Relations between tactile sensitivity of the finger, arm, and cheek skin over the lifespan showing decline only on the finger.

Touch sensitivity generally declines with age, contributing to loss of manual dexterity and tactile function. We investigated how touch changes over the lifespan, using different tests and on three body sites. We used a classical test of force detection sensitivity, where calibrated monofilaments were applied passively to the right index finger pad, forearm, and cheek. In addition, at the index, we used an active touch spatial discrimination task, developed by our group. Spatial discrimination was estimated through participants' ability to evaluate the distance between parallel bands printed on acrylic plates. Data were collected from 96 healthy women, aged 20-75 years. Force detection and tactile spatial discrimination on the index deteriorated significantly with age; however, no change was found for tactile detection on the forearm or cheek. Tactile detection on the cheek remained remarkably highly sensitive throughout life. There was a significant positive relationship between force detection and spatial discrimination on the index. Further, force detection on the forearm was significantly associated with detection on the index and cheek. Our results suggest a decrease in touch perception with age on the index finger pad, yet a preservation of tactile sensitivity in hairy skin. This opens discussion about the impact of daily activities upon the glabrous hand skin and on the function of hairs in tactile sensitivity. We highlight the need for new methods in evaluating tactile sensitivity on hairy skin.

Effects of inflammation on the properties of Nav1.8-ChR2-positive and Nav1.8-ChR2-negative afferent mechanoreceptors in the hindpaw glabrous skin of mice.

We recently used Nav1.8-ChR2 mice in which Nav1.8-expressing afferents were optogenetically tagged to classify mechanosensitive afferents into Nav1.8-ChR2-positive and Nav1.8-ChR2-negative mechanoreceptors. We found that the former were mainly high threshold mechanoreceptors (HTMRs), while the latter were low threshold mechanoreceptors (LTMRs). In the present study, we further investigated whether the properties of these mechanoreceptors were altered following tissue inflammation. Nav1.8-ChR2 mice received a subcutaneous injection of saline or Complete Freund's Adjuvant (CFA) in the hindpaws. Using the hind paw glabrous skin-tibial nerve preparation and the pressure-clamped single-fiber recordings, we found that CFA-induced hind paw inflammation lowered the mechanical threshold of many Nav1.8-ChR2-positive Aß-fiber mechanoreceptors but heightened the mechanical threshold of many Nav1.8-ChR2-negative Aß-fiber mechanoreceptors. Spontaneous action potential impulses were not observed in Nav1.8-ChR2-positive Aß-fiber mechanoreceptors but occurred in Nav1.8-ChR2-negative Aß-fiber mechanoreceptors with a lower mechanical threshold in the saline goup, and a higher mechanical threshold in the CFA group. No significant change was observed in the mechanical sensitivity of Nav1.8-ChR2-positive and Nav1.8-ChR2-negative Aδ-fiber mechanoreceptors and Nav1.8-ChR2-positive C-fiber mechanoreceptors following hind paw inflammation. Collectively, inflammation significantly altered the functional properties of both Nav1.8-ChR2-positive and Nav1.8-ChR2-negative Aß-fiber mechanoreceptors, which may contribute to mechanical allodynia during inflammation.

Modulation of Motor Cortical Inhibition and Facilitation by Touch Sensation from the Glabrous Skin of the Human Hand.

Touch sensation from the glabrous skin of the hand is essential for precisely controlling dexterous movements, yet the neural mechanisms by which tactile inputs influence motor circuits remain largely unexplored. By pairing air-puff tactile stimulation on the hand's glabrous skin with transcranial magnetic stimulation (TMS) over the primary motor cortex (M1), we examined the effects of tactile stimuli from single or multiple fingers on corticospinal excitability and M1's intracortical circuits. Our results showed that when we targeted the hand's first dorsal interosseous (FDI) muscle with TMS, homotopic (index finger) tactile stimulation, regardless of its point (fingertip or base), reduced corticospinal excitability. Conversely, heterotopic (ring finger) tactile stimulation had no such effect. Notably, stimulating all five fingers simultaneously led to a more pronounced decrease in corticospinal excitability than stimulating individual fingers. Furthermore, tactile stimulation significantly increased intracortical facilitation (ICF) and decreased long-interval intracortical inhibition (LICI) but did not affect short-interval intracortical inhibition (SICI). Considering the significant role of the primary somatosensory cortex (S1) in tactile processing, we also examined the effects of downregulating S1 excitability via continuous theta burst stimulation (cTBS) on tactile-motor interactions. Following cTBS, the inhibitory influence of tactile inputs on corticospinal excitability was diminished. Our findings highlight the spatial specificity of tactile inputs in influencing corticospinal excitability. Moreover, we suggest that tactile inputs distinctly modulate M1's excitatory and inhibitory pathways, with S1 being crucial in facilitating tactile-motor integration.

Bovine Meissner-like corpuscle and evolutionary ecology of mammalian somatosensory acuity.

The mammalian snout has Meissner's corpuscles (MCs), which transmit epicritic sensations as the animal explores its surroundings. To comprehend the somatosensory acuity in mammals, we examined the structural organization and density of bovine Meissner-like corpuscles (BMLCs) at various ages and compared the changes with other mammalian MCs. The skin from the snout of cows or oxen (2-11 years old) was obtained and processed through routine histological technique. Five-µm thick sections were prepared, silver stained according to the Bielschowsky technique as modified by Winkelman and Schmidt (Mayo Clinic Proceedings, 1957, 217), and observed under a compound light microscope quantitatively and qualitatively. The glabrous skin of the cow snout consisted of two types of BMLCs: One was a cylindrical or elongated structure found in the dermal papillae. The other type was spherical and developed in the superficial layers of the epidermis. BMLCs consisted of both coarse and fine nerve fibres. In the young, the corpuscle comprised thin nerve fibres with indistinct cell outlines. In adults, nerve fibres in the corpuscles were closely packed, and networks, varicosities and end bulbs were well developed. With advancing age, the MCs attenuated into a disorganized mass of nerve fibres. The bovine snout is a highly evolved somatosensory organ due to its rich nerve supply and functionally resembles the anthropoid fingertip. Somatosensory acuity will be lower in the glabrous bovine skin than in primate glabrous skin of the fingertip, as the nerve terminals within the BMLCs are less elaborate in content and structural complexity.

Immunohistochemical detection of PIEZO1 and PIEZO2 in human digital Meissner´s corpuscles.

BACKGROUND: The cutaneous end organ complexes or cutaneous sensory corpuscles are specialized sensory organs associated to low-threshold mechanoreceptors. Mechano-gated proteins forming a part of ion channels have been detected in both the axon and terminal glial cells of Meissner corpuscles, a specific cutaneous end organ complex in the human glabrous skin. The main candidates to mechanotransduction in Meissner corpuscles are members of the Piezo family of cationic ion channels. PIEZO2 has been detected in the axon of these sensory structures whereas no data exists about the occurrence and cell localization of PIEZO1. METHODS: Skin samples (n = 18) from the palmar aspect of the distal phalanx of the first and second fingers were analysed (8 female and 10 males; age range 26 to 61 26-61 years). Double immunofluorescence for PIEZO1 and PIEZO2 together with axonal or terminal glial cell markers was captured by laser confocal microscopy, and the percentage of PIEZOs positive Meissner corpuscles was evaluated. RESULTS: MCs from human fingers showed variable morphology and degree of lobulation. Regarding the basic immunohistochemical profile, in all cases the axons were immunoreactive for neurofilament proteins, neuron specific enolase and synaptophysin, while the lamellar cells displayed strong S100P immunoreactivity. PIEZO1 was detected co-localizing with axonal markers, but never with terminal glial cell markers, in the 56% of Meissner corpuscles; weak but specific immunofluorescence was additionally detected in the epidermis, especially in basal keratinocytes. Similarly, PIEZO2 immunoreactivity was found restricted to the axon in the 85% of Meissner corpuscles. PIEZO2 positive Merkel cells were also regularly found. CONCLUSIONS: PIEZO1 and PIEZO2 are expressed exclusively in the axon of a subpopulation of human digital Meissner corpuscles, thus suggesting that not only PIEZO2, but also PIEZO1 may be involved in the mechanotransduction from low-threshold mechanoreceptors.

Cortical Response Variation with Social and Non-Social Affective Touch Processing in the Glabrous and Hairy Skin of the Leg: A Pilot fMRI Study.

Despite the crucial role of touch in social development and its importance for social interactions, there has been very little functional magnetic resonance imaging (fMRI) research on brain mechanisms underlying social touch processing. Moreover, there has been very little research on the perception of social touch in the lower extremities in humans, even though this information could expand our understanding of the mechanisms of the c-tactile system. Here, variations in the neural response to stimulation by social and non-social affective leg touch were investigated using fMRI. Participants were subjected to slow a (at 3-5 cm/s) stroking social touch (hand, skin-to-skin) and a non-social touch (peacock feather) to the hairy skin of the shin and to the glabrous skin of the foot sole. Stimulation of the glabrous skin of the foot sole, regardless of the type of stimulus, elicited a much more widespread cortical response, including structures such as the medial segment of precentral gyri, left precentral gyrus, bilateral putamen, anterior insula, left postcentral gyrus, right thalamus, and pallidum. Stimulation of the hairy skin of the shin elicited a relatively greater response in the left middle cingulate gyrus, left angular gyrus, left frontal eye field, bilateral anterior prefrontal cortex, and left frontal pole. Activation of brain structures, some of which belong to the "social brain"-the pre- and postcentral gyri bilaterally, superior and middle occipital gyri bilaterally, left middle and superior temporal gyri, right anterior cingulate gyrus and caudate, left middle and inferior frontal gyri, and left lateral ventricle area, was associated with the perception of non-social stimuli in the leg. The left medial segment of pre- and postcentral gyri, left postcentral gyrus and precuneus, bilateral parietal operculum, right planum temporale, left central operculum, and left thalamus proper showed greater activation for social tactile touch. There are regions in the cerebral cortex that responded specifically to hand and feather touch in the foot sole region. These areas included the posterior insula, precentral gyrus; putamen, pallidum and anterior insula; superior parietal cortex; transverse temporal gyrus and parietal operculum, supramarginal gyrus and planum temporale. Subjective assessment of stimulus ticklishness was related to activation of the left cuneal region. Our results make some contribution to understanding the physiology of the perception of social and non-social tactile stimuli and the CT system, including its evolution, and they have clinical impact in terms of environmental enrichment.

Comparison of brain functional response to mechanical prickling stimuli to the glabrous and hairy skin.

BACKGROUND: A kind of prickle sensation, which is a composite feeling of pain and itch, can be evoked by mechanical stimulation of fiber ends from fabric surface against to human hairy skin, rather than glabrous skin. Now, a functional magnetic resonance imaging (fMRI) study was conducted to investigate the cognitive differences in the brain for mechanical prickling stimuli to the two types of skin. MATERIALS AND METHODS: A nylon filament with the diameter of 205 µm and the length of 8 mm was used to deliver mechanical prickling stimuli respectively to two skin sites, fingertip (glabrous skin) and volar forearm (hairy skin), of eight healthy male subjects. Simultaneously, the technology of fMRI was adopted to acquire BOLD (Blood Oxygen Level-Dependent) signals of brain functional response of the subjects. RESULTS: Somatosensory areas, emotional areas, and the posterior parietal cortex (especially the precuneus) are important brain regions that distinguish between the two conditions. The representation of mechanical prickling stimulation to glabrous skin in the brain favors much more the tactile information of the stimulation and contains no itch, while the key brain area, precuneus, involved in itch was activated by the same mechanical prickling stimulation to hairy skin, and brain response for the condition of hairy skin contains more emotional information, which plays an important role in pain processing. CONCLUSION: Therefore, it can be inferred that a kind of stronger prickle sensation, which contains both pain and itch, was evoked by mechanical stimulation to hairy skin than glabrous skin.

Exploring somatosensory innervation of the human lip: A focus on the vermilion.

BACKGROUND: The lips are a vital component of the face and are densely innervated to perform various functions. The lip edges are covered with mucocutaneous tissue called vermilion which is particularly receptive to touch and temperature. The aim of this study was to investigate the somatosensory innervation of human lips, focusing on sensory corpuscles and the presence of mechano-gated (ASIC2, PIEZO2, and TRPV4) and thermosensing (TRPV1, TRPM2, and RPM8) ion channels within them. METHODS: Twelve intact lips (6 upper and 6 lower) were obtained from non-embalmed frozen cadavers (five females and seven males) with an age range of 60-80 years. The specimens were divided into three zones (medial, lateral, and median). The morphotypes of sensory corpuscles and their immunohistochemical profile was analysed. The occurrence of ion channels involved in mechanosensation and temperature detection was examined using various antibodies. Sensory corpuscle density was quantified in vermilion sections, and statistical analyses were conducted to assess differences between the upper and lower lips, as well as between females and males (p < 0.05). RESULTS: Different morphotypes of sensory corpuscles were identified: Ruffini-like associated with hair follicles, Meissner and glomerular corpuscles in the vermilion, and less classifiable sensory corpuscles within the mucosa. The density of sensory corpuscles in the vermilion was higher in the upper lip than in the lower lip; glomerular corpuscles predominated in the medial and median segments, whereas Meissner corpuscles were more abundant in the lateral segment. No sex-related differences were observed in the density or distribution of the two main corpuscular morphotypes. In contrast, the axons of both the glomeruli and Meissner corpuscles regularly displayed ASIC2 and PIEZO2 immunoreactivity, whereas immunoreactivity for TRPV1, TRPV4, TRPM2, and TRPV8 was absent. CONCLUSIONS: These results demonstrate that the sensory corpuscles of the vermilion are a mixture of those typical of glabrous skin mucocutaneous tissues. The presence of PIEZO2 and ASIC2 in their axons suggests that these sensory corpuscles function as mechanosensors.

Skin type and nerve effects on cortical tactile processing: a somatosensory evoked potentials study.

Somatosensory evoked potential (SEP) studies typically characterize short-latency components following median nerve stimulations of the wrist. However, these studies rarely considered 1) skin type (glabrous/hairy) at the stimulation site, 2) nerve being stimulated, and 3) middle-latency (>30 ms) components. Our aim was to investigate middle-latency SEPs following simple mechanical stimulation of two skin types innervated by two different nerves. Eighteen adults received 400 mechanical stimulations over four territories of the right hand (two nerves: radial/median; two skin types: hairy/glabrous skin) while their EEG was recorded. Four middle-latency components were identified: P50, N80, N130, and P200. As expected, significantly shorter latencies and larger amplitudes were found over the contralateral hemisphere for all components. A skin type effect was found for the N80; glabrous skin stimulations induced larger amplitude than hairy skin stimulations. Regarding nerve effects, median stimulations induced larger P50 and N80. Latency of the N80 was longer after median nerve stimulation compared with radial nerve stimulation. This study showed that skin type and stimulated nerve influence middle-latency SEPs, highlighting the importance of considering these parameters in future studies. These modulations could reflect differences in cutaneous receptors and somatotopy. Middle-latency SEPs can be used to evaluate the different steps of tactile information cortical processing. Modulation of SEP components before 100 ms possibly reflects somatotopy and differential processing in primary somatosensory cortex.NEW & NOTEWORTHY The current paper highlights the influences of stimulated skin type (glabrous/hairy) and nerve (median/radial) on cortical somatosensory evoked potentials. Mechanical stimulations were applied over four territories of the right hand in 18 adults. Four middle-latency components were identified: P50, N80, N130, and P200. A larger N80 was found after glabrous skin stimulations than after hairy skin ones, regardless of the nerve being stimulated. P50 and N80 were larger after median than radial nerve stimulations.

Human glabrous skin contains crystallized urea dendriform structures in the stratum corneum which affect the hydration levels.

Glabrous skin is hair-free skin with a high density of sweat glands, which is found on the palms, and soles of mammalians, covered with a thick stratum corneum. Dry hands are often an occupational problem which deserves attention from dermatologists. Urea is found in the skin as a component of the natural moisturizing factor and of sweat. We report the discovery of dendrimer structures of crystalized urea in the stratum corneum of palmar glabrous skin using laser scanning microscopy. The chemical and structural nature of the urea crystallites was investigated in vivo by non-invasive techniques. The relation of crystallization to skin hydration was explored. We analysed the index finger, small finger and tenar palmar area of 18 study participants using non-invasive optical methods, such as laser scanning microscopy, Raman microspectroscopy and two-photon tomography. Skin hydration was measured using corneometry. Crystalline urea structures were found in the stratum corneum of about two-thirds of the participants. Participants with a higher density of crystallized urea structures exhibited a lower skin hydration. The chemical nature and the crystalline structure of the urea were confirmed by Raman microspectroscopy and by second harmonic generated signals in two-photon tomography. The presence of urea dendrimer crystals in the glabrous skin seems to reduce the water binding capacity leading to dry hands. These findings highlight a new direction in understanding the mechanisms leading to dry hands and open opportunities for the development of better moisturizers and hand disinfection products and for diagnostic of dry skin.

Revealing the Meissner Corpuscles in Human Glabrous Skin Using In Vivo Non-Invasive Imaging Techniques.

The presence of mechanoreceptors in glabrous skin allows humans to discriminate textures by touch. The amount and distribution of these receptors defines our tactile sensitivity and can be affected by diseases such as diabetes, HIV-related pathologies, and hereditary neuropathies. The quantification of mechanoreceptors as clinical markers by biopsy is an invasive method of diagnosis. We report the localization and quantification of Meissner corpuscles in glabrous skin using in vivo, non-invasive optical microscopy techniques. Our approach is supported by the discovery of epidermal protrusions which are co-localized with Meissner corpuscles. Index fingers, small fingers, and tenar palm regions of ten participants were imaged by optical coherence tomography (OCT) and laser scan microscopy (LSM) to determine the thickness of the stratum corneum and epidermis and to count the Meissner corpuscles. We discovered that regions containing Meissner corpuscles could be easily identified by LSM with an enhanced optical reflectance above the corpuscles, caused by a protrusion of the strongly reflecting epidermis into the stratum corneum with its weak reflectance. We suggest that this local morphology above Meissner corpuscles has a function in tactile perception.

Properties of Nav1.8ChR2-positive and Nav1.8ChR2-negative afferent mechanoreceptors in the hindpaw glabrous skin of mice.

Nav1.8-positive afferent fibers are mostly nociceptors playing a role in mediating thermal and mechanical pain, but mechanoreceptors within these afferents have not been fully investigated. In this study, we generated mice expressing channel rhodopsin 2 (ChR2) in Nav1.8-positive afferents (Nav1.8ChR2), which showed avoidance responses to mechanical stimulation and nocifensive responses to blue light stimulation applied to hindpaws. Using ex vivo hindpaw skin-tibial nerve preparations made from these mice, we characterized properties of mechanoreceptors on Nav1.8ChR2-positive and Nav1.8ChR2-negative afferent fibers that innervate the hindpaw glabrous skin. Of all Aß-fiber mechanoreceptors, small portion was Nav1.8ChR2-positive. Of all Aδ-fiber mechanoreceptors, more than half was Nav1.8ChR2-positive. Of all C-fiber mechanoreceptors, almost all were Nav1.8ChR2-positive. Most Nav1.8ChR2-positive Aß-, Aδ-, and C-fiber mechanoreceptors displayed slowly adapting (SA) impulses in response to sustained mechanical stimulation, and their mechanical thresholds were high in the range of high threshold mechanoreceptors (HTMRs). In contrast, sustained mechanical stimulation applied to Nav1.8ChR2-negative Aß- and Aδ-fiber mechanoreceptors evoked both SA and rapidly adapting (RA) impulses, and their mechanical thresholds were in the range of low threshold mechanoreceptors (LTMRs). Our results provide direct evidence that in the mouse glabrous skin, most Nav1.8ChR2-negative Aß-, Aδ-fiber mechanoreceptors are LTMRs involving in the sense of touch, whereas Nav1.8ChR2-positive Aß-, Aδ-, and C-fiber mechanoreceptors are mainly HTMRs involving in mechanical pain.

Novel temperature-controlled sleep system to improve sleep: a proof-of-concept study.

The sleep-wake cycle is regulated by circadian Process C and homeostatic Process S. Selective thermal stimulation (STS) of the cervical spine region enhances glabrous skin blood flow (GSBF) and augments body heat dissipation to increase distal-to-proximal skin gradient (DPG) causing decrease of core body temperature (CBT), which can shorten sleep onset latency (SOL) and improve sleep quality. A total of 11 young healthy/normal sleeper males challenged to go to bed (lights-off) 2 h earlier than usual were subjected in a randomised order to non-consecutive treatment and control night-time sleep sessions. The treatment night entailed activation of a dual-temperature zone mattress with a cooler centre and warmer periphery plus STS pillow that applied mild heating to the cervical spinal skin for 30 min after lights-off for sleep. During the first 30 min after lights-off, GSBF (mean [standard error (SE)] Δ = 49.77 [19.13] perfusion units, p = 0.013) and DPG (mean [SE] Δ = 2.05 [0.62] °C, p = 0.005) were significantly higher and CBT (mean [SE] Δ = -0.15 [0.07] °C, p = 0.029) was significantly lower in the treatment than control night, while there was no significant difference in these variables during the 45 min prior to lights-off (baseline). Moreover, SOL was significantly reduced (mean [SE] Δ = -48.6 [23.4] min, p = 0.032) and subjective sleep quality significantly better (p < 0.001) in the treatment than control night. In conclusion, the novel sleep facilitating system comprised of the STS pillow plus dual-temperature zone mattress induced earlier increase in GSBF and DPG and earlier decline in CBT. This resulted in statistically significant shortened SOL and improved overall sleep quality, thereby reducing sleep pressure of Process S, even under the challenging investigative protocol requiring participants to go to sleep 2 h earlier than customary.

Skin and Mechanoreceptor Contribution to Tactile Input for Perception: A Review of Simulation Models.

We review four current computational models that simulate the response of mechanoreceptors in the glabrous skin to tactile stimulation. The aim is to inform researchers in psychology, sensorimotor science and robotics who may want to implement this type of quantitative model in their research. This approach proves relevant to understanding of the interaction between skin response and neural activity as it avoids some of the limitations of traditional measurement methods of tribology, for the skin, and neurophysiology, for tactile neurons. The main advantage is to afford new ways of looking at the combined effects of skin properties on the activity of a population of tactile neurons, and to examine different forms of coding by tactile neurons. Here, we provide an overview of selected models from stimulus application to neuronal spiking response, including their evaluation in terms of existing data, and their applicability in relation to human tactile perception.

Second-Layer Palmar Graft for Fingertip Reconstruction: An Analysis of Aesthetic and Functional Outcomes.

BACKGROUND:  Fingertip injuries are very common and require a stable and durable cover. The end result after reconstruction must be a painless finger with good aesthetic appearance. Skin loss in fingertip, with or without partial loss of pulp fat, is often managed with a split-thickness skin graft, which causes a poor aesthetic result due to color mismatch of the grafted skin in the glabrous volar skin of fingertip. The full-thickness and partial-thickness skin graft harvested from palmar skin provide color match but may cause donor site morbidity in the form of painful scar or contour deformity. Harvest of the second layer from the palm (intermediate part of dermis) allowed the first layer (epidermis with superficial part of dermis) to be reposed over the remaining dermis in palm, thus allowing closure of donor defect without any tension. This technique provides a good color match for the primary defect, along with reduced donor site morbidity. AIM: The study aims to analyze the outcomes of second-layer palmar graft (SLPG) in patients with fingertip injuries. MATERIALS AND METHODS:  The retrospective study was conducted in January 2012 on 40 patients who underwent SLPG. RESULT:  The graft take was 100% in 36 patients with an average static two-point discrimination (2PD) of 6 mm. The average cosmetic visual analog score for the donor area was 100 and recipient site was 80. CONCLUSION:  The SLPG is a good surgical procedure for reconstructing fingertip defects, providing excellent aesthetic appearance and optimal function.

Mechanical Impedance of Rat Glabrous Skin and Its Relation With Skin Morphometry.

The mechanical impedance of intact and epidermis-peeled rat glabrous skin was studied at two sites (digit and sole) and at two frequencies (40 Hz and 250 Hz). The thicknesses of skin layers at the corresponding regions were measured histologically from intact- and peeled-skin samples in every subject. Compared to intact sole skin, digital rat skin has thicker layers and higher mechanical resistance, and it is less stiff. The resistance of the skin significantly decreased after epidermal peeling at both the digit and the sole. Furthermore, peeling caused the reactance to become positive due to inertial effects. As the frequency was increased from 40 to 250 Hz, the resistance and stiffness also increased for the intact skin, while the peeled skin showed less frictional (i.e., resistance) but more inertial (i.e., positive reactance) effects. We estimated the mechanical properties of epidermis and dermis with lumped-element models developed for both intact and peeled conditions. The models predicted that dermis has higher mass, lower stiffness, and lower resistance compared to epidermis, similar to the experimental impedance results obtained in the peeled condition which consisted mostly of dermis. The overall impedance was simulated more successfully at 40 Hz. When both frequencies are considered, the models produced consistent results for resistance in both conditions. The results imply that most of the model parameters should be frequency-dependent and suggest that mechanical properties of epidermis can be related to its thickness. These findings may help in designing artificial skin for neuroprosthetic limbs.

Efficacy and Function of Feathers, Hair, and Glabrous Skin in the Thermoregulation Strategies of Domestic Animals.

The objective of this review is to describe and analyze the effect of feathers, hair, and glabrous (hairless) skin on the thermoregulation of domestic and endotherm animals, especially concerning the uses and scope of infrared thermography (IRT), scientific findings on heat and cold stress, and differences among species of domestic animals. Clinical medicine considers thermoregulation a mechanism that allows animals to adapt to varying thermal environmental conditions, a process in which the presence of feathers, hair, or glabrous skin influences heat loss or heat retention, respectively, under hot and cold environmental conditions. Evaluating body temperature provides vital information on an individual's physiological state and health status since variations in euthermia maintenance in vertebrates reflect a significant cellular metabolism deviation that needs to be assessed and quantified. IRT is a non-invasive tool for evaluating thermal responses under thermal stress conditions in animals, where the presence or absence of feathers, hair, and glabrous skin can affect readings and the differences detected. Therefore, anatomical regions, the characteristics of feathers, hair, glabrous skin such as structure, length, color, and extension, and strategies for dissipating or retaining heat together constitute a broad area of opportunity for future research into the phenomena of dermal thermoregulation in domestic species.

Involvement of Cutaneous Sensory Corpuscles in Non-Painful and Painful Diabetic Neuropathy.

Distal diabetic sensorimotor polyneuropathy (DDSP) is the most prevalent form of diabetic neuropathy, and some of the patients develop gradual pain. Specialized sensory structures present in the skin encode different modalities of somatosensitivity such as temperature, touch, and pain. The cutaneous sensory structures responsible for the qualities of mechanosensitivity (fine touch, vibration) are collectively known as cutaneous mechanoreceptors (Meissner corpuscles, Pacinian corpuscles, and Merkel cell-axonal complexes), which results are altered during diabetes. Here, we used immunohistochemistry to analyze the density, localization within the dermis, arrangement of corpuscular components (axons and Schwann-like cells), and expression of putative mechanoproteins (PIEZO2, ASIC2, and TRPV4) in cutaneous mechanoreceptors of subjects suffering clinically diagnosed non-painful and painful distal diabetic sensorimotor polyneuropathy. The number of Meissner corpuscles, Pacinian corpuscles, and Merkel cells was found to be severely decreased in the non-painful presentation of the disease, and almost disappeared in the painful presentation. Furthermore, there was a marked reduction in the expression of axonal and Schwann-like cell markers (with are characteristics of corpuscular denervation) as well as of all investigated mechanoproteins in the non-painful distal diabetic sensorimotor polyneuropathy, and these were absent in the painful form. Taken together, these alterations might explain, at least partly, the impairment of mechanosensitivity system associated with distal diabetic sensorimotor polyneuropathy. Furthermore, our results support that an increasing severity of DDSP may increase the risk of developing painful neuropathic symptoms. However, why the absence of cutaneous mechanoreceptors is associated with pain remains to be elucidated.

Treating complex palmar-plantar wounds using a bilaminar 'trapdoor' technique: a case series.

OBJECTIVE: Due to the similarities of glabrous skin, the plantar region is an excellent donor area for covering complex palmar-plantar wounds. However, taking grafts from the plantar area often results in significant morbidity at the donor site or non-integration of the graft due to the greater thickness of the plantar corneal layer. METHOD: This is a prospective case series including patients with burns or wounds who have been treated with a dermal graft using the bilaminar 'trapdoor' technique. This procedure is used to remove a thin graft from the deep plantar dermis after the partial elevation of the first layer including the entire epidermis and superficial part of the dermis. RESULTS: At the donor area in the four patients in this case series, we observed healing at around 10 days, and absence of hypertrophic scar in all patients. There was complete re-epithelialisation between two and three weeks from the periphery to the centre of the deep dermal graft, and from the glandular epithelium transferred with the graft. During the follow-up, patients presented aesthetic and functional features of glabrous and amelanotic skin, with similar resistance to those of the adjacent areas of the wound in the palmar-plantar region. CONCLUSION: This technique has some advantages, such as less surgical time, minimal morbidity in the plantar donor area, easy integration of the grafts, and maintenance of the functional and aesthetic properties of glabrous skin both in the plantar donor area and in the palmar-plantar recipient region. DECLARATION OF INTEREST: The authors have no conflicts of interest to declare.