CGRP (rat)

Stimulation of rat cranial dura mater with potassium chloride causes CGRP release into the cerebrospinal fluid and increases medullary blood flow.[Pubmed:28202186]

Neuropeptides. 2017 Aug;64:61-68.

Primary headaches may be accompanied by increased intracranial blood flow induced by the release of the potent vasodilator calcitonin gene-related peptide (CGRP) from activated meningeal afferents. We aimed to record meningeal and medullary blood flow simultaneously and to localize the sites of CGRP release in rodent preparations in vivo and ex vivo. Blood flow in the exposed rat parietal dura mater and the medulla oblongata was recorded by laser Doppler flowmetry, while the dura was stimulated by topical application of 60mM potassium chloride (KCl). Samples of jugular venous plasma and cerebrospinal fluid (CSF) collected from the cisterna magna were analysed for CGRP concentrations using an enzyme immunoassay. In a hemisected rat skull preparation lined with dura mater the CGRP releasing effect of KCl superfusion was examined. Superfusion of the dura mater with KCl decreased meningeal blood flow unless alpha-adrenoceptors were blocked by phentolamine, whereas the medullary blood flow was increased. The same treatment caused increased CGRP concentrations in jugular plasma and CSF and induced significant CGRP release in the hemisected rat skull preparation. Anaesthesia of the trigeminal ganglion by injection of lidocaine reduced increases in medullary blood flow and CGRP concentration in the CSF upon meningeal KCl application. CGRP release evoked by depolarisation of meningeal afferents is accompanied by increased blood flow in the medulla oblongata but not the dura mater. This discrepancy can be explained by the smooth muscle depolarising effect of KCl and the activation of sympathetic vasoconstrictor mechanisms. The medullary blood flow response is most likely mediated by CGRP released from activated central terminals of trigeminal afferents. Increased blood supply of the medulla oblongata and CGRP release into the CSF may also occur in headaches accompanying vigorous activation of meningeal afferents.

Development of CGRP-dependent pain and headache related behaviours in a rat model of concussion: Implications for mechanisms of post-traumatic headache.[Pubmed:27899434]

Cephalalgia. 2018 Feb;38(2):246-258.

Background and objective Posttraumatic headache (PTH) is one of the most common, debilitating and difficult symptoms to manage after a mild traumatic brain injury, or concussion. However, the mechanisms underlying PTH remain elusive, in part due to the lack of a clinically relevant animal model. Here, we characterized for the first time, headache and pain-related behaviours in a rat model of concussion evoked by a mild closed head injury (mCHI) - the major type of military and civilian related trauma associated with PTH - and tested responses to current and novel headache therapies. Methods Concussion was induced in adult male rats using a weight-drop device. Characterization of headache and pain related behaviours included assessment of cutaneous tactile pain sensitivity, using von Frey monofilaments, and ongoing pain using the conditioned place preference or aversion (CPP/CPA) paradigms. Sensitivity to headache/migraine triggers was tested by exposing rats to low-dose glyceryl trinitrate (GTN). Treatments included acute systemic administration of sumatriptan and chronic systemic administration of a mouse anti-CGRP monoclonal antibody. Results Concussed rats developed cephalic tactile pain hypersensitivity that was resolved by two weeks post-injury and was ameliorated by treatment with sumatriptan or anti-CGRP monoclonal antibody. Sumatriptan also produced CPP seven days post mCHI, but not in sham animals. Following the resolution of the concussion-evoked cephalic hypersensitivity, administration of GTN produced a renewed and pronounced cephalic pain hypersensitivity that was inhibited by sumatriptan or anti-CGRP antibody treatment as well as a CGRP-dependent CPA. GTN had no effect in sham animals. Conclusions Concussion leads to the development of headache and pain-related behaviours, in particular sustained enhanced responses to GTN, that are mediated through a CGRP-dependent mechanism. Treatment with anti-CGRP antibodies may be a useful approach to treat PTH.

Effect of cannabinoids on CGRP release in the isolated rat lumbar spinal cord.[Pubmed:26762784]

Neurosci Lett. 2016 Feb 12;614:39-42.

Cannabinoids produce analgesia through a variety of mechanisms. It has been proposed that one mechanism is by modulating the release of CGRP in the spinal cord pain pathways. Previous studies have reported that cannabinoids, particularly CB2 receptor agonists, can modulate CGRP release in the isolated rat spinal cord. In our experiments, the TRPV1 agonist capsaicin evoked CGRP release and this was supressed by the TRPV1 antagonist capsazepine and by the opioid receptor agonist DAMGO. However, none of the cannabinoid receptor agonists that we tested were able to modulate evoked CGRP release; including WIN 55,212-2, methanandamide, and GW405833. These results question the role of spinal cord cannabinoid receptors in the regulation of CGRP signaling.

Surgical intestinal manipulation increases gene expression of TrkA, CGRP, and PAR-2 IN dorsal root ganglia in the rat.[Pubmed:26909771]

Neurogastroenterol Motil. 2016 Jun;28(6):816-26.

BACKGROUND: Surgical handling of the bowel evokes degranulation of peritoneal mast cells (PMC). Nonetheless, role of PMCs in postoperative ileus (POI) is somewhat controversial. We aimed to investigate if intestinal manipulation elicits changes in afferent mediators related to MC activation and alteration of gastrointestinal (GI) motility. METHODS: Postoperative ileus was induced by intestinal manipulation in Sprague-Dawley rats. Additionally, compound 48/80 (C48/80) and ketotifen were used to modulate MC activity. Rat mast cell protease 6 (RMCP-6, ELISA) release was determined in peritoneal lavage 20 min after intestinal manipulation. At 24 h, GI transit was determined. Gene expression of calcitonin gene-related peptide (CGRP), protease-activated receptor-2 (PAR-2), nerve growth factor (NGF), and TrkA receptor was determined (PCR) in dorsal root ganglia (DRG). Ileal wall inflammation was assessed by myeloperoxidase (MPO) activity, interleukin-6 expression (IL-6). KEY RESULTS: Intestinal manipulation and exposure to C48/80-induced degranulation of PMCs delayed GI transit and up-regulated IL-6 and MPO activity. Intestinal manipulation, but not C48/80, up-regulated CGRP, PAR-2, and NGF/TrkA in DRGs. Ketotifen only improved gastric emptying and fecal output. Up-regulation of CGRP and TrkA expression in DRG was not prevented by ketotifen. CONCLUSIONS & INFERENCES: Postoperative ileus is accompanied by activation of CGRP, NGF-TrkA, and PAR-2 in DRGs. Our results suggest that these mediators could be a target in further POI studies in order to find new therapeutic targets for this medical condition.

Calcitonin gene-related peptide as a GH secretagogue in human and rat pituitary somatotrophs.[Pubmed:9757038]

Brain Res. 1998 Oct 5;807(1-2):203-7.

To elucidate the role of calcitonin gene-related peptide (CGRP) in regulating pituitary function, we investigated the effects of CGRP and the related peptide adrenomedullin (AdM) on the secretion of growth hormone (GH) in vitro from human pituitary adenoma cells, rat pituitary tumor (GH3) cells, and normal rat pituitary cells. In 3 of 5 human somatotroph adenomas, GH secretion was stimulated by CGRP (1-100 nM). In one case of somatotroph adenoma, GH release was observed following the addition of 10 nM GHRH and 10 nM CGRP. The addition of CGRP or AdM (1 pM-10 nM) evoked GH secretion from GH3 cells with a bell-shaped distribution curve. CGRP (100 pM) caused the maximum increase of GH secretion (172+/-14 (mean+/-S.D.)% of control). The addition of CGRP8-37, an antagonist of CGRP type 1 receptors, inhibited the stimulatory effect of AdM but did not inhibit the effect of CGRP. The addition of CGRP and AdM evoked moderate GH secretion from normal rat pituitary cells. These results suggested that CGRP is a new GH secretagogue in human and rat pituitary tumor cells.

Calcitonin gene-related peptide potentiates nicotinic acetylcholine receptor-operated slow Ca2+ mobilization at mouse muscle endplates.[Pubmed:9786499]

Br J Pharmacol. 1998 Sep;125(2):277-82.

1. The involvement of calcitonin gene-related peptide (CGRP) in the non-contractile slow Ca2+ mobilization induced by prolonged nicotinic stimulation was investigated by measurement of [Ca2+], levels in mouse single muscle cells (flexor digitorum brevis; FDB) loaded with a Ca2+ indicator fluo-3 using confocal laser scanning microscopy. 2. CGRP (3-30 nM) potentiated acetylcholine (ACh, 1 microM)-elicited slow Ca2+ mobilization in a concentration-dependent manner. 3. The potentiation by CGRP of the slow Ca2+ component was greatly depressed by a competitive nicotinic antagonist (+)-tubocurarine (5 microM). The Ca2+ channel blocker nitrendipine (1 microM) affected neither ACh responses nor the CGRP potentiation. 4. The slow Ca2+ component was completely abolished by reducing [Ca2+]0 from 2.5 to 0.25 mM whereas the fast component was not affected. The CGRP-induced potentiation of slow Ca2+ signal was also depressed by decreasing [Ca2+]0. 5. Isoproterenol (30 microM) and 8-bromo-adenosine 3',5'-cyclic monophosphate (1 mM) potentiated the ACh-elicited slow Ca2+ response. The potentiation by CGRP of the slow Ca2+ component was completely abolished by a protein kinase-A inhibitor H-89 (1 microM). 6. These findings indicate that CGRP potentiates the nicotinic ACh receptor-operated slow Ca2+ signal via the activation of protein kinase-A system at the skeletal muscle endplates.

Pharmacology of receptors for calcitonin gene-related peptide and amylin.[Pubmed:8578616]

Trends Pharmacol Sci. 1995 Dec;16(12):424-8.

Calcitonin gene-related peptide (CGRP), a widespread neuropeptide with multiple actions, has substantial homology with amylin, a peptide implicated in insulin-resistant diabetes, and adrenomedullin, a recently discovered potent vasodilator. There is controversy over the existence of CGRP receptor subtypes, and whether independent receptors exist for amylin and adrenomedullin. In this article, the current status of CGRP receptor classification is reviewed by David Poyner, taking particular account of species differences, and evidence is presented supporting the existence of multiple receptors for CGRP, as well as independent binding sites for amylin.

Calcitonin gene-related peptide is a potent vasodilator.[Pubmed:3917554]

Nature. 1985 Jan 3-9;313(5997):54-6.

A novel peptide, calcitonin gene-related peptide (CGRP), has been predicted to result from alternative processing of the primary RNA transcript of the calcitonin gene in the rat. Several lines of evidence suggest that CGRP is a transmitter in the central and peripheral nervous system. Human CGRP has been isolated and characterized, and shown to have potent effects on the heart. The observations presented here indicate that human and rat CGRP also have potent effects on blood vessels. Intradermal injection of CGRP in femtomole doses induces microvascular dilatation resulting in increased blood flow, which we have detected in the rabbit by using a 133Xe clearance technique. In human skin, CGRP induces persistent local reddening. Microscopic observation of the hamster cheek pouch in vivo revealed that topical application of CGRP induces dilatation of arterioles. Furthermore, CGRP relaxes strips of rat aorta in vitro by an endothelial cell-dependent mechanism. Therefore, we suggest that local extravascular release of CGRP may be involved in the physiological control of blood flow and that circulating CGRP may contribute to hyperaemia in certain pathological conditions.

Isolation and characterization of human calcitonin gene-related peptide.[Pubmed:6609312]

Nature. 1984 Apr 19-25;308(5961):746-8.

The rat calcitonin gene has recently been shown to encode a novel peptide (rat calcitonin gene-related peptide, rCGRP) thought to be produced in nervous tissue after tissue-specific RNA processing. This peptide has so far been identified only in rat tissue, by immunocytochemistry and immunoassay. We now report the isolation of a related (89% homology) peptide from human tissue (hCGRP) which we have sequenced using a novel mass spectrometric approach, fast atom bombardment (FAB) mapping. The human peptide differs significantly from the predicted rCGRP structure in four positions in the amino acid sequence (three effecting charge changes), and the presence of a disulphide bridge and an amide, surmised in the rat work, is proven in the hCGRP molecule. hCGRP was present in plasma from 10 patients with medullary thyroid carcinoma (MTC) and in 6 MTC tumours removed at surgery, suggesting the tissue distribution may differ from that in the rat where the peptide is reported to be absent from thyroid tissue. hCGRP is shown to have biological activity and it is possible that its presence in MTC plasma may be responsible for some of the symptoms in this disease.