Occurrence, distribution and ontogeny of CGRP immunoreactivity in the rat lower respiratory tract: effect of capsaicin treatment and surgical denervations

Increased intracellular levels of calcitonin gene-related peptide-like immunoreactivity in pulmonary endocrine cells of hypoxic rats

The mammalian respiratory tract contains innervated groups of endocrine cells which are believed to respond to hypoxia. We have demonstrated the involvement of a specific regulatory peptide produced by the cells, calcitonin gene-related peptide (CGRP), in this response. Cells immunoreactive for CGRP or for protein gene product 9.5 (PGP 9.5), a general marker of nerves and endocrine cells, were quantified in sections of lungs from hypoxic (21 days, 10 per cent O2) and normoxic rats. An immunostaining method employing supra-optimal dilutions of primary antiserum was used. This detects variations in antigen concentration which may be masked if the routine, optimal dilution is used. The number of CGRP-immunoreactive endocrine cells was significantly (P less than 0.001) greater in the lungs of hypoxic rats (76.9 +/- 10.1 cells/cm2, mean +/- SEM) compared with controls (19.7 +/- 2.4). However, the numbers of PGP 9.5-immunoreactive cells were the same in both groups (81.3 +/- 12.2, hypoxic; 79.5 +/- 9.8 control), suggesting that the total number of endocrine cells did not change. It is concluded therefore that the apparent increase in CGRP-immunoreactive endocrine cells in hypoxic rat lungs is due to increased intracellular levels of the peptide. Since CGRP is a vasodilator, this could have important implications in the vasoconstrictor response to hypoxia.

Characterization of the peptidergic afferent innervation of the stomach in the rat, mouse and guinea-pig

Retrograde tracing of the fluorescent marker, True Blue, has been used together with immunohistochemistry employing antibodies to substance P, calcitonin gene-related peptide, somatostatin, vasoactive intestinal polypeptide and morphine-modulating peptide to study the afferent innervation of the stomach in rat, mouse and guinea-pig. Up to 85% of spinal afferents to the stomach in all three species contained immunoreactive calcitonin gene-related peptide, and up to 50% contained substance P. In all three species less than 10% of vagal afferents to the stomach reacted with antibodies to calcitonin gene-related peptide, or substance P. Cacitonin gene-related peptide-immunoreactive fibres were found in the myenteric plexus, circular muscle and around submucosal blood vessels in the stomach. In the rat, removal of the coeliac ganglion, splanchnic nerve section, or capsaicin treatment virtually abolished calcitonin gene-related peptide immunoreactivity in the stomach. Capsaicin and splanchnic section also abolished the staining of immunoreactive calcitonin gene-related peptide fibres in the coeliac ganglion. The same treatments abolished substance P staining of fibres around submucosal blood vessels, but in the myenteric plexus and circular smooth muscle there were still abundant immunoreactive fibres, presumably arising from intrinsic cell bodies. No somatostatin-containing visceral afferents could be found, although somatostatin was localized to cell bodies in rat dorsal root ganglia. Immunoreactive vasoactive intestinal polypeptide-containing dorsal root ganglia neurons were not found; although antibodies to morphine-modulatory peptide revealed immunoreactive nerve cell bodies, we were unable to exclude the possibility that this result is attributable to cross reactivity with calcitonin gene-related peptide. These results provide direct evidence that calcitonin gene-related peptide is a marker for a major subset of visceral primary afferent neurons and suggest that this population of spinal afferents makes a major contribution to the total gastric content of calcitonin gene-related peptide.

Differential expression of alpha-CGRP and beta-CGRP by primary sensory neurons and enteric autonomic neurons of the rat

Expression of the calcitonin gene-related peptide, alpha-calcitonin gene-related peptide (CGRP), and the homologous beta-CGRP were compared in sensory and enteric nerves of the rat. Analysis of CGRP-like immunoreactivity by cation exchange chromatography and radioimmunoassay showed that in the dorsal root ganglia, dorsal spinal cord and in those peripheral tissues where CGRP-like immunoreactivity is primarily localized to sensory fibres, alpha-CGRP concentrations were three to six times greater than beta-CGRP concentrations. In the intestine, however, beta-CGRP concentrations were up to seven times greater than alpha-CGRP concentrations. Only beta-CGRP was detected in the intestines of capsaicin-treated rats. Northern blot and in situ hybridization to alpha-CGRP- and beta-CGRP-specific probes showed that while both alpha-CGRP and beta-CGRP messenger ribonucleic acids occurred in the dorsal root ganglia, only beta-CGRP messenger ribonucleic acid occurred in the intestine, where it was localized to enteric neurons. Receptor binding sites on membranes of rat heart and colon had approximately equal affinities for alpha-CGRP and beta-CGRP. The two peptides were equipotent in increasing the rate and force of atrial contractions but alpha-CGRP was slightly (2.6 times) more potent than beta-CGRP in relaxing colonic smooth muscle. Thus, both alpha-CGRP and beta-CGRP occur in the rat nervous system and are both biologically active. Sensory neurons and enteric neurons have been identified as populations which preferentially express alpha-CGRP and beta-CGRP, respectively.

Calcitonin gene-related peptide and the lung: neuronal coexistence with substance P, release by capsaicin and vasodilatory effect

The occurrence and distribution of calcitonin gene-related peptide (CGRP) in the lower airways was studied by means of immunohistochemistry and radioimmunoassay (RIA) in combination with high performance liquid chromatography (HPLC). CGRP-like immunoreactivity (-LI) was observed in nerves from the epiglottis down to peripheral bronchi in rat, cat and guinea pig and also in human bronchi. Double staining revealed colocalization of CGRP-LI and substance P (SP)-LI in cell bodies of nodose and jugular ganglia as well as in axons and nerve terminals of the airways. Systemic capsaicin pretreatment induced a marked loss of the CGRP- and SP-immunoreactive (-IR) nerves in the lower airways. CGRP-IR was also present in epithelial endocrine cells and neuroepithelial bodies. The content of CGRP-LI as measured with RIA in guinea pig bronchi was significantly lower after capsaicin pretreatment. Analysis of human bronchial extracts revealed that CGRP-LI coeluted with synthetic human CGRP on HPLC. In the isolated perfused guinea pig lung capsaicin exposure caused overflow of CGRP-LI suggesting release from peripheral branches of sensory nerves. Both in vivo experiments in the guinea pig measuring insufflation pressure as well as in vitro studies on isolated guinea pig and human bronchi showed that whereas tachykinins contracted bronchial smooth muscle no contractile or relaxing effect was elicited by human or rat CGRP. However, CGRP caused relaxation of serotonin precontracted guinea pig and human pulmonary arteries. In conclusion, the presence and release of CGRP-LI from capsaicin sensitive nerves in the lower airways adds another possible mediator, in addition to tachykinins, of vascular reactions upon sensory nerve irritation.

Control of vascular permeability and vascular smooth muscle in the respiratory tract by multiple neuropeptides

Recent evidence suggests that a population of primary afferent neurons which terminate in the upper and lower airways contains several coexisting peptides. Thus, substance P was found to coexist with at least three structurally related tachykinins, viz. neurokinin A, neuropeptide K and an eledoisin-like peptide. Furthermore, calcitonin gene-related peptide which is structurally not related to tachykinins is also present in the same neurons which innervate a variety of peripheral tissues. Substance P, neurokinin A, eledoisin-like peptide and calcitonin gene-related peptide can simultaneously be released from central and peripheral branches of primary sensory neurons, whereas a release of neuropeptide K could not be demonstrated. Local inflammatory mediators like bradykinin or histamine also released multiple peptides in the airways and caused vascular protein leakage which is partly dependent on intact sensory nerves. In experimental animals, tachykinins as well as calcitonin gene-related peptide caused vasodilatation, whereas tachykinins but not calcitonin gene-related peptide caused an increase in vascular protein leakage. In humans, intranasally administered substance P (but not calcitonin gene-related peptide) lead to nasal obstruction as measured by rhinomanometry, and to secretion. It is suggested that activation of peripheral endings of perivascular primary sensory neurons causes vasodilatation and increase in vascular protein leakage by simultaneous action of several neuropeptides including tachykinins and calcitonin gene-related peptide.

Ontogeny of immunoreactive calcitonin gene-related peptide in thyroid C cells from dogs, rabbits, and guinea pigs

Ontogeny of immunoreactive calcitonin gene-related peptide (CGRP) in thyroid C cells of dogs, rabbits, and guinea pigs from early fetuses to adults was investigated by an immunoperoxidase method, in comparison with the development of immunoreactive calcitonin and somatostatin. The presence of immunoreactive CGRP in mature C cells was different from species to species. Dog and rabbit C cells revealed intense immunoreactivity for CGRP, whereas guinea pig C cells revealed very weak immunoreactivity or none. In dog fetuses, the appearance of immunoreactive CGRP was early. At around 35 days of gestation, when the follicular cells were not yet organized into follicles, immunoreactivities for three peptides--calcitonin, somatostatin, and CGRP--began to appear in C cells. While the highest population of somatostatin-positive cells was attained when the primordial follicles were vigorously formed throughout whole thyroid parenchyma and their frequency progressively declined thereafter, CGRP-positive cells as well as calcitonin-positive cells gradually increased in number and intensity with gestational age. The developmental pattern of immunoreactive CGRP coincided with that of immunoreactive calcitonin in dog C cells. In rabbit fetuses, at 25 days of gestation, when thyroid follicles stored large amounts of colloid and C cells already exhibited intense immunoreactivity for calcitonin, CGRP immunoreactivity as well as somatostatin immunoreactivity began to appear. Subsequently, immunoreactivities for the three peptides gradually increased with age, although calcitonin immunoreactivity was outstandingly intense among them. In guinea pig C cells, intense immunoreactivity for CGRP was not observed in any stages of development. These results indicate that there are developmental profiles of CGRP characteristic for each animal, and the ratio of CGRP and calcitonin produced from calcitonin genes in C cells seems to be fixed for life.

Changes in bombesin, calcitonin, and serotonin immunoreactive pulmonary neuroendocrine cells in cystic fibrosis and after prolonged mechanical ventilation

Increases in bombesin, calcitonin, and serotonin immunoreactive pulmonary neuroendocrine cells have been documented in infants with bronchopulmonary dysplasia. As some of the secretory products of these postulated airway chemoreceptors are known to adversely affect pulmonary vasomotor and bronchomotor tone, the present study was undertaken to determine if similar changes occur in the lungs of older pediatric patients with chronic respiratory disease. Immunoreactive cells were identified using the antibody-peroxidase-antiperoxidase technique and expressed as immunoreactive bronchioles/cm2 of lung tissue. In subjects dying an accidental or noncardiopulmonary death (control group: n = 48, zero to 24 yr of age), the total number of bombesin, calcitonin, and serotonin immunoreactive bronchioles/cm2 was greatest at birth, then decreased rapidly to extremely low levels after the first year of life. In the cystic fibrosis (n = 55, 3 days to 29 yr of age) and prolonged ventilation (n = 24, 4 months to 18 yr of age) groups, there was a significant increase (p less than 0.035) in bombesin, calcitonin, and serotonin immunoreactive bronchioles/cm2 from 1 to 11 yr of age. In the cystic fibrosis group, there was a sixfold increase in the number of serotonin immunoreactive bronchioles/cm2 lung tissue (p less than 0.015) compared with that in the other 2 groups during the first decade of life, suggesting a response to specific factors present only in the lungs of patients with this disease. In all 3 groups, immunoreactive cells were infrequently identified after 11 yr, implying a fundamental change in neuroendocrine cell biology coincident with the termination of lung growth and/or the onset of puberty.(ABSTRACT TRUNCATED AT 250 WORDS)

The electrophysiologic and neurochemical properties of paratracheal neurones in situ and in dissociated cell culture

Although our knowledge of the intrinsic innervation of the airways is at present rather limited, it would appear that these neurones have several features in common with other intramural ganglia. They show a level of electrophysiologic diversity that might permit considerable integration and modulation to take place. Furthermore, the localization of a wide variety of neuropeptides in the neurones and in fibers within the paratracheal ganglia indicates that they may also possess the neurochemical specialization necessary to allow these ganglia to act as sites of complex local regulation.

Distribution and characterization of calcitonin gene-related peptide immunoreactivity in the digestive system of normal and capsaicin-treated rats

The distribution and characterization of calcitonin gene-related peptide immunoreactivity in the digestive system of normal, capsaicin-treated, and littermate control rats were studied by radioimmunoassay, chromatography, and immunohistochemistry. The highest concentrations of calcitonin gene-related peptide immunoreactivity were found in the stomach (45 +/- 2.8 pmol/g wet wt, nonsecretory region; 38.7 +/- 4.4 pmol/g wet wt, secretory region) and rectum (30.9 +/- 1.6 pmol/g wet wt). Significant amounts of peptide were also found in the other regions of the gut and in the pancreas. Neonatal treatment with capsaicin, which causes a permanent degeneration of most of the small-diameter sensory neurons, reduced calcitonin gene-related peptide content by greater than 95% in the esophagus and stomach, by 60% in the pancreas, and by less than 50% in the intestine, when compared with littermate controls. Separation of extracts from the gut, pancreas, and brain by chromatography gave major peaks corresponding to the predicted rat calcitonin gene-related peptide and small unidentified peaks, which presumably arise from metabolism of the peptide. Immunohistochemical studies demonstrated that in the esophagus and stomach, calcitonin gene-related peptide immunoreactivity is restricted to nerve fibers, whereas in the intestine it is localized in both nerve fibers and enteric ganglion cells. In capsaicin-treated rats there was a virtually complete elimination of calcitonin gene-related peptide immunoreactive fibers innervating the esophagus and stomach, whereas in the small and large intestine there was a dramatic reduction and often a complete elimination of those associated with blood vessels and a slighter reduction of the nonvascular immunoreactive fibers. The results of this study indicate that calcitonin gene-related peptide immunoreactive nerve fibers innervating the rat digestive system originate from both intrinsic (enteric) and extrinsic (presumably sensory) sources and that both the intrinsic and extrinsic components appear to contain a substance that corresponds to the predicted calcitonin gene-related peptide.

Retrograde tracing shows that CGRP-immunoreactive nerves of rat trachea and lung originate from vagal and dorsal root ganglia

The origins of sensory innervation of the lower respiratory tract are thought to be principally the nodose and jugular ganglia of the vagus nerve. It has been suggested and partially demonstrated that there is also a component arising from dorsal root ganglia, but the segmental levels involved are not known precisely. We have therefore investigated the origins of sensory nerves within the rat respiratory tract, particularly those containing calcitonin gene-related peptide (CGRP), using the technique of retrograde axonal tracing combined with immunohistochemistry. Injections of True blue were made into extra-thoracic trachea (n = 4 rats) and percutaneously into the right and left lung (n = 4 each). Retrogradely labelled neuronal perikarya were detected in vagal and dorsal root ganglia, and sympathetic chain ganglia. CGRP-immunoreactive cells were seen only in vagal and dorsal root ganglia. Tracheal innervation arose bilaterally in the vagal sensory ganglia but those on the right side represented the principal source; the majority of CGRP-containing neurons occurred in the jugular ganglion. A very small component of labelling occurred in spinal ganglia at levels C2-C6. The sensory innervation of the lungs was seen to arise predominantly from the ipsilateral dorsal root ganglia (45% of cells CGRP-immunoreactive) at levels T1-T6. In contrast to the trachea, the contribution of vagal sensory neurones to the lungs appeared to be less than that of the spinal ganglia. These results show that the sensory innervation of the rat lungs has a major origin in the dorsal root ganglia, in which almost half of the involved neurons contain CGRP, and confirm that most CGRP-immunoreactive nerves in the trachea arise in the right jugular ganglion.

Regulatory peptides in the respiratory tract of Macaca fascicularis

The quantitative distribution and localisation of seven regulatory peptides (vasoactive intestinal peptide (VIP), peptide histidine methionine (PHM), calcitonin gene related peptide (CGRP), galanin, substance P, neuropeptide tyrosine (Y), and bombesin like peptides) were determined by radioimmunoassay and immunocytochemistry in six different regions of the respiratory tract of the cynomolgus monkey, Macaca fascicularis. In general, peptide concentrations were higher in the airways than in lung tissue itself. VIP and PHM were found in greatest abundance and in equimolar concentrations. Concentrations of substance P, neuropeptide Y, and bombesin were substantially lower. Immunocytochemistry localised all the peptides to nerve fibres, whose density generally paralleled the tissue concentrations by radioimmunoassay except in the case of bombesin, which was not detected. VIP, PHM, and galanin were mostly associated with glands of trachea and bronchus and with blood vessels and smooth muscle; CGRP and substance P were found principally beneath airway epithelium and around smooth muscle fibres and blood vessels; neuropeptide Y was found around blood vessels and seromucous glands only. The pattern of peptide distribution in the Macaca fascicularis respiratory tract is similar to that previously reported in human postmortem material, suggesting that the cynomolgus monkey may be a useful model for examining the pathophysiological role of peptides in human respiratory disease.

Calcitonin gene-related peptide is localised to human airway nerves and potently constricts human airway smooth muscle

In human airways synthetic human sequence calcitonin gene-related peptide (hCGRP), a novel peptide produced by alternative processing of mRNA from the calcitonin gene, caused concentration-dependent contraction of human bronchi (EC50 4.9 X 10(-9) M) and was significantly more potent than substance P or carbachol. The contractile response was unaffected by atropine (2 X 10(-6) M), propranolol (10(-6) M), indomethacin (10(-5) M), tetrodotoxin (3 X 10(-6) M), chlorpheniramine (10(-4) M), cimetidine (10(-5) M), or FPL55712 (10(-4) M) suggesting a direct effect of CGRP on airways smooth muscle. CGRP was detected in human airways by radioimmunoassay with highest concentrations in cartilaginous airways. CGRP was localised by immunocytochemistry to both nerves and ganglia in human airways. CGRP, is a potent constrictor of human airways and may have important effects on airway function and be implicated in the pathogenesis of bronchial hyper-responsiveness and asthma.