Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Role of central calcitonin gene-related peptide (CGRP) in locomotor and anxiety- and depression-like behaviors in two mouse strains exhibiting a CGRP-dependent difference in thermal pain sensitivity

We have previously shown that, in AKR and C57BL/6 mice, a genetic polymorphism results in differential expression of the peptide, calcitonin gene-related polypeptide (CGRP), explaining a strain difference in thermal pain sensitivity. Although CGRP is widely distributed in the brain, little is known about the effects of supraspinal CGRP. We used AKR and C57BL/6 mice as a model to explore the effects of centrally (intracerebroventricular) injected CGRP and the CGRP receptor antagonists, CGRP(8-37) and BIBN4096BS, in a series of behavioral assays. Locomotor activity was significantly increased in C57BL/6 mice following the injection of BIBN4096BS and in both strains after the administration of CGRP(8-37) into the third ventricle. CGRP increased paw-withdrawal latencies in C57BL/6 mice only, while decreasing depression-like behaviors in both strains in the forced-swimming test. CGRP and CGRP receptor antagonists failed to modulate activity in the elevated plus maze, a model of anxiety. Taken together, these results suggest a complex role for supraspinal CGRP systems in the regulation of locomotion, nociception, and depression-like behaviors.

Inhibition of calcitonin gene-related peptide function: a promising strategy for treating migraine

The neuropeptide calcitonin gene-related peptide (CGRP) is implicated in the underlying pathology of migraine. Serum levels of CGRP, which are elevated during a migraine attack, have been reported to return to normal with alleviation of pain. In addition, CGRP administration has been shown to cause a migraine-like headache in susceptible individuals. Importantly, CGRP receptors are found on many cell types within the trigeminovascular system that are thought to play important roles in controlling inflammatory and nociceptive processes. Based on these findings, it was proposed that blockage of CGRP receptor function and, hence, the physiological effects of CGRP would be effective in aborting a migraine attack. This review will summarize key preclinical data that support the therapeutic potential of using CGRP receptor antagonists or molecules that bind CGRP within the context of current neurovascular theories on migraine pathology.

Calcitonin Gene-Related Peptide Receptor Inhibition Reduces Neuronal Activity Induced by Prolonged Increase in Nitric Oxide in the Rat Spinal Trigeminal Nucleus

Infusion of nitric oxide (NO) donors is known to induce delayed attacks of migraine and cluster headache or aggravate tension-type headaches in patients suffering from these primary headaches. Previously we have reported that infusion of NO donors in the rat causes delayed neuronal activity in the spinal trigeminal nucleus, which parallels the above clinical observations. Suggesting that endogenous NO production is involved in the generation of primary headaches, we used this animal model of meningeal nociception to determine whether a prolonged increase in NO levels causes an increase in neuronal activity. In anaesthetized rats spinal trigeminal neurons with afferent input from the exposed dura were recorded. Continuous intravenous infusion of the NO donors sodium nitroprusside (25 μg/kg/h) or glycerol trinitrate (250 μg/ kg/h) for 2h induced a persisting increase in neuronal activity but no change in systemic blood pressure. In this activated trigeminal system the calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS (900 μg/ kg) was infused. Spinal trigeminal activity was significantly reduced within minutes and to a similar extent as previously reported in animals not treated with NO. Slow continuous NO infusion may be a model of the active headache phase, and inhibition of CGRP receptors can reverse the induced neuronal activity.

Effect of calcitonin gene-related peptide (CGRP), adrenomedullin and adrenomedullin-2/intermedin on food intake in goldfish (Carassius auratus)

The purpose of the present study was to elucidate the possible role of calcitonin gene-related peptide (CGRP), adrenomedullin (AM) and adrenomedullin-2/intermedin (IMD) on food intake regulation in goldfish (Carassius auratus). We examined the effects of intracerebroventricular (ICV) administration of these related hormones on food intake. Food-deprived goldfish were subjected to ICV injections of CGRP, AM and IMD and their food intake were quantified. CGRP at 10ng/g body weight (bw) significantly decreased food intake as compared to saline-treated fish. IMD at 10 and 50ng/g bw both significantly decreased food intake as compared to saline group. No significant differences were observed after AM administration. Our results suggest, for the first time in fish, a role for both CGRP and IMD in the central regulation of feeding in fish.

Sumatriptan does not change calcitonin gene-related peptide in the cephalic and extracephalic circulation in healthy volunteers

Triptans are effective and well tolerated in acute migraine management but their exact mechanism of action is still debated. Triptans might exert their antimigraine effect by reducing the levels of circulating calcitonin gene-related peptide (CGRP). To examine this question, we examined whether sumatriptan modulate the baseline CGRP levels in vivo, under conditions without trigeminovascular system activation. We sampled blood from the internal and external jugular, the cubital veins, and the radial artery before and after administration of subcutaneous sumatriptan in 16 healthy volunteers. Repeated-measure ANOVA showed no interaction between catheter and time of sampling and thus no significant difference in CGRP between the four catheters (P=0.75). CGRP did not change over time in the four compartments (P>0.05). The relative changes in CGRP between baseline and maximal sumatriptan concentration did not differ between the four vascular compartments (P=0.49). It was found that Sumatriptan did not change the levels of circulating CGRP in the intra or extracerebral circulation in healthy volunteers. This speaks against a direct CGRP-reducing effect of sumatriptan in vivo in humans when the trigemino vascular system is not activated.

Age-related changes in dorsal root ganglia, circulating and vascular calcitonin gene-related peptide (CGRP) concentrations in female rats: effect of female sex steroid hormones

The aim of the present study is to investigate whether immunoreactive (I) calcitonin gene-related peptide (CGRP) content is decreased in plasma and mesenteric arteries (resistance arteries) in middle-aged rats and if so, whether sex steroid hormones enhance I-CGRP in middle-aged female rats. We also examined whether vascular CGRP receptor components, calcitonin receptor like receptor (CRLR) and receptor activity modifying protein 1 (RAMP1) are elevated by sex steroid hormones treatment in middle-aged female rats. Young adult (3 months old) and middle-aged (10-12 months old) ovariectomized rats were treated subcutaneously with estradiol-17beta (E2; 2 mg), progesterone (P4; 5 mg), E2+P4 (2 mg+20 mg) or placebo (control). Radioimmunoassay and Western blot analysis were performed to measure I-CGRP content and CGRP receptor components in dorsal root ganglia (DRG), in resistance arteries and in plasma. Immunofluorescent staining methods were employed to determine cellular localization of CRLR, RAMP1 in resistance arteries. Our data demonstrated that I-CGRP content was significantly (p<0.05) lower in the plasma and resistance arteries of middle-aged female rats compared to young controls. Both RAMP1 and CRLR were concentrated in vascular endothelium and the underlying smooth muscle cells. RAMP1 but not CRLR appeared to be decreased in middle-aged rat vasculature. Chronic perfusion of sex steroid hormones to ovariectomized rats: 1 significantly (p<0.05) elevated I-CGRP in the DRG and in the plasma, and (2) significantly elevated RAMP1 (p<0.05) but did not alter CRLR in resistance arteries. These data suggest that female sex steroid treatment enhances I-CGRP and its receptors, and thus regulate the blood pressure in aged female rats.

Inflammation and neuropeptides: the connection in diabetic wound healing

Abnormal wound healing is a major complication of both type 1 and type 2 diabetes, with nonhealing foot ulcerations leading in the worst cases to lower-limb amputation. Wound healing requires the integration of complex cellular and molecular events in successive phases of inflammation, cell proliferation, cell migration, angiogenesis and re-epithelialisation. A link between wound healing and the nervous system is clinically apparent as peripheral neuropathy is reported in 30-50% of diabetic patients and is the most common and sensitive predictor of foot ulceration. Indeed, a bidirectional connection between the nervous and the immune systems and its role in wound repair has emerged as one of the focal features of the wound-healing dogma. This review provides a broad overview of the mediators of this connection, which include neuropeptides and cytokines released from nerve fibres, immune cells and cutaneous cells. In-depth understanding of the signalling pathways in the neuroimmune axis in diabetic wound healing is vital to the development of successful wound-healing therapies.

Efficacy and tolerability of MK-0974 (telcagepant), a new oral antagonist of calcitonin gene-related peptide receptor, compared with zolmitriptan for acute migraine: a randomised, placebo-controlled, parallel-treatment trial

BACKGROUND

Calcitonin gene-related peptide (CGRP) probably has a role in migraine pathophysiology, and antagonism of its receptors might provide treatment without the vasoconstrictor effects of triptans. We aimed to assess the clinical profile of MK-0974 (telcagepant), an orally bioavailable antagonist of CGRP receptor.

METHODS

In a randomised, parallel-treatment, placebo-controlled, double-blind, trial at 81 sites in the Europe and the USA, adults with migraine diagnosed by International Headache Society criteria treated moderate or severe attacks with either oral telcagepant 150 mg or 300 mg, zolmitriptan 5 mg, or placebo. The five co-primary endpoints were pain freedom, pain relief, or absence of photophobia, phonophobia, or nausea at 2 h after treatment. Analysis was by the full analysis set and multiplicity was controlled for with a step-down closed-testing procedure. This trial is registered with ClinicalTrials.gov, number NCT00442936.

FINDINGS

1380 patients were randomly assigned to receive telcagepant 150 mg (n=333) or 300 mg (354), zolmitriptan (345), or placebo (348). Telcagepant 300 mg was more effective than placebo for pain freedom (95 [27%] of 353 patients vs 33 [10%] of 343 [p<0.0001]), pain relief (194 [55%] of 353 vs 95 [28%] of 343 [p<0.0001]), and absences of phonophobia (204 [58%] of 353 vs 126 [37%] of 342 [p<0.0001]), photophobia (180 [51%] of 353 vs 99 [29%] of 342 [p<0.0001]), and nausea (229 [65%] of 352 vs 189 [55%] of 342 [p=0.0061]). Efficacy of telcagepant 300 mg and zolmitriptan 5 mg were much the same, and both were more effective than telcagepant 150 mg. Adverse events were recorded for 31% taking telcagepant 150 mg, 37% taking telcagepant 300 mg, 51% taking zolmitriptan 5 mg, and 32% taking placebo.

INTERPRETATION

Telcagepant 300 mg is effective as an acute treatment for migraine with efficacy comparable to that of zolmitriptan 5 mg, but with fewer associated adverse effects.

FUNDING

Merck Research Laboratories.

Release of calcitonin gene-related peptide from the jugular-nodose ganglion complex in rats--a new model to examine the role of cardiac peptidergic and nitrergic innervation

OBJECTIVE

Afferent information from the heart and the lung is conveyed to the brainstem by primary afferent fibers originating from vagal sensory neurons (jugular-nodose ganglion complex, JNC). The present study was made to evaluate if release of the sensory neuropeptide calcitonin gene-related peptide (CGRP) from the JNC can be used as a model for future studies on changes in neuropeptide release under pathological conditions of the heart.

METHODS

Freshly isolated rat JNC's were passed through a series of solutions based on oxygenated synthetic interstitial fluid (SIF). Substances such as the TRPV1 receptor agonist capsaicin and the nitric oxide (NO) donor sodium nitroprusside (SNP) were added as excitatory test stimuli. The eluates were processed using an enzyme immuno-assay (EIA) for measurement of CGRP concentrations. Immunohistochemistry was used to visualize CGRP containing and NO producing neurons in the JNC.

RESULTS

Both SNP and capsaicin caused significant increases in CGRP release. CGRP-immunoreactive neurons (somata) were preferentially found in the jugular ganglion, whereas neurons immunoreactive for neuronal NO synthase were mostly localized in the nodose ganglion.

CONCLUSION

The present study demonstrates an easily reproducible model for measuring stimulated CGRP release from vagal afferents arising from the JNC. Nitric oxide produced by vagal afferents may stimulate CGRP release upon afferent activation.

Differential effects of olanzapine, haloperidol and risperidone on calcitonin gene-related peptide in the rat brain

Calcitonin gene-related peptide (CGRP) is a 37 amino acid peptide which acts on central nervous system (CNS) neurons and is involved in activities related to dopamine. These effects of CGRP suggest that the peptide may have a role in pathophysiology and treatment of schizophrenia where dopaminergic system hypoactivity in the frontal cortex and hyperactivity in the subcortical structures have been demonstrated. In this study we measured by radioimmunoassay (RIA) the brain levels of CGRP-like immunoreactivity (CGRP-LI) in rats treated with either classical (haloperidol) or atypical (risperidone and olanzapine) antipsychotic drugs. Both haloperidol and risperidone decreased CGRP-LI in the striatum. Risperidone also decreased CGRP-LI in the occipital cortex. On the other hand, olanzapine increased CGRP-LI in the striatum, the frontal cortex and hypothalamus. The differential effects on CGRP could reflect a different profile of side effects and further suggest that CGRP is involved in CNS functions related to psychiatric disorders.

Use of a commercial protease and yeasts to obtain CGRP-like molecules from saithe protein

Different bioactive molecules, such as CGRP-like peptides, can be found in fish protein hydrolysates. Calcitonin gene-related peptide (CGRP) is a neuropeptide known to act as a potent arterial and venous vasodilator in humans. This study focuses on the industrial obtaining of CGRP-like molecules from saithe (Pollachius virens) byproduct, derived from the filleting process. Protein from P. virens was primarily hydrolyzed with Alcalase and later treated with Saccharomyces cerevisiae live cells. Treatment with Saccharomyces doubled the quantity of bioactive molecules obtained. The CGRP-like molecules were partially purified by chromatography, and the immunoreactive material was further analyzed for its CGRP-like bioactivity, using a specific radioreceptor assay. The concentration of CGRP-like molecules increased over 100-fold after purification. The bioactive molecules were able to induce cyclic AMP stimulation in rat liver membranes. Finally, partial sequencing of the bioactive peptide was performed, showing some homology with alpha-actin and myosin of several fish species.

Molecular characterization of calcitonin gene-related peptide (CGRP) related peptides (CGRP, amylin, adrenomedullin and adrenomedullin-2/intermedin) in goldfish (Carassius auratus): cloning and distribution

To further characterize the structure and function of calcitonin gene-related peptide (CGRP) related peptides in fish, we have cloned cDNA sequences for CGRP, amylin, adrenomedullin (AM) and adrenomedullin-2/intermedin (IMD) in goldfish (Carassius auratus) and examined their tissue distribution. CGRP, amylin, AM and IMD cDNAs were isolated by reverse transcription (RT) and rapid amplification of cDNA ends (RACE). The cloned sequences contain the complete four mature peptides, which present a high degree of identity with mature peptide sequences from other fish. Phylogenetic analyses show that goldfish AM and IMD form a sub-family within the CGRP-related peptides that is distinct from the CGRP/amylin sub-family. The distribution of goldfish CGRP-like peptides mRNA expression in different tissues and within the brain was studied by RT-PCR. CGRP, IMD and AM are detected throughout the brain, in pituitary and in most peripheral tissues examined. Amylin mRNA is mostly expressed in the brain, in particular posterior brain, optic tectum and hypothalamus, but is also present in pituitary, gonad, kidney and muscle. Our results suggest that goldfish CGRP, amylin, AM and IMD are conserved peptides that show the typical structure characteristics present in their mammalian counterparts. The widespread distributions of CGRP, AM and IMD suggest that these peptides could be involved in the regulation of many diverse physiological functions in fish. Amylin mRNA distribution suggests possible new roles for this peptide in teleosts, including the control of reproduction.

Involvement of CGRP and CGRPl receptor in nociception in the basolateral nucleus of amygdala of rats

The present study was performed to investigate the role of calcitonin gene-related peptide (CGRP) and its receptor in nociception in the basolateral nucleus of amygdala (BLA) of rats. Hindpaw withdrawal latencies (HWLs) to noxious thermal and mechanical stimulations were measured by hot plate and Randall Selitto tests. The HWL to both thermal and mechanical stimulations increased significantly after intra-BLA administration of 1.0 or 2.0 nmol CGRP, but not 0.5 nmol, indicating that CGRP plays an anti-nociceptive role in BLA of rats. The anti-nociceptive effect of 1.0 nmol CGRP was blocked significantly by administration of 1.0 or 2.0 nmol CGRP8-37, a selective antagonist of CGRP1 receptor, which suggests that the anti-nociceptive effect of CGRP is mediated by the CGRP1 receptor. Taken together, the results indicate that both CGRP and CGRP1 receptor play important roles in nociceptive modulation in the BLA of rats.

Estrogen elicits dorsal root ganglion axon sprouting via a renin-angiotensin system

Many painful conditions occur more frequently in women, and estrogen is a predisposing factor. Estrogen may contribute to some pain syndromes by enhancing axon outgrowth by sensory dorsal root ganglion (DRG) neurons. The objective of the present study was to define mechanisms by which estrogen elicits axon sprouting. The estrogen receptor-alpha agonist propyl pyrazole triol induced neurite outgrowth from cultured neonatal DRG neurons, whereas the estrogen receptor-beta agonist diarylpropionitrile was ineffective. 17beta-Estradiol (E2) elicited sprouting from peripherin-positive unmyelinated neurons, but not larger NF200-positive myelinated neurons. Microarray analysis showed that E2 up-regulates angiotensin II (ANGII) receptor type 2 (AT2) mRNA in vitro, and studies in adult rats confirmed increased DRG mRNA and protein in vivo. AT2 plays a central role in E2-induced axon sprouting because AT2 blockade by PD123,319 eliminated estrogen-mediated sprouting in vitro. We assessed whether AT2 may be responding to locally synthesized ANGII. DRG from adult rats expressed mRNA for renin, angiotensinogen, and angiotensin converting enzyme (ACE), and protein products were present and occasionally colocalized within neurons and other DRG cells. We determined if locally synthesized ANGII plays a role in estrogen-mediated sprouting by blocking its formation using the ACE inhibitor enalapril. ACE inhibition prevented estrogen-induced neuritogenesis. These findings support the hypothesis that estrogen promotes DRG nociceptor axon sprouting by up-regulating the AT2 receptor, and that locally synthesized ANGII can induce axon formation. Therefore, estrogen may contribute to some pain syndromes by enhancing the pro-neuritogenic effects of AT2 activation by ANGII.

The role of corticotrophin-releasing hormone receptors in the calcitonin gene-related peptide-induced suppression of pulsatile luteinising hormone secretion in the female rat

Corticotrophin-releasing hormone (CRH) plays a pivotal role in the suppression of the gonadotrophin-releasing hormone (GRH) pulse generator in response to stress and intracerebroventricular (i.c.v.) administration of calcitonin gene-related peptide (CGRP). We have previously shown both CRH receptor subtypes, CRH-R1 and CRH-R2, are involved in the stress-induced suppression of LH pulses. The aims of the present study were to examine the role of CRH-R1 and CRH-R2 in CGRP-induced suppression of LH pulses, and to investigate the effects of CGRP on CRH expression in the paraventricular nucleus (PVN) and central nucleus of the amygdala (CeA), which have prominent CRH neurone populations that receive dense CGRP innervations. The suppression of LH pulses by CGRP (1.5 microg i.c.v.) was completely prevented by intravenous administration of the CRH-R1 antagonist SSR125543Q (7.5 mg/rat i.v., 30 min before CGRP), but was not affected by the CRH-R2 antagonist, astressin(2)-B (100 microg i.c.v., 10 min before CGRP). CGRP increased the CRH mRNA expression in PVN and CeA. These results provide evidence of a role for CRH-R1 in mediating the suppressive effects of CGRP on pulsatile LH secretion in the female rat, and additionally raise the possibility of an involvement of PVN and CeA CRH neuronal populations in this suppression.

Adrenomedullin-2/intermedin induces cAMP accumulation in dissociated rat spinal cord cells: evidence for the existence of a distinct class of sites of action

Adrenomedullin-2/intermedin is structurally related to the calcitonin family of peptides, which includes calcitonin gene-related peptide (CGRP), adrenomedullin, and amylin. We recently reported that CGRP and adrenomedullin act through distinct receptors to induce cyclic adenosine monophosphate (cAMP) accumulation in dispersed cells from embryonic rat spinal cord. Here, we investigated the apparent affinity and efficacy of adrenomedullin-2/intermedin for these receptors. Adrenomedullin-2/intermedin competed with [(125)I]-CGRP for binding to specific embryonic spinal cord cells with a pIC(50) of 9.73 +/- 0.06. Interestingly, adrenomedullin-2/intermedin competed for specific [(125)I]-adrenomedullin binding in a biphasic manner with pIC(50) of 9.03 +/- 0.22 and 6.45 +/- 0.24, respectively. Cellular levels of cAMP were increased by adrenomedullin-2/intermedin (pEC(50) 7.84 +/- 0.08) when cells were exposed to this peptide for 10 min at 37 degrees C. This effect was partially inhibited by the non-peptide antagonist BIBN4096BS (pA(2) 6.56 +/- 0.12), the adrenomedullin antagonist hAM(22-52) (pA(2) 6.36 +/- 0.30), and the adrenomedullin/CGRP antagonist CGRP(8-37) (pA(2) 7.24 +/- 0.60). More interestingly, a highly significant effect of adrenomedullin-2/intermedin on cAMP accumulation (pEC(50) 7.3 +/- 0.14) was still observed even in the presence of a mixture of saturating concentrations of BIBN4096BS, hAM(22-52), and the amylin antagonist AC187. Taken together, these data provide evidence for the possible existence of a distinct class of receptor sites for adrenomedullin-2/intermedin in embryonic rat spinal cord cells.

Gastric emptying in response to IAPP and CCK in rats with subdiaphragmatic afferent vagotomy

In the subdiaphragmatic vagal deafferentation procedure (SDA), the afferent fibers of the vagus are surgically severed unilaterally where they enter the brain stem. The technique includes a subdiaphragmal truncal vagotomy performed on the contralateral side. This procedure has been used to study the control of food intake, but it has not been used previously to investigate the role of vagal afferent fibers in the control of gastric emptying (GE). The current experiment studied the effect of SDA on the inhibition of GE by islet amyloid polypeptide (IAPP or amylin) and cholecystokinin (CCK) in awake, unrestrained rats with gastric cannulas. The experimental group underwent subdiaphragmatic vagal deafferentation; the control group had sham operations. All rats received 20-min intravenous infusions of IAPP (1, 3, 9, 27, and 81 pmol/kg/min), CCK (3, 30 and 90 pmol/kg/min), and normal saline in random order. Gastric emptying of saline was measured by the phenol red method during the last 5 min of each infusion period. CCK dose-dependently inhibited gastric emptying in both the control and SDA animals. The inhibition of GE by CCK was significantly attenuated by SDA (p<0.01). IAPP also inhibited gastric emptying dose-dependently, but the difference between the SDA and control groups was not significant. The current experiment, which used a different methodology than previous studies, provides support for the hypothesis that the inhibition of gastric emptying by CCK, but not by IAPP, is mediated partly by afferent vagal fibers.

Pharmacological profile of the clonidine-induced inhibition of vasodepressor sensory outflow in pithed rats: correlation with alpha(2A/2C)-adrenoceptors

BACKGROUND AND PURPOSE

Resistance blood vessels are innervated by sympathetic and primary sensory nerves, which modulate vascular tone through the release of noradrenaline and calcitonin gene-related peptide (CGRP), respectively. Moreover, electrical stimulation of the perivascular sensory outflow in pithed rats results in vasodepressor responses which are mainly mediated by CGRP release. The present study has investigated the role of alpha(2)-adrenoceptors in the inhibition of these vasodepressor responses.

EXPERIMENTAL APPROACH

144 pithed male Wistar rats were pretreated with hexamethonium (2 mg kg(-1) min(-1)) followed by i.v. continuous infusions of either methoxamine (15 and 30 microg kg(-1) min(-1)) or clonidine (3, 10 and 30 microg kg(-1) min(-1)). Under these conditions, electrical stimulation (0.56-5.6 Hz; 50 V and 2 ms) of the spinal cord (T(9)-T(12)) resulted in frequency-dependent decreases in diastolic blood pressure.

KEY RESULTS

The infusion of clonidine (10 microg kg(-1) min(-1)), as compared to those of methoxamine (15 or 30 microg kg(-1) min(-1)), inhibited the vasodepressor responses to electrical stimulation without affecting those to i.v. bolus injections of alpha-CGRP (0.1-1 microg kg(-1)). This inhibition by clonidine was: (i) antagonized by 300 microg kg(-1) rauwolscine (alpha(2A/2B/2C)), 300 and 1000 microg kg(-1) BRL44408 (alpha(2A)), or 10 and 30 microg kg(-1) MK912 (alpha(2C)); and (ii) unaffected by 1 ml kg(-1) saline, 100 microg kg(-1) BRL44408, 3000 and 10,000 microg kg(-1) imiloxan (alpha(2B)) or 3 microg kg(-1) MK912.

CONCLUSIONS AND IMPLICATIONS

The inhibition produced by 10 microg kg(-1) min(-1) clonidine on the vasodepressor (perivascular) sensory outflow in rats may be mainly mediated by prejunctional alpha(2A)/alpha(2C)-adrenoceptors.

Calcitonin gene-related peptide stimulation of nitric oxide synthesis and release from trigeminal ganglion glial cells

Clinical and basic science data support an integral role of calcitonin gene-related peptide (CGRP) in migraine pathology. Following trigeminal nerve activation, afferent release of CGRP causes vasodilation while efferent release leads to pain. Although CGRP can also be secreted from cell bodies of trigeminal neurons located within the ganglion, the function of CGRP released in the ganglion is poorly understood. Initially, we showed that SNAP-25, a protein required for CGRP release, was localized in cell bodies of trigeminal ganglia neurons. We also found that satellite glial cells in the ganglia express the CGRP1 receptor protein RAMP1. To determine whether CGRP could directly activate glial cells, primary cultures of rat trigeminal ganglia were utilized to study the effects of CGRP on glial nitric oxide (NO) synthesis and release. Under our culture conditions, >95% of the cells expressed glial fibrillary acidic protein and RAMP1. While weak iNOS staining was observed in glia under basal conditions, CGRP treatment greatly increased glial iNOS expression and NO release. This stimulatory effect was blocked by the CGRP1 receptor antagonist, CGRP(8-37) peptide. Treatment of glial cultures with forskolin or cAMP also increased iNOS expression and stimulated NO release to levels similar to CGRP. To our knowledge, this is the first evidence that activation of CGRP1 receptors regulates glial iNOS and NO release. We propose that following trigeminal nerve activation, CGRP secretion from neuronal cell bodies activates satellite glial cells that release NO and initiate inflammatory events in the ganglia that contribute to peripheral sensitization in migraine.

The effects of botulinum toxin type A on muscle blood perfusion and metabolism

BACKGROUND

Botulinum toxin type A is approved by the U.S. Food and Drug Administration for the treatment of facial rhytides. However, the complete spectrum of action of botulinum toxin A has not yet been completely defined. Little is known about the metabolism of muscle after botulinum toxin A injection. This information may give insight into the additional effects botulinum toxin A may have on muscle. The authors assessed the influence of botulinum toxin A on the metabolism of muscle using dynamic investigative techniques.

METHODS

Twenty New Zealand White rabbits were divided into control, paralysis, and sham groups. Masseter muscle paralysis was achieved with botulinum toxin A. Dynamic computed tomographic and positron emission tomographic scans were obtained. Masseter muscle blood flow, blood volume, permeability surface, and mean transit time and glucose uptake were measured.

RESULTS

Eighteen animals completed the study. Masseter blood perfusion showed consistent results across all parameters. Blood flow, blood volume, and permeability surface were significantly increased at weeks 4 and 8 on the paralyzed side. Mean transit time at week 4 was decreased on the paralyzed side. Positron emission tomographic scans showed that injected muscles in the botulinum toxin A group tended to have increased glucose uptake compared with untreated muscles.

CONCLUSIONS

Botulinum toxin A injection increases muscle blood perfusion parameters and glucose uptake for a transient period. This increase is similar in duration to the known interval of botulinum toxin A-induced paralysis. These changes have been identified in a dynamic fashion and may represent changes in calcitonin gene-related peptide release.

Repression of calcitonin gene-related peptide expression in trigeminal neurons by a Theobroma cacao extract

ETHNOPHARMACOLOGICAL RELEVANCE

Cocoa bean preparations were first used by the ancient Maya and Aztec civilizations of South America to treat a variety of medical ailments involving the cardiovascular, gastrointestinal, and nervous systems. Diets rich in foods containing abundant polyphenols, as found in cocoa, underlie the protective effects reported in chronic inflammatory diseases. Release of calcitonin gene-related peptide (CGRP) from trigeminal nerves promotes inflammation in peripheral tissues and nociception.

AIM OF THE STUDY

To determine whether a methanol extract of Theobroma cacao L. (Sterculiaceae) beans enriched for polyphenols could inhibit CGRP expression, both an in vitro and an in vivo approach was taken.

RESULTS

Treatment of rat trigeminal ganglia cultures with depolarizing stimuli caused a significant increase in CGRP release that was repressed by pretreatment with Theobroma cacao extract. Pretreatment with Theobroma cacao was also shown to block the KCl- and capsaicin-stimulated increases in intracellular calcium. Next, the effects of Theobroma cacao on CGRP levels were determined using an in vivo model of temporomandibular joint (TMJ) inflammation. Capsaicin injection into the TMJ capsule caused an ipsilateral decrease in CGRP levels. Theobroma cacao extract injected into the TMJ capsule 24h prior to capsaicin treatment repressed the stimulatory effects of capsaicin.

CONCLUSIONS

Our results demonstrate that Theobroma cacao extract can repress stimulated CGRP release by a mechanism that likely involves blockage of calcium channel activity. Furthermore, our findings suggest that the beneficial effects of diets rich in cocoa may include suppression of sensory trigeminal nerve activation.

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.

Effect of carbon dioxide on calcitonin gene-related peptide secretion from trigeminal neurons

OBJECTIVE

The goal of this study was to determine whether the physiological effects of carbon dioxide (CO(2)) involve regulation of CGRP secretion from trigeminal sensory neurons.

BACKGROUND

The neuropeptide calcitonin gene-related peptide (CGRP) is implicated in the pathophysiology of allergic rhinosinusitis and migraine. Recent clinical evidence supports the use of noninhaled intranasal delivery of 100% CO(2) for treatment of these diseases. Patients report 2 distinct physiological events: first, a short duration stinging or burning sensation within the nasal mucosa, and second, alleviation of primary symptoms.

METHODS

Primary cultures of rat trigeminal ganglia were utilized to investigate the effects of CO(2) on CGRP release stimulated by a depolarizing stimulus (KCl), capsaicin, nitric oxide, and/or protons. The amount of CGRP secreted into the culture media was determined using a CGRP-specific radioimmunoassay. Intracellular pH and calcium levels were measured in cultured trigeminal neurons in response to CO(2) and stimulatory agents using fluorescent imaging techniques.

RESULTS

Incubation of primary trigeminal ganglia cultures at pH 6.0 or 5.5 was shown to significantly stimulate CGRP release. Similarly, CO(2) treatment of cultures caused a time-dependent acidification of the media, achieving pH values of 5.5-6 that stimulated CGRP secretion. In addition, KCl, capsaicin, and a nitric oxide donor also caused a significant increase in CGRP release. Interestingly, CO(2) treatment of cultures under isohydric conditions, which prevents extracellular acidification while allowing changes in PCO(2) values, significantly repressed the stimulatory effects of KCl, capsaicin, and nitric oxide on CGRP secretion. We found that CO(2) treatment under isohydric conditions resulted in a decrease in intracellular pH and inhibition of the KCl- and capsaicin-mediated increases in intracellular calcium.

CONCLUSIONS

Results from this study provide the first evidence of a unique regulatory mechanism by which CO(2) inhibits sensory nerve activation, and subsequent neuropeptide release. Furthermore, the observed inhibitory effect of CO(2) on CGRP secretion likely involves modulation of calcium channel activity and changes in intracellular pH.

What makes a CGRP2 receptor?

1. Heterogeneity in the receptors for the neuropeptide calcitonin gene-related peptide (CGRP) has been apparent for nearly 20 years. This is most clearly manifested in the observation of CGRP(8-37)-sensitive and -insensitive populations of CGRP-activated receptors. The pA(2) values for CGRP(8-37) in excess of 7 are widely considered to be the result of antagonism of CGRP(1) receptors, whereas those below 7 are believed to be the consequence of antagonism of a second population of receptors, namely CGRP(2) receptors. 2. However, a multitude of pA(2) values exist for CGRP(8-37), spanning several log units, and as such no obvious clusters of values are apparent. Understanding the molecular nature of the receptors that underlie this phenomenon is likely to aid the development of selective pharmacological tools to progress our understanding of the physiology of CGRP and related peptides. Because there is active development of CGRP agonists and antagonists as therapeutics, such information would also further this pursuit. 3. The CGRP(1) receptor is pharmacologically and molecularly well defined as a heterodimer of the calcitonin receptor-like receptor (CL) and receptor activity modifying protein (RAMP) 1. The CL/RAMP1 complex is highly sensitive to CGRP(8-37). Conversely, the constituents of the CGRP(2) receptor have not been identified. In fact, there is little evidence for a distinct molecular entity that represents the CGRP(2) receptor. 4. Recent pharmacological characterization of receptors related to CGRP(1) has revealed that some of these receptors may explain CGRP(2) receptor pharmacology. Specifically, AMY(1(a)) (calcitonin receptor/RAMP1) and AM(2) (CL/RAMP3) receptors can be activated by CGRP but are relatively insensitive to CGRP(8-37). 5. This, along with other supporting data, suggests that the 'CGRP(2) receptor' that has been extensively reported in the literature may, in fact, be an amalgamation of contributions from a variety of CGRP-activated receptors. The use of appropriate combinations of agonists and antagonists, along with receptor expression studies, could allow such receptors to be separated.

Calcitonin gene-related peptide affects synaptic and membrane properties of bronchial parasympathetic neurons

Calcitonin gene-related peptide (CGRP) is located with substance P in nerve varicosities in close apposition to principal neurons in airway parasympathetic ganglia. Substance P has multiple effects on airway parasympathetic neurons but the role of CGRP is unknown. Using intracellular current clamp recording of ganglionic neurons, stimulation of vagal afferent nerves in the presence of neurokinin receptor antagonists evoked hyperpolarization of the membrane potential which was blocked by the CGRP-1 receptor antagonist, CGRP(8-37). Exogenous application of alpha-CGRP (0.001-0.1 microM) hyperpolarized the membrane potential, which was either blocked or reversed to depolarization in the presence of CGRP(8-37), whereas higher concentrations of alpha-CGRP (1.0-10.0 microM) caused depolarization. Action potential accommodation in phasic-type neurons decreased in the presence of alpha-CGRP (0.1-10 microM). The co-localization of substance P- and CGRP-immunoreactivity was observed in nerve varicosities within ganglia; prolonged exposure to capsaicin in vitro depleted substance P and CGRP immunostaining in nerve varicosities. These results demonstrate that CGRP has multiple effects on the excitability of airway parasympathetic neurons and may alter their activity, ultimately affecting parasympathetic tone in the lower airways.

Evolution of the CT/CGRP family: comparative study with new data from models of teleosts, the eel, and cephalopod molluscs, the cuttlefish and the nautilus

In mammals, alternative splicing of the calcitonin gene generates two distinct peptides: calcitonin (CT), synthesised in the thyroid C cells and involved in the regulation of calcium metabolism, and calcitonin gene-related peptide (CGRP), brain neuromediator synthesised in the peripheral and central nerves. CGRP is well represented and molecularly conserved during evolution whereas CT has not been detected in any of the invertebrates analysed so far. In order to better understand the evolution of this CT/CGRP peptide family we reviewed the major data concerning its evolution from the literature and our recent data obtained in models of teleosts and cephalopod molluscs. The presence of both CGRP-like molecules and its specific bindings sites in the central nervous system of eel, cuttlefish and nautilus, suggests that the brain neurotransmitter role of CGRP could represent an ancient role in metazoa, already present in cephalopods and conserved among vertebrates, as still observed in mammals. In contrast, the presence of CGRP specific binding sites, and not the peptide itself, in the gills suggests an endocrine role for CGRP, in cephalopods and teleosts, that may have been lost during the evolution of the tetrapod lineage. These data, and the absence of CT-like molecules that we observed in cephalopods, support the hypothesis that CGRP represents the ancestral molecule of the CT/CGRP family, appeared in metazoa before the vertebrate emergence. The distinction between CT and CGRP receptors appears to be an event posterior to the emergence of ecdysozoan and lophotrochozoan protostomes, probably in relation to the CT appearance. The evolution of the CT/CGRP peptide family is probably similar to the evolution of the CT/CGRP receptor family. In fact, the genic duplication that induced the appearance of the two separate molecules, CT and CGRP, may constitute an event close to that, which induced the appearance of the two specific receptors. These events remain to be further studied in order to better understand the peptide and receptor evolution of the CT/CGRP family.

Calcitonin receptor-like receptor and receptor activity modifying protein 1 in the rat dorsal horn: localization in glutamatergic presynaptic terminals containing opioids and adrenergic alpha2C receptors

Calcitonin gene-related peptide (CGRP) is abundant in the central terminals of primary afferents. However, the function of CGRP receptors in the spinal cord remains unclear. CGRP receptors are heterodimers of calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 1 (RAMP1). We studied the localization of CRLR and RAMP1 in the rat dorsal horn using well-characterized antibodies against them, which labeled numerous puncta in laminae I-II. In addition, RAMP1 was found in cell bodies, forming patches at the cell surface. The CRLR- and RAMP1-immunoreactive puncta were further characterized using double and triple labeling. Colocalization was quantified in confocal stacks using Imaris software. CRLR did not colocalize with primary afferent markers, indicating that these puncta were not primary afferent terminals. CRLR- and RAMP1-immunoreactive puncta contained synaptophysin and vesicular glutamate transporter-2 (VGLUT2), showing that they were glutamatergic presynaptic terminals. Electron microscopic immunohistochemistry confirmed that CRLR immunoreactivity was present in axonal boutons that were not in synaptic glomeruli. Using tyramide signal amplification for double labeling with the CRLR and RAMP1 antibodies, we found some clear instances of colocalization of CRLR with RAMP1 in puncta, but their overall colocalization was low. In particular, CRLR was absent from RAMP1-containing cells. Many of the puncta stained for CRLR and RAMP1 were labeled by anti-opioid and anti-enkephalin antibodies. CRLR and, to a lesser extent, RAMP1 also colocalized with adrenergic alpha(2C) receptors. Triple label studies demonstrated three-way colocalization of CRLR-VGLUT2-synaptophysin, CRLR-VGLUT2-opioids, and CRLR-opioids-alpha(2C) receptors. In conclusion, CRLR is located in glutamatergic presynaptic terminals in the dorsal horn that contain alpha(2C) adrenergic receptors and opioids. Some of these terminals contain RAMP1, which may form CGRP receptors with CRLR, but in others CRLR may form other receptors, possibly by dimerizing with RAMP2 or RAMP3. These findings suggest that CGRP or adrenomedullin receptors modulate opioid release in the dorsal horn.

In vitro effects of adrenomedullin and calcitonin gene related peptide on the release of serotonin and amino acids from rat dorsal spinal cord

Adrenomedullin (AM) and calcitonin gene-related peptide (CGRP) are structurally related, interact with each others receptors and show overlapping biological activities. Immunoreactivity (IR) and mRNAs along with binding sites for both CGRP and adrenomedullin have been shown in the rat spinal cord. CGRP mediates the transmission of nociceptive information at the spinal cord level and both peptides has shown to induces c-fos expression and accumulation of cAMP in spinal cells. In this study, HPLC methods were used to investigate the effects of AM and CGRP on the basal and K+-evoked release of serotonin, glutamate (Glu), aspartate (Asp), glycine (Gly) and gamma amino butyric acid (GABA) from the slices prepared from the rat spinal cord. Neither CGRP (10(-7) and 10(-6) M) nor AM (10(-7) and 10(-6) M) had significant effects on the basal release of serotonin and the amino acids tested in this study. However, CGRP produced statistically significant increases in the K+-evoked release of Asp and Glu, whereas AM failed to do so. Neither AM nor CGRP (10(-7) and 10(-6) M) showed any significant effects on the K+-evoked release of serotonin, GABA and Gly. Present data suggest that the stimulatory effects of CGRP on the release of Asp and Glu were exerted by distinct types of CGRP receptors.

The colocalization of CGRP receptor and AMPA receptor in the spinal dorsal horn neuron of rat: A morphological and electrophysiological study

Both the calcitonin gene-related peptide (CGRP) receptor and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor are involved in the transmission of sensory information from primary afferent to the spinal cord. The present study found that there was a colocalization of CGRP receptor and AMPA receptor in a single spinal dorsal horn neuron in rat determined by double immunofluorescence labeling image methods. Furthermore, our results showed that the evoked discharge frequency of the wide dynamic range (WDR) neuron, one type of the dorsal horn neurons, increased significantly after micro-iontophoretic delivery of CGRP or AMPA alone tested by extracellular recording, indicating a functional colocalization of CGRP receptor and AMPA receptor in a single spinal dorsal horn neuron. The results of the present study found a morphological and functional colocalization of the CGRP receptor and AMPA receptor in a single dorsal horn neuron that involved in the transmission and modulation of sensory information from primary afferent to the spinal cord in rats.

Calcitonin gene-related peptide analogues with aza and indolizidinone amino acid residues reveal conformational requirements for antagonist activity at the human calcitonin gene-related peptide 1 receptor

Calcitonin gene-related peptide antagonists have potential for the treatment and prevention of disease states such as non-insulin-dependent diabetes mellitus, migraine headache, pain, and inflammation. To gain insight into the spatial requirements for CGRP antagonism, three strategies were employed to restrict the conformation of the potent undecapeptide antagonist, [D31,P34,F35]CGRP27-37. First, aza-amino acid scanning was performed, and ten aza-peptide analogues were synthesized and examined for biological activity. Second, (3S,6S,9S)-2-oxo-3-amino-indolizidin-2-one amino acid (I2aa) and (2S,6S,8S)-9-oxo-8-amino-indolizidin-9-one amino acid (I9aa) both were introduced at positions 31-32, 32-33, 33-34, and 34-35, regions of the backbone expected to adopt turns. Finally, the conformation of the backbone and side-chain of the C-terminal residue, Phe35-Ala36-Phe37-NH2, was explored employing (2S,4R,6R,8S)-9-oxo-8-amino-4-phenyl-indolizidin-9-one amino acid (4-Ph-I9aa) as a constrained phenylalanine mimic. The structure-activity relationships exhibited by our 26 analogues illustrate conformational requirements important for designing CGRP antagonists and highlight the importance of beta-turns centered at Gly33-Pro34 for potency.

Post-endocytic sorting of calcitonin receptor-like receptor and receptor activity-modifying protein 1

Calcitonin receptor-like receptor (CLR) and the receptor activity-modifying protein 1 (RAMP1) comprise a receptor for calcitonin gene-related peptide (CGRP). Although CGRP induces endocytosis of CLR/RAMP1, little is known about post-endocytic sorting of these proteins. We observed that the duration of stimulation with CGRP markedly affected post-endocytic sorting of CLR/RAMP1. In HEK and SK-N-MC cells, transient stimulation (10(-7) M CGRP, 1 h), induced CLR/RAMP1 recycling with similar kinetics (2-6 h), demonstrated by labeling receptors in living cells with antibodies to extracellular epitopes. Recycling of CLR/RAMP1 correlated with resensitization of CGRP-induced increases in [Ca(2+)](i). Cycloheximide did not affect resensitization, but bafilomycin A(1), an inhibitor of vacuolar H(+)-ATPases, abolished resensitization. Recycling CLR and RAMP1 were detected in endosomes containing Rab4a and Rab11a, and expression of GTPase-defective Rab4aS22N and Rab11aS25N inhibited resensitization. After sustained stimulation (10(-7) M CGRP, >2 h), CLR/RAMP1 trafficked to lysosomes. RAMP1 was degraded approximately 4-fold more rapidly than CLR (RAMP1, 45% degradation, 5 h; CLR, 54% degradation, 16 h), determined by Western blotting. Inhibitors of lysosomal, but not proteasomal, proteases prevented degradation. Sustained stimulation did not induce detectable mono- or polyubiquitination of CLR or RAMP1, determined by immunoprecipitation and Western blotting. Moreover, a RAMP1 mutant lacking the only intracellular lysine (RAMP1K142R) internalized and was degraded normally. Thus, after transient stimulation with CGRP, CLR and RAMP1 traffic from endosomes to the plasma membrane, which mediates resensitization. After sustained stimulation, CLR and RAMP1 traffic from endosomes to lysosomes by ubiquitin-independent mechanisms, where they are degraded at different rates.

Potential role of female sex hormones in the pathophysiology of migraine

Clinical evidence indicates that female sex steroids may contribute to the high prevalence of migraine in women, as well as changes in the frequency or severity of migraine attacks that are in tandem with various reproductive milestones in women's life. While female sex steroids do not seem to be involved in the pathogenesis of migraine per se, they may modulate several mediators and/or receptor systems via both genomic and non-genomic mechanisms; these actions may be perpetuated at the central nervous system, as well as at the peripheral (neuro)vascular level. For example, female sex steroids have been shown to enhance: (i) neuronal excitability by elevating Ca(2+) and decreasing Mg(2+) concentrations, an action that may occur with other mechanisms triggering migraine; (ii) the synthesis and release of nitric oxide (NO) and neuropeptides, such as calcitonin gene-related peptide CGRP, a mechanism that reinforces vasodilatation and activates trigeminal sensory afferents with a subsequent stimulation of pain centres; and (iii) the function of receptors mediating vasodilatation, while the responses of receptors inducing vasoconstriction are attenuated. The serotonergic, adrenergic and gamma-aminobutyric acid (GABA)-ergic systems are also modulated by sex steroids, albeit to a varying degree and with potentially contrasting effects on migraine outcome. Taken together, female sex steroids seem to be involved in an array of components implicated in migraine pathogenesis. Future studies will further delineate the extent and the clinical relevance of each of these mechanisms, and will thus expand the knowledge on the femininity of migraine.

Neuropeptide and kinin antagonists

Neuropeptides and kinins are important messengers in the nervous system and--on the basis of their anatomical localisation and the effects produced when the substances themselves are administered, to animals or to human subjects-a significant number of them have been suggested to have a role in pain and inflammation. Experiments in gene deletion (knock-out or null mutant) mice and parallel experiments with pharmacological receptor antagonists in a variety of species have strengthened the evidence that a number of peptides, notably substance P and calcitonin gene-related peptide (CGRP), and the kinins have a pathophysiological role in nociception. Clinical studies with non-peptide pharmacological antagonists are now in progress to determine if blocking the action of these peptides might have utility in the treatment of pain.

Retrograde neuron tracing with microspheres reveals projection of CGRP-immunolabeled vestibular afferent neurons to the vestibular efferent nucleus in the brainstem of rats

OBJECTIVE

A new retrograde neuron-tracing technique with microspheres was used to explore the possible innervation of calcitonin gene-related peptide (CGRP)-immunolabeled vestibular afferent neurons in the vestibular efferent immunolabeled nucleus in the brainstem.

METHODS

0.1 microl of 5% microfluorospheres was injected into the area of the vestibular efferent nucleus, which is located lateral to the genu of the facial nerve. CGRP immunohistochemistry was processed in serial sections of the brainstem at the facial nerve genu level. Double-labeled neurons with both CGRP immunoreactivity and microfluorospheres were examined with fluorescence and confocal laser microscopy.

RESULTS

Three types of labeled neurons were observed: (1) neurons only retrogradely microfluorosphere-labeled that were mainly located in the medial vestibular nucleus, lateral vestibular nucleus, superior vestibular nucleus and parvicellular reticular nucleus on the ipsilateral side of the injection; (2) neurons that were both immunolabeled with CGRP and also retrogradedly labeled with microfluorospheres, indicating that they are CGRP cells projecting to the area of vestibular efferent nucleus, these cells were mainly distributed in the superior vestibular nucleus and dorsal vestibular nucleus, and (3) cells only immunolabeled for CGRP that were scattered extensively in the brainstem.

CONCLUSION

The presented methodical contribution demonstrates the suitability of fluorescein-labeled microspheres for retrograde neuronal tracing. The vestibular nuclei contain numerous afferent neurons that send projections to the vestibular efferent nucleus, some of which are CGRP cells. This afferent innervation provides morphological evidence that the vestibular efferent neurons receive input from the vestibular afferent neurons including CGRP cells. These vestibular primary CGRP afferent neurons may have an influence on vestibular efferent neurons. CGRP acts as an important co-transmitter or modulator in the afferent-mediated activity of vestibular efferent neurons, which in turn affect afferents in the vestibular end organs.

Two alphaherpesvirus latency-associated gene products influence calcitonin gene-related peptide levels in rat trigeminal neurons

Herpes simplex virus type-1 (HSV-1) initially infects mucoepithelial tissues of the eye and the orofacial region. Subsequently, the virus is retrogradely transported through the axons of the trigeminal sensory neurons. HSV-1 establishes a life-long latent infection in these neurons, during which the transcription of the viral genome is silent, except for the sequences encoding the latency-associated transcript (LAT). To determine if HSV-1 latency might affect calcitonin gene-related peptide (CGRP) expression in trigeminal sensory neurons, we transfected primary neuronal cultures of trigeminal ganglia from rat embryos with plasmids expressing LAT. In the presence of Bone Morphogenetic Protein-7 (BMP7), CGRP was expressed in 49% of sensory neurons. However, this percentage was reduced to 19% in neurons transfected with LAT expressing plasmids. We also found that transfection of the IE63 gene of varicella-zoster virus (VZV) reduced the percentage of trigeminal neurons containing CGRP. However, the observed effect of IE63 in contrast to that of LAT was completely reversed by treatment of cultures with MgCl2, which indicates that the effect of IE63 was due to increased release of CGRP from trigeminal neurons. We provide here the first evidence that HSV-1 LAT decreases the level of CGRP in trigeminal neurons. These effects may be important for reducing the neuroinflammatory response, thus protecting host neuronal cells during HSV-1 latency in trigeminal neurons. In contrast, increased release of CGRP in the presence of IE63 protein may contribute to the neuralgias associated with VZV infection.

CGRP stimulates gill carbonic anhydrase activity in molluscs via a common CT/CGRP receptor

The physiological significance of calcitonin gene-related peptide (CGRP) during biomineralization was investigated by assessing the effect of human CGRP on the carbonic anhydrase activity in gill membranes of the pearl oyster, Pinctada margaritifera. Salmon CT and human CGRP were able to induce a 150% increase of the basal activity. No additive effect was observed suggesting that both activities are mediated by the same receptor. The CGRP-stimulated effect was specific as demonstrated by the inhibition produced by the CGRP antagonist, hCGRP8-37. So, CGRP by its specific action on gill carbonic anhydrase controls the calcification process, an ancient role both in invertebrates and non-mammalian vertebrates.

A role for adrenomedullin as a pain-related peptide in the rat

Adrenomedullin (AM) belongs to the calcitonin gene-related peptide (CGRP) family and is a well known potent vasodilator. We show here that AM is a powerful pain-inducing neuropeptide. AM-like immunoreactivity is widely distributed in both CGRP-containing and lectin IB4-binding nociceptors in dorsal root ganglion and axon terminals in the superficial dorsal horn of the rat spinal cord. Specific binding sites for the radioligand, [(125)I]AM13-52 as well as immunoreactivity for receptor markers such as the calcitonin receptor-like receptor and three receptor-activity-modifying proteins are localized in the superficial dorsal horn, demonstrating the existence of AM/CGRP receptors in this region. Intrathecal injection of rat AM1-50, dose- and time-dependently, induced long-lasting heat hyperalgesia and increased the phosphorylation of Akt and GSK3beta in the dorsal horn. Pre- and posttreatments with the AM receptor antagonist AM22-52 and PI3 kinase inhibitors (LY294002 and Wortmannin) significantly blocked or reversed AM-induced heat hyperalgesia. Pre- and posttreatments with AM22-52 and Wortmannin also significantly blocked or reversed intraplantar capsaicin-induced heat hyperalgesia. Taken together, our results demonstrate that AM acts as a pain-inducing peptide in the dorsal horn. By activating specific receptors (likely AM2) and the PI3K/Akt/GSK3beta signaling pathway, AM could play a significant role in long-lasting heat hypersensitivity and inflammatory heat hyperalgesia.

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.

Donitriptan, but not sumatriptan, inhibits capsaicin-induced canine external carotid vasodilatation via 5-HT1B rather than 5-HT1D receptors

BACKGROUND AND PURPOSE

It has been suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene-related peptide (CGRP), resulting in cranial vasodilatation and central nociception; hence, trigeminal inhibition may prevent this vasodilatation and abort migraine headache. This study investigated the effects of the agonists sumatriptan (5-HT(1B/1D) water-soluble), donitriptan (5-HT(1B/1D) lipid-soluble), PNU-142633 (5-HT(1D) water-soluble) and PNU-109291 (5-HT(1D) lipid-soluble) on vasodilator responses to capsaicin, alpha-CGRP and acetylcholine in dog external carotid artery.

EXPERIMENTAL APPROACH

59 vagosympathectomized dogs were anaesthetized with sodium pentobarbitone. Blood pressure and heart rate were recorded with a pressure transducer, connected to a cannula inserted into a femoral artery. A precalibrated flow probe was placed around the common carotid artery, with ligation of the internal carotid and occipital branches, and connected to an ultrasonic flowmeter. The thyroid artery was cannulated for infusion of agonists.

KEY RESULTS

Intracarotid infusions of capsaicin, alpha-CGRP and acetylcholine dose-dependently increased blood flow through the carotid artery. These responses remained unaffected after intravenous (i.v.) infusions of sumatriptan, PNU-142633, PNU-109291 or physiological saline; in contrast, donitriptan significantly attenuated the vasodilator responses to capsaicin, but not those to alpha-CGRP or acetylcholine. Only sumatriptan and donitriptan dose-dependently decreased the carotid blood flow. Interestingly, i.v. administration of the antagonist, SB224289 (5-HT(1B)), but not of BRL15572 (5-HT(1D)), abolished the inhibition by donitriptan.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that the inhibition produced by donitriptan of capsaicin-induced external carotid vasodilatation is mainly mediated by 5-HT(1B), rather than 5-HT(1D), receptors, probably by a central mechanism.

Nitric oxide regulation of calcitonin gene-related peptide gene expression in rat trigeminal ganglia neurons

Calcitonin gene-related peptide (CGRP) and nitric oxide are involved in the underlying pathophysiology of migraine and other diseases involving neurogenic inflammation. We have tested the hypothesis that nitric oxide might trigger signaling mechanisms within the trigeminal ganglia neurons that would coordinately stimulate CGRP synthesis and release. Treatment of primary trigeminal ganglia cultures with nitric oxide donors caused a greater than four-fold increase in CGRP release compared with unstimulated cultures. Similarly, CGRP promoter activity was also stimulated by nitric oxide donors and overexpression of inducible nitric oxide synthase (iNOS). Cotreatment with the antimigraine drug sumatriptan greatly repressed nitric oxide stimulation of CGRP promoter activity and secretion. Somewhat surprisingly, the mechanisms of nitric oxide stimulation of CGRP secretion did not require cGMP or PI3-kinase signaling pathways, but rather, nitric oxide action required extracellular calcium and likely involves T-type calcium channels. Furthermore, nitric oxide was shown to increase expression of the active forms of the mitogen-activated protein kinases Jun amino-terminal kinase and p38 but not extracellular signal-related kinase in trigeminal neurons. In summary, our results provide new insight into the cellular mechanisms by which nitric oxide induces CGRP synthesis and secretion from trigeminal neurons.