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Neuropathic itch is clinically important but has received much less attention as compared to neuropathic pain. In the past decade, itch-specific pathways have been characterized on a cellular and molecular level, but their exact role in the pathophysiology of neuropathic itch is still unclear. Traditionally, mutually exclusive theories for itch such as labeled line, temporal/spatial pattern, or intensity theory have been proposed, and experimental studies in mice mainly favor the specificity theory of itch. By contrast, results in humans also suggest a role for spatial and temporal patterns in neuropathic itch. Rarefication of skin innervation in neuropathy could provide a "spatial contrast" discharge pattern, and axotomy could induce de novo expression of the itch-specific spinal neuropeptide, gastrin-releasing peptide, in primary afferent nociceptors, thereby modulating itch processing in the dorsal horn. Thus, clinical neuropathy may generate itch by changes in the spatial and temporal discharge patterns of nociceptors, hijacking the labeled line processing of itch and abandoning the canonical scheme of mutual exclusive itch theories. Moreover, the overlap between itch and pain symptoms in neuropathy patients complicates direct translation from animal experiments and, on a clinical level, necessitates collaboration between medical specialities, such as dermatologists, anesthesiologists, and neurologists.

Nerve growth factor (NGF) induces local hyperalgesia for a few days after intramuscular injection, but longer-lasting muscle pain upon systemic administration. As the muscle fascia is densely innervated by free nerve endings, we hypothesized a lasting sensitization of fascia nociceptors by NGF. We administered 1 μg NGF (dissolved in 100 μL saline) ultrasound-guided to the fascia of the Musculus erector spinae muscle at the lumbar level of 14 male volunteers and assessed hypersensitivity after 6 hours, and 1, 3, 7, 14, and 21 days. Pain upon mechanical stimuli (constant pressure and dynamic impact), upon exercise and electrically induced M. erector spinae contraction, and upon injection of 100 μL phosphate buffer pH4 (at day 7 and 14 only) to the fascia of both NGF- and saline-treated muscles, was investigated. Injections into the muscle fascia did not cause acute pain. Local heat pain thresholds were unchanged following NGF and saline (control) administration. NGF evoked a lasting (days 1-7) and significant reduction of pressure pain, pressure thresholds, exercise-evoked muscle pain, and hyperalgesia to impact stimuli (12 m/s). Pain upon injected protons was significantly elevated (P<0.04) for 2 weeks. NGF induced a sensitization of the muscle fascia to mechanical and chemical stimuli lasting for up to 2 weeks. As nociceptors in the fascia appear to be particularly prone to sensitization, they may contribute to acute or chronic muscle pain., (Copyright © 2012 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

The complement system is an important part of innate immunity. Complement activation generates a set of effector molecules with diverse biological functions. C5a is a crucial terminal component of the complement cascade. Several reports suggest that C5a can support nociceptive sensitization and inflammation in various models, including models of incisional pain. However, information concerning the differential effects of C5a on specific modalities of nociception, the role of C5a in supporting neutrophil infiltration, secondary nociceptive mediator generation, and the location of the relevant populations of C5a receptors supporting incisional sensitization are needed. In these studies we utilized C5a receptor-null mice (C5aR(-/-)) and matched controls to study nociceptive changes after hind paw incision. Heat hyperalgesia and mechanical allodynia were measured for 4 days after incision. We also followed hind paw edema, wound area neutrophil infiltration using the myeloperoxidase assay, and interleukin-1β and nerve growth factor levels using both enzyme-linked immunosorbent assay and immunohistochemical techniques. The main findings were: (1) Heat vs mechanical nociceptive sensitization after incision were differentially reduced in C5aR(-/-) mice, with thermal sensitization affected throughout the postincisional period but mechanical sensitization affected only at later time points; (2) Edema developed after incision in wild-type mice but only slightly and transiently in C5aR(-/-) mice, and (3) Deletion of C5aR blocked interleukin-1β and nerve growth factor production near the wound site. These findings demonstrate that the complement system component C5a is a novel biomarker and mediator associated with postsurgical nociceptive processing. C5aR may provide a novel target for the control of pain and inflammation after surgery., (Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Both serotonergic and dopaminergic receptor modulation can alter trigeminal nociceptive processing, and descending A11 dopaminergic projections can affect trigeminal nociceptive transmission. Here we aimed to test the interaction between dopamine D(2) and serotonin 5-HT(1B/1D) receptors and their individual and combined effects in order to better understand the relationship of the descending influences of these systems on nociceptive trigeminovascular afferents. Extracellular recordings were made in the rat trigeminocervical complex in response to electrical stimulation of the dura mater and mechanical noxious and innocuous stimulation of the ipsilateral ophthalmic dermatome. The A11 nucleus was lesioned, and following the resultant facilitation of neuronal firing, one of a selective 5-HT(1B/1D) receptor agonist (naratriptan), selective 5-HT(1B/1D) receptor antagonist (GR127935), a selective D(2)-like receptor agonist (quinpirole), and a selective D(1)-like receptor agonist (dihydrexidine), or a combination of the above, were administered. Both quinpirole and quinpirole with naratriptan inhibited firing in the trigeminocervical complex evoked by noxious stimuli, reducing it below prelesion baseline, while the response to innocuous stimuli was reduced back to baseline. Both naratriptan alone, and quinpirole combined with GR127935, inhibited firing in the trigeminocervical complex evoked by noxious stimuli, returning it to prelesion baseline, while the response to innocuous stimuli remained facilitated. Immunohistochemical staining demonstrated D(2)-receptor and 5-HT(1B/1D)-receptor colocalization in the trigeminocervical complex. The data suggest that the serotonergic and dopaminergic antinociceptive pathways act simultaneously on neurons in the trigeminocervical complex, and both amine systems need to be functioning for trigeminal sensitization to be reversed., (Published by Elsevier B.V.)

Venoms peptides have produced exceptional sources for drug development to treat pain. In this study we examined the antinociceptive and side effects of Tx3-3, a peptide toxin isolated from Phoneutria nigriventer venom, which inhibits high-voltage-dependent calcium channels (VDCC), preferentially P/Q and R-type VDCC. We tested the effects of Tx3-3 in animal models of nociceptive (tail-flick test), neuropathic (partial sciatic nerve ligation and streptozotocin-induced diabetic neuropathy), and inflammatory (intraplantar complete Freund's adjuvant) pain. In the tail-flick test, both intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of Tx3-3 in mice caused a short-lasting effect (ED(50) and 95% confidence intervals of 8.8 [4.1-18.8] and 3.7 [1.6-8.4] pmol/site for i.t. and i.c.v. injection, respectively), without impairing motor functions, at least at doses 10-30 times higher than the effective dose. By comparison, ω-conotoxin MVIIC, a P/Q and N-type VDCC blocker derived from Conus magus venom, caused significant motor impairment at doses close to efficacious dose in tail flick test. Tx3-3 showed a long-lasting antinociceptive effect in neuropathic pain models. Intrathecal injection of Tx3-3 (30 pmol/site) decreased both mechanical allodynia produced by sciatic nerve injury in mice and streptozotocin-induced allodynia in mice and rats. On the other hand, i.t. injection of Tx3-3 did not alter inflammatory pain. Taken together, our data show that Tx3-3 shows prevalent antinociceptive effects in the neuropathic pain models and does not cause adverse motor effects at antinociceptive efficacious doses, suggesting that this peptide toxin holds promise as a novel therapeutic agent for the control of neuropathic pain. The Brazilian armed spider Tx3-3, a new P/Q and R-type calcium channel blocker, effectively alleviates allodynia in animal neuropathic pain models., (Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Peripheral serotonin (5HT) has been implicated in migraine and temporomandibular pain disorders in humans and animal models and yet the mechanism(s) by which 5HT evokes pain remains unclear. Trigeminal pain can be triggered by activation of the transient receptor potential V1 channel (TRPV1), expressed by a subset of nociceptive trigeminal ganglia (TG) neurons and gated by capsaicin, noxious heat, and other noxious stimuli. As 5HT is released in the periphery during inflammation and evokes thermal hyperalgesia, and TRPV1 is essential for thermal hyperalgesia, we hypothesized that 5HT increases the activity of capsaicin-sensitive trigeminal neurons and that this increase can be attenuated by pharmacologically targeting peripheral 5HT receptors. TG cultures were pretreated with 5HT (10 nM-100 μM), sumatriptan (5HT(1B/1D) agonist), ketanserin (5HT(2A) antagonist), granisetron (5HT(3) antagonist), or vehicle prior to capsaicin (30-50 nM). Single-cell accumulation of intracellular calcium was recorded or calcitonin gene-related peptide (CGRP) release was measured following each treatment. In addition, using in situ hybridization and immunohistochemistry, we detected the colocalization of 5HT(1B), 5HT(1D), 5HT(2A), and 5HT(3A), but not 5HT(2C) mRNA with TRPV1 in TG cells. 5HT pretreatment evoked a significant increase in calcium accumulation in capsaicin-sensitive trigeminal neurons and enhanced capsaicin-evoked CGRP release, but had no significant effect when given alone. Sumatriptan, ketanserin, and granisetron treatment attenuated calcium accumulation and 5HT enhancement of capsaicin-evoked CGRP release. Together these results indicate that 5HT increases the activity of capsaicin-sensitive peripheral nociceptors, which can be attenuated by pharmacologically targeting peripheral 5HT receptors, thereby providing a mechanistic basis for peripheral craniofacial pain therapy., (Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Odontoblasts form the outermost cellular layer of the dental pulp where they have been proposed to act as sensory receptor cells. Despite this suggestion, evidence supporting their direct role in mediating thermo-sensation and nociception is lacking. Transient receptor potential (TRP) ion channels directly mediate nociceptive functions, but their functional expression in human odontoblasts has yet to be elucidated. In the present study, we have examined the molecular and functional expression of thermo-sensitive TRP channels in cultured odontoblast-like cells and in native human odontoblasts obtained from healthy wisdom teeth. PCR and western blotting confirmed gene and protein expression of TRPV1, TRPA1 and TRPM8 channels. Immunohistochemistry revealed that these channels were localised to odontoblast-like cells as determined by double staining with dentin sialoprotein (DSP) antibody. In functional assays, agonists of TRPV1, TRPA1 and TRPM8 channels elicited [Ca2+]i transients that could be blocked by relevant antagonists. Application of hot and cold stimuli to the cells also evoked rises in [Ca2+]i which could be blocked by TRP-channel antagonists. Using a gene silencing approached we further confirmed a role for TRPA1 in mediating noxious cold responses in odontoblasts. We conclude that human odontoblasts express functional TRP channels that may play a crucial role in mediating thermal sensation in teeth. Cultured and native human odontoblasts express functional TRP channels that may play a crucial role in mediating thermal sensation in teeth., (Copyright © 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

The perception of pain is initiated by the transduction of noxious stimuli through specialized ion channels and receptors expressed by primary nociceptive neurons. The molecular mechanisms that orchestrate the expression and function of ion channels relevant for pain processing are poorly understood. We demonstrate here a central role of the transcription factor Smad-interacting protein 1 (Sip1/Zfhx1b/Zeb2), a 2-handed zinc finger DNA-binding protein with essential functions in neural crest and forebrain development, in controlling nociceptive neuron excitability and pain sensitivity. Mutant mice lacking 1 Zfhx1b allele displayed decreased thermal pain responses, whereas mechanical pain was unaffected. In parallel, repetitive firing of capsaicin/heat-sensitive nociceptive DRG neurons was markedly impaired. Analysis of the voltage-gated currents underlying repetitive firing revealed a significant increase in persistent sodium currents and a reduction in delayed rectifier potassium currents. Modeling experiments in conjunction with experimental results suggest that these changes cause a depolarization-induced block of action potential propagation past the DRG axon T-junction. These data suggest that Sip1 controls the transduction properties of heat-sensitive primary sensory neurons and thus thermal pain sensitivity in a novel manner via coordinated changes in DRG-neuron voltage-gated ion channels., (Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Brainstem and spinal mechanisms mediating visceral nociception are investigated here using electrophysiology and immunohistochemistry techniques in a model of acute visceral pain. Colorectal distension (CRD) produced graded visceromotor responses (VMR) in normal rats, and these were facilitated by intracolonic mustard oil (MO) that generated acute visceral hyperalgesia. The neuropathic pain drug pregabalin (PGB) is thought to have state-dependent effects in attenuating neuropathic, but not acute somatic pain, likely by impairing calcium-channel trafficking. We found that systemic PGB produced antinociceptive effects on CRD-evoked VMRs in naïve rats lacking pathophysiology and in MO-pretreated rats. Systemic PGB also significantly reduced Fos labelling in lumbosacral spinal cords of rats given noxious repetitive CRD; however, PGB did not alter this measure of neural activity in the brainstem. Differential brainstem processing of noxious somatic and visceral stimuli may underlie the unique lack of state-dependent actions of PGB in this visceral pain model. Single-unit recordings in the rostral ventromedial medulla (RVM) verify that brainstem processing of somatic and visceral stimuli differs. The effects of CRD on RVM cells classed as ON, OFF, or NEUTRAL were independent of their somatic responses, with surprising changes in RVM cell activity to innocuous visceral stimulation. PGB also markedly reduced the visceral responses of RVM ON-cells to noxious CRD. These results illustrate clear differences in the central processing of visceral and somatic stimuli, yet a common role for descending modulation by brainstem activity in mediating evoked pain measures., (Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

This study analyzed the relationship between the density of intraepidermal nerve fibers (IENF) and the characteristics of either nociceptive laser-evoked potentials (LEPs) or contact heat-evoked potentials (CHEPs) in patients with painful sensory polyneuropathy with the aim to determine which parameters of LEPs and CHEPs more reliably reflect IENF loss. A total of 96 patients and 35 healthy volunteers took part in the study. Based on clinical examination, nerve conduction tests, and quantitative sensory testing, we identified 52 patients with small-fiber neuropathy (SFN), 40 with mixed (small-fiber and large-fiber) neuropathy (MFN), and 4 who were excluded from the analysis because of no evidence of involvement of small fibers. The latency of the N2 was delayed for both LEPs and CHEPs in patients with MFN and for CHEPs only in patients with SFN. The amplitude of the vertex N2/P2 potential was similarly reduced in both types of neuropathy, but LEPs were more frequently absent than CHEPs in MFN patients (68% vs 40%). In general, latency and amplitude of LEPs and CHEPs were well correlated with IENF density. SFN patients were characterized by abnormal EPs and slightly decreased but morphologically abnormal IENF. MFN patients were characterized by frequently absent LEPs and CHEPs and a rather severe IENF loss. The correlation between nociceptive evoked potentials (laser-evoked potentials and contact heat-evoked potentials) and skin biopsy aids in the diagnosis of painful neuropathies., (Copyright © 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Although the formalin test is a widely used model of persistent pain, the primary afferent fiber types that underlie the cellular and behavioral responses to formalin injection are largely unknown. Here we used a combined genetic and pharmacological approach to investigate the effect of ablating subsets of primary afferent nociceptors on formalin-induced nocifensive behaviors and spinal cord Fos protein expression. Intrathecal capsaicin-induced ablation of the central terminals of TRPV1+neurons greatly reduced the behavioral responses and Fos elicited by low-dose (0.5%) formalin. In contrast, genetic ablation of the MrgprD-expressing subset of non-peptidergic unmyelinated afferents, which constitute a largely non-overlapping population, altered neither the behavior nor the Fos induced by low-dose formalin. Remarkably, nocifensive behavior following high-dose (2%) formalin was unchanged in mice lacking either afferent population, or even in mice lacking both populations, which together make up the great majority of C-fiber nociceptors. Thus, at high doses, which are routinely used in the formalin test, formalin-induced "pain" behavior persists in the absence of the vast majority of C-fiber nociceptors, which points to a contribution of a large spectrum of afferents secondary to non-specific formalin-induced tissue and nerve damage., (Copyright © 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.)

Study Design: Investigation of sensory innervation of rat osteoporotic lumbar vertebrae using in vitro and in vivo models., Objective: To investigate (1) sensory innervation of osteoporotic rat vertebrae, (2) effects of risedronate on sensory neurons, (3) effects of osteoporosis treatment on bone mineral densities (BMDs) and the sensory innervation., Summary of Background Data: Osteoporotic patients without fractures sometimes experience vague low back pain of unknown origin. The mechanisms of osteoporosis treatments against the pain are unclear., Methods: (1) The expression of calcitonin gene-related peptide (CGRP) immunoreactive (-ir) or transient receptor potential vanilloid 1 (TRPV1)-ir nerve fibers in vertebrae and dorsal root ganglions (DRG) innervating L3 vertebrae of Sprague Dawley rats labeled with neurotracer were examined in control, sham, and ovariectomized (OVX) rats. (2) Cultured rat neonate DRG neurons in media containing different concentrations of risedronate were immunostained for CGRP, and we measured its activity using axonal length and proportion of CGRP-ir neurons. (3) BMDs and CGRP expression in DRG neurons innervating L3 vertebrae were examined in the following 5 groups: sham (treated with saline), OVX (saline), OVX+EXE (treadmill exercise), OVX+RIS (risedronate), and OVX+RIS+EXE (risedronate and exercise)., Results: (1) A few CGRP-ir or TRPV1-ir nerve fibers were observed in the bone marrow. CGRP or TRPV1 expression in DRG was elevated in the OVX group (P < 0.05). (2) The axonal length and proportion of CGRP-ir neurons were dose-dependently suppressed (P < 0.05). (3) BMDs improved and the CGRP expression decreased in the risedronate-treated groups (P < 0.05), especially in the OVX+RIS+EXE group., Conclusion: Sensory innervation of osteoporotic rat vertebrae showed increased expression of CGRP and TRPV1 in DRG neurons. Risedronate suppressed activity of CGRP-ir neurons in vitro, improved BMD, and decreased CGRP expression, especially together with exercise in vivo.

Central neuropathic pain (CNP) developing after spinal cord injury (SCI) is described by the region affected: above-level, at-level and below-level pain occurs in dermatomes rostral, at/near, or below the SCI level, respectively. People with SCI and rodent models of SCI develop above-level pain characterized by mechanical allodynia and thermal hyperalgesia. Mechanisms underlying this pain are unknown and the goals of this study were to elucidate components contributing to the generation of above-level CNP. Following a thoracic (T10) contusion, forelimb nociceptors had enhanced spontaneous activity and were sensitized to mechanical and thermal stimulation of the forepaws 35 days post-injury. Cervical dorsal horn neurons showed enhanced responses to non-noxious and noxious mechanical stimulation as well as thermal stimulation of receptive fields. Immunostaining dorsal root ganglion (DRG) cells and cord segments with activating transcription factor 3 (ATF3, a marker for neuronal injury) ruled out neuronal damage as a cause for above-level sensitization since few C8 DRG cells expressed AFT3 and cervical cord segments had few to no ATF3-labeled cells. Finally, activated microglia and astrocytes were present in thoracic and cervical cord at 35 days post-SCI, indicating a rostral spread of glial activation from the injury site. Based on these data, we conclude that peripheral and central sensitization as well as reactive glia in the uninjured cervical cord contribute to CNP. We hypothesize that reactive glia in the cervical cord release pro-inflammatory substances which drive chronic CNP. Thus a complex cascade of events spanning many cord segments underlies above-level CNP.

Local cold injury often induces hypersensitivity to cold and cold allodynia. Sensitisation of TRPM8 or TRPA1 could be the underlying mechanisms. This was evaluated by psychophysics and axon-reflex-flare induction following topical menthol and cinnamaldehyde application in cold injury patients and healthy subjects. The patients had no signs of neuropathy except cold allodynia. We applied 20% cinnamaldehyde and 40% menthol solutions in the cold-allodynic area of the patients and in a corresponding area in healthy subjects and obtained sensory ratings during application. Thermotesting and Laser Doppler Imaging were performed before and after exposure to the compounds. Menthol did not induce axon-reflex-erythema in patients or in controls. After menthol cold pain threshold was decreased in healthy subjects; however, no further sensitisation was observed in the patients moreover in some patients an amelioration of their cold allodynia was observed. Cinnamaldehyde-induced pain sensation did not differ between patients and controls. Heat pain thresholds following cinnamaldehyde were lowered to a similar extent in patients and controls (43-39.8 and 44-39 degrees C) and also the axon-reflex-flare responses were comparable. No evidence for sensitisation of responses to TRPM8 or TRPA1-stimulation was found in patients with cold injury-induced cold allodynia. The lack of TRPM8 induced axon-reflex indicates that also de-novo expression of TRPM8 on mechano-insensitive C-nociceptors does not underlie cold allodynia in these patients. We conclude from these data that the mechanisms for the induction of cold allodynia in the patients with cold injury are independent of TRPM8 or TRPA1 and differ therefore from neuropathic pain patients.

Background: Trigeminal neuralgia (TN) usually leads to paroxysms of short lasting but very severe pain. Between the attacks the patient is usually asymptomatic, but a constant dull background pain may persist in some cases. The mechanisms associated with the development of this chronic pain are not well understood., Objective: To determine trigeminal nociceptive fiber impairment in patients with TN comparing symptomatic and nonsymptomatic sides using the nociceptive blink reflex (nBR) and pain-related evoked potentials (PREP) and to identify possible central mechanisms of pain chronicity., Methods: We investigated 24 patients with TN without and 18 patients with TN with concomitant chronic facial pain. PREP and nBR were investigated following nociception specific electrical stimulation on both sides of the face and in each division of the trigeminal nerve (V1, V2, and V3)., Results: We found prolonged PREP and nBR latencies and reduced amplitudes comparing symptomatic and nonsymptomatic sides in all patients with TN. In patients with chronic facial pain, however, PREP amplitudes were larger and latencies shorter compared to patients with TN without facial pain, while nBR results were similar across groups., Conclusion: The data suggest an impairment of the trigeminal nociceptive system due to demyelination and/or axonal dysfunction on the symptomatic side and locate this defect close to the root entry zone in the brainstem. Moreover, central facilitation of trigeminal nociceptive processing was observed in patients with trigeminal neuralgia with concomitant chronic facial pain indicating overactivation of central sensory transmission. This may represent a possible adaptive mechanism for the development of chronic pain.

Halothane and isoflurane, in the peri-minimum alveolar anesthetic concentration (MAC) range, exert differential effects on spinal nociceptive neurons, whereby halothane further depresses their responses from 0.8 to 1.2 MAC, whereas isoflurane does not. We presently investigated if these anesthetics differentially affect windup, the progressive increase in neuronal responses to repetitive noxious stimuli, over a broad concentration range from 0 to 1.2 MAC. In decerebrated rats, single-unit recordings were made from dorsal horn neurons exhibiting windup to 20 1-Hz C-fiber strength electrical stimuli. Halothane and isoflurane (0, 0.4, 0.8, and 1.2 MAC) were tested in a counterbalanced crossover protocol. Increasing halothane and isoflurane from 0 to 1.2 MAC progressively suppressed the response to the first stimulus, as well as summed responses to all stimuli (to 34% +/- 8% and 50% +/- 8%, respectively; P < 0.05). Absolute windup (summed response minus 20x the first response) was suppressed by both anesthetics from 0 to 0.8 MAC, with further depression by halothane but not isoflurane at 1.2 MAC. Responses of neurons isolated at 0 MAC were partially, but never totally, depressed at 0.8 MAC. The dose-dependent suppression of windup is consistent with reduced temporal summation of pain. Further depression at 1.2 MAC halothane, but not isoflurane, suggests different sites of immobilizing action for these two anesthetics. Immobility seems to not be mediated by severe anesthetic depression of a subpopulation of nociceptive neurons.

Dysesthesia, allodynia, distal muscle weakness, and sensory impairment were noted in two patients with acute thallium intoxication. Two months later, nerve conduction studies showed an axonal degeneration. Sural nerve biopsy disclosed a decreased fiber density in the large myelinated fibers. Quantitative sensory testing also revealed an impairment of pinprick, temperature, and touch sensations. Cutaneous nerve biopsy confirmed a loss of epidermal nerves indicating an involvement of the small sensory nerves.

Study Design: Human cadaveric lumbar spines were used to assess the temperature and thermal dose distribution during intradiscal electrothermal therapy in vitro., Objectives: To determine whether intradiscal electrothermal therapy produces adequate tissue temperatures to denature annular collagen or ablate nerve cells., Summary of Background Data: Several hypothesized mechanisms for the effect of intradiscal electrothermal therapy have been suggested and include: 1) shrinkage of the nucleus and/or the annulus fibrosus by contraction of collagen fibers; and 2) thermal ablation of sensitive nerve fibers in the outer annulus., Methods: Intradiscal electrothermal therapy was performed using the standard clinical protocol on 12 lumbar specimens in a 37.0 degrees C water bath using the SpineCath by Oratec. Temperatures were recorded simultaneously at 40 different locations in the disc. Thermal dose (Equivalent Minutes 43.0 degrees C) was calculated at each temperature point., Results: The highest temperature measured (out of 520 points) was 64.0 degrees C and was within 1 mm of the heating coil. Temperatures in excess of 60 degrees C were all within 1 to 2 mm of the intradiscal electrothermal therapy catheter surface, the 50 to 60 degrees C range extended approximately 6 mm, above 48 degrees C extended approximately 7 mm, and above 45 degrees C extended to approximately 10 mm. Less than 2% of points achieved temperatures sufficient for collagen denaturation (>60 degrees C). On average, 42.5% of points accumulated >250 Equivalent Minutes 43.0 degrees C, a conservative common dose threshold for thermal necrosis of cells. The time history of thermal measurements demonstrated that the disc temperature had not reached steady state by the end of the heating protocol (16.5 minutes)., Conclusions: Except for a very limited margin (1-2 mm) around the catheter, the temperature necessary to induce collagen shrinkage was not observed within the disc. Temperatures sufficient to ablate nerves were developed in some areas but were not reliably produced in clinically relevant regions, such as the posterior annulus. These results suggest that beneficial clinical outcomes may be critically dependent on probe placement or other factors unknown.

We investigated the integrity of the ascending pathways for pain sensitivity in the early stage of type 1 diabetes mellitus, by measuring the N1 component and the conventional N2/P2 vertex potentials of laser evoked potentials (LEPs). Brain responses to laser stimuli were obtained in 21 healthy volunteers and 21 type 1 diabetic patients, without either clinical neuropathy or electrophysiological evidence of large-fiber damage. In diabetic patients N1 and P2 latencies were prolonged and the N1 and N2/P2 amplitudes were decreased after foot stimulation. A significant reduction of the conduction velocity of Adelta fibers in the lower limbs was also observed. LEPs reveal an early, subclinical and selective damage of pain sensation in diabetic patients. N1 and P2 potentials are delayed and decreased in parallel giving evidence that LEP abnormalities are not secondary to a cognitive dysfunction and mostly reflect a small-fiber dysfunction.

Skin biopsies that are immunostained to identify nerve fibers provide a new tool for assessing the small caliber nociceptors that terminate in the epidermis, as well as other cutaneous nerve fibers. Skin biopsies can be performed in multiple sites and can be repeated over time, so that a spatiotemporal profile of epidermal innervation can be constructed. This approach may help assess the progression of fiber loss in disease and of regeneration and re-innervation with treatment.

Objective: To assess the distribution and type of nerve fibers present in human peritoneal adhesions and to relate data on location and size of nerves with estimated age and with clinical parameters such as reports of chronic pelvic pain., Summary Background Data: Peritoneal adhesions are implicated in the cause of chronic abdominopelvic pain, and many patients are relieved of their symptoms after adhesiolysis. Adhesions are thought to cause pain indirectly by restricting organ motion, thus stretching and pulling smooth muscle of adjacent viscera or the abdominal wall. However, in mapping studies using microlaparoscopic techniques, 80% of patients with pelvic adhesions reported tenderness when these structures were probed, an observation suggesting that adhesions themselves are capable of generating pain stimuli., Methods: Human peritoneal adhesions were collected from 25 patients undergoing laparotomy, 20 of whom reported chronic pelvic pain. Tissue samples were prepared for histologic, immunohistochemical, and ultrastructural analysis. Nerve fibers were characterized using antibodies against several neuronal markers, including those expressed by sensory nerve fibers. In addition, the distribution of nerve fibers, their orientation, and their association with blood vessels were investigated by acetylcholinesterase histochemistry and dual immunolocalization., Results: Nerve fibers, identified histologically, ultrastructurally, and immunohistochemically, were present in all the peritoneal adhesions examined. The location of the adhesion, its size, and its estimated age did not influence the type of nerve fibers found. Further, fibers expressing the sensory neuronal markers calcitonin gene-related protein and substance P were present in all adhesions irrespective of reports of chronic abdominopelvic pain. The nerves comprised both myelinated and nonmyelinated axons and were often, but not invariably, associated with blood vessels., Conclusions: This study provides the first direct evidence for the presence of sensory nerve fibers in human peritoneal adhesions, suggesting that these structures may be capable of conducting pain after appropriate stimulation.

The mechanisms of chronic neuropathic pain are not well understood. Postherpetic neuralgia (PHN), which occurs in some patients after shingles (herpes zoster), was used to investigate the neural determinants of chronic pain. Skin biopsies were obtained from 38 adults with or without PHN at least 3 months after healing of shingles on the torso. Vertical sections were immunolabeled against PGP9.5, a pan-axonal marker, to measure the density of remaining nerve endings in skin previously affected by shingles. All axons that end in the epidermis are nociceptors, neurons that transmit pain messages. The densities ranged between 2 and 3976 neurites/mm2 skin surface, but the overlap between subjects and without PHN was small. Of 19 subjects without PHN, 17 had more than 670 neurites/mm2 skin surface area (mean +/- SEM = 1569 +/- 230), and 18 of 19 subjects with PHN had 640 or fewer neurites/mm2 (mean +/- SEM = 367 +/- 92). PHN may be a 'phantom-skin' pain associated with loss of nociceptors. This threshold of approximately 650 neurites/mm2 skin surface was not detected in previous studies that used summary statistics. It implies that the absence of pain after shingles may require the preservation of a minimum density of primary nociceptive neurons, and that the density of epidermal innervation may provide an objective correlate for the presence or absence of PHN pain.

Patients with peripheral neuropathy have symptoms involving small-diameter nociceptive nerves and elevated thermal thresholds. Nociceptive nerves terminate in the epidermis of the skin and are readily demonstrated with the neuronal marker, protein gene product 9.5 (PGP 9.5). To investigate the pathological characteristics of elevated thermal thresholds, we performed PGP 9.5 immunocytochemistry on 3 mm punch skin biopsies (the forearm and the leg) from 55 normal subjects and 35 neuropathic patients. Skin innervation was evaluated by quantifying epidermal nerve densities. Epidermal nerve densities were reduced in neuropathic patients compared to normal subjects. Epidermal nerve densities were variably correlated with thermal thresholds. The proportion of neuropathic patients with reduced epidermal nerve densities was larger than the proportion of neuropathic patients with elevated thermal thresholds. These results indicated that degeneration of epidermal nerve terminals preceded the elevation of thermal thresholds. Skin biopsy together with immunocytochemical demonstration of epidermal innervation offers a new approach to evaluate small-fiber sensory neuropathy.

Study Design: A study of the relation between the development of mechanical allodynia and the reorganization of primary afferent terminals in the sensory lamina of the rat spinal cord dorsal horn after partial dorsal root ganglion injury in rats., Objectives: To investigate the pathologic mechanisms of mechanical allodynia after partial dorsal root ganglion injury., Summary of Background Data: After experimental peripheral nerve injury causing neuropathic pain, myelinated afferent fibers sprout into lamina II of the dorsal horn. This lamina is associated with nociceptive-specific neurons that generally are not stimulated by myelinated fiber input from mechanical receptors. These morphologic changes are suggested to have significance in the pathogenesis of chronic mechanical allodynia, although it is not known whether this kind of morphologic change occurs after dorsal root ganglion injury., Methods: After partial dorsal root ganglion crush injury, the mechanical force causing footpad withdrawal was measured with von Frey hairs, and myelinated primary afferents were labeled with cholera toxin B subunit horseradish peroxidase, a selective myelinated fiber tracer that identifies transganglionic synapses., Results: After partial dorsal root ganglion injury, mechanical allodynia developed in the corresponding footpad within 3 days and persisted throughout the experimental period. At 2 and 4 weeks after the injury, B subunit horseradish peroxidase-positive fibers, presumably myelinated afferents, were observed to be sprouting into lamina II of the dorsal horn on the injured side, but not on the contralateral control side., Conclusions: Morphologic change in spinal cord dorsal horn lamina II occurs after partial dorsal root ganglion injury. This change may have significance in the pathogenesis of chronic mechanical allodynia after partial dorsal root ganglion injury.