Electrical matrix stimulation suppresses acute itch independently of activation of sleeping nociceptors.

INTRODUCTION: Itch can be reduced by pain. Activation of sleeping nociceptors (CMi) is a crucial mechanism for the peripheral component of intense and long-lasting pain. Thus, activation of CMi might be especially effective in itch reduction. Electrical stimulation using sinusoidal pulses activates CMi with tolerable pain intensity, whereas short rectangular pulses with low intensity do not. In humans, histaminergic itch is mediated by histamine-sensitive CMi, whereas other pruritogens activate polymodal nociceptors (CM). METHODS: In a psychophysical approach in a balanced crossover repeated-measures design in healthy volunteers, we activated nociceptors by two different electrical stimulation paradigms via a matrix electrode: 4 Hz sinusoidal pulses that activate C-nociceptors including CMi or 4 Hz rectangular stimuli to activate nociceptors excluding CMi. After 5-min stimulation, itch was induced by either histamine iontophoresis or application of cowhage spicules. Itch ratings were assessed via a numerical rating scale (NRS). RESULTS: Electrical 4 Hz sine wave stimulation (0.1 mA) with low pain ratings of 1.5 (NRS; 0-10) induced an axon reflex erythema (3 cm2 ), indicating activation of CMi, whereas rectangular 0.2 ms pulses (average 0.91 mA) with the same pain rating did not. Both electrical stimulation paradigms reduced itch magnitude over time evoked by either histamine or cowhage to a similar extent. Peak maximum itch evoked by histamine was reduced by both stimulation paradigms, but not cowhage maximum itch. DISCUSSION: Since electrical stimulation with the rectangular pulse paradigm reduces itch to a similar extent as the sine wave stimulation paradigm, the input of CMi is not necessarily required for itch suppression. The input of A-fibres and polymodal nociceptors, similarly, as also achieved by scratching, seems to be sufficient for both forms of chemically evoked itch. SIGNIFICANCE: Since activation of CMi does not provide additional benefit for itch suppression, spinal pain pathways transmitted via CM versus CMi have differential effects on itch-processing circuits. This is important knowledge for using electrical matrix stimulation as itch suppressor since activation of sleeping nociceptors either requires significantly painful stimulation paradigms or specialized stimulation paradigms as sinusoidal pulses. An alternative approach using half-sine wave pulses with low pain intensity activating specifically polymodal nociceptors to suppress itch via matrix electrode stimulation may be considered.

[Physiology of the scalp]. / Physiologie der Kopfhaut.

BACKGROUND: Human scalp reveals a remarkable difference to hairy skin of other body regions. The structure of the scalp offers effective protection against water loss and contributes to thermoregulation due to significant vascularization. The scalp is innervated by the trigeminus nerve. OBJECTIVES: The majority of the population complain about "sensitive" scalp. However, sensory, regional, ethnic or pathologic parameters contributing to "sensitive" scalp are largely unknown. MATERIALS AND METHODS: Quantitative sensory tests and superficial topical application test of irritant substances were performed. RESULTS: Extremely high thresholds to thermal and mechanical stimuli were recorded at the vertex compared to occipital or temporal scalp regions, or the hairy skin of other body regions such as trunk or distal extremities. Pronounced scalp hypersensitivity can be found in Asians as compared to Caucasians and under pathologic conditions, such as alopecia, dandruff, or migraine. CONCLUSIONS: Putative causes of "sensitive" scalp can be a facilitated transdermal penetration of irritant substances, altered neuronal innervation or receptor expression, or peripheral and central sensitization of sensory afferents.

Short lasting transient effects of a capsaicin 8% patch on nociceptor activation in humans.

BACKGROUND: At high concentration, the TRPV-1 agonist capsaicin de-sensitizes nociceptors and reduces the intra-epidermal nerve density. METHODS: We investigated the effects of a 5 × 10 cm capsaicin 8% patch on C- and A-delta-nociceptor activation in ten healthy subjects before and at days 1-3-7-21 after patch application. Thermal thresholds, infrared thulium-YAG laser-evoked potentials (LEP) and heat pain (numeric rating scale, NRS, 0-10), electrically induced pain (10 pulses, 1.5-fold pain threshold intensity, five randomized series of 5-10-20-50-100 Hz), and axon-reflex flare (laser Doppler imaging) were recorded. RESULTS: Thermal hypoesthesia developed upon capsaicin 8% treatment. Warmth detection thresholds increased at day 1-3, heat pain thresholds were increased by about 2.6 °C after day 3, and laser-evoked heat pain remained significantly reduced for 7 days. Axon-reflex flare responses (days 1-3), but not supra-threshold electrically induced pain were significantly reduced by the capsaicin patch. CONCLUSIONS: Axonal nociceptor function assessed by electrical excitability tests supplements threshold tests of nociceptive endings. The differential analgesic effects of 8% capsaicin patches may be attributed to the kinetics of capsaicin and the different depth of nociceptive nerve fibres, yet, the time course does not match the long-lasting analgesia observed in neuropathic pain patients treated with the same patch. WHAT DOES THIS STUDY ADD?: Axonal nociceptor function assessed by supra-threshold electrical excitability tests did not coincide with capsaicin-induced transduction changes supplementing threshold measures of terminal nociceptor endings. Threshold measurements do not reflect the sustained effect of pain relief seen in neuropathic pain patients. Capsaicin-sensitive nociceptors responsible for spontaneous pain are either not specifically tested with currently available sensory stimulation protocols or have higher capsaicin sensitivity or slower recovery under neuropathic conditions.

Mechano-sensitive nociceptors are required to detect heat pain thresholds and cowhage itch in human skin.

BACKGROUND: Mechano-sensitive and mechano-insensitive C-nociceptors in human skin differ in receptive field sizes and electrical excitation thresholds, but their distinct functional roles are yet unclear. METHODS: After blocking the lateral femoral cutaneous nerve (NCFL) in eight healthy male subjects (3-mL Naropin(®) 1%), we mapped the skin innervation territory being anaesthetic to mechanical pin prick but sensitive to painful transcutaneous electrical stimuli. Such 'differentially anaesthetic zones' indicated that the functional innervation with mechano-sensitive nociceptors was absent but the innervation with mechano-insensitive nociceptors remained intact. In these areas, we explored heat pain thresholds, low pH-induced pain, cowhage- and histamine-induced itch, and axon reflex flare. RESULTS: In differentially anaesthetic skin, heat pain thresholds were above the cut-off of 50°C (non-anaesthetized skin 47 ± 0.4°C). Pain ratings to 30 µL pH 4 injections were reduced compared to non-anaesthetized skin (48 ± 9 vs. 79 ± 6 VAS; p < 0.01). The axon reflex flare area did not differ between these zones (7.8 ± 1.4 cm(2) vs. 8.3 ± 0.5 cm(2) ). Histamine iontophoresis still caused pruritus in differentially anaesthetized skin in five of eight subjects (VAS 26 ± 14), whereas itch upon cowhage spicules was absent (VAS 0 vs. 29 ± 11 in non-anaesthetized skin). CONCLUSIONS: We conclude that activation of mechano-insensitive nociceptors is sufficient to provoke itch by histamine- and acid-induced pain. The mechano-sensitive nociceptors are crucial for cowhage-induced itch and for the assessment of heat pain thresholds.

Laser-evoked potentials mediated by mechano-insensitive nociceptors in human skin.

OBJECTIVES: Laser-evoked potentials (LEP) were assessed after peripheral nerve block of the lateral femoral cutaneous nerve (LFCN) in healthy volunteers from partially anesthetized skin areas to differentially stimulate mechano-insensitive nociceptors. METHODS: An ultrasound-guided nerve block of the LFCN was performed in 12 healthy male subjects with Ropivacain 1%. After 30 min, the nerve block induced significantly larger anesthetic areas to mechanical stimuli than to electrical stimuli revealing an area of differential sensitivity. LEPs, reaction times and pain ratings were recorded in response to the laser stimuli of (1) completely anesthetic skin, (2) mechano-insensitive, but electrically excitable skin ('differential sensitivity'), (3) normal skin. RESULTS: LEP latencies in the area of differential sensitivity were increased compared to unaffected skin (228 ± 8.5 ms, vs. 181 ± 3.6 ms, p < 0.01) and LEP amplitudes were reduced (14.8 ± 1.2 µV vs. 24.6 ± 1.7 µV, p < 0.01). Correspondingly, psychophysically assessed response latencies in the differentially anesthetic skin were increased (649 ms vs. 427 ms, p < 0.01) and pain ratings reduced (1.5/10 vs. 5/10 NRS, p < 0.01). CONCLUSION: The increase in LEP latency suggests that mechano-insensitive heat-sensitive Aδ nociceptors (MIA, type II) have a slower conduction velocity or higher utilization time than mechano-sensitive type II Aδ nociceptors. Moreover, widely branched, slowly conducting and mechano-insensitive branches of Aδ nociceptors can explain our finding. LEPs in the differentially anesthetized skin provide specific information about a mechanically insensitive but heat-sensitive subpopulation of Aδ nociceptors. These findings support the concept that A-fibre nociceptors exhibit a similar degree of modality specificity as C-fibre nociceptors.

Differential time course of NGF-induced hyperalgesia to heat versus mechanical and electrical stimulation in human skin.

BACKGROUND: Nerve growth factor (NGF) causes early heat and delayed mechanical hyperalgesia. Axonal transport might contribute to lasting responses. Temporal hyperalgesia development was investigated by administering NGF in paraspinal skin. Transient receptor potential ankyrin 1 (TRPA1) is up-regulated by NGF and chemical responsiveness to cinnamon aldehyde (TRPA1 agonist) was quantified. METHODS: Eight healthy volunteers received 1 µg human recombinant NGF (i.d. 50 µL) to L4/L5 processi spinosi skin. Mechanical, thermal and electrical sensitization was assessed at 3-6 h and at days 1, 2, 3, 5, 7, 10, 14 and 21, and pain upon cinnamon aldehyde (20%, 60 µL) recorded at days 3 and 21. RESULTS: Heat hyperalgesia developed with an initial maximum at 3 h [heat pain threshold -3.9°; peak pain ratings +22 visual analogue scale (VAS)] that decreased by day 1, subsequently increased to a maximum around day 5 (-5 ± 0.2 °C, +41 ± 4 VAS), and thereafter declined to ∼20% at day 21. Mechanical and electrical hyperexcitability developed within 3 days and gradually increased to peak between days 14 and 21. Pain intensity upon cinnamon aldehyde stimulation was doubled at the NGF site at day 3 and was still increased by about 50% at day 21. CONCLUSIONS: NGF causes immediate heat hyperalgesia probably linked to an up-regulation and sensitization of transient receptor potential vanilloid 1 and possibly other proteins involved in heat transduction. The delayed mechanical hyperalgesia is apparently independent of the time required for axonal transport of NGF receptor complexes. Local mRNA translation at axonal terminals and protein accumulation is hypothesized being involved in sustained NGF-evoked hyperalgesia.

Skin innervation at different depths correlates with small fibre function but not with pain in neuropathic pain patients.

BACKGROUND: Neuropathy can lead not only to impaired function but also to sensory sensitization. We aimed to link reduced skin nerve fibre density in different levels to layer-specific functional impairment in neuropathic pain patients and tried to identify pain-specific functional and structural markers. METHODS: In 12 healthy controls and 36 patients with neuropathic pain, we assessed clinical characteristics, thermal thresholds (quantitative sensory testing) and electrically induced pain and axon reflex erythema. At the most painful sites and at intra-individual control sites, skin biopsies were taken and innervation densities in the different skin layers were assessed. Moreover, neuronal calcitonin gene-related peptide staining was quantified. RESULTS: Perception of warm, cold and heat pain and nerve fibre density were reduced in the painful areas compared with the control sites and with healthy controls. Warm and cold detection thresholds correlated best with epidermal innervation density, whereas heat and cold pain thresholds and axon reflex flare correlated best with dermal innervation density. Clinical pain ratings correlated only with epidermal nerve fibre density (r = 0.38, p < 0.05) and better preserved cold detection thresholds (r = 0.39, p < 0.05), but not with other assessed functional and structural parameters. CONCLUSIONS: Thermal thresholds, axon reflex measurements and assessment of skin innervation density are valuable tools to characterize and quantify peripheral neuropathy and link neuronal function to different layers of the skin. The severity of small fibre neuropathy, however, did not correspond to clinical pain intensity and a specific parameter or pattern that would predict pain intensity in peripheral neuropathy could not be identified.

Differential effects of lidocaine on nerve growth factor (NGF)-evoked heat- and mechanical hyperalgesia in humans.

We investigated the effects of a non-specific sodium channel blocker (lidocaine) on heat pain thresholds and mechanical impact pain at day 7 and 21 after intradermal injection of 1 µg NGF. Measurements were performed in 12 healthy male subjects prior to and 5 min after intradermal injection of 150 µl lidocaine administered at concentrations of 0.01% (∼0.4 mM) and 0.1% (∼4 mM) to both NGF and control skin sites. NGF caused a maximum reduction of heat pain thresholds at day 7 (NGF 42.6 ± 0.6 vs. 49.4 ± 0.3 °C in control skin). Lidocaine sensitized normal skin for heat pain, but reduced heat hyperalgesia after NGF at day 7 (44.3 ± 0.8 °C, lidocaine 0.1%; p < 0.005). Pain upon supra-threshold mechanical impact stimulation was increased after NGF at day 7 (VAS 29 + 5) and massively enhanced at day 21 (VAS 64 + 5, p < 0.001). Lidocaine dose-dependently attenuated mechanically-induced pain at both control and NGF-treated sites. Maximum lidocaine effects on mechanical hyperalgesia were recorded at day 21 in NGF skin (pain reduction to VAS 37 ± 4, p < 0.00001). Repetitive impact stimuli caused increasingly more pain at the NGF sites at day 21 and this pain increase was efficiently suppressed by lidocaine 0.1%. Lidocaine differentially affects NGF-induced mechanical hyperalgesia (analgesic effect) and heat sensitivity of nociceptors (sensitizing effect). These opposing responses may be attributed to block of sodium channels vs. sensitization of TRPV1. NGF-evoked extreme mechanical impact pain indicates high action potential discharge frequencies, which might be more susceptible to lidocaine block.

Cross-over evaluation of electrically induced pain and hyperalgesia.

Background Anewexperimental protocol of electrically induced pain and hyperalgesia was established to examine orally administered drugs. In a randomized, double-blind, placebo-controlled cross-over study this experimental protocol was used to assess the effects of paracetamol. Methods Twenty-four subjects were enrolled in this study. The magnitude of pain, axon reflex flare, and areas of pin-prick hyperalgesia and touch-evoked allodynia were assessed in two consecutive sessions; prior to, and 2 h after drug administration. This protocol was repeated after 1 week. Subjects were randomized to receive either paracetamol (2 g) or a placebo. Results In comparison to the placebo arm there were no significant effects of paracetamol on pain, hyperalgesia, allodynia, or axon reflex flare. Pain and flare responses were highly reproducible on the same day (r = 0.77 and r = 0.79, respectively), and after 1 week (r = 0.6 and r = 0.71, respectively). The correlation between areas of hyperalgesia and allodynia was, however, significantly improved when the protocol was repeated on the same day (r = 0.8 and r = 0.75), as opposed to after a week (r = 0.54 and r = 0.53). Discussion The electrical pain model is a well established method for the assessment of intravenously applied analgesics. In order to assess effects of orally applied drugs the model had to be modified: for the assessment of hyperalgesia and allodynia a protocol repeating the model within 1 day proved to have advantages over repetition after 1 week.

[Cannabinoids--signal transduction and mode of action]. / Cannabinoide--Signaltransduktion und Wirkung.

The therapeutic use of cannabinoids, the components of cannabis sativa L., was investigated in numerous researches in detail. Animal studies revealed that cannabinoid receptor agonists alter pain-associated behaviour, have immune-suppressive properties, suppress tumor growth, modulate sensitisation processes and influence memory and learning. Those effects are mediated by two membrane-bound cannabinoid receptors and as mechanisms of signal transduction blockade of ion channels, inhibition of adenylate cyclase and retrograde inhibition of neurotransmitter release are currently being discussed. In clinical studies oral administration of cannabinoids indicated beneficial results during the therapy of multiple sclerosis, weight loss, nausea and vomiting due to chemotherapy, and intractable pruritus. However, therapy of chronic pain conditions revealed conflicting results and unequivocal success could not have been delivered due to unwanted side effects. Further multicentre studies are required to estimate cannabinoids as novel therapeutic tools for the treatment of chronic pain.

Controlled dermal cell damage as human in vivo model for localised pain and inflammation.

OBJECTIVE AND DESIGN: An unspecific human in vivo model of dermal pain and inflammation was developed by means of limited, localised and controlled cell damage. SUBJECTS: Twelve participants were recruited. TREATMENT: Dermal microdialysis was used to deliver randomised and single blinded aqueous sodium dodecyl sulphate (SDS) at concentrations of 0.01%, 0.1% and 0.5% w/v to the volar forearm. METHODS: Nociceptive responses were recorded on a numerical scale, vasodilatation was assessed by laser Doppler scanning and sampled tissue fluid was analysed for PGE2 by ELISA. RESULTS: Saline control and 0.01% SDS did not differ in their ability to cause vasodilatation, flare reaction or pain. In contrast, SDS (0.1 and 0.5%) evoked a significant increase of blood flow (p<0.005), a widespread reddening (p<0.01), and stinging-burning pain (p<0.005). PGE2 concentration in the dialysate did not change during 0.01% SDS perfusion (p>0.9), but increased significantly following the stimulation with 0.1% and 0.5% SDS (20 to 30-fold). No significant differences of released PGE2 levels were determined between 0.1% and 0.5% SDS stimulation (p>0.05). CONCLUSIONS: We demonstrated that localised intradermal administration of SDS induces a limited pain and inflammatory response in humans. Excitation of nociceptors was accompanied by a massive PGE2 release. Employing this experimental model, the relative contribution of endogenous mediators to induce, maintain or facilitate pain and vasodilatation can be investigated.

Histamine induced responses are attenuated by a cannabinoid receptor agonist in human skin.

OBJECTIVE AND DESIGN: In the present study we examined the effects of the cannabinoid receptor agonist HU210 on histamine-evoked somatosensory and vascular responses in humans. SUBJECTS: Two sets of experiments were performed, in which twelve (Study 1, iontophoresis) and six participants (Study 2, microdialysis) were recruited. TREATMENT: HU210 was administered peripherally by skin patch (50 mM) or dermal microdialysis (5 mM), whereas histamine was applied by iontophoresis (50 microAmps) or dermal microdialysis (5 microM). METHODS: Skin blood flow was monitored by laser Doppler, widespread flare reaction was evaluated planimetrically, extravasation of plasma proteins was measured in the dialysate and perceived itch was recorded using a visual analogue scale. Data were evaluated by analysis of variance. RESULTS: Experimentally induced itch was significantly reduced by peripheral administration of HU210 (p < 0.05). Additionally, skin blood flow and neurogenic mediated flare responses were attenuated (p < 0.003 and p < 0.03, respectively), whereas protein extravasation due to histamine was enhanced by co-administration of HU210, as investigated by dermal microdialysis. CONCLUSIONS: In humans peripheral administration of a cannabinoid receptor agonist attenuates histamine-induced itch. The observation that protein extravasation was not decreased demonstrates that the alleviation of itch is not due to an anti-histaminergic property of HU210. The reduced neurogenic flare reaction indicates an attenuated antidromic nerve fibre activation and neuropeptide release.

Nociceptor activation and protein extravasation induced by inflammatory mediators in human skin.

Protein extravasation (PE) is known to play an important role in inflammatory conditions. In this study we used dermal microdialysis to apply inflammatory mediators (histamine, bradykinin, serotonin) to human skin. Locally induced PE was compared to pain ratings and axon reflex erythema measured simultaneously. Linear microdialysis capillaries (outer diameter 0.4 mm; cut-off 3000 kDa) were inserted intracutaneously at a length of 1.5 cm in the volar forearm of healthy volunteers. The capillaries were perfused with Ringer's solution at a constant flow rate of 4 microl/min. The perfusate was sampled at 15-min intervals and was analysed for total protein concentration. After a baseline of 60 min, the perfusion was switched to inflammatory mediators for 30 min and then back to vehicle again. Sensations evoked by the stimulation were assessed on a visual analogue scale and visible axon reflex erythema was measured planimetrically.Dose-dependent increases in PE could be assessed for all inflammatory mediators tested. Bradykinin (10(-7)M) induced a significant PE, whereas serotonin was effective only at a concentration of 10(-3)M. While serotonin in lower concentrations induced moderate burning pain and an axon reflex flare but no PE, bradykinin provoked PE without pain or axon reflex flare at a concentration of 10(-7)M. Application of histamine similarly evoked PE at lower concentrations as compared to the induction of itch sensation and axon reflex flare. It is concluded that there is no link between nociceptor activation and protein extravasation induced by inflammatory mediators in healthy human skin.

Acute effects of substance P and calcitonin gene-related peptide in human skin--a microdialysis study.

Upon activation nociceptors release neuropeptides in the skin provoking vasodilation and plasma protein extravasation in rodents, but only vasodilation in humans. Pivotal peptides in the induction of neurogenic inflammation comprise calcitonin gene-related peptide and substance P, the latter being suggested to act partly via degranulation of mast cells. In this study substance P and calcitonin gene-related peptide-induced vasodilation, protein extravasation, histamine release, and sensory effects were investigated simultaneously in human skin by dermal microdialysis. The vasodilatory prostaglandin E(2) and the mast cell activator codeine served as positive controls. Substance P and calcitonin gene-related peptide applied intradermally via large cut-off plasmapheresis capillaries induced dose-dependent local vasodilation, but only SP provoked protein extravasation in concentrations greater than 10(-9) M. Substance P-induced (10(-8)-10(-6) M) protein extravasation was not accompanied by histamine release and was unaffected by cetirizine (histamine H1 blocker, 200 microg per ml). Only the highest concentration of substance P (10(-5) M) induced significant histamine release. Neither neuropeptide caused any axon reflex erythema or any itch or pain sensation, whereas mast cell degranulation by codeine dose dependently provoked itch, flare, protein extravasation, and histamine release. In human skin calcitonin gene-related peptide and substance P induce vasodilation by a mechanism not involving histamine. No evidence for neuropeptide-induced activation of nociceptors was obtained. Our results suggest that endogenous calcitonin gene-related peptide and substance P have no acute sensory function in human skin. The lack of neurogenic protein extravasation in humans can most probably be attributed to low local concentrations of this neuropeptide still sufficient to exert trophic and immunomodulatory effects (10(-11) M), but too low to induce protein extravasation (10(-8) M) or even mast cell degranulation (10(-5) M). J Invest Dermatol 115:1015-1020 2000

Mast cell mediators other than histamine induce pruritus in atopic dermatitis patients: a dermal microdialysis study.

While histamine is the crucial mediator of pruritus in type 1 allergic reactions, its role in atopic dermatitis (AD) is unclear. In this study, the role of mast cell mediators in protein extravasation and pruritus was evaluated using intradermal microdialysis. The microdialysis capillaries were used to apply the mast cell degranulating substance compound 48/80 (C48/80; 0.05%) or histamine (0.01%) and also to deliver H1-blockers (cetirizine, 200 microg mL-1) in nine AD patients and nine controls. Large pore size membranes (3000 kDa) enabled simultaneous analysis of protein extravasation. Itch sensation was measured psychophysically and weal and flare reaction were evaluated planimetrically. Protein extravasation induced by histamine and C48/80 was significantly reduced in AD patients. Blockade of H1-receptors by cetirizine significantly reduced C48/80-induced protein extravasation in AD patients and controls to an identical level. C48/80-induced pruritus was abolished by cetirizine in controls, whereas pruritus in AD patients was unchanged after H1 blockade. We conclude that mast cell mediators others than histamine are involved in C48/80-induced pruritus in AD patients. Whether the reduced capacity of AD patients to induce protein extravasation is of pathophysiological relevance for pruritus remains to be established.

Mast cell tryptase in dermal neurogenic inflammation.

BACKGROUND: Mast cell activation has been assumed to play a role in dermal neurogenic inflammation: C fibre-derived neuropeptides activating mast cells and releasing histamine, which in turn would activate C fibres. OBJECTIVE: To test this hypothesis mast cell tryptase (MCT) was measured inside the axon reflex flare area. Axon reflexes were elicited by histamine or compound 48/80, a polyanionic mast cell-degranulating substance. The time course of plasma extravasation and release of histamine and MCT from dermal mast cells in neurogenic inflammation was measured in vivo by intradermal microdialysis in humans. METHODS: Single hollow plasmapheresis fibres (pore cutoff size: 3000 kDa) were inserted intracutaneously at the volar forearm and perfused with Ringer's solution (4 microL/min) with one microdialysis fibre located at the planned stimulation site and a second inside the axon reflex area. Neurogenic inflammation was induced by intraprobe delivery of either histamine or the mast cell-degranulating agent compound 48/80. Mediator release was measured at the stimulation sites and inside the arising axon reflex flare area. RESULTS: Mast cell degranulation induced marked plasma protein extravasation (PPE 0.25 +/- 0.04-1.31 +/- 0.6 mg/mL; pre- and post-stimulation, mean +/- sem, n = 7) and release of histamine (2.0 +/- 0.9-38.7 +/- 1.4 ng/mL) and MCT (9.84 +/- 2.4-92.2 +/- 21.6 ng/mL). Interestingly, in addition to increasing PPE (0.33 +/- 0. 11-1.85 +/- 0.9 mg/mL), histamine also induced a slight but significant increase in MCT (11.3 +/- 3.0-12.4 +/- 2.3 ng/mL). No evidence for mast cell activation was observed inside the axon reflex areas, where PPE (0.34 +/- 0.03-0.25 +/- 0.02 mg/mL), histamine (1.64 +/- 0.5-1.46 +/- 0.4 ng/mL) and MCT concentration (11.6 +/- 3.1-7.6 +/- 1.7 ng/mL) gradually decreased. CONCLUSION: It is concluded that dermal neurogenic inflammation does not degranulate mast cells.

Administration of acetylcholine and vasoactive intestinal polypeptide to atopic eczema patients.

Responses to acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) were investigated in atopic eczema (AE) patients. To elucidate the involvement of histamine to ACh-provoked vasoreactions and sensations, we applied a selective H1-antagonist (cetirizine) 3 h prior to the ACh-administration. Solutions of acetylcholine (ACh, 0.55 M) and vasoactive intestinal polypeptide (VIP, 1.5x 10(-5) M) were injected (10 microl) intracutaneously into the volar forearm of 14 healthy subjects and 14 atopic eczema (AE) patients. The substances were applied as single stimulus as well as in combination. Sensations evoked by the stimulation were recorded using 2 visual analog scales (VAS). Vasoreactions were analyzed with the new technique of computer assisted video image analysis. With this method we measured the dynamics of the flare development and the extension of the final flare size independent of the observer's assessment. In control subjects the development and extension of the final flare size was almost similar, regardless whether ACh and VIP were applied in combination or separately. Compared to healthy controls, after injection of ACh, VIP and the combination of VIP and ACh smaller flare sizes were recorded in AE patients. After VIP was given, the control subjects reported pruritus, which was significantly augmented compared to AE patients. In contrast, controls reported a burning pain after the injection of ACh, whereas AE patients felt predominantly pruritus. Itch sensation after the combined application of VIP and ACh was significantly elevated in AE patients. Consequently, we assume that mediators of sudomotor neurons, i.e., VIP and ACh meet in AE patients apparently sensitized nociceptive primary afferents and induce exaggerated itch, pain and flare responses. When pretreated with the selective H1-antagonist cetirizine before ACh was injected, pain and erythema due to ACh was diminished in healthy controls. In contrast, cetirizine did not influence the size of erythema and the magnitude of sensation in AE patients. We conclude, that the release of histamine is not involved in ACh-induced erythema and pruritus in AE. These data provide evidence that pruritus can be elicited in atopic eczema by a cholinergic, histamine independent mechanism.

Cutaneous reactions and sensations after intracutaneous injection of vasoactive intestinal polypeptide and acetylcholine in atopic eczema patients and healthy controls.

We analysed vasoreactions and sensations of atopic eczema (AE) patients and healthy controls after intracutaneous (i.c.) injection of vasoactive intestinal polypeptide (VIP) and acetylcholine (ACh). Blood flow was measured by laser Doppler flowmetry (LDF). Plasma extravasation and flare size were evaluated planimetrically, and sensations were recorded using visual analog scales. Three groups of subjects (controls, AE patients suffering from acute eczema and AE patients during a symptom-free period) were investigated. We administered VIP separately at concentrations of 1.5 x 10(-7), 1.5 x 10(-6) and 1.5 x 10(-5) M and in combination with ACh (5.5 x 10(-6) M) into the volar forearm of the subjects. Both substances led to an increase in LDF measurements and induced a wheal and flare reaction. Blood flow was elevated as a function of dose after a single VIP application in all groups. Compared with healthy controls, a significant increase in blood flow was measured after combined VIP and ACh administration in AE patients suffering from acute AE, whereas flare area and plasma extravasation were significantly reduced after single VIP and combined VIP and ACh injections, respectively. In all groups, VIP induced dose-dependent pruritus. Compared with a control stimulus (0.9% sodium chloride and ACh), combined injections of VIP and ACh had no additional effect on the magnitude of the sensation. In AE patients, the intensity was similar to that experienced by the control subjects, but the quality of sensation was different: ACh induced pain in the control subjects, pruritus in AE patients, and a mixture of pain and itching in AE patients showing no symptoms. Our results suggest that VIP- and ACh-induced skin reactions and the quality of the sensations depend on the activity of the atopic eczema. Confirming our former studies, AE patients develop a different quality of sensation after ACh administration and also after administration of VIP combined with ACh. Therefore, we suggest that ACh might be involved in the pathomechanisms of pruritus in AE.

Flare responses of atopic eczema patients analysed with true colour images.

OBJECTIVE AND DESIGN: Attenuated flare responses of atopic eczema (AE) patients to histamine are well documented, but their origin is still unknown. SUBJECTS AND METHODS: Here we studied the development of erythema after histamine iontophoresis in 12 AE patients and 12 healthy volunteers by means of a RGB-camera for recording true colour images. TREATMENT: 10 mg cetirizine or placebo was administered orally 3 h before the experiment in a crossover design. RESULTS: The flare reaction was found to develop after termination of histamine iontophoresis in two phases: a first phase lasting 1-2 min in which the flare increased by about 10 mm2/s and a second phase lasting another 10-15 min characterized by a slower growth in the range of 1 mm2/s. CONCLUSIONS: Flare size was diminished in AE patients, mainly due to a slower or absent growth in the second phase. Oral application of the H1-antagonist cetirizine (Zyrtec) reduced the flare reaction in both groups of volunteers significantly, indicating that the reaction is dependent on the activation of chemosensitive nerve fibres via H1-receptors.