Changes in the distribution of the substance P and calcitonin gene-related peptide immunoreactive nerve fibers in the laryngeal mucosa of chronically hypoxic rats.

The distribution and abundance of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive nerve fibers in four different regions of the laryngeal mucosa were compared between normoxic and chronically hypoxic rats (10% O2 and 3.0-4.0% CO2 for 3 months). In the chronically hypoxic laryngeal mucosa, the number of SP and CGRP fibers within and just beneath the epithelium, and around the laryngeal gland was increased in comparison with those in the normoxic controls. Especially in the epiglottic and arytenoid regions, the number of intraepithelial SP fibers was increased remarkably. Most intraepithelial SP and CGRP fibers penetrated into the epithelium to extend to the luminal surface. There was no distinct difference in the distribution and abundance of these peptidergic fibers in the mucosa of the normoxic and chronically hypoxic vocal cord regions. These results suggest that the increased density of SP and CGRP fibers within the epithelium of the upper laryngeal mucosa is a predominant feature of hypoxic adaptation, and this may be involved in airway protection, swallowing, and other functions in the chronically hypoxic environment. In addition, the increased SP and CGRP fibers around the laryngeal gland suggest an enhanced mucous secretion, and this may participate in the airway defense mechanism in low O2 conditions.     

Chronic hypoxia alters calbindin D-28k immunoreactivity in lingual and laryngeal taste buds in the rat

The distribution and abundance of the calcium binding protein, calbindin D-28k (CB) immunoreactivity in the taste buds of the circumvallate papillae and larynx were compared between normoxic and chronically hypoxic rats (10% O2 for 8 weeks). In the normoxic rats, CB immunoreactivity was observed in some cells and fibers of the intragemmal region of the taste buds in the circumvallate papillae. In contrast, in the subgemmal region of the laryngeal taste buds, fibers but not cells were immunoreactive for CB. In chronically hypoxic rats, CB immunoreactive cells and fibers in the taste buds were decreased in the circumvallate papillae. In the laryngeal taste buds, the density of the subgemmal CB immunoreactive fibers in chronically hypoxic rats was greater than in normoxic rats. It is considered that function of the laryngeal taste buds is different from that of the lingual taste buds, so that laryngeal taste buds may be involved in chemosensation other than taste. The altered density of CB immunoreactive cells and fibers in the lingual and laryngeal taste buds is a predominant feature of hypoxic adaptation, and chronic hypoxic exposure might change the chemical sensitivity of the circumvallate papillae and larynx through the regulation of intracellular Ca2+.     

Changes in the peptidergic innervation in the carotid body of rats chronically exposed to hypercapnic hypoxia: an effect of arterial CO2 tension

The abundance of neuropeptide Y (NPY)-, vasoactive intestinal polypeptide (VIP)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers in the carotid body was examined in chronically hypercapnic hypoxic rats (10% O2 and 6-7% CO2 for 3 months), and the distribution and abundance of these four peptidergic fibers were compared with those of previously reported hypocapnic- and isocapnic hypoxic carotid bodies to evaluate the effect of arterial CO2 tension. The vasculature in the carotid body of chronically hypercapnic hypoxic rats was found to be enlarged in comparison with that of normoxic control rats, but the rate of vascular enlargement was smaller than that in the previously reported hypocapnic- and isocapnic hypoxic carotid bodies. In the chronically hypercapnic hypoxic carotid body, the density per unit area of parenchymal NPY fibers was significantly increased, and that of VIP fibers was unchanged, although the density of NPY and VIP fibers in the previously reportetd chronically hypocapnic and isocapnic hypoxic carotid bodies was opposite to that in hypercapnic hypoxia as observed in this study. The density of SP and CGRP fibers was decreased. These results along with previous reports suggest that different levels of arterial CO2 tension change the peptidergic innervation in the carotid body during chronically hypoxic exposure, and altered peptidergic innervation of the chronically hypercapnic hypoxic carotid body is one feature of hypoxic adaptation.     

Morphological changes in the rat carotid body 1, 2, 4, and 8 weeks after the termination of chronically hypocapnic hypoxia

Morphological changes in the rat carotid bodies 1, 2, 4, and 8 weeks after the termination of chronically hypocapnic hypoxia (10% O2 for 8 weeks) were examined by means of morphometry and immunohistochemistry. The rat carotid bodies after 8 weeks of hypoxic exposure were enlarged several fold with vascular expansion. The carotid bodies 1 and 2 weeks after the termination of 8 weeks of hypoxic exposure were diminished in size, although their diameter remained larger than the normoxic controls. The expanded vasculature in chronically hypoxic carotid bodies returned to the normoxic control state. In the carotid bodies 1 week after the termination of chronic hypoxia, the density of NPY fibers was remarkably increased and that of VIP fibers was dramatically decreased in comparison with the density in chronically hypoxic carotid bodies. In the carotid bodies 2 and 4 weeks after the termination of hypoxia, the density of SP and CGRP fibers was gradually increased. In the carotid bodies 8 weeks after the termination of hypoxia, the appearance of the carotid body returned to a nearly normoxic state, and the density of SP, CGRP, VIP, and NPY fibers also recovered to that of normoxic controls. These results suggest that the morphological changes in the recovering carotid bodies start at a relatively early period after the termination of chronic hypoxia, and a part of these processes may be under the control of peptidergic innervation.     

Peptidergic innervation in the rat carotid body after 2, 4, and 8 weeks of hypocapnic hypoxic exposure

The distribution and abundance of neuropeptide-containing nerve fibers were examined in the carotid bodies of rats exposed to hypocapnic hypoxia (10% O2 in N2) for 2, 4, and 8 weeks. The carotid bodies after 2, 4, and 8 weeks of hypoxic exposure were enlarged by 1.2-1.5 times in the short axis, and 1.3-1.7 times in the long axis in comparison with the normoxic control ones. The enlarged carotid bodies contained a number of expanded blood vessels. Mean density per unit area (10(4) microm2) of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive fibers was transiently high in the carotid bodies after 4 weeks of hypoxic exposure, and decreased significantly to nearly or under 50% after 8 weeks of hypoxic exposure. Density of vasoactive intestinal polypeptide (VIP) immunoreactive fibers increased significantly in all periods of hypoxic exposure observed, and was especially high in the carotid bodies after 4 weeks of hypoxic exposure. Density of neuropeptide Y immunoreactive fibers was unchanged in the carotid bodies during hypoxic exposure. These characteristic changes in the density of SP, CGRP, and VIP fibers in the carotid bodies after 4 weeks of hypoxic exposure suggest that the role of these neuropeptide-containing fibers may be different in the carotid bodies after each of three periods of hypoxic exposure, and that the peptidergic innervation after 8 weeks of hypoxic exposure may show an acclimatizing state.     

Calbindin D-28k immunoreactive nerve fibers in the carotid body of normoxic and chronically hypoxic rats

The distribution and ultrastructural characteristics of calbindin D-28k immunoreactive nerve fibers were examined in the carotid body of the normoxic control rats by light and electron microscopy, and the abundance of calbindin D-28k fibers in the carotid body was compared in normoxic and chronically hypoxic rats (10% O2 and 3.0-4.0% CO2 for 3 months). Calbindin D-28k immunoreactivity was recognized in nerve fibers within the carotid body. Calbindin D-28k immunoreactive nerve fibers appeared as thin processes with many varicosities. They were distributed around clusters of glomus cells, and around blood vessels. Immunoelectron microscopy revealed that the calbindin D-28k immunoreactive nerve terminals are in close apposition with the glomus cells, and membrane specialization is visible in some terminals. Some dense-cored vesicles in the glomus cells were aggregated in this contact region. The chronically hypoxic carotid bodies were found to be enlarged several fold, and a relative abundance of calbindin D-28k fibers was lesser than in the normoxic carotid bodies. When expressed by the density of varicosities per unit area of the parenchyma, the density of calbindin D-28k fibers associated with the glomus cells in chronically hypoxic carotid bodies was decreased by 70%. These immunohistochemical findings indicate a morphological basis for involvement of calcium binding protein in the neural pathway that modulates carotid body chemoreception.     

Tissue distribution and innervation pattern of peptide immunoreactivities in the rat pancreas.

The distribution of calcitonin gene-related peptide (CGRP), substance P/tachykinin (SP/TK), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY) and gastrin-releasing peptide (GRP) immunreactivities (IR) in the rat pancreas was investigated using radioimmunoassay and immunohistochemistry. CGRP, NPY and VIP tissue contents are much higher than GRP and SP/TK concentrations. Peptide-containing nerves are distributed to both the exocrine and endocrine pancreas. However, differences exist in terms of density and targets of innervation for each peptidergic system. In the acini and through the stroma, fibers IR for CGRP, NPY and VIP are greater than GRP- and SP/TK-containing processes. The vasculature is supplied by a prominent NPY, CGRP and, to a lesser extent, SP/TK innervation. VIP-IR is found occasionally, and GRP-IR is never detected, in fibers associated with blood vessels. Around ducts, CGRP- and NPY-positive neurites are greater than SP/TK- greater than or equal to VIP-IR fibers, whereas GRP-containing nerves are not visualized. In the islets, the density of peptidergic nerves is: VIP-, GRP- greater than or equal to CGRP-IR greater than NPY or SP/TK. In intrapancreatic ganglia. VIP- and, to a lesser extent, NPY-IRs are found in numerous neuronal cell bodies and in nerve fibers; GRP-IR is present in numerous nerve processes and in few cell bodies; CGRP- and SP/TK-IRs are detected only in fibers wrapping around unlabeled ganglion cells. The majority of CGRP-IR fibers contain SP/TK-IR. The existence of differential patterns of peptidergic nerves suggests that peptides exert their effects on pancreatic functions via different pathways.     

Distribution of immunoreactive neuropeptides in the pancreas of the bullfrog,Rana catesbeiana,demonstrated by immunofluorescence

Indirect double immunofluorescence labelling for eight neuropeptides in the pancreas of the bullfrog, Rana catesbeiana, demonstrated the occurrence, distribution, and coexistence of certain neuropeptides in the exocrine and endocrine pancreas. Immunoreactivity of substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), FMRFamide (FMRF), and galanin (GAL) was localized in nerve fibers distributed between the acini and around the duct system and vasculature of the exocrine pancreas. In these regions, CGRP-immunoreactive fibers were more numerous than those containing the other five peptides. Almost all SP fibers showed coexistence of SP with CGRP, and about one third of fibers also showed coexistence of SP with VIP, NPY, FMRF, and GAL. In the endocrine pancreas, SP, CGRP, VIP, and GAL were recognized in the nerve fibers around and within the islets of Langerhans, and VIP and GAL fibers were more numerous than SP and CGRP fibers. All CGRP fibers, and about half of the VIP and GAL fibers were immunoreactive for SP. NPY- and FMRF-immunoreactive cells were found at the periphery of the islets. These findings suggest that the exocrine and endocrine pancreatic functions of the bullfrog are under the control of peptidergic innervation.     

Immunohistochemical localization of neuron-specific enolase and calcitonin gene-related peptide in rat taste papillae.

Calcitonin gene-related peptide-like and neuron-specific enolase-like immunoreactivity (CGRP-IR and NSE-IR) were surveyed immunohistochemically in the fungi-form, foliate and circumvallate papillae in rats. A dense CGRP-IR network (subgemmal and extragemmal) in the taste papillae is linked to the presence of taste buds, even though CGRP-IR fibers are rarely present in the taste buds. Three typical fiber populations were detected with these two markers. (a) A population of coarse NSE-IR intragemmal fibers characterized by thick neural swellings, never expressing CGRP-immunoreactivity. (b) A population of thin varicose intragemmal NSE/CGRP-IR fibers. (c) A population of subgemmal and extragemmal NSE-/CGRP-IR fibers that partly penetrated the epithelium. The common distribution of CGRP-IR and NSE-IR fibers at the base of taste buds, their differential distribution and morphology within taste buds, added to their restricted nature (gustatory or somatosensory) suggest that a population of CGRP-IR fibers undergoes a target-induced inhibition of its CGRP phenotype while entering the taste buds. The combined use of NSE and CGRP allowed a better characterization of nerve fibers within and between all three types of taste papillae. NSE was also a very good marker for a subtype of taste bud cells in the foliate and in the circumvallate papillae, but no such cells could be observed in the fungiform papillae.     

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.     

Neurochemistry of the gustatory subgemmal plexus

Nerve fibers present in the basal plexus of the vallate papilla of the rat tongue were analyzed using cytochemical, immunocytochemical and ultrastructural methods to investigate whether the subgemmal plexus is subdivided into neurochemical compartments and to provide a clear definition of the reciprocal spatial relationships between nitrergic, peptidergic and acetylesterase positive structures. Several neuronal fibers were detected under the chemoreceptorial epithelium. Some of these fibers were in contact with the taste buds and in some cases neuronal projections were also present between the buds or inside them; some others fibers were present below this layer but in a more peripheral area. Antibodies against CGRP, SP and CCK stained fibers just below the chemoreceptorial epithelium, whereas fibers more distally located were immunolabeled by anti VIP, NOS-1 and NF-200 antibodies. Some double staining experiments were conducted using confocal microscopy. Other sections were processed cytochemically for AChE and subsequently for NADPH-d in colocalization experiments. All the data obtained using these techniques confirmed the results obtained with single immunostaining, as did the ultrastructural results. In conclusion, the present work demonstrates that the subgemmal plexus is a bilayered structure, suggesting that the complex relationship between the two layers plays a pivotal role in taste and in the control of processes ancillary to taste, such as control of vascular or secretory mechanisms.     

The peptidergic innervation of the guinea pig uterine artery in pregnancy

The influence of pregnancy on the density and pattern of the peptidergic innervation of the guinea pig uterine artery was studied. Whole mount stretch preparations of the uterine artery from estrus and late pregnant guinea pigs were processed for the immunohistochemical demonstration of neuropeptide Y (NPY)-, vasoactive intestinal polypeptide (VIP)-, calcitonin gene-related peptide (CGRP)- and substance P (SP)- immunoreactive nerve fibres. In late pregnancy the density of NPY- and CGRP- containing nerve fibres was remarkably decreased, while that of VIP- and SP- immunoreactive nerves showed a moderate reduction. The meaning and the possible physiological relevance of the decreased density of peptide-immunoreactive nerves in the uterine artery in late pregnancy are discussed.     

Immunohistochemical localization of neuron-specific enolase and calcitonin gene-related peptide in pig taste papillae.

Immunoreactivity to neuron-specific enolase (NSE), a specific neuronal marker, and calcitonin gene-related peptide (CGRP) was localized in lingual taste papillae in the pigs. Sequential staining for NSE and CGRP by an elution technique allowed the identification of neuronal subpopulations. NSE-staining revealed a large neuronal network within the subepithelial layer of all taste papillae. NSE-positive fibers then penetrated the epithelium as isolated fibers, primarily in the foliate and circumvallate papillae, or as brush-shaped units formed by a multitude of fibers, especially in the fungiform papillae and in the apical epithelium of the circumvallate papilla. Taste buds of any type of taste papillae were found to express a dense subgemmal/intragemmal NSE-positive neuronal network. CGRP-positive nerve fibers were numerous in the subepithelial layer of all three types of taste papillae. In the foliate and circumvallate papillae, these fibers penetrated the epithelium to form extragemmal and intragemmal fibers, while in the fungiforms, they concentrated almost exclusively in the taste buds as intragemmal nerve fibers. Intragemmal NSE- and CGRP-positive fiber populations were not readily distinguishable by typical neural swellings as previously observed in the rat. The NSE-positive neuronal extragemmal brushes never expressed any CGRP-like immunoreactivity. Even more surprising, fungiform taste buds, whether richly innervated by or devoid of NSE-positive intragemmal fibers, always harboured numerous intragemmal CGRP-positive fibers. Consequently, NSE is not a general neuronal marker in porcine taste papillae. Our observations also suggest that subgemmal/intragemmal NSE-positive fibers are actively involved in synaptogenesis within taste buds. NSE-positive taste bud cells were found in all three types of taste papillae. CGRP-positive taste bud cells were never observed.     

TH-, NPY-, SP-, and CGRP-immunoreactive nerves in interscapular brown adipose tissue of adult rats acclimated at different temperatures: an immunohistochemical study

Interscapular brown adipose tissue (IBAT), a site of nonshivering thermogenesis in mammals, is neurally controlled. The co-existence of sympathetic and peptidergic innervation has been demonstrated in different brown adipose depots. We studied the morphological profile of IBAT innervation and tested by immunohistochemical methods whether cold and warm stimulation are accompanied by modifications in the density of parenchymal noradrenergic nerve fibers. We also studied the immunoreactivity of afferent fibers—which contain calcitonin gene-related peptide (CGRP) and substance P (SP)<197>in different functional conditions. IBAT was obtained from adult rats (6 weeks old) acclimated at different temperatures (4°, 20°, and 28°C). Tissue activity was evaluated by studying the immunolocalization of uncoupling protein (UCP-1), a specific marker of brown adipose tissue. Noradrenergic and peptidergic innervation were seen to arise from morphologically different nerves. Fibers staining for tyrosine hydroxylase (TH) were thin, unmyelinated hilar nerves, and CGRP- and SP-positive fibers were in thick nerves containing both myelinated and unmyelinated fibers. Under cold stimulation, noradrenergic neurons produce greater amounts of TH, and their axons branch, resulting in increased parenchymal nerve fibers density. Neuropeptide Y (NPY) probably co-localizes with TH in noradrenergic neurons, but only in the perivascular nerve fiber network. The parenchymal distribution of NPY to interlobular arterioles and capillaries suggests that this peptide must have other functions besides that of innervating arteriovenous anastomoses, as hypothesized by other researchers. The different distribution of CGRP and SP suggests the existence of different sensory neuronal populations. The detection of CGRP at the parenchymal level is in line with the hypothesis of a trophic action of this peptide.     

Origin and colocalization of CGRP- and SP-reactive nerves in cat airway epithelium.

A combination of neuroanatomic techniques was used to examine the origin and neuropeptide content of nerve fibers in the airway epithelium of adult cats. By the use of immunocytochemical methods, the peptides substance P (SP) and calcitonin gene-related peptide (CGRP) were colocalized in airway epithelial nerve fibers. Two days after wheat germ agglutinin (WGA) was injected into the nodose ganglion, fibers containing WGA immunoreactivity (IR) were detected in the airway epithelium. SP-like immunoreactivity (LI) and CGRP-LI were demonstrated separately in the WGA-IR fibers, establishing their origin from nerve cell bodies of nodose ganglion. Vagal transection inferior to the nodose ganglion reduced the number of SP- and CGRP-IR fibers by greater than 90% in ipsilateral airways. In contralateral airways, SP-IR fibers were substantially reduced, whereas the effect on CGRP-IR fibers was not statistically significant. Vagotomy superior to the nodose ganglion did not alter the density of peptide-IR fibers. The results prove that SP- and CGRP-IR nerve fibers of cat airway epithelium originate from nerve cell bodies in the nodose ganglion and that SP- and CGRP-like peptides may be stored together in some nerve fibers of the airway epithelium.     

Targeted blocking of gene expression for CGRP receptors elevates pulmonary artery pressure in hypoxic rats

We previously described the protection by calcitonin gene-related peptide (CGRP) against hypoxic pulmonary hypertension. Here, we examine the roles of its putative receptor RDC-1 and receptor activity-modifying protein (RAMP) 1 in mediating this protection by selectively inhibiting their synthesis. RAMP1 is an accessory protein for another putative CGRP receptor, calcitonin receptor-like receptor. Antisense oligodeoxyribonucleotides (ASODNs, 5 mg.kg-1.day-1 or 5 and 10 mg.kg-1.day-1 for RDC-1) targeting RAMP1 and RDC-1 mRNAs were chronically infused to the pulmonary circulation of male Sprague-Dawley rats during 7 days of normoxia or hypobaric hypoxia (380 mmHg), and alpha-CGRP ASODN was used as a technical control. CGRP, RAMP1, and RDC-1 ASODNs significantly elevated pulmonary artery pressure (PPA) in chronic hypoxic rats compared with hypoxic mismatched ASODN (MMODN) and saline vehicle controls. CGRP and RAMP1 ASODNs raised PPA in normoxic rats briefly exposed to 10% O2 above MMODN and saline controls. Moreover, normoxic rats treated with CGRP ASODN had higher basal pulmonary vascular tone compared with controls. These data confirm the protective role of CGRP in the pulmonary circulation and suggest that endogenous RAMP1 and RDC-1 are essential in regulation of PPA in hypoxia. This is the first in vivo evidence supporting RDC-1 and RAMP1 as functional CGRP receptor and receptor component.     

Localization of substance P,CGRP, VIP,neuropeptide Y,and somatostatin immunoreactive nerve fibers in the carotid labyrinths of some amphibian species

Summary Immunohistochemical localization of substance P (SP), CGRP, VIP, neuropeptide Y (NPY), and somatostatin (SOM) in the carotid labyrinth were compared in some species of amphibians using the peroxidase-antiperoxidase method. Immunoreactivity of SP, CGRP, VIP, and NPY was found in the nerve fibers distributed in the intervascular stroma of the carotid labyrinth. SP, CGRP, and VIP immunoreactive varicose fibers were densely distributed in the peripheral portion of the carotid labyrinth. Some SP-immunoreactive fibers were distributed similarly to CGRP-immunoreactive fibers. The density of NPY and SOM immunoreactive varicose fibers was low. No immunoreactivity of enkephalins was observed in the labyrinth. The intensities of these peptides were varied from species to species. No glomus cells showed immunoreactivity for any of the 7 peptides studied. These results suggest that the vascular regulatory function, which is one of the possible functions of the carotid labyrinth, is controlled by the peptidergic mechanisms in addition to regulation through intimate apposition of glomus and smooth muscle cells (g-s connection).     

Localization of substance P, CGRP, VIP, neuropeptide Y, and somatostatin immunoreactive nerve fibers in the carotid labyrinths of some amphibian species.

Immunohistochemical localization of substance P (SP), CGRP, VIP, neuropeptide Y (NPY), and somatostatin (SOM) in the carotid labyrinth were compared in some species of amphibians using the peroxidase-antiperoxidase method. Immunoreactivity of SP, CGRP, VIP, and NPY was found in the nerve fibers distributed in the intervascular stroma of the carotid labyrinth. SP, CGRP, and VIP immunoreactive varicose fibers were densely distributed in the peripheral portion of the carotid labyrinth. Some SP-immunoreactive fibers were distributed similarly to CGRP-immunoreactive fibers. The density of NPY and SOM immunoreactive varicose fibers was low. No immunoreactivity of enkephalins was observed in the labyrinth. The intensities of these peptides were varied from species to species. No glomus cells showed immunoreactivity for any of the 7 peptides studied. These results suggest that the vascular regulatory function, which is one of the possible functions of the carotid labyrinth, is controlled by the peptidergic mechanisms in addition to regulation through intimate apposition of glomus and smooth muscle cells (g-s connection).     

Neuropeptides in guinea pig trachea: Distribution and evidence for the release of CGRP into tracheal lumen

The airways of the guinea pig are richly innervated by peptide-containing nerve fibers. Among the most abundant neuropeptides are calcitonin gene-related peptide (CGRP) and substance P (SP), which are stored in nerve fibers located predominantly within and beneath the epithelium, and vasoactive intestinal peptide (VIP), which is located in fibers running mainly among smooth muscle bundles and seromucous glands. Sensory denervation (capsaicin treatment) of adult guinea pigs caused an almost total disappearance of CGRP- and SP-containing nerve fibers, while the density of VIP-containing nerve fibers located in smooth muscle seemed to increase. In the isolated trachea, perfused luminally, CGRP was found to appear in the intraluminal fluid after exposure to capsaicin but not after electrical vagal stimulation. CGRP concentrations in the tracheal wall did not change significantly. Luminally applied CGRP did not affect smooth muscle tension, measured as intraluminal volume changes.