Thermoreception and nociception of the skin: a classic paper of Bessou and Perl and analyses of thermal sensitivity during a student laboratory exercise

Improvement of transdermal absorption rate by nonthermal biocompatible atmospheric pressure plasma

Nonthermal biocompatible plasma (NBP) is a promising option for improving medication absorption into the human skin. Currently, most plasma devices for cosmetics employ a floating-electrode plasma source for treating the skin. Human skin serves as the ground electrode in the floating-electrode plasma discharge, and discharge occurs between the skin and electrodes of the device. In this in vitro study, we aimed to evaluate the effect of NBP on the skin permeation of niacinamide. We have quantified the transdermal absorption rates of niacinamide in both untreated skin and skin treated with NBP for a duration of 10 s. The absorption of niacinamide for both without and with NBP treatment was observed until 12 h incubation time. Without plasma treatment, the human skin exhibited stable and low transdermal absorption of niacinamide up to 12 h. However, the NBP treatment significantly increased the transdermal absorption of niacinamide from 0.5 h to 6 h and continuously increased skin penetration over a duration of more than 12 h incubation period. The obtained results suggest that NBP-treated human skin showed a 60-fold higher penetration rate than non-treated skin. The increased penetration rate of niacinamide can be mainly attributed to plasmaporation subsequent to NBP treatment. The findings of this study demonstrate that NBP treatment results in remarkable skin permeability, making it a promising candidate for both cosmetic and pharmaceutical delivery applications.

Thermal Perception for Information Transmission: Theoretical Analysis, Device Design, and Experimental Verification

Information transmission is a fundamental issue for human-computer interaction (HCI). Traditional interaction methods through visual, voice, and force haptics are very mature. However, the thermal perception (TP) for HCI is not studied in depth. This work proposes the TP-based information transmission framework. Firstly, we investigated the human hand-object contact heat transfer model and the temperature perception resolution of the hand and verified the feasibility of spatiotemporal temperature stimulation for information transmission by simulations. Then, a thermal device was designed, which utilized a 7×5 Peltier array, a water cooler, temperature sensors, and a control module to realize various static and dynamic spatiotemporal temperature patterns stimulation. Finally, we implemented a device prototype and recruited 20 subjects for experimental studies. The results show that the device can display various temperature patterns and provide thermal stimulations with high precision and speed. Furthermore, the subjects can accurately recognize different temperature values, icons, codes, and waveforms with their palm and fingers after a few times of training, which validates the TP-based information transmission method. Therefore, people can apply this method to interact with machines for information feedback, virtual reality, augmented reality, etc.

Randomized cross-over evaluation of investigator gender on pain thresholds in healthy volunteers

Background and aims: This randomized cross-over study in healthy volunteers was designed primarily to evaluate the potential impact of investigator gender on electrical pain threshold (EPT) and corresponding pain intensity levels, and secondly to evaluate potential differences in those interventions between female and male study participants. Methods: Forty adult volunteers (22 females) were included. An electrical stimulation device was used to determine EPT levels (in pain magnitude scores) in series of three in each study participant - once by a female, and once by a male investigator - according to a predefined cross-over design schedule. Corresponding levels of pain intensity were scored on a visual analog scale (VAS) slide ruler. Results: Study data was obtained and analysed in all participants. Significantly higher EPT levels were determined by the female investigator compared with the male investigator (median 22 (IQR 12-31) vs. 8 (6-10) pain magnitude scores; p<0.0001), despite similar levels of reported pain intensity (1.9 (1.2-3.0) vs. 2.0 (1.1-3.4) VAS units; p>0.300). There were no differences in EPT levels between female and male subjects evaluated by female (p>0.300) and male (p=0.125) investigators, or between the first and second series of stimulation (p>0.300). Conclusions: Our finding of significantly higher EPT levels when study participants of both genders - despite no difference in reported pain intensity - were evaluated by a female than by a male investigator, indicates a potential impact of investigator gender on the individual perception of pain. Implications: By contributing to a better understanding of how individual pain threshold levels are potentially influenced by investigator gender, this study might facilitate future evaluation of pain conditions in both preclinical and clinical settings.

Sex differences in the consumption of over-the-counter analgesics among amateur volleyball players

Background

Compared with the normal adult population, athletes of several sport disciplines, such as endurance sports, ball sports, cycling and swimming, have higher use of over-the-counter analgesics (OTC analgesics). The aim of this study was to describe the epidemiology of OTC analgesic use in volleyball players as a typical competitive sport discipline. One particular focus was placed on the analysis whether the athletes’ use of OTC analgesics was influenced by their performance motivation.

Methods

A cross-sectional survey among amateur volleyball players was carried out using a web-based sports questionnaire. The study included athletes of both sexes, 18 years and older, currently playing in a German volleyball league. The athletes’ sport-related complaints were evaluated regarding the use of OTC analgesics. The use of OTC analgesics by athletes was compared with their performance motivation, based on the „Achievement Motives Scale - Sport” (AMS-Sport) questionnaire.

Results

The analysis of 114 completed questionnaires of amateur athletes revealed that the use of OTC analgesics was sex dependent, with a higher prevalence of use in female players (60%) versus male players (38%). The main reasons for consumption of OTC analgesics were pain in the head, knee and shoulder. The most frequently taken drug was ibuprofen, most often taken at competitions and over a period of 4 years (median). The analysis of the AMS-Sport questionnaire revealed that a logistic regression model for estimating the probability of drug use can be explained by the factors hope of success and years of playing practise in female players but not male players. In females, an increase in the factor hope of success resulted in a lower probability of OTC analgesic use, while an increase in years of playing practise resulted in a higher probability of use.

Conclusion

The average duration that volleyball players in this study took OTC analgesics was higher than that of the German population, and OTC analgesic use was more prevalent in female than male volleyball players. Thus, to reduce the prevalence of OTC analgesic use, educational programs should be implemented in sports teams; and, to reduce direct and indirect social pressure, sports teams should also receive sex-specific psychological support.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13102-021-00273-5.

Sex Differences in Thermal Comfort, Perception, Feeling, Stress and Focus During Exercise Hyperthermia

It is unclear whether men and women perceive thermal stress differently when changes in intestinal temperature (ΔTin) and metabolic heat production (MHprod) are matched between sexes during exercise hyperthermia. This study tested the hypothesis that females have enhanced sensitivity to comfort and perception of thermal stress during exercise hyperthermia in these conditions. We had 22 healthy active adults (11 males, 11 females; M age = 22.4 years, SD = 4.9; M height = 169 cm, SD = 7.6; M weight = 68.3 kg, SD = 13) exercise in random order, separated by at least three days at similar MHprod (M = 7.0 W/kg, SD = 1.5; p = 0.32) for 60 minutes on a cycle ergometer in cool (M = 24.0⁰C, SD = 0.0; M = 14.4%Rh, SD = 3.6) and hot (M = 42.3°C, SD = 0.2; M = 10-60%Rh) environments with a progressive increase in humidity conditions. We measured ΔTin, and thermal stress indices for sensation (TS), comfort (TC), pleasantness (TP), and stickiness (S), feeling (FS scale), stress (visual analogue stress scale, VAS), focus (F) and felt arousal (FAS scale). We examined environmental conditions as wet bulb globe temperatures (WBGT). Males and females had similar increases in ΔTin (ME: WBGT; p < 0.0001), and both groups reported increased TS and TC and decreased TP (ME: WBGT, p ≤ 0.01). However, females reported that TS, TC, and TP, felt hotter overall, more uncomfortable, and more unpleasant, compared to males (ME: Sex; p < 0.04). Overall, females felt worse and were more stressed compared to males (ME: Sex; p ≤ 0.05). Females also reported greater internal focus as WBGT increased compared to males (I: WBGT × Sex; p < 0.003). Knowing that females perceive thermal stress during exercise hyperthermia to be hotter, more uncomfortable, more unpleasant, and more stressful compared to males can help coaches/trainers plan different exercise routines for exercisers of both sexes.

The emerging potential of cold atmospheric plasma in skin biology

The maintenance of skin integrity is crucial to ensure the physiological barrier against exogenous compounds, microorganisms and dehydration but also to fulfill social and aesthetic purposes. Besides the development of new actives intended to enter a formulation, innovative technologies based on physical principles have been proposed in the last years. Among them, Cold Atmospheric Plasma (CAP) technology, which already showed interesting results in dermatology, is currently being studied for its potential in skin treatments and cares. CAP bio-medical studies gather several different expertise ranging from physics to biology through chemistry and biochemistry, making this topic hard to pin. In this review we provide a broad survey of the interactions between CAP and skin. In the first section, we tried to give some fundamentals on skin structure and physiology, related to its essential functions, together with the main bases on cold plasma and its physicochemical properties. In the following parts we dissected and analyzed each CAP parameter to highlight the already known and the possible effects they can play on skin. This overview aims to get an idea of the potential of cold atmospheric plasma technology in skin biology for the future developments of dermo-cosmetic treatments, for example in aging prevention.

Thermal sensitivity mapping - warmth and cold detection thresholds of the human torso

Skin as the largest organ of the human body accomplishes many important functions, including thermoregulation. In this context, investigating cold (CDT) and warmth detection thresholds (WDT) constitutes an important research branch, and investigating thermal thresholds has a significant impact on the clothing and fabric textile industry. In this regard, not only the extremities, but also torso regions are of high relevance. However, only few examinations have conducted detailed mapping studies of the human torso. Additionally, some of these studies show certain methodological limitations. Furthermore, the issue of whether cutaneous thermal sensitivity is gender-dependent is still controversial. Therefore, the present study investigated the cutaneous thermal sensitivity (CDT, WDT) of 42 male and female young and healthy subjects. Measurements were taken at 11 anatomical regions. We found that gender plays an important role when investigating thermal thresholds: Females tended to be more sensitive than males. We also found considerable differences between the tested regions, even within the anterior torso, for example. We identified locations which were constantly sensitive (lower back), while others were consistently insensitive (e.g. scapula). We also detected greater data variability for males compared to females, and for WDT compared to CDT. Furthermore, mainly for WDT, we found a proximal-to-distal increase of thermal torso and upper arm sensitivity. In line with previous investigations, our subjects were more sensitive to cold than to warmth. The findings of this study have important implications. First, our data may complement basic research, e.g. in terms of reference data of body regional maps. Second, our data provides important insights that could be leveraged in the textile industry, and also used to optimize current broadly applicable test methods and tools, like thermal manikins and thermophysiological models.

Cold and heavy: grasping the temperature-weight illusion

The apparent heaviness of weights placed on the skin depends on their temperature. We studied the effects of such a temperature–weight illusion (TWI) on perception and action in 21 healthy volunteers. Cold (18 °C), thermal-neutral (32 °C, skin temperature) and warm (41 °C) test objects were placed onto the palm of the non-dominant hand. Their veridical mass was 350 g (light) or 700 g (heavy). Perception of heaviness was assessed with two psychophysical experiments (magnitude estimation, cross modal matching). Cold heavy objects felt about 20% heavier than thermal-neutral objects of the same mass, shape and material. In a subsequent grip-lift experiment, the test objects were grasped with a precision grip of the dominant hand and lifted off the palm of the non-dominant hand. The grip and lift forces exerted by the fingertips were recorded. The temperature of the objects had significant effects (ANOVA, p < 0.05) on the peak grip and lift forces and on the peak grip force rate (i.e., the initial force incline). The peak grip force was about 10% higher when cold heavy objects were grasped and lifted, compared to lifts of otherwise identical thermal-neutral objects. The TWI was less pronounced when light objects or warm objects were handled. In conclusion, cooling of an object increases its apparent heaviness (perception) and influences scaling of the fingertip forces during grasping and lifting (action).

An updated review on pathophysiology and management of burning mouth syndrome with endocrinological, psychological and neuropathic perspectives

Burning mouth syndrome (BMS) is a chronic oro-facial pain disorder of unknown cause. It is more common in peri- and post-menopausal women, and sex hormone dysregulation is believed to be an important causative factor. Psychosocial events often trigger or exacerbate symptoms, and persons with BMS appear to be predisposed towards anxiety and depression. Atrophy of small nerve fibres in the tongue epithelium has been reported, and potential neuropathic mechanisms for BMS are now widely investigated. Historically, BMS was thought to comprise endocrinological, psychosocial and neuropathic components. Neuroprotective steroids and glial cell line-derived neurotrophic factor family ligands may have pivotal roles in the peripheral mechanisms associated with atrophy of small nerve fibres. Denervation of chorda tympani nerve fibres that innervate fungiform buds leads to alternative trigeminal innervation, which results in dysgeusia and burning pain when eating hot foods. With regard to the central mechanism of BMS, depletion of neuroprotective steroids alters the brain network-related mood and pain modulation. Peripheral mechanistic studies support the use of topical clonazepam and capsaicin for the management of BMS, and some evidence supports the use of cognitive behavioural therapy. Hormone replacement therapy may address the causes of BMS, although adverse effects prevent its use as a first-line treatment. Selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) may have important benefits, and well-designed controlled studies are expected. Other treatment options to be investigated include brain stimulation and TSPO (translocator protein 18 kDa) ligands.

Philosophy and Application of High-Resolution Temperature Sensors for Stratified Waters

Every application may have its specifically designed sensor. For studying the effects of short-term temperature variations on life in water, a high-resolution sensor has been designed with low noise level <0.1 mK. Pro and cons of the design include its adequacy for use in large heat-capacity environments like water but less in air. The sensor can be used under high static environmental pressure of >1000 Bar (>10⁸ N m-2) in the deepest ocean regions. Its response time of 0.5 s in water allows quantitative studies of internal wave turbulent mixing effects, e.g., on the redistribution of matter and on nearly completely submerged human bodies. In a chain of >100 sensors, clocks are synchronized to sample within 0.02 s and a verified range of 600 m.

Efficacy of a Novel Sigma-1 Receptor Antagonist for Oxaliplatin-Induced Neuropathy: A Randomized, Double-Blind, Placebo-Controlled Phase IIa Clinical Trial

This trial assessed the efficacy of MR309 (a novel selective sigma-1 receptor ligand previously developed as E-52862) in ameliorating oxaliplatin-induced peripheral neuropathy (oxaipn). A discontinuous regimen of MR309 (400 mg/day, 5 days per cycle) was tested in patients with colorectal cancer receiving FOLFOX in a phase II, randomized, double-blind, placebo-controlled, multicenter clinical trial. Outcome measures included changes in 24-week quantitative measures of thermal sensitivity and total neuropathy score. In total, 124 patients were randomized (1:1) to MR309 or placebo. Sixty-three (50.8%) patients withdrew prematurely before completing 12 planned oxaliplatin cycles. Premature withdrawal because of cancer progression was less frequent in the MR309 group (7.4% vs 25.0% with placebo; p = 0.054). MR309 significantly reduced cold pain threshold temperature [mean treatment effect difference (SE) vs placebo: 5.29 (1.60)°C; p = 0.001] and suprathreshold cold stimulus-evoked pain intensity [mean treatment effect difference: 1.24 (0.57) points; p = 0.032]. Total neuropathy score, health-related quality-of-life measures, and nerve-conduction parameters changed similarly in both arms, whereas the proportion of patients with severe chronic neuropathy (National Cancer Institute Common Terminology Criteria for Adverse Events ≥ 3) was significantly lower in the MR309 group (3.0% vs 18.2% with placebo; p = 0.046). The total amount of oxaliplatin delivered was greater in the active arm (1618.9 mg vs 1453.8 mg with placebo; p = 0.049). Overall, 19.0% of patients experienced at least 1 treatment-related adverse event (25.8% and 11.9% with MR309 and placebo, respectively). Intermittent treatment with MR309 was associated with reduced acute oxaipn and higher oxaliplatin exposure, and showed a potential neuroprotective role for chronic cumulative oxaipn. Furthermore, MR309 showed an acceptable safety profile.

Sex differences in thermal detection and thermal pain threshold and the thermal grill illusion: a psychophysical study in young volunteers

BACKGROUND

Sex-related differences in human thermal and pain sensitivity are the subject of controversial discussion. The goal of this study in a large number of subjects was to investigate sex differences in thermal and thermal pain perception and the thermal grill illusion (TGI) as a phenomenon reflecting crosstalk between the thermoreceptive and nociceptive systems. The thermal grill illusion is a sensation of strong, but not necessarily painful, heat often preceded by transient cold upon skin contact with spatially interlaced innocuous warm and cool stimuli.

METHODS

The TGI was studied in a group of 78 female and 58 male undergraduate students and was evoked by placing the palm of the right hand on the thermal grill (20/40 °C interleaved stimulus). Sex-related thermal perception was investigated by a retrospective analysis of thermal detection and thermal pain threshold data that had been measured in student laboratory courses over 5 years (776 female and 476 male undergraduate students) using the method of quantitative sensory testing (QST). To analyse correlations between thermal pain sensitivity and the TGI, thermal pain threshold and the TGI were determined in a group of 20 female and 20 male undergraduate students.

RESULTS

The TGI was more pronounced in females than males. Females were more sensitive with respect to thermal detection and thermal pain thresholds. Independent of sex, thermal detection thresholds were dependent on the baseline temperature with a specific progression of an optimum curve for cold detection threshold versus baseline temperature. The distribution of cold pain thresholds was multi-modal and sex-dependent. The more pronounced TGI in females correlated with higher cold sensitivity and cold pain sensitivity in females than in males.

CONCLUSIONS

Our finding that thermal detection threshold not only differs between the sexes but is also dependent on the baseline temperature reveals a complex processing of "cold" and "warm" inputs in thermal perception. The results of the TGI experiment support the assumption that sex differences in cold-related thermoreception are responsible for sex differences in the TGI.

Spatial and Temporal Brain Responses to Noxious Heat Thermal Stimuli in Burning Mouth Syndrome

Burning mouth syndrome (BMS) is an idiopathic orofacial pain condition. Although the pathophysiology of BMS is not clearly understood, central and peripheral neuropathic mechanisms are thought to be involved. The authors compared brain response to noxious heat stimuli in 16 right-handed women with primary BMS and 15 sex- and age-matched right-handed healthy female controls. A thermal stimulus sequence of 32 °C to 40 °C to 32 °C to 49 °C was repeated 4 times in a cycle. Warm and noxious heat stimuli were delivered with a Peltier thermode placed on the right palm or right lower lip for 32 s each in a session. Functional magnetic resonance imaging data were obtained by recording echoplanar images with a block design. Statistical Parametric Mapping 8 software was used to analyze the data. Patients and controls both reported feeling more pain during palm stimulation than during lip stimulation. Repetition of noxious heat stimulus on the lower lip but not on the palm induced habituation in brain activity in the cingulate cortex without reduction in pain perception. Multiple regression analysis revealed a correlation between perceived pain intensity and suppression of brain activity in the anterior cingulate cortex when the repeated thermal sequence was applied at the lower lip. Furthermore, the response of the parahippocampal area differed in BMS patients and controls when the same repeated thermal sequence was applied at the palm. The authors’ findings indicate that BMS patients show specific brain responses due to impaired function of the central and peripheral nervous systems (clinical trial registration: UMIN000015002).

Higher body fat percentage is associated with enhanced temperature perception in NAFLD: results from the randomised Wessex Evaluation of fatty Liver and Cardiovascular markers in NAFLD with OMacor thErapy trial (WELCOME) trial

AIMS/HYPOTHESIS

The effect of n-3 fatty acid treatment on temperature perception as a sensory nerve function modality is uncertain. In patients with non-alcoholic fatty liver disease (NAFLD) both with and without type 2 diabetes, we: (1) tested whether 15-18 months' treatment with 4 g/day of docosahexaenoic plus eicosapentaenoic acid (DHA+EPA) improved hot (HPT) and cold (CPT) temperature perception thresholds and (2) explored factors associated with HPT and CPT, in a randomised, double-blind, placebo-controlled trial.

METHODS

The effect of treatment (n = 44) on HPT, CPT and temperature perception index (TPI: difference between HPT and CPT) was measured at the big toe in 90 individuals without neuropathy (type 2 diabetes; n = 30). Participants were randomised 1:1, using sequential numbering, by personnel independent from the trial team. All participants and all members of the research team were blinded to group assignment. Data were collected in the Southampton National Institute for Health Research Biomedical Research Centre. Treatment effects and the independence of associations were testing by regression modelling.

RESULTS

Mean ± SD age was 50.9 ± 10.6 years. In men (n = 53) and women (n = 37), HPTs (°C) were 46.1 ± 5.1 and 43.1 ± 6.4 (p = 0.02), CPTs (°C) were 22.7 ± 3.4 and 24.5 ± 3.6 (p = 0.07) and TPIs (°C) were 23.4 ± 7.4 and 18.7 ± 9.5 (p = 0.008), respectively. In univariate analyses, total body fat percentage (measured by dual-energy x-ray absorptiometry [DXA]) was associated with HPT (r = -0.36 p = 0.001), CPT (r = 0.35 p = 0.001) and TPI (r = 0.39 p = 0.0001). In multivariable-adjusted regression models, adjusting for age, sex and other potential confounders, only body fat percentage was independently associated with HPT, CPT or TPI (p = 0.006, p = 0.006 and p = 0.002, respectively). DHA+EPA treatment did not modify HPT, CPT or TPI (p = 0.93, p = 0.44 and p = 0.67, respectively). There were no important adverse effects or side effects reported.

CONCLUSIONS/INTERPRETATION

Higher body fat percentage is associated with enhanced temperature perception. There was no benefit of treatment with high-dose n-3 fatty acids on the thresholds to detect hot or cold stimuli.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00760513 FUNDING: This work was supported by the National Institute for Health Research through the NIHR Southampton Biomedical Research Unit grant and by a Diabetes UK allied health research training fellowship awarded to KMcC (Diabetes UK. BDA 09/0003937).

Reliability and accuracy of quantitative sensory testing for oxaliplatin-induced neurotoxicity

OBJECTIVES

Thermal quantitative sensory testing (QST) is a non-invasive procedure helpful in the assessment of the function of small Aδ and C nerve sensory fibres. Oxaliplatin (OXA) is an effective chemotherapeutic agent, but is frequently associated with neurotoxic dose-limiting side effects. This controlled clinical trial evaluated the reliability and accuracy of thermal QST for assessing the OXA-induced acute neuropathic syndrome, whose clinical hallmark is cold-triggered painful paraesthesia.

MATERIALS & METHODS

A testing protocol with the Thermal Sensory Analyzer (Medoc) was carried out in 20 colorectal cancer patients during the initial four cycles of OXA-based chemotherapy and in 20 age- and sex-matched healthy volunteers. Testing was carried out on the hands and included the determination of thermal detection and pain thresholds and the intensity of pain evoked by cold stimuli. Calculations were made of: coefficients of test-retest and inter-rater reliability, indices of responsiveness and parameters that quantify diagnostic accuracy.

RESULTS

Thermal thresholds showed moderate to good reliability (ρ ≥ 0.383), but were not consistently responsive to the effects of chemotherapy (cold pain thresholds decreased in both groups, although almost twice in patients compared to healthy volunteers). Conversely, the intensity of pain evoked by suprathreshold cold stimuli was reliable (ρ ≥ 0.822), responsive (detected changes over time) and discriminated between patients and healthy volunteers (area under the ROC curve = 0.700).

CONCLUSIONS

The procedure was reliable and accurate to evaluate cold hyperalgesia resulting from OXA administration. The data provided may be used to define efficacy endpoints for future clinical trials of therapies for OXA-induced neuropathies and calculate appropriate sample sizes.

An improved model of heat-induced hyperalgesia--repetitive phasic heat pain causing primary hyperalgesia to heat and secondary hyperalgesia to pinprick and light touch

This study tested a modified experimental model of heat-induced hyperalgesia, which improves the efficacy to induce primary and secondary hyperalgesia and the efficacy-to-safety ratio reducing the risk of tissue damage seen in other heat pain models. Quantitative sensory testing was done in eighteen healthy volunteers before and after repetitive heat pain stimuli (60 stimuli of 48°C for 6 s) to assess the impact of repetitive heat on somatosensory function in conditioned skin (primary hyperalgesia area) and in adjacent skin (secondary hyperalgesia area) as compared to an unconditioned mirror image control site. Additionally, areas of flare and secondary hyperalgesia were mapped, and time course of hyperalgesia determined. After repetitive heat pain conditioning we found significant primary hyperalgesia to heat, and primary and secondary hyperalgesia to pinprick and to light touch (dynamic mechanical allodynia). Acetaminophen (800 mg) reduced pain to heat or pinpricks only marginally by 11% and 8%, respectively (n.s.), and had no effect on heat hyperalgesia. In contrast, the areas of flare (−31%) and in particular of secondary hyperalgesia (−59%) as well as the magnitude of hyperalgesia (−59%) were significantly reduced (all p<0.001). Thus, repetitive heat pain induces significant peripheral sensitization (primary hyperalgesia to heat) and central sensitization (punctate hyperalgesia and dynamic mechanical allodynia). These findings are relevant to further studies using this model of experimental heat pain as it combines pronounced peripheral and central sensitization, which makes a convenient model for combined pharmacological testing of analgesia and anti-hyperalgesia mechanisms related to thermal and mechanical input.

Pathology of human diabetic neuropathy

Pathologic study of a disease provides insights into the precise mechanisms and targets of damage and may provide insights into new therapies. The main targets in diabetic neuropathy are myelinated and unmyelinated fibers as dysfunction and damage to them explains the symptoms of painful neuropathy and the major end points of foot ulceration and amputation as well as mortality. Demyelination and axonal degeneration are established hallmarks of the pathology of human diabetic neuropathy and were derived from pioneering light and electronmicroscopic studies of sural nerve biopsies in the late 1960s and early 1970s. Additional abnormalities, which are relevant to the pathogenesis of human diabetic neuropathy, include pathology of the microvessels and extracellular space. Intraepidermal and sudomotor nerve quantification in skin biopsies provides a minimally invasive means for the detection of early nerve damage. Studies of muscle biopsies are limited and show significant alterations in the expression of neurotrophins, but limited changes in muscle fiber size and capillary density.

Differential roles of galanin on mechanical and cooling responses at the primary afferent nociceptor

Background

Galanin is expressed in a small percentage of intact small diameter sensory neurons of the dorsal root ganglia and in the afferent terminals of the superficial lamina of the dorsal horn of the spinal cord. The neuropeptide modulates nociception demonstrating dose-dependent pro- and anti-nociceptive actions in the naïve animal. Galanin also plays an important role in chronic pain, with the anti-nociceptive actions enhanced in rodent neuropathic pain models. In this study we compared the role played by galanin and its receptors in mechanical and cold allodynia by identifying individual rat C-fibre nociceptors and characterising their responses to mechanical or acetone stimulation.

Results

Mechanically evoked responses in C-fibre nociceptors from naive rats were sensitised after close intra-arterial infusion of galanin or Gal2-11 (a galanin receptor-2/3 agonist) confirming previous data that galanin modulates nociception via activation of GalR2. In contrast, the same dose and route of administration of galanin, but not Gal2-11, inhibited acetone and menthol cooling evoked responses, demonstrating that this inhibitory mechanism is not mediated by activation of GalR2. We then used the partial saphenous nerve ligation injury model of neuropathic pain (PSNI) and the complete Freund’s adjuvant model of inflammation in the rat and demonstrated that close intra-arterial infusion of galanin, but not Gal2-11, reduced cooling evoked nociceptor activity and cooling allodynia in both paradigms, whilst galanin and Gal2-11 both decreased mechanical activation thresholds. A previously described transgenic mouse line which inducibly over-expresses galanin (Gal-OE) after nerve injury was then used to investigate whether manipulating the levels of endogenous galanin also modulates cooling evoked nociceptive behaviours after PSNI. Acetone withdrawal behaviours in naive mice showed no differences between Gal-OE and wildtype (WT) mice. 7-days after PSNI Gal-OE mice demonstrated a significant reduction in the duration of acetone-induced nociceptive behaviours compared to WT mice.

Conclusions

These data identify a novel galaninergic mechanism that inhibits cooling evoked neuronal activity and nociceptive behaviours via a putative GalR1 mode of action that would also be consistent with a TRP channel-dependent mechanism.

Internal wave turbulence near a Texel beach

A summer bather entering a calm sea from the beach may sense alternating warm and cold water. This can be felt when moving forward into the sea (‘vertically homogeneous’ and ‘horizontally different’), but also when standing still between one’s feet and body (‘vertically different’). On a calm summer-day, an array of high-precision sensors has measured fast temperature-changes up to 1°C near a Texel-island (NL) beach. The measurements show that sensed variations are in fact internal waves, fronts and turbulence, supported in part by vertical stable stratification in density (temperature). Such motions are common in the deep ocean, but generally not in shallow seas where turbulent mixing is expected strong enough to homogenize. The internal beach-waves have amplitudes ten-times larger than those of the small surface wind waves. Quantifying their turbulent mixing gives diffusivity estimates of 10⁻⁴–10⁻³ m² s⁻¹, which are larger than found in open-ocean but smaller than wave breaking above deep sloping topography.

Small fibre neuropathy: role in the diagnosis of diabetic sensorimotor polyneuropathy

Small fibres constitute 70-90% of peripheral nerve fibres and regulate several key functions such as tissue blood flow, temperature and pain perception as well as sweating, all of which are highly relevant to the clinical presentation and adverse outcomes associated with foot ulcerations in patients with diabetes. Recent studies demonstrated significant abnormalities in the small fibres in subjects with impaired glucose tolerance and diabetes, despite normal electrophysiology, suggesting that the earliest nerve fibre damage is to the small fibres. Unfortunately, guidelines and consensus statements focus on large fibres and continue to advocate electrophysiology as a diagnostic modality and as a primary end point for the assessment of therapeutic benefit. (In part, this reflects the difficulties in quantifying small fibre dysfunction and damage.) We have therefore critically assessed currently available techniques that measure small fibre dysfunction in diabetic neuropathy, using quantitative sensory and sudomotor testing. We have assessed the role of identifying structural damage by quantifying intraepidermal nerve fibre density in skin biopsies and corneal nerve morphology using corneal confocal microscopy. Finally, we propose a definition for diabetic neuropathy that incorporates small fibre damage.