Light Brush Research Articles

Peripheral Mechanobiology of Touch-Studies on Vertebrate Cutaneous Sensory Corpuscles.

The vertebrate skin contains sensory corpuscles that are receptors for different qualities of mechanosensitivity like light brush, touch, pressure, stretch or vibration. These specialized sensory organs are linked anatomically and functionally to mechanosensory neurons, which function as low-threshold mechanoreceptors connected to peripheral skin through Aβ nerve fibers. Furthermore, low-threshold mechanoreceptors associated with Aδ and C nerve fibers have been identified in hairy skin. The process of mechanotransduction requires the conversion of a mechanical stimulus into electrical signals (action potentials) through the activation of mechanosensible ion channels present both in the axon and the periaxonal cells of sensory corpuscles (i.e., Schwann-, endoneurial- and perineurial-related cells). Most of those putative ion channels belong to the degenerin/epithelial sodium channel (especially the family of acid-sensing ion channels), the transient receptor potential channel superfamilies, and the Piezo family. This review updates the current data about the occurrence and distribution of putative mechanosensitive ion channels in cutaneous mechanoreceptors including primary sensory neurons and sensory corpuscles.

Changes in Neuronal Activity in the Anterior Cingulate Cortex and Primary Somatosensory Cortex With Nonlinear Burst and Tonic Spinal Cord Stimulation

Although nonlinear burst and tonic SCS are believed to treat neuropathic pain via distinct pain pathways, the effectiveness of these modalities on brain activity in vivo has not been investigated. This study compared neuronal firing patterns in the brain after nonlinear burst and tonic SCS in a rat model of painful radiculopathy. Neuronal activity was recorded in the ACC or S1 before and after nonlinear burst or tonic SCS on day 7 following painful cervical nerve root compression (NRC) or sham surgery. The amplitude of nonlinear burst SCS was set at 60% and 90% motor threshold to investigate the effect of lower amplitude SCS on brain activity. Neuronal activity was recorded during and immediately following light brush and noxious pinch of the paw. Change in neuron firing was measured as the percent change in spikes post-SCS relative to pre-SCS baseline. ACC activity decreases during brush after 60% nonlinear burst compared to tonic (p < 0.05) after NRC and compared to 90% nonlinear burst (p < 0.04) and pre-SCS baseline (p < 0.03) after sham. ACC neuron activity decreases (p < 0.01) during pinch after 60% and 90% nonlinear burst compared to tonic for NRC. The 60% of nonlinear burst decreases (p < 0.02) ACC firing during pinch in both groups compared to baseline. In NRC S1 neurons, tonic SCS decreases (p < 0.01) firing from baseline during light brush; 60% nonlinear burst decreases (p < 0.01) firing from baseline during brush and pinch. Nonlinear burst SCS reduces firing in the ACC from a painful stimulus; a lower amplitude nonlinear burst appears to have the greatest effect. Tonic and nonlinear burst SCS may have comparable effects in S1.

Test-Retest and Inter-Examiner Reliability of a Novel Bedside Quantitative Sensory Testing Battery in Postherpetic Neuralgia Patients

In health and disease, the somatosensory system has been interrogated with standardized research techniques, collectively referred to as quantitative sensory testing (QST). In neuropathic pain, QST has been used to characterize multiple sensory derangements. However, the use of QST outside the lab has been limited by several factors, including a lack of standardization, variability in procedural technique, and duration of testing that would be unacceptable for clinic. To address these shortcomings, the Neuropathic Pain Research Consortium designed an easy and low-cost “bedside” QST procedure. To test the hypothesis that this procedure would be clinically reliable over time and across different examiners, a multisite, blinded study was performed in subjects with postherpetic neuralgia. Generally, agreement between 2 examiners and over 2 study visits with 1 examiner was high. Additionally, intraclass correlation coefficients and Kappa statistics calculated showed that the battery of QST tests included were highly reliable. Interestingly, mechanical modalities (light brush, pinprick, pressure, and vibration) showed the highest reliability. The least reliable modalities were cool (room temperature) and warmth (38°C). These data demonstrate that the Neuropathic Pain Research Consortium beside QST protocol is reliable across examiner and over time, providing a validated QST tool for use in clinical practice and clinical trials. PerspectiveThis blinded, multicenter trial in 32 patients with postherpetic neuralgia demonstrates bedside QST is reliable and suitable as a clinical trial outcome. The novel bedside battery could be used in clinical trials or in clinical practice over time given the reliability data presented in this article.

The effects of using soil protective mats of varying compositions and amounts on the intensity of soil disturbances caused by machine traffic

ABSTRACTWe quantified the effectiveness of different soil protective mat compositions (brush, sawdust, combination of brush and sawdust) and densities (light density of 10 kg m−2 and heavy density of 20 kg m−2) on compaction and rutting on skid trails in mountainous forests following one, four, and 10 machine passes on two trail gradient classes (≤ 20% and > 20%). Soil bulk density and rut depth increased markedly with traffic frequency on both slope gradient classes on bare and protected soil, but soil protective mats delayed the onset of adverse soil responses and reduced the level of soil damage. Brush mats provided a more effective protection than sawdust and the combination of brush and sawdust and heavy density brush mats more so than light density mats. Compared to bare soil, heavy brush reinforcement significantly reduced bulk density for up to 10 passes on trail gradients ≤ 20% and four passes on gradients > 20%, regardless of soil protective mat composition. Light and heavy brush mats significantly reduced rut depth at all traffic frequencies on both slope classes. Because the effectiveness of soil protection afforded by the mats diminished with increasing traffic, brush mats provide a particularly effective protection for less trafficked trail segments where brush mats substantially diminished or even eliminated rutting altogether.

Differing roles for parvalbumin neurons after nerve injury.

Neuropathic pain is abnormal, persistent pain that is caused by injury to the somatosensory system. It commonly involves damage to the peripheral nerves as a result of physical trauma, metabolic diseases such as diabetes, infections such as HIV or shingles, or toxicity induced neuropathies as a result of cancer treatments. Neuropathic pain is common, with epidemiological studies suggesting that around 18–30% of American, European and Australian adults suffer from chronic pain. This leads to significant disabilities and suffering. People with chronic pain complain of spontaneous pains that may be electric-shock like or continuous. Often coexisting with these are abnormal, evoked sensations such as tactile allodynia (pain in response to innocuous stimuli e.g., light brush or pressure) and cold allodynia (pain in response to innocuous cooling), or hyperalgesia (increase pain in response to an already noxious stimulus), as well as ataxia and proprioceptive deficits. The management of these conditions is often suboptimal for two main reasons: firstly, an incomplete knowledge of the mechanisms that are involved (and which of them are the most important). Secondly, patients often have compliance issues with pharmacological medications (Attal, 2012). Both peripheral and central neuronal mechanisms contribute to the pathophysiology and since the turn of the century particular emphasis has focussed on the role of glial cells in pain (West et al., 2015).

Pain and Sensory Abnormalities in Parkinson’s Disease—An Age- and Gender-matched Controlled Pilot Study

Background/aims:To test whether patients with Parkinson’s disease (PD) have an altered sensory perception in response to painful and nonpainful stimuli and if the PD medications can influence the responses.Methods:PD patients (12) and healthy subjects (12) were recruited. Sensory perception was examined in forearms, low back, and hands by light brush, pinprick, cold pressure test (CPT), and pressure algometry.Results:A significant difference was found in PD patients in response to brush (p&lt;0.05) and pinprick (p&lt;0.001). Lower back and forearms were found to be more sensitive. Tolerance time in CPT was shorter in PD patients (p=0.016). Pressure pain threshold (PPT) before (p=0.011) and after (p=0.050) the CPT showed a higher sensitivity in the patients regardless of the site. No association was found between the sensory perception and the medications.Conclusion:PD patients demonstrated an altered perception to touch and pain stimuli with a general increased in pain intensity and independent of the PD medications.

Pregnancy Is Characterized by Widespread Deep-Tissue Hypersensitivity Independent of Lumbopelvic Pain Intensity, a Facilitated Response to Manual Orthopedic Tests, and Poorer Self-Reported Health

Lumbopelvic pain is common in pregnancy but the sensitization factors underlying the condition are largely unknown. This study characterized the somatosensory profile of pregnant and nonpregnant women and the relationship between pain, hypersensitivity, and commonly used manual clinical tests. Thirty-nine pregnant and 22 nonpregnant women were included. Although lumbopelvic pain was not an inclusion criterion, the pregnant women were divided into low- and high-pain groups following data collection. The sensitivity to light brush, pin-prick, and pressure pain was assessed bilaterally at 3 sites in the lumbopelvic region, at the shoulder, and in the lower leg. Responses to the active straight leg raise test and pain provocation tests of the sacroiliac joint were recorded. Participants completed questionnaires addressing emotional and physical well-being and rated disability using the Pelvic Girdle Questionnaire. Compared with controls, the high-pain group rated the active straight leg raise test as more difficult (P < .05), and both pain groups had more positive pain provocation tests (P < .05). The pregnant groups demonstrated significantly lower pressure pain thresholds at most assessment sites compared with controls (P < .05), but self-reported disability and pain were not correlated with pressure pain thresholds within pregnant participants. The high-pain group reported worse emotional health and poorer sleep quality than controls (P < .05). PerspectiveThis article presents the somatosensory profile of a healthy pregnant cohort. The results indicate that pain sensitivity increases during pregnancy possibly owing to the physical changes the body undergoes during pregnancy but also owing to changes in emotional health. This should be accounted for in clinical management of pregnant women with lumbopelvic pain.

Discriminative and affective touch: sensing and feeling.

The multimodal properties of the human somatosensory system continue to be unravelled. There is mounting evidence that one of these submodalities-touch-has another dimension, providing not only its well-recognized discriminative input to the brain, but also an affective input. It has long been recognized that touch plays an important role in many forms of social communication and a number of theories have been proposed to explain observations and beliefs about the "power of touch." Here, we propose that a class of low-threshold mechanosensitive C fibers that innervate the hairy skin represent the neurobiological substrate for the affective and rewarding properties of touch.

Prevalence of saphenous nerve injury after adductor‐canal‐blockade in patients receiving total knee arthroplasty

Adductor-canal-blockade is a new technique for pain relief after knee surgery. This block could cause nerve injury and the aim of this follow-up study was to determine the prevalence of saphenous nerve injury in patients receiving adductor-canal-blockade for pain treatment after total knee arthroplasty. All patients included in two former studies of adductor-canal-blockade following total knee arthroplasty were invited to participate in this follow-up study 3-6 months after surgery. We examined the cutaneous area on the medial aspect of the lower leg (medial crural branch of the saphenous nerve), as well as the anterior, posterior, lateral and infrapatellar part of the affected and contralateral lower leg. Sensory function was tested with pinprick (sharp and blunt needle), temperature discrimination (cold disinfectant swabs) and light brush. We included 97 patients. None of the patients [0-5.3% (99% confidence interval)] had sensory changes related to temperature or light brush corresponding to the medial crural branch of the saphenous nerve, but 10 patients could not discriminate between blunt and sharp stimulation with a needle. In the infrapatellar area of the operated knee, 76 patients could not discriminate between blunt and sharp stimulation with a needle, 81 patients could not discriminate between cold and warmth, and 82 patients displayed an altered sensation to light brush. We found no indications of saphenous nerve injury caused by the adductor-canal-blockade at the mid-thigh level. However, 84% of the patients had signs of injury to the infrapatellar branch of the saphenous nerve in the operated leg. Such findings are well-known complications to the surgical procedure.

High-concentration capsaicin for the treatment of post-herpetic neuralgia and other types of peripheral neuropathic pain

SUMMARY Post-herpetic neuralgia (PHN) is a common complication of shingles, but current therapies often only provide partial pain relief in a proportion of patients treated. Results of six randomized controlled studies in patients with PHN have demonstrated the efficacy and safety of a high-concentration capsaicin (8% w/w) (NGX-4010; QUTENZA™) patch following a single 60-minute application. Patients treated with capsaicin achieved greater pain relief during Weeks 2–8 and Weeks 2–12 compared with a 0.04% w/w capsaicin control patch in two pivotal Phase III studies. In the first study the mean percentage change in Numeric Pain Rating Scale score for Weeks 2–8 was −29.6% versus −19.9% (p = 0.01) for the high-concentration capsaicin patch versus control, respectively. This result was confirmed by a second similar study. Patients also reported a significant improvement in quality of life on the Patient Global Impression of Change following a single 60-minute application. An integrated analysis further demonstrated the efficacy of the high-concentration capsaicin patch and confirmed its good safety and tolerability profile. Sensory testing showed little or no effect on light brush, pinprick or warmth sensations following treatment and a slight improvement in vibration sensation. An open-label study that administered repeated applications of the high-concentration capsaicin patch over 1 year demonstrated its long-term safety with no increased incidence or severity of adverse events and no impact on neurologic function. The high-concentration capsaicin patch was well tolerated and the most common adverse events were application site-related, mild to moderate, and transient.

Energy Cost and Pole Forces during Nordic Walking under Different Surface Conditions

The purpose of the study was to identify the effect of three different surfaces on energy consumption and the forces acting on the walking poles during ground contact in Nordic walking (NW). Thirteen female NW instructors (age = 26 +/- 4 yr, weight = 58.5 +/- 4.2 kg, height = 168.1 +/- 4.6 cm) volunteered in the study. The subjects walked a distance of 1200 m at a controlled, constant speed of 2.2 m x s(-1) on each of a concrete surface (C), an artificial athletics track (A), and a naturally grown soccer lawn (G). They used NW poles with inbuilt strain gauge force transducers to measure ground reaction forces acting along the long axes of the poles. Oxygen uptake, capillary blood lactate (La), HR, and RPE were measured before and after the tests. Impact forces, maximum forces, force rates during ground contact identified from the registered force time histories, displayed significant differences related to the surface conditions. However, force time integrals did not show surface-related differences. Relative oxygen consumption showed significant differences between NW on C and on G whereas no surface-related differences could be identified between the surface conditions for the parameters La, HR, and RPE. Our data indicate that the impulse that is generated by the poles on the subjects is identical between the varying surfaces. Because there are differences for the oxygen uptake between C and G, the main regulator for the propulsion must be the musculature of the lower extremities. The work of the upper extremities seems to be a luxury effort for Nordic walkers with a proper technique.

EVALUATION OF EROSION RELEASE AND SUPPRESSION OF ASBESTOS FIBERS FROM ASBESTOS BUILDING PRODUCTS

Test methods have been developed to measure the release of asbestos fibers from the surfaces of a range of asbestos building products when subjected to an airstream (air erosion) or to light brush contact (brush erosion). The tests allowed discrimination of differences in fiber release from the products and assessment of the effectiveness of encapsulants in suppressing fiber release. Application of “good” encapsulants (by using tough binders and optimum application rates) reduced fiber release to very low or nondetectable levels for all products tested.

Actions of capsaicin on peripheral nociceptors of the neonatal rat spinal cord‐tail in vitro: dependence of extracellular ions and independence of second messengers

1. We have tested the hypothesis that capsaicin-induced activation, desensitization and impairment of peripheral nociceptor function is mediated by separate mechanisms. This was investigated by use of an in vitro preparation of the neonatal rat spinal cord with the functionally attached tail in which the cord and tail were separately superfused with physiological solution. Activation of peripheral fibres by noxious (capsaicin, bradykinin, 5-hydroxytrptamine, heat, pinch) and innocuous (light brush) stimuli was assessed by recording the depolarization of a spinal ventral root (L3-L5). 2. Brief administration of capsaicin produced dose-related depolarizing responses (EC50 = 280 nM). These responses could be reproduced for many hours following the repeated application of capsaicin at a submaximal concentration. Prolonged application of 0.5-2.0 microM capsaicin induced a selective desensitization to subsequent brief administrations of capsaicin. Prolonged administration at 20-50 microM produced an additional non-selective reduction in responses to all noxious stimuli without changing innocuous brush responses. 3. Removal of extracellular calcium from the tail superfusate did not reduce the response to capsaicin or prevent capsaicin-induced desensitization. However, high concentrations of capsaicin no longer induced a non-specific reduction of responses to other noxious stimuli. The response to a brief administration of capsaicin was unaffected by calcium channel blocking drugs including nifedipine, cadmium or omega-conotoxin. On the other hand high extracellular calcium increased the incidence of the non-selective reduction of responses to all noxious stimuli produced by high concentrations of capsaicin. 4. Replacement of extracellular sodium with choline blocked peripheral nerve conduction but did not prevent the desensitization produced by capsaicin. In addition, high concentrations of capsaicin were less effective in reducing the responsiveness to other noxious stimuli. 5. Neither capsaicin-evoked responses nor capsaicin-induced desensitization were affected by the administration of forskolin, dibutyryl cyclic AMP, nitroprusside, dibutyryl cyclic GMP, beta-12,13 phorbol dibutyrate, trifluoperazine, indomethacin, staurosporine or mepacrine, in the tail superfusate. 6. These data suggest that capsaicin-induced activation, desensitization and impairment of peripheral nociceptors may be separable phenomena. Extracellular calcium is not required for capsaicin-induced activation or desensitization but calcium as well as sodium are important for capsaicin-induced impairment of nociceptive responses. Desensitization may occur independently of peripheral fibre activation and cannot be attributed to a central mechanism. Finally neither capsaicin-induced activation nor desensitization require the participation of a second messenger.

Capsaicin desensitization of peripheral nociceptive fibres does not impair sensitivity to other noxious stimuli

Capsaicin was tested on peripheral fibres in vitro to determine whether evoked depolarization or desensitization were likely to explain the antinociception observed after acute systemic capsaicin in vivo. The activation of peripheral fibres by noxious (capsaicin, bradykinin, heat) and innocuous (light brush) stimuli was recorded as a depolarization of a spinal ventral root (L 3-L 5) in the neonatal rat spinal cord with attached tail. Prolonged superfusion of the tail with low doses (0.2–2 μM) of capsaicin produced a short lasting depolarization followed by a complete loss of sensitivity to capsaicin without changes in sensitivity to other noxious or innocuous stimuli. Partial recovery from this selective desensitization could be observed 3–5 h later. In most preparations superfusion of the tail with 20 μM capsaicin produced a prolonged and non-selective impairment of sensitivity to all noxious stimuli. These data suggest that neither depolarization by capsaicin nor the selective desensitization of peripheral fibres to capsaicin are likely to account for the acute antinociceptive effect of systemic capsaicin. On the other hand the non-selective reduction in sensitivity to noxious stimuli induced by capsaicin may contribute to its antinociceptive action.

Textbook of Pain

This book, with 79 chapters written by 102 contributors, has three parts: basic science related to pain, clinical conditions with pain, and therapy. The chapters on basic aspects are all uniformly good, and most are excellent. The discussions are well written, succinct, and substantially documented. Written mostly by basic scientists, the book maintains the interest of the clinician reader because the clinical relevance of the discussion is pointed out. Experts on pain may learn a few things. These include the dual action (analgesia and pain-threshold reduction) of substance P, the reasons to doubt that pain is the only result of C-fiber action, and the subdivision of lamina II into an outer (IIo) and an inner (IIi) layer. The subdivision of lamina II is to understand better the analgesia-related circuitry within the dorsal horn; Hi responds only to innocuous light brush while IIo contains specialized nociceptive cells that respond to mechanical

Cord cells responding to fine myelinated afferents from viscera, muscle and skin.

1. Micro-electrode recordings were made in the thoracic cord of acute spinal cats. Cells, which were located in the histologically defined lamina 5, responded both to the fine myelinated afferents from the splanchnic nerve and to afferents from the skin. Splanchnic afferents inhibit the effect of converging cutaneous inputs for periods up to 150 msec. Skin stimuli may also inhibit the effect of afferent nerve impulses from viscera. Some cells respond monosynaptically to the splanchnic afferents, others indirectly.2. Fine myelinated afferents from gastrocnemius (group 3) stimulate lamina 5 cells which also have cutaneous receptive fields. Cutaneous and group 3 muscle afferents interact by mutual inhibition in their effect on the cells.3. Fine myelinated afferents from skin excite lamina 5 cells. The cutaneous responses of lamina 5 cells contrast with those of lamina 4 cells in the following respects: (a) the receptive fields are larger, (b) they respond with an increased latency to Abeta afferents, (c) there is a low pressure threshold at the edge, (d) they respond to a wide range of pressure stimuli from light brush to heavy pinch applied to the centre of the receptive fields and (e) they respond to ADelta afferents.4. Lamina 5 cells receive fine myelinated afferents either from viscera or from muscle or from skin. Lamina 4 receives large myelinated afferents from skin and lamina 6 receives large myelinated afferents from muscle. The results suggest the hypothesis that some fine myelinated afferents form a class of afferents which signal the state of tissue, and end on lamina 5 cells.