Types Of Nerve Fibers Research Articles

Functional assessment of neuropathic pain

The assessment of the nervous system in patients with neuropathic pain is particularly challenging. Conventional electrophysiological testing, such as nerve conduction studies and somatosensory-evoked potentials, may prove normal as these techniques only evaluate large fibre function (A beta). In a clinical setting, two evaluation methods may prove useful to examine the nociceptive system or to explore small fibre function (A delta et C). First, quantitative sensory testing, derived from psychophysics, explores different sensory modalities (tactile, thermal and vibratory sensations) corresponding to different types of nerve fibres. Second, CO2 lasers allow for powerful and selective thermal stimuli to evoke brain potentials that are specifically related to the cutaneous activation of A delta and C nociceptors. Finally, other assessments of the nervous system, such as nociceptive reflexes and microneurography, are available for use in a more experimental setting.

On the identification of sensory information from mixed nerves by using single-channel cuff electrodes

BackgroundSeveral groups have shown that the performance of motor neuroprostheses can be significantly improved by detecting specific sensory events related to the ongoing motor task (e.g., the slippage of an object during grasping). Algorithms have been developed to achieve this goal by processing electroneurographic (ENG) afferent signals recorded by using single-channel cuff electrodes. However, no efforts have been made so far to understand the number and type of detectable sensory events that can be differentiated from whole nerve recordings using this approach.MethodsTo this aim, ENG afferent signals, evoked by different sensory stimuli were recorded using single-channel cuff electrodes placed around the sciatic nerve of anesthetized rats. The ENG signals were digitally processed and several features were extracted and used as inputs for the classification. The work was performed on integral datasets, without eliminating any noisy parts, in order to be as close as possible to real application.ResultsThe results obtained showed that single-channel cuff electrodes are able to provide information on two to three different afferent (proprioceptive, mechanical and nociceptive) stimuli, with reasonably good discrimination ability. The classification performances are affected by the SNR of the signal, which in turn is related to the diameter of the fibers encoding a particular type of neurophysiological stimulus.ConclusionsOur findings indicate that signals of acceptable SNR and corresponding to different physiological modalities (e.g. mediated by different types of nerve fibers) may be distinguished.

Case Scenario: Neurologic Complication after Continuous Interscalene Block

A 33-YR-OLD woman, American Society of Anesthesiologists risk classification I, was referred for surgical treatment of left shoulder instability. Her medical history was unremarkable, but she had undergone two previous shoulder surgeries: anterior stabilization of left shoulder 3 yr ago followed by a posterior Bankart stabilization 2 yr later because of recurrent luxation and pain. At examination, she still complained about pain in her left shoulder, and movement was severely limited. A left Bankart operation and capsulotomy were scheduled. A preoperative interscalene catheter was placed according to the modified lateral approach. The interscalene brachial plexus was identified using a nerve stimulator (Stimuplex® HNS II, B. Braun Melsungen AG, Melsungen, Germany) connected to the proximal end of the metal inner part of a short beveled needle. A contraction of the deltoid muscle was observed with a current output of 0.35 mA, with an impulse duration of 0.1 ms. The insertion of the perineural catheter was performed using the cannula-over-needle technique with a plastic cannula (Polymedic®, Polyplex N-50 T, 20 gauge external diameter, te me na, Bondy, France). The catheter was introduced distally between the anterior and middle scalene muscle up to 3 cm. A bolus of 30 ml ropivacaine (0.5%) was administered, and the procedure was uneventful. No pain, dysesthesias, or paresthesias occurred at any time. Fifteen minutes later, a complete sensorimotor block of the left arm was observed. Then, general anesthesia with targetcontrolled infusion (TCI Diprifusor, SIMS Graseby Ltd., Watford, Herts, United Kingdom) of propofol and remifentanil was administered. The patient was positioned in the beach chair for surgery. The procedure lasted 3 h 30 min and was described by the surgeon as difficult. Postoperative analgesia was performed with patient-controlled interscalene analgesia using ropivacaine (0.2%) and was started 4 h after the end of the surgery. The pump settings were basal rate of 5 ml/h with supplementary boli of 4 ml for every 20 min. The patient was pain free, and the patient-controlled interscalene analgesia was stopped after 54 h. Even after 36 h of termination of patient-controlled interscalene analgesia, no motor or sensory recovery was observed. An ultrasonography of the brachial plexus was performed to exclude a hematoma and revealed no irregular finding. A complete neurologic examination including neurophysiologic recordings on the following day (72 h after surgery) demonstrated a motor and sensory incomplete lesion of nerve fibers originating from the upper brachial plexus (involving the following muscles: deltoid M0/5, biceps M0/5, and triceps M3/5). Motor nerve conduction studies (figs. 1 and 2) and somatosensory-evoked potentials (SSEPs) of the median and ulnar nerves that originate from the lower brachial plexus revealed normal recordings. Electromyography at the initial examination did not show signs of denervation (fibrillation or positive waves) but resulted in complete paralysis (no retrievable voluntary electromyography activity). The later finding at this early stage after injury can be in line with a neurapraxia (conduction failure) or axonotmesis (structural neural damage). Eventually, 1 month later, at the first follow-up, electromyographies showed signs of denervation most severe within the deltoid and biceps muscles, disclosing objective signs of neural damage (fig. 3) congruent to the clinical condition in which no motor improvement was observed. Six months later, although no clinical improvement occurred, a surgical exploration was performed that revealed no pathologic findings. At this time, a perioperative stimulation of the trunks of the brachial plexus elicited reliable responses for the three trunks. In repeated electromyographic recordings during a period of 2 yr, increasing signs of motor recovery could be observed, although the patient still demonstrated severe proximal muscle weakness that could not be * Professor and Chief-of-Staff, † Consultant, Department of Anesthesiology, ‡ Professor and Chairman, Spinal Cord Injury Center, University of Zurich, Balgrist University Hospital, Zurich, Switzerland.

Sensory Perception Thresholds in Men With Chronic Pelvic Pain Syndrome

To compare sensory thresholds in different nerve-fiber types in men with chronic pelvic pain syndrome (CPPS) and healthy controls, using thermal sensory testing and measuring current perception thresholds (CPT). We enrolled 22 men with CPPS and 20 healthy control participants. We determined the thermal sensory perception thresholds of C and Adelta nerve fibers on the perineum and left posterior thigh. To test CPT, we used sine wave electrical stimulation at 5, 250, and 2000 Hz, resulting in the selective depolarization of small unmyelinated C fibers, small myelinated Adelta, and large myelinated Abeta fibers, respectively. We bilaterally tested the hypothenar surface of the palms, medial parts of soles, midshaft of penis, and 1 site in the midperineum, for a total of 7 sites. The mean age of men with CPPS was similar to that of controls [42.8 (standard deviation, 9.4) and 40.4 (standard deviation, 13.2) years, respectively, P = .548]. There was no significant difference between the 2 groups for thermal perception thresholds in both the perineum and left thigh (P >.05). There was also no difference between the 2 groups for CPT values of all 3 frequencies of stimuli in each area tested (P >.05 for all comparisons). The absence of sensory threshold differences between men with CPPS and controls, with either thermal stimulation of C and Adelta fiber afferents or electrical stimulation of C, Adelta, and Abeta fiber afferents, discounts the existence of a peripheral neuropathy as a cause for pain in men with CPPS.

Measurements and mapping of 282,420 nerve fibers in the S1–5 nerve roots

The study aims to analyze nerve fiber types in the sacral nerve roots as a prerequisite for stimulation. One-micrometer cross-sections of human ventral and dorsal S1-5 roots were stained with osmium and toluidine blue. The total fiber diameter and myelin sheath were measured in 282,420 nerve fibers. The analysis revealed the following 3 main nerve fiber types: Aalpha fibers (diameter 6-14 microm), Agamma fibers (diameter 2-4 microm), and B fibers (diameter < 2 microm). The B fibers were absent in S-1, present in some S-2 fascicles, and abundant from S-3 to S-5. The Aalpha fibers dominated the S-1 roots and most fascicles of S-2 roots. In the S3-5 roots, only a few Aalpha fibers were present. The relative occurrence of Agamma fibers increased from S-1 to S-5. In dorsal roots, Agamma fibers represented approximately 70% of all nerve fibers in every root and fascicle. The B fibers represented efferent parasympathetic fibers. These fibers were concentrated in certain areas of the nerve roots, not randomly distributed. The Aalpha fibers innervate lower-extremity muscles and sphincters. The inverse correlation of Aalpha and Agamma fibers in the ventral roots from S-1 to S-5 is surprising. In dorsal roots, Agamma fibers may conduct pain, touch, and temperature signals. Highly selective fiber stimulation specific for type, location, and direction may improve sacral nerve stimulation for a spastic bladder in paraplegic individuals.

C-fiber-related EEG-oscillations induced by laser radiant heat stimulation of capsaicin-treated skin

Nociceptive input reaches the brain via two different types of nerve fibers, moderately fast A-delta and slowly conducting C-fibers, respectively. To explore their distinct roles in normal and inflammatory pain we used laser stimulation of normal and capsaicin treated skin at proximal and distal arm sites in combination with time frequency transformation of electroencephalography (EEG) data. Comparison of phase-locked (evoked) and non-phase-locked (total) EEG to laser stimuli revealed three significant pain-related oscillatory responses. First, an evoked response in the delta-theta band, mediated by A-fibers, was reduced by topical capsaicin treatment. Second, a decrease of total power in the alpha-to-gamma band reflected both an A- and C-nociceptor-mediated response with only the latter being reduced by capsaicin treatment. Finally, an enhancement of total power in the upper beta band was mediated exclusively by C-nociceptors and appeared strongly augmented by capsaicin treatment. These findings suggest that phase-locking of brain activity to stimulus onset is a critical feature of A-delta nociceptive input, allowing rapid orientation to salient and potentially threatening events. In contrast, the subsequent C-nociceptive input exhibits clearly less phase coupling to the stimulus. It may primarily signal the tissue status allowing more long-term behavioral adaptations during ongoing inflammatory events that accompany tissue damage.

Effect of progestogens and combined oral contraceptives on nerve fibers in peritoneal endometriosis

To investigate how progestogens and combined oral contraceptives change nerve fiber density in peritoneal endometriotic lesions and to identify the types of nerve fibers still present during hormone treatment. Laboratory study using human tissue. University-based laboratory. Hormonally treated and untreated women with endometriosis undergoing laparoscopy, hysteroscopy, and curettage. Biopsy samples from peritoneal endometriotic lesions in hormonally treated and untreated women with endometriosis. Types and density of nerve fibers were immunohistochemically determined in peritoneal endometriotic lesions from hormonally treated and untreated women with endometriosis. The nerve fiber density (mean +/- standard deviation/mm(2)) in peritoneal endometriotic lesions from hormone-treated women with endometriosis (10.6 +/- 2.2/mm(2)) was statistically significantly lower than in peritoneal endometriotic lesions from untreated women with endometriosis (16.3 +/-10.0/mm(2)). Nerve growth factor and nerve growth factor receptor p75 expression in peritoneal endometriotic lesions were slightly reduced in hormone-treated women with endometriosis compared with untreated women with endometriosis. Progestogens and combined oral contraceptives reduced nerve fiber density and nerve growth factor and nerve growth factor receptor p75 expression in peritoneal endometriotic lesions.

Phenotyping parallel visual pathways in autosomal dominant optic atrophy

Abstract Purpose To characterize different phenotypes of Kjer optic atrophy along different visual pathways. Methods Novel computerized psychophysical assessment methods (CCT ‐ Cambridge Colour Test and CSF ‐ Metropsis Contrast Sensitivity Function Test) were used to evaluate visual function in a population of 13 subjects (26 eyes) from 8 families with Autosomal Dominant Optic Atrophy (ADOA). This evaluation was completed with electrophysiological assessment (Pattern ERG, Pattern and Multifocal VEP) and Automated Static Perimetry (ASP). Results CCT shows evidence for severe damage of all cone populations (p&lt;&lt;0.0001), and of similar magnitude, implying concomitant damage of parvo and koniocellular pathways. Achromatic contrast sensitivity is severely impaired for all six spatial frequency channels studied (p&lt;0.002), suggesting mixed magno/parvocellular impairment. A decrease of both P‐50 and N‐95 amplitudes of PERG is found (p&lt;&lt;0.001), while implicit times are normal. MfVEP results show significant impairment in amplitudes of the most central rings (1, 2 ‐ p&lt;0.001), with concomitant local increased implicit times, no significant changes being found at most eccentric rings. Pattern VEP impairment is consistent with these results. Amplitude values of MfVEP in visual quadrants are significantly correlated with the decreased retinal sensitivity obtained in the 4 quadrants by ASP. Conclusion Our results suggest that all functional types of nerve fibers are damaged in ADOA, with a predominance of the parvocellular ones. Multimodal psychophysical and electrophysiological methods are good quantitative markers to understand the pathophysiology of damage of central and peripheral pathways in this condition.

Selective Stimulation of Autonomic Nerves and Recording of Electroneurograms in a Canine Model

The article presents the results of modeling, design, and experimental testing of a multielectrode spiral cuff (CUFF) to determine to what extent a CUFF could be used for selective stimulation of different types of nerve fibers within particular compartments and for selective recording of electoneurograms (ENGs) from particular compartments of the peripheral autonomic nerve. The CUFF was implanted on the left cervical vagus nerve (LVN) of a dog. The relative positions of the particular nerve regions that innervated the cardiovascular (CV) and respiratory system (RS) were identified by delivering the stimuli to the particular group of three electrodes (GTE). The stimuli caused both selective stimulation of mainly B fibers within the particular compartments, and differential block of A fibers by membrane hyperpolarization. It was shown that when the stimuli were delivered to GTE9, the heart rate began to fall and when the stimuli were delivered to GTE4, the rate of breathing decreased. The defined and randomly chosen GTEs were used also as recording GTEs while CV or RS were stimulated by carotid artery massage, epinephrine injection, and noninvasive positive end-expiratory pressure ventilation (NIPEEPV). Results demonstrate that the function of a particular internal organ can be modulated via the selective stimulation of the innervating compartment of the peripheral nerve. Results also showed that stimulations elicited site-specific changes in ENG power spectra recorded from the particular compartments of the LVN.

Automated characterization of nerve fibers labeled fluorescently: Determination of size, class and spatial distribution

Morphological classification of nerve fibers could help interpret the assessment of neural regeneration and the understanding of selectivity of nerve stimulation. Specific populations of myelinated nerve fibers can be investigated by retrograde tracing from a muscle followed by microscopic measurements of the labeled fibers at different anatomical levels. Gastrocnemius muscles of adult rats were injected with the retrograde tracer Fluoro-Gold. After a survival period of 3 days, cross-sections of spinal cords, ventral roots, sciatic, and tibial nerves were collected and imaged on a fluorescence microscope. Nerve fibers were classified using a variation-based criterion acting on the distribution of their equivalent diameters. The same criterion was used to classify the labeled axons using the size of the fluorescent marker. Measurements of the axons were paired to those of the entire fibers (axons + myelin sheaths) in order to establish the correspondence between so-established axonal and fiber classifications. It was found that nerve fibers in L6 ventral roots could be classified into four populations comprising two classes of Aα (denoted Aα 1 and Aα 2), Aγ, and an additional class of Aγα fibers. Cut-off borders between Aγ and Aγα fiber classes were estimated to be 5.00 ± 0.09 μm (SEM); between Aγα and Aα 1 fiber classes to be 6.86 ± 0.11 μm (SEM); and between Aα 1 and Aα 2 fiber classes to be 8.66 ± 0.16 μm (SEM). Topographical maps of the nerve fibers that innervate the gastrocnemius muscles were constructed per fiber class for the spinal root L6. The major advantage of the presented approach consists of the combined indirect classification of nerve fiber types and the construction of topographical maps of so-identified fiber classes.

Brain activation upon selective stimulation of cutaneous C- and Aδ-fibers

Thermal and nociceptive cutaneous stimuli activate the brain via two types of nerve fibers, slightly myelinated Aδ-fibers with moderate conduction velocity and unmyelinated C-fibers with slow conduction velocity. Differences in central processing upon selective stimulation of these two fiber types in healthy human subjects still remain poorly understood. By means of event-related functional magnetic resonance imaging the present study investigated brain activation in response to stimulation of Aδ- and C-fibers in healthy subjects. We used the stimulation of tiny skin areas to perform a selective stimulation upon cutaneous C-fibers. Besides similar activation in several brain areas in response to both kinds of stimulation, we observed pronounced brain activation to selective C-fiber stimulation as compared to Aδ-fiber stimulation in the right frontal operculum and anterior insula. Based on a putative function of these structures we suggest that the C-fiber system might be engaged in homeostatic and interoceptive functions in a manner other than the Aδ-fiber system, producing a signal of greater emotional salience.

(120) Physiological relevance of a rodent model of degenerative disc disease

The American Pain Society estimates that 45% of the U.S. population seeks medical help for chronic pain at some point in their lives. Those affected include the 15% of Americans with persistent back pain. There are many potential sources including degenerative disc disease (DDD), which is one of the primary causes of chronic low back pain (LBP). Natural age related degeneration of lumbar intervertebral discs (IVDs) is common, but abnormal degeneration can occur, often resulting in pain, instability, and biomechanical movement disadvantages. IVDs are articular joints between vertebra and they act to distribute loads placed on the spine through hydrostatic pressures. The disc is composed of the exterior annulus fibrosus surrounded by ligaments and the central nucleus pulposus. The presence of nerve fibres and nerve endings in the lumbar IVDs and in the adjacent longitudinal ligaments has been demonstrated by many authors. In healthy discs, innervation is mostly limited to the posterior and anterior longitudinal ligaments and the superficial layers of the annulus fibrosus. Human IVDs are supplied by a variety of nerve fiber types including C- and A-delta fibers (substance P and CGRP), A-beta fibers (myelin basic protein) and sympathetic fibers entering from the sympathetic nerve truck. Specialized sensory nerve endings have also been described (i.e. pacinian corpuscles and golgi tendon organs). The goal of this study is to assess if the rat is of potential use to develop a relevant, rodent model of DDD-related LBP. Lumbar IVD innervation will be assessed in rats by immunohistochemistry to examine total innervation and fiber type(s). Preliminary results suggest that IVD innervation in rat and human are similar. Supported by grants from the Canadian Institute for Health Research (LSS) and the American Pain Society (MM). The American Pain Society estimates that 45% of the U.S. population seeks medical help for chronic pain at some point in their lives. Those affected include the 15% of Americans with persistent back pain. There are many potential sources including degenerative disc disease (DDD), which is one of the primary causes of chronic low back pain (LBP). Natural age related degeneration of lumbar intervertebral discs (IVDs) is common, but abnormal degeneration can occur, often resulting in pain, instability, and biomechanical movement disadvantages. IVDs are articular joints between vertebra and they act to distribute loads placed on the spine through hydrostatic pressures. The disc is composed of the exterior annulus fibrosus surrounded by ligaments and the central nucleus pulposus. The presence of nerve fibres and nerve endings in the lumbar IVDs and in the adjacent longitudinal ligaments has been demonstrated by many authors. In healthy discs, innervation is mostly limited to the posterior and anterior longitudinal ligaments and the superficial layers of the annulus fibrosus. Human IVDs are supplied by a variety of nerve fiber types including C- and A-delta fibers (substance P and CGRP), A-beta fibers (myelin basic protein) and sympathetic fibers entering from the sympathetic nerve truck. Specialized sensory nerve endings have also been described (i.e. pacinian corpuscles and golgi tendon organs). The goal of this study is to assess if the rat is of potential use to develop a relevant, rodent model of DDD-related LBP. Lumbar IVD innervation will be assessed in rats by immunohistochemistry to examine total innervation and fiber type(s). Preliminary results suggest that IVD innervation in rat and human are similar. Supported by grants from the Canadian Institute for Health Research (LSS) and the American Pain Society (MM).

Analysis of the Selective Nature of Sensory Nerve Stimulation Using Different Sinusoidal Frequencies

This study examines the ability to selectively activate different nerve fibers in a finger by using different sinusoidal stimulation frequencies. Specifically, the stimulation of A-β, A-δ, and C-fibers is looked into, and responses from each of three different stimuli (5 Hz, 250 Hz, and 2000 Hz) are compared. Action potential (AP) responses from the different nerve fibers are simulated. Activation thresholds are determined for each fiber type. The resulting firing frequencies are compared with thresholds found in the literature to determine the stimulating signal amplitude at which sensations begin to be perceived for each stimulation frequency. Results indicate that while selective stimulation of C-fibers and A-β fibers appears to be possible with 5 Hz and 2000 Hz, respectively, selective stimulation of A-δ fibers may not be possible due to them requiring a higher stimulating signal amplitude to cause the nerve to reach the physiological threshold than A-β fibers for 250 Hz. Thus, selective stimulation of the three types of nerve fibers may not be possible for all three examined frequencies.

Effects of hormonal treatment on nerve fibers in endometrium and myometrium in women with endometriosis

To investigate how hormonal treatment can change nerve fiber density and to identify types of nerve fibers in endometrium and myometrium in women with endometriosis. Laboratory study using human tissue. University-based laboratory. Hormonally treated and untreated women with endometriosis undergoing hysterectomy or curettage. Endometrial and myometrial tissues were prepared from women with hormonally treated endometriosis and women with untreated endometriosis. Types and density of nerve fibers in endometrium and myometrium in women with hormonally treated and untreated endometriosis were determined immunohistochemically. The nerve fiber density (mean density +/- SD per square millimeter) in the functional and the basal layers of endometrium (0.2 +/- 0.7/mm(2) and 0.9 +/- 1.3/mm(2), respectively) and myometrium (1.5 +/- 0.8/mm(2)) from women with hormonally treated endometriosis was much lower than that of endometrium (functional layer: 11 +/- 5/mm(2), basal layer: 18 +/- 8/mm(2), respectively) and myometrium (3 +/- 1/mm(2)) from women with untreated endometriosis. Nerve growth factor and nerve growth factor receptor p75 expression was also significantly reduced in women with hormonally treated endometriosis compared with women with untreated endometriosis. Hormonal treatment significantly reduced nerve fiber density in endometrium and myometrium in women with endometriosis.

Eye Dryness Sensations After Refractive Surgery: Impaired Tear Secretion or "Phantom" Cornea?

The cornea is richly innervated by various functional types of sensory nerve fibers. When stimulated, these fibers evoke conscious sensations of different quality including ocular dryness, discomfort, and pain. Refractive surgery involves a variable degree of damage to corneal nerves. This leads to an altered expression of membrane ion channels at the injured and regenerating nerve fibers, giving rise to aberrant spontaneous and stimulus-evoked nerve impulse firing. It is speculated that these abnormal sensory discharges are read by the brain as ocular surface dryness. This would explain the high incidence of eye dryness sensations after photorefractive surgery, which are experienced by a large number of patients despite the often modest disturbance of tear secretion. Therefore, drugs that reduce abnormal activity in injured nerves may represent a therapeutic alternative for eye dryness sensations after refractive surgery.

Different types of small nerve fibers in eutopic endometrium and myometrium in women with endometriosis

To investigate types of nerve fibers in endometrium and myometrium in women with endometriosis. Laboratory study using human tissue. University-based laboratory. Women with and without endometriosis undergoing hysterectomy. Histologic sections of contiguous endometrial and myometrial tissues were prepared from hysterectomies performed on women with and without endometriosis. Types and density of nerve fibers in endometrium and myometrium in women with and without endometriosis were determined using a series of specific markers for neuronal structure and function: PGP9.5, NF, SP, CGRP, TH, VAChT, VIP, and NPY. Nerve fibers stained with PGP9.5 and NF in endometrium and myometrium were significantly increased in women with endometriosis compared with women without endometriosis. Nerve fibers in the functional layer of endometrium in women with endometriosis were likely to be sensory C, a mixture of sensory A delta, sensory C, and adrenergic fibers in the basal layer of the endometrium, a mixture of sensory A delta, sensory C, adrenergic and cholinergic fibers in the myometrium. Increased nerve fiber density in endometrium and myometrium, and sensory C fibers and adrenergic nerve fibers in the endometrium in women with endometriosis may play an important role in the mechanisms of pain generation in this condition.

Effects of spinal cord stimulation on the cortical somatosensory evoked potentials in failed back surgery syndrome patients

Objective To evaluate the functional activation of the somatosensory cortical regions in neuropathic pain patients during therapeutic spinal cord stimulation (SCS). Methods In nine failed back surgery syndrome patients, the left tibial and the left sural nerves were stimulated in two sessions with intensities at motor and pain thresholds, respectively. The cortical somatosensory evoked potentials were analyzed using source dipole analysis based on 111 EEG signals. Results The short-latency components of the source located in the right primary somatosensory cortex (SI: 43, 54 and 65 ms) after tibial nerve stimulation, the mid-latency SI component (87 ms) after sural nerve stimulation, and the mid-latency components in the right (≈161 ms) and left (≈168 ms) secondary somatosensory cortices (SII) were smaller in the presence of SCS than in absence of SCS. The long-latency source component arising from the mid-cingulate cortex (≈313 ms) was smaller for tibial and larger for sural nerve stimuli during SCS periods compared to periods without SCS. Conclusions SCS attenuates the somatosensory processing in the SI and SII. In the mid-cingulate cortex, the effect of SCS depends on the type of stimulation and nerve fibers involved. Significance Results suggest that the effects of SCS on cortical somatosensory processing may contribute to a reduction of allodynia during SCS.

Congenital insensitivity to pain—review and report of a case with dental implications

Pain is a protective mechanism for the body. Absence of pain is a symptom in several disorders, both congenital and acquired. The congenital types are present at birth and affect the number and distribution of types of nerve fibers. At present, 5 types of hereditary sensory and autonomic neuropathies have been identified. The various disorders within this group are classified according to the different patterns of sensory and autonomic dysfunction and peripheral neuropathy and the presence of additional clinical features such as learning disability. However, the field is currently moving away from classification based on clinical presentation toward classification based on underlying genetic abnormality. In the absence of pain, patients are at risk of late presentation with illnesses or injuries, and have an increased incidence of traumatic injury. Self-mutilation is an almost invariable feature of these disorders. We report the case of a patient with congenital insensitivity to pain that presented with self-mutilation injuries to his hands and oral tissues caused by biting. The severe nature of these injuries necessitated serial extraction of his primary teeth soon after eruption, which led to a cessation of the problem. The mutilation has not returned following the eruption of the first of his permanent teeth, suggesting that he has learned not to bite himself, even though to do so causes him no discomfort.

The touch dome in human skin is supplied by different types of nerve fibers

Receptor end organs and free-nerve endings in the skin are the peripheral sentinels of the sensorial nervous system encoding for touch, temperature, and pain. Using a novel approach to analyze the outermost nerves of the skin, we visualized for the first time the distinct microanatomical structure of the touch dome of human hairy skin. The dermal nerve fibers of this slowly adapting type 1 mechanoreceptor were embedded in dermal protrusions that could be readily discerned by Laminin-5 staining. Concerning the nerves supplying the touch domes, we found, unexpectedly, that besides Abeta-fibers, Adelta- and C-fibers also were regularly present. The epidermis overlying the nerve convolutes showed a distinctive architecture of the rete ridges clearly demarcated from the surroundings and extending over 0.193 +/- 0.138 mm(2) (mean +/- standard deviation). Within this area, 756 +/- 386 Merkel cells/mm(2) (mean +/- standard deviation) were present compared with less than 50/mm(2) outside the touch dome, demonstrating for the first time a highly discontinuous distribution of these cells in nonglabrous skin. Our findings strongly suggest that the receptive qualities of human touch domes exceed mechanosensation, and that they may serve as multifunctional nerve end organs in human skin.

Assessment of Peripheral Neuropathy Using Measurement of the Current Perception Threshold with the Neurometer® in Patients with Type 2 Diabetes Mellitus

Measurement of current perception threshold (CPT) using the Neurometer at 2000, 250 and 5 Hz assesses function in three different nerve fibre types. This method was used to investigate peripheral neuropathy in 116 patients with type 2 diabetes mellitus and 38 healthy controls. The CPT at 2000 Hz was significantly higher in diabetic patients than in controls, and showed a significant negative correlation with motor and sensory nerve conduction velocities. At 250 Hz, CPT showed a significant positive correlation with the vibration perception threshold. At 5 Hz, the change in systolic blood pressure in the Schellong test in patients with hypoaesthesia tended to be less than in those with normal sensation or hyperaesthesia. Significantly higher CPT values were obtained in patients with proliferative diabetic retinopathy and macroalbuminuria. These data suggest that CPT is useful in detecting abnormalities of myelinated as opposed to unmyelinated nerve fibres in patients with type 2 diabetes.