Paw Skin Research Articles

Role of mast cell histamine in the formation of rat paw edema: A microdialysis study

We determined the endogenous histamine concentration in the subplantar space of rat hind paws using an in vivo microdialysis technique. A microdialysis probe was implanted into the rat hind paw and the histamine content in dialysates was measured by high performance liquid chromatography–fluorometry. In wild type (+/+) rats, the histamine output (basal level 25.7±0.9 pmol/ml) increased 115-, 199- and 426-fold rapidly after subplantar injection of compound 48/80 at doses of 0.5, 5 and 50 μg/paw, respectively. In genetically mast cell-deficient (Ws/Ws) rats, the basal level of histamine was one third of that obtained from +/+ rats, and was not increased by compound 48/80 injection. With this treatment, marked, dose dependent, but relatively gradual development of the paw edema was found in +/+ rats. However, no edema formation was observed in Ws/Ws rats. Histological observations showed neither mast cells nor edema to be present in the paw skin of Ws/Ws rats. These findings indicate the critical role of histamine as a trigger for the development of edema in vivo. In addition, Ws/Ws rats will provide important information as to the roles of mast cells in the inflammatory response.

Improved neurochemical recovery of 6-hydroxydopamine-lesioned postganglionic sympathetic neurons by nerve growth factor in the adult rat

Intraplantar injections of nerve growth factor (NGF; five injections of 4 μg each in 30 h intervals) were able to locally improve the recovery of the noradrenaline content in 6-hydroxydopamine (6-OHDA)-lesioned sympathetic nerves in adult rats. Whereas 8 days after the 6-OHDA treatment the noradrenaline content in the paw skin was still less than 10% of control, it reached up to 40% of control levels in NGF injected paws. Intraplantar NGF also significantly improved the recovery of the noradrenaline content in the innervating sciatic nerve, but not in distant tissues. The NGF-induced recovery of noradrenergic nerves was independent of the presence of sensory peptidergic afferents and it could not be mimicked by a local inflammatory response known to raise endogenous NGF production. These results show that rather low doses of exogenous NGF were able to locally restore peripheral noradrenergic nerves after an acute neurotoxin lesion.

Biochemical and histopathological evaluation of changes in sled dog paw skin associated with physical stress and cold temperatures.

Biochemical and histopathological evaluation of changes in sled dog paw skin associated with physical stress and cold temperatures.

Complete recovery by nerve growth factor of neuropeptide content and function in capsaicin-impaired sensory neurons

In the present study the ability of nerve growth factor (NGF) to facilitate the recovery of peptidergic primary sensory C-fibers after an acute capsaicin treatment (50 mg/kg s.c.) was investigated in adult rats. NGF (4 μg 1 /day for 3 days) was injected into the plantar of one hind paw starting 24 h after the capsaicin treatment. Without NGF, there was a significant reduction of calcitonin gene-related peptide (CGRP) and substance P content of the paw skin and the sciatic nerve. CGRP and substance P levels were completely replenished in the NGF-treated paw skin and in the innervating sciatic nerve they even increased over control levels as determined 40 h after the last injection of NGF. CGRP levels also recovered in the contralateral paw and sciatic nerve, but no recovery was observed in other tissues such as the front paw, the auricle, or the urinary bladder. Mustard oil-induced neurogenic plasma extravasation, taken as a functional parameter for peptidergic primary sensory C-fibers, was significantly decreased after the capsaicin treatment and showed a complete recovery by NGF in the injected paw as well as in the contralateral paw skin. These results show that NGF not only was able to reverse the decrease of transmitter content caused by capsaicin but also restored the peripheral function of primary afferent neurons.

Nociceptive responses to high and low rates of noxious cutaneous heating are mediated by different nociceptors in the rat: electrophysiological evidence

Behavioral nociceptive responses evoked by relatively high rates of noxious radiant skin heating appear to be mediated by Aδ nociceptor activation, whereas responses evoked by low rates of skin heating appear to be mediated by the activation of C-fiber nociceptors. This hypothesis was confirmed by the results of single unit recordings of Aδ and C nociceptive afferent fibers isolated from the saphenous nerves of pentobarbital anesthetized rats. Heating the hind paw skin of the rat at a relatively high rate of 6.5°C/sec activated Aδ units within 2 sec after the onset of the stimulus. This response latency is similar to the 2.5 sec latency of the foot withdrawal response to a similar stimulus. In contrast, C-fibers were only slightly activated at a longer latency of 5–6 sec. Conversely, heating the hind paw skin at a relatively low rate of 0.9°C/sec activated C-fibers, but evoked only a few action potentials in Aδ nociceptors. C-fibers began firing at a rate less than 1 Hz between 8 and 10 sec after the onset of heating and fired at a mean rate of 1.5 Hz between 10 and 12 sec, which corresponds to the latency of the foot withdrawal response. Topical application of capsaicin to the hind paw skin decreased the latency of C-fiber responses from control values of 8–12 sec to approximately 4 sec after topical capsaicin treatment. The mean latency of the foot withdrawal response to skin heating at the low rate is also reduced from control values of 12–14 sec to 4–5 sec after capsaicin treatment. In contrast, capsaicin treatment did not significantly affect the responses of Aδ nociceptors. These results support the conclusion that nociceptive foot withdrawal responses to a low rate of skin heating are mediated predominantly by the activation of C-fiber nociceptors. These results provide direct evidence that, under the conditions of these experiments, nociceptive foot withdrawal responses evoked by high rates of skin heating are primarily mediated by Aδ nociceptors, and foot withdrawal responses evoked by low rates of skin heating are primarily mediated by C-fiber nociceptors.

Effect of a 5-lipoxygenase inhibitor on nerve growth factor-induced thermal hyperalgesia in the rat

Intraplantar injection of mouse β (2.5S) nerve growth factor (NGF) caused thermal hyperalgesia and stimulated release of immunoreactive leukotriene B 4 from the rat paw skin. Both effects of NGF were prevented by the 5-lipoxygenase inhibitor, ( R)-2-[4-quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid (BAY X1005). BAY X1005 did not affect bradykinin-induced thermal hyperalgesia. These results suggest the participation of 5-lipoxygenase products of arachidonate in NGF-induced local thermal hyperalgesia.

Effect of increased interstitial fluid flux on fractional catabolic rate of high molecular weight [3H]hyaluronan injected in rabbit skin.

The removal rate of high molecular weight (M(r) 3 x 10(6) [3H]hyaluronan has been measured in rabbit paw skin in control and during increased local venous pressure induced by ligation of the femoral vein. The increased venous pressure resulted in a 20% increase of interstitial volume at 4 h after ligation, a value which relates to at least a doubling of lymph flow, i.e. also to doubling of fluid flux through the tissues. The fractional catabolic rate of hyaluronan was 0.0918 +/- 0.0170 h-1 (n = 10) and 0.0775 +/- 0.0206 h-1 (n = 11) in control and following increased venous pressure respectively (P > 0.05). Since the fractional catabolic rate of hyaluronan is not affected by increased venous pressure, the removal of hyaluronan via lymphatic drainage in rabbit paw skin must be small compared to the local turnover of the polysaccharide.

Mediation by prostaglandins of the nitric oxide-induced neurogenic vasodilatation in rat skin.

1. Intraplantar administration of the nitric oxide (NO) donor, sodium nitroprusside (SNP), induces hyperaemia in the rat paw skin, which is in part due to release of calcitonin gene-related peptide (CGRP) from afferent nerve fibres. The present study examined whether prostaglandins or other inflammatory mediators participate in the neurogenic vasodilatation caused by SNP. Blood flow in the plantar hindpaw skin of urethane-anaesthetized rats was measured by laser Doppler flowmetry. 2. The hyperaemic responses to intraplantar administration of the NO donors SNP (150 pmol) and 3-morpholino-sydnonimine (SIN-1, 15 nmol) were attenuated by 45% and 61%, respectively, after injection of the CGRP antagonist, CGRP8-37 (50 nmol kg-1, i.v.) which did not significantly change baseline blood flow. 3. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 15 mg kg-1, i.v.), the bradykinin antagonist Hoc-140 (100 nmol kg-1, i.v.) and the histamine antagonists, pyrilamine (2 mg kg-1, i.v.) plus cimetidine (10 mg kg-1, i.p.) were without effect on baseline blood flow and the vasodilatation caused by SNP. 4. The cyclo-oxygenase inhibitors, indomethacin (10 mg kg-1, i.p.) and flurbiprofen (5 mg kg-1, i.p.) depressed the SNP-induced hyperaemia by 65% and 42%, respectively, without altering baseline blood flow. The ability of CGRP8-37 to inhibit the vasodilator response to SNP was lost in indomethacin-treated rats. 5. Intraplantar administration of prostaglandin E2 (PGE2, 15 pmol) evoked cutaneous vasodilatation which was attenuated by 66% after administration of CGRP8-37 but remained unaltered by indomethacin or L-NAME. 6. These data indicate that the neurogenic hyperaemia which in rat skin is induced by intraplantar administration of NO donors involves the formation of prostaglandins which in turn cause release of the vasodilator peptide, CGRP, from perivascular afferent nerve fibres.

Nitric oxide synthase and chemical coding in cat sympathetic postganglionic neurons.

Nitric oxide synthase-like immunoreactivity was found in a subpopulation of sympathetic postganglionic neurons in the cat stellate and lower lumbar ganglia. In the ganglia of other segments such cells were rare. Double staining for tyrosine hydroxylase-like immunoreactivity and nitric oxide synthase-like immunoreactivity or the reduced nicotinamide adenine dinucleotide phosphate diaphorase reaction indicated that nitric oxide synthase-like immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate diaphorase reactivity was always co-localized and was confined to tyrosine hydroxylase-negative (presumably cholinergic) ganglion cells, and was present in most of them. The occurrence of nitric oxide synthase in two subpopulations of cholinergic postganglionic neurons was investigated in triple staining experiments. Presumptive sudomotor neurons have been previously defined as scattered cells containing calcitonin gene-related peptide-like immunoreactivity, usually accompanied by vasoactive intestinal peptide-like immunoreactivity: 99% of these contained nitric oxide synthase. Presumptive muscle vasodilator neurons have been previously identified as clumped cells with strong vasoactive intestinal peptide-like immunoreactivity but no calcitonin gene-related peptide-like immunoreactivity: 70% of these contained nitric oxide synthase. Sweat glands were found in the paw pad skin surrounded by varicose fibres showing calcitonin gene-related peptide-like immunoreactivity and vasoactive intestinal peptide-like immunoreactivity, confirming previous work. Such fibres also stained for nitric oxide synthase-like immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate diaphorase reactivity, although their staining was relatively weaker than in the corresponding cell bodies. Varicose fibres with the same chemical coding were also found around all large and most medium and small arteries in the paw skin as well as around arteriovenous anastomoses. Fibres with the muscle vasodilator coding (vasoactive intestinal peptide-like immunoreactivity without calcitonin gene-related peptide-like immunoreactivity) were not seen in paw skin. These results suggest that nitric oxide may act as a co-transmitter (with acetylcholine, substance P, vasoactive intestinal peptide and calcitonin gene-related peptide) in sudomotor neurons and (with acetylcholine and vasoactive intestinal peptide) in vasodilator neurons. Collateral branches of sudomotor neurons may innervate skin vessels, and release vasodilator transmitters including nitric oxide to cause the vasodilatation which provides the fluid supply for sweat formation. Alternatively, separate vasodilator neurons to skin may share the same chemical code as sudomotor neurons.

Histamine-induced edema in the rat paw — effect of capsaicin denervation and a CGRP receptor antagonist

Histamine is known to cause edema and excitation of small-diameter primary afferent neurons. In the present study we wanted to investigate to which extent afferent neurons participate in histamine-induced edema and, subsequently, determine possible inhibitory effects of a tachykinin NK 1 receptor and CGRP receptor antagonist on the histamine response. Intraplantar injection of histamine (0.5 μmol) into the rat hind paw caused a 34% increase of paw volume. In capsaicin-denervated rats, this effect of histamine was nearly abolished. The calcitonin gene-related peptide (CGRP) receptor antagonist CGRP-(8-37), but not the tachykinin NK 1 receptor antagonist SR140333, caused significant inhibition of the edema response. Further indication that CGRP can promote the histamine action was obtained in capsaicin-denervated rats, where co-injection of CGRP (0.3 pmol) increased the edema response to intraplantar histamine. In additional experiments, plasma protein extravasation in the paw skin was evaluated after close arterial infusion of histamine. Also in these experiments CGRP-(8-37), but not SR140333, significantly reduced the histamine effect. The observation that in the rat hind paw a CGRP receptor antagonist, but not a tachykinin NK 1 receptor antagonist, attenuates histamine-induced vascular leakage raises the possibility that in some tissues CGRP receptor antagonists may be superior to tachykinin NK 1 receptor antagonists in reducing histamine-induced neurogenic inflammatory responses.

Warm and cold signals from the preoptic area: which contribute more to the control of shivering in rats?

1. To find out whether the thermosensitive neurones in the preoptic area that control shivering are predominantly warm or cold sensitive, we tested the effects of injecting the excitatory amino acid L-glutamate at various sites in and adjacent to the preoptic area of anaesthetized rats shivering at ambient temperatures of 15-21 degrees C. 2. L-Glutamate injections (0.2 mM in 0.5-1.0 microliter), as well as preoptic warming and electrical stimulation, suppressed shivering, whereas control saline injections had no effect. Effective sites were restricted to the anterior part of the preoptic area, and a tenfold lower concentration of L-glutamate did not influence shivering. 3. Injections of procaine (0.2 M) into the sites where L-glutamate suppressed shivering did not affect strong shivering activity, but facilitated shivering in three out of seven cases when shivering was weak or absent at higher ambient temperatures (25-30 degrees C). 4. L-Glutamate injections, as well as preoptic warming and electrical stimulation, also elicited vasodilatation of the paw skin and the tail. Procaine elicited vasoconstriction when it was applied during vasodilatation induced by local preoptic warming. 5. These results indicate that the contribution of the preoptic area to the control of shivering and vasomotion is influenced more by signals from warm-sensitive neurones than by signals from cold-sensitive neurones.

Effect of a 5-HT1 receptor agonist, CP-122,288, on oedema formation induced by stimulation of the rat saphenous nerve.

Neurogenic oedema formation in the rat hind paw skin induced by electrical stimulation of the saphenous nerve and measured by extravasation of [125I]-albumin, was inhibited by the 5-HT1B receptor agonist, CP-93,129, and the novel tryptamine analogue, CP-122,288. Significant inhibition of up to 66% of control was observed with CP-122,288 (2 x 10(-14) - 2 x 10(-7) mol kg-1) and CP-93,129 (5 x 10(-7) - 5 x 10(-6) mol kg-1), with the minimum effective dose for CP-122,288 being about 10(7) fold less than that for CP-93,129. Oedema formation induced by the intradermal administration of exogenous mediators (substance P and histamine) in rat dorsal skin was not inhibited by CP-122,288 (2 x 10(-10) mol kg-1). These results suggest that CP-122,288 is a potent inhibitor of neurogenic inflammation in rat skin and that the effect may be due to a prejunctional inhibition of neuropeptide release.

Essential Role for Nitric Oxide in Neurogenic Inflammation in Rat Cutaneous Microcirculation

The possible modulatory role of nitric oxide (NO) in neurogenic edema formation in rat paw skin, induced by electrical stimulation of the saphenous nerve, was investigated by using two NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI). Both L-NAME (100 mg/kg IV, P < .05) and 7-NI (10 mg/kg IV, P < .05) caused an L-arginine (100 mg/kg IV, P < .01)-reversible inhibition of neurogenic edema as measured by 125I-albumin accumulation, whereas D-NAME (inactive enantiomer of L-NAME) and 6-aminoindazole (structurally similar to 7-NI) were without inhibitory effect. L-NAME produced the predicted vasopressor effect (before, 115 +/- 18 mm Hg; 5 minutes after, 174 +/- 18 mm Hg; n = 6; P < .05), whereas 7-NI showed no significant increase in blood pressure (before, 96 +/- 9 mm Hg; 5 minutes after, 102 +/- 10 mm Hg; n = 6), and neither L-NAME nor 7-NI had any effect on basal or vasodilator calcitonin gene-related peptide (CGRP, 10 pmol per site)-stimulated local blood flow in rat skin, as measured by laser Doppler flowmetry. Furthermore, systemic and local 7-NI had no effect on edema formation induced by local administration of substance P (with or without CGRP) and histamine (with or without CGRP) in rat skin. Since 7-NI blocks edema produced by stimulation of the saphenous nerve, it is suggested that release of NO is involved in neurogenic edema formation, but the vasodilator action of NO is unimportant in this context.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleviation of neuropathic pain symptoms by xenogeneic chromaffin cell grafts in the spinal subarachnoid space

Recent data have suggested that adrenal medullary tissue allografts in the spinal cord subarachnoid space, by releasing catecholamines and opioid peptides, attenuate responses to various acute noxious stimuli and chronic pain-related behaviors. However, the application of this approach is limited by the low availability of allogeneic donor material. Alternatively, chromaffin cells from xenogeneic sources such as the bovine adrenal medulla are plentiful and simple to extract. The goal of this study was to evaluate the potential for bovine chromaffin cell xenografts in the rat spinal subarachnoid space to alleviate chronic pain. This was assessed in an animal model of neuropathic pain induced by loose ligation of the sciatic nerve, which resulted in allodynia, hyperalgesia, and skin temperature abnormalities. Two weeks after nerve injury, animals were implanted with either isolated bovine chromaffin cells or control bovine adrenal fibroblasts in the spinal subarachnoid space at the level of lumbar enlargement and immunosuppressed with cyclosporine A. In animals with chromaffin cell implants, but not fibroblast implants, both cold allodynia and thermal hyperalgesia were markedly reduced or eliminated as early as 1 week following implantation and hind paw skin temperature asymmetry was also normalized. These beneficial effects were maintained without decrement or apparent tolerance for the 9 week course of the symptomology. The analgesic effects of chromaffin cell grafts were partially attenuated following i.t. injection of naloxone and phentolamine separately and in combination, suggesting involvement of spinal opioid and α-adrenergic receptors. Following termination of behavioral studies, immunocytochemical analysis revealed robust survival of chromaffin cells in the implants. These results demonstrate that chromaffin cell xenografts may be effective in alleviating pain of neurogenic origin.

Suppressive effect of 2-phenyl-4-quinolone (YT-1) on hind-paw edema and cutaneous vascular plasma extravasation in mice.

Like indomethacin, BW755C, diphenhydramine and methysergide, 2-phenyl-4-quinolone (YT-1) suppressed the polymyxin B-induced hind-paw edema. This inhibitory effect of YT-1 was also demonstrated in adrenalectomized mice. YT-1 inhibited the antidromic stimulation of saphenous nerve-induced plasma leakage in dorsal paw skin and reduced the volume of plasma exudation in PCA reaction. Bradykinin-, substance P- and compound 48/80-induced mouse ear edema was suppressed by YT-1 in a dose-dependent manner. In isolated rat peritoneal mast cells, YT-1 produced a dose-dependent inhibition of bradykinin-, substance P- and compound 48/80-induced histamine and beta-glucuronidase release. YT-1 also reduced the TXB2 formation from PMN leukocytes with IC50 2.0 +/- 0.5 microM, however with little effect on LTB4 formation. Histamine- and serotonin-induced plasma exudation in ear edema were reduced by YT-1. Moreover, the maximal response of ileum contraction caused by histamine and serotonin were also suppressed by YT-1 in a dose-dependent manner. In compound 48/80-pretreatment mice, YT-1 failed to suppress the bradykinin- and substance P-induced ear edema to a significantly greater extent than diphenhydramine combined with methysergide did. These results indicate that the inhibitory effect of YT-1 on local edema formation is not through the release of steroid hormones from adrenal gland, and is probably by suppressing the release of chemical mediators from mast cells, inhibition of prostaglandins formation, and noncompetitive but selective protection of the vasculature against the histamine- and serotonin-induced plasma extravasation.

Opioids suppress spontaneous activity of polymodal nociceptors in rat paw skin induced by ultraviolet irradiation

Changes in chemical sensitivity of periperal nociceptors following injury or inflammation have been studied in in vitro preparation of the saphenous nerve-hind paw skin from adult rats. Heat hyperalgesia in the hind paw was induced by a prior ultraviolet irradiation and the skin from these animals was investigated five days later. Polymodal nociceptors were quiescent in normal skin but were spontaneously active in the majority of fibres after ultraviolet exposure. Capsaicin-induced activation of fine fibres was enhanced after ultraviolet pretreatment. Direct administration of morphine, DAGOL (μ-receptor agonist) and U-69593 ( k-receptor agonist), but not DPDPE (δ-receptor agonist) to the receptive field produced a concentration-related and naloxone-reversible suppression of spontaneous firing in polymodal nociceptors of ultraviolet-treated skin. Morphine did not reduce the activity of fibres in normal skin when these were driven by KCl depolarization. These data show that polymodal nociceptors change their activity and sensitivity to exogenous chemicals following the induction of peripheral hyperalgesia by ultraviolet irradiation. Specifically, evidence is provided for the expression of opioid sensitivity and inhibition of polymodal nociceptor activity through μ- and k-opioid receptors. These observations may account for peripheral antinociceptive actions of opioids during specific states of peripheral hyperalgesia.

Role of nitric oxide in the vasodilator but not exudative component of mustard oil-induced inflammation in rat skin.

The participation of nitric oxide (NO) in the neurogenic inflammatory reaction of the rat hindpaw skin to topical application of mustard oil was examined by the use of NG-nitro-L-arginine methyl ester (L-NAME, 43 mumol kg-1 i.v.), an inhibitor of NO formation. Control rats received the same dose of the inactive enantiomer D-NAME. Vasodilatation was recorded by contactless infrared emission thermography, and plasma protein exudation was measured by the Evans Blue leakage technique and by measurement of the paw volume in anaesthetized rats. L-NAME reduced the cutaneous hyperaemia caused by topical administration of mustard oil by about 50% but did not change the exudative reaction to mustard oil. These findings indicate that NO plays a mediator role in the vasodilator component of neurogenic inflammation in the rat paw skin, whereas the increase in vascular permeability does not appear to depend on NO.

A non-peptide NK1-receptor antagonist, RP 67580, inhibits neurogenic inflammation postsynaptically.

1. The non-peptide neurokinin NK1-receptor antagonist, RP 67580 (3aR, 7aR), a perhydroisoindolone derivative, powerfully reduced plasma extravasation in rat hind paw skin induced by local application of xylene (ID50 = 0.03 mg kg-1, i.v.) or capsaicin (ID50 = 0.06 mg kg-1, i.v.), or by i.v. injection of exogenous substance P (SP) or septide ([pGlu6,Pro9]SP(6-11)) (ID50 = 0.04-0.05 mg kg-1, i.v.). RP 67580 (1 mg kg-1, i.v.) also abolished capsaicin-induced nasal fluid hypersecretion (by 82 +/- 5%). These effects were found to be stereospecific, the enantiomer, RP 68651 (3aS, 7aS), being inactive at 1 mg kg-1, i.v. 2. In rats neonatally treated with capsaicin (50 mg kg-1, s.c.), plasma extravasation induced by SP was significantly increased (by 43 +/- 7%). RP 67580 (1 mg kg-1, i.v.) completely inhibited the SP-induced plasma extravasation in capsaicin neonatally treated-animals, as it did in control animals. This result suggests that RP 67580 acts at the postsynaptic level for the inhibition of plasma extravasation. 3. Opioid receptor agonists, mu-(morphine) and kappa-(PD-117302) at 10 mg kg-1, s.c., in contrast to NK1-receptor antagonists, did not inhibit plasma extravasation induced by exogenous SP. They were, however, partially effective against plasma extravasation induced by electrical nerve stimulation (74 +/- 4% and 48 +/- 9% inhibition at 10 mg kg-1, s.c. of morphine and PD-117302, respectively, compared to 90 +/- 3% inhibition obtained with RP 67580, 3 mg kg-1, s.c.). These results indicate the presynaptic action of opioid receptor agonists, in contrast to the postsynaptic action of NK1-receptor antagonists for the inhibition of plasma extravasation.4. Ligature of the saphenous nerve distal to the point of electrical stimulation, local application of lignocaine to the saphenous nerve, neonatal capsaicin pretreatment, and colchicine at very low doses(120 microg kg-1 day-1 given for 3 days) were found to prevent plasma extravasation elicited by electrical nerve stimulation.5. The foregoing results demonstrate that the non-peptide NK1-receptor antagonist, RP67580, is a potent inhibitor of plasma extravasation induced in skin by NK1-receptor agonists, by local application of chemical irritants (capsaicin or xylene) or by electrical nerve stimulation. Moreover, opioid receptor agonists and colchicine inhibit plasma extravasation induced by electrical nerve stimulation but not that elicited by exogenous SP. Therefore, it is possible to inhibit neurogenic inflammation either at the presynaptic level with opioid receptor agonists and colchicine, or at the postsynaptic level withNK1-receptor antagonists, and that the new non-peptide NK1-receptor antagonists may have a great potential for alleviation of inflammation in various pathological syndromes in man.

Participation of nitric oxide in the mustard oil-induced neurogenic i inflammation of the rat paw skin

The possibility of nitric oxide (NO) participating in the neurogenic inflammatory reaction of the rat hindpaw skin to topical application of mustard oil was examined in anaesthetized rats. Vasodilatation was measured by contactless infrared emission thermography, plasma protein exudation was measured by the Evans blue leakage technique, and formation of oedema was determined by measurement of the paw volume. Topical administration of mustard oil increased the temperature of the paw skin by 2–3° C, a response that was accompanied by plasma protein extravasation and followed by development of slight oedema amounting to a 7–8% increase in paw volume. That the mustard oil-induced increase in paw temperature and oedema formation was neurogenic was shown by the finding that both responses were absent in adult rats treated with a neurotoxic dose of capsaicin (0.16 mmol kg −1 s.c.) as neonates. N G-Nitro-L-arginine methyl ester (L-NAME, 43 μmol kg −1 i.v.), an inhibitor of NO formation, caused a significant increase in mean arterial blood pressure and a moderate decrease in cutaneous blood flow, whereas the same dose of the inactive enantiomer, D-NAME, was without effect. L-NAME, but not D-NAME, reduced the cutaneous hyperaemia caused by topical administration of mustard oil by about 50% but did not significantly diminish the exudative reaction to mustard oil. These findings indicate that endothelium-derived NO plays a mediator role in the vasodilator component of mustard oil-induced neurogenic inflammation in the rat paw skin whereas the increase in vascular permeability does not seem to involve NO directly as a mediator.

Effect of scopolamine on the electrical resistance of the paw pads of mice

We examined the electrical resistance of the paw pads of mice under the same conditions as used previously in studies of the passive avoidance response. Administration of scopolamine (0.05–1 mg/kg, SC) 10 or 30 min prior to placement of animals in an experimental box resulted in a profound increas in electrical resistance. In contrast, subcutaneous injection of butylscopolamine (1–20 mg/kg), diazepam (1 or 2 mg/kg), or pentobarbital (10 or 20 mg/kg) did not substantially alter subject resistance. Scopolamine may act on the CNS to induce increased paw skin resistance.