[Bavarian online database for corona screening tests-development and use of a digital solution in the pandemic]. / Bayerisches Meldeportal für Corona-Reihenuntersuchungen ­ Entwicklung und Einsatz einer digitalen Lösung in der Pandemie.

During the SARS-CoV­2 pandemic, various data had to be collected to support political decisions for pandemic preparedness and response. Nevertheless, using analogue tools like paper and pencil as well as sending files with media discontinuity that have to be merged later are not useful and can hardly provide usable data in real time. With the selected system architecture, the Bavarian Online Database for Corona Screening Tests (BayCoRei) is a central, Bavaria-wide, consistent digital solution that is agile and easy to use. BayCoRei uses established technical components and interfaces. Apart from this, the support of the individual stakeholders (e.g., health authorities, service providers, and district governments) plays a decisive role in the success of the solution. The present article describes BayCoRei and two other online databases as examples that comprise the technology and architecture that have proven to be (rapidly) deployable and points out the gap between intention and reality regarding pandemic management.

Aligning recycling behaviors and the recycling system - Towards a full cycle of materials and behavioral methods.

In a transdisciplinary project with the Municipality of Trelew (Argentina), we assessed barriers to households disposing of separated waste, developed supportive behavioral interventions, tested the interventions in a randomized controlled trial, and supported the Municipality in upscaling the most successful and cost-effective intervention to a total of 20,000 households. The interventions were designed to address the three main barriers to waste separation detected through a baseline study: a lack of knowledge on how separation works; the additional hassle it represents; and the self-regulation challenge it poses. The interventions consisted of envelopes containing simplifying information, empathetic messages, a magnetic calendar acting as a reminder, or a combination thereof. The interventions roughly halved the prevalence of bags containing unusable mixed waste two weeks after the intervention. This impact was still present after six months. We did not find evidence for an additional effect of empathetic messages or the reminder. Based on these results, the simplified information intervention was rolled out. The results provide evidence of the high potential of using the full range of behavioral methods to increase sustainable behaviors, particularly in the context of limited options to adapt the waste management system as such.

Evaluation of Screening Tests in Bavarian Healthcare Facilities during the Second Wave of the SARS-CoV-2 Pandemic.

Due to the lack of data on asymptomatic SARS-CoV-2-positive persons in healthcare institutions, they represent an inestimable risk. Therefore, the aim of the current study was to evaluate the first 1,000,000 reported screening tests of asymptomatic staff, patients, residents, and visitors in hospitals and long-term care (LTC) facilities in the State of Bavaria over a period of seven months. Data were used from the online database BayCoRei (Bavarian Corona Screening Tests), established in July 2020. Descriptive analyses were performed, describing the temporal pattern of persons that tested positive for SARS-CoV-2 by real-time polymerase chain reaction (RT-PCR) or antigen tests, stratified by facility. Until 15 March 2021, this database had collected 1,038,146 test results of asymptomatic subjects in healthcare facilities (382,240 by RT-PCR, and 655,906 by antigen tests). Of the RT-PCR tests, 2.2% (n = 8380) were positive: 3.0% in LTC facilities, 2.2% in hospitals, and 1.2% in rehabilitation institutions. Of the antigen tests, 0.4% (n = 2327) were positive: 0.5% in LTC facilities, and 0.3% in both hospitals and rehabilitation institutions, respectively. In LTC facilities and hospitals, infection surveillance using RT-PCR tests, or the less expensive but less sensitive, faster antigen tests, could facilitate the long-term management of the healthcare workforce, patients, and residents.

A hospital-wide initiative to eliminate or reduce needle pain in children using lean methodology.

INTRODUCTION: Pain remains common, underrecognized, and undertreated in children's hospitals and pediatric clinics. Over 200,000 patients experience needle pain annually in our institution, caused by blood draws, intravenous access, vaccinations, and injections on all inpatient units, emergency departments, outpatient laboratories, and ambulatory clinics. OBJECTIVES: We implemented a hospital-based, system-wide initiative called the "Children's Comfort Promise," and created a new standard of care for needle procedures that required staff to consistently offer 4 strategies: (1) topical anesthetics, (2) sucrose or breastfeeding for infants 0 to 12 months, (3) comfort positioning (including swaddling, skin-to-skin, or facilitated tucking for infants; sitting upright for children), and (4) age-appropriate distraction. METHODS: The protocol was established system-wide in one of the largest children's hospitals in the United States using a staggered implementation approach over a 3-year period to allow for unit-specific customization and facilitation of knowledge transfer from one unit to another. All departments were required to offer all 4 strategies with appropriate education at least 95% of the time. RESULTS: Comparison of baseline audits with continuous postimplementation audits revealed that wait times for services decreased, patient satisfaction increased, and staff concerns about implementation were allayed (eg, concerns about wait times and success rates of venipuncture after topical anesthesia). CONCLUSION: This is the first report of a successful system-wide protocol implementation to reduce or eliminate needle pain, including pain from vaccinations, in a children's hospital across all inpatient units, emergency departments, outpatient laboratories, and ambulatory clinics through consistent use of topical anesthesia, sucrose/breastfeeding, positioning, and distraction.

NaV1.7 and pain: contribution of peripheral nerves.

The sodium channel NaV1.7 contributes to action potential (AP) generation and propagation. Loss-of-function mutations in patients lead to congenital indifference to pain, though it remains unclear where on the way from sensory terminals to central nervous system the signalling is disrupted. We confirm that conditional deletion of NaV1.7 in advillin-expressing sensory neurons leads to impaired heat and mechanical nociception in behavioural tests. With single-fiber recordings from isolated skin, we found (1) a significantly lower prevalence of heat responsiveness to normally mechanosensitive C-fibers, although (2) the rare heat responses seemed quite vigorous, and (3) heat-induced calcitonin gene-related peptide release was normal. In biophysical respects, although electrical excitability, rheobase, and chronaxy were normal, (4) axonal conduction velocity was 20% slower than in congenic wild-type mice (5) and when challenged with double pulses (<100 milliseconds interval), the second AP showed more pronounced latency increase (6). On prolonged electrical stimulation at 2 Hz, (7) activity-dependent slowing of nerve fiber conduction was markedly less, and (8) was less likely to result in conduction failure of the mutant single fibers. Finally, recording of compound APs from the whole saphenous nerve confirmed slower conduction and less activity-dependent slowing as well as the functional absence of a large subpopulation of C-fibers (9) in conditional NaV1.7 knockouts. In conclusion, the clear deficits in somatic primary afferent functions shown in our study may be complemented by previously reported synaptic dysfunction and opioidergic inhibition, together accounting for the complete insensitivity to pain in the human mutants lacking NaV1.7.

Reduced excitability and impaired nociception in peripheral unmyelinated fibers from Nav1.9-null mice.

The upregulation of the tetrodotoxin-resistant voltage-gated sodium channel NaV1.9 has previously been associated with inflammatory hyperalgesia. Na1.9 knockout (KO) mice, however, did not seem insensitive in conventional tests of acute nociception. Using electrophysiological, neurochemical, and behavioral techniques, we now show NaV1.9-null mice exhibit impaired mechanical and thermal sensory capacities and reduced electrical excitability of nociceptors. In single-fiber recordings from isolated skin, the electrical threshold of NaV1.9 KO C fibers was elevated by 55% and the median von Frey threshold was 32 mN in contrast to 8 mN in wild types (WTs). The prevalence of C mechano-heat-sensitive (CMH) fibers was only 25.6% in NaV1.9 KO animals compared to 75.8% in the WT group, and the heat threshold of these CMH fibers was 40.4°C in the control vs 44°C in the KO group. Compound action potential recordings from isolated sciatic nerve segments of NaV1.9 KO mice revealed lower activity-induced slowing of conduction velocity upon noxious heat stimulation: 8% vs 30% in WTs. Heat-induced calcitonin gene-related peptide release from the skin was less in the KO than in the WT group. The reduced noxious heat sensitivity was finally confirmed with the Hargreaves test using 2 rates of radiant heating of the plantar hind paws. In conclusion, NaV1.9 presumably contributes to acute thermal and mechanical nociception in mice, most likely through increasing the excitability but probably also by amplifying receptor potentials irrespective of the stimulus modality.

Use dependence of peripheral nociceptive conduction in the absence of tetrodotoxin-resistant sodium channel subtypes.

KEY POINTS: This study examines conduction in peripheral nerves and its use dependence in tetrodotoxin-resistant (TTXr) sodium channel (Nav 1.8, Nav 1.9) knockout and wildtype animals. We observed use-dependent decreases of single fibre and compound action potential amplitude in peripheral mouse C-fibres (wildtype). This matches the previously published hypothesis that increased Na/K-pump activity is not the underlying mechanism for use-dependent changes of neural conduction. Knocking out TTXr sodium channels influences use-dependent changes of conductive properties (action potential amplitude, latency, conduction safety) in the order Nav 1.8 KO > Nav 1.9KO > wildtype. This is most likely explained by different subsets of presumably (relatively) Nav 1.7-rich conducting fibres in knockout animals as compared to wildtypes, in combination with reduced per-pulse sodium influx. ABSTRACT: Use dependency of peripheral nerves, especially of nociceptors, correlates with receptive properties. Slow inactivation of voltage-gated sodium channels has been discussed to be the underlying mechanism - pointing to a receptive class-related difference of sodium channel equipment. Using electrophysiological recordings of single unmyelinated cutaneous fibres and their compound action potential (AP), we evaluated use-dependent changes in mouse peripheral nerves, and the contribution of the tetrodotoxin-resistant (TTXr) sodium channels Nav 1.8 and Nav 1.9 to these changes. Nerve fibres were electrically stimulated using single or double pulses at 2 Hz. Use-dependent changes of latency, AP amplitude, and duration as well as the fibres' ability to follow the stimulus were evaluated. AP amplitudes substantially diminished in used fibres from C57BL/6 but increased in Nav 1.8 knockout (KO) mice, with Nav 1.9 KO in between. Activity-induced latency slowing was in contrast the most pronounced in Nav 1.8 KOs and the least in wildtype mice. The genotype was also predictive of how long fibres could follow the double pulsed stimulus with wildtype fibres blocking first and Nav 1.8 KO fibres enduring the longest. In contrast, changes in spike duration were less pronounced and displayed no significant tendency. Thus, all major measures of peripheral nerve accommodation (amplitude, latency and durability) depended on genotype. All use-dependent changes appeared in the order NaV 1.8 KO > NaV 1.9 KO > wildtype, which is most likely explained by the relative contribution of Nav 1.7 varying in the same order and the amounts of per-pulse sodium influx expected in the opposite order.

Analgesic Effects of GpTx-1, PF-04856264 and CNV1014802 in a Mouse Model of NaV1.7-Mediated Pain.

Loss-of-function mutations of Na(V)1.7 lead to congenital insensitivity to pain, a rare condition resulting in individuals who are otherwise normal except for the inability to sense pain, making pharmacological inhibition of Na(V)1.7 a promising therapeutic strategy for the treatment of pain. We characterized a novel mouse model of Na(V)1.7-mediated pain based on intraplantar injection of the scorpion toxin OD1, which is suitable for rapid in vivo profiling of Na(V)1.7 inhibitors. Intraplantar injection of OD1 caused spontaneous pain behaviors, which were reversed by co-injection with Na(V)1.7 inhibitors and significantly reduced in Na(V)1.7(-/-) mice. To validate the use of the model for profiling Na(V)1.7 inhibitors, we determined the Na(V) selectivity and tested the efficacy of the reported Na(V)1.7 inhibitors GpTx-1, PF-04856264 and CNV1014802 (raxatrigine). GpTx-1 selectively inhibited Na(V)1.7 and was effective when co-administered with OD1, but lacked efficacy when delivered systemically. PF-04856264 state-dependently and selectively inhibited Na(V)1.7 and significantly reduced OD1-induced spontaneous pain when delivered locally and systemically. CNV1014802 state-dependently, but non-selectively, inhibited Na(V) channels and was only effective in the OD1 model when delivered systemically. Our novel model of Na(V)1.7-mediated pain based on intraplantar injection of OD1 is thus suitable for the rapid in vivo characterization of the analgesic efficacy of Na(V)1.7 inhibitors.

Specific changes in conduction velocity recovery cycles of single nociceptors in a patient with erythromelalgia with the I848T gain-of-function mutation of Nav1.7.

Seven patients diagnosed with erythromelalgia (EM) were investigated by microneurography to record from unmyelinated nerve fibers in the peroneal nerve. Two patients had characterized variants of sodium channel Nav1.7 (I848T, I228M), whereas no mutations of coding regions of Navs were found in 5 patients with EM. Irrespective of Nav1.7 mutations, more than 50% of the silent nociceptors in the patients with EM showed spontaneous activity. In the patient with mutation I848T, all nociceptors, but not sympathetic efferents, displayed enhanced early subnormal conduction in the velocity recovery cycles and the expected late subnormality was reversed to supranormal conduction. The larger hyperpolarizing shift of activation might explain the difference to the I228M mutation. Sympathetic fibers that lack Nav1.8 did not show supranormal conduction in the patient carrying the I848T mutation, confirming in human subjects that the presence of Nav1.8 crucially modulates conduction in cells expressing EM mutant channels. The characteristic pattern of changes in conduction velocity observed in the patient with the I848T gain-of function mutation in Nav1.7 could be explained by axonal depolarization and concomitant inactivation of Nav1.7. If this were true, activity-dependent hyperpolarization would reverse inactivation of Nav1.7 and account for the supranormal CV. This mechanism might explain normal pain thresholds under resting conditions.

C-fiber recovery cycle supernormality depends on ion concentration and ion channel permeability.

Following each action potential, C-fiber nociceptors undergo cyclical changes in excitability, including a period of superexcitability, before recovering their basal excitability state. The increase in superexcitability during this recovery cycle depends upon their immediate firing history of the axon, but also determines the instantaneous firing frequency that encodes pain intensity. To explore the mechanistic underpinnings of the recovery cycle phenomenon a biophysical model of a C-fiber has been developed. The model represents the spatial extent of the axon including its passive properties as well as ion channels and the Na/K-ATPase ion pump. Ionic concentrations were represented inside and outside the membrane. The model was able to replicate the typical transitions in excitability from subnormal to supernormal observed empirically following a conducted action potential. In the model, supernormality depended on the degree of conduction slowing which in turn depends upon the frequency of stimulation, in accordance with experimental findings. In particular, we show that activity-dependent conduction slowing is produced by the accumulation of intraaxonal sodium. We further show that the supernormal phase results from a reduced potassium current Kdr as a result of accumulation of periaxonal potassium in concert with a reduced influx of sodium through Nav1.7 relative to Nav1.8 current. This theoretical prediction was supported by data from an in vitro preparation of small rat dorsal root ganglion somata showing a reduction in the magnitude of tetrodotoxin-sensitive relative to tetrodotoxin -resistant whole cell current. Furthermore, our studies provide support for the role of depolarization in supernormality, as previously suggested, but we suggest that the basic mechanism depends on changes in ionic concentrations inside and outside the axon. The understanding of the mechanisms underlying repetitive discharges in recovery cycles may provide insight into mechanisms of spontaneous activity, which recently has been shown to correlate to a perceived level of pain.

Pain Outcomes in a US Children's Hospital: A Prospective Cross-Sectional Survey.

BACKGROUND AND OBJECTIVES: Pain in hospitalized children may be underrecognized and undertreated. The objective of this survey was to benchmark pain prevalence, intensity, assessment, and pharmacologic as well as integrative treatment of pain in inpatients in a US children's hospital. METHODS: This was a single-day, cross-sectional survey and electronic medical record review of inpatients who received medical care at a pediatric hospital. Inpatients and emergency department patients were asked to report their experience with pain and its management during the previous 24 hours. RESULTS: Of 279 inpatients listed on the morning census, 178 children and parents were located and completed the survey. Seventy-six percent had experienced pain during the previous 24 hours, usually acute or procedural pain, 12% of whom possibly suffered from chronic pain. Twenty percent of all children surveyed experienced moderate and 30% severe pain in that time period. The worst pain reported by patients was caused by needle pokes (40%), followed by trauma/injury (34%). Children and their parents rated 5 integrative, nonpharmacologic modalities as more effective than medications. Pain assessments and management were documented in the medical record for 58% of patients covering the 24-hour period before the morning census. The most commonly prescribed analgesics were acetaminophen, morphine, and ibuprofen. CONCLUSIONS: Despite existing hospital policies and a pain consult team, significant room for improvement in pain management was identified. A hospital-wide, 3-year Lean quality improvement initiative on reducing pain was commenced as a result of this survey.

Bisphenol A binds to the local anesthetic receptor site to block the human cardiac sodium channel.

Bisphenol A (BPA) has attracted considerable public attention as it leaches from plastic used in food containers, is detectable in human fluids and recent epidemiologic studies link BPA exposure with diseases including cardiovascular disorders. As heart-toxicity may derive from modified cardiac electrophysiology, we investigated the interaction between BPA and hNav1.5, the predominant voltage-gated sodium channel subtype expressed in the human heart. Electrophysiology studies of heterologously-expressed hNav1.5 determined that BPA blocks the channel with a K(d) of 25.4±1.3 µM. By comparing the effects of BPA and the local anesthetic mexiletine on wild type hNav1.5 and the F1760A mutant, we demonstrate that both compounds share an overlapping binding site. With a key binding determinant thus identified, an homology model of hNav1.5 was generated based on the recently-reported crystal structure of the bacterial voltage-gated sodium channel NavAb. Docking predictions position both ligands in a cavity delimited by F1760 and contiguous with the DIII-IV pore fenestration. Steered molecular dynamics simulations used to assess routes of ligand ingress indicate that the DIII-IV pore fenestration is a viable access pathway. Therefore BPA block of the human heart sodium channel involves the local anesthetic receptor and both BPA and mexiletine may enter the closed-state pore via membrane-located side fenestrations.

Time course of acetylcholine-induced activation of sympathetic efferents matches axon reflex sweating in humans.

Action potentials from postganglionic C-fibres were recorded in healthy volunteers by microneurography in the peroneal nerve. Their responsiveness to mechanical or heat stimuli or to sympathetic reflex provocation tests was determined by transient slowing of conduction velocity following activation. Twenty units were classified as sympathetic efferent units. Acetylcholine (ACh) iontophoresis (10%, 1 mA, 1 min) inside their innervation territory activated 8 of 20 sympathetic fibres with a mean delay of 61 ± 12 s, peak response at 175 ± 38 s, and a duration of 240 ± 42 s, whereas iontophoresis of saline did not activate any of them. The time course of neuronal activation correlated with the axon reflex sweating measured by an evaporimeter in a separate session (delay 76 ± 9 s, peak at 195 ± 12 s, decline to 50% of peak 312 ± 25 s). No ACh-induced vasoconstriction was observed by laser Doppler scanning (n = 11) even after depletion of neuropeptides by chronic topical capsaicin treatment (n = 8). We conclude that ACh iontophoresis activates about half of the sympathetic fibres in human skin and provokes a corresponding axon reflex sweating. The absence of ACh-induced vasoconstriction even after the depletion of neuropeptides by capsaicin suggests that only sudomotor fibres, but not sympathetic vasoconstrictor fibres are activated by this stimulus.

The human vasodilator axon reflex - an exclusively peripheral phenomenon?

The effect of regional anesthesia of the brachial plexus on the size and intensity of the histamine-induced axon reflex flare (neurogenic inflammation) of the forearm and the upper arm was compared to that of the contralateral arm as control in humans. No changes in the axon reflex could be assessed. Thus the lateral spread of the axon reflex flare must be transmitted by peripheral nerve branches not affected by the anesthesia in the axilla. This excludes the existence of physiologically relevant amounts of proximal branchpoints, DRG neurons with multiple peripheral axons or spinal interneurons transmitting action potentials between peripheral C-afferents involved in the axon reflex flare. Mechanoinsensitive C-fibres are known to be activated by histamine and to be responsible for the neuropeptide release in the skin inducing the axon reflex flare. Reports on those proximal connections can therefore obviously not extend to mechanoinsensitive C-fibres and do not explain the origin of neurogenic inflammation in humans without prior sensitization.

Response of human oral mucosa and skin to histamine provocation: laser Doppler perfusion imaging discloses differences in the nociceptive nervous system.

OBJECTIVE: To investigate the existence of histamine-excitable nerve fibers in the oral mucosa and to compare the response to histamine provocation in healthy volunteers with that in a small group of patients with chronic oral pain. MATERIAL AND METHODS: Thirteen healthy volunteers and six patients suffering from chronic oral pain took part in the study. Blood perfusion was monitored in the hard palate, the tongue, and the skin of the cheek using laser Doppler perfusion imaging (Perimed; Sweden). Baseline scannings were performed, followed by 15 scannings after iontophoresis of histamine (1%). A free description of the sensations was then obtained from the participants after finishing the measurements. RESULTS: Compared to pre-histamine scanning, histamine application resulted in a considerable increase in blood perfusion in all regions (p<0.001) that was significantly higher in skin than in oral mucosa (p<0.001). There were no significant differences between the healthy volunteers and the patients regarding baseline blood flow, increased blood perfusion, or flare size after histamine provocation. The sensory impression was reported to be more persistent and intense in the skin than in the oral mucosa. No effect on mucosa could be detected by visual inspection. CONCLUSIONS: Intra-oral flare could be induced by activating histamine-excitable nerve fibers. Both duration and intensity of the flare were considerably less pronounced than in the control skin site. Histamine application was not clearly associated with itch.

Endothelin 1 activates and sensitizes human C-nociceptors.

Microneurography was used to record action potentials from afferent C-fibers in cutaneous fascicles of the peroneal nerve in healthy volunteers. Afferent fibers were classified according to their mechanical responsiveness to von Frey stimulation (75g) into mechano-responsive and mechano-insensitive nociceptors. Various concentrations of Endothelin1 (ET1) and Histamine were injected into the receptive fields of C-fibers. Activation and heat sensitization were monitored. Axon reflex flare and psychophysical ratings were assessed after injection of ET1 and codeine into the forearms after pre-treatment with an H1 blocker or sodium chloride. 65% of mechanosensitive nociceptors were activated by ET1. One-third showed long lasting responses (>15min). In contrast, none of thirteen mechano-insensitive fibers were activated. Sensitization to heat was observed in 62% of mechanosensitive and in 46% of mechano-insensitive fibers. Injection of ET1 produced a widespread axon reflex flare, which was suppressed by pre-treatment with an H1 receptor blocker. In addition, pain sensations were induced more often than itching by ET1 in contrast to codeine. No wheal was observed after injection of ET1. Both itching and pain were decreased after H1 blocker treatment. In summary: (1) In humans ET1 activates mechanosensitive, but not mechano-insensitive, nociceptors. (2) Histamine released from mast cells is not responsible for all effects of ET1 on C-nociceptors. (3) ET1 could have a differential role in pain compared to other chemical algogens which activate additionally or even predominantly mechano-insensitive fibers.

Abnormal function of C-fibers in patients with diabetic neuropathy.

The mechanisms underlying the development of painful and nonpainful neuropathy associated with diabetes mellitus are unclear. We have obtained microneurographic recordings from unmyelinated fibers in eight patients with diabetes mellitus, five with painful neuropathy, and three with neuropathy without pain. All eight patients had large-fiber neuropathy, and seven patients had pathological thermal thresholds in their feet, indicating the involvement of small-caliber nerve fibers. A total of 163 C-fibers were recorded at knee level from the common peroneal nerve in the patients (36-67 years old), and these were compared with 77 C-fibers from healthy controls (41-64 years old). The ratio of mechano-responsive to mechano-insensitive nociceptors was approximately 2:1 in the healthy controls, whereas in the patients, it was 1:2. In patients, a fairly large percentage of characterized fibers (12.5% in nonpainful and 18.9% in painful neuropathy) resembled mechano-responsive nociceptors that had lost their mechanical and heat responsiveness. Such fibers were rarely encountered in age-matched controls (3.2%). Afferent fibers with spontaneous activity or mechanical sensitization were found in both patient groups. We conclude that small-fiber neuropathy in diabetes affects receptive properties of nociceptors that leads to an impairment of mechano-responsive nociceptors.

Mechanically induced axon reflex and hyperalgesia in human UV-B burn are reduced by systemic lidocaine.

The mechanisms for the induction of primary mechanical hyperalgesia are unclear. We analyzed the neurogenic axon reflex erythema (flare) following phasic mechanical stimulation in normal and in UV-B irradiated skin. In a cross-over double blind design (n = 10), low dose of systemic lidocaine suppressed mechanical hyperalgesia in sunburned skin and in the mechanically induced flare. Phasic mechanical stimulation, even at painful intensities, did not evoke a flare reaction in normal skin. However, stimulation within the UV-B burn dose-dependently provoked an immediate flare reaction. Systemic lidocaine suppressed the mechanically induced flare as well as the mechanical hyperalgesia in sunburned skin, while leaving the impact-induced ratings in normal skin unchanged. Systemic lidocaine reduced these effects of sensitization, but did not reduce ratings in normal skin. As mechanically insensitive ("sleeping") nociceptors have been shown to mediate the axon-reflex in human skin, sensitization of this class of nociceptors might contribute also to the UV-B-induced primary mechanical hyperalgesia.

Pathological C-fibres in patients with a chronic painful condition.

Little is known about the contribution of C-afferent fibres to chronic painful conditions in humans. We sought to investigate the role of C-fibres in the pathophysiology of pain and hyperalgesia in erythromelalgia as a model disease for chronic pain. Erythromelalgia is a condition characterized by painful, red and hot extremities, and patients often report tenderness on walking. We made microneurographic recordings from single C-fibres in cutaneous fascicles of the peroneal nerve in patients suffering from this disease. All patients had had a pain attack recently and psychophysical signs of allodynia and punctate hyperalgesia were found. We obtained recordings from a total of 103 C-fibres and found significantly lower conduction velocities and increased activity-dependent slowing of the conduction velocity of afferent C-fibres in the patients compared with healthy controls. Furthermore, several units with biophysical properties of mechano-insensitive fibres were pathological, being spontaneously active or sensitized to mechanical stimuli. Since these fibres also mediate the axon reflex flare, their hyperexcitability might account not only for ongoing pain and tenderness but also for redness and warming in this pain syndrome. The changes in conductive properties found in the C-fibres of these patients could be the first signs of a small-fibre neuropathy. This is the first systematic study of single C-fibres in patients and it shows an active contribution of mechano-insensitive fibres to chronic pain.