Nerve lesions and the generation of pain

[Etiopathogenetic substantiation of surgical treatment of neurogenic pain syndromes]

The purpose of the study was to improve classification of neurogenic (neuropathic) pain syndromes. This will make it possible to define the indications for appropriate analgesic surgery for each type of drug-resistant neurogenic pain syndrome. Incorrect management of neurogenic pain syndromes is usually associated with underestimation of pathogenetic prerequisites for its occurrence. Differentiation of compression, deafferentation and mixed neurogenic pain syndromes makes it possible to determine appropriate surgery and avoid tactical errors. Moreover, this approach allows you to save patients from unreasonable long-standing suffering. Patients with chronic pain syndromes often become disabled, sometimes in the prime of life, and isolated from society and family. Therefore, treatment of chronic pain is currently an urgent problem.

Targeted muscle reinnervation for a recurrent traumatic neuroma of the sural nerve: illustrative case

BACKGROUND

Traumatic neuromata often recur after resection. Recently, targeted muscle reinnervation (TMR) has been shown to be a promising alternative for the treatment of traumatic neuroma, also in nonamputees. This case shows that TMR can also be applied for this indication in recurrent traumatic neuroma.

OBSERVATIONS

A 55-year-old patient with a history of cerebral palsy presented with a painful swelling in his right knee, 40 years after multiple Achilles tendon surgeries for contractures. On imaging, the lesion was suspect for a traumatic neuroma of the posterior sural nerve. After two failed resections, TMR was performed by connecting the proximal end of the sural nerve to the motor branch of the lateral gastrocnemius muscle. During outpatient visits at 3, 6, and 12 months, the patient reported significantly less pain compared to before the TMR. He had no weakness of plantar flexion. Postoperative imaging, however, showed atrophy of the lateral gastrocnemius muscle.

LESSONS

This case shows that TMR can be a successful strategy to treat recurrent traumatic neuroma after previous failed transection of single neuromata in nonamputee cases. In the authors’ patient, TMR did not result in motor deficit, but more research is needed to investigate this consequence of TMR for this indication.

Suprainguinal Re-Resection of the Lateral Femoral Cutaneous Nerve in Persistence or Recurrence of Meralgia Paresthetica After Previous Transection: Results of a Case Series

OBJECTIVE

Suprainguinal re-resection of the proximal nerve stump can be performed in case of persistent or recurrent symptoms of meralgia paresthetica after previous transection of the lateral femoral cutaneous nerve (LFCN). Currently, no long-term results for this procedure have been reported in the literature.

METHODS

In this study, 20 consecutive patients with persistent (13 cases) or recurrent (7 cases) symptoms of meralgia paresthetica were reoperated at a mean interval of 16 months after the first transection of the LFCN. The proximal nerve stump was sent for histopathologic analysis of a potential traumatic neuroma. Outcome was assessed using a 5-point Likert scale, which was obtained at a mean interval of 3.5 years after the suprainguinal re-resection.

RESULTS

The proximal stump of the LFCN was identified in 90% of the cases. Successful pain relief (Likert 1 or 2) was obtained in 65% of the patients. A neuroma was found in 11 cases (55%), mostly in recurrent cases after a pain-free interval. The indication for recurrence of symptoms more frequently resulted in successful pain relief (71%) compared with results for the indication for persistence of symptoms (62%). There was no correlation between the presence of a neuroma and the chance for pain relief.

CONCLUSIONS

Suprainguinal re-resection of the LFCN can be a successful procedure, both for persistence and recurrence of symptoms of meralgia paresthetica after previous transection, with long-lasting pain relief. Several factors, however, should be considered before performing this relatively new technique in patients that are discussed in this article.

Age-related molecular changes in the lumbar dorsal root ganglia of mice: Signs of sensitization, and inflammatory response

Aging is a major risk factor for numerous painful, inflammatory, and degenerative diseases including disc degeneration. A better understanding of how the somatosensory nervous system adapts to the changing physiology of the aging body will be of great significance for our expanding aging population. Previously, we reported that chronological aging of mouse lumbar discs is pathological and associated with behavioral changes related to pain. It is established that with age and degeneration the lumbar discs become inflammatory and innervated. Here we analyze the aging lumbar dorsal root ganglia (DRGs) and spinal cord dorsal horn (SCDH) in mice between 3 and 24 months of age for age-related somatosensory adaptations. We observe that as mice age there are signs of peripheral sensitization, and response to inflammation at the molecular and cellular level in the DRGs. From 12 months onwards the mRNA expression of vasodilator and neurotransmitter, Calca (CGRP); stress (and survival) marker, Atf3; and neurotrophic factor, Bdnf, increases linearly with age in the DRGs. Further, while the mRNA expression of neuropeptide, Tac1, precursor of Substance P, did not change at the transcriptional level, TAC1 protein expression increased in 24-month-old DRGs. Additionally, elevated expression of NFκB subunits, Nfkb1 and Rela, but not inflammatory mediators, Tnf, Il6, Il1b, or Cox2, in the DRGs suggest peripheral nerves are responding to inflammation, but do not increase the expression of inflammatory mediators at the transcriptional level. These results identify a progressive, age-related shift in the molecular profile of the mouse somatosensory nervous system and implicates nociceptive sensitization and inflammatory response.

Unique Characteristics of the Dorsal Root Ganglion as a Target for Neuromodulation

Objective

The dorsal root ganglion (DRG) is a novel target for neuromodulation, and DRG stimulation is proving to be a viable option in the treatment of chronic intractable neuropathic pain. Although the overall principle of conventional spinal cord stimulation (SCS) and DRG stimulation—in which an electric field is applied to a neural target with the intent of affecting neural pathways to decrease pain perception—is similar, there are significant differences in the anatomy and physiology of the DRG that make it an ideal target for neuromodulation and may account for the superior outcomes observed in the treatment of certain chronic neuropathic pain states. This review highlights the anatomy of the DRG, its function in maintaining homeostasis and its role in neuropathic pain, and the unique value of DRG as a target in neuromodulation for pain.

Methods

A narrative literature review was performed.

Results

Overall, the DRG is a critical structure in sensory transduction and modulation, including pain transmission and the maintenance of persistent neuropathic pain states. Unique characteristics including selective somatic organization, specialized membrane characteristics, and accessible and consistent location make the DRG an ideal target for neuromodulation. Because DRG stimulation directly recruits the somata of primary sensory neurons and harnesses the filtering capacity of the pseudounipolar neural architecture, it is differentiated from SCS, peripheral nerve stimulation, and other neuromodulation options.

Conclusions

There are several advantages to targeting the DRG, including lower energy usage, more focused and posture-independent stimulation, reduced paresthesia, and improved clinical outcomes.

Dextran-based tube-guides for the regeneration of the rat sciatic nerve after neurotmesis injury

In this work, dextran-based nerve tube-guides were prepared, characterized and used in a standardized animal model of neurotmesis injury. Non-porous and porous transparent tube-guides were obtained by photocrosslinking of two co-macromonomers based on dextran and poly(ε-caprolactone) (PCL). Swelling capacity of the tube-guides ranged from 40-60% with no visible constriction of their inner diameter. In vitro hydrolytic degradation tests showed that the tube-guides maintained their structural integrity up to 6 months. The in vivo performance of the tube-guides was evaluated by entubulation of the rat sciatic nerve after a neurotmesis injury, with a 10 mm-gap between the nerve stumps. The results showed that the tube-guides were able to promote the regeneration of the nerve in a similar manner to what was observed with conventional techniques (nerve graft and end-to-end suture). Stereological analysis proved that nerve regeneration occurred, and both tube-guides presented fibre diameter and g-ratio closer to healthy sciatic nerves. The histomorphometric analysis of Tibialis anterior (TA) skeletal muscle showed decreased neurogenic atrophy in the porous tube-guides treated group, presenting measurements that are similar to the uninjured control.

Clinical and in vivo confocal microscopic features of neuropathic corneal pain

Aims

To describe clinical and in vivo confocal microscopy (IVCM) features of neuropathic corneal pain (NCP) without clinically visible signs.

Methods

Prospective, observational study of 27 eyes of 14 patients who had continuous severe ocular pain for one or more years, with minimal or no ocular surface signs and were non-responsive to topical lubricants, steroids and/or ciclosporin. All patients were evaluated using Ocular Surface Disease Index, Oxford grading scale, Schirmer test 1, Cochet Bonnet esthesiometry and response to topical anaesthesia. Central and paracentral regions of the cornea of patients and seven healthy controls were studied by IVCM. Corneal epithelial thickness and sub-basal nerve density were measured in patients and controls.

Results

Four patients responded to topical anaesthesia (responsive group (RG)), indicating peripheral NCP while 10 patients did not show any improvement (non-responsive group (NRG)), indicating central NCP. Schirmer-1 test was within normal limits in the RG but significantly greater in the NRG (p<0.001). None of the other clinical parameters nor corneal epithelial thickness were statistically significantly different. The sub-basal nerve density was significantly reduced (p<0.008) in patients compared with controls. Stroma of all patients demonstrated activated keratocytes and spindle, lateral and stump microneuromas. There was a statistically significant greater number of microneuromas (p<0.0001) and activated keratocytes in RG compared with NRG.

Conclusion

NCP without visible clinical signs does not represent typical dry eye disease. Distinct signs demonstrated on IVCM suggest that peripheral NCP, which responds to topical anaesthesia, and central NCP, which does not, are separate entities.

Pain in Urology: Pathophysiological Aspects of Pain and Chronicity

Chronic pain has been traditionally defined by pain duration, but this approach has limited empirical support and does not account for chronic pain multidimensionality. Defining chronic pain solely by duration is based on the view that acute pain signals potential tissue damage, whereas chronic pain results from central sensitization in which pain is sustained after nociceptive inputs have diminished. Chronic urological pain is a prevalent condition, which can represent a major challenge to health care providers due to its complex aetiology and poor response to therapy. In most cases, clear signs of on-going tissue trauma, inflammation or infection are not present. Despite this, more underhanded pathophysiological mechanisms, affecting the urinary system or other pelvic organ systems (musculoskeletal, neurologic, urologic, gynaecologic) and some psychological aspects may be present. In this article, some pathophysiological aspects of visceral pain are discussed; the definition of ‘chronic pain’, the mechanism of action of drugs used in the treatment of pain and the rationale for association therapy are also reviewed.

Injection Therapy for Headache and Facial Pain

Peripheral nerve blocks are an increasingly viable treatment option for selected groups of headache patients, particularly those with intractable headache or facial pain. Greater occipital nerve block, the most widely used local anesthetic procedure in headache conditions, is particularly effective, safe, and easy to perform in the office. Adverse effects are few and infrequent. These procedures can result in rapid relief of pain and allodynia, and effects last for several weeks or months. Use of nerve block procedures and potentially onabotulinum toxin therapy should be expanded for patients with intractable headache disorders who may benefit, although more studies are needed for efficacy and clinical safety.

A randomized, double-blind, placebo-controlled trial of injected capsaicin for pain in Morton's neuroma

Intermetatarsal neuroma or Morton's neuroma is a painful condition of the foot resulting from an entrapment of the common digital nerve typically in the third intermetatarsal space. The pain can be severe and especially problematic with walking. Treatment options are limited and surgery may lead to permanent numbness in the toes. Capsaicin, the pungent ingredient of hot peppers, produces analgesia by inducing retraction of nociceptive afferents from the area of innervation and is effective in treating certain neuropathic pain disorders. A randomized double-blind placebo-controlled study was conducted to test the efficacy, tolerability, and safety of a single 0.1 mg dose of capsaicin vs placebo injected into the region of the neuroma. A total of 58 subjects diagnosed with Morton's neuroma with foot pain ≥4 (0-10 numerical pain rating scale) were injected with 2 mL of lidocaine into the intermetatarsal space proximal to the neuroma to provide local anesthesia. After 5 minutes, 0.1 mg capsaicin or placebo was injected into the intermetatarsal space containing the painful neuroma. Average foot pain was rated for 2 weeks before through 4 weeks after injection. At weeks 1 and 4, the decrease in pain was significantly greater in the subjects treated with capsaicin (P = 0.021 and P = 0.019, respectively). A trend toward significance was noted at weeks 2 and 3. Improvements in functional interference scores and reductions in oral analgesic use were also seen in the capsaicin-treated group. These findings suggest that injection of capsaicin is an efficacious treatment option for patients with painful intermetatarsal neuroma.

Differential drug effects on spontaneous and evoked pain behavior in a model of trigeminal neuropathic pain

PURPOSE

Baclofen and morphine have shown efficacy against mechanical allodynia after infraorbital nerve chronic constriction injury (IoN-CCI). No drug effects have yet been reported on spontaneous trigeminal neuropathic pain. It has been proposed that the directed face grooming behavior that also develops following IoN-CCI offers a measure of spontaneous trigeminal neuropathic pain.

SUBJECTS AND METHODS

We examined the effects of a continuous 1-week infusion of 30 mg/day carbamazepine (the first-line drug treatment for trigeminal neuralgia), 1.06 mg/day baclofen, 4.18 mg/day clomipramine, and 5 mg/day morphine on spontaneous and mechanically evoked pain behavior (ie, directed face grooming and von Frey testing) in IoN-CCI rats.

RESULTS

Isolated face grooming was significantly reduced in rats receiving carbamazepine and baclofen but not in clomipramine- or morphine-treated rats. All drugs showed significant antiallodynic effects; carbamazepine showed the strongest effects, whereas clomipramine had only minor efficacy.

CONCLUSION

The tested drugs have differential effects in the IoN-CCI model, and different neuropathological mechanisms may underlie the different somatosensory symptoms in this model. A mechanism-based approach may be needed to treat (trigeminal) neuropathic pain. The present data support IoN-CCI as a model of trigeminal neuralgia in which isolated face grooming is used as a measure of spontaneous neuropathic pain.

NR2B Expression in Rat DRG Is Differentially Regulated Following Peripheral Nerve Injuries That Lead to Transient or Sustained Stimuli-Evoked Hypersensitivity

Following injury, primary sensory neurons undergo changes that drive central sensitization and contribute to the maintenance of persistent hypersensitivity. NR2B expression in the dorsal root ganglia (DRG) has not been previously examined in neuropathic pain models. Here, we investigated if changes in NR2B expression within the DRG are associated with hypersensitivities that result from peripheral nerve injuries. This was done by comparing the NR2B expression in the DRG derived from two modalities of the spared nerve injury (SNI) model, since each variant produces different neuropathic pain phenotypes. Using the electronic von Frey to stimulate the spared and non-spared regions of the hindpaws, we demonstrated that sural-SNI animals develop sustained neuropathic pain in both regions while the tibial-SNI animals recover. NR2B expression was measured at Day 23 and Day 86 post-injury. At Day 23 and 86 post-injury, sural-SNI animals display strong hypersensitivity, whereas tibial-SNI animals display 50 and 100% recovery from post-injury-induced hypersensitivity, respectively. In tibial-SNI at Day 86, but not at Day 23 the perinuclear region of the neuronal somata displayed an increase in NR2B protein. This retention of NR2B protein within the perinuclear region, which will render them non-functional, correlates with the recovery observed in tibial-SNI. In sural-SNI at Day 86, DRG displayed an increase in NR2B mRNA which correlates with the development of sustained hypersensitivity in this model. The increase in NR2B mRNA was not associated with an increase in NR2B protein within the neuronal somata. The latter may result from a decrease in kinesin Kif17, since Kif17 mediates NR2B transport to the soma’s plasma membrane. In both SNIs, microglia/macrophages showed a transient increase in NR2B protein detected at Day 23 but not at Day 86, which correlates with the initial post-injury induced hypersensitivity in both SNIs. In tibial-SNI at Day 86, but not at Day 23, satellite glia cells (SGCs) displayed an increase in NR2B protein. This study is the first to characterize of cell-specific changes in NR2B expression within the DRG following peripheral nerve injury. We discuss how the observed NR2B changes in DRG can contribute to the different neuropathic pain phenotypes displayed by each SNI variant.

Tumor necrosis factor-alpha induces expression of C/EBP-beta in primary afferent neurons following nerve injury

CCAAT/enhancer binding protein-beta (C/EBP-beta) is a transcription factor that belongs to the C/EBP family. To understand the role of C/EBP-beta in the peripheral nervous system, we investigated the expression of C/EBP-beta in the dorsal root ganglion. C/EBP-beta was weakly detected in nuclei of naive dorsal root ganglion (DRG) neurons. Spinal nerve ligation increased the expression of C/EBP-beta in L4 and L5 DRG neurons. Treatment with anti-TNF-alpha prevented SNL-induced pain hypersensitivity and C/EBP-beta expression in the DRG. Injection of TNF-alpha into the sciatic nerve produced transient pain hypersensitivity and induction of C/EBP-beta expression in the DRG. These results demonstrate that C/EBP-beta is activated in the DRG neurons by a TNF-alpha-dependent manner and might be involved in the activation of primary afferent neurons after nerve injury.

Epigenetic modification of DRG neuronal gene expression subsequent to nerve injury: etiological contribution to complex regional pain syndromes (Part I)

DRG is of importance in relaying painful stimulation to the higher pain centers and therefore could be a crucial target for early intervention aimed at suppressing primary afferent stimulation. Complex regional pain syndrome (CRPS) is a common pain condition with an unknown etiology. Recently added new information enriches our understanding of CRPS pathophysiology. Researches on genetics, biogenic amines, neurotransmitters, and mechanisms of pain modulation, central sensitization, and autonomic functions in CRPS revealed various abnormalities indicating that multiple factors and mechanisms are involved in the pathogenesis of CRPS. Epigenetics refers to mitotically and meiotically heritable changes in gene expression that do not affect the DNA sequence. As epigenetic modifications potentially play an important role in inflammatory cytokine metabolism, neurotransmitter responsiveness, and analgesic sensitivity, they are likely key factors in the development of chronic pain. In this dyad review series, we systematically examine the nerve injury-related changes in the neurological system and their contribution to CRPS. In this part, we first reviewed and summarized the role of neural sensitization in DRG neurons in performing function in the context of pain processing. Particular emphasis is placed on the cellular and molecular changes after nerve injury as well as different models of inflammatory and neuropathic pain. These were considered as the potential molecular bases that underlie nerve injury-associated pathogenesis of CRPS.

The up-regulation of IL-6 in DRG and spinal dorsal horn contributes to neuropathic pain following L5 ventral root transection

Our previous works have shown that pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) plays an important role in neuropathic pain produced by lumber 5 ventral root transection (L5-VRT). In the present work we evaluate the role of interleukin-6 (IL-6), another key inflammatory cytokine, in the L5-VRT model. We found that IL-6 was up-regulated in the ipsilateral L4 and L5 dorsal root ganglian (DRG) neurons and in bilateral lumbar spinal cord following L5-VRT. Double immunofluorescence stainings revealed that in DRGs the increased immunoreactivity (IR) of IL-6 was almost restricted in neuronal cells, while in the spinal dorsal horn IL-6-IR up-regulated in both glial cells (astrocyte and microglia) and neurons. Intrathecal administration of IL-6 neutralizing antibody significantly delayed the induction of mechanical allodynia in bilateral hindpaws after L5-VRT. Furthermore, inhibition of TNF-α synthesis by intraperitoneal thalidomide prevented both mechanical allodynia and the up-regulation of IL-6 in DRGs following L5-VRT. These data suggested that the increased IL-6 in afferent neurons and spinal cord contribute to the development of neuropathic pain following motor fiber injury, and that TNF-α is responsible for the up-regulation of IL-6.

Expression of TRPV1 channels after nerve injury provides an essential delivery tool for neuropathic pain attenuation

Increased expression of the transient receptor potential vanilloid 1 (TRPV1) channels, following nerve injury, may facilitate the entry of QX-314 into nociceptive neurons in order to achieve effective and selective pain relief. In this study we hypothesized that the level of QX-314/capsaicin (QX-CAP) - induced blockade of nocifensive behavior could be used as an indirect in-vivo measurement of functional expression of TRPV1 channels. We used the QX-CAP combination to monitor the functional expression of TRPV1 in regenerated neurons after inferior alveolar nerve (IAN) transection in rats. We evaluated the effect of this combination on pain threshold at different time points after IAN transection by analyzing the escape thresholds to mechanical stimulation of lateral mental skin. At 2 weeks after IAN transection, there was no QX-CAP mediated block of mechanical hyperalgesia, implying that there was no functional expression of TRPV1 channels. These results were confirmed immunohistochemically by staining of regenerated trigeminal ganglion (TG) neurons. This suggests that TRPV1 channel expression is an essential necessity for the QX-CAP mediated blockade. Furthermore, we show that 3 and 4 weeks after IAN transection, application of QX-CAP produced a gradual increase in escape threshold, which paralleled the increased levels of TRPV1 channels that were detected in regenerated TG neurons. Immunohistochemical analysis also revealed that non-myelinated neurons regenerated slowly compared to myelinated neurons following IAN transection. We also show that TRPV1 expression shifted towards myelinated neurons. Our findings suggest that nerve injury modulates the TRPV1 expression pattern in regenerated neurons and that the effectiveness of QX-CAP induced blockade depends on the availability of functional TRPV1 receptors in regenerated neurons. The results of this study also suggest that the QX-CAP based approach can be used as a new behavioral tool to detect dynamic changes in TRPV1 expression, in various pathological conditions.

Nociceptors as chronic drivers of pain and hyperreflexia after spinal cord injury: an adaptive-maladaptive hyperfunctional state hypothesis

Spinal cord injury (SCI) causes chronic peripheral sensitization of nociceptors and persistent generation of spontaneous action potentials (SA) in peripheral branches and the somata of hyperexcitable nociceptors within dorsal root ganglia (DRG). Here it is proposed that SCI triggers in numerous nociceptors a persistent hyperfunctional state (peripheral, synaptic, and somal) that originally evolved as an adaptive response to compensate for loss of sensory terminals after severe but survivable peripheral injury. In this hypothesis, nociceptor somata monitor the status of their own receptive field and the rest of the body by integrating signals received by their peripheral and central branches and the soma itself. A nociceptor switches into a potentially permanent hyperfunctional state when central neural, glial, and inflammatory signal combinations are detected that indicate extensive peripheral injury. Similar signal combinations are produced by SCI and disseminated widely to uninjured as well as injured nociceptors. This paper focuses on the uninjured nociceptors that are altered by SCI. Enhanced activity generated in below-level nociceptors promotes below-level central sensitization, somatic and autonomic hyperreflexia, and visceral dysfunction. If sufficient ascending fibers survive, enhanced activity in below-level nociceptors contributes to below-level pain. Nociceptor activity generated above the injury level contributes to at- and above-level sensitization and pain (evoked and spontaneous). Thus, SCI triggers a potent nociceptor state that may have been adaptive (from an evolutionary perspective) after severe peripheral injury but is maladaptive after SCI. Evidence that hyperfunctional nociceptors make large contributions to behavioral hypersensitivity after SCI suggests that nociceptor-specific ion channels required for nociceptor SA and hypersensitivity offer promising targets for treating chronic pain and hyperreflexia after SCI.

Randomized control trial of topical clonidine for treatment of painful diabetic neuropathy

A length-dependent neuropathy with pain in the feet is a common complication of diabetes (painful diabetic neuropathy). It was hypothesized that pain may arise from sensitized-hyperactive cutaneous nociceptors, and that this abnormal signaling may be reduced by topical administration of the α(2)-adrenergic agonist, clonidine, to the painful area. This was a randomized, double-blind, placebo-controlled, parallel-group, multicenter trial. Nociceptor function was measured by determining the painfulness of 0.1% topical capsaicin applied to the pretibial area of each subject for 30minutes during screening. Subjects were then randomized to receive 0.1% topical clonidine gel (n=89) or placebo gel (n=90) applied 3 times a day to their feet for 12weeks. The difference in foot pain at week 12 in relation to baseline, rated on a 0-10 numerical pain rating scale (NPRS), was compared between groups. Baseline NPRS was imputed for missing data for subjects who terminated the study early. The subjects treated with clonidine showed a trend toward decreased foot pain compared to the placebo-treated group (the primary endpoint; P=0.07). In subjects who felt any level of pain to capsaicin, clonidine was superior to placebo (P<0.05). In subjects with a capsaicin pain rating ⩾2 (0-10, NPRS), the mean decrease in foot pain was 2.6 for active compared to 1.4 for placebo (P=0.01). Topical clonidine gel significantly reduces the level of foot pain in painful diabetic neuropathy subjects with functional (and possibly sensitized) nociceptors in the affected skin as revealed by testing with topical capsaicin. Screening for cutaneous nociceptor function may help distinguish candidates for topical therapy for neuropathic pain.

The longitudinal spinal cord injury: lessons from intraspinal plexus, cauda equina and medullary conus lesions

Spinal nerve root avulsion injury interrupts the transverse segmental spinal cord nerve fibers. There is degeneration of sensory, motor, and autonomic axons, loss of synapses, deterioration of local segmental connections, nerve cell death, and reactions among non neuronal cells with central nerve system (CNS) scar formation, i.e., a cascade of events similar to those known to occur in any injury to the spinal cord. This is the longitudinal spinal cord injury (SCI). For function to be restored, nerve cells must survive and there must be regrowth of new nerve fibers along a trajectory consisting of CNS growth-inhibitory tissue in the spinal cord as well as peripheral nervous system (PNS) growth-promoting tissue in nerves. Basic science results have been translated into a successful surgical strategy to treat root avulsion injuries in man. In humans, this technique is currently the most promising treatment of any spinal cord injury, with return of useful muscle function together with pain alleviation. Experimental studies have also identified potential candidates for adjunctive therapies that, together with surgical replantation of avulsed roots after brachial plexus and cauda equina injuries, can restore not only motor but also autonomic and sensory trajectories to augment the recovery of neurological function. This is the first example of a spinal cord lesion that can be treated surgically, leading to restoration of somatic and autonomic activity and alleviation of pain.

Nerve Injury Triggers Changes in the Brain

It is well known that the adult brain is capable of profound plasticity. Much of our understanding of the mechanisms underlying injury-induced changes in the brain is based on animal models. The development of sophisticated noninvasive neuroimaging techniques over the past decade provides a unique opportunity to examine brain plasticity in humans. In this article, the authors examine the consequences of nerve injury and surgical repair on peripheral nerve degeneration and regeneration and review classic animal literature that laid the foundation of injury-induced plasticity research. They relate these concepts to recent findings of functional and structural changes in the human brain following peripheral nerve injury. They then present a working theoretical model that links behavioral outcomes of nerve injury with functional and structural brain plasticity and personality.

Dynamic changes in the microRNA expression profile reveal multiple regulatory mechanisms in the spinal nerve ligation model of neuropathic pain

Neuropathic pain resulting from nerve lesions or dysfunction represents one of the most challenging neurological diseases to treat. A better understanding of the molecular mechanisms responsible for causing these maladaptive responses can help develop novel therapeutic strategies and biomarkers for neuropathic pain. We performed a miRNA expression profiling study of dorsal root ganglion (DRG) tissue from rats four weeks post spinal nerve ligation (SNL), a model of neuropathic pain. TaqMan low density arrays identified 63 miRNAs whose level of expression was significantly altered following SNL surgery. Of these, 59 were downregulated and the ipsilateral L4 DRG, not the injured L5 DRG, showed the most significant downregulation suggesting that miRNA changes in the uninjured afferents may underlie the development and maintenance of neuropathic pain. TargetScan was used to predict mRNA targets for these miRNAs and it was found that the transcripts with multiple predicted target sites belong to neurologically important pathways. By employing different bioinformatic approaches we identified neurite remodeling as a significantly regulated biological pathway, and some of these predictions were confirmed by siRNA knockdown for genes that regulate neurite growth in differentiated Neuro2A cells. In vitro validation for predicted target sites in the 3′-UTR of voltage-gated sodium channel Scn11a, alpha 2/delta1 subunit of voltage-dependent Ca-channel, and purinergic receptor P2rx ligand-gated ion channel 4 using luciferase reporter assays showed that identified miRNAs modulated gene expression significantly. Our results suggest the potential for miRNAs to play a direct role in neuropathic pain.

Enhanced artemin/GFRα3 levels regulate mechanically insensitive, heat-sensitive C-fiber recruitment after axotomy and regeneration

We have shown recently that following saphenous nerve transection and successful regeneration, cutaneous polymodal nociceptors (CPMs) lacking transient receptor potential vanilloid 1 (TRPV1) are sensitized to heat stimuli and that mechanically insensitive, heat-sensitive C-fibers (CHs) that contain TRPV1 increase in prevalence. Target-derived neurotrophic factor levels were also enhanced after axotomy and regeneration. In particular, the glial-cell line-derived neurotrophic factor (GDNF) family member artemin was found to be significantly enhanced in the hairy hindpaw skin and its receptor GDNF family receptor α3 (GFRα3) was increased in the L2/L3 dorsal root ganglia (DRGs) following nerve injury. In this study, we assessed the role of enhanced artemin/GFRα3 levels on the changes in mouse cutaneous CH neurons following saphenous nerve regeneration. We used a newly developed siRNA-mediated in vivo knockdown strategy to specifically inhibit the injury-induced expression of GFRα3 and coupled this with an ex vivo recording preparation to examine response characteristics and neurochemical phenotype of different types of functionally defined neurons after injury. We found that inhibition of GFRα3 did not affect the axotomy-induced decrease in CPM threshold, but transiently prevented the recruitment of CH neurons. Western blot and real-time PCR analysis of hairy hindpaw skin and L2/L3 DRGs after saphenous nerve regeneration suggested that inhibition of the potential initial injury-induced increase in enhanced target-derived artemin signaling resulted in dynamic changes in TRPV1 expression after regeneration. These changes in TRPV1 expression may underlie the functional alterations observed in CH neurons after nerve regeneration.

Effects of collagen membranes enriched with in vitro-differentiated N1E-115 cells on rat sciatic nerve regeneration after end-to-end repair

Peripheral nerves possess the capacity of self-regeneration after traumatic injury but the extent of regeneration is often poor and may benefit from exogenous factors that enhance growth. The use of cellular systems is a rational approach for delivering neurotrophic factors at the nerve lesion site, and in the present study we investigated the effects of enwrapping the site of end-to-end rat sciatic nerve repair with an equine type III collagen membrane enriched or not with N1E-115 pre-differentiated neural cells. After neurotmesis, the sciatic nerve was repaired by end-to-end suture (End-to-End group), end-to-end suture enwrapped with an equine collagen type III membrane (End-to-EndMemb group); and end-to-end suture enwrapped with an equine collagen type III membrane previously covered with neural cells pre-differentiated in vitro from N1E-115 cells (End-to-EndMembCell group). Along the postoperative, motor and sensory functional recovery was evaluated using extensor postural thrust (EPT), withdrawal reflex latency (WRL) and ankle kinematics. After 20 weeks animals were sacrificed and the repaired sciatic nerves were processed for histological and stereological analysis. Results showed that enwrapment of the rapair site with a collagen membrane, with or without neural cell enrichment, did not lead to any significant improvement in most of functional and stereological predictors of nerve regeneration that we have assessed, with the exception of EPT which recovered significantly better after neural cell enriched membrane employment. It can thus be concluded that this particular type of nerve tissue engineering approach has very limited effects on nerve regeneration after sciatic end-to-end nerve reconstruction in the rat.

Translational pain research: achievements and challenges

The achievements in both preclinical and clinical pain research over the past 4 decades have led to significant progress in clinical pain management. However, pain research still faces enormous challenges and there remain many obstacles in the treatment of clinical pain, particularly chronic pain. Translational pain research needs to involve a number of important areas including: 1) bridging the gap between pain research and clinical pain management; 2) developing objective pain-assessment tools; 3) analyzing current theories of pain mechanisms and their relevance to clinical pain; 4) exploring new tools for both preclinical and clinical pain research; and 5) coordinating research efforts among basic scientists, clinical investigators, and pain-medicine practitioners. These issues are discussed in this article in light of the achievements and challenges of translational pain research.

PERSPECTIVE

The subjective nature of clinical pain calls for innovative research approaches. As translational pain research emerges as an important field in pain medicine, it will play a unique role in improving clinical pain management through coordinated bidirectional research approaches between bedside and bench.

Microneurographic single-unit recordings to assess receptive properties of afferent human C-fibers

Action potentials in unmyelinated peripheral axons can be recorded in awake humans by microneurography with small electrodes placed in a peripheral nerve. This technique provides extracellular recordings of single C-fibers and thus enables characterization of their sensory and axonal properties. By using microneurographical basic properties of afferent C-fibers such as conduction velocities, innervation territories, sensory thresholds and chemical responsiveness were measured. Moreover, axonal excitability changes induced by repetitive activation were assessed. Sensory and axonal properties of the different fiber classes cluster. Based on those specific properties, unitary functional classes of nociceptors (such as polymodal nociceptors and mechano-insensitive nociceptors) and non-nociceptors (such as tactile afferents and warm fibers) were classified. With normal data available, sensitization and desensitization of afferent fibers have been found in pathophysiologic states as detected in chronic pain patients. As subjects and patients are awake during the recording, microneurography provides a unique tool to correlate the discharge behaviour of afferent nerve fibers with the sensation evoked by certain stimuli.

Use of PLGA 90:10 scaffolds enriched with in vitro-differentiated neural cells for repairing rat sciatic nerve defects

Poly(lactic-co-glycolic acid) (PLGA) nerve tube guides, made of a novel proportion (90:10) of the two polymers, poly(L-lactide): poly(glycolide) and covered with a neural cell line differentiated in vitro, were tested in vivo for promoting nerve regeneration across a 10-mm gap of the rat sciatic nerve. Before in vivo testing, the PLGA 90:10 tubes were tested in vitro for water uptake and mass loss and compared with collagen sheets. The water uptake of the PLGA tubes was lower, and the mass loss was more rapid and higher than those of the collagen sheets when immersed in phosphate-buffered saline (PBS) solution. The pH values of immersing PBS did not change after soaking the collagen sheets and showed to be around 7.4. On the other hand, the pH values of PBS after soaking PLGA tubes decreased gradually during 10 days reaching values around 3.5. For the in vivo testing, 22 Sasco Sprague adult rats were divided into four groups--group 1: gap not reconstructed; group 2: gap reconstructed using an autologous nerve graft; group 3: gap reconstructed with PLGA 90:10 tube guides; group 4: gap reconstructed with PLGA 90:10 tube guides covered with neural cells differentiated in vitro. Motor and sensory functional recovery was evaluated throughout a healing period of 20 weeks using sciatic functional index, static sciatic index, extensor postural thrust, withdrawal reflex latency, and ankle kinematics. Stereological analysis was carried out on regenerated nerve fibers. Both motor and sensory functions improved significantly in the three experimental nerve repair groups, although the rate and extent of recovery was significantly higher in the group where the gap was reconstructed using the autologous graft. The presence of neural cells covering the inside of the PLGA tube guides did not make any difference in the functional recovery. By contrast, morphometric analysis showed that the introduction of N1E-115 cells inside PLGA 90:10 tube guides led to a significant lower number and size of regenerated nerve fibers, suggesting thus that this approach is not adequate for promoting peripheral nerve repair. Further studies are warranted to assess the role of other cellular systems as a foreseeable therapeutic strategy in peripheral nerve regeneration.

Sensitization of cutaneous nociceptors after nerve transection and regeneration: possible role of target-derived neurotrophic factor signaling

Damage to peripheral nerves is known to contribute to chronic pain states, including mechanical and thermal hyperalgesia and allodynia. It is unknown whether the establishment of these states is attributable to peripheral changes, central modifications, or both. In this study, we used several different approaches to assess the changes in myelinated (A) and unmyelinated (C) cutaneous nociceptors after transection and regeneration of the saphenous nerve. An ex vivo recording preparation was used to examine response characteristics and neurochemical phenotype of different types of functionally defined neurons. We found that myelinated nociceptors had significantly lower mechanical and thermal thresholds after regeneration, whereas C-polymodal nociceptors (CPMs) had lower heat thresholds. There was a significant increase in the percentage of mechanically insensitive C-fibers that responded to heat (CHs) after regeneration. Immunocytochemical analysis of identified afferents revealed that most CPMs were isolectin B4 (IB4) positive and transient receptor potential vanilloid 1 (TRPV1) negative, whereas CHs were always TRPV1 positive and IB4 negative in naive animals (Lawson et al., 2008). However, after regeneration, some identified CPMs and CHs stained positively for both markers, which was apparently attributable to an increase in the total number of IB4-positive neurons. Real-time PCR analysis of L2/L3 DRGs and hairy hindpaw skin at various times after saphenous nerve axotomy suggested multiple changes in neurotrophic factor signaling that correlated with either denervation or reinnervation of the cutaneous target. These changes may underlie the functional alterations observed after nerve regeneration and may explain how nerve damage leads to chronic pain conditions.

"Listening" and "talking" to neurons: implications of immune activation for pain control and increasing the efficacy of opioids

It is recently become clear that activated immune cells and immune-like glial cells can dramatically alter neuronal function. By increasing neuronal excitability, these non-neuronal cells are now implicated in the creation and maintenance of pathological pain, such as occurs in response to peripheral nerve injury. Such effects are exerted at multiple sites along the pain pathway, including at peripheral nerves, dorsal root ganglia, and spinal cord. In addition, activated glial cells are now recognized as disrupting the pain suppressive effects of opioid drugs and contributing to opioid tolerance and opioid dependence/withdrawal. While this review focuses on regulation of pain and opioid actions, such immune-neuronal interactions are broad in their implications. Such changes in neuronal function would be expected to occur wherever immune-derived substances come in close contact with neurons.

PLGA 90/10 and caprolactone biodegradable nerve guides for the reconstruction of the rat sciatic nerve

The purpose of this study was to test in vivo two different nerve guides for promoting nerve regeneration across a 10-mm gap of the rat sciatic nerve: 1) one made of PLGA in a novel proportion (90:10) of the two polymers poly(L-lactide):poly(glycolide); 2) another made of (DL-lactide-epsilon-caprolactone) copolyester (Neurolac) tube, by comparing its healing efficacy with that of the more traditional methods of end-to-end nerve suture and autologous graft. Motor and sensory functional recovery were assessed throughout the healing period of 20 weeks, and the repaired nerves were processed for morphological and histomorphometrical analysis. Both motor and sensory functions improved significantly in all experimental nerve repaired groups. At the end of the 20-week follow-up, the end-to-end group showed better recovery of motor function when compared with the groups treated with guiding tubes. However, at this time point, the level of motor function in the Neurolac(R) and PLGA groups was similar to the one of the graft group. Nociception function also recovered faster in the end-to-end group compared with the Neurolac(R) and PLGA groups, and in this case, recovery was also delayed in the graft group. At the end of follow-up, nociception was similar in all experimental groups. Morphological and histomorphometrical analysis showed that axon regeneration occurred in both PLGA and Neurolac(R) experimental groups, with no significant differences in the total number of regenerated fibers, but disclosed a different pattern of degradation of the two types of tubes with larger biodegradation of PLGA material by the end of 20 weeks. These results suggest that both types of biomaterials are a good substrate for preparing tubular nerve guides, and their different pattern of degradation does not seem to influence the degree of nerve regeneration.

Sensing the air around us: the voltage-gated-like ion channel family

Ion channels are a complex set of proteins having many important physiologic and potentially pathologic roles. The flow of ions through these channels and the subsequent cellular depolarization can trigger complex mechanisms such as cardiac rhythm, hormone secretion, and numerous sensory experiences. The transient receptor potential (TRP) channels are an important means for multiple organ systems to interact with their environment. The various TRP channel subfamilies respond to voltage or to ligands such as G-protein coupled receptors. Their ability to sense temperature, pain, stretch, and osmolarity among others enables them to mediate responses such as smooth muscle contraction, cough, or sensation of pain.

Mechanisms of neuropathic pain

Neuropathic pain refers to pain that originates from pathology of the nervous system. Diabetes, infection (herpes zoster), nerve compression, nerve trauma, "channelopathies," and autoimmune disease are examples of diseases that may cause neuropathic pain. The development of both animal models and newer pharmacological strategies has led to an explosion of interest in the underlying mechanisms. Neuropathic pain reflects both peripheral and central sensitization mechanisms. Abnormal signals arise not only from injured axons but also from the intact nociceptors that share the innervation territory of the injured nerve. This review focuses on how both human studies and animal models are helping to elucidate the mechanisms underlying these surprisingly common disorders. The rapid gain in knowledge about abnormal signaling promises breakthroughs in the treatment of these often debilitating disorders.

Evaluation of donor site pain after anterior iliac crest harvesting for cervical fusion: a prospective study on 50 patients

BACKGROUND

Autologous anterior iliac crest bone graft is still widely considered the gold standard for anterior cervical fusion after discectomy or corporectomy. Postoperative pain at the donor site is one of the main disadvantages to this technique. This prospective study aimed to evaluate pain at the donor site, after careful, standardised bone harvesting.

METHODS

From March 2003 to March 2004, a prospective study was performed in a single neurosurgical department on 50 patients who underwent anterior iliac crest bone harvesting using a standard and careful surgical technique. During a one year follow-up, patient donor site pain was assessed with a Visual Analogous Scale (VAS) at 2, 7 and 60 days from surgery and finally, by a telephone interview, at one year.

FINDINGS

The duration of time in hospital ranged from 4 to 9 days. On the 2(nd) day after surgery, pain, according to the VAS score, was recorded as being >7 by 4 patients (8%), 5-7/10 by 27 patients and >5/10 in 19 cases. On the 7(th) day after surgery, none of the patients reported any VAS > 7, 1 patient's VAS score was 6/10 and 49 patients had a VAS < 5. At 2 month follow-up, 45 patients were completely without pain (VAS 0) and the remaining 5 had a VAS < 5. At one year, 46 patients reported no pain (one patient was lost to follow-up); three continued to have pain <5 in VAS scale.

CONCLUSIONS

After harvesting of bone from the iliac crest, using a standardised approach based on anatomised principles, most patients do not experience persisting pain at the donor site.

Pain phenomena and sensory recovery following brachial plexus avulsion injury and surgical repairs

Seventy-six patients with severe brachial plexus avulsion injuries were studied using pain questionnaires and quantitative sensory testing. There was significant correlation between pain intensity and the number of roots avulsed prior to surgery (P=0.0004) and surgical repairs were associated with pain relief. Sensory recovery to thermal stimuli was observed, mainly in the C5 dermatome. Allodynia to mechanical and thermal stimuli was observed in the border zone of affected and unaffected dermatomes in 18% of patients assessed early (<6 months) and 37% patients at later stages. Pain and sensations referred to the original source of afferents occurred at a later stage (>6 months) in 12% of patients and were related to nerve regeneration. By contrast, "wrong-way" referred sensations (e.g. down the affected arm while shaving or drinking cold fluids) were reported by 44% of patients and often occurred early, suggesting CNS plasticity. Understanding sensory mechanisms will help develop new treatments for severe brachial plexus injuries.

Recent developments in transient receptor potential vanilloid receptor 1 agonist-based therapies

Capsaicin and other naturally occurring pungent molecules have been used for centuries as topical analgesics and rubefactants to treat a variety of chronically painful conditions. Recently, instillations of high-concentration capsaicin and resiniferatoxin solutions have been found to be useful for the management of persistent bladder pain or overactive bladder. However, only within the last 7 years has it been appreciated that the selective action of these compounds on a subset of sensory nerve fibres is mediated by agonist activity at a ligand-gated ion channel called the transient receptor potential vanilloid receptor 1 (TRPV1). Accordingly, this discovery has fueled intensive research and drug development efforts, mainly in a search for novel analgesic or anti-inflammatory therapies. Two different, but non-mutually exclusive, strategies are being pursued: optimisation of TRPV1 agonist-based therapies, which can functionally inactivate nociceptive nerve fibres, and identification of receptor antagonists, which would prevent nociceptive fibres from being activated by ongoing inflammatory stimuli. Available information on TRPV1 agonists in development and their biological rationale will be summarised in this review.

Chemical mediators enhance the excitability of unmyelinated sensory axons in normal and injured peripheral nerve of the rat

Ectopic excitation of nociceptive axons by chemical mediators may contribute to symptoms in neuropathic pain. In this study, we have measured the excitability of unmyelinated rat C-fiber axons in isolated segments of sural nerves under different experimental conditions. (1) We demonstrate in normal rats that several mediators including ATP, serotonin (5-HT), 1-(3-chlorophenyl)biguanide (5-HT3 receptor agonist), norepinephrine, acetylcholine and capsaicin alter electrophysiological parameters of C-fibers which indicate an increase of axonal excitability. Other mediators such as histamine, glutamate, prostaglandin E(2) and the cytokines tumor necrosis factor alpha, interleukin-1beta and interleukin-6 did not produce such effects. (2) The effects of several mediators were tested after peripheral nerve injury (partial ligation or spared nerve injury). Sural nerves from such animals did not show significant changes when compared with controls. (3) We tested whether the effects of chemical mediators on axonal excitability are due to actions on the sensory C-fiber afferents or the postganglionic sympathetic efferents. In order to distinguish these effects, we performed surgical sympathectomy of the lumbar sympathetic chain, including the L3, L4 and L5 ganglia. Sympathectomy did not markedly influence the effects of mediators on axonal excitability (except that the norepinephrine effect was significantly diminished). In conclusion, our data suggest a constitutive rather than inducible expression of axonal receptors for some chemical mediators on the axonal membrane of unmyelinated fibers. Most of the changes in axonal excitability take place in sensory C-fiber afferents rather than in postganglionic sympathetic efferents. Thus, it is possible that certain immune and glial cell mediators released in or around the nerve following injury or inflammation influence the excitability of intact nociceptive fibers. This mechanism could contribute to ectopic excitation of axons in neuropathic pain.

Sciatic nerve regeneration in mice and rats: recovery of sensory innervation is followed by a slowly retreating neuropathic pain-like syndrome

Peripheral nerve regeneration has been studied extensively in the sciatic nerve crush model, at the level of both function and gene expression. The crush injury allows full recovery of sensory and motor function in about 3 weeks as assessed by the foot reflex withdrawal test and De Medinacelli walking patterns. We used the recently developed CatWalk paradigm to study walking patterns in more detail in mice and rats. We found that, following the recovery of sensory function, the animals developed a state of mechanical allodynia, which retreated slowly over time. The motor function, although fully recovered with the conventional methods, was revealed to be still impaired because the animals did not put weight on their previously injured paw. The development of neuropathic pain following successful sensory recovery has not been described before in crush-lesioned animals and may provide an important new parameter to assess full sensory recovery.

A preclinical post laminectomy rat model mimics the human post laminectomy syndrome

Chronic low back pain with sciatica complicating post laminectomy surgery is poorly understood. It is likely that some aspects of persistent pain of the syndrome results from spinal facilitation in which there is lowering of pain excitation levels. A small animal preclinical model is needed that mimics the clinical condition to permit detailed studies of the underlying altered neurochemistry of the sensory pathways. We propose herein a rat laminectomy model containing the elements required for study of the neurobiology of the condition. The model consists of a surgical laminectomy that includes L5 spinal nerve manipulation and disc injury, elements necessarily employed in human disc herniation surgery. At 8 weeks post laminectomy the proposed model demonstrates paraspinous muscle spasm, tail contracture, behavioral pain behavior, tactile allodynia, epidural and nerve root scarring, and nerve root adherence by scar to the underlying disc and adjacent pedicle. Two underlying pain facilitation states are invoked in the clinical condition: (1) an inflammatory state required to achieve wound healing; and (2) a nerve injury state resulting from nerve manipulation and subsequent epidural scarring, spinal nerve scarring, and spinal nerve tethering to the adjacent disc and pedicle. Both pain facilitation states are active in the model.

Vulnerability of the subcostal nerve to injury during bone graft harvesting from the iliac crest

Object. Autologous bone graft harvesting from the iliac crest remains the gold standard for fusion surgery. One disadvantage of autologous bone harvesting is the patient's enduring postoperative pain at the donor site. Nerve injury is one of the postulated mechanisms that may account for this pain. The object of this study was to determine whether the lateral cutaneous branch of the subcostal nerve is vulnerable to injury in the process of obtaining grafts from the anterior iliac crest.

Methods. Anatomical dissections were performed on 10 cadaveric specimens to ascertain the size of the T-12 subcostal nerve and its position in relation to the iliac crest.

Conclusions. The lateral cutaneous branch of the subcostal nerve may lie as close as 6 cm from the anterior superior iliac spine. This nerve is very vulnerable to injury when harvesting bone from the anterior iliac crest. Knowledge of the anatomy may decrease the risk of injury to this nerve.

Severity and duration of hyperalgesia in rat varies with type of nerve lesion

OBJECTIVE

To learn how lesions with differing capacity for nerve regeneration affect the severity and duration of hyperalgesia in an animal model of neuropathic pain.

METHODS

Three groups of rats were studied: 1). L5 nerve root crush (favorable for regeneration); 2). L5 root ligation and section; and 3). sham-operated group. An experimenter who did not know the rats' groups tested the animals for hyperalgesia to mechanical and cold stimuli.

RESULTS

Measures of adverseness of mechanical and cooling stimuli for the crush group and ligation/cut groups were significantly higher than for the sham-operated group (P < 0.001 for both) for the first 30 days after lesioning. By 40 days, the crush group recovered from mechanical hyperalgesia, whereas the ligation/cut group continued to have significant hyperalgesia. At this time, both lesion groups displayed hyperalgesia to the cooling stimulus (P < 0.001), but the hyperalgesia in the ligation/cut group was significantly greater (P < 0.01). No recovery from cooling hyperalgesia was evident during the 54-day period of observation. Histological studies of the sciatic nerve indicated higher numbers of regenerating fibers in the crush group compared with the ligation/cut group.

CONCLUSION

This study demonstrates that axotomy, regardless of how it is induced, produces hyperalgesia to both mechanical and cold stimuli. However, the lesion that favors regeneration is associated with earlier signs of recovery from mechanical hyperalgesia and less severe signs of cooling hyperalgesia. The data support the hypothesis that inputs from the injured afferents play an ongoing role in neuropathic pain from nerve injury. Nerve ligation induces more severe and more sustained behavioral signs of pain than nerve crush.

Functional assessment of sciatic nerve recovery: biodegradable poly (DLLA-epsilon-CL) nerve guide filled with fresh skeletal muscle

The aim of this study was to compare functional peripheral nerve recovery in the rat sciatic nerve model after reconstruction of a 10-mm gap with a biodegradable poly (DLLA-epsilon-CL) nerve guide, as filled with either fresh skeletal muscle or phosphate-buffered saline (PBS). During 24 weeks of recovery, motor and sensory functional evaluation was tested by extensor postural thrust (EPT) and withdrawal reflex latency (WRL), respectively. At the end of the experiment, anesthetized animals were prepared for motor nerve conduction velocity (MNCV) studies, followed by gastrocnemius and soleus muscle weight measurement. Motor functional recovery was greater in the muscle-grafted group, and reached a significant difference from weeks 8-12 (P < 0.05). The results of this investigation suggest that filling a nerve guide with fresh skeletal muscle induces faster maturation of regenerated nerve fibers in comparison with traditional tubular repair.