Arm cycling increases the short-latency reflex from ankle dorsiflexor afferents to knee extensor muscles.

Low-intensity electrical stimulation of the common peroneal nerve (CPN) evokes a short latency reflex in the heteronymous knee extensor muscles (referred to as the CPN reflex). The CPN reflex is facilitated at a heel strike during walking, contributing to body weight support. However, the origin of the CPN reflex increase during walking remains unclear. We speculate that this increase originates from multiple sources due to a body of evidence suggesting the presence of neural coupling between the arms and legs. Therefore, we investigated the extent to which the CPN reflex is modulated during rhythmic arm cycling. Twenty-eight subjects sat in an armchair and were asked to perform arm cycling at a moderate cadence using a stationary ergometer while performing isometric contraction of the knee extensors, such that the CPN reflex was evoked. The CPN reflex was evoked by stimulating the CPN [0.9-2.0× the motor threshold (MT) in the tibialis anterior muscle] at the level of the neck of the fibula. The CPN-reflex amplitude was measured from the vastus lateralis (VL). The biphasic reflex response in the VL was evoked within 27-45 ms following CPN stimulation. The amplitude of the CPN reflex increased during arm cycling compared with that before cycling. The modulation of the CPN reflex during arm cycling was detected only for CPN stimulation intensity around 1.2× MT. Furthermore, CPN-reflex modulation was not observed during the isometric contraction of the arm or passive arm cycling. Our results suggest the presence of neural coupling between the CPN-reflex pathways and neural systems generating locomotive arm movement.NEW & NOTEWORTHY Whether locomotive arm movements contribute to the control of the reflex pathway from ankle dorsiflexor afferents to knee extensor muscles [common peroneal nerve (CPN)-reflex] is an unresolved issue. The CPN reflex in the stationary leg was facilitated only by arm cycling, and not by passive or isometric motor tasks. Our results suggest that the arm locomotor system modulates the reflex pathway from ankle dorsiflexor afferents to the knee extensor muscles.

Fix the problem - A practical guide to whole-mount immunohistochemistry of teased nerve fibres.

BACKGROUND: Immunohistochemical staining of entire nerve fibres allows for studying the molecular composition of functional fibre subunits and may add to the diagnostic value of nerve fibre teasing. NEW METHOD: In this study, we established a sealed-slide method for reproducible immunostaining of deep axoplasmic proteins in permanently straightened nerve fibres. RESULTS: Immunostaining of teased nerve fibres very much is facilitated by tip-fixation with biocompatible glass adhesives. Antibody penetration in fresh nerves can be achieved by thermic and chemical permeabilisation while enzymatic digestion allows for sufficient permeability after aldehyde fixation. COMPARISON WITH EXISTING METHODS: The methods recommended herein are easy to perform and represent a reliable and reproducible way to whole mount immunostaining. CONCLUSIONS: Sealed-slide immunostaining of tip-fixed and permeabilised nerve biopsies will help to validate neurophysiological abnormalities and to screen for target molecules and predictive markers of peripheral nerve disorders such as in inherited neuropathies and Guillain-Barré syndrome.

RetroDISCO: Clearing technique to improve quantification of retrograde labeled motor neurons of intact mouse spinal cords.

BACKGROUND: Quantification of the number of axons reinnervating a target organ is often used to assess regeneration after peripheral nerve repair, but because of axonal branching, this method can overestimate the number of motor neurons regenerating across an injury. Current methods to count the number of regenerated motor neurons include retrograde labeling followed by cryosectioning and counting labeled motor neuron cell bodies, however, the process of sectioning introduces error from potential double counting of cells in adjacent sections. NEW METHOD: We describe a method, retroDISCO, that optically clears whole mouse spinal cord without loss of fluorescent signal to allow imaging of retrograde labeled motor neurons using confocal microscopy. RESULTS: Complete optical clearing of spinal cords takes four hours and confocal microscopy can obtain z-stacks of labeled motor neuron pools within 3-5min. The technique is able to detect anticipated differences in motor neuron number after cross-suture and conduit repair compared to intact mice and is highly repeatable. COMPARISON WITH EXISTING METHOD: RetroDISCO is inexpensive, simple, robust and uses commonly available microscopy techniques to determine the number of motor neurons extending axons across an injury site, avoiding the need for labor-intensive cryosectioning and potential double counting of motor neuron cell bodies in adjacent sections. CONCLUSIONS: RetroDISCO allows rapid quantification of the degree of reinnervation without the confounding produced by axonal sprouting.

Nerve cross-bridging to enhance nerve regeneration in a rat model of delayed nerve repair.

There are currently no available options to promote nerve regeneration through chronically denervated distal nerve stumps. Here we used a rat model of delayed nerve repair asking of prior insertion of side-to-side cross-bridges between a donor tibial (TIB) nerve and a recipient denervated common peroneal (CP) nerve stump ameliorates poor nerve regeneration. First, numbers of retrogradely-labelled TIB neurons that grew axons into the nerve stump within three months, increased with the size of the perineurial windows opened in the TIB and CP nerves. Equal numbers of donor TIB axons regenerated into CP stumps either side of the cross-bridges, not being affected by target neurotrophic effects, or by removing the perineurium to insert 5-9 cross-bridges. Second, CP nerve stumps were coapted three months after inserting 0-9 cross-bridges and the number of 1) CP neurons that regenerated their axons within three months or 2) CP motor nerves that reinnervated the extensor digitorum longus (EDL) muscle within five months was determined by counting and motor unit number estimation (MUNE), respectively. We found that three but not more cross-bridges promoted the regeneration of axons and reinnervation of EDL muscle by all the CP motoneurons as compared to only 33% regenerating their axons when no cross-bridges were inserted. The same 3-fold increase in sensory nerve regeneration was found. In conclusion, side-to-side cross-bridges ameliorate poor regeneration after delayed nerve repair possibly by sustaining the growth-permissive state of denervated nerve stumps. Such autografts may be used in human repair surgery to improve outcomes after unavoidable delays.

Celsr3 is required in motor neurons to steer their axons in the hindlimb.

The cadherin Celsr3 regulates the directional growth and targeting of axons in the CNS, but whether it acts in collaboration with or in parallel to other guidance cues is unknown. Furthermore, the function of Celsr3 in the peripheral nervous system is still largely unexplored. Here we show that Celsr3 mediates pathfinding of motor axons innervating the hindlimb. In mice, Celsr3-deficient axons of the peroneal nerve segregate from those of the tibial nerve but fail to extend dorsally, and they stall near the branch point. Mutant axons respond to repulsive ephrinA-EphA forward signaling and glial cell-derived neurotrophic factor (GDNF). However, they are insensitive to attractive EphA-ephrinA reverse signaling. In transfected cells, Celsr3 immunoprecipitates with ephrinA2, ephrinA5, Ret, GDNF family receptor α1 (GFRα1) and Frizzled3 (Fzd3). The function of Celsr3 is Fzd3 dependent but Vangl2 independent. Our results provide evidence that the Celsr3-Fzd3 pathway interacts with EphA-ephrinA reverse signaling to guide motor axons in the hindlimb.

Arrangement of sympathetic fibers within the human common peroneal nerve: implications for microneurography.

Recently, interest has grown in the firing patterns of individual or multiunit action potential firing patterns in human muscle sympathetic nerve recordings using microneurography. Little is known, however, about sympathetic fiber distribution in human lower limb nerves that will affect the multiunit recordings. Therefore, the purpose of this study was to examine the sympathetic fiber distribution within the human common peroneal nerve using immunohistochemical techniques (tyrosine hydroxylase, avidin-biotin complex technique). Five-micrometer transverse and 10-µm longitudinal sections, fixed in formaldehyde, were obtained from the peroneal nerve that had been harvested from three human cadavers (83 ± 11 yr) within 24 h of death. Samples of rat adrenal gland and brain served as controls. Sympathetic fiber arrangement varied between left and right nerves of the same donor, and between donors. However, in general, sympathetic fibers were dispersed throughout ∼25-38 fascicles of the peroneal nerve. The fibers were grouped in bundles of ∼2-44 axons or expressed individually throughout the fascicles, and the distribution was skewed toward smaller bundles with median and interquartile ratio values of 5 and 1 axons/bundle, respectively. These findings confirm the bundled organization of sympathetic axons within the peroneal nerve and provide the anatomical basis for outcomes in microneurographic studies.

Specific paucity of unmyelinated C-fibers in cutaneous peripheral nerves of the African naked-mole rat: comparative analysis using six species of Bathyergidae.

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.

Histological analysis of single peripheral nerve fiber in acute nerve elongation process.

To observe the histological alterations of single nerve fiber structures after nerve elongation by employing a rabbit peroneal nerve stretching model. 14 rabbits weighing mean 3. 0 kg (2.02-3.31 kg.) were used in the experiment. Two rabbits were used as control when only a sham operation was done (group one, 0% stretch). Acute stretching of the peroneal nerves to elongate them by 10% was done in 6 rabbits (group two, 10% elongation) and by 20% (group three, 20% elongation) in another 6 rabbits. All animals were evaluated by tissue staining technology in a teased-fiber study. The internodal lengths were measured, and nodes of Ranvier and Schmidt-Lanterman notch were observed. The nerve fiber length was increased after stretching. The mean internodal length was 1208.31 microm in group one, 1347.26 microm in group two, and 1411.35 microm in group three. Compared with the control group, mean internodal length was elongated by 11.50% in group two and 16.80% in group three. The difference was statistically significant. The node of Ranvier and Schmidt-Lanterman notch was wider in both group two and group three. Rupture of nerve fiber at the node of Ranvier was observed in group three. The peroneal nerve in rabbits can adapt to mild stretching by internodal length elongation. Elongation by 20% will cause structural rupture and therefore is the limit for nerve elongation.

Improving electrophysiologic and histologic outcomes by photochemically sealing amnion to the peripheral nerve repair site.

BACKGROUND: The surgical approach used today in the repair of peripheral nerve injuries rarely achieves full functional recovery. This study determines whether isolation of the nerve repair site using photochemical tissue bonding (PTB) in combination with human amniotic membrane can improve both functional and histologic recovery. METHODS: New Zealand white rabbits (n = 24) underwent transection of the right common peroneal nerve. Epineural nerve repair was performed using 10-0 nylon sutures. The repair site was then wrapped in a cuff of human amniotic membrane, which either was secured with sutures or sealed using PTB. Standard neurorrhaphy alone was assessed as a control group. Functional recovery was recorded at 30-day intervals postoperatively by electrophysiologic assessment. At 120 days, animals were killed humanely and nerves harvested for histomorphometry. RESULTS: Nerves treated with amnion wraps and sealed with PTB demonstrated a statistically significant improvement across both functional and histologic parameters. Functional recovery, as measured by repeated electrophysiologic studies over time, revealed a 26.2% improvement over standard neurorrhaphy alone (P < .05). Nerves treated with PTB-sealed amnion wraps had significantly greater (P < .001) axon (5.08 +/- 1.06 microm) and fiber diameters (7.46 +/- 1.37 microm), as well as myelin thickness (2.39 +/- 0.7 microm) and the g ratio (axon diameter/fiber diameter ratio; 0.68 +/- 0.07) distal to the repair site compared to standard neurorrhaphy alone (4.98 +/- 1.81 microm, 6.77 +/- 1.94 microm, 1.79 +/- 0.42 microm, and 0.71 +/- 0.09, respectively). CONCLUSION: Isolation of the repair site using a photochemically sealed amnion wrap improves electrophysiologic and histologic recovery compared to standard suture neurorrhaphy.

Neuropathy patterns differ in patients with diabetic complications.

PURPOSE: Diabetic polyneuropathy (PNP) is an important risk factor for foot ulcers. Diabetic dermopathy is more frequent in patients with diabetic neuropathy. We compared clinical and electrophysiological characteristics of PNP localizations/recurrences of foot ulcers, and diabetic dermopathy (DD) between sexes. METHODS: Eighty-eight diabetic patients (44 men, 44 women) had an evaluation regarding detailed history of their diseases, lesion-related data, and clinical examination. Nerve conduction velocities (NCV), compound motor action potentials (CMAP), distal latencies (DL), and sensory nerve action potentials were assessed from the right and left peroneal, right median/ulnar nerves. RESULTS: The presence of DD was more common in men (p < 0.001). The mean NCV of ulnar nerves was slower (p < 0.001); mean CMAP values were lower (p = 0.006); and mean DL was longer in men with compared to women (p = 0.003). Although EMG features of peroneal nerves showed no significant difference, diabetic men had more common and severe peroneal nerve involvement (p = 0.004). Carpal tunnel syndrome was more common in women, though not significant. Patients with right-sided ulcers had lower CMAP amplitudes on the right peroneal nerves in regard to left peroneal nerves (p = 0.009). CONCLUSIONS: Our findings suggest that ulnar nerves are more commonly involved in men, with lower CMAP slower NCV values, and longer DL values.

Reflex sympathetic activity after intravenous administration of midazolam in anesthetized cats.

BACKGROUND: Although intrathecal midazolam has been reported to produce antinociceptive effects mediated by gamma-aminobutyric acid type A-benzodiazepine receptor complexes in the spinal cord, the effects of systemic midazolam on nociception remain unclear. We performed this study to examine the effects of IV-administered midazolam on somatosympathetic Adelta and C reflex discharges in brain-intact cats and decerebrate cats (with transection at midbrain level). METHODS: Somatosympathetic Adelta and C reflexes were elicited in the inferior cardiac sympathetic nerve by electrical stimulation of myelinated (Adelta) and unmyelinated (C) afferent fibers of the superficial peroneal nerve in 28 mature cats. After control somatosympathetic reflex responses were obtained, midazolam was administered IV to four groups of randomly allocated cats as follows: brain-intact cats at a dose of 0.03 mg/kg, brain-intact cats at a dose of 0.1 mg/kg, brain-intact cats at a dose of 0.5 mg/kg, and decerebrate cats at a dose of 0.1 mg/kg. RESULTS: C reflex discharges were significantly augmented at the dose of 0.03 mg/kg and significantly depressed at the dose of 0.1 and 0.5 mg/kg in brain-intact cats. C reflex discharges were also significantly depressed at the dose of 0.1 mg/kg in decerebrate cats. CONCLUSIONS: We have demonstrated that IV midazolam produces dose-related effects on somatosympathetic reflex discharges. The clinical implication of these findings is that the effect of midazolam on nociception depends on its dosage. It also appears that the infra-midbrain region plays a major role in mediating the depressive effects of midazolam on somatosympathetic C reflex discharges.

A device for the electrophysiological recording of peripheral nerves in response to stretch.

The functional consequences of nervous tissue subjected to mechanical loads are of vital importance in successful clinical outcomes and in tissue engineered applications. In this paper, we developed a new ex vivo device that permitted the recording of nerve action potentials while the nerve was subjected to elongation. Experimental results showed guinea pig nerves to possess an inherent tolerance to mild stretch. The mean elongation at which the compound action potential (CAP) amplitude began to decrease was found to be 8.3 +/- 0.56%. The CAP response to stretch was immediate beyond this threshold. After 17.5 +/- 0.74% elongation, the CAP levels decreased to approximately 50% of its uninjured values. When allowed to relax, the CAP recovered almost completely within minutes. Based on the temporal scale of the CAP response and the presence of oxygen during testing, we conclude that the initial mechanism to CAP degradation cannot be ischemia. Since it is inherently difficult to study mechanical damage independent of hemodynamic factors in vivo, the developed model could be used to further elucidate the injury mechanisms of stretch-induced trauma. The design of the ex vivo chamber will also permit the administration and assessment of pharmacological agents on electrical conduction in various deformation conditions.

Single-unit analysis of sympathetic nervous discharges in patients with panic disorder.

Patients with panic disorder are at increased cardiac risk. While the mechanisms responsible remain unknown, activation of the sympathetic nervous system may be implicated. Using isotope dilution methodology, investigations of whole-body and regional sympathetic nervous activity have failed to show any differences between patients with panic disorder and healthy subjects. Using direct recording of single unit efferent sympathetic vasoconstrictor nerve activity by microneurography we examined sympathetic nervous function in patients with panic disorder more precisely than previously reported. The activity of multiunit and single unit vasoconstrictor sympathetic nerves was recorded at rest at the level of the peroneal nerve in 10 patients diagnosed with panic disorder and in nine matched healthy volunteers. Multiunit sympathetic activity was not different between the two groups (26+/-3 bursts min-1 in patients with panic disorder and 28+/-3 bursts min-1 in controls). The firing frequency of single unit vasoconstrictor neurones was also similar between the two groups (0.38+/-0.09 versus 0.22+/-0.03 Hz). However, the probability of firing during a sympathetic burst was higher in patients with panic disorder compared with healthy controls (45+/-5%versus 32+/-3%, P<0.05). When only the neural bursts during which the vasoconstrictor neurone was active were considered, we found that in patients with panic disorder the neurones tended to fire more often in a 'multiple spike' pattern than in the controls (i.e. the probability of the neurone firing twice was 25+/-3% in patients with panic disorder compared with 14+/-3% in controls). Quantification from single vasoconstrictor unit recording provides evidence of a disturbed sympathetic firing pattern in patients with panic disorder.

Neural tissue engineering: a self-organizing collagen guidance conduit.

We report a novel implantable device that will deliver a tethered aligned collagen guidance conduit containing Schwann cells into a peripheral nerve injury site. Cells (Schwann cells and fibroblasts) incorporated into tethered rectangular collagen gels contracted and resulted in uniaxial alignment. This tissue-engineered construct was tested in three-dimensional culture and demonstrated the ability to guide neurite extension from dissociated dorsal root ganglia. A silicone tube was adapted to provide tethering sites for an implantable construct such that uniaxial cell-generated tension resulted in the formation of a bridge of aligned collagen fibrils, with a resident Schwann cell population. The potential of this device for surgical nerve regeneration was assessed in a 5-mm defect in a rat sciatic nerve model. Neural regeneration through this device was significantly greater than in controls, demonstrating that this system has potential both as a simple robust clinical implant and as a three-dimensional engineered tissue model.

End-to-side nerve coaptation: is an additional proximal coaptation useful when available?

The aim of this experimental study was to evaluate the effects of end-to-side coaptation of the proximal end of a severed nerve to the same intact nerve, in addition to traditional end-to-side coaptation of the distal end, with an aim to use the intact nerve as a nerve conduit in a rat model and to compare the functional and histologic results of this modality to those obtained after nerve grafting and traditional end-to-side nerve coaptation. In group A, a peroneal nerve defect measuring 1 cm was created in the left hind limb, and a nerve graft 1 cm long was used to bridge the defect. In group B, only the distal stump of the peroneal nerve was coapted to the intact tibial nerve. In group C, both ends of the peroneal nerve defect were coapted to the intact tibial nerve in an end-to-side fashion 1.5 cm apart from each other, and in group D, the peroneal nerve defect was left unrepaired. Group E was consisted of nonoperated peroneal nerves that were used to obtain normative data. Although significantly higher myelinated axon densities were observed in groups B and C compared with group A and group E, total number of the myelinated axons was significantly higher only in group C. Peroneal functional index assessments demonstrated that nerve recovery in the peroneal nerve was similar in groups A and C, and both were better than those observed in groups B and D. Collectively, these results suggest that end-to-side coaptation of both ends of a severed nerve to an intact nerve, in case of a nerve defect in this length, may serve as an alternative for nerve grafting.

Octyl 2-cyanoacrylate for repair of peripheral nerve.

The repair of peripheral nerves with sutures is time consuming. The aim of this study was to evaluate the benefits and functional outcome of repairing nerves with octyl 2-cyanoacrylate adhesive. The right peroneal nerve of 64 male, Lewis rats was sectioned and repaired. The rats were randomized into 3 experimental groups: A (n = 27), using only octyl 2-cyanoacrylate; B (n = 27), using 4, 10-0 nylon sutures; and C (n = 10), a sham operation. The recovery of nerve function was quantified through walking-track analyses; group A showed faster return of nerve function than B, especially at 15 days (P < 0.017). Histologic analysis showed a greater axonal regeneration in group A versus group B and no indication of tissue toxicity in group A. No dehiscence occurred during the 6-month study. Use of adhesive shortened the anastomosis time from 12 minutes to 4 minutes. These results indicate that the use of octyl 2-cyanoacrylate adhesive for nerve anastomoses is safe and effective and may have benefits compared with the use of sutures.

Each sensory nerve arising from the geniculate ganglion expresses a unique fingerprint of neurotrophin and neurotrophin receptor genes.

Neurons in the geniculate ganglion, like those in other sensory ganglia, are dependent on neurotrophins for survival. Most geniculate ganglion neurons innervate taste buds in two regions of the tongue and two regions of the palate; the rest are cutaneous nerves to the skin of the ear. We investigated the expression of four neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and NT-4, and five neurotrophin receptors, trkA, trkB, trkC, p75, and truncated trkB (Trn-B) in single sensory neurons of the adult rat geniculate ganglion associated with the five innervation fields. For fungiform papillae, a glass pipette containing biotinylated dextran was placed over the target papilla and the tracer was iontophoresed into the target papilla. For the other target fields, Fluoro-Gold was microinjected. After 3 days, geniculate ganglia were harvested, sectioned, and treated histochemically (for biotinylated dextran) or immunohistochemically (for Fluoro-Gold) to reveal the neurons containing the tracer. Single labeled neurons were harvested from the slides and subjected to RNA amplification and RT-PCR to reveal the neurotrophin or neurotrophin receptor genes that were expressed. Neurons projecting from the geniculate ganglion to each of the five target fields had a unique expression profile of neurotrophin and neurotrophic receptor genes. Several individual neurons expressed more than one neurotrophin receptor or more than one neurotrophin gene. Although BDNF is significantly expressed in taste buds, its primary high affinity receptor, trkB, was not prominently expressed in the neurons. The results are consistent with the interpretation that at least some, perhaps most, of the trophic influence on the sensory neurons is derived from the neuronal somata, and the trophic effect is paracrine or autocrine, rather than target derived. The BDNF in the taste bud may also act in a paracrine or autocrine manner on the trkB expressed in taste buds, as shown by others.

Deep peroneal motor nerve conduction velocity distribution and correlation between nerve conduction groups and the number of innervated muscle fibers.

In this study, the distribution of peroneal-nerve conduction velocity was studied in 17 normal subjects, using the collision method. Paired supramaximal stimuli with predetermined interstimulus intervals (ISI) were applied at distal and proximal points of peroneal nerve and the resultant compound muscle action potentials (CMAPs) were recorded. The change in CMAP amplitudes and areas with ISI were deduced, and the relative number of fibers corresponding to each conduction velocity group (CVG) were computed. Conduction velocities of the peroneal motor nerve innervating the Extensor Digitorum Brevis (EDB) muscle were found to be in the range of 28-52 m/s and CVG innervating the greatest number appears to be in 40-48 m/s range, which consists of 70% of all fibers. These results show that, compared with the median motor nerve, deep peroneal motor nerve that innervates the EDB muscle consist of slow fibers.

NGF, BDNF, NT-3, and GDNF mRNA expression in rat skeletal muscle following denervation and sensory protection.

Poor muscle and nerve functional recovery after nerve damage is a serious clinical problem, particularly if there is prolonged delay before nerve-muscle contact is reestablished. Our previous studies showed that sensory nerve cross-anastomosis (sensory protection) provides support to the denervated muscle. In the present study, we analyzed neurotrophic factor mRNA expression by RT-PCR in denervated rat gastrocnemius muscle receiving sensory protection with the saphenous nerve, compared to normal innervated muscle, to denervated muscle, and to denervated muscle repaired immediately with the peroneal (motor) nerve, after periods of 3 days to 3 months. No significant differences in mRNA levels of beta-actin, nerve growth factor, brain-derived neurotrophic factor or neurotrophin-3 were found between the sensory protection treatment and the denervated or the motor repair groups. However, sensory protection resulted in levels of muscle glial cell line-derived neurotrophic factor mRNA expression that were lower than in denervated muscle and higher than in muscle given immediate motor repair. These results demonstrate that glial cell line-derived neurotrophic factor mRNA is elevated following denervation but is partially down-regulated by sensory protection. Our study suggests that sensory protection provides a modified trophic environment by modulating neurotrophic factor synthesis in muscle.

Effects of immunosuppression on regrowth of adult rat retinal ganglion cell axons into peripheral nerve allografts.

Analysis of the effectiveness of allografts and immunosuppression in the repair of nerve defects in the adult peripheral nervous system (PNS) has a long experimental and clinical history. There is little information, however, on the use of allografts in peripheral nerve (PN) transplantation into the injured central nervous system (CNS). We assessed the ability of PN allografts (from Dark-Agouti rats) to support regeneration of adult rat retinal ganglion cell (RGC) axons in immunosuppressed host Lewis rats. PN allografts were sutured onto intraorbitally transected optic nerves. Three weeks after grafting, regenerating RGC axon numbers were determined using retrograde fluorescent labelling, and total axons within PN grafts were assessed using pan-neurofilament immunohistochemistry. In the absence of immunosuppression, PN allografts contained few axons and there were very few labelled RGC. These degenerate grafts contained many T cells and macrophages. Systemic (intraperitoneal) application of the immunosuppressants cyclosporin-A or FK506 reduced cellular infiltration into allografts and resulted in extensive axonal regrowth from surviving RGCs. The average number of RGCs regenerating axons into immunosuppressed allografts was not significantly different from that seen in PN autografts in rats sham-injected with saline. Many pan-neurofilament-positive axons, a proportion of which were myelinated, were seen in immunosuppressed allografts, particularly in proximal regions of the grafts toward the optic nerve-PN interface. This study demonstrates that PN allografts can support axonal regrowth in immunosuppressed adult hosts, and points to possible clinical use in CNS repair.