Morphology, histochemistry, and distribution of serotonin-containing cells in tracheal epithelium of adult rabbit

alpha7-Nicotinic receptor antagonists at the beginning of a clinical era for NSCLC and Mesothelioma?

Of the human solid cancers, Non-Small Cell Lung Cancer (NSCLC) and Malignant Pleural Mesothelioma (MPM) display a natural history supporting the concept that they develop from multiple preneoplastic pathways. Recently, new evidence suggested that nicotinic Acetylcholine Receptors (nAChRs) play a significant role in lung cancer predisposition and natural history. This review is based on some translational research aimed at evaluating the potential therapeutic effect of nAChR antagonists on NSCLC and MPM. The background and rationale of this approach are based on the experimental observations that: (a) NSCLC and MPM cells express nAChRs and (b) the activation of these receptors by agonists, namely nicotine, inhibits apoptosis, whereas receptor antagonists have a pro-apoptotic effect.

Structure of the respiratory tract of the red-bellied newt Cynops pyrrhogaster, with reference to serotonin-positive neuroepithelial endocrine cells

To investigate the distribution of serotonin-positive neuroepithelial endocrine (NEE) cells in the respiratory tract of the red-bellied newt Cynops pyrrhogaster, serial sections of the respiratory tract were stained using immunohistochemical methods for serotonin, a periodic acid-Schiff method and hematoxylin-eosin staining. The respiratory tract of the red-bellied newt consisted of a tubular laryngotrachea and two pulmonary sacs. Serotonin-positive solitary NEE cells were distributed widely throughout the ciliomucous epithelium of the laryngotrachea. The innervated clusters of NEE cells, termed neuroepithelial bodies, were rarely found in the caudal portion of the laryngotrachea. The density of NEE cells was high in the middle portion of the laryngotrachea, particularly in the region surrounded by a striated laryngeal sphincter, and the densities were low cranially towards the aditus laryngis and caudally in the pulmonary sacs, the epithelium of which consisted of both ciliomucous epithelial cells and non-ciliated respiratory epithelial cells or pneumocytes. The NEE cells were not observed in the vicinity of non-ciliated respiratory epithelial cells. The morphology and distribution of serotonin-positive NEE cells in the respiratory tract of the red-bellied newt were similar to those described in mammals, including humans. The close localization of NEE cells with ciliary and mucous cells and the distribution of NEE cells in the laryngotrachea suggest that NEE cells play important roles in the defense and repair of the ciliomucous epithelium, such as increasing mucous secretion, ciliary beat frequency and the proliferation of epithelial cells.

The airway cholinergic system: physiology and pharmacology

The present review summarizes the current knowledge of the cholinergic systems in the airways with special emphasis on the role of acetylcholine both as neurotransmitter in ganglia and postganglionic parasympathetic nerves and as non-neuronal paracrine mediator. The different cholinoceptors, various nicotinic and muscarinic receptors, as well as their signalling mechanisms are presented. The complex ganglionic and prejunctional mechanisms controlling the release of acetylcholine are explained, and it is discussed whether changes in transmitter release could be involved in airway dysfunctions. The effects of acetylcholine on different target cells, smooth muscles, nerves, surface epithelial and secretory cells as well as mast cells are described in detail, including the receptor subtypes involved in signal transmission.

Phosphodiesterase inhibitors suppress alpha2-adrenoceptor-mediated 5-hydroxytryptamine release from tracheae of newborn rabbits

The outflow of 5-hydroxytryptamine (5-HT) from isolated tracheae of newborn rabbits was determined by high pressure liquid chromatography with electrochemical detection. This 5-HT outflow reflects release from neuroendocrine epithelial cells of the airway mucosa, as previously shown. Phenylephrine, via alpha2B-adrenoceptors, caused a transient increase in 5-HT outflow, maximally by about 250%, an effect mediated by liberation of intracellular Ca2+, as previously shown. The non-selective phosphodiesterase inhibitor 2-isobutyl-1-methylxanthine (IBMX) concentration-dependently inhibited phenylephrine-induced 5-HT release (completely at 100 microM, IC50: 1.3 microM). Likewise, benzafentrine (inhibitor of phosphodiesterase 3 and 4) and siguazodan (inhibitor of phosphodiesterase 3) also almost completely inhibited phenylephrine-induced 5-HT release with IC50 values of 1.7 and 4.2 microM, respectively. Rolipram (inhibitor of phosphodiesterase 4), in a concentration of 10 microM, which exceeds more than 10-fold the reported IC50 for phosphodiesterase 4, did not significantly affect phenylephrine-induced 5-HT release. 5-HT release induced by depolarizing concentrations of K+ (45 mM), which largely depends on extracellular Ca2+, was not affected by IBMX. In conclusion, phosphodiesterases, with characteristics of phosphodiesterase 3, appear to play an important role in the control of cyclic nucleotide mediated inhibition of 5-HT release from neuroendocrine epithelial cells.

Adrenoceptor- and cholinoceptor-mediated mechanisms in the regulation of 5-hydroxytryptamine release from isolated tracheae of newborn rabbits

1. Isolated tracheae of newborn rabbits were incubated in vitro and the outflow of 5-hydroxytryptamine (5-HT) was determined by h.p.l.c. with electrochemical detection. Evidence has previously been provided that this 5-HT outflow derives from neuroendocrine epithelial (NEE) cells of the airway mucosa. 2. Phenylephrine (1, 10 and 30 microM) enhanced the outflow of 5-HT by 80, 290 and 205%, respectively. 5-HT outflow evoked by 10 microM phenylephrine was not affected by the presence of the neurotoxin tetrodotoxin (1 microM). 3. Rauwolscine, ARC 239 (an alpha(2B)-adrenoceptor preferring antagonist), yohimbine and prazosin antagonized the effect of 10 microM phenylephrine in a concentration-dependent manner with IC50 values of 150, 295, 300 and 1,700 nM, respectively. Comparison of the ratios (between all antagonists) of the present IC50 values with the corresponding ratios of Ki values obtained in binding studies for the alpha(2A)-, alpha(2B)-, alpha(2C)- and alpha(2D)-adrenoceptor subtypes strongly suggests the involvement of an alpha(2B)-receptor. 4. 5-HT outflow evoked by 10 microM phenylephrine was inhibited by 65% in the presence of 1 microM forskolin and abolished in the presence of 10 microM forskolin. 5. 5-HT outflow evoked by 10 microM phenylephrine was inhibited by about 45 and 70% in the presence of 0.1 and 1 microM isoprenaline, respectively. The inhibitory effect of 1 microM isoprenaline was only marginally antagonized by 1 microM, but blocked by 10 microM propranolol. 6. 5-HT outflow was not affected by the muscarine receptor agonist oxotremorine (10 microM), but was enhanced by 175% by 100 microM nicotine. The effect of nicotine was blocked by 100 microM hexamethonium and prevented by 1 microM tetrodotoxin or 1 microM yohimbine. 7. In conclusion, 5-HT release from NEE cells of the rabbit trachea is stimulated via alpha-adrenoceptors most likely of the alpha(2B)-subtype localized directly at the NEE cells. Activation of beta-adrenoceptors as well as direct activation of adenylyl cyclase by forskolin exert inhibitory effects on 5-HT release. Activation of nicotinic, but not of muscarinic receptors, also evokes the release of 5-HT. However, the effect of nicotine appears to be mediated indirectly via the release of noradrenaline.

Characterization of 5-hydroxytryptamine release from isolated rabbit and rat trachea: the role of neuroendocrine epithelia cells and mast cells

Rabbit or rat isolated tracheae were incubated in vitro, and the release of 5-hydroxytryptamine (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) was determined by HPLC with electrochemical detection. Release of 5-HT from rabbit tracheae could be evoked by the calcium ionophore A 23187 and, in a calcium-dependent manner, by depolarizing concentrations of potassium (45 mmol/l), but not by the mast cell degranulating drug compound 48/80. High potassium- and A 23187-evoked release of 5-HT was markedly higher from tracheae of newborn compared to adult rabbits. In rabbit tracheae, mechanical removal of the mucosa resulted in 80-90% reduction in tissue 5-HT and in a similar reduction in high potassium-evoked 5-HT release. 5-Hydroxytryptophan, but not tryptophan, caused a marked increase in the spontaneous outflow of 5-HT and 5-HIAA from tracheae of newborn rabbits, and the effect on 5-HT, but not that on 5-HIAA, required an intact mucosa. Furthermore, treatment with 5-hydroxytryptophan caused an increase in tissue 5-HT and 5-HIAA, and these effects required an intact mucosa. In tracheae of adult rabbits 5-hydroxytryptophan caused similar, although less profound, effects. Adrenaline (1 micromol/1) enhanced the release of 5-HT from newborn rabbit tracheae, and this effect was inhibited by 1 micro mol/l phentolamine or 1 micromol/1 prazosin, but not affected by 100 nmol/1 propranolol. In rat tracheae, compound 48/80 evoked a large release of 5-HT, whereas depolarizing concentrations of potassium (45 mmol/1) had only a very minor effect. In rat tracheae, 5-hydroxytryptophan had small effects on the outflow and tissue contents of 5-HT and 5-HIAA in comparison to the effects on rabbit tracheae; and removal of the mucosa resulted in only a minor reduction in tissue 5-HT. In conclusion, neuroendocrine epithelial (NEE) cells and mast cells are the major source of 5-HT in tracheae of the rabbit and rat, respectively. Isolated tracheae of newborn rabbits appear to be a useful model to study 5-HT secretion from NEE cells. 5-HT secretion from NEE cells is activated by a rise in intracellular calcium, and calcium influx through voltage-regulated channels appears to be one activating pathway. 5-HT secretion from NEE cells can be stimulated via alpha-adrenoceptors.

Immunohistochemical colocalization of 7B2 and 5HT in the neuroepithelial bodies of the lung of Rana temporaria

The neuroendocrine cell population of the lung of Rana temporaria has been studied by means of immunocytochemistry. Serotonin (5HT)- and polypeptide 7B2-immunoreactive neuroepithelial bodies have been observed in the epithelial lining of the lung. 5HT- but not 7B2-immunoreactive isolated endocrine cells have also been observed.

Ultrastructure and innervation of neuroepithelial bodies in the lungs of newborn cats

Neuroepithelial bodies (NEB) occur throughout the airway mucosa and alveolar parenchyma of kitten lungs. In the bronchi, they are often situated on top of a cartilage plate. They form compact corpuscles containing 10-20 corpuscular cells and appear covered with a layer of flattened Clara cells. Kitten NEB are occasionally observed to display mitosis of the corpuscular epithelial cells. A prominent blood capillary lies at their basal pole. The corpuscular cells contain numerous dense core vesicles (DCV), whose number and diameter remain unchanged with age. Kitten NEB are innervated by nerve fibres that "loop" through the corpuscle and form morphologically afferent as well as efferent nerve endings. The nerve endings display afferent synaptic junctions with the corpuscular cells and sometimes run in clusters, so that they contact each other. Many nerve endings undergo spontaneous degeneration. We conclude that kitten NEB are well adapted to function as chemoreceptors and as endocrine or paracrine organs. Their chemoreceptor activity could be modulated by axon reflexes since their afferent nerve endings are often continuous with the efferent ones, as well as by interneural modulation since nerve endings often form clusters. In addition, kitten NEB innervation appears to involute rapidly soon after birth. This may indicate that their chemoreceptor function is only of primary importance during gestation and at birth. However, the secretory function of kitten NEB, as evidenced by the unchanged numbers and dimensions of their DCV, seems to remain steady throughout life.

Cholinergic-nicotinic control of growth and secretion of cultured pulmonary neuroendocrine cells

Dispersed newborn hamster lung cells were established in vitro in a defined, low-serum growth medium. Neuroendocrine markers (immunohistochemistry for bombesin/gastrin-releasing peptide and calcitonin) revealed a cellular predominance of pulmonary neuroendocrine (PNE) cells. While the supernatant concentration remained stable, the concentration of PNE cell immunoreactive calcitonin (iCT) gradually declined over 4 weeks. Supplementation of the medium with nicotine for 3 weeks prevented this decline in cellular iCT. Concurrently, the number of cells and [3H]thymidine incorporation were significantly increased. The stimulatory effect of chronic nicotine was reversed by the coadministration of the nicotinic antagonist hexamethonium. In another set of experiments, prior multiple transplacental nicotine pretreatments resulted in a significant increase in iCT in the lungs of newborns; when these lungs were subsequently placed in cell culture without nicotine, despite the higher concentration of iCT, there was a drop in iCT similar to that observed in the control culture. In contrast, in vivo, the lung iCT remained significantly elevated at 1 week post-parturition. Cell culture supernatants were analyzed at week 4 for the evoked release of iCT; cholinergic-nicotinic agonists promptly increased the supernatant iCT, which was blocked by nicotinic but not by muscarinic antagonists. We suggest that this in vitro system provides a useful tool to study directly the PNE cell. The acute and chronic effects of nicotine are most likely related to stimulation of cholinergic-nicotinic receptors on iCT-containing PNE cells.

Endothelin, vasopressin, and substance P like immunoreactivity in cultured and intact epithelium from rabbit trachea

BACKGROUND

The control of airways reactivity is essential to our understanding of disease processes such as asthma. Many studies have examined the neural control of the airways, but more recently there has been evidence to show that the epithelium lining the airways may influence airways reactivity.

METHODS

Rabbit tracheal epithelial cells were dispersed with enzymes, grown in primary culture and fixed. Tissue from intact tracheas was also sampled and fixed. Localisation of the vasoactive substances endothelin-1, arginine-vasopressin, and substance P was investigated by immunolabelling techniques.

RESULTS

Scattered immunolabelling to endothelin-1, arginine-vasopressin, and substance P was found throughout the cultures (with < 20% of cells staining positively to each antibody). At the ultrastructural level this immunoreactivity was found in the cytoplasmic matrix. In addition, immunoreactivity of intact tissue to endothelin-1, arginine-vasopressin, and substance P was examined and positively staining cells were found to be scattered through the epithelium.

CONCLUSIONS

The presence of these vasoactive substances within the epithelium lining the airways supports the view that epithelial cells may provide an additional mechanism in the control of airways reactivity.

Solitary neuroendocrine cells and neuroepithelial bodies in the lower airways of embryonic, fetal, and postnatal sheep

The sheep pulmonary intraepithelial APUD system was studied by histochemical, immunocytochemical, and electron microscopy techniques during different periods of lung development: embryonic, fetal (pseudoglandular, canalicular, and alveolar), and postnatal. The cells of the ovine pulmonary intraepithelial APUD system were found randomly distributed throughout the conducting and respiratory or undifferentiated airways. They appeared as isolated cells (solitary neuroendocrine cells) or in groups (neuroepithelial bodies). These cells were argyrophilic and immunoreactive for neuron-specific enolase but were not argentaffin. Ultrastructurally they were characterized by a basal position in the respiratory epithelium and by the presence of neurosecretory granules (dense-core vesicles) ranging between 65 and 230 nm of diametre. Quantitative studies showed that single neuroendocrine cells were more numerous in distal conducting airways and at fetal stages. The earliest identifiable argyrophilic and NSE-immunoreactive neuroendocrine cells in sheep airways appeared at gestational week 5, close to the term of the embryonic period.

Co-occurrence of immunoreactive calcitonin and calcitonin gene-related peptide in neuroendocrine cells of rat lungs

Neuroendocrine cells of the lung, occurring singly or in clusters known as neuroepithelial bodies, contain a variety of biologically active compounds, including several neuropeptides. We have investigated the localization of calcitonin and calcitonin gene-related peptide (CGRP) within single and grouped neuroendocrine cells in the respiratory epithelium of rats by an immunohistochemical double-staining technique which uses specific antisera raised in heterogeneous animal species. Calcitonin- and CGRP-immunoreactivities were nearly totally co-localized in both single neuroendocrine cells and neuroepithelial bodies. CGRP-immunoreactivity was also present in neurons in the jugular, nodose and dorsal root ganglia. The calcitonin-immunoreactivity in neuroendocrine cells, as in thyroid parafollicular (C) cells, was abolished by preincubation of the anti-calcitonin serum with synthetic calcitonin. The CGRP-immunoreactivity in neuroendocrine cells and in the neuronal cells was abolished by preincubation of anti-CGRP serum with synthetic CGRP. Thus, while the calcitonin gene is expressed exclusively or predominantly as either calcitonin or CGRP in all other tissues except thyroid C-cells, our results strongly suggest that both peptides are expressed in the rat bronchopulmonary neuroendocrine cells.

Pulmonary calcitonin gene-related peptide immunoreactivity: nerve-endocrine cell interrelationships

Respiratory epithelium has been reported to be supplied with sensory nerves and to contain irritant and other receptors. In this immunohistochemical study, we examined the incidence, morphology, and distribution of calcitonin gene-related peptide (CGRP) immunoreactivity in epithelial cells the rat respiratory tract, using peroxidase anti-peroxidase (PAP) techniques. CGRP immunoreactivity was localized in capsaicin-sensitive nerve fibers and in capsaicin-nonsensitive endocrine cells occurring singly or in groups. These CGRP-immunoreactive structures reached close to or actually touched the airway lumen, were widely and abundantly present in the respiratory epithelium, and were arranged in distinct and characteristic patterns. CGRP-immunoreactive nerves innervated not only grouped cells but also single cells, and the innervation of these cells differed depending on whether they were in extrapulmonary or intrapulmonary epithelium. The specificity of the immunoreactivity was confirmed by absorption tests that excluded cross-reactivity with other peptides. The results suggest that epithelial nerve fibers and endocrine-like cells exhibiting CGRP immunoreactivity form a morphologic, and probably also a functional, complex throughout the respiratory epithelium. CGRP innervation may be related to receptor functions of respiratory epithelium.

Topographic intermingling of striatonigral and striatopallidal neurons in the rhesus monkey

The topography and interrelationship of striatofugal neurons have been examined using a double retrograde tracing paradigm to label striatopallidal and striatonigral neurons in the same neostriatum. The rostral globus pallidus and the rostral substantia nigra in the same hemisphere were injected simultaneously with fluorescent tracers in three monkeys. In addition, the caudal globus pallidus and the caudal substantia nigra were injected separately in a fourth and fifth monkey with a fluorescent dye and wheat germ agglutinin-horseradish peroxidase (WGA-HRP), respectively. Digitized plots of fluorescent dye-labeled neurons revealed that large numbers of striatonigral projection neurons lie within both neostriatal nuclei, i.e., the caudate and putamen. Similarly, neurons innervating the globus pallidus were found in both caudate and putamen. The distribution of retrogradely labeled neurons observed was consistent with the topography of striatofugal projections that has been described previously, i.e., the rostrocaudal and mediolateral axes of the neostriatum are preserved in the striatopallidal and striatonigral projections (e.g., Szabo, '62, '67, '70, '72) and the dorsoventral axis is inverted in the projection of the neostriatum onto the nigra but not in the striatopallidal projection (Nauta and Domesick, '79; Gerfen, '85). Analysis of cases in which striatonigral and striatopallidal neurons were present in large numbers within the same region of the neostriatum disclosed that the two populations are intermingled such that small clusters of striatopallidal neurons are surrounded by striatonigral neurons and vice versa. The clustered arrangement of striatofugal neurons observed in the fluorescent cases was unambiguous in a case in which HRP was injected into the caudal substantia nigra. In this case, both anterogradely labeled terminals and retrogradely labeled neurons exhibited a striking, compartmental-like distribution in the posterior putamen. Our observations indicate that the matrix compartment of the neostriatum is comprised of a patchwork of interposed clusters of nigral and pallidal efferent neurons. We hypothesize that these clusters of efferent neurons may direct interdigitated cortical inputs into distinct nigro- and pallido-thalamic pathways. In view of the parallel nature of processing throughout the basal ganglia, it appears that convergence of these segregated nigral and pallidal loops must occur at the cortical level where prefrontal and premotor targets of the basal ganglia are interconnected via corticocortical projections (Selemon and Goldman-Rakic, '88).

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.

Microspectrofluorimetric analysis of the formaldehyde-induced fluorophores of 5-hydroxytryptamine and dopamine in intrapulmonary neuroepithelial bodies after administration of L-5-hydroxytryptophan and L-dopa

To demonstrate the intracellular store of 5-hydroxytryptamine and dopamine in pulmonary neuroepithelial bodies of the neonatal rabbit after treatment with the corresponding amino-acid precursors L-5-hydroxytryptophan or L-3,4-dihydroxyphenylalanine, formaldehyde-induced fluorescence in combination with microspectrofluorimetric analysis has been used. Emission spectra and excitation spectra in an extended wavelength range from 240 to 460 nm, the displacement of excitation peaks after exposure to hydrochloric acid vapour, and calculation of peak ratio values 410/260, 380/320, 320/260 for phenylethylamine fluorophores and 385/315 for indolylethylamine fluorophores were performed. Thus, the presence of 5-hydroxytryptamine without occurrence of 5-hydroxytryptophan was demonstrated in pulmonary neuroepithelial bodies after administration of the corresponding biological precursor, while dopamine combined with 5-hydroxytryptamine were clearly revealed after administration of L-3,4-dihydroxyphenylalanine. The rate of photodecomposition always corroborated these findings.

Characterization of human pulmonary endocrine cells maintained in vitro

Endocrine cells located in the epithelium of human fetal airways contain the amine, 5-hydroxytryptamine (5HT), and the peptide, bombesin (BOM), but difficulties in studying these cells experimentally have slowed progress in understanding their functional roles. This investigation describes an in vitro method to maintain pulmonary neuroendocrine cells (PNEC) in organ culture. Bronchial trees from human fetal lungs were dissected free of adherent blood vessels and lung tissue. Explants of the airways were placed in culture dishes containing defined tissue culture medium for five days. Using indirect immunofluorescence, 5HT- and BOM-like immunoreactive cells were observed both in nonincubated airways and in explants maintained for five days in organ culture. The number of 5HT-immunoreactive cells/0.1 mm2 of airway epithelium was not significantly different in the two groups, although there was a significant reduction in 5HT content measured by HPLC after the five-day culture period. The diameter of dense core vesicles and the number of dense core vesicles/micron2 of endocrine cell cytoplasm in cultures were not significantly different from non-incubated controls. Treatment of the explants with the 5HT-synthesis inhibitor p-chlorophenylalanine resulted in a significant reduction both in the number of 5HT-containing cells/0.1 mm2 of airway epithelium and in the 5HT content. These results demonstrate that both 5HT and BOM content in endocrine cells of explants from human fetal airways can be well maintained in organ culture for at least 5 days and that they are responsive to pharmacologic inhibition of 5HT synthesis.

Morphologic and cytochemical characteristics of amine-containing globule leukocytes in rat tracheal epithelium

Amine-containing cells in the tracheal epithelium are typically of the small-granule type (diameter approximately 100 nm). However, in the rat, another amine-containing cell type has been identified that possesses the amine-handling features of the APUD-series of cells (amine precursor uptake and decarboxylation) but not the ultrastructural characteristics. It has been postulated that these cells may be related to cutaneous melanocytes. In this study, fluorescent cells were present in the laryngeal and tracheal epithelial lining of adult Sprague-Dawley rats following freeze-drying and exposure to formaldehyde vapor (FIF or formaldehyde-induced fluorescence). Microspectrofluorimetry revealed an emission maximum at 493 nm. The excitation maximum could not be calculated but appeared to be around or below 350 nm (to record spectra below requires the use of quartz optics). Yellow fluorescence also emanated from serotonin-containing mast cells (excitation and emission maxima: 401/515 nm). Tracheal segments processed according to the aqueous formaldehyde ( AFIF ) technique, for the demonstration of 5- hydroxytryptophan (5-HTP) or serotonin (5-HT), failed to identify fluorescent cells in the epithelial lining even though connective-tissue mast cells were evident. Subsequent treatment of AFIF -fixed sections with formaldehyde and HCl vapors ( AFIF -HCl) resulted in the formation of a fluorogenic compound within numerous cells in the tracheal lining (455/537 nm). This spectral shift and increase in intensity of fluorescence following acidification are characteristic for standards and/or cells that contain tryptamine, tryptophan, or peptides with NH2-terminal tryptophan and are markedly different from microspectrofluorimetric data reported for the phenylethylamines or serotonin. It is therefore postulated that these cells contain a closely related beta-(3-indolyl) ethylamine-like compound, serotonin excluded. The morphology of the fluorescent cells was similar when prepared according to the FIF or AFIF -HCl techniques. Conjunctive staining, the examination of a single section first by fluorescence microscopy and subsequently by other histochemical and cytochemical methods, demonstrated that the fluorescent granules were also methylene blue, alcian blue, periodic-acid Schiff, and ferric- fericyanide positive. Subsequent correlative electron microscopic examination of Epon-embedded AFIF -HCl-treated tracheal sections demonstrated that these amine-containing cells were globule leukocytes.

A correlative light-, fluorescence- and electron-microscopic study of neuroepithelial bodies in the lung of the red-eared turtle, Pseudemys scripta elegans

Neuroepithelial bodies (NEB) were identified for the first time in the respiratory tract of a reptile by the use of combined morphological and histochemical methods. In the red-eared turtle, Pseudemys scripta elegans, NEB were found within the trabecular epithelium of the respiratory tract, mainly in the branching regions of the trabeculae. An intracellular formaldehyde-induced fluorescent compound was identified as 5-hydroxytryptamine (5-HT) by means of microspectrofluorometry. Subsequent histochemical staining of the same fluorescent sections showed the 5-HT-containing cells to be argentaffin. In electron micrographs cell clusters characterized by the presence of distinctive cytoplasmic, membrane-bounded dense granules (+/- 100 nm) were observed, correlating with the distribution of the yellow-fluorescent epithelial cells. The granules of the NEB are positive when the argentaffin technique is performed directly on ultrathin sections. Cells of the NEB extend into the lumen of the airway via apical microvilli and a single modified cilium displaying a 9 X 2 + 0 or 8 X 2 + 2 microtubular pattern. Unmyelinated axons containing mostly small, clear vesicles were seen in close association with NEB cells, often forming synaptic junctions. Occasionally, axons containing a few small dense-cored vesicles were found. The relationship between NEB cells and capillaries, the images of emiocytotic granule release and the occurrence of synaptic contacts between axons and granule-containing cells are indicative of endocrine secretion. These features and the presence of intracytoplasmic granules containing 5-HT may justify the inclusion of NEB-cells of the turtle lung into the diffuse neuroendocrine system. Furthermore, structurally these cells appear to represent sensory elements capable of an intrapulmonary receptor-secretory function.

Dynamics of the neuroendocrine cell--regulatory peptide system in the lung. Specific overview and new results

We assessed the changes in argyrophil neuroendocrine (NE) cell numbers, intensity of 5-HT fluorescence, and arterial medial thickness in the lungs of neonatal rabbits under various oxygen treatments. NE cell numbers and 5-HT fluorescence in normoxic rabbits increased from 12 hr before to 1 day after birth, and NE cells declined thereafter to the 10th day. In acute hypoxic (520 mm Hg for 2-2.5 hr) 5-day-old rabbits, 5-HT fluorescence was decreased, whereas NE cell numbers and medial thickness were unchanged. Neonates hypoxic from birth had higher NE cell numbers and increased medial thickness at 3 and 5 days, whereas 5-HT fluorescence was decreased compared with that in normoxic controls. These chronically hypoxic neonates showed a dramatic drop in argyrophil NE cell numbers to below normal when they were exposed to normoxia for 1 hr, but cell numbers and medial thickness returned to normal at 4 and 24 hr, respectively. We also tested the effect of acute and chronic hyperoxia: 100% O2 for 2-2.5 hr caused a significant drop in detectable NE cell numbers, whereas 40% O2 in N2 caused no change; chronic 40% O2 in N2 caused a fivefold increase in argyrophil NE cells by day 5, and medial thickness was below normal; 5-HT fluorescence decreased in acute 100% and chronic 40% hyperoxia and was elevated in acute 40% O2.

Morphological and cytochemical characterization of neuroepithelial bodies in fetal rabbit lung. I. Studies of isolated neuroepithelial bodies

Neuroepithelial bodies (NEB) in 29-day fetal rabbit lung were examined by light microscopy and cytochemistry to demonstrate their structural and biochemical properties in situ. Longitudinal sections of NEB at airway bifurcations demonstrated their chemoreceptor-like appearance. Furthermore, the cytochemical presence of serotonin, acetylcholinesterase, formaldehyde-induced fluorescence, and silver-staining properties demonstrated the neural-like biochemical properties of NEB cells. Forty-one NEB and eight single neuroendocrine cells from whole fetal lungs were examined ultrastructurally. Juxtaluminal junctional complexes composed of tight and intermediate junctions, desmosomes, and cytoplasmic filaments were demonstrated in the corpuscular-shaped NEB. Basal bodies were apparent in NEB cell cytoplasm; cilia extended from NEB cells. Dense-core vesicles (DCV) were of at least three types: type 1, type 2, and enterochromaffin type. The majority of epithelial cells adjacent to NEB in near-term airway epithelium were undifferentiated, with large amounts of glycogen. However, ciliated cells were adjacent to some small NEB and single neuroendocrine cells; mucus or Clara-type cells were not observed. NEB isolated by collagenase treatment revealed an intact organoid structure, DCV, and desmosomes and retained their argyrophilia and formaldehyde-induced fluorescence. NEB were recovered in cell fractions separated by unit gravity that had cells in clumps of four or more. One to five NEB stained with silver in cytocentrifuge preparations of control, mixed cells, whereas up to 20 intact NEB were demonstrated in the clump-containing, separated fractions. We propose that isolated NEB retain certain biochemical and metabolic properties similar to those of their counterparts in situ. Serotonin and 5-hydroxyindole acetic acid were found by high-performance liquid chromatography analysis in the fractions containing NEB, and amine precursor uptake and decarboxylation (APUD) activity were demonstrated. Moreover, muscarinic cholinergic receptors were detected, consistent with the occurrence of acetylcholinesterase in NEB. The elution profile of bombesin radioimmunoactivity substantiated that isolated fetal rabbit NEB contained this neuropeptide and that NEB were enriched by unit gravity sedimentation. These studies suggest that NEB are structurally and functionally developed before other cell types in immature airway epithelium and can be isolated as intact organoids, which retain some of their structural and metabolic integrity.

Small-granule (neuro)endocrine cells in the infracardiac lobe of a hamster lung. Number, subtypes, and distribution

Small-granule APUD (amine precursor uptake and decarboxylation) endocrine cells were surveyed in 600 3 microns glycol methacrylate-embedded, periodic acid-Schiff (PAS)-lead hematoxylin-stained serial sections comprising 95% of the infracardiac lobe of a hamster lung. Results were confirmed by less systematic study of other hamster lungs. Positions of endocrine cells were marked on cardboard profiles of bronchi and bronchioles for assembly into a 70 X enlarged three-dimensional model from which size and branching of the airway were determined. Records were made for computer analysis of the number and staining patterns of endocrine cells, the nature of contiguous epithelial cells, and the presence of underlying smooth muscle and blood and lymph vessels. APUD cells occurred in 95% of all airways, at a mean density of six solitary cells and 10 cell clusters (neuroepithelial bodies) per millimeter of airway length, measured along the bronchial-bronchiolar long axis. Nineteen percent of endocrine cell loci (29% of all cells) were found at bronchioloalveolar portals in all regions of peripheral lung. Twenty percent of loci (28% of all cells) occurred about the origins of lateral airway branches; these included 4% of loci on carinal points of bifurcation. Two groups of APUD cells had distinctive anatomic relationships: 1) 13% of loci (20% of cells) were related to pulmonary capillaries and venules, mainly at bronchioloalveolar portals; and 2) 39% of loci (53% of cells) overlaid peribronchial muscle, mainly in larger airways where changes in diameter might affect ventilation. In this lobe, APUD cells were not related to goblet or mast cells; 74% of loci abutted Clara and/or ciliated cells, 17% great alveolar cells. Few loci were associated with pulmonary arteries and veins. Five APUD cell types were identified by PAS-lead hematoxylin staining. Types I, II, and V, with granules approximately 0.2 micron in diameter, made up 38%, 45%, and 2% of cells, respectively. Types III and IV, 10% and 5% of cells, respectively, had larger granules. Types I, II, III, and V occurred as solitary cells as well as in neuroepithelial bodies. One-third of the neuroepithelial bodies contained a single cell type; the rest were mixed. Type IV cells, with coarse lead hematoxylin-positive granules, usually were found in large neuroepithelial bodies containing two to four cell types and were never seen occurring alone. We conclude that 1) hamster lungs contain different kinds of APUD cells; 2) those likely have a variety of functions; 3) distinctions merely between solitary and clustered cells may not be significant; 4) the histophysiology of many neuroepithelial bodies probably is more complex than previously suspected; and 5) PAS-lead hematoxylin is superior to argyrophilia and amine fluorescence for light microscopic counting and analysis of pulmonary APUD cells in this species.

Immunohistochemical localization of serotonin in intrapulmonary neuro-epithelial bodies

A recently developed immunohistochemical technique for serotonin (Steinbusch et al. 1978) was used in the present investigation to study the occurrence of this indoleamine in the granulated epithelial cells of neuro-epithelial bodies (NEB). Lungs from neonatal rabbits and pigs exhibit immunoreactive cell groups identical in morphology and their preferential location (i.e., at bronchiolar bifurcations) to the recently described intrapulmonary NEB. Moreover, in the trachea and lung of rabbits isolated immunoreactive cells, presumably of Kultschitsky type, were found in the lining respiratory mucosa. Such single cells were also frequently observed in the bronchial epithelium of pig lungs. It is concluded that the corpuscular cells, being modulated by the central nervous system, probably represent intrapulmonary neuro(chemo-)receptors with local secretory activities, one of the substances released being serotonin and reacting to the oxygen composition of the inhaled air. It is proposed that the cells of Kultschitsky type exert a more local effect upon the airways.

The effects of carbon monoxide and hypoxic hypoxia on amine-containing cells in the tracheal epithelium of young rabbits

Endogenously fluorescent, singly occurring amine-containing cells in tracheal epithelium were examined in 3-, 10-, and 28-day-old rabbits. These cells are pyramidal in shape with the apex projected toward the tracheal lumen. The cytoplasm exhibits a yellow fluorescence which is predominantly supranuclear. Occasional, infranuclear, fluorescent cytoplasmic processes project from the cells. The numbers of fluorescent cells per unit length of trachea increase with age. Acute exposure of 10-day-old rabbits to 13% O2 decreases the number of detectable fluorescent cells in the tracheal compared to controls exposed to room air. Similarly, exposure to 750 ppm carbon monoxide decreases the number of fluorescent epithelial cells appearing in tracheas of 10- and 28-day-old rabbits. These results suggest that the amine-containing epithelial cells of the trachea respond to tissue hypoxia and that decreased airway pO2 is not necessary to elicit a response.