Sonography of the skin at 100 MHz enables in vivo visualization of stratum corneum and viable epidermis in palmar skin and psoriatic plaques.
A main drawback of 20-25 MHz ultrasound units for skin imaging is their limited resolution. We used a transducer with a center frequency of 95 MHz and a resolution of 8.5 microm axially and 27 microm laterally - an almost 10-fold increase compared with 20 MHz. By means of a new scanning technology we reached a depth of field of 3.2 mm. We examined normal palmar skin, normal glabrous skin on the abdomen, the upper back, the calf and the dorsal forearm, and 35 lesions of psoriasis vulgaris. From 11 psoriatic plaques biopsies were taken for correlation with the sonograms. In normal palmar skin, the horny layer is represented as an echopoor band below the skin entry echo, traversed by echorich coils, which correspond to eccrine sweat gland ducts. The thickness of this band significantly increases after occlusive application of petrolatum. Its lower border is defined by an echorich line, representing the stratum corneum/stratum Malpighii-interface. Underneath, a second echopoor band is visible, which corresponds to the viable epidermis plus the papillary dermis, bordered by the scattered echo reflexes of the reticular dermis. This band is also visible in glabrous skin; however, the stratum corneum cannot be detected. In psoriatic lesions, the thickened horny layer appears echorich; after application of petrolatum, its echodensity decreases. Below, the acanthotic epidermis plus the dermis with the inflammatory infiltrate are represented as an echopoor band. There is an excellent correlation between the sonometric thickness of this band and the histometric thickness of the acanthosis plus the infiltrated dermis. Our results show that 100 MHz sonography is a valuable tool for in vivo examination of the upper skin layers. (+info)
Mechanical cutaneous stimulation alters Ia presynaptic inhibition in human wrist extensor muscles: a single motor unit study.
Reflex responses were evoked by radial nerve stimulation in 25 single motor units in the extensor carpi radialis muscles of seven subjects during voluntary isometric wrist extension. The responses consisted of narrow peaks in the post-stimulus time histograms with latencies compatible with monosynaptic activation. When the skin of the palm and finger tips was continuously swept using a soft rotating brush, the purely monosynaptic components of the motor unit responses, as assessed from the contents of the first two 0.25 ms bins of the peak, were found to increase. This increase did not affect the motoneurone net excitatory drive, as assessed by measuring the mean duration of the inter-spike intervals. The cutaneous inputs activated by the brush may have reduced the tonic presynaptic inhibition exerted on the Ia afferents homonymous to the extensor motor units tested. To further investigate whether Ia presynaptic inhibition was involved, the responses of the extensor motor units were conditioned by stimulating the median nerve 20 ms earlier, using a protocol which is known to induce Ia extensor presynaptic inhibition originating from flexor Ia afferents. The median nerve stimulation did not affect the motoneurone excitatory drive, but led to a decrease in the responses of the extensor motor units to the radial nerve stimulation, especially in the purely monosynaptic components. This decrease was consistent with the Ia presynaptic inhibition known to occur under these stimulation conditions. The cutaneous inputs activated by the brush were found to reduce the Ia presynaptic inhibition generated by the median nerve stimulation, without affecting the distribution of the Ia presynaptic inhibition among the various types of motor units tested. The present data suggest that cutaneous inputs from the palm and finger tips may relieve the Ia presynaptic inhibition exerted on the wrist extensor motor nuclei, and thus enhance the proprioceptive assistance to fit the specific requirements of the ongoing motor task. (+info)
Stratum corneum tryptic enzyme in normal epidermis: a missing link in the desquamation process?
Stratum corneum chymotryptic enzyme may be important in desquamation. It has also been suggested that other proteases, especially stratum corneum tryptic enzyme, may be involved. Stratum corneum tryptic enzyme has been purified and its cDNA has been cloned. Results from expression analyses indicate that stratum corneum tryptic enzyme is as skin specific as stratum corneum chymotryptic enzyme. In this work we have produced and characterized antibodies specific for stratum corneum tryptic enzyme. We have also by means of biochemical, immunochemical, and immunohistochemical methods performed studies on stratum corneum tryptic enzyme in normal human epidermis. Antibodies against bacterial recombinant stratum corneum tryptic enzyme were produced and purified by affinity chromatography. Two types of antibodies were obtained: one reacting only with pro-stratum corneum tryptic enzyme and one specific for the catalytically active part of stratum corneum tryptic enzyme. Immunohistochemistry with the antibodies reacting with pro-stratum corneum tryptic enzyme showed a staining pattern similar to stratum corneum chymotryptic enzyme-specific antibodies, i.e., the expression was confined to cornifying epithelia with a need of desquamation-like processes. Extracts of tape strips with superficial human stratum corneum were found to contain precursors as well as active forms of stratum corneum tryptic enzyme and stratum corneum chymotryptic enzyme. The enzymes had maximal activity at pH 8, but both had considerable activity also at pH 5.5. The results were compatible for a role of stratum corneum tryptic enzyme in desquamation. Stratum corneum tryptic enzyme may act in concert with stratum corneum chymotryptic enzyme and/or function as a stratum corneum chymotryptic enzyme-activating enzyme. The presence in normal superficial stratum corneum of precursors as well as of active forms of stratum corneum chymotryptic enzyme and stratum corneum tryptic enzyme, and the activity of both enzymes over a broad range of pH-values, suggest some possible ways by which the desquamation may be regulated. (+info)
Modulation of arterial baroreflex control of heart rate by skin cooling and heating in humans.
The purpose of this study was to examine the effects of skin cooling and heating on the heart rate (HR) control by the arterial baroreflex in humans. The subjects were 15 healthy men who underwent whole body thermal stress (esophageal temperatures, approximately 36.8 and approximately 37.0 degrees C; mean skin temperatures, approximately 26.4 and approximately 37.7 degrees C, in skin cooling and heating, respectively) produced by a cool or hot water-perfused suit during supine rest. The overall arterial baroreflex sensitivity in the HR control was calculated from spontaneous changes in beat-to-beat arterial pressure and HR during normothermic control and thermal stress periods. The carotid baroreflex sensitivity was evaluated from the maximum slope of the HR response to changes in carotid distending pressure, calculated as mean arterial pressure minus neck pressure. The overall arterial baroreflex sensitivity at existing arterial pressure increased during cooling (-1.32 +/- 0.25 vs. -2.13 +/- 0.20 beats. min(-1). mmHg(-1) in the control and cooling periods, respectively, P < 0.05), whereas it did not change significantly during heating (-1.39 +/- 0. 23 vs. -1.40 +/- 0.15 beats. min(-1). mmHg(-1) in the control and heating periods, respectively). Neither the cool nor heat loadings altered the carotid baroreflex sensitivity in the HR control. These results suggest that the sensitivity of HR control by the extracarotid (presumably aortic) baroreflex was augmented by whole body skin cooling, whereas the sensitivities of HR control by arterial baroreflex remain unchanged during mild whole body heating in humans. (+info)
Effects of atropine and L-NAME on cutaneous blood flow during body heating in humans.
We sought to investigate further the roles of sweating, ACh spillover, and nitric oxide (NO) in the neurally mediated cutaneous vasodilation during body heating in humans. Six subjects were heated with a water-perfused suit while cutaneous blood flow was measured with a laser-Doppler flowmeter. After a rise in core temperature (1. 0 +/- 0.1 degrees C) and the establishment of cutaneous vasodilation, atropine and subsequently the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) were given to the forearm via a brachial artery catheter. After atropine infusion, cutaneous vascular conductance (CVC) remained constant in five of six subjects, whereas L-NAME administration blunted the rise in CVC in three of six subjects. A subsequent set of studies using intradermal microdialysis probes to selectively deliver drugs into forearm skin confirmed that atropine did not affect CVC. However, perfusion of L-NAME resulted in a significant decrease in CVC (37 +/- 4%, P < 0.05). The results indicate that neither sweating nor NO release via muscarinic receptor activation is essential to sustain cutaneous dilation during heating in humans. (+info)
Effects of anion substitution on hydration behavior and water uptake of the red-spotted toad, Bufo punctatus: is there an anion paradox in amphibian skin?
Amphibians absorb water osmotically across their skins and rely on chemosensory information from the skin to assess the suitability of hydration sources. The time spent with skin in contact with a moist surface provides a quantitative measure of their ability to perceive the ionic and osmotic properties of aqueous solutions. Dehydrated toads given hyperosmotic (250 mM) solutions of NaCl or Na-gluconate showed significantly longer periods of hydration behavior on the gluconate solution, but they lost water osmotically when immersed in either solution. Similarly, dehydrated toads given 250 mM solutions of NaCl, Na-acetate, Na-phosphate or Na-gluconate showed a progressively greater length of hydration time on solutions with the larger mol. wt anions. These results are consistent with the chemosensory phenomenon previously described in mammalian tongue as 'anion paradox'. On dilute (50 mM) solutions of NaCl or Na-gluconate, the hydration time was not different between anions, despite toads gaining water more rapidly when immersed in dilute NaCl than in Na-gluconate solutions. The differing behavioral results with hyperosmotic and hypoosmotic salt solutions suggest that chemosensory transduction through toad skin involves both transcellular and paracellular pathways. (+info)
Encoding of location and intensity of noxious indentation into rat skin by spatial populations of cutaneous mechano-nociceptors.
The ability of a spatial population of cutaneous, Adelta, and C mechano-nociceptors to encode the location and intensity of a noxious, cutaneous indentation was examined using an isolated preparation in a rat model. Skin and its intact innervation were harvested from the medial thigh of the rat hindlimb and placed in a dish, with the corium side down, containing synthetic interstitial fluid. The margins of the skin were coupled to an apparatus that could stretch and apply compression to the skin. The skin was suspended on top of a deformable platform whose bulk, nonlinear, compressive compliance emulated that found in vivo. The isolated preparation facilitated examination of the spatial population response by eliminating the nonlinear geometry and inhomogeneous compressive compliance present in-vivo. Spatial population responses (SPR) were formed from recordings of single neurons that were stimulated by compressing the skin with an indenter (flat cylinder, 3-mm diam) at discrete intervals from the center of their receptive fields. SPR were composed of the neural responses (z axis) at each indentation location (x, y plane), and were analyzed quantitatively using nonlinear regression to fit an equation of a Gaussian surface. Both Adelta and C SPR accurately encoded the location and intensity of noxious indentation. The intensity of the stimulus was encoded in the peak neural response of the SPR, which had a nonlinear relationship to the compressive force. The location of the stimulus was encoded in the x, y position of the peak of the SPR. The position of the peak remained constant with increasing magnitudes of compressive force. The overall form of the SPR also remained constant with changes of compressive load, suggesting a possible role for encoding in the SPR some aspects of shape of a noxious stimulus. (+info)
Skin development: delta laid bare.
Notch signalling is best known for its role in lateral inhibition, where it acts to prevent differentiation of cells neighbouring one that has 'won out' in a competition to differentiate. Recent results suggest that Notch signalling can work in the opposite way, and promote differentiation of the receiving cells. (+info)