Bacterially produced metabolites protect C. elegans neurons from degeneration

Caenorhabditis elegans and its cognate bacterial diet comprise a reliable, widespread model to study diet and microbiota effects on host physiology. Nonetheless, how diet influences the rate at which neurons die remains largely unknown. A number of models have been used in C. elegans as surrogates for neurodegeneration. One of these is a C. elegans strain expressing a neurotoxic allele of the mechanosensory abnormality protein 4 (MEC-4d) degenerin/epithelial Na+ (DEG/ENaC) channel, which causes the progressive degeneration of the touch receptor neurons (TRNs). Using this model, our study evaluated the effect of various dietary bacteria on neurodegeneration dynamics. Although degeneration of TRNs was steady and completed at adulthood in the strain routinely used for C. elegans maintenance (Escherichia coli OP50), it was significantly reduced in environmental and other laboratory bacterial strains. Strikingly, neuroprotection reached more than 40% in the E. coli HT115 strain. HT115 protection was long lasting well into old age of animals and was not restricted to the TRNs. Small amounts of HT115 on OP50 bacteria as well as UV-killed HT115 were still sufficient to produce neuroprotection. Early growth of worms in HT115 protected neurons from degeneration during later growth in OP50. HT115 diet promoted the nuclear translocation of DAF-16 (ortholog of the FOXO family of transcription factors), a phenomenon previously reported to underlie neuroprotection caused by down-regulation of the insulin receptor in this system. Moreover, a daf-16 loss-of-function mutation abolishes HT115-driven neuroprotection. Comparative genomics, transcriptomics, and metabolomics approaches pinpointed the neurotransmitter γ-aminobutyric acid (GABA) and lactate as metabolites differentially produced between E. coli HT115 and OP50. HT115 mutant lacking glutamate decarboxylase enzyme genes (gad), which catalyze the conversion of GABA from glutamate, lost the ability to produce GABA and also to stop neurodegeneration. Moreover, in situ GABA supplementation or heterologous expression of glutamate decarboxylase in E. coli OP50 conferred neuroprotective activity to this strain. Specific C. elegans GABA transporters and receptors were required for full HT115-mediated neuroprotection. Additionally, lactate supplementation also increased anterior ventral microtubule (AVM) neuron survival in OP50. Together, these results demonstrate that bacterially produced GABA and other metabolites exert an effect of neuroprotection in the host, highlighting the role of neuroactive compounds of the diet in nervous system homeostasis.

Measuring peripheral nerve involvement in Friedreich's ataxia

OBJECTIVE

Experimental therapies under development for Friedreich's Ataxia (FRDA) require validated biomarkers. In-vivo reflectance confocal microscopy (RCM) of skin is a noninvasive way to quantify Meissner's corpuscle (MC) density and has emerged as a sensitive measure of sensory polyneuropathies. We conducted a prospective, cross-sectional study evaluating RCM of MCs and conventional peripheral nerve measures as candidate peripheral nerve markers in FRDA.

METHODS

Sixteen individuals with FRDA and 16 age- and gender-matched controls underwent RCM of MC density and morphology, skin biopsies for epidermal nerve fiber density (ENFD), nerve conduction studies (NCS), and quantitative sensory testing (QST) including touch, vibration, and cooling thresholds.

RESULTS

MC densities were measurable in all participants with FRDA, and were lower at digit V (hand), thenar eminence, and arch (foot) compared to controls. By contrast, sensory NCS showed floor effects and were obtainable in only 13% of FRDA participants. QST thresholds for touch, vibration, and cooling were higher at the hand and foot in FRDA than controls. Reductions in ENFDs were present in more severely affected individuals with FRDA (Friedreich's Ataxia Rating Scale (FARS) >60) compared to matched controls, although skin biopsies were not well tolerated in children. MC densities, ENFDs, and touch and vibration thresholds were associated with clinical disease severity (FARS and modified FARS) and duration since symptom onset.

INTERPRETATION

MC density, ENFD, and QST thresholds provide structural and physiologic markers of sensory involvement in FRDA. Longitudinal evaluation is needed to determine whether these measures can identify changes associated with disease progression or treatment.

Impaired Nociception in the Diabetic Ins2+/Akita Mouse

The mechanisms responsible for painful and insensate diabetic neuropathy are not completely understood. Here, we have investigated sensory neuropathy in the Ins2^+/Akita mouse, a hereditary model of diabetes. Akita mice become diabetic soon after weaning, and we show that this is accompanied by an impaired mechanical and thermal nociception and a significant loss of intraepidermal nerve fibers. Electrophysiological investigations of skin-nerve preparations identified a reduced rate of action potential discharge in Ins2^+/Akita mechanonociceptors compared with wild-type littermates, whereas the function of low-threshold A-fibers was essentially intact. Studies of isolated sensory neurons demonstrated a markedly reduced heat responsiveness in Ins2^+/Akita dorsal root ganglion (DRG) neurons, but a mostly unchanged function of cold-sensitive neurons. Restoration of normal glucose control by islet transplantation produced a rapid recovery of nociception, which occurred before normoglycemia had been achieved. Islet transplantation also restored Ins2^+/Akita intraepidermal nerve fiber density to the same level as wild-type mice, indicating that restored insulin production can reverse both sensory and anatomical abnormalities of diabetic neuropathy in mice. The reduced rate of action potential discharge in nociceptive fibers and the impaired heat responsiveness of Ins2^+/Akita DRG neurons suggest that ionic sensory transduction and transmission mechanisms are modified by diabetes.

Changes of mechanoreceptors in different-state remnants of ruptured anterior cruciate ligament

OBJECTIVE

To observe the changes in the quantity and morphology of mechanoreceptors in different-state remnant stumps of ruptured anterior cruciate ligaments (ACLs).

METHODS

Specimens of completely ruptured ACL remnants were collected from 57 patients. The injury time from injury to surgery was recorded. According to the degree of pre-operative anterior displacement of knee joint, these patients were divided into two groups: group 1 (≤ 6 mm) and group 2 (> 6 mm). The morphology type of ligament remnant in each patient was identified. The correlations of mechanoreceptor number in the remnant stumps with the morphology of ligament stump, injured knee stability, and injury time were analyzed. Subsequently, based on ACL lesion type, patients were divided into four groups including groups A, B, C, and D, and then, the items above were compared among the four groups.

RESULTS

Group 1 contained 20 specimens including three with type B and 17 with type C. Group 2 contained 37 specimens including 20 with type A, 1 with type B, 2 with type C, and 14 with type D. The distributions of four-type remnant morphologies (X² = 49.406, P = 0.000) and mechanoreceptors (X² = 13.84, P = 0.002) were all significantly different between the two groups. The number of mechanoreceptors was positively correlated with the injured knee stability (r = 0.63,P = 0.018). The number of the mechanoreceptors was not obviously correlated with the injury time in group 1 (r = - 0.37,P = 0.136), while it was negatively correlated with the injury time in group 2 (r = - 0.51,P = 0.022). There was a significant difference in pre-operative anterior displacement of knee joint among groups A, B, C, and D (F = 85.59, P = 0.000), and the pre-operative anterior displacement of knee joint was less in groups B and C than in groups A and D. There was a significant difference in the distribution of typical and atypical mechanoreceptors among groups A, B, C, and D (X² = 68.16, P = 0.032).

CONCLUSIONS

The ruptured ACL remnants connecting the femur to tibia can still play a role in maintaining knee stability; thus, the mechanoreceptors can persist in these remnants for a long time.

In-vivo reflectance confocal microscopy of Meissner's corpuscles in diabetic distal symmetric polyneuropathy

OBJECTIVE

To evaluate in-vivo reflectance confocal microscopy (RCM) of Meissner's corpuscles (MC) in diabetic distal symmetric polyneuropathy (DSP).

METHODS

Forty-three adults with diabetes and 21 control subjects underwent RCM of MC density at the fingertip of digit V, thenar eminence (TE), and arch of the foot, ankle skin biopsy for epidermal nerve fiber density (ENFD), electrophysiological studies, monofilament threshold testing, and timed vibration at the toe. Subjects with diabetes were subdivided into groups with and without clinical DSP using the American Academy of Neurology (AAN) case definition and neuropathy outcomes were compared across groups.

RESULTS

Both diabetic groups (with and without AAN clinical DSP criteria) had objective evidence of peripheral sensory involvement using conventional sensory measures, although those with clinical DSP criteria had greater abnormalities. MC densities were lower in the entire diabetic group at the TE and digit V relative to controls. MC densities at all imaging sites were associated with corresponding conventional sensory measures. MC densities were reduced in subjects without AAN clinical DSP criteria at the TE and digit V compared to controls whereas conventional upper limb sensory measures did not differ between these groups.

CONCLUSIONS

In-vivo RCM of MC density at digit V is a non-invasive, painless, objective marker in diabetes that offers a window into early large fiber sensory nerve terminal loss. Further studies are needed to determine whether RCM of MCs can identify quantitative changes in DSP associated with disease progression or treatment.

A morphologic and quantitative comparison of mechanoreceptors in the tibial remnants of the ruptured human anterior cruciate ligament

Reconstruction of the ruptured anterior cruciate ligament (ACL) does not always result in expected successful outcome. A satisfactory outcome depends not only on the tightness or strength of the graft but also on the quality of proprioceptive restoration. Mechanoreceptors of ACL are supposed to play considerable roles in the proprioceptive feedback system of knee. This study aimed to observe the condition and number of the surviving mechanoreceptors in the tibial remnant of ruptured ACL in human knees.From April 2009 to January 2012, 60 patients with existing free tibial remnants who had undergone arthroscopic ACL reconstruction were enrolled and divided into 4 groups according to the time duration of injury to surgery (Group I: no more than 3 months; Group II: 3 to 6 months; Group III, 6 months to 1 year; Group IV: more than 1 year). Six normal ACL specimens were taken as controls. Specimens were obtained from ACL tibial remnant and stained by the immunohistochemical staining method. The type, size, and quantity of mechanoreceptors were observed under the light microscope. A total of 92 Ruffini-like corpuscles, 9 Pacini-like corpuscles, 5 unclassified neural endings, and free nerve endings were identified via immunohistochemical staining.There were no significant differences in the number of mechanoreceptors in the 5 groups (P = 0.238). Some degenerative changes were observed in Group IV. The results suggest that the residual mechanoreceptors in the ruptured ACL exhibit long-term survival and showed no obvious signs of withering within 1 year.Residual mechanoreceptors do exist in the tibial remnants of ruptured anterior cruciate ligament in human knees and identified clearly by using immunohistochemistry staining. No significant difference was found regarding quantitative variation of the residual mechanoreceptors about the injury duration.

Psychophysical Investigations into the Role of Low-Threshold C Fibres in Non-Painful Affective Processing and Pain Modulation

We recently showed that C low-threshold mechanoreceptors (CLTMRs) contribute to touch-evoked pain (allodynia) during experimental muscle pain. Conversely, in absence of ongoing pain, the activation of CLTMRs has been shown to correlate with a diffuse sensation of pleasant touch. In this study, we evaluated (1) the primary afferent fibre types contributing to positive (pleasant) and negative (unpleasant) affective touch and (2) the effects of tactile stimuli on tonic muscle pain by varying affective attributes and frequency parameters. Psychophysical observations were made in 10 healthy participants. Two types of test stimuli were applied: stroking stimulus using velvet or sandpaper at speeds of 0.1, 1.0 and 10.0 cm/s; focal vibrotactile stimulus at low (20 Hz) or high (200 Hz) frequency. These stimuli were applied in the normal condition (i.e. no experimental pain) and following the induction of muscle pain by infusing hypertonic saline (5%) into the tibialis anterior muscle. These observations were repeated following the conduction block of myelinated fibres by compression of sciatic nerve. In absence of muscle pain, all participants reliably linked velvet-stroking to pleasantness and sandpaper-stroking to unpleasantness (no pain). Likewise, low-frequency vibration was linked to pleasantness and high-frequency vibration to unpleasantness. During muscle pain, the application of previously pleasant stimuli resulted in overall pain relief, whereas the application of previously unpleasant stimuli resulted in overall pain intensification. These effects were significant, reproducible and persisted following the blockade of myelinated fibres. Taken together, these findings suggest the role of low-threshold C fibres in affective and pain processing. Furthermore, these observations suggest that temporal coding need not be limited to discriminative aspects of tactile processing, but may contribute to affective attributes, which in turn predispose individual responses towards excitatory or inhibitory modulation of pain.

Comparative analysis of inter- and intraligamentous distribution of sensory nerve endings in ankle ligaments: a cadaver study

BACKGROUND

The aim of this study was to analyze the inter-, intraligamentous, and side-related patterns of sensory nerve endings in ankle ligaments.

METHODS

A total of 140 ligaments from 10 cadaver feet were harvested. Lateral: calcaneofibular, anterior-, posterior talofibular; sinus tarsi: lateral- (IERL), intermediate-, medial-roots inferior extensor retinaculum, talocalcaneal oblique and canalis tarsi (CTL); medial: tibionavicular (TNL), tibiocalcaneal (TCL), superficial tibiotalar, anterior/posterior tibiotalar portions; syndesmosis: anterior tibiofibular. Following immunohistochemical staining, the innervation and vascularity was analyzed between ligaments of each anatomical complex, left/right feet, and within the 5 levels of each ligament.

RESULTS

Significantly more free nerve endings were seen in all ligaments as compared to Ruffini, Pacini, Golgi-like, and unclassifiable corpuscles (P ≤ .005). The IERL had significantly more free nerve endings and blood vessels than the CTL (P ≤ .001). No significant differences were seen in the side-related distribution, except for Ruffini endings in right TCL (P = .016) and unclassifiable corpuscles in left TNL (P = .008). The intraligamentous analysis in general revealed no significant differences in mechanoreceptor distribution.

CONCLUSIONS

The IERL at the entrance of the sinus tarsi contained more free nerve endings and blood vessels, as compared to the deeper situated CTL. Despite different biomechanical functions in the medial and lateral ligaments, the interligamentous distribution of sensory nerve endings was equal.

CLINICAL RELEVANCE

The intrinsic innervation patterns of the ankle ligaments provides an understanding of their innate healing capacities following injury as well as the proprioception properties in postoperative rehabilitation.

Immunohistochemical analysis of mechanoreceptors in the human posterior cruciate ligament: association with aging male

INTRODUCTION

The aim of this study was to evaluate the association between frequency of the posterior cruciate ligament (PCL) mechanoreceptors and age in men.

METHODS

Nineteen normal right knees harvested from human male cadavers were evaluated. Age ranged from 17 to 64 years with a mean of 35 years old. PCL was separated for sampling in femoral and tibial portions. Topographic distribution and frequency within the ligament texture were determined employing the Pro-Image digital analysis system. Mechanoreceptors were counted and classified according to the criteria proposed by Freeman & Wyke.

RESULTS

A total of 1820 mechanoreceptors were found, type II being the most frequent one. Analysis of the femoral portion of the ligament showed an equivalent predominance of Types II and IV mechanoreceptors. Tibial portion had a predominance of type II mechanoreceptors, followed by type IV. At this portion, receptors Types I and III were less commonly identified.

CONCLUSION

In the tibial portion of the PCL, there is predominance of Type II mechanoreceptors followed by types IV, I and III mechanoreceptors, respectively. No relationship was found between the total number of mechanoreceptors and age in the femoral and tibial portions of the PCL.

[Ultrastructure of dendritic spines in the somatosensory cortex of rat's brain following 5- and 33-day hypergravity]

Electron microscopy examination of layers III-IV in the somatosensory cortex of rat's brain following 5- and 33-day and repeated 5-day exposure to 2 G revealed ultrastructural changes in dendritic spines, synapses, axon terminals and nervous cell body suggesting their functional activation and increase of the afferent input from hindlimb mechanoreceptors Hypertrophy of the acicular apparatus (AA) due to hypergravity, growth of AA destruction as a result of 33-day exposure and its ample evidence after repeated 5-day exposure lead to the conclusion that AA ultrastructure can be used for assessing afferent input into the brain cortex of animals exposed in a changed field of gravity.

The characteristics of the mechanoreceptors of the hip with arthrosis

Mechanoreceptors have been extensively studied in different joints and distinct signals that convey proprioceptive information to the cortex. Several clinical reports have established a link between the number of mechanoreceptors and a deficient proprioceptive system; however, little or no literature suggest concentration of mechanoreceptors might be affected by hip arthrosis. The purpose of this study is first to determine the existence of mechanoreceptors and free nerve endings in the hip joint and to distinguish between their conditions: those with arthrosis and without arthrosis. Samples of 45 male hips were analyzed: 30 taken from patients with arthrosis that were submitted to total arthroplasty and 15 taken from male cadavers without arthrosis. The patients' ages ranged from 38 to75 years (average 56.5) and the cadavers' ages ranged from 21 to 50 years (average 35.5). The capsule, labrum, and femoral head ligament tissues were obtained during the arthroplasty procedure from 30 patients with arthrosis and from 15 male cadavers. The tissue was cut into fragments of around 3 mm. Each fragment was then immediately stained with gold chloride 1% solution and divided into sections of 6 μm thickness. The Mann-Whitney test was used for two groups and the ANOVA, Friedman and Kruskal-Wallis tests for more than two groups. Results show the mechanoreceptors (Pacini, Ruffini and Golgi corpuscles) and free nerve endings are present in the capsule, femoral head ligament, and labrum of the hip joint. When all the densities of the nerve endings were examined with regard to those with arthrosis and those without arthrosis, the mechanoreceptors of cadavers without arthrosis were found to be more pronounced and an increase in free nerve endings could be observed (p = 0.0082). Further studies, especially electrophysiological studies, need to be carried out to clarify the functions of the mechanoreceptors in the joints.

Muscle spindle and Pacinian corpuscle: conceptions, misconceptions, and the far-fetched hypothesis of an experienced surgical pathologist

The muscle or neuromuscular spindle is a proprioceptive microanatomic structure, which together with the Golgi tendon organ, is responsible for the reflex are that determines the tonic state of muscle. The Pacinian corpuscle (or corpuscle of Vater-Pacini) is a pure mechanoreceptor, sensitive to pressure, typically found in the skin, subcutis and superficial soft tissues. Generally, both the muscle spindle and Pacinian corpuscle are microanatomical findings that are too unremarkable to focus on during the course of routine work in surgical pathology. We recently encountered such a structure, which required full attention to be correctly identified: the incidental finding was a curious muscle spindle, the "fibrous capsule" of which mimicked the "lamellar body" of Pacinian corpuscle. This report accurately mirrors the manner in which the events occurred and emphasizes the fundamental anatomical notions that were ignored, and is also an opportunity to mention some of the pathological conditions affecting the aforementioned often-neglected receptors.

[Quantitative study on mechanoreceptors in tibial remnants of ruptured anterior cruciate ligament in human knees]

OBJECTIVE

To evaluate the survival condition and quantitative variation of mechanoreceptors in the tibial remnant of ruptured anterior cruciate ligament (ACL) in human knees.

METHODS

Between April 2009 and May 2010, 60 patients who underwent arthroscopic ACL reconstruction were included and divided into 4 groups according to the time of injury, with 15 patients in each group. In group A, there were 14 males and 1 female aged 20-37 years (mean, 27 years); the injury was caused by traffic accident in 5 cases and by sports in 10 cases, and the time between injury and surgery was not more than 3 months. In group B, there were 14 males and 1 female aged 17-43 years (mean, 24 years); the injury was caused by traffic accident in 2 cases and by sports in 13 cases; and the time between injury and surgery was 3 to 6 months. In group C, there were 11 males and 4 females aged 16-53 years (mean, 28 years); the injury was caused by traffic accident in 2 cases and by sports in 13 cases; and the time between injury and surgery was 6 to 12 months. In group D, there were 12 males and 3 females aged 18-41 years (mean, 26 years); the injury was caused by sports in 11 cases, and the other 4 cases had no defined etiology; and the time between injury and surgery was more than 12 months. Specimens were donated by the volunteers from the anteromedial side of the ACL tibial remnant (40 slices per specimen) and stained via immunohistochemical method. The type, size, and quantity of mechanoreceptors were observed under light microscope.

RESULTS

Totally 80 Ruffini-like corpuscles, 8 Pacini-like corpuscles, 5 atypical neural endings and no distinct Golgi organ-like corpuscles were observed under light microscope in 60 specimens (2 400 slices) of 4 groups. There was no obvious difference in size and type of mechanoreceptors among 4 groups. However, some degenerative and atrophic changes could be observed in the specimens of group D. The total number of mechanoreceptors was 31 (35.2%) in group A, 22 (25.0%) in group B, 23 (26.1%) in group C, and 12 (13.7%) in group D. There was no significant difference (P > 0.05) in Ruffini-like corpuscles and Pacini-like corpuscles among 4 groups. Mechanoreceptors were found in 9, 8, 9, and 6 patients in groups A, B, C, and D, respectively; the detection rates were 60.0%, 53.3%, 60.0%, and 40.0%, respectively; showing no significant difference (P > 0.05).

CONCLUSION

The mechanoreceptors in tibial residual of ruptured ACL have a long survival without obvious degeneration and atrophy within 12 months. So it may contribute to restoration of proprioceptive function after operation if the remnant is preserved during ACL reconstruction.

Immunohistological evaluation of proprioceptive potential of the residual stump of injured anterior cruciate ligaments (ACL)

To evaluate proprioceptive potential in residual remnants, tissue harvested from ruptured ACLs in 63 consecutive patients was examined for evidence of residual proprioceptive fibres using H&E, and monoclonal antibodies to S-100 and NFP (neurofilament protein). Histological examination showed good subsynovial and intra-fascicular vascularity with free nerve endings in the majority. Morphologically normal mechanoreceptors (H&E) and proprioceptive fibres (positivity with monoclonal antibody for NFP) were found in 46% and 52.4% of stumps, respectively. A statistically significant correlation between injury duration and persistence of mechanoreceptors and proprioceptive fibres was noted. More fibres were seen where ACL remnant was adherent to PCL. Our study has shown that persistent residual proprioceptive fibres in injured ACLs (especially early cases with PCL adherence) are significant; not shaving ACL remnants may be of potential benefit during ACL reconstruction, as some re-innervation and recovery of proprioceptive potential may be possible, thus improving clinical outcomes.

Neurotrophin-4/5-depletion induces a delay in maturation of the periodontal Ruffini endings in mice

Neurotrophin-4/5 (NT-4/5) - a member of the neurotrophic factors - is a ligand for TrkB, which has been reported to be expressed in the mechanoreceptive Ruffini endings of the periodontal ligament. The present study examined developmental changes in the terminal morphology and neural density in homozygous mice with a targeted disruption of the nt-4/5 gene and wild-type mice by immunohistochemistry for protein gene product 9.5 (PGP 9.5), a general neuronal marker, and by quantitative analysis using an image analyzer. Postnatal development of terminal Schwann cells was also investigated by enzymatic histochemistry for non-specific cholinesterase activity (ChE). Furthermore, the immuno-expression of TrkB and low affinity nerve growth factor receptor (p75-NGFR) was surveyed in the periodontal Ruffini endings as well as trigeminal ganglion. At postnatal 1 week, the lingual periodontal ligament of both types of mice contained PGP 9.5-positive nerve fibers showing a tree-like ramification with axonal swellings in their course. In both types of mice at 2 weeks of age, comparatively thick nerve fibers with a smooth outline increased in number, and frequently ramified to form nerve terminals with dendritic profiles. However, no typical Ruffini endings with irregular outlines observed in the adult wild-type mice were found in the periodontal ligament at this stage. At postnatal 3 weeks, typical Ruffini endings with irregular outlines were discernable in the periodontal ligament of the wild-type mice while the dendritic endings showing smooth outlines were restricted to the homozygous mice. After postnatal 8 weeks, both types of mice showed an increase in the number of Ruffini endings, but the morphology differed between the wild-type and NT-4/5 homozygous mice. In the wild-type mice, a major population of the Ruffini endings expanded their axonal branches and developed many microprojections, resulting in a reduction of endings with smooth outlines. In contrast, we failed to find such typical Ruffini endings in the periodontal ligament of the homozygous mice: A majority of the periodontal Ruffini endings continued to show smooth outlines at postnatal 12 weeks. Quantitative analysis on neural density demonstrated a reduction in the homozygous mice with a significant difference by postnatal 8 weeks. Enzymatic histochemistry for non-specific ChE did not exhibit a distinct difference in the distribution and density of terminal Schwann cells between wild-type and homozygous mice. Furthermore, TrkB and p75-NGFR mRNA and proteins did not differ in the trigeminal ganglion between the two types. The periodontal Ruffini endings also displayed immunoreactivities for TrkB and p75- NGFR in both phenotypes. These findings suggest that the nt-4/5 gene depletion caused a delay in the formation and maturation of the periodontal Ruffini endings in the mice by inhibiting the growth of the periodontal nerves at an early stage, and indicate that multiple neurotrophins such as NT- 4/5 and BDNF might play roles in the development and/or maturation of the periodontal Ruffini endings.

In vivo confocal microscopy of Meissner corpuscles as a measure of sensory neuropathy

OBJECTIVE

To assess feasibility of noninvasive in vivo reflectance confocal microscopy (RCM) of Meissner corpuscles (MCs) as a measure of sensory neuropathy (SN).

BACKGROUND

MCs are touch-pressure sensation receptors in glabrous skin. Skin biopsy studies suggest that fingertip MC density (MCs/mm(2)) is a sensitive measure of diabetic and idiopathic SN. In vivo RCM of skin is an emerging field, with applications including evaluation of cancer. It is painless and noninvasive. Feasibility of in vivo RCM of MCs has not been explored.

METHODS

Fifteen adults (10 controls, 5 SN subjects) underwent in vivo RCM at the fingertip (Digit V) and thenar eminence. In vivo RCM was conducted to determine whether MCs were visible within dermal papillae and, if visible, to characterize their imaging appearance and assess MCs/mm(2) at each site.

RESULTS

MCs were identified in dermal papillae at all sites in controls. MCs appeared as heterogeneous bright structures within dermal papillae, which appeared as dark "pits." Mean MC density in controls was 12 +/- 5.3/mm(2) (Digit V) and 5.1 +/- 2.2/mm(2) at the thenar eminence. MC density in SN was lower than controls at Digit V (2.8 +/- 5.7/mm(2), p = 0.01) and the thenar eminence (1.4 +/- 1.1/mm(2), p = 0.004). MCs were absent in a sensory neuronopathy; milder reductions in MC density were seen among diabetic and HIV-positive subjects.

CONCLUSIONS

Meissner corpuscles (MCs) can be visualized and quantitated in controls and sensory neuropathy (SN) using in vivo reflectance confocal microscopy (RCM). In vivo RCM of MCs has potential for noninvasive detection and monitoring of SN, if subsequent studies show that with denervation or reinnervation, reliable and recognizable changes or loss can be detected using our described approaches.

Neurotized nevi of the oral mucosa: an immunohistochemical and ultrastructural analysis of nevic corpuscles

BACKGROUND

Nevic corpuscle (NC), a stacked lamellar structure reminiscent of Meissner corpuscle, is frequently observed in dermal melanocytic nevi. Although the heading 'neurotized' is classically used for these nevi, the exact neural nature of NC has been a topic of considerable debate. Neurotized nevi have received little attention in the dental literature, and there was no information on NC in oral melanocytic nevi.

METHODS

Six cases of oral intramucosal nevi with a significant number of NC (two completely and four partially neurotized nevi) were examined immunohistochemically and ultrastructurally.

RESULTS

NC was composed of closely piled laminar cells devoid of visible melanin. NC and associated spindle nevus cells were immunopositive for S-100 protein but negative for HMB-45, myelin basic protein and epithelial membrane antigen. Within NC, no reactivity for neurofilament protein, protein gene product 9.5 or peripherin was evident. Numerous CD34-positive dendritic cells were located between nevus cells and often encircled NC. Ultrastructurally, NC consisted of concentrically layered elongated cells with a slender lamellated cytoplasm rich in thin filaments and pinocytotic vesicles. Their cytoplasmic processes were focally covered by external basal lamina and continuous to spindle nevus cells. Occasional NC cells contained a few melanosomes. There was no interposed axon in NC.

CONCLUSIONS

Despite the close resemblance to Meissner corpuscle, NC showed no axonal supply. NC cells lacked terminal Schwannian differentiation and appeared to be modified melanocytes with some perineurial ultrastructural characteristics. The presence of CD34-positive cells, presumably corresponding to endoneurial fibroblasts, further supports an organizational relationship of NC and peripheral nerve sheath elements.

Pressure and stretch mechanosensitivity of peripheral nerve fibres following local inflammation of the nerve trunk

Patients with non-specific limb pain often show signs of nerve mechanosensitivity, i.e. local tenderness over nerve trunks and pain in response to limb movements that cause nerve stretch. In such patients a nerve lesion is not apparent, and it has been suggested that local neural inflammation may be a key factor. The present study examines the extent to which nerve fibres in regions of local inflammation respond to small stretches, and whether functional changes occur throughout the primary afferent neurone. A local neuritis was induced in adult rats by wrapping oxidised cellulose saturated in complete Freund's adjuvant (CFA) around the peroneal or sciatic nerves. A small cut was made in the perineurium of some of the peroneal lesioned animals. A- and C-fibre recordings were made 2-10 days post-surgery from filaments dissected proximal to the lesion. Local mechanosensitivity was assessed using a glass probe and by small stretches. Responses to stretch and local pressure were recorded in 7% of C- and 8% of A-fibres from the peroneal nerve following CFA treatment with the sheath opened. A smaller proportion of stretch sensitive fibres were seen in sciatic and peroneal nerves after CFA treatment alone (2% of C- and 3% of A-fibres), but such fibres were not seen in control preparations. The most responsive fibres fired to 3% stretch, which is within the range of nerve stretch seen during normal limb movements. Less than 1% of stretch sensitive fibres had peripheral fields, indicating that most had probably degenerated distally.

Progressive neurodegeneration in C. elegans model of tauopathy

Discovery of various mutations in the tau gene among frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) families suggests gain-of-toxic function of wild-type or mutant tau as the mechanism for extensive neuronal loss. We thus generated transgenic nematode (Caenorhabditis elegans) expressing wild-type or mutant (P301L and R406W) tau in the touch (mechanosensory) neurons. Whereas the worm expressing wild-type tau showed a small decrease in the touch response across the lifespan, the worm expressing mutant tau displayed a large and progressive decrease. When the touch neurons lost their function, neuritic abnormalities were found prominent, and microtubular loss became remarkable in the later stage. A substantial fraction of degenerating neurons developed tau accumulation in the cell body and neuronal processes. This neuronal dysfunction is not related to the apoptotic process because little recovery from touch abnormality was observed in the ced-3 or ced-4-deficient background. Expression of GSK3 brought about slight deterioration in the touch response, while expression of HSP70 led to some improvement.

Sensory perception and neuroanatomical structures in normal and grafted skin of burn survivors

BACKGROUND

This study compared the neural structures found in grafted skin of burn survivors with neural structures found in site-matched normal skin and correlated these structures with psychophysical measures of sensation.

METHODS

Fifteen skin-grafted male burn survivors (47.7+/-10.4 years old) with deep partial- or full-thickness thermal burn injuries covering an average of 11+/-5.6% of their total body surface and with normal skin at a matching, unburned, contralateral site were recruited into this study. Threshold determinations and magnitude estimations for touch, cold, warmth and heat-pain were performed at sites with grafted and normal skin, using Semmes-Weinstein monofilaments and the Medoc TSA 2001 thermal stimulator. Skin biopsies from both the grafted and normal sites were stained with antibodies for protein gene product 9.5 (PGP) and neurofilament 200 kDa. Nerve fibers in the epidermis and nerve fibers or bundles of nerve fibers in the superficial and deep dermis as well as innervated blood vessels, hair follicles and sweat glands were counted.

RESULTS

On average, the data were collected 43.1+/-10.4 months after grafting. When thresholds on grafted skin were compared to thresholds on normal skin, they showed elevated sensory thresholds [touch (p<0.003), cold (p<0.031), warmth (p<0.009)]. Magnitude estimates of touch, cold and warmth differed on the two sides with sensations elicited from grafts being smaller than those from normal skin. Heat-pain thresholds and heat-pain magnitude estimations were not statistically different on the two sites. By comparison to the normal side, and consistent with the attenuated sensory functions of the grafts, counts of neural structures showed a reduction in innervation density; PGP-immunoreactive nerve fibers/bundles were reduced in grafted epidermis (p<0.026) and superficial dermis (p<0.001). The numbers of sweat glands (p<0.006) and hair follicles (p<0.001) were also reduced. The number of innervated blood vessels did not differ significantly on the two sides. There were significant correlations between sensory thresholds and the neuroanatomical variables: thresholds of cold and touch were correlated with the number of sweat glands in both grafted and normal skin (r2=0.56 and 0.50, respectively; p<0.001), while warmth thresholds were significantly correlated with the number of innervated blood vessels in grafted skin (r2=0.62, p<0.001). Encapsulated mechanoreceptors were not encountered in this study of hairy skin.

CONCLUSIONS

Touch, cold and warmth thresholds and magnitude estimations do not return to normal levels after skin grafting in burn survivors. The elevation of thresholds and reduction of sensory intensity is accompanied by a general decrease in the density of nerve terminals. The lack, or numerical reduction, of sweat glands and innervated blood vessels was also indicative of diminished sensation on grafted skin.

The structure and response properties of Golgi tendon organs in control and hypodynamia–hypokinesia rats

The Golgi tendon organs (GTOs) are encapsulated mechano-receptors that, in normal conditions, monitor via Ib afferent fibers the contractile force. A 14-day period of hypodynamia, absence of weight bearing and hypokinesia, and reduction of motor activity (HH) is known to induce changes in postural muscles such as the soleus. At present, there is no data available regarding the Ib afferent feedback in normal rats (CONT group) and in rats after a hypodynamia-hypokinesia (HH group) period. Consequently, the aim of our study was to determine the HH effects on the morphological (histochemistry on gross morphology) and electrophysiological properties of the GTOs in rat soleus muscle. In the histological study, nine CONT and nineteen HH GTOs of the soleus muscle were identified. The results demonstrated that HH GTOs were morphologically similar to the CONT GTOs. Regarding the electrophysiological study, a L2-L6 laminectomy was performed under deep anesthesia (sodium pentobarbital, 60 mg kg(-1)). Responses in single Ib fibers from the L5 dorsal root to the isometric twitch and tetanic fused contractions of "in-series" motor units (MUs) were recorded. Twenty-three and twenty-eight GTO/MU pairs were studied in the CONT and HH groups, respectively. In the HH group, the Ib afferent response exhibited a decrease in dynamic peak for the high stimulation frequencies and an increase in static sensitivity for all stimulation frequencies. Our results suggest that after an HH period, the GTOs continue to fulfil their mechano-sensory function to signal the contractile force but with a higher static sensitivity.

Tactile corpuscle-like bodies in colonic mucosa

During the routine examination of a segment of colon resected for adenocarcinoma, a diffuse proliferation of mucosal tactile corpuscle-like bodies was identified. The bodies showed a lamellar structure by light microscopy and were S-100 positive. Electron microscopy demonstrated parallel slender processes with prominent surface caveolae, arising from peripheral cell bodies. Similar structures sometimes occur in neurofibromas but they have not previously been reported in the gastrointestinal tract.

Shoulder proprioception and function following thermal capsulorraphy

PURPOSE

Because monopolar radiofrequency energy has a denaturing effect on the glenohumeral joint capsule during thermal capsulorraphy, we hypothesized that thermal treatment would have a deleterious effect on the mechanoreceptors present within the capsule, thereby affecting proprioception and function. The purpose of this study was to evaluate proprioception and function following thermal capsulorraphy.

TYPE OF STUDY

Case series.

METHODS

Twenty subjects (13 male, 7 female) diagnosed with unilateral anterior, anteroinferior, or multidirectional glenohumeral instability with no significant concomitant pathologies, were treated with monopolar radiofrequency thermal capsulorraphy by one surgeon. Capsular redundancy was the primary diagnosis in all subjects. Subjects were bilaterally tested retrospectively 6 to 24 months (11.90 +/- 5.65 months) following surgery. Each subject's ability to actively reproduce joint positions (ARJP) and reproduce paths of motion (PMR) was measured with an electromagnetic motion analysis system. Both passive reproduction of joint positions (PRJP) and threshold to detect passive motion (TTDPM) were measured using a proprioception testing device. Function was quantified with the Shoulder Rating Questionnaire (SRQ). Proprioception data were analyzed with separate repeated measures ANOVA (P <.05).

RESULTS

Statistical analysis revealed a significant ARJP difference between the involved and uninvolved limb (P =.005) indicating that reproduction error was less with the involved limb compared to the uninvolved limb. No significant interactions were present for TTDPM, PRJP, or PMR. The SRQ indicates that the subjects returned to near normal function (91.86/100 +/- 5.38 points) at the time of testing.

CONCLUSIONS

The results from this study do not support our hypothesis of proprioception and functional deficits following thermal treatment. Normalized proprioception following thermal capsulorraphy may have resulted from the healing effects of thermal treated ligament, as reported in the literature, as well as facilitation of other mechanoreceptors present in adjacent tissue about the shoulder joint during rehabilitation. The results of this study indicate that no appreciative deleterious effects exist with proprioception and function following treatment of shoulder instability with thermal capsulorraphy.

Impairment of peripheral sensory innervation in senescence

Sensorimotor disturbances are common among elderly and one of the main factors depreciating life quality in senescence. Mechanistically sensory deficits during aging include not only degenerative and regressive events but also phenotypic switches among sensory neurons as well as remodeling of sensory innervation. The pattern of changes suggests that an underlying mechanism is a sustained dependence of sensory neurons on target tissues, and that this dependence, at least in part, appears to be mediated through signaling by target-derived trophic factors. This review presents and discusses evidence supporting this notion.

Increased sodium channel SNS/PN3 immunoreactivity in a causalgic finger

The sodium channels SNS/PN3 and NaN/SNS2 are regulated by the neurotrophic factors-nerve growth factor (NGF) and glial-derived neurotrophic factor (GDNF), and may play an important role in the development of pain after nerve injury or inflammation. These key molecules have been studied in an amputated causalgic finger and control tissues by immunohistochemistry. There was a marked increase in the number and intensity of SNS/PN3-immunoreactive nerve terminals in the affected finger, while GDNF-immunoreactivity was not observed, in contrast to controls. No differences were observed for NGF, trk A, NT-3 or NaN/SNS2-immunoreactivity. While further studies are required, these findings suggest that accumulation of SNS/PN3 and/or loss of GDNF may contribute to pain in causalgia, and that selective blockers of SNS/PN3 and/or rhGDNF may provide effective novel treatments.

The presence of proprioceptive mechanoreceptors in the remnants of the ruptured ACL as a possible source of re-innervation of the ACL autograft

This study investigated the presence of neural mechanoreceptors in the remnants of the ruptured ACL as a possible source of reinnervation of the ACL autologous graft. The remainder of the torn ACL was selected for further histological investigation from 17 patients during ACL reconstruction 3 months to 3.5 years after injury. Perioperatively two types of ACL remnant were identified. Fifteen patients had portions of ACL adapted at the PCL. In all of these patients we found mechanoreceptors (I and II). In five patients we found mushroomlike remnants which included either none or small numbers of mechanoreceptors. Free neural ends were found in both patient groups. There was a significant difference between the groups in regard to the mean number of mechanoreceptors I and II per slice. In conclusion, in patients with an ACL remnant adapted to the PCL, mechanoreceptors exist even 3 years after injury. If we accept that restoration of proprioception is the result of reinnervation of the ACL, leaving the ACL remnants as a source, if this is surgically possible without risk of Cyclop's lesion, may be of potential benefit to the patient.

Neurotrophin-4 deficient mice have a loss of vagal intraganglionic mechanoreceptors from the small intestine and a disruption of short-term satiety

Intraganglionic laminar endings (IGLEs) and intramuscular arrays (IMAs) are the two putative mechanoreceptors that the vagus nerve supplies to gastrointestinal smooth muscle. To examine whether neurotrophin-4 (NT-4)-deficient mice, which have only 45% of the normal number of nodose ganglion neurons, exhibit selective losses of these endings and potentially provide a model for assessing their functional roles, we inventoried IGLEs and IMAs in the gut wall. Vagal afferents were labeled by nodose ganglion injections of wheat germ agglutinin-horseradish peroxidase, and a standardized sampling protocol was used to map the terminals in the stomach, duodenum, and ileum. NT-4 mutants had a substantial organ-specific reduction of IGLEs; whereas the morphologies and densities of both IGLEs and IMAs in the stomach were similar to wild-type patterns, IGLEs were largely absent in the small intestine (90 and 81% losses in duodenum and ileum, respectively). Meal pattern analyses revealed that NT-4 mutants had increased meal durations with solid food and increased meal sizes with liquid food. However, daily total food intake and body weight remained normal because of compensatory changes in other meal parameters. These findings indicate that NT-4 knock-out mice have a selective vagal afferent loss and suggest that intestinal IGLEs (1) may participate in short-term satiety, probably by conveying feedback about intestinal distension or transit to the brain, (2) are not essential for long-term control of feeding and body weight, and (3) play different roles in regulation of solid and liquid diet intake.

Inflammation with no axonal damage of the rat saphenous nerve trunk induces ectopic discharge and mechanosensitivity in myelinated axons

Inflammation along a nerve trunk with no frank axonal nerve damage produced by complete Freund's adjuvant (CFA) or Carrageenan is known to induce a painful peripheral neuropathy. In the present study, we examined the electrophysiological properties of myelinated axons (spontaneous discharge and mechanical sensitivity) at the inflamed nerve site. The rat saphenous nerves were exposed at mid-thigh level and wrapped in 2 mm wide bands of haemostatic oxidized cellulose (Oxycel) that were saturated with undiluted CFA. In the control rats the Oxycel) was saturated with saline. At postoperative days (PODs) 2-5 and 6-10, fine axon bundles were teased from the nerve, and electrophysiological recordings performed. At both time points spontaneous activity at the site of the application in CFA rats (PODs 2-5=9.9+/-2.5%: PODs 6-10=6.1+/-1.4%) was significantly higher than in the control animals (PODs 2-5=2.9+/-1.1%: PODs 6-10=1.6+/-1.4%: P=0.03, P=0.02, respectively). Mechanical sensitivity at both time points was significantly higher in CFA rats (PODs 2-5=12.6+/-3.1%: PODs 6-10=10.3+/-3.1%) than in saline rats (PODs 2-5=3.4+/-2.91%: PODs 6-10=0.8+/-1.0%: P=0.03, P=0.04, respectively). This study clearly shows that perineural inflammation with no axonal nerve damage induced by CFA application around the nerve trunk elevates spontaneous activity and induces mechanosensitivity in myelinated axons.

Distribution of TGF-beta, the TGF-beta type I receptor and the R-II receptor in peripheral nerves and mechanoreceptors; observations on changes after traumatic injury

The mechanisms governing the regeneration of denervated peripheral mechanoreceptors are similar to those of peripheral nerves. The ability to regenerate depends partly on changes of the Schwann cell phenotype. The transforming growth factor beta (TGF-beta) family have been implicated in induction of Schwann cell proliferation, production of extracellular matrix and neurotrophin synthesis as well as synthesis or repression of cell adhesion molecules. Hence, they may prove to be of importance for regenerative mechanisms in peripheral mechanoreceptors. The distribution of TGF-beta, the receptors I and II and intra-cellular second messengers, Smad 2/3 and 4 was assessed in sensory neurones, peripheral nerves and mechanoreceptors by immuno-histochemistry, immuno-electron microscopy and in situ hybridisation. TGF-beta2 mRNA and TGF-beta2-like immunoreactivity (IR) were expressed in injured small and medium sized rat sensory neurones of dorsal root ganglia. TGF-beta and receptor II mRNA and immunoreactivities (IR) were present in satellite cells. Intact and injured sensory neurones expressed receptor I mRNA and Smad 2 mRNA. TGF-beta2 mRNA was found in transected nerve stumps and in sensory mechanoreceptors. TGF-beta1, 2 and Smad 4 were also observed in inner core lamellar cells of intact and denervated cat Pacinian corpuscles. Lamellar cells of intact and denervated Meissner corpuscles were TGF-beta immunoreactive. Merkel cells were receptors I and II immunoreactive. In conclusion, cutaneous and subcutaneous mechanoreceptors differ with regard to the expression of TGF-beta isoforms and receptors.

MK-801 reduces non-noxious stimulus-evoked Fos-like immunoreactivity in the spinal cord of rats with chronic constriction nerve injury

We investigated the role of N-methyl-D-aspartate (NMDA) receptors on non-noxious stimulus-induced pain by examining the effect of MK-801, a non-competitive NMDA receptor antagonist, on Fos-like immunoreactivity (FLI) in the spinal dorsal horn by non-noxious stimulation to rats with chronic constriction injury (CCI) of the sciatic nerve. In CCI rats that did not receive the non-noxious stimulus, FLI was significantly increased in laminae V/VI of the dorsal horn at the 7th and 14th days after surgery relative to sham rats. When CCI rats received non-noxious stimuli, rubbing the plantar of the hind paw, FLI in laminae I/II at the 14th day was significantly increased relative to CCI rats that did not receive the stimulation. In sham rats, the same stimulus significantly decreased FLI in laminae III/IV and V/VI at the 7th and 14th day. When MK-801 was administered intraperitoneally prior to non-noxious stimulation in CCI rats at the 14th day after surgery, the stimulus-induced FLI in laminae I/II in CCI rats was significantly reduced. This study indicates that NMDA receptor is involved in upregulating FLI in response to non-noxious stimulation of CCI rats.

[Histological and ultrastructural studies of extraocular muscle proprioceptor in concomitant strabismus]

OBJECTIVE

To investigate the morphological change of extraocular muscle proprioceptor (EMP) in concomitant strabismus and study its pathogenesis.

METHODS

The samples were obtained from the extraocular muscles of patients with concomitant strabismus and enucleated eyeballs. After being stained, the samples were examined under light microscopy (LM) and transmission electron microscopy (TEM) to count the number of the mitochondria in each sample in an area of 4,000 mm(2) of the axon under the same amplification.

RESULTS

Under light microscopy, at the myotendinous junction of the extraocular muscle, the EMP nerve fibers were ended at the initial site or the bilateral sides of a nearby single extrafusal fiber. Under electron microscopy, the general architecture of the receptors in concomitant strabismus was completely disorganized. The nerve component in them had disappeared. The number of the mitochondria in 4,000 mm(2) of the axon in the experimental group was significantly lower than that in the control group (P < 0.05).

CONCLUSION

The results indicate that in concomitant strabismus, the reception and transmission of proprioceptive information are abnormal, and the morphological EMP disturbance plays an important role in the pathogenesis of concomitant strabismus.

S100A6 expression in fibrohistiocytic lesions

BACKGROUND

S100A6, an S100 calcium-binding protein, has been found in a variety of cutaneous and extracutaneous lesions including: melanocytic nevi, melanoma, some salivary gland and epithelial tumors, and malignant fibrous histiocytoma (MFH). Dermal dendrocytes (DD) in the papillary dermis of skin also express S100A6 protein. We evaluated a variety of cutaneous fibrohistiocytic lesions to determine if the immunophenotype of S100A6 positivity can be expanded to include some or all of these lesions.

METHODS

Formalin-fixed, paraffin-embedded tissues from fibrous papules (FP, 20), dermatofibromas (DF, 20), dermatofibrosarcoma protuberans (DFSP, 5), atypical fibroxanthomas (AFX, 5), oral fibromas (3), digital fibroma (1), and dermatomyofibroma (1) were evaluated with antibodies to S100A6, S100B, factor XIIIa, and MAC387 using a one-hour capillary action-based immunohistochemical procedure.

RESULTS

DD in 20/20 FP, 19/20 DF, and 4/4 fibromas stained positively with anti-S100A6 in a pattern similar to anti-factor XIIIa. No DFSP cases stained with anti-S100A6. Anti-S100A6 showed superior staining to anti-factor XIIIa in 4/5 AFX cases.

CONCLUSIONS

The immunophenotypes of some fibrohistiocytic lesions can be expanded to include S100A6 protein. With the exception of AFX, the use of anti-S100A6 does not appear to offer added benefit over anti-factor XIIIa in the differential diagnosis of fibrohistiocytic lesions.

Cyclooxygenase-2 inhibitor SC-236 attenuates mechanical allodynia following nerve root injury in rats

Low back pain is a common problem, affecting approximately two-thirds of the adult population. Of these individuals, a significant percentage will exhibit symptoms of radicular pain or sciatica. The purpose of this study was to determine the effect of one systemic (2 mg/kg) or intrathecal (0.2 mg/kg) dose of a selective cyclooxygenase-2 inhibitor (SC-236) in decreasing existing mechanical allodynia in a rat model of radiculopathy. Gait disturbance and mechanical allodynia (increased response to non-noxious von Frey monofilament stimuli) were assessed daily until the rats were killed 7 days after surgery. Robust mechanical allodynia developed in the rats in all groups except for those in the sham group by day 1 after surgery. Mechanical allodynia was significantly lower in the rats that received the systemic or the intrathecal dose of SC-236 than in those in the vehicle control group (analysis of variance followed by Bonferroni multiple comparison test, p = 0.002). The intrathecal drug route of administration produced greater attenuation in allodynia than the systemic dose, supporting a central mechanism of action of the cyclooxygenase-2 inhibitor (p = 0.002). The hypothesis that cyclooxygenase-2 is involved in spinal nociceptive processing after a nerve root injury was supported by this study. In addition, these data support continued basic science research to further elucidate central inflammatory processes that follow nerve root injury.

AIDA reduces glutamate release and attenuates mechanical allodynia after spinal cord injury

Spinal cord injury (SCI) leads to an increase in extracellular excitatory amino acid (EAA) concentrations, resulting in glutamate receptor-mediated excitotoxicity and central sensitization. To test contributions of group I metabotropic glutamate receptors (mGluRs) in SCI induced release of glutamate and in behavioral outcomes of central sensitization following injury, we administered 1-aminoindan-1,5-dicarboxylic acid (AIDA; 0.1 nmol intraspinally), a potent group I mGluR antagonist, to rats immediately after spinal cord contusion injury. EAAs were collected by microdialysis and quantified using HPLC. AIDA significantly decreased extracellular glutamate but not aspartate concentrations and significantly attenuated the development of mechanical but not thermal allodynia. These results suggest mGluRs play an important role in injury-induced EAA release and in central sensitization following SCI.

Effects of neutralizing antibodies to TNF-alpha on pain-related behavior and nerve regeneration in mice with chronic constriction injury

Inhibition of proinflammatory cytokines reduces hyperalgesia in animal models of painful neuropathy. We set out to investigate the consequences of this treatment for nerve regeneration. Here we examined the sequels of epineurial application of neutralizing antibodies to tumor necrosis factor-alpha (TNF) in chronic constriction injury (CCI) of the sciatic nerve in C57/BL 6 mice. The mice were tested behaviorally for manifestations of thermal hyperalgesia and mechanical allodynia. Nerve regeneration was assessed by morphometry of myelinated nerve fibers in the sciatic nerve and of the epidermal innervation density in the glabrous skin of the hindpaws. Antibodies to TNF reduced thermal hyperalgesia and mechanical allodynia after CCI. Myelinated fiber density in the sciatic nerve was reduced to 30% of normal on day 7 after surgery, and reached 60% on day 45, with no difference between antibody-treated and untreated animals. Epidermal innervation density as shown by PGP 9.5 and CGRP immunohistochemistry was reduced to 25-47% at both time points after CCI, again without differences between antibody treated and untreated mice. Myelinated fiber density but not epidermal innervation density was correlated to thermal and mechanical withdrawal thresholds. We conclude that neutralization of endoneurial TNF attenuates pain related behavior but has no effect on nerve regeneration. Furthermore, the number of epidermal nerve fibers is not relevant to the magnitude of behavioral hyperalgesia in CCI.

Sensory recovery and Meissner corpuscle number after toe-to-hand transplantation

This study investigated the possible relationship between sensory recovery and receptor number after toe-to-hand transplantation. Moving two-point discrimination was measured after a course of sensory re-education. Meissner corpuscle number was then quantified by light microscopic examination of multiple sections of glabrous skin obtained at pulp reduction and from site-matched normal toe and fingertip skin. Meissner corpuscle number per millimeter was 0.94 in normal toe skin (n = 4), and 0.37 after toe-to-hand transplantation (n = 34). A significant correlation existed between moving two-point discrimination and Meissner corpuscle number (r = -0.62; p < 0.001). No significant relationship was found between moving two-point discrimination and patient age or interval from injury to reconstruction. The results suggest that despite sensory re-education, there may be a level of receptor reinnervation below which good sensory recovery may not be obtained.

Mechanoreceptors in collateral knee ligaments: an animal experiment

The mechanoreceptors in the collateral ligaments of the knee joint in rat hindlimbs were studied. In group II (n=10) the femoral and obturator nerves were sectioned. In both groups III and V (n=20) the sciatic nerve was sectioned. In group V (n=10) the sectioned sciatic nerve was sutured 4 weeks after sectioning. In group IV (n=10) all three nerves were sectioned. Group I (n=10) served as control. After 4 months all animals were killed. The ligaments of the knee joint were preserved and stained with gold chloride, paraffin-embedded and cut in sagittal serial sections. The results showed that 4 months after partial or total denervation of the limb, there was necrosis and a decrease in the number of mechanoreceptors, which was dependent upon the severity and site of the lesion. After suture of the sciatic nerve the increase in mechanoreceptors suggested a regenerative process.

Morphological changes in periodontal mechanoreceptors of mouse maxillary incisors after the experimental induction of anterior crossbite: a light and electron microscopic observation using immunohistochemistry for PGP 9.5

Ruffini nerve endings (mechanoreceptors) in the periodontal ligament (PDL) of mouse incisors were examined to elucidate whether experimentally-induced crossbites cause any changes or abnormalities in their morphology and distribution. Anterior guiding planes were attached to the mandibular incisors of 3-week-old C3H/HeSlc mice. At 3 days and 1, 2, 4, 6, and 8 weeks post-attachment of the appliance, the mice were sacrificed by perfusion fixation. Frozen sagittal cryostat sections of the decalcified maxillary incisors were processed for immunohistochemistry of protein gene product 9.5, followed by histochemical determination of tartrate-resistant acid phosphatase activity to reveal sites of alveolar bone resorption. Despite the absence of bone resorption within the lingual PDL of control mice, distinct resorption sites were seen in the respective regions of the experimental animals. Unlike the controls, many Ruffini endings showing vague and swollen contours, with unusually long and pedunculated micro-projections were observed in the affected lingual PDL of the incisors in the experimental animals with short-term anterior crossbite induction. Club-shaped nerve terminations with few, if any, micro-projections were observed in the lingual PDL of experimental animals with long-term induction, as well as in aged control mouse incisors. Differences in the distribution of Ruffini endings were also observed. These results indicate that changing the direction of the force applied to the PDL results in rapid and prolonged changes in the morphology of Ruffini-like mechanoreceptors.

Effect of mechanogated membrane ion channel blockers on experimental traumatic brain oedema

Traumatic head injury leads to marked swelling of endothelial cells, both in human patients and in Marmarou's rat model. We used this model to test the hypothesis of mechanogated ion channels being involved in the formation of traumatic brain oedema. All mechanogated channel blockers tested (gadolinium, amiloride, gentamicin) significantly reduced traumatic brain oedema evaluated by Evans blue extraction ratio, either when given 15 minutes before or 30 minutes after induction of trauma (evaluation 2 hours after trauma). These results clearly support our hypothesis, opening a new way for the investigation of the treatment of a clinical situation endowed with high morbidity and mortality.

Morphological study of mechanoreceptors on the coracoacromial ligament

We performed gold chloride staining of coracoacromial ligaments removed at operation, observed the peripheral nerve endings in the ligament, and studied their distribution and changes with aging in order to clarify the proprioception of the shoulder joint. The coracoacromial ligament was found to contain four types of typical nerve endings: Pacinian corpuscles, Ruffini receptors, Golgi tendon organ-like receptors, and free nerve endings. In addition, non-typical Pacinian corpuscles and Ruffini receptors with non-typical morphology were present. There were also unclassifiable nerve endings with a morphology which did not fit any of the above categories. These typical, non-typical, and unclassifiable nerve endings were all widely distributed on the surface of the subacromial side at the insertion into the acromion and around the coracoid process in the ligament. Free nerve endings were found sporadically on the surface of the subacromial bursal side in the ligament. The resected coracoacromial ligaments (23 specimens) were divided into two groups based on the disorder that required surgery: a fracture group without subacromial impingement (5 specimens) and a group with subacromial impingement (18 specimens). Age-related changes in the number of nerve endings were compared in each group. The total number of nerve endings decreased with age in both groups. The number of Pacinian corpuscles, Ruffini receptors, Golgi tendon organ-like receptors, and free nerve endings of typical morphology tended to decrease with age. The data from the fracture and subacromial impingement groups were not analyzed statistically because of the difference in the number of specimens in each group. However, the total number of nerve endings was lower in the subacromial impingement group than in the fracture group at all ages. The typical nerve endings of the coracoacromial ligament in both groups tended to decrease in the elderly, suggesting that the proprioception of the shoulder joint may become impaired with aging.

Dysfunction of Ib (autogenic) spinal inhibition in patients with progressive supranuclear palsy

We compared the activity of Ib spinal interneurons in five patients with progressive supranuclear palsy (PSP) with six age-matched control subjects. Stimulation of the medial gastrocnemius nerve at motor threshold intensity activated Ib afferents that in turn inhibit H reflexes from the soleus muscle. Maximum inhibition occurred at interstimulus intervals of 6 and 8 ms for both control subjects and PSP patients and was significantly greater in the PSP patients. Increased Ib activity of PSP patients may be caused by loss of inhibition of Ib interneurons through degeneration of the medullary reticulospinal pathway. The corticospinal pathways, unopposed by the medullary reticulospinal tract, may excessively activate Ib interneurons.

Mechanoreceptors of patellar tendon used for ACL reconstruction. Rabbit experiments

In 17 Japanese white rabbits (weighing 2.6-3.7 kg), the anterior cruciate ligament of the right knee was resected and then reconstructed, using the lateral half of the patellar tendon. The contralateral side served as control. Rabbits were killed 10, 20, or 30 weeks postoperatively. Then the reconstructed ligament was harvested and stained, using a modified gold chloride method. Under the light microscope, sensory nerve endings in serial sections were counted after being morphologically identified. With respect to the number of Pacinian and Ruffini corpuscles, there were no significant differences between the reconstructed ligament and the control patellar tendon at any time after surgery.

Innervation of "painful" lumbar discs

STUDY DESIGN

The authors investigated the innervation of discographically confirmed degenerated and "painful" human intervertebral discs.

OBJECTIVE

To determine the type and distribution patterns of nerve fibers present in degenerated human intervertebral discs.

SUMMARY OF BACKGROUND DATA

The innervation of intervertebral discs has previously been extensively described in fetal and adult animals as well as humans. However, little is yet known about the innervation of severely degenerated human lumbar discs. The question may be posed whether a disc that has been removed for low back pain possesses an increased innervation compared with normal discs.

METHODS

The presence of nerve fibers was investigated using acetylcholinesterase enzyme histochemistry, as well as neurofilament and substance P immunocytochemistry. From 10 degenerated and 2 control discs, the anterior segments were excised and their nerve distribution studied by examining sequential sections.

RESULTS

In all specimens, nerve fibers of different diameters were found in the anterior longitudinal ligament and in the outer region of the disc. In 8 of 10 degenerated discs, fibers were also found in the inner parts of the disc. Substance P-immunoreactive nerve fibers were sporadically observed in the anterior longitudinal ligament and the outer zone of the anulus fibrosus.

CONCLUSIONS

Findings indicate a more extensive disc innervation in the severely degenerated human lumbar disc compared with normal discs. The nociceptive properties of at least some of these nerves are highly suggested by their substance P immunoreactivity, which provides further evidence for the existence of a morphologic substrate of discogenic pain.

A new type of "bioartificial" nerve graft for bridging extended defects in nerves

In the rat sciatic nerve, a gap of around 10 mm in nerve continuity seems to be the maximal distance which can be successfully repaired by silicone tubes. In this study we tested if a new artificial nerve graft, composed of eight polyamide filaments (diameter 250 microns) placed inside silicone tubes (1.8 mm inner diameter), could be used to bridge an extended gap (15 mm) in rat sciatic nerve. Silicone tubes containing eight polyamide sutures were found to support regeneration across such a gap. After 4 weeks sensory fibres had bridged the gap and grown into the distal nerve segment as revealed by a positive pinch reflex test as well as positive staining for neurofilaments in the distal nerve segment. Myelinated axons could be observed in the tissue matrix formed in between and peripheral to the synthetic filaments along the whole length of the tube. In contrast, when silicone tubes without filaments were used to bridge the 15 mm gap, the tubes contained only fluid or in two cases a thin tissue strand. No positive pinch reflex response was elicited in the nerve segment distal to such a tube. We conclude that the new artificial nerve graft can be used to support regeneration across extended gaps in nerves.