Effects of calcitonin gene-related peptide-(8-37) on withdrawal responses in rats with inflammation

Potamotrygon motoro stingray venom induces both neurogenic and inflammatory pain behavior in rodents

Freshwater stingray accidents cause an immediate, intense, and unrelieved pain which is followed by edema, erythema and necrosis formation. Treatment for stingray envenomation is based on administration of analgesic, antipyretic and anti-inflammatory drugs. Concerning pain control, it is prescribed to immerse punctured limb on hot water to alleviate pain. There are no studies demonstrating specific targets on which stingray venom acts to promote pain. Therefore, the aim of this work was to investigate some mechanisms of Potamotrygon motoro venom (PmV) that contribute to nociception induction. Evaluating spontaneous pain behavior in mice injected i.pl. with PmV, it was seen that PmV induced both neurogenic and inflammatory pain. PmV also induced hyperalgesia in both mice and rats, evaluated through electronic von Frey and rat paw pressure test, respectively. Partial inhibition of hyperalgesia was observed in mice treated with cromolyn or promethazine, which indicated that mast cell and histamine via H1 receptor participate in the inflammatory pain. To search for some targets involved in PmVinduced hyperalgesia, the participation of TRPV1, calcium channels, neurokinins, CGRP, and norepinephrine, was evaluated in rats. It was seen that PmV-induced hyperalgesia occurs with the participation of neurokinins, mainly via NK1 receptor, CGRP, and calcium influx, through both P/Q and L-type voltage-dependent calcium channels, besides TRPV1 activation. The data presented herein indicate that PmV causes hyperalgesia in rodents which is dependent on the participation of several neuroinflammatory mediators.

Involvements of galanin and its receptors in antinociception in nucleus accumbens of rats with inflammatory pain

This study tested the hypothesis that antinociceptive effects of galanin and its receptors in nucleus accumbens (NAc) of rats with inflammatory pain provoked by subcutaneous injection of 0.1 ml of 2% carrageenin into the sole of the rat's left hindpaw. The hindpaw withdrawal latencies (HWLs) in response to thermal and mechanical stimulation significantly decreased in bilateral hindpaws at 3 and 4 hour after a subcutaneous injection of carrageenin. However intra-NAc injection of 2 and 3 nmol, but not 1 nmol of galanin markedly induced an increase in the HWLs in a dose-dependent way. Western blot also showed, that the expression of galanin receptor 1 (GalR1) and galanin receptor 2 (GalR2) were significantly upregulated in NAc at 3 hour after a subcutaneous injection of carrageenin. In addition, the rats were intra-NAc injected galanin, 5 min later following by intra-NAc injection of galanin receptor antagonist galantide, the galanin-induce antinociceptive effects were suppressed by galantide. The results demonstrated that galanin and its receptors might be involved in antinociception in the NAc of rats with inflammatory pain.

Assessment of thermal sensitivity in rats using the thermal place preference test: description and application in the study of oxaliplatin-induced acute thermal hypersensitivity and inflammatory pain models

Thermal sensitivity is an essential characteristic of some painful states, including oxaliplatin-induced neuropathy. The thermal place preference test (TPPT) was designed to finely assess thermal sensitivity in rodents. The TPPT monitors the time spent by unrestrained rodents on a test plate at fixed temperatures (5-50°C) compared with an adjacent reference plate at a neutral temperature (25°C). Here, we report the results of a study designed (i) to validate the optimal methodological parameters for measuring thermal sensitivity in rats, (ii) to assess the thermal sensitivity of healthy rats and animal models of pain and (iii) to explore the pharmacological effects of analgesic drugs. The most reproducible conditions occurred when the TPPT was performed in the morning and in the dark for 3 min with the reference plate set to 25°C. The temperature preferences of healthy rats were more than 17°C and less than 40°C. When compared with control animals, oxaliplatin-treated rats showed thermal hypersensitivity at 12, 20 and 35°C, and carrageenan-treated rats showed thermal hypersensitivity at 15 and 45°C. Duloxetine (2.5 mg/kg, intraperitoneal) reversed oxaliplatin-induced cold hypersensitivity (20°C) and morphine (1 mg/kg, intravenous) reversed carrageenan-induced heat hypersensitivity (45°C). We conclude that the TPPT enables a fine-grained assessment of thermal sensitivity that is relevant to the pathophysiological exploration of animal pain models and to the pharmacological assessment of analgesic drugs.

Antinociceptive properties of physalins from Physalis angulata

Pain is the most common reason a patient sees a physician. Nevertheless, the use of typical painkillers is not completely effective in controlling all pain syndromes; therefore further attempts have been made to develop improved analgesic drugs. The present study was undertaken to evaluate the antinociceptive properties of physalins B (1), D (2), F (3), and G (4) isolated from Physalis angulata in inflammatory and centrally mediated pain tests in mice. Systemic pretreatment with 1-4 produced dose-related antinociceptive effects on the writhing and formalin tests, traditional screening tools for the assessment of analgesic drugs. On the other hand, only 3 inhibited inflammatory parameters such as hyperalgesia, edema, and local production of TNF-α following induction with complete Freund's adjuvant. Treatment with 1, 3, and 4 produced an antinociceptive effect on the tail flick test, suggesting a centrally mediated antinociception. Reinforcing this idea, 2-4 enhanced the mice latency reaction time during the hot plate test. Mice treated with physalins did not demonstrate motor performance alterations. These results suggest that 1-4 present antinociceptive properties associated with central, but not anti-inflammatory, events and indicate a new pharmacological property of physalins.

Secondary and tertiary sulfonamides: a patent review (2008 - 2012)

INTRODUCTION

Secondary and tertiary sulfonamides (R-SO(2)NR(1)R(2)) are defined by the single or double N-alkyl or N-aryl/heteroaryl substitution of the primary sulfonamide respectively. They can be obtained easily by the classical S(N)2 or nucleophile acyl substitution displacements using the appropriate synthones. Many classes of compounds used in therapy present the substituted sulfonamide groups and there is also a continuous interest in different fields such as the herbicides herein schematically reported.

AREAS COVERED

The intent of this article is to give a comprehensive overview of the most important patents in the last decade related to pathologies of great interest. All selected patents claim new compounds bearing the secondary or/and tertiary sulfonamide moiety, and state to have biological activities. The article is neither intended for detailed discussions of the sulfonamides mode of action on the specific therapeutic targets, nor for their contribution to the physicochemical properties of the molecules they are introduced into, as the scientific literature in such topics is exhaustive and in many cases, debates are still ongoing. The main fields covered are related to pathologies affecting the CNS, cardiac disorders, anti-virals, inflammation diseases, glaucoma, bone remodeling, anti-cancer, and finally a section is also dedicated to herbicides.

EXPERT OPINION

The insertion of the secondary/tertiary sulfonamide group into the organic scaffolds is chemically straightforward and not associated to particular toxicity in the cells or in the organisms. Therefore, it is possible to create large libraries of compounds, which can be tested for different diseases. As demonstrated by the patents reported in the present review, the research in medicinal chemistry, and other fields, takes big advantages as new leads are created, and might be further developed.

Evidence for anti-inflammatory and putative analgesic effects of a monoclonal antibody to calcitonin gene-related peptide

BACKGROUND

Calcitonin gene-related peptide (CGRP) is a powerful pro-inflammatory mediator thought to play a significant role in the development of inflammation and pain. We investigated the role of CGRP in trigeminal inflammatory pain by determining the ability of a monoclonal antibody to CGRP to modify central Fos expression in response to stimulation of the inflamed ferret tooth pulp. We also assessed the effect of the antibody on pulpal inflammation.

METHODS

Ten adult ferrets were prepared under anaesthesia to allow stimulation of the upper and lower left canine pulps, recording from the digastric muscle and intravenous injections at subsequent experiments. In all animals, pulpal inflammation was induced by introducing human caries into a deep buccal cavity. Four days later animals were treated intravenously with either CGRP antibody (n=5) or vehicle (n=5). After a further 2 days animals were re-anaesthetised and the tooth pulps stimulated at 10 times jaw-opening reflex threshold. Brainstems and tooth pulps were processed immunohistochemically for Fos and the common leucocyte marker CD45, respectively.

RESULTS

Fos was expressed in ipsilateral trigeminal subnuclei caudalis (Vc) and oralis (Vo). Significantly fewer Fos-positive nuclei were present within Vc of CGRP antibody-treated animals (p=0.003 vs vehicle-treated). Mean percentage area of staining for CD45 was significantly less in antibody-treated animals (p=0.04 vs vehicle-treated).

CONCLUSIONS

This is the first direct evidence that sequestration of CGRP has anti-inflammatory and putative analgesic effects. Previous studies using this Fos model have demonstrated that it is able to predict clinical analgesic efficacy. Thus these data indicate that this antibody may have analgesic effects in dental pain and other types of inflammatory-mediated transmission, and suggest that this is in part due to peripheral anti-inflammatory effects.

Antagonism of 5-HT(2A) receptors inhibits the expression of pronociceptive mediator and enhances endogenous opioid mechanism in carrageenan-induced inflammation in rats

We have recently reported that treatment with the 5-HT(2A) receptor antagonist ketanserin in the inflamed paw raises the nociceptive threshold above normal level (hypoalgesia) and this response is naloxone-reversible. The present study aimed to investigate neurochemical changes at the site of inflammation and in dorsal root ganglia (DRG) and the spinal cord following the blockade of 5-HT(2A) receptors. Intraplantar injection of ketanserin (20 μg) inhibited carrageenan-induced increase in CGRP immunoreactivity-positive neurons in DRG. On the other hand, administration of ketanserin (20 μg) and 5-HT (10 μg), but not vehicle, enhanced and inhibited recruitment of β-endorphin-expressing immune cells, respectively, in subcutaneous loci of inflamed hindpaw. Moreover, the treatment with ketanserin increased the number of endomorphine-containing cells in the inflamed paw and μ-opioid receptor-expressing neurons in DRG at L4-5 but reduced the expression of endomorphine in superficial layers of the lumbar spinal cord. The present study provided evidence at the cellular level showing that the blockade of 5-HT(2A) receptors inhibited inflammation-associated increase in pronociceptive mediator, and that the pronociceptive property of 5-HT is mediated by the suppression of inflammation-activated opioid mechanism. Therefore, targeting the 5-HT(2A) receptors in the site of inflammation may be a promising approach to inhibit inflammatory pain.

Spinal CGRP1 receptors contribute to supraspinally organized pain behavior and pain-related sensitization of amygdala neurons

CGRP receptor activation has been implicated in peripheral and central sensitization. The role of spinal CGRP receptors in supraspinal pain processing and higher integrated pain behavior is not known. Here we studied the effect of spinal inhibition of CGRP1 receptors on supraspinally organized vocalizations and activity of amygdala neurons. Our previous studies showed that pain-related audible and ultrasonic vocalizations are modulated by the central nucleus of the amygdala (CeA). Vocalizations in the audible and ultrasonic range and hindlimb withdrawal thresholds were measured in awake adult rats before and 5-6h after induction of arthritis by intra-articular injections of kaolin and carrageenan into one knee. Extracellular single-unit recordings were made from neurons in the latero-capsular division of the CeA (CeLC) in anesthetized rats before and after arthritis induction. CGRP1 receptor antagonists were applied to the lumbar spinal cord intrathecally (5 microl/min) 6h postinduction of arthritis. Spinal administration of peptide (CGRP8-37, 1 microM) and non-peptide (BIBN4096BS, 1 microM) CGRP1 receptor antagonists significantly inhibited the increased responses of CeLC neurons to mechanical stimulation of the arthritic knee but had no effect under normal conditions. In arthritic rats, the antagonists also inhibited the audible and ultrasonic components of vocalizations evoked by noxious stimuli and increased the threshold of hindlimb withdrawal reflexes. The antagonists had no effect on vocalizations and spinal reflexes in normal rats. These data suggest that spinal CGRP1 receptors are not only important for spinal pain mechanisms but also contribute significantly to the transmission of nociceptive information to the amygdala and to higher integrated behavior.

N-terminal bis-(2-chloroethyl)amino and fluorosulphonyl analogues of calcitonin gene-related peptide(8-37): irreversible antagonists at calcitonin gene-related peptide receptors

Synthesis of the first irreversible calcitonin gene-related peptide receptor antagonists is described. bis-(2-chloroethyl)amino and fluorosulphonyl groups were incorporated into the 4-position of the N-terminal benzoyl group of a potent competitive antagonist, N-alpha-benzoyl-h-alpha-CGRP(8-37) (analogues 4 and 6). Based on previous structure-activity relationships, a second pair of N-terminally modified analogues was synthesized containing a novel benzylated-His residue in position 10 (analogues 5 and 7). In separate experiments, SK-N-MC cells and mouse thoracic aortas were bathed in solutions containing 5 microM and 1.5 microM of each analogue, respectively. After extensive washing, calcitonin gene-related peptide concentration-response curves were generated for cAMP production in SK-N-MC cells and relaxation of mouse aortas. All analogues caused >20% reductions in maximal calcitonin gene-related peptide efficacy in both assays with analogue 5 containing an N-terminal bis-(2-chloroethyl)amino-benzoyl group and a benzylated-His10 residue completely abolishing cAMP production in SK-N-MC cells. Reductions in maximal responses were dependent on the analogue concentration. Analogue 4 also caused more than 10-fold reductions in the potency of the calcitonin gene-related peptide-mediated effects, whereas analogues 5, 6 and 7 have no significant effect on calcitonin gene-related peptide potency. These data indicate that all analogues bind irreversibly to calcitonin gene-related peptide receptors. The bis-(2-chloroethyl)amino-modified analogues 4 and 5 were more effective than the fluorosulphonyl-modified analogues 6 and 7.

Pain-related synaptic plasticity in spinal dorsal horn neurons: role of CGRP

Background

The synaptic and cellular mechanisms of pain-related central sensitization in the spinal cord are not fully understood yet. Calcitonin gene-related peptide (CGRP) has been identified as an important molecule in spinal nociceptive processing and ensuing behavioral responses, but its contribution to synaptic plasticity, cellular mechanisms and site of action in the spinal cord remain to be determined. Here we address the role of CGRP in synaptic plasticity in the spinal dorsal horn in a model of arthritic pain.

Results

Whole-cell current- and voltage-clamp recordings were made from substantia gelatinosa (SG) neurons in spinal cord slices from control rats and arthritic rats (> 6 h postinjection of kaolin/carrageenan into the knee). Monosynaptic excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation of afferents in the dorsal root near the dorsal root entry zone. Neurons in slices from arthritic rats showed increased synaptic transmission and excitability compared to controls. A selective CGRP1 receptor antagonist (CGRP8-37) reversed synaptic plasticity in neurons from arthritic rats but had no significant effect on normal transmission. CGRP facilitated synaptic transmission in the arthritis pain model more strongly than under normal conditions where both facilitatory and inhibitory effects were observed. CGRP also increased neuronal excitability. Miniature EPSC analysis suggested a post- rather than pre-synaptic mechanism of CGRP action.

Conclusion

This study is the first to show synaptic plasticity in the spinal dorsal horn in a model of arthritic pain that involves a postsynaptic action of CGRP on SG neurons.

Involvement of spinal neurokinins, excitatory amino acids, proinflammatory cytokines, nitric oxide and prostanoids in pain facilitation induced by Phoneutria nigriventer spider venom

The major local symptom of Phoneutria nigriventer envenomation is an intense pain, which can be controlled by infiltration with local anesthetics or by systemic treatment with opioid analgesics. Previous work showed that intraplantar (i.pl) injection of Phoneutria nigriventer venom in rats induces hyperalgesia, mediated peripherally by tachykinin and glutamate receptors. The present study examined the spinal mechanisms involved in pain-enhancing effect of this venom. Intraplantar injection of venom into rat hind paw induced hyperalgesia. This phenomenon was inhibited by intrathecal (i.t.) injection of tachykinin NK1 (GR 82334) or NK2 (GR 94800) receptor antagonists, a calcitonin gene-related peptide (CGRP) receptor antagonist (CGRP8-37) and N-methyl-D-aspartate (NMDA; MK 801 and AP-5), non-NMDA ionotropic (CNQX), or metabotropic (AIDA and MPEP) glutamate receptor antagonists, suggesting the involvement of spinal neurokinins and excitatory amino acids. The role of proinflammatory cytokines, nitric oxide (NO), and prostanoids in spinally mediated pain facilitation was also investigated. Pharmacological blockade of tumour necrosis factor-alpha (TNFalpha) or interleukin-1beta (IL-1beta) reduced the hyperalgesic response to venom. Intrathecal injection of L-N6-(1-iminoethyl)lysine (L-NIL), but not of 7-nitroindazole (7-NI), inhibited hyperalgesia induced by the venom, indicating that NO, generated by the activity of the inducible form of nitric oxide synthase, also mediates this phenomenon. Furthermore, indomethacin, an inhibitor of cyclooxigenases (COX), or celecoxib, a selective inhibitor of COX-2, abolished venom-induced hyperalgesia, suggesting the involvement of spinal prostanoids in this effect. These data indicate that the spinal mechanisms of pain facilitation induced by Phoneutria nigriventer venom involves a plethora of mediators that may cooperate in the genesis of venom-induced central sensitization.

Involvement of oxytocin in spinal antinociception in rats with inflammation

The present study was conducted on rats with inflammation induced by subcutaneous injection of carrageenan into the left hindpaw. Intrathecal administration of oxytocin produced dose-dependent increases in the hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation in rats with inflammation. The antinociceptive effect of oxytocin was blocked by intrathecal administration of atosiban, a selective oxytocin antagonist, indicating that oxytocin receptor mediates oxytocin-induced antinociception in the spinal cord. The oxytocin-induced antinociceptive effect was attenuated by intrathecal administration of the opioid antagonist naloxone, suggesting an involvement of the endogenous opioid system in oxytocin-induced antinociception in the spinal cord of rats with inflammation. Furthermore, the antinociceptive effect of oxytocin was attenuated by intrathecal injections of the mu-receptor antagonist beta-funaltrexamine and the kappa-receptor antagonist nor-binaltorphimine, but not by the delta-receptor antagonist naltrindole, illustrating that mu- and kappa-receptors, but not delta-receptor, are involved in oxytocin-induced antinociception in the spinal cord of rats with inflammation. Moreover, intrathecal administration of atosiban alone induced a hyperalgesia in rats with inflammation, indicating that endogenous oxytocin is involved in the transmission and regulation of nociceptive information in the spinal cord of rats with inflammation. The present study showed that both exogenous and endogenous oxytocin displayed antinociception in the spinal cord in rats with inflammation, and mu- and kappa-receptors were involved in oxytocin-induced antinociception.

Flurbiprofen inhibits capsaicin induced calcitonin gene related peptide release from rat spinal cord via an endocannabinoid dependent mechanism

Calcitonin gene related peptide (CGRP) is involved in nociceptive transmission and modulation at the spinal level. In the spinal superperfusion model, Delta(9) tetrahydrocannabinol inhibited capsaicin induced CGRP release in a concentration dependent manner. Similarly, flurbiprofen (3 microM) inhibited spinal CGRP release. This inhibition was reversed by the CB(1) antagonist AM-251 (1 microM), but not by co-administration of prostaglandin E(2) (PGE(2); 285 nM). AM-251 had no modulatory effect on flurbiprofen-induced cyclooxygenase (COX) inhibiting capacity as shown by PGE(2) levels. Furthermore, the phospholipase A(2) inhibitor palmityl trifluromethyl ketone (15 microM) reversed flurbiprofen's inhibitory effect. In conclusion the present work provides evidence on the shift of arachidonic acid metabolism towards endocannabinoids formation in response to COX inhibition as a mechanism for flurbiprofen inhibitory effect on spinal CGRP release.

Role of calcitonin gene-related peptide and its antagonist on the evoked discharge frequency of wide dynamic range neurons in the dorsal horn of the spinal cord in rats

The present study was performed to explore the effect of calcitonin gene-related peptide (CGRP) and its antagonist CGRP8-37 on the evoked discharge frequency of wide dynamic range (WDR) neurons in the dorsal horn of the spinal cord in rats. Recording was performed with a multibarrelled glass micropipette and the chemicals were delivered by iontophoresis. The discharge of WDR neurons was evoked by transdermic electrical stimulation applied on the ipsilateral hindpaw. (1) Iontophoretic application of CGRP at an ejection current of 100 nA increased the discharge frequency of WDR neurons significantly. (2) Iontophoretic application of CGRP8-37 at an ejection current of 80 or 160 nA induced significant decreases in the discharge frequency of WDR neurons, but not at 40 nA. (3) Iontophoretic application of CGRP8-37 not only antagonized the CGRP-induced increase in the evoked discharge frequency of WDR neurons but also induced a significant decrease in the evoked discharge frequency of WDR neurons compared to basal levels. The results indicate that CGRP and its receptors play a facilitary role on the transmission and/or modulation of nociceptive information in the dorsal horn of the spinal cord in rats.

Crossed and uncrossed projections to the cat sacrocaudal spinal cord: III. Axons expressing calcitonin gene-related peptide immunoreactivity

We have investigated the projection patterns of peptidergic small-diameter primary afferent fibers to the cat sacrocaudal spinal cord, a region associated with midline structures of the lower urogenital system and of the tail. Calcitonin gene-related peptide (CGRP)-immunoreactive (CGRP-IR) primary afferent fibers were observed within the superficial laminae, rostrally as the typical inverted U-shaped band that capped the separate dorsal horns (S1 to rostral S2) and caudally as a broad band that spanned the entire mediolateral extent of the fused dorsal horns (caudal S2 and caudal). Within the dorsal gray commissure, labeling was seen as a periodic vertical, midline band. CGRP-IR labeling was prevalent in an extensive mediolateral distribution at the base of the dorsal horn, originating from both lateral and medial collateral bundles that extend from the superficial dorsal horn. Some bundles, in part traveling within the dorsal commissure, conspicuously crossed the midline. In addition to the robust projection to the superficial dorsal horn, there was a more extensive distribution of CGRP-IR fibers within the deeper portions of the cat sacrocaudal dorsal horn than has been reported for other regions of the cat spinal cord. Presumably, these deep projections convey visceral information to projection or segmental neurons at the neck of the dorsal horn and in the region of the central canal. This deep distribution overlaps the reported projections of the pelvic and pudendal nerves. In addition, the contralateral projections of CGRP-IR fibers may form an anatomical substrate of the bilateral receptive fields for selective dorsal horn neurons. The density and variety of CGRP-IR projection patterns is a reflection of the functional attributes of the innervated structures.

Anti-nociceptive effect of neuropeptide Y in periaqueductal grey in rats with inflammation

Experimental inflammation was induced by subcutaneous injection of carrageenan into the left hindpaw of rats. Intra-periaqueductal grey (PAG) injection of 0.02 or 0.1 nmol of neuropeptide Y (NPY), but not 0.004 nmol, induced significant increases in hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation in rats with inflammation. Furthermore, the anti-nociceptive effect of NPY was blocked partly by following intra-PAG injection of the Y1 receptor antagonist NPY28-36. The results demonstrated that NPY plays an anti-nociceptive role in PAG in rats with inflammation, in which Y1 receptor is involved.

Anti-nociceptive effects of calcitonin gene-related peptide in nucleus raphe magnus of rats: an effect attenuated by naloxone

The present study investigated the role of calcitonin gene-related peptide (CGRP) on nociception in nucleus raphe magnus (NRM) and the interaction between CGRP and opioid peptides in NRM of rats. CGRP-like immunoreactivity was found at a concentration of 6.0+/-0. 77 pmol/g in NRM tissue of ten samples of rats, suggesting that it may contribute to physiological responses orchestrated by the NRM. The hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation increased significantly after intra-NRM administration of 0.5 or 1 nmol of CGRP in rats, but not 0.25 nmol. The anti-nociceptive effect induced by CGRP was antagonized by following intra-NRM injection of 1 nmol of the CGRP receptor antagonist CGRP8-37. Furthermore, the CGRP-induced anti-nociceptive effect was attenuated by following intra-NRM administration of 6 nmol of naloxone. The results indicate that CGRP and its receptors play an important role in anti-nociception, and there is a possible interaction between CGRP and opioid peptides in NRM of rats.

A comparative study of the ability of calcitonin gene-related peptide and adrenomedullin(13 - 52) to modulate microvascular but not thermal hyperalgesia responses

Calcitonin gene-related peptide (CGRP), a neuropeptide, is a potent vasodilator. Adrenomedullin (ADM) is suggested to be produced by vascular cells in inflamed tissue. ADM shares some structural homology with CGRP. We have compared the ability of CGRP and ADM to modulate microvascular and thermal hyperalgesic responses in rat skin. Vasodilator activity was assessed by laser Doppler flowmetry, inflammatory oedema by the extravascular accumulation of intravenously-injected labelled albumin, and neutrophil accumulation by tissue myeloperoxidase, in dorsal skin. Hyperalgesia was assessed by a thermal hyperalgesimeter in paw skin. ADM (10-300 pmol) was 3 fold less potent than CGRP (3-100 pmol) as a direct vasodilator. CGRP (30 pmol) potentiated oedema formation induced by mediators of increased microvascular permeability, as expected (P<0.01). However, ADM (30-100 pmol) was without a potentiating effect, although ADM (300 pmol) was effective (P<0.01). By comparison ADM (100 pmol) potentiated neutrophil accumulation induced by interleukin-1beta (P<0.05), whereas CGRP (30 pmol) did not. No thermal hyperalgesia was observed to either CGRP or ADM, when given as single or repeated treatments. Thus despite a dilator activity neither CGRP nor ADM appears to mediate hyperalgesic activity in the periphery. However ADM, like CGRP, has the ability to potentiate inflammatory oedema formation and, in addition, ADM can potentiate neutrophil accumulation. ADM may, as suggested for CGRP, act as a modulator of the vascular phases of inflammation. The property of the two compounds of evoking differential microvascular responses and neutrophil accumulation may be due to differing mechanisms of action.

Antinociceptive effects of calcitonin gene-related peptide injected into periaqueductal grey of rats with mononeuropathy

Intra-periaqueductal grey (PAG) injection of calcitonin gene-related peptide (CGRP) induced dose-dependent increases in hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation in rats with mononeuropathy. CGRP-induced increases in HWLs were blocked by intra-PAG injection of the CGRP antagonist CGRP8-37. The results demonstrated that CGRP and CGRP receptors in PAG play an important role in antinociception in rats with mononeuropathy.

Calcitonin gene-related peptide 8-37 inhibits the evoked discharge frequency of wide dynamic range neurons in dorsal horn of the spinal cord in rats

The present study was performed to explore the effect of calcitonin gene-related peptide 8-37 (CGRP8-37) on the electrical stimulation-evoked discharge frequency of wide dynamic range (WDR) neurons in the dorsal horn of the spinal cord in rats. The discharge frequencies of WDR neurons were evoked by transdermic electrical stimulation applied on the ipsilateral hindpaw. CGRP8-37 was applied directly on the dorsal surface of the L3 to L5 spinal cord. After the administration of 3 nmol of CGRP8-37, the evoked discharge frequency of WDR neurons decreased significantly, an effect lasting more than 30 min. The results indicate that CGRP receptors play an important role in the transmission of presumed nociceptive information in the dorsal horn of the spinal cord.

Effects of intrathecal galanin on nociceptive responses in rats with mononeuropathy

The present study was performed on rats with experimental mononeuropathy induced by left common sciatic nerve loose ligation. Unilateral sciatic nerve loose ligation induced decreases of the hindpaw withdrawal latency to the hot-plate test, cold-plate test and the Randall Selitto test. Sciatic nerve loose ligation induced hyperesponsiveness to touch at room temperature also. Intrathecal administration of either 3 or 6 nmol of galanin, but not 1 nmol, induced significant bilateral increases in hindpaw withdrawal latencies to the hot-plate test, cold-plate test and the Randall Selitto tests in rats with left mononeuropathy. The results indicate that galanin may play important roles in transmission of presumed nociceptive information in the spinal cord of mononeuropathic rats.