns were investigated by determining the number of components in the induced compound EPSPs during spontaneous activity and during visual stimulation. For our sample of 43 cells, >70% of all EPSPs were of the compound type composed of two or three EPSPs. During spontaneous activity, the number of components in each compound EPSP was not related to the latency to the succeeding compound EPSP. Conversely, the number of components in each compound EPSP was related to its latency after the preceding compound EPSP. This latency increased from 0.62 s for one-component EPSPs to 1.69 s for compound EPSPs with four or more components. The effect of visual stimulation on the climbing fiber activity was studied in 19 floccular Purkinje cells whose low-frequency interburst climbing fiber response was modulated by movement about the vertical axis. During sinusoidal oscillation (0.1 Hz, +/-10 degrees), compound EPSPs with a larger number of components tended to be more prevalent during movement in the excitatory direction than in the inhibitory direction. Thus, climbing fibers can, in addition to modulation of their low interburst frequency, transmit signals in the form of the number of spikes within each high-frequency burst.

Morphometry of saphenous nerve in young rats.

The rat saphenous nerve contains only somato-sensory fibers and is used in investigations of neuropathic pain and its treatment. Due to its superficial anatomical path, the saphenous nerve is also widely used in electrophysiological studies. Nevertheless, morphologic and morphometric descriptions of the normal saphenous nerve are scanty in the literature and information on useful morphometric parameters of this nerve is still missing. Thus, the present study aimed to investigate the longitudinal and lateral symmetry of the saphenous nerve in young rats. Proximal and distal segments of the left and right saphenous nerves from female Wistar rats, aged 30 days (N=5) were morphometrically evaluated and comparisons were made between sides and segments. Our results show that the saphenous nerve is longitudinally and laterally symmetric since there were no morphometric differences between proximal and distal segments, as well as between right and left sides. This lateral symmetry is important in order to validate those experiments in which the contralateral nerve is used as the control. Also, the longitudinal symmetry information is fundamental to further studies involving the "dying back" neuropathy models. The present study adds to the literature new morphometric information on the rat saphenous nerve that might be useful for a better interpretation of further studies involving this nerve and experimental models of nerve diseases.

Comparison of paclitaxel and cisplatin effects on the slowly adapting type I mechanoreceptor.

Cisplatin and paclitaxel are two of the most widely used chemotherapy drugs for the treatment of several forms of cancer. Both agents produce significant levels of peripheral neuropathy that can result in changes of treatment regimen. Although there have been recent efforts to understand the effects of these agents on nociceptor populations, little study has been made on their effects on large afferent populations. Here we report acute and chronic effects of paclitaxel and cisplatin administration on the type I mechanoreceptor using a skin-nerve preparation in rat and a standardized mechanical stimulus to compare mechanoreceptor response before and after treatment. In a control preparation, suppression of type I mechanoreceptor response during 2-min, arterial infusion of paclitaxel or cisplatin was significant for paclitaxel (28%, 1 microM; 33%, 10 microM; p<0.025), but not cisplatin (9%, 500 microM; 19%, 5 mM; p>0.05). Response returned to baseline within a 2-min washout period. Following pretreatment with paclitaxel or cisplatin, baseline response was significantly reduced from control animals. In addition, unlike the control preparation, a subsequent infusion of paclitaxel induced prolonged response suppression. Nerve fascicles innervating the preparation showed significant reduction in conduction velocity relative to control (cisplatin pretreatment: Abeta, 22%, p<0.01; C-fiber, 33%, p<0.01. paclitaxel pretreatment: Abeta, 17%, p<0.05; C-fiber, 23%, p<0.05). It was concluded that chronic paclitaxel or cisplatin treatment not only significantly alters the type I mechanotransduction process, but also increases susceptibility of the type I ending to further paclitaxel exposure.

Quantitative analysis of the distribution of the motor cortex representations of the fore-and hindlimbs in the red nucleus of the cat.

A quantitative analysis of the distribution of corticorubral fibers was performed after precise electrolytic lesioning of the lateral and medial margins of the posterior sigmoid gyrus--the motor representations of the fore-and hindlimbs respectively--in cats. The cortical representations of the forelimbs were found to project to the whole of the rostrocaudal extent of the red nucleus (RN). The number of efferent fibers terminating at the rostral margin of the RN was almost twice that terminating in the caudal third of the RN. Efferent fibers of the cortical representation of the hindlimbs did not project to the rostral two thirds of the RN but ended in its caudal third; the number of projecting corticorubral fibers was the same as the number running from the cortical representation of the forepaws to the caudal third of the RN. The significantly (almost double) greater number of fibers running from the cortical representation of the forelimbs in comparison with the number directed from the representation of the hindlimbs found in the present study is probably evidence of the greater functional importance of corticorubral connections in movement reactions performed by the forelimbs.

A brief historical note on the classification of nerve fibers.

This is a brief review of the literature focused on the articles that formed the basis for the classification of the nerve fibers. Mention is also made to the origin of the nomenclature of the different motoneurons (alpha, beta and gamma).

Morphometric analysis of the fiber populations of the rat sciatic nerve, its spinal roots, and its major branches.

Correspondence between the nerve composition and the functional characteristics of its fiber populations is not always evident. To investigate such correspondence and to give a systematic picture of the morphology of the rat hind limb nerves, extensive morphometric study was performed on the sciatic nerve, its founding dorsal and ventral spinal roots, and its major branches. Nerve histology was examined in semithin sections via microscopic image analysis. Variation in the density of myelinated fibers, fiber interspace, and nerve cross-sectional area was studied in individual roots and nerves. In the dorsal roots, fiber numbers and cross-sectional areas were directly linearly proportional to the spinal root level number. Constituent fiber populations were identified using multicomponent lognormal models, and an optimal model for every nerve or root was selected by using an information theoretic approach. For the dorsal and ventral roots and the sciatic and peroneal nerves, optimal fiber population models consisted of three components, whereas, for the tibial and sural nerves, two components were optimal. Functional identities of the revealed fiber populations were established by using calculations of corresponding conduction velocities according to Arbuthnott et al. (J. Physiol. [1980] 308:125-157) and anatomical considerations. It is anticipated that morphological parameters established in this study would advance the development of neural prostheses in humans. The proximodistal correspondences among the fiber populations of different nerves were established by parametric statistical comparisons. The proposed approach provides a conceptual framework for understanding the comparative anatomy of the peripheral nerves and spinal roots and can be further applied in other species.

[In vivo imaging of the corneal nerve plexus : From single image to large scale map]. / In-vivo-Bildgebung des kornealen Nervenplexus : Vom Einzelbild zur großflächigen Darstellung.

The sub-basal nerve plexus (SNP) of the cornea provides the possibility of in vivo and non-invasive examination of peripheral nerve structures by corneal confocal microscopy (CCM). Thus morphological alterations of the SNP can be directly detected and quantified. A single CCM image is insufficient for a well-founded diagnosis because of the inhomogeneous distribution of the nerve fibers; therefore, there is a demand for techniques for large area imaging of the SNP. This article provides an overview of published approaches to the problem. Current developmental work at the Karlsruhe Institute of Technology and the University of Rostock Eye Clinic is expected to lead to a simplified handling of the technology and a further improvement in the image quality.

Cell morphology and circuitry in the central lobes of the mormyrid cerebellum.

The cerebellum of mormyrid electric fish is large and unusually regular in its histological structure. We have examined the morphology of cellular elements in the central lobes of the mormyrid cerebellum. We have used intracellular injection of biocytin to determine the morphology of cells with somas in the cortex, and we have used extracellular placement of anterograde tracers in the inferior olive to label climbing fibers. Our results confirm previous Golgi studies and extend them by providing a more complete description of axonal trajectories. Most Purkinje cells in mormyrids and other actinopterygian fishes are interneurons that terminate locally in the cortex on efferent neurons that are equivalent to cerebellar nucleus cells in mammals. We confirm the markedly sagittal distribution of the fan-like dendrites of Purkinje cells, efferent cells, and molecular layer interneurons. We show that Purkinje cell axons extend further than was previously thought in the sagittal plane. We show that climbing fibers are distributed in narrow sagittal strips and that these fibers terminate exclusively in the ganglionic layer below the molecular layer where parallel fibers terminate. Our results together with those of others show that the central lobes of the mormyrid cerebellum, similar to the mammalian cerebellum, are composed of sagittally oriented modules made up of Purkinje cells, climbing fibers, molecular layer interneurons, and cerebellar efferent cells (cerebellar nucleus cells in mammals) that Purkinje cells inhibit. This modular organization is more apparent and more sharply defined in the mormyrid than in the mammal.

Medullary dorsal horn neurons providing axons to both the parabrachial nucleus and thalamus.

It has often been suggested that the trigemino- and spino-thalamic pathways are highly implicated in sensory-discriminative aspects of pain, whereas the trigemino- and spino-parabrachial pathways are strongly implicated in affective/emotional aspects of pain. On the other hand, the superficial laminae of the spinal dorsal horn, where many nociceptive neurons are distributed, have been reported to contain projection neurons innervating both the parabrachial nucleus (PBN) and thalamus by way of axon collaterals (Hylden et al., 1989). For the medullary dorsal horn (caudal subnucleus of spinal trigeminal nucleus: Vc), however, the existence of such neurons has not been reported. Thus, in the present study, we examined whether the Vc might contain projection neurons sending their axons to both the thalamus and PBN. Dual retrograde labeling with fluorescence dyes was attempted. In each rat, tetramethylrhodamine-dextran amine and Fluoro-gold were stereotaxically injected into the PBN and thalamic regions, respectively. The proportion of the dually labeled Vc cells in the total population of all labeled Vc cells was about 20%. More than 90% of the dually labeled neurons were distributed in lamina I (marginal zone), less than 10% of them were located in lamina II (substantia gelatinosa), and only a few (about 1%) were found in lamina III (magnocellular zone). The results indicate that some Vc neurons in the superficial laminae mediate nociceptive information directly to the PBN and thalamus by way of axon collaterals and that the vast majority of them project to the ipsilateral PBN and contralateral thalamus.

Development of the corticospinal tract in the mouse spinal cord: a quantitative ultrastructural analysis.

The growth of corticospinal tract (CST) axons was studied quantitatively at the 7th cervical (C7) and the 4th lumbar (L4) spinal segments in the balb/cByJ mice at the ages of postnatal day (P) 0, 2, 4, 6, 8, 10, 14, and 28. The cross-sectional area of the CST increased progressively with time. Unmyelinated axons, the most prominent CST element during early development, reached maximum at C7 and L4 on P14. Two phases of increase in the number of unmyelinated axons were observed at C7, while only one surge of axonal outgrowth was found at the L4 level. Pro-myelinated axons, defined as axons surrounded by only one layer of oligodendrocytic process, were first seen at P2 and P4 in the C7 and the L4 level, respectively, followed by a dramatic increase in the number of myelinated axons from P14 onwards at both spinal levels. Myelination of the CST axons occurred topographically in a dorsal-to-ventral pattern. The number of growth cones increased rapidly at the C7 level to reach its maximum at P4, while those at L4 increased steadily to the peak at P10. Growth cones with synapse-like junctions were occasionally observed in the growing CST. Degenerating axons and growth cones partly accounted for the massive axon loss at both spinal segments during CST development. Overall, the mouse CST elements changed dynamically in numbers during postnatal development, suggesting a vigorous growing and pruning activity in the tract. The mouse CST also showed a similar growth pattern to that of the rat CST.

Formation and distribution of the sural nerve based on nerve fascicle and nerve fiber analyses.

The formation and distribution of the sural nerve are presented on the basis of an investigation of 31 legs of Japanese cadavers using nerve fascicle and fiber analyses. Nerve fibers constituting the medial sural cutaneous nerve were designated as 'T', whereas those constituting the peroneal communicating branch were designated as 'F'. In 74.2% of cases (23/31), the T and F fibers joined each other in the leg, whereas in 9.7% of cases (3/31) they descended separately. In 16.1% of cases (5/31), the sural nerve was formed of only the T fibers. The sural nerve gave off lateral calcaneal branches and medial and lateral branches at the ankle. The lateral calcaneal branches always contained T fibers. The medial branches consisted of only T fibers, whereas most of the lateral branches consisted of only F fibers (71.0%; 22/31). In addition to the T and F fibers, P fibers, which derived from the superficial and deep peroneal nerves, formed the dorsal digital nerves. The P fibers were entirely supplied to the medial four and one-half toes. However, they were gradually replaced by the T and F fibers in the lateral direction. The 10th proper dorsal digital nerve consisted of T fibers only (38.7%; 12/31), of F fibers only (19.4%; 6/31) or of both T and F fibers (38.7%; 12/31). These findings suggest that the T fibers are essential nerve components for the skin and deep structures of the ankle and heel rather than the skin of the lateral side of the fifth toe. The designation of the medial sural cutaneous nerve should be avoided and only the T fibers are appropriate components for naming as the sural nerve.

Delivery of neurotrophin-3 from fibrin enhances neuronal fiber sprouting after spinal cord injury.

Neurotrophins have been shown to promote axonal growth and regeneration after spinal cord injury. The therapeutic utility of neurotrophins may be enhanced by using a controlled delivery system to increase the duration of neurotrophin availability following injury. Such a delivery system can be incorporated into a bioactive scaffold to serve as a physical bridge for regeneration. This study assessed the effect of controlled delivery of neurotrophin-3 (NT-3) from fibrin scaffolds implanted in spinal cord lesions immediately following 2-mm ablation injury in adult rats. Nine days after injury, fibrin scaffolds containing the delivery system and NT-3 (1000 ng/mL) elicited more robust neuronal fiber growth into the lesion than did control scaffolds or saline (1.5- to 3-fold increase). Implantation of fibrin scaffolds resulted in a dramatic reduction of glial scar formation at the white matter border of the lesion. Hindlimb motor function of treated animals did not improve relative to controls at 12 weeks post-injury. Thus, controlled delivery of NT-3 from fibrin scaffolds enhanced the initial regenerative response by increasing neuronal fiber sprouting and cell migration into the lesion, while functional motor recovery was not observed in this model.