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Background: While the risks associated with the use of electrosurgery near nerves are well known, few studies have examined the neurophysiologic effects of application of the Harmonic Blade, an ultrasonic scalpel, in the vicinity of nerve fibres. This study sought to compare the sub-acute neurophysiologic effects of the Harmonic Blade and electrosurgery after incisions close to the sciatic nerve., Methods: Incisions were made in rats with the Harmonic Blade and electrosurgery at distances of 1, 2, 3 and 4 mm from the sciatic nerve. Sham surgery was also performed. The compound action potential, conduction velocity and calibrated nylon filament (von Frey hair, VFH) stimulating force were monitored for up to 3 hours after surgery. The sciatic nerve was assessed for inflammation via H&E staining and impaired axonal transport by β-APP immunohistochemistry., Results: Electrosurgery incisions produced a significantly greater decrease in compound action potential and conduction velocity, and increase in the VFH force than the Harmonic Blade over all time points and distances from the sciatic nerve. The Harmonic Blade was similar to sham surgery for the compound action potential and VFH force. Electrosurgery yielded significantly greater leukocyte infiltration than the Harmonic Blade and produced the highest levels of β-APP immunoreactive swellings., Conclusions: Incisions with electrosurgery in the range of 1-4 mm of the sciatic nerve caused substantial changes in neurophysiologic functioning and inflammation. In contrast, the Harmonic Blade was similar to sham surgery in the vicinity of the nerve, producing little observable acute trauma.

For the first time we report the complete genomic sequence of an H11N3 influenza virus from domestic ducks in China. Phylogenetic analysis showed that the H11N3 virus was a novel reassortant with its genes from different subtypes of domestic duck-origin avian influenza viruses, which further underlined that domestic ducks play a key role in the genetic reassortment and evolution of influenza viruses in China.

Isolates of the A(H1N1)pdm2009 virus were first identified in asymptomatic swine in Jiangsu province, China in January 2010, indicating that the virus has retro-infected swine after circulating through humans in mainland China. The purpose of this study was to determine whether the avian-origin European H1N1 swine influenza virus (SIV) and the A(H1N1)pdm2009 virus are cocirculating in swine in Jiangsu province of China. From May 2010 to May 2011, 1,030 nasal swab samples were collected from healthy swine in Jiangsu province of China and were tested for influenza A H1N1 using reverse transcription-PCR. Fragments of the complete genomes of viruses from the samples that were positive for influenza A H1N1 were sequenced and analysed. A total of 32 avian-origin European H1N1 SIVs were isolated, and no A(H1N1)pdm2009 viruses were identified; full-length genomes of 18 strains were sequenced. The eight gene segments of some of the isolated H1N1 viruses have 99.1-99.8% sequence identity with the human A/Jiangsu/ALS1/2011(H1N1) isolates in the same region. Our study indicates that the avian-origin European H1N1 SIVs remain endemic in swine and have retro-infected humans after circulating through swine, which may present a risk factor for public health.

Aim: To assess the presence of nerves in ventral facet joint capsules as facet capsules are generally implicated in neck pain., Methods: Twenty-four ventral cervical facet joint capsules were harvested from 3 unembalmed cadavers. Paraffin sections from these capsules were processed to identify neurofilament and substance P immunoreactive fibers. Nerve fiber presence was also verified by a silver impregnation method., Results: Neurofilament reactive fibers were observed in sections from 9 capsules. They were observed in areas with collagen fibers and areas with irregular connective tissue. Substance P reactive nerve fibers were found in sections from 7 capsules in similar areas. Silver impregnation also revealed the presence of nerve fibers. The nerve fibers were also found as bundles in the lateral margins of the capsule. A Pacinian corpuscle-like ending was also observed in one specimen., Conclusion: Nerve fibers revealed by neurofilament immunoreactivity and silver staining support innervation of the ventral aspect of the facet joint capsule. The presence of substance P reactive fibers supports the potential role of these elements in mediating pain. The presence of a Pacinian-like ending implicates a potential role in joint movement.

This study examined the cervical muscle response to physiologic, high-rate (100 mm/s) tensile facet joint capsule (FJC) stretch. Six in-vivo caprine C5/6 FJC preparations were subjected to an incremental tensile loading paradigm. EMG activity was recorded from the right trapezius (TR) and multifidus (MF) muscle groups at the C5 and C6 levels; and from the sternomastoid (SM) and longus colli (LC) muscle groups bilaterally at the C5/6 level; during FJC stretch. Capsule load during the displacement applications was recorded via a miniature load cell, and 3D capsule strains (based on stereoimaging of an array of markers on the capsule surface) were reconstructed using finite element methods. EMG traces from each muscle were examined for onset of muscular activity. Capsule strains and loads at the time of EMG onset were recorded for each muscle, as was the time from the onset of FJC stretch to the onset of muscle activity. All muscles were responsive to physiologic high-rate FJC stretch. The deep muscles (MF and LC) were recruited at significantly smaller capsule loads and onset latencies than the superficial muscles (TR and SM). MF activation strain was significantly smaller than LC and TR activation strains. These data were also compared to previously published low-rate data. MF was the first muscle group to be recruited regardless of the activation criterion under consideration (i.e. strain, load, or latency) or the rate of FJC stretch. LC recruitment occurred significantly sooner under high-rate vs. low-rate FJC stretch. The results of this study provide further evidence of extensive ligamento-muscular reflex pathways between the FJC and the cervical musculature, which are responsive to both low-rate and high-rate FJC stretch. These data add to our knowledge of the dynamic response of paraspinal muscles relative to facet joint motion and provide a unique contribution to enhance the precision of computer-simulated impacts.

The aim of this study was to investigate the response of cervical muscles to physiologic tensile stretch of cervical facet joint capsule (FJC) at a quasi-static displacement rate of 0.5mm/s. In vivo caprine left C5-C6 FJC preparations were subjected to an incremental tensile displacement paradigm. EMG activity was recorded during FJC stretch from the right trapezius (TR) and multifidus (MF) muscle groups at the C5 and C6 levels and bilaterally from the sternomastoid (SM) and longus colli (LC) muscle groups at the C5-C6 level. Onset of muscular activity was later analyzed using visual and computer-based methods. Capsule load and strain at the time of onset were recorded and compared between the muscle groups. Results indicated capsule load was a better indicator of the tensile stretch thresholds for muscular recruitment than capsule strain. MF responded at significantly smaller capsule loads than TR and LC, while TR and LC activation loads were not significantly different. SM did not respond to physiologic FJC stretch. Muscle group recruitment order reflected the muscles' fiber type compositions and functional roles in the spine. This study provides the first evidence that the cervical ligamento-muscular reflex pathways are activated via tensile FJC stretch and extend to superficial and deep musculature on the anterior and posterior aspects of the neck, ipsilateral and contralateral to the side of FJC stretch.

This study investigates the functional and structural responses of spinal nerve roots in vivo to various strains and strain rates. Seventy-two L5 dorsal nerve roots from male Sprague-Dawley rats were each subjected to a predetermined strain (<10%, 10-20%, and >20%; n = 8) and rate (0.01 mm/sec, 1 mm/sec, or 15 mm/sec; n = 24). Neurophysiologic recordings were performed before and after stretch to determine changes in conduction velocity (CV), amplitude, and area of the compound action potential (CAP). Morphological injury as evident by primary and secondary axotomy as well as impaired axoplasmic transport (IAT) was determined using the palmgren silver impregnation technique and betaAPP immunostaining, respectively. The results from neurophysiologic recordings indicate that as strain and rate increased, there was a decrease in CV, amplitude, and area of the CAP. Further, high strains led to a complete conduction block that appeared to be rate dependent. Strains of 16%, 10%, and 9%, at 0.01 mm/sec, 1 mm/sec, and 15 mm/sec, respectively, led to 50% probability of complete conduction block in the nerve roots. Results from histological assessment indicate an increase in periaxonal spacing (secondary axotomy) and torn fibers (primary axotomy), as well as impaired IAT, with increasing strain and rate. Overall, the results from the current study indicate that (1) functional nerve root injuries as evident by changes in the CV, amplitude, and area of the CAP are strain- and rate-dependent; (2) high strains at low rates cause complete conduction block in the roots, while a similar block was observed at lower strains at the high rate; (3) the extent of IAT and primary and secondary axotomy occurred concomitant with functional injury and were strain- and rate-dependent.

This study examines axonal changes in goat cervical facet joint capsules (FJC) subjected to low rate loading. Left C5-C6 FJC was subjected to a series of tensile tests from 2 mm to failure using a computer-controlled actuator. The FJC strain on the dorsal aspect was monitored by a stereo-imaging system. Stretched (n = 10) and unstretched (n = 7) capsules were harvested and serial sections were processed by a silver impregnation method. The mean peak actuator displacement was 21.3 mm (range: 12-30 mm). The average peak strain encompassing various regions of the capsule was 72.9 +/- 7.1%. Complete failure of the capsule was observed in 70% of the stretched capsules. Silver impregnation of the sections revealed nerve fibers and bundles in all the regions of the capsule. A blinded analysis of digital photomicrographs of axons revealed a statistically significant number of swollen axons with non-uniform caliber in stretched FJCs. Axons with terminal retraction balls, with occasional beaded appearance or with vacuolations were also observed. Stretching the FJC beyond physiological range could result in altered axonal morphology that may be related to secondary or delayed axotomy changes similar to those seen in central nervous system injuries where axons are subjected to stretching and shearing. These may contribute to neuropathic pain and are potentially related to neck pain after whiplash events.

Traumatic brain injury (TBI) continues to be a major health problem, with over 500,000 cases per year with a societal cost of approximately $85 billion in the US. Motor vehicle accidents are the leading cause of such injuries. In many cases of TBI widespread disruption of the axons occurs through a process known as diffuse axonal injury (DAI) or traumatic axonal injury (TAI). In the current study, an in vivo TAI model was developed using spinal nerve roots of adult rats. This model was used to determine functional and structural responses of axons to various strains and displacement rates. Fifty-six L5 dorsal nerve roots were each subjected to a predetermined strain range (<10%, 10-20% and >20%) at a specified displacement rate (0.01 mm/sec and 15 mm/sec) only once. Image analysis was used to determine actual strains on the roots during the pull. Neurophysiologic recordings were performed on the nerve root before and after stretch to determine functional changes in response to stretch, including conduction velocity (CV) and area of the evoked compound action potential (CAP). Structural changes including vascular injury, axotomy, and impaired axoplasmic transport (IAT) were evaluated using hematoxylin and eosin, Palmgren silver impregnation and beta-APP staining techniques, respectively. Results showed that CV and the area of the CAP decreased as strain and displacement rate increased. Also, threshold strains for complete nerve conduction loss were 16% and 9% at 0.01 mm/sec and 15 mm/sec rate, respectively. These threshold values indicate the rate dependency of functional injury and indicate that axons tolerate slow loading rates better than higher loading rates. Histological studies revealed increased spacing, tearing of axons, IAT and occurrence of hemorrhage to be strain and displacement rate dependent. Linear relationships existed between the increasing strain and the occurrence rate of axonal injury as evidenced by multiple indicators (IAT, hemorrhage, torn fibers or primary axotomy) at both rates. In conclusion, the results from this study indicate that the severity of both functional and structural injury increased with increases in strain and displacement rate.

Background: It has been proposed that cervical facet joint capsules are a major source of whiplash pain. However, there is a paucity of neurophysiologic data to support this hypothesis. The purposes of this study were to determine the distribution of A-delta and C-fiber sensory receptors in the facet joint capsule and to test their patterns of response to stretch and related sensory function., Methods: Laminectomy from C4 to C7 was performed in seventeen goats, while they were under general anesthesia, to expose the C6 nerve roots. Customized dual bipolar electrodes were used to record neural activity from one of the C6 branches. An 8 or 15-V electrical stimulus was used to provoke receptor activity in nine designated areas on the dorsal part of the C5-C6 facet joint capsule. Receptors were classified on the basis of conduction velocities. The waveform of an identified receptor was set up as a template to determine its neural activity in response to capsular stretch. The characteristics of each single receptor's response to capsular stretch were analyzed to determine its sensory function as a mechanoreceptor or nociceptor., Results: Two hundred and forty-eight receptors on the dorsal part of the C5-C6 facet joint capsule were evoked by electrical stimulation in the seventeen goats. More C-fiber receptors were found on the dorsolateral aspect of the facet joint capsule, where tendons and muscles were attached. The response to stretch of 120 receptors, from twelve goats, were analyzed to classify them into one of four categories (high-threshold mechanoreceptors, non-saturated low-threshold mechanoreceptors, saturated low-threshold mechanoreceptors, and silent receptors) or as unclassified receptors., Conclusions: The existence of receptors in the facet joint capsule indicates that the capsule has pain and proprioceptive sensory functions.

Facet joints are implicated as a major source of neck and low-back pain. Both cervical and lumbar facet syndromes have been described in the medical literature. Biomechanical studies have shown that lumbar and cervical facet-joint capsules can undergo high strains during spine-loading. Neuroanatomic studies have demonstrated free and encapsulated nerve endings in facet joints as well as nerves containing substance P and calcitonin gene-related peptide. Neurophysiologic studies have shown that facet-joint capsules contain low-threshold mechanoreceptors, mechanically sensitive nociceptors, and silent nociceptors. Inflammation leads to decreased thresholds of nerve endings in facet capsules as well as elevated baseline discharge rates. Recent biomechanical studies suggest that rear-end motor-vehicle impacts give rise to excessive deformation of the capsules of lower cervical facet joints. Still unresolved is whether this stretch is sufficient to activate nociceptors in the joint capsule. To answer this question, recent studies indicate that low stretch levels activate proprioceptors in the facet-joint capsule. Excessive capsule stretch activates nociceptors, leads to prolonged neural afterdischarges, and can cause damage to the capsule and to axons in the capsule. In instances in which a whiplash event is severe enough to injure the joint capsule, facet capsule overstretch is a possible cause of persistent neck pain.

An understanding of the biomechanical and physiological properties of spinal nerve roots, particularly in response to tension, is critical in understanding the pathomechanisms of pain and nerve root injury and subsequent management of related injuries. Biomechanical properties of dorsal nerve roots at the lumbar and sacral levels were evaluated at various strain rates. Nerve roots were stretched at two different rates, 0.01 mm/s (Group A, quasistatic) and 15 mm/s (Group B, dynamic). Load, displacement and digital video data were obtained as the nerve roots were stretched until failure. Maximum stress, strain at maximum stress and modulus of elasticity (E) were calculated from the load-displacement measurements. Comparison of mechanical properties and failure patterns of nerve roots at two different rates revealed significant differences. Maximum load, maximum stress and E values of 5.7+/-2.7 gm, 257.9+/-111.3 kPa and 1.3+/-0.8 MPa were observed for Group A and 13.9+/-7.5 gm, 624.9+/-306.8 kPa and 2.9+/-1.5 MPa were observed for Group B, respectively. Higher maximum load, maximum stress and E values occurred at the dynamic stretch rate as compared to the quasistatic stretch rate, illustrating the strain-rate dependency of spinal nerve roots. No differences were observed in the strain values. Differences in mechanical behavior of nerve roots were also observed among the four root levels (L4-S1). A significant interaction effect was observed between nerve root diameter and stretch rates. Overall, results from the present study demonstrate viscoelastic material properties of spinal nerve roots and provide better insight on the tensile properties of nerve roots at different strain rates.

This study investigated cytokine expression, behavioral and neurophysiologic changes in Lewis rats whose lumbar nerve roots were exposed to nucleus pulposus (NP). Allografted NP or fat was implanted over the left L5 nerve root. Sham rats had no NP or fat implantation. Control rats had no surgery. Rats were allowed to survive for 7 days and were tested daily for hind-paw mechanical and thermal withdrawal response (TWR). Granulation tissue was processed by immunohistochemistry for cytokines--interleukin 1 beta (IL-1beta), interleukin 6 (IL-6) and tumor necrosis factor (TNF). Neurophysiological response from the L5 nerve roots was also characterized after 7 days. Significant staining density for IL-1beta, IL-6 and TNF was observed in NP granulation tissue compared with fat and sham (p<0.05). However, there were no significant thermal and mechanical behavioral changes. TWR data computed as percentage-difference scores indicated no significant changes in withdrawal response between the four groups, although NP-treated group showed a trend of decreasing withdrawal latency. Comparison of combined percentage-difference scores revealed increased sensitivity in the NP group on days 4, 5 and 6, 7 when compared with control rats only, with no significant changes in the percentage-difference scores of fat and sham rats when compared to control. Neurophysiologically, the percentage increase in discharge rate in NP-treated rats was higher than control (p<0.05) but not higher than fat and sham rats. These results support the inflammatory nature of NP but offer limited support to NP-mediated thermal behavioral changes.

Cervical facet joints are implicated as a major source of pain after whiplash injury. The purpose of this study was to investigate the proposed capsule strain injury mechanism of whiplash pain using neurophysiologic methods. Strain thresholds, threshold distribution, saturation strains and afterdischarge responses of capsule neural receptors were characterized in vivo. Goat C5-C6 facet joint capsules were used to identify and characterize capsule receptors in response to controlled uniaxial stretch by recording C6 dorsal rootlet nerve discharge. The joints were stretched at 0.5 mm/sec in a series of tests with 2 mm increments until the capsule ruptured. Ninety-two identified units were responsive to physiologic or noxious stretch while 28 were silent receptors. Among the 50 characterized responsive units, 42 showed low strain thresholds at 10.2+/-4.6% while 8 had high strain thresholds at 47.2+/-9.6%. Further, 35 of the 42 low-threshold units displayed discharge saturation at various strains (44.2+/-16.7%). A significant finding was that twelve low-threshold units exhibited afterdischarge for greater than 30 sec after stretch release at 36.6+/-12.5% strains, and displayed longer-lasting afterdischarge (greater than 4 min) at higher strains (39.0+/-14.4%) with significant difference (p = 0.019) in strains. Two high-threshold units had afterdischarges for greater than 30 sec or 4 min at 50.3+/-5.9% and 57.7+/-10.6% strains, respectively. In addition, the spatial distribution of the 42 low-threshold receptors demonstrated that the receptors on the joint gap were more strain-sensitive, with significantly lower strain thresholds compared to the rostral and caudal regions. No significant difference in strain threshold was observed in the medial-lateral direction. When compared to the reported strains that facet joint capsules experienced in whiplash (35-60%) and the reported capsule subfailure strains (35-67%), the low strain thresholds are substantially lower whereas the high thresholds and afterdischarge strains are within that range. Thus, low threshold units appear to signal proprioception within the physiologic range. High threshold units likely signal nociception (pain sensation) while afterdischarge may signal capsule strain injury and contribute to persistent pain.

Facet joint capsules (FJC) may experience large mechanical deformation under spine motion. There has been no previous quantitative study of the relationship between capsular strain and sensory nerve activation in spine FJC in vivo. Space limitation in the cervical spine makes such a study difficult, as the facet joint must be loaded while simultaneously monitoring nerve discharge from nerve roots immediately adjacent to the loaded tissue. A new methodology was developed to investigate biomechanical and neurophysiological properties of spine facet joint capsules in vivo. The method incorporated a custom-fabricated testing frame for facet joint loading, a stereoimaging system, and a template-matching technique to obtain single afferent response. It was tested by loading goat C5-C6 FJC in vivo with simultaneous nerve root recordings and 3D strain tracking of the capsules. Preliminary data showed that 18 of 23 afferents (78.3%) were found to be mechanosensitive to tensile stretch, and five were not responsive, even under tensile load as high as 27.5 N. Mechanosensitive afferents in goat capsules had tensile strain thresholds of 0.119+/-0.080. Neural responses of all mechanosensitive units showed statistically significant correlations (all P<<0.05) with both capsular load (r(2)=0.744+/-0.109) and local strain (r(2)=0.868+/-0.088). This method enables the investigation of the correlation between tissue load, deformation and neural responses of mechanoreceptors in spine facet joint capsules, and can be adapted to investigate tissue loading and neural response of other soft tissues.

Cervical facet joints have been implicated as a major source of pain after whiplash injury. We sought to identify facet joint capsule receptors in the cervical spine and quantify their responses to capsular deformation. The response of mechanosensitive afferents in C5-C6 facet joint capsules to craniocaudal stretch (0.5 mm/s) was examined in anaesthetized adult goats. Capsular afferents were characterized into Group III and IV based on their conduction velocity. Two-dimensional strains across the capsules during stretch were obtained by a stereoimaging technique and finite element modeling. 17 (53%) Group III and 14 (56%) Group IV afferents were identified with low strain thresholds of 0.107+/-0.033 and 0.100+/-0.046. A subpopulation of low-strain-threshold afferents had discharge rate saturation at the strains of 0.388+/-0.121 (n=9, Group III) and 0.341+/-0.159 (n=9, Group IV). Two (8%) Group IV units responded only to high strains (0.460+/-0.170). 15 (47%) Group III and 9 (36%) Group IV units could not be excited even by noxious capsular stretch. Simple linear regressions were conducted with capsular load and principal strain as independent variables and neural response of low-strain-threshold afferents as the dependent variable. Correlation coefficients (R2) were 0.73+/-0.11 with load, and 0.82+/-0.12 with principal strain. The stiffness of the C5-C6 capsules was 16.8+/-11.4 N/mm. Our results indicate that sensory receptors in cervical facet joint capsules are not only capable of signaling a graded physiological mechanical stimulus, but may also elicit pain sensation under excessive deformation.

Study Design: To establish a methodology for the neurophysiologic study of mechanoreceptors in the cervical facet joint capsule., Objectives: To test a custom designed miniature dual bipolar electrode for recording the neural activity in cervical dorsal roots. To determine if the neural activity from different receptors in the capsule can be differentiated using this methodology., Summary of Background Data: Injury to cervical facet joint capsules has been regarded as an important source of whiplash pain, but no neurophysiologic study has been performed to demonstrate or characterize sensory nerve function in the capsule., Methods: Nineteen goats weighing 34 to 55 kg were used under general anesthesia. A C4-C6 laminectomy was performed to expose the C6 nerve root. Custom designed miniature dual bipolar electrodes were used to record neural activity in the left C6 branches. Electrical and mechanical stimuli were used to evoke receptor activity in the dorsal aspect of the C5/6 capsule. Conduction velocities (CVs) of evoked units were determined by electrical stimulation and dual-bipolar-electrode recording methods. The units were classified based on their CVs. The waveform of each classified unit was saved as a template for later single unit discharge search among multiunit discharges during the stretch of the capsule. The C5/6 facet joint with capsule was pulled by a computer-controlled actuator instrumented with a load cell at a rate of 0.5 mm per second. The evoked neural activity and load were recorded, digitized, and analyzed to determine CV, discharge rate, and response to the stretch., Results: Miniature bipolar electrodes recorded the neural activity in both channels, with single unit CVs being measured. There was no discernible motion between the electrode and dorsal root when the capsule was pulled. Both local compression and stretch on capsule evoked multiunit discharges. A-beta, A-delta, and C-fiber units were found among these multiunit discharges. The rate of single unit and multiunit discharges increased during capsule stretch in the physiologic range and afterdischarges occurred beyond the physiologic range., Conclusions: The novel miniature electrodes not requiring a micromanipulator made it feasible and reliable to record neural activity from short cervical spinal roots. Waveforms of different units could be identified, making it possible to study sensory functions of the facet joint capsule. A-beta, A-delta, and C-fiber units were found responding to mechanical stimuli, indicating that facet joint capsule has functional proprioceptors and nociceptors.

Study Design: Human cervical facet joint capsules were evaluated by immunohistochemistry., Objectives: To study the neuropeptide innervation of the cadaveric cervical facet joint capsules., Summary of Background Data: Various clinical and biomechanical studies indicate a role for cervical facet joint capsules in the etiology of neck pain. However, studies on innervation of these capsules are very limited. There is also a dearth of studies on the neuropeptide nature of this innervation., Methods: Facet joint capsules harvested from unembalmed cadavers were studied by the avidin biotin peroxidase method for the presence of nerve fibers. Neuropeptide innervation was investigated by using antisera to substance P and calcitonin gene-related peptide. Antisera to protein gene product 9.5 (PGP 9.5), a general neuronal marker, were also used., Results: In a study of 12 human cervical facet joint capsules, short segments of substance P were observed in 6 capsules, while fibers reactive to calcitonin gene-related peptide were demonstrated in 7 capsules. Nerve fibers immunoreactive to protein gene product 9.5 were also observed in 9 of the 14 capsules studied. Protein gene product 9.5 reactive fibers were the most extensively distributed fibers, observed as bundles and also as single fibers., Conclusions: An abundance of protein gene product 9.5 reactive nerve fibers indicates an extensive innervation of the cervical facet joint capsules. The presence of substance P and calcitonin gene-related peptide reactive nerve fibers in a population of these lends credence to cervical facet joint capsules as a key source of neck pain.

Study Design: This study analyzed the effects of autografted nucleus pulposus on nerve root axon morphology, neurophysiologic function, and sodium channel expression., Objectives: To investigate the chronic effects of the epidural implantation of nucleus pulposus on nerve root morphology, neural activity, ectopic discharge, mechanosensitivity, and sodium channel expression., Summary of Background Data: It has been reported that ectopic discharges were recorded antidromically from sural nerve on compressing nucleus pulposus exposed spinal nerves. However, it is not clear what the effects of nucleus pulposus are on ectopic discharges recorded directly from the spinal nerve roots. It is also not clear what the effects of nucleus pulposus are on the threshold pressure to provoke ectopic discharges in the spinal nerves. Sodium channel content increases in remodeling axons after nerve injury, but it is not clear what the effects of nucleus pulposus are on sodium channel expression in spinal nerve., Methods: Forty-six male Sprague-Dawley rats were used, 20 in a nucleus pulposus-implanted group, 18 in a fat-implanted group, and 8 in a normal group. Fresh autografted nucleus pulposus or fat tissue was implanted into the dorsal epidural space at the L4-L5 disc level. On the 7th, 21st, or 42nd day, neurophysiologic recordings were made to determine nerve root response to compression. Nerve roots were then harvested to determine sodium channel protein concentration and histologic changes in the nerve root. The correlations between sodium channel density and neural activity and mechanosensitivity of dorsal root were analyzed statistically., Results: Ectopic discharge rate was higher in nucleus pulposus 7-day group. Threshold pressure to evoke ectopic discharges was lower in the nucleus pulposus 7-day group, and higher in the nucleus pulposus 42-day group compared to the normal group. Sodium channel protein density increased in the nucleus pulposus 7-day and nucleus pulposus 21-day group compared to normal nerve. Sodium channel density changes were not correlated to threshold pressure. Ectopic discharge rate increased with increase of sodium channel density in the nerve roots. The number of axons with neuropathy increased in the nucleus pulposus 7-day and 21-day groups., Conclusions: Acute exposure of nerve root to nucleus pulposus resulted in increased number of axons with neuropathy, higher intensity of ectopic discharges on compression, and nerve mechanosensitization. Chronic exposure resulted in mechanical desensitization. Changes of sodium channel density were correlated to ectopic discharge rate.