Calcitonin gene-related peptide coexists with substance P in capsaicin sensitive neurons and sensory ganglia of the rat

Immunohistochemical and radioimmunoassay studies revealed that both CGRP- and SP-like immunoreactivity in the caudal spinal trigeminal nucleus and tract, the substantia gelatinosa and the dorsal cervical spinal cord as well as in cell bodies of the trigeminal ganglion and the spinal dorsal root ganglion is markedly depleted by capsaicin which is known to cause degeneration of a certain number of primary sensory neurons. Higher brain areas and the ventral spinal cord were not affected by capsaicin treatment. Furthermore CGRP and substance P-like immunoreactivity were shown to be colocalized in the above areas and to coexist in cell bodies of the trigeminal ganglion and the spinal dorsal root ganglia. It is suggested that CGRP, like substance P, may have a neuromodulatory role on nociception and peripheral cardiovascular reflexes.     

Calcitonin gene-related peptide and substance P in the pharynx and lung of the bullfrog,Rana catesbeiana

Indirect double immunofluorescence labelling in the pharynx and lung of the bullfrog, Rana catesbeiana, demonstrated the occurrence, distribution, and coexistence of two neuropeptides. In the pharynx, immunoreactive calcitonin gene-related peptide (CGRP) and substance P (SP) were localized in nerve fibers distributed within and just beneath the ciliated epithelium. In the lung, CGRP and SP were localized in nerve fibers in five principal locations: 1) within the smooth muscle layer in the interfaveolar septa; 2) in the luminal thickened edges of the septa; 3) around the pulmonary vasculature; 4) within, and 5) under the ciliated epithelium. Within the smooth muscle layer in the septa, luminal thickened septa, and around blood vessels, almost all fibers showed coexistence of CGRP and SP. Within and just beneath the ciliated epithelium in the thickened septa, all fibers showed coexistence of CGRP and SP. No immunoreactivity for vasoactive intestinal polypeptide, neuropeptide Y, galanin, somatostatin, FMRFamide, and leucine-and methionine-enkephalins was detected in the nerve fibers within the larynx and the lung. Together with our previous data, the present findings suggest that peptidergic mechanisms are involved in the regulation of amphibian respiratory systems throughout their life.     

Calcitonin gene-related peptide is metabolized by an endopeptidase hydrolyzing substance P

Calcitonin gene-related peptide (CGRP) is cleaved by an endopeptidase, also known to hydrolyze substance P (SP). The enzyme which was isolated from human cerebrospinal fluid, converted rCGRP into two products, clearly separable on HPLC. Amino acid analysis showed cleavage to occur at Leu16-Ser17. The carboxy-terminal fragment, rCGRP-(17-37), was weakly active in inhibiting 125I-rCGRP binding to a rat medulla oblongata membrane preparation, but it showed no binding to spinal cord membranes. The N-terminal fragment, rCGRP-(1-16), had very low or no affinity. Autoradiography with 125I-rCGRP showed distinct labelling of rat dorsal spinal cord, while there was no consistent pattern with 125I-rCGRP-(1-16). In the isolated guinea pig ileum preparation, the two fragments showed no CGRP-like activity. The ability of CGRP to interfere with SP degradation is offered as the explanation why CGRP has been reported to potentiate several biologic actions of SP.     

Calcitonin gene-related peptide (CGRP) in capsaicin-sensitive substance P-immunoreactive sensory neurons in animals and man: distribution and release by capsaicin

The presence of calcitonin-gene related peptide (CGRP)-like immunoreactivity (-LI) in sensory neurons was established by immunohistochemistry and radioimmunoassay (RIA) in combination with high performance liquid chromatography (HPLC). CGRP-immunoreactive (-IR) nerve fibres were present in many peripheral organs including heart, ureter, uterus and gall bladder of guinea-pig and man. The distribution of CGRP-IR nerves in the dorsal horn of the spinal cord, of positive cell bodies in thoracic spinal and nodose ganglia and nerves in peripheral organs was closely related to that of substance P-LI. Double staining experiments revealed that in most cases peripheral CGRP-IR nerve terminals also contained SP-LI. However, different localization of SP- and CGRP-IR neurons was observed in the nucleus of the solitary tract as well as in the ventral horn of the spinal cord. In the heart, CGRP-IR nerves were associated with myocardial cells (mainly atria), coronary vessels, local parasympathetic ganglia as well as with the epi- and endocardia. Three to 4-fold higher levels of native CGRP-LI were observed in the atria than in the ventricles of the heart. HPLC analysis revealed that the major peak of CGRP-LI in the heart of rat and man had the same retention times as the synthetic equivalents. Systemic capsaicin pretreatment and adult guinea-pigs caused a loss of CGRP-IR terminals in the dorsal horn of the spinal cord as well as in peripheral organs including the heart. After capsaicin treatment, the content of CGRP-IR was reduced by 70% in the heart and by 60% in the dorsal part of the spinal cord. In superfusion experiments with slices from the rat spinal cord, a release of CGRP-LI was induced by 60 mM K+ and 3 microM capsaicin in a calcium-dependent manner.     

Calcitonin gene-related peptide (CGRP): perivascular distribution and vasodilatory effects

The distribution of perivascular nerve fibers displaying calcitonin gene-related peptide (CGRP) immunoreactivity and the effect of CGRP on vascular smooth muscle were studied in the guinea-pig. Perivascular CGRP fibers were seen in all vascular beds. Generally, they were more numerous around arteries than veins. Small arteries in the respiratory tract, gastrointestinal tract and genitourinary tract had numerous CGRP fibers. The gastroepiploic artery in particular received a rich supply of such fibers. Coronary blood vessels had a moderate supply of CGRP fibers. In the heart, a moderate number of CGRP fibers was seen running close to myocardial fibers. The atria had a richer supply than the ventricles. Numerous CGRP immunoreactive nerve cell bodies and nerve fibers were seen in sensory (trigeminal, jugular and spinal dorsal root) ganglia. Sequential or double immunostaining with antibodies against substance P and CGRP suggested co-existence of the two peptides in nerve cell bodies in the ganglia and in perivascular fibers. In agreement with previous findings CGRP turned out to be a strong vasodilator in vitro as tested on several blood vessels (e.g. basilar, gastroepiploic and mesenteric arteries). Conceivably, perivascular CGRP/SP fibers have a dual role as regulator of local blood flow and as carrier of sensory information.     

Calcitonin gene-related peptide in hamster lung and its coexistence with serotonin: a chemical and immunocytochemical study

The mammalian lung may have an important endocrine function besides being involved in gas exchange mechanisms. A number of peptide hormones have been localized to neurons and endocrine cells in the lung where they may contribute to the regulation of local pulmonary functions. We have investigated the presence of calcitonin gene-related peptide (CGRP), in the hamster lung by radioimmunoassay and by immunocytochemistry. Measurable quantities of CGRP were detected in lung tissue. Females had higher lung tissue levels of CGRP-like immunoreactivity (IR) than males. This was not reflected in an observable increase in the intensity or distribution of CGRP-like reactivity with immunocytochemistry. Distinct CGRP-like IR was recorded in clustered (NEB) and solitary (NEC) neuroendocrine cells in neonates, weanlings and adults, including all airways from trachea (NEC only) to bronchi, bronchioles, and alveolar ducts to the level of alveoli (NEC and NEB). In adult hamsters, there seemed to be fewer immunoreactive cells, although intensity was unchanged. In addition some NEB contained serotonin-like IR, and colocalization of the peptide and the amine was noted within some cells. Intra-epithelial beaded nerve fibers, subepithelial fibers, and large-caliber nerves in the hilus region and tracheal wall were also CGRP-IR, and immunoreactive nerves were occasionally found in close association with NEB at the basal pole. Positive nerve fibers were not observed in vessels within the lung, and were sparse in the adventitia of tracheal arteries.     

Calcitonin gene-related peptide and substance P contribute to reduced blood pressure in sympathectomized rats

CGRP and substance P (SP) are produced in dorsal root ganglia (DRG) sensory neurons and modulate vascular tone. Sympathetic and sensory nerves compete for NGF, a potent stimulator of CGRP and SP, and it has been suggested that sympathetic hyperinnervation in spontaneously hypertensive rats may reduce the availability of NGF to sensory nerves, thus reducing CGRP and SP. The purpose of this study was to determine whether destruction of peripheral sympathetic nerves in normal rats would increase the availability of NGF for sensory neurons and enhance expression of CGRP and SP. Sympathectomy was produced in rats by guanethidine sulfate administration. Control rats received saline. Sympathectomized rats displayed reductions in blood pressure (BP) and atria norepinephrine levels, whereas NGF levels in the DRG, spleen, and ventricles were increased. Sympathectomy also enhanced CGRP and SP mRNA and peptide content in DRG. Administration of CGRP and SP receptor antagonists increased the BP in sympathectomized rats but not in the controls. Thus sympathectomy enhances sensory neuron CGRP and SP expression that contributes to the BP reduction.     

Calcitonin gene-related peptide and capsaicin inhibit the circular muscle of the guinea-pig ileum

Calcitonin gene-related peptide (CGRP) is known to excite, through the release of acetylcholine, the circular muscle (CM) of the guinea-pig ileum in vitro. In the present experiments, the effect of rat CGRP was investigated on the CM of tetrodotoxin-treated, spontaneously active ileum preparations. CGRP (1-10 nM) caused concentration-dependent inhibition of both the amplitude and frequency of spontaneous CM contractions. Capsaicin (a sensory stimulant known to release CGRP from primary afferents) also inhibited CM activity. The effect of 1 microM capsaicin underwent rapid desensitization, indicating specific action on afferent structures, whereas a high concentration of the drug (33 microM) inhibited CM activity most probably on the smooth muscle itself.     

Calcitonin gene-related peptide immunoreactivity in the biliary pathway and liver of the guinea-pig: distribution and colocalization with substance P

Summary Calcitonin gene-related peptide immunoreactivity was localized immunohistochemically in nerve fibers innervating the biliary pathway and liver of the guinea-pig. Immunoreactive fibers are present in all layers of the gallbladder and biliary tract and are particularly numerous around blood vessels. In the liver, immunoreactive processes are usually restricted to the interlobular space and porta hepatis, and only a few, very thin, beaded processes were observed in the hepatic parenchyma. A rich innervation is also associated with the vena portae. Positive ganglion cell bodies were not visualized within the ganglionated plexus of the biliary system, whereas they were found in the myenteric and submucosal plexus in the cranial portion of the duodenum corresponding to the sphincter of Oddi. The vast majority, if not all, of calcitonin gene-related peptide-immunoreactive fibers contain substance P immunoreactivity; however, there are some substance P-containing fibers lacking calcitonin gene-related peptide immunoreactivity. The lack of co-occurrence of calcitonin gene-related peptide and substance P immunoreactivities in intrinsic ganglion cells suggests that these two peptides are coexpressed in the extrinsic component of the innervation of the hepatobiliary system.     

Osteotropic effects by the neuropeptides calcitonin gene-related peptide, substance P and vasoactive intestinal peptide

Immunohistochemical phenotypic characterization of skeletal nerve fibers has demonstrated the expression of a restricted number of neuropeptides, including calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP). According to the neuro-osteological hypothesis, such neuropeptides can be released and exert paracrine biological effects on bone cells present close to the nerve endings expressing these signaling molecules. The existence of such interplay is most convincingly shown by the hypothalamic control of bone formation, in the case of leptin stimulation of hypothalamic nuclei mediated by the sympathetic nervous system and inhibitory beta-adrenergic receptors on osteoblasts. In addition to these receptors, osteoblasts and osteoclasts express functional receptors for CGRP, SP and VIP, which can regulate both bone formation and bone resorption. The evidence for these observations is summarized in the present paper.     

Calcitonin gene-related peptide in the eye: release by sensory nerve stimulation and effects associated with neurogenic inflammation

Calcitonin gene-related peptide (CGRP) in the anterior uvea coexists with tachykinins (substance P and neurokinin A) in sensory nerve fibers deriving from the trigeminal ganglion. Mechanical or electrical stimulation of the intracranial part of the trigeminal nerve/ganglion in rabbits produced a marked hyperemia in the anterior segment of the eye, increased intraocular pressure, breakdown of the blood-aqueous barrier and miosis. Simultaneously, CGRP-like immunoreactivity was released into the aqueous humor. This suggests that the highly vasoactive CGRP can be released from sensory nerve fibers to participate in vascular responses. Unlike the tachykinins, CGRP per se was without effect on the pupillary diameter while disrupting the blood-aqueous barrier (resulting in aqueous flare) upon intravitreal injection. In addition, CGRP enhanced the aqueous flare evoked by a minimal eye trauma (infrared irradiation of the iris). The miosis evoked by the intravitreal injection of substance P was more pronounced when CGRP was injected simultaneously, and finally, substance P induced aqueous flare much more effectively when given together with a threshold dose of CGRP.     

Effects of capsaicin in rat and pigeon on peripheral nerves containing substance P and calcitonin gene-related peptide

Summary Substance P and calcitonin gene-related peptide were immunohistochemically identified in axons innervating the cornea and the ureter of adult rats and pigeons. The two neuropeptides were similarly distributed in both species. Capsaicin pretreatment induced depletion of the immunoreactivity; this was quantitatively and qualitatively different in rats and pigeons. Topical application of capsaicin (1%) reduced the immunoreactivity in the cornea in both species by 50%. Systemic capsaicin treatment completely depleted both peptides from the corneal innervation of rats but reduced the peptide content only by 50% in the cornea of pigeons. In the ureter of rats, capsaicin pretreatment completely depleted the peptide immunoreactivity. In pigeons the peptide depletion was only complete in the outer longitudinal muscle layer. Whereas only a few immunoreactive fibres were observed in the circular muscle layer, about 50% of the peptide remained in the inner longitudinal muscle layer. The results demonstrate that peptidergic afferents in the cornea and ureter of pigeons are sensitive to capsaicin, although birds do not show nociceptive responses to local administration of the drug. The long-term depletion of substance P and calcitonin gene-related peptide by capsaicin is discussed with regard to the possibility that functionally capsaicin receptors may exist in the axon but not at nerve endings.Part of the thesis of Gerhard Harti, to be presented to the Fachbereich Biologie, Justus-Liebig-Universität, Giessen     

Calcitonin gene-related peptide in human fetal lung and in neonatal lung disease

The ontogeny of calcitonin gene-related peptide immunoreactivity (CGRP-IR) was evaluated immunohistochemically in 67 human fetal or newborn lungs previously analyzed for calcitonin immunoreactivity (CT-IR). CGRP-IR was present by 10 weeks of gestation in rare, solitary neuroendocrine (NE) cells of developing conducting airways in two of eight first-trimester lungs. During the second trimester, cells with CGRP-IR were found consistently (21/23 fetuses). However, the numbers of positively staining cells did not appear to increase in these fetuses or in third-trimester infants dying of non-pulmonary causes. The highest concentrations of CGRP-IR cells were seen in lungs of premature infants with advancing chronic lung disease associated with bronchopulmonary dysplasia (BPD). CGRP-IR was seen earlier in gestation and in greater numbers of NE cells than was calcitonin immunoreactivity (CT-IR) reported previously in these same fetal lungs (Lab Invest 52:52, 1985). Its presence paralleled that of CT-IR in postnatal chronic lung disease.     

Calcitonin gene-related peptide, neurokinin A and substance P: effects on nociception and neurogenic inflammation in human skin and temporal muscle.

Calcitonin gene-related peptide (CGRP) was injected alone and in combination with substance P (SP) or neurokinin A (NKA) into the forearm skin and temporal muscle of human volunteers. In the skin, 50 pmol of CGRP induced a wheal response and a delayed erythema. No pain was recorded. No interaction between CGRP and SP or NKA was observed. In the temporal muscle, 200 pmol of CGRP alone did not induce pain or tenderness but, in combination with SP or NKA, CGRP elicited a significant pain sensation. It is concluded that CGRP may be involved in neurogenic inflammation and that only SP, of the three peptides present in nociceptive C fibers, seems to be of major importance in relation to cutaneous nociception. Simultaneous neurogenic release of CGRP and other neuropeptides in skeletal muscle may induce myofascial pain.     

Calcitonin gene-related peptide and adrenomedullin release in humans: effects of exercise and hypoxia

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) are potent vasorelaxant peptides. This study examined exercise-induced changes in CGRP and AM levels in 12 healthy sea level natives at sea level (SL) and subsequently after 24 h (HA1) and 5 days (HA5) in high altitude hypoxia (4559 m). Plasma values of CGRP, AM, calcitonin, noradrenaline, adrenaline, lactate and heart rate were measured at rest and during maximal exercise (W(max)). On each study day, the dopamine D(2)-receptor antagonist, domperidone (30 mg; n=6), or no medication (n=6) was given 1 h before exercise. W(max) at SL, HA1 and HA5 increased CGRP and AM along with heart rate, lactate and catecholamines, whereas, calcitonin remained unchanged. The maximal CGRP levels at W(max) were significantly decreased at HA1 (74.3+/-6.1 pmol/l; p=0.002) and HA5 (69.6+/-6.0 pmol/l; p<0.001) compared to maximal CGRP at SL (85.1+/-4.9 pmol/l). A similar pattern was observed for lactate and the relation between CGRP and lactate release showed a close linear correlation (r(2)=0.63, P<0.0001). Domperidone produced a marked increase in noradrenaline at W(max), but had no affect on CGRP or AM. In conclusion, CGRP release during hypoxic exercise does not respond to domperidone-induced changes in circulating levels of noradrenaline, rather the release may be directly related to the production of lactate.     

Effects of substance P, calcitonin gene-related peptide and capsaicin on tension and membrane potential of pig coronary artery in vitro

The effects of substance P (SP), calcitonin gene-related peptide (CGRP) and capsaicin were studied on isometric tension and membrane potential of pig coronary arterial strips in vitro. CGRP induced an endothelium-independent relaxation without change in the smooth muscle membrane potential whereas SP relaxed and hyperpolarized the strip via the endothelium. Applied together, the mechanical effects of SP plus CGRP were additive. CGRP did not affect the hyperpolarization due to SP. In order to examine a possible role of endogenous SP and CGRP, capsaicin was used. It provoked a contraction which was adventitia-dependent, and was inhibited by indomethacin. In presence of indomethacin, capsaicin caused a relaxation. It was accompanied by a hyperpolarization of smooth muscle membrane potential only when the strip had an intact endothelium. When the strip was de-endothelialized capsaicin relaxation subsisted. This indicates that capsaicin produced a relaxation of indomethacin-treated strip by releasing a hyperpolarizing endothelial factor and probably endogenous CGRP.     

Calcitonin gene-related peptide,substance P and GAP-43/B-50 immunoreactivity in the normal and arthrotic knee joint of the mouse

The aim of this study was to describe the normal distribution of calcitonin gene-related peptide (CGRP) and substance P (SP) containing fibres in the knee joint of the mouse and to obtain insight into the changes in innervation associated with degenerative processes in the joint. Arthrosis was induced by a single subpatellar intra-articular injection of bacterial collagenase. After decalcification in EDTA solutions, the CGRP and SP fibres were visualized by peroxidase-antiperoxidase pre-embedding immunocytochemistry for light microscopy. Control experiments on the mouse brain as a reference for the effect of EDTA on the immunostaining showed that the decalcification procedure with EDTA had not impaired the immunostaining. A rich innervation of thin varicose CGRP and SP immunoreactive fibres was found in most peri- and intra-articular tissue components. The periosteum, synovial tissues, the joint capsule and the intra-articular fat tissues were richly innervated. Less intense innervations were also found in the subchondral bone plates of the tibio-femoral joint and of the patella. Fibres were also found in the soft tissues between the patellar tendon and the femoral groove. No differences could be found between the location of CGRP and SP fibres with respect to the localization in the joint, but generally more CGRP fibres were found. The collagenase-induced osteoarthrosis was characterized by sclerosis of the subchondral bone, patellar dislocation, osteophyte formation, synovial proliferation and by severe cartilage abrasion, particularly on the medial side of the femoro-tibial joint. The overall distribution of CGRP and SP fibres was the same as in the control joints. However, major differences were found in all studied joints at specific locations around the cruciate ligaments, in the synovium around the patella, in the soft tissues lateral of the patella and in plica tissue between the patella and femoral groove. The CGRP and SP innervation was no longer detectable by immunolabelling with the antibodies. With a polyclonal antibody to the growth associated protein GAP-43/B-50, signs of degenerated axonal profiles were observed in these locations. At other peripheral locations, such as the muscles, the GAP-43/B-50 distribution was normal. In conclusion, the present study provides detailed information on the localization of CGRP and SP fibres, which may be involved in pain perception. Knowledge of the changes that occur during arthrosis may give more insight into the clinical symptoms.     

Catabolism of calcitonin gene-related peptide and substance P by neutral endopeptidase.

Calcitonin gene-related peptide (CGRP) and substance P (SP) are released from sensory nerves upon exposure to irritating stimuli. Neutral endopeptidase (NEP), a membrane-bound peptidase, cleaves many peptides including SP, thereby limiting their biological actions. Recombinant NEP cleaved CGRP1 approximately 88-fold less rapidly than it cleaved SP. The slow cleavage by NEP of CGRP compared to SP suggests that this enzyme is likely to have weaker physiologic effects on CGRP than have been demonstrated for SP.     

Calcitonin gene-related peptide: antinociceptive activity in rats, comparison with calcitonin

The effects of synthetic human calcitonin gene-related peptide (CGRP) on nociceptive response were evaluated in rats by two behavioral tests (tail-flick and hot-plate) and by electrophysiological recording of the firing of thalamic neurons evoked by peripheral noxious mechanical stimuli. CGRP was administered intracerebroventricularly (i.c.v.) and its effects were compared with that of salmon calcitonin (sCT). In the tail-flick test, CGRP (0.25, 2.5 and 5 micrograms/rat) dose-dependently increased response latencies, whereas sCT (0.125, 2.5, 5 and 10 micrograms/rat) did not. Conversely, in the hot-plate test CGRP was effective in enhancing response latencies only at the highest dose of 10 micrograms/rat, while sCT (0.125, 0.25 and 2.5 micrograms/rat) inhibited the hot-plate response dose-dependently. In electrophysiological studies, CGRP (2.5 micrograms/rat, i.c.v.) completely inhibited the evoked neuronal thalamic firing and the same dose of sCT induced only a partial reduction. Furthermore, the antinociceptive effects of CGRP in the tail-flick test and in the electrophysiological studies were not prevented by naloxone. These results demonstrate that central administration of CGRP is effective in inhibiting nociceptive responses and its action like that of sCT does not involve an opioid mechanism. The differences in the antinociceptive profiles of CGRP and sCT suggest that the inhibitory effects of these peptides may involve different neuronal pathways.