Fluorescence and electron microscopy of amine-storing enterochromaffin-like cells in tracheal epithelium of mouse

CXCL13 is expressed in a subpopulation of neuroendocrine cells in the murine trachea and lung

The conducting airways are lined by distinct cell types, comprising basal, secretory, ciliated, and rare cells, including ionocytes, solitary cholinergic chemosensory cells, and solitary and clustered (neuroepithelial bodies) neuroendocrine cells. Airway neuroendocrine cells are in clinical focus since they can give rise to small cell lung cancer. They have been implicated in diverse functions including mechanosensation, chemosensation, and regeneration, and were recently identified as regulators of type 2 immune responses via the release of the neuropeptide calcitonin gene-related peptide (CGRP). We here assessed the expression of the chemokine CXCL13 (B cell attracting chemokine) by these cells by RT-PCR, in silico analysis of publicly available sequencing data sets, immunohistochemistry, and immuno-electron microscopy. We identify a phenotype of neuroendocrine cells in the naïve mouse, producing the chemokine CXCL13 predominantly in solitary neuroendocrine cells of the tracheal epithelium (approx. 70% CXCL13⁺) and, to a lesser extent, in the solitary neuroendocrine cells and neuroepithelial bodies of the intrapulmonary bronchial epithelium (< 10% CXCL13⁺). In silico analysis of published sequencing data of murine tracheal epithelial cells was consistent with the results obtained by immunohistochemistry as it revealed that neuroendocrine cells are the major source of Cxcl13-mRNA, which was expressed by 68–79% of neuroendocrine cells. An unbiased scRNA-seq data analysis of overall gene expression did not yield subclusters of neuroendocrine cells. Our observation demonstrates phenotypic heterogeneity of airway neuroendocrine cells and points towards a putative immunoregulatory role of these cells in bronchial-associated lymphoid tissue formation and B cell homeostasis.

Morphological characterization of brush cells in the rat trachea

Brush cells have recently been classified as solitary chemosensory cells. However, tracheal brush cells have not been morphologically and immunohistochemically characterized yet. In the present study, the morphological and immunohistochemical characteristics of tracheal brush cells were analyzed using immunohistochemistry and scanning, and transmission electron microscopies. Brush cells in the tracheal epithelium were barrel-like or columnar in shape and were immunoreactive for villin. Scanning and transmission electron microscopies revealed densely arranged thick microvilli on the apical surface of tracheal brush cells and tubular membranous elements and/or vesicular formations in the supranuclear region. A morphometrical analysis of tracheal whole-mount preparations showed that the density of brush cells was greater in the cranial third and the mucosa on the annular ligament. Double immunofluorescence revealed that the morphology of villin-immunoreactive brush cells was distinct from other non-ciliated cells in the tracheal epithelium, i.e., MUC5AC-immunoreactive mucous cells, SNAP25-immunoreactive neuroendocrine cells, and GNAT3-immunoreactive solitary chemosensory cells. On the other hand, tracheal brush cells were immunoreactive for the marker proteins for intestinal brush cells, CK18, DCLK1, and Cox1; however, these antibodies also recognized cells other than brush cells. Furthermore, immunoreactivity for PKD2L1, a cation channel subunit, was detected in brush cells. The present results demonstrated that tracheal brush cells are independent cell types. These brush cells may be activated by acid and the secretion of prostaglandins. In conclusion, the present study revealed that tracheal brush cells are independent cell types based on the morphological and immunohistochemical characteristics.

Presence of paraneuronal pseudobranchial neurosecretory system in the gill region of two air-breathing clupeids, Notopterus chitala and Notopterus notopterus

The pseudobranchial neurosecretory system (PNS) is a system of neurosecretion observed in certain groups of teleosts, which are air-breathing or known to tolerate low oxygen tension in the surrounding water. Like other neuroendocrine cells of gill, cells belonging to this system have also been observed to have a role in condition of hypoxia. Uniformly found in all catfish species, the system was reported to be present in few non-catfish groups also, viz.-Atheriniformes, Channiformes (Devi, 1987), Perciformes, and Clupeiformes (Srivastava et al., 1981; Gopesh, 1983). In an attempt to study the structure and organization of the pseudobranchial neurosecretory system in non-catfish species of teleost, present investigation was undertaken in two species of Notopterus, viz. Notopterus chitala and Notopterus notopterus. The histological observations, using neurosecretion specific stains, undertaken on two clupeids are reported and the findings are discussed in the light of association of PNS with Carotid gland-a structure of intermediate stage in the process of transformation of pseudobranch into the carotid labyrinth, in course of evolution and also the air-breathing habit of the fish.

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.

Long-term safety of proton pump inhibitors: risks of gastric neoplasia and infections

After Helicobacter pylori eradication was introduced and largely eliminated the need for maintenance therapy for peptic ulcer disease, gastroesophageal reflux disease (GERD) became the main indication for prolonged gastric acid inhibition. The drug effect on GERD depends on the degree of acid inhibition, thus the efficacious proton pump inhibitors are preferred. The proton pump inhibitors have few immediate side effects, the main concern being the profound hypoacidity and hypergastrinaemia they induce. In short-term, hypergastrinaemia causes rebound hyperacidity, possibly worsening GERD and reducing the efficacy of histamine H(2) blockers. In the long-term, hypergastrinaemia causes enterochromaffin-like cell hyperplasia and carcinoids. Since enterochromaffin-like cells may be important in gastric carcinogenesis, iatrogenic hypergastrinaemia may predispose to carcinoma. Gastric hypoacidity also increases gut bacterial infections, and the barrier function of acid against viral and prion infections requires further assessment.

Personal review: is profound acid inhibition safe?

Inhibitors of gastric acid secretion, particular proton pump inhibitors, are effective drugs in the treatment and prophylaxis of acid-related diseases. Proton pump inhibitors are therefore prescribed widely, often for minor complaints. Gastric acidity kills swallowed microorganisms, and acid secretion must be of biological importance because it is maintained in phylogenesis. Acid secretion is controlled by feedback mechanisms, mainly via gastrin. A decrease in acidity always causes an increase in plasma gastrin. The trophic effect of gastrin leads to hyperplasia and neoplasia of the enterochromaffin-like (ECL) cell. ECL cell derived tumours in man were previously regarded as rare, and also as rather benign. It is now clear that the ECL cell gives rise to a significant proportion of gastric carcinomas. Moreover, ECL cell carcinoids secondary to hypergastrinaemia may develop into highly malignant tumours. Treatment with a proton pump inhibitor is followed by rebound acid hypersecretion and decreased efficiency of H2-blockers, thus such treatment may induce a type of physical dependence. It is therefore reasonable to be cautious and not to treat younger (< 50 years) patients for long periods of time with profound inhibitors of gastric acid secretion. Chromogranin A in the blood is a sensitive marker of the ECL cell mass, and it could be used to survey patients on long-term proton pump inhibitors.

Neuroepithelial bodies and solitary neuroendocrine cells in the lungs of amphibia

In the lungs of 12 species of Amphibia investigated so far, solitary neuroendocrine (NE) cells, as well as groups of these cells called "neuroepithelial bodies" (NEB), are observed. They occur in the position strategic to monitoring gas composition, mainly in the ciliated epithelium of the apical part of the septa. A great diversity in the structure of NEB is observed. The NE cells and NEB in Amphibia are predominantly of the "closed type," separated from the air space by a thin cytoplasmic layer of ciliated cells, goblet cells or pneumocytes. In two species, Bufo marinus and Ambystoma tigrinum, the "open type" of NEB occur, where NEB communicate with the air space, by apical cells in Bufo and type II NE cells in Ambystoma. Both types of cells possess single atypical cilia with an 8+1 microtubule arrangement and microvilli on the free surface. Single and grouped NE cells are characterized by small dense core vesicles (DCV) dispersed in the cytoplasm. In Salamandra and Ambystoma the second type of NE cells with large DCV are observed. The DCV represent sites of storage of serotonin and several neuropeptides. The basal parts of NEB and of some solitary cells are invested by the intraepithelial sensory nerve terminals, both afferent and efferent morphologically. In the lungs of Amphibia, similarly to other vertebrates, NE cells, which act as endocrine/paracrine receptors, form epithelial endocrine systems.

Comparative histology of pulmonary neuroendocrine cell system in mammalian lungs

It is increasingly recognized that neuroepithelial endocrine cells and organoid clusters of these cells termed neuroepithelial bodies are widely distributed in the respiratory tract of vertebrates. This review focuses on the neuroepithelial endocrine system in the airway epithelium of mammals according to observations made in a wide range of species, as it appears in light and electron microscopy by means of various visualization techniques under normal and experimental conditions. Because there are similarities but also marked differences between species, wherever possible studies in human airways are emphasized. Conventional histochemical and ultrastructural studies including microspectrofluorimetry have demonstrated the amine-handling properties and the presence of neurosecretory granules in neuroendocrine cells of the epithelium of all mammals studies so far. The neuroepithelial bodies are innervated by morphological afferent- and efferentlike synaptic specializations. These, together with the presence of reciprocal synapses, emphasize that these cells may be involved in dual functions of chemoreception and secretion. Light and electron microscopic immunohistochemistry has demonstrated that neuroepithelial endocrine cells may contain various biogenic agents, suggesting that the neuroendocrine system is highly heterogeneous. Neural elements may interact in a complex manner, and the activation of certain neural pathways may control the release of biogenic substances to influence physiological airway functions. They may be particularly relevant in pulmonary diseases. Consequently, the function of this system is complex and it is highly probable that many of its aspects are still not elucidated.

Long-term effects of inhaled nicotine

Tobacco smoking has been reported to be associated with increased risk of cardiovascular disease and cancer, particularly of the lungs. In spite of extensive research on the health effects of tobacco smoking, the substances in tobacco smoke exerting these negative health effects are not completely known. Nicotine is the substance giving the subjective pleasure of smoking as well as inducing addiction. For the first time we report the effect on the rat of long-term (two years) inhalation of nicotine. The rats breathed in a chamber with nicotine at a concentration giving twice the plasma concentration found in heavy smokers. Nicotine was given for 20 h a day, five days a week during a two-year period. We could not find any increase in mortality, in atherosclerosis or frequency of tumors in these rats compared with controls. Particularly, there was no microscopic or macroscopic lung tumors nor any increase in pulmonary neuroendocrine cells. Throughout the study, however, the body weight of the nicotine exposed rats was reduced as compared with controls. In conclusion, our study does not indicate any harmful effect of nicotine when given in its pure form by inhalation.

Calcitonin, CGRP and helodermin in endocrine cells of the developing rat lung

Calcitonin gene-related peptide (CGRP), calcitonin and immunoreactive helodermin occur in endocrine cells in the murine airways. In the lungs these cells form clusters, while they occur scattered in the larynx and trachea. In the present study of the developing rat CGRP-immunoreactive cells were more numerous at all stages than the calcitonin- and helodermin-containing ones. A subpopulation of the CGRP-containing cells contained either calcitonin or helodermin. Immunocytochemistry revealed a higher density of CGRP-containing endocrine cells in the lungs of fetal and newborn rats than in the lungs of older rats, while the density of calcitonin-containing cells was largely unchanged. The helodermin-containing cells were few at all developmental stages examined. The concentration and content of CGRP were highest in newborn rats; the levels decreased postnatally. The calcitonin concentration did not change during development while the content increased with age. The concentration and content of helodermin increased with age.

Ontogeny of endocrine cells in the respiratory system of Syrian golden hamsters. I. Larynx and trachea

The ontogeny of protein gene product 9.5 (PGP 9.5), serotonin (5-HT), calcitonin gene-related peptide (CGRP), and calcitonin (CT) immunoreactivity was evaluated in small-granule endocrine cells of hamster laryngotracheal epithelium from fetal day 11 to adulthood. Two centrifugal (proximal-to-distal) patterns of differentiation occur. The first pattern begins during fetal life. Endocrine cells, single and clustered in groups (presumptive- or protoneuroepithelial bodies, pNEBs), initially colocalize immunostaining for PGP 9.5, 5-HT, and CGRP in the larynx and proximal 2/3 of the trachea on day 12 and spread to the caudal trachea on day 13. 5-HT disappears fleetingly during the 24 h preceding birth; otherwise immunoreactivity for all three substances persists into adulthood. The clusters of endocrine cells survive beyond birth but are so diluted by expansion of the nonendocrine epithelium as to become inconspicuous. Since innervation was not actually observed, these clusters may persist as pNEBs, without developing connections to afferent or efferent nerve fibers. The second pattern concerns single small-granule cells stainable for CGRP but not for 5-HT. These cells first appear in the larynx and cartilaginous part of the cranial trachea on postnatal day 3, and in the middle and caudal trachea, on day 5. The cells increase in number on day 7. In adults, they predominate among endocrine cells of the cartilaginous region. A subset of these cells begins to co-express CT proximally on postnatal day 10, reaching the caudal end of the trachea by 3 weeks. A few elements of the older 5-HT-positive population may also become immunoreactive for CT in juvenile hamsters.

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.

Ultrastructure and immunocytochemistry of the neuroepithelial bodies in the lung of the tiger salamander, Ambystoma tigrinum (Urodela, Amphibia)

Light and electron microscopy of the lungs of Ambystoma tigrinum (Urodela) revealed a relatively complex pattern of the neuroendocrine (NE) cells. In the apical parts of smaller septa single NE cells not associated with nerve fibres were covered and surrounded by pneumocytes. The larger septa possessed small areas of ciliated epithelium, in which the NE cells were grouped in a form of neuroepithelial bodies (NEB) consisting of 3-5 cells and covered by goblet cells. NE cells possessed a large nucleus with patches of condensed chromatin, clear cytoplasm, and membrane-bound vesicles of variable morphology and size, containing an electron dense interior surrounded by a lucent space. The size of these dense core vesicles (DCV) ranged from 70-140 nm, while rarely the larger ones exhibited a diameter of 300-600 nm. In some NEB a second type of NE cells was observed for the first time in an amphibian species: these cells communicated with the air space and exhibited on their surface microvilli and a single modified cilium with a 8 + 1 microtubule arrangement. Their cytoplasm contained two types of DCV: dense core granules with a diameter of 140-260 nm and vesicles 320-700 nm in diameter with a moderately electron dense interior. The NEB were associated with intracorpuscular, sensory nerve terminals morphologically afferent and efferent. By immunocytochemistry, the NE cells revealed the presence of serotonin, met-enkephalin, and leu-enkephalin. A paracrine and chemoreceptor role is proposed for NEB of Ambystoma tigrinum.

The neuroepithelial cells of the fish gill filament: indolamine-immunocytochemistry and innervation

The neuroepithelial cells (NECs) of the fish gill filament share several morphofunctional features with the cells of the neuroepithelial bodies in the lungs of air-breathing vertebrates. In the present study, a detailed indolamine-immunocytochemical analysis of the branchial neuroepithelial cells and nerves was undertaken in non-teleost and teleost species, with particular emphasis on the latter. In the rainbow trout, Oncorhynchus mykiss, the chemical degeneration of either catecholaminergic (by 5- and 6-hydroxydopamines) or indolaminergic (by 5,6-dihydroxy-tryptamine) innervations associated with the NECs was studied using electron microscopy. In teleosts, the NECs are located primarily on the distal half of the filament. In the trout particularly, these cells are innervated mainly by non-indolaminergic nerves taking up sympathetic neurotoxins. The proximal half of the filament contains isolated NECs innervated additionally by intrinsic indolaminergic neurons. Serotonin-like immunoreactivity of the NECs is evident in the granular vesicles packed within the basal soma and processes which surround non-vascular and vascular smooth muscles in the filament. Apical processes from the neuroepithelial cells occasionally contact the water on the surface of the filament epithelium. The secretory function of the NECs is discussed with reference to the probable involvement of serotonin in the modulation of fish gill function. In addition, their connections with both central and branchial nervous systems suggest a possible chemoreceptor role.

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.

Chemical coding of endocrine cells of the airways: presence of helodermin-like peptides

The epithelium of the airways is rich in endocrine cells containing serotonin and/or a wide variety of regulatory peptides. These cells usually occur in clusters in the lungs but are also found scattered in the larynx and trachea. In the present study, endocrine cells in the airways of mouse, rat, hamster, guinea pig, pig, sheep and squirrel monkey were examined for the presence of serotonin, helodermin-like peptides and other regulatory peptides using immunocytochemistry and radioimmunoassay. In addition, we looked for the protein gene product 9.5 (PGP), which occurs in many peptide hormone-producing endocrine cells in the body. Both clustered and scattered endocrine cells in the airways were found to display coexistence of serotonin and peptides, such as a helodermin-like peptide, calcitonin and calcitonin gene-related peptide (CGRP). The PGP-immunoreactive cells were numerous and included elements containing serotonin and/or regulatory peptides. An additional PGP-immunoreactive endocrine cell population lacked serotonin and regulatory peptides. Helodermin-immunoreactive material was demonstrated in endocrine cells of the airways in the mouse and hamster but not in any of the other species studied. Serotonin was an endocrine cell constituent in all the species studied. Calcitonin and CGRP could be demonstrated by immunocytochemistry in the mouse, rat, and hamster, but not in the guinea pig, sheep, pig and monkey.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroendocrine (NE) cells in rat neonatal lungs. A histochemical and immunocytochemical study

A study has been carried out to determine the presence of NE cells in the newborn rat lung. The localization of these cell was achieved by an argyrophil method. Both single NE and NEB, were found. Immunoperoxidase techniques were performed to determine NSE, serotonin and calcitonin production in these NE formations.

Ultrastructural architecture of pulmonary small-granule cell clusters in adult Syrian golden hamster

Throughout the epithelial lining of the respiratory system is a class of cells with characteristics similar to Amine Precursor Uptake and Decarboxylation (APUD) polypeptide hormone-producing cells. In the intrapulmonary airways, these small-granule cells (SGCs) occur either singly or in organized clusters. Although no specific peptide has yet been identified, subclasses have been postulated based on granule geometry or light microscopic staining. The present study characterizes the architectonic and cellular organization of clustered SGCs in the adult Syrian golden hamster. Two morphologically distinct cells can be defined in such clusters, "light" and "dark." Thid distinction was based primarily on differences in the electron density of the cytoplasmic matrix rather than on the remarkable variations in cellular organelles or dense-core secretory vesicles. Both cell types were normal as judged by uniform spherical nuclei, chromatin organization, and distribution of cellular organelles. The "dark" cells, however, presented the profile of a cell actively involved in synthesis with a markedly dilated perinuclear cisterna and endoplasmic reticulum. Additionally, the "dark" cells contained membrane-delimited structures containing concentric membranous whorls, clear vacuoles, and lipofuscin granules. Occasionally, cells were observed to contain features of both cell types, suggesting that they may represent a continuum of common cell lineage. Accordingly, in the absence of additional morphologic or biochemical data, the "light" and "dark" cells most probably correspond to different stages of functional activity or age-related changes of a single type of cell. Unmyelinated nerve endings were occasionally interposed between cells, but synaptic specializations were not observed. Beneath the clusters, nerve fibers were also present, but they were never observed to penetrate the basal lamina or contact any of the SGCs. Of equal occurrence were elements of the vascular system and smooth muscle, suggesting that some SGCs in the adult hamster may function in a paracrine or endocrine manner. Such knowledge is essential to any study attempting to delineate the functional role or roles of these enigmatic organoids.

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.

Application of Grimelius argyrophil staining to the study of tumour ultrastructure. I. Effects of fixatives

Two methods have so far been proposed for staining samples by the argyrophil technique of Grimelius for electron microscopy. For Håkanson glutaraldehyde prevented argyrophilia, so the author stained sections from samples previously fixed by double formaldehyde/osmium tetroxide treatment and embedding. Vassallo used en bloc staining after fixation with glutaraldehyde-formaldehyde mixtures. We examined each factor which could directly interfere in argyrophil staining en bloc and on section. In the present experiment we compared effects of fixatives after staining en bloc. Glutaraldehyde prevented argyrophilia in 1 case out of 15, that of A-like cells in the oxyntic gland of the rat positivity was maintained in EC-like cells of this gland and adrenalin cells of the adrenal gland contrary to the previous description.

Scanning electron microscopy of isolated epithelium of the murine gastrointestinal tract: morphology of the basal surface and evidence for paracrinelike cells

By using the method of Bjerknes and Cheng, isolated murine gastrointestinal epithelial sheets were prepared for scanning electron microscopy. Examination of isolated epithelium from fundic stomach revealed numerous branched gastric glands. Parietal cells were easily detected bulging from the basal surface of the glandular epithelium. The basal surface membrane of parietal cells appeared smooth, with only sparse microvilluslike projections, whereas adjacent glandular cells had numerous 1- to 2-micron fingerlike projections which interdigitated laterally with similar processes from adjacent cells. Occasionally, paracrinelike cells having long cytoplasmic processes ranging from 10 to 20 micron in length were observed on the basal epithelial surface of the stomach and the colon, but not the small intestine. In isolated intestinal epithelia, the basal surface of crypt epithelial cells showed extensive cytoplasmic interdigitations, but no distinct morphology permitting recognition of individual cell types. Various stages of intestinal crypt bifurcation were seen. Craterlike spaces in the basal surface of crypt epithelium, presumably due to migrating leukocytes, were also numerous. Examination of the luminal surface of the isolated intestinal epithelium revealed that intimate associations between epithelium and mucosal-associated microorganisms were maintained, thus suggesting that minimal alterations in surface morphology were incurred by epithelial isolation. These observations on epithelial structure suggest that isolated gastrointestinal epithelia may be well suited for physiological studies of epithelial function and interactions with the microbial flora.

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.

Development of neuroepithelial bodies in intact and cultured lungs of fetal rats

Intact, 14- to 21-day fetal rat lung pairs, neonatal lungs, and cultured 15- and 16-day lung explants were examined in 2-micron-thick glycol methacrylate sections stained by PAS-lead hematoxylin. Selected stages were also studied in histochemical preparations for aliesterase and formaldehyde-induced monoamine fluorescence, as well as by scanning and transmission electron microscopy. Neuroepithelial bodies (NEBs) first appear in pseudoglandular lungs at 15 days in vivo as pyramidal groups of basal, diffusely lead-hematoxylin-positive cells in glycogen-depleted epithelium of main and lobar bronchi. By day 16, primitive NEBs occur within three to four generations of the terminal buds, and older, proximal bodies are larger and more distinctive than at 15 days. Aliesterase activity is first detected in basally located, developing NEBs on day 16. During the canalicular and alveolar sac periods, NEBs appear and mature on a proximal-to-distal gradient along the airway, as they do in developing rabbit and human lungs. As earlier-formed airways elongate, additional NEBs appear and supplement the population already present. By days 20-21, NEBs occur at all airway levels down to the bronchiolo-alveolar junctions, and many of the cells have discrete PAS- and lead-hematoxylin-positive, infranuclear granules. Near term some NEBs exhibit serotonin fluorescence after incubation in 5-hydroxytryptophan and have abundant, ca. 100-nm, electron-dense granules. These are concentrated toward the cell base like the stained granules visualized by light microscopy. Similar results were obtained from lungs placed in organ culture. From 2 days in culture to a time equivalent to term, NEB formation parallels that in vivo, indicating that developmental requirements are met in in vitro. Taken altogether, morphologic and cytochemical evidence suggests that NEBs of rats are functional in late fetal life and that their development is relatively independent of extrapulmonary influences and of the intraepithelial ingrowth of sensory nerve endings.

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.

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.

Neuroendocrine cells of the lung. An overview of morphologic characteristics and development

The detailed morphology of pulmonary neuroendocrine (NE) cells has been defined only during the last decade. The purpose of this paper is to review the main morphologic features of the NE cells, to review the methods and techniques used for their identification, and to discuss the development and functional significance of these cells. The main emphasis is on NE cells in human lung, but where appropriate, studies in animal lungs are also included. NE cells are present in the airway epithelium of human and various animal species and occur singly as well as in clusters called neuroepithelial bodies (NEB). The general cytochemical features (common to both single NE cells and NEB) include cytoplasmic argyrophilia, fluorogenic amine content, positive staining with lead-hematoxylin, and masked metachromasia. These staining properties are similar to those found in APUD cells scattered in various tissues. More specific cell markers are immunoreactivity to peptide hormones (bombesin, calcitonin, leu-enkephalin) identified so far in NE cells of human lung, and immunoreactivity to serotonin found in both human and animal lungs. At the ultrastructural level, NE cells are characterized by the presence of cytoplasmic dense core granules (90-150 nm in diameter), which are considered the storage site of amine and peptide hormones. The distinctive feature of NEB, not found with single NE cells, is the presence of nonmyelinated nerve endings in contact with granulated cells, and positive staining for acetylcholinesterase. The single NE cells are scattered throughout the tracheobronchial epithelium, whereas NEB are found only within the intrapulmonary airways. In postnatal lungs, both the single NE cells and NEB appear concentrated in small peripheral airways. In developing human lung, the first NE cells appear at 8 weeks' gestation, when all other epithelial cells are still undifferentiated. The development and cytodifferentiation of NE cells progresses in a centrifugal direction. By the end of the glandular period, single and groups of NE cells are found along the entire length of primitive bronchial epithelium. Based on differences in the size and morphology of cytoplasmic granules, three distinct types of NE cells can be recognized. During terminal stages of development, NE cells appear in small peripheral airways and primitive saccules. The functional considerations include the possible role of NE cells as endocrine, paracrine, or receptosecretory cells involved in neurohormonal regulation of pulmonary vascular or bronchial responses, and possible function of NEB as intrapulmonary hypoxia-sensitive chemoreceptors.

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.

Lung endocrine-like cells in hamsters treated with diethylnitrosamine: alterations in vivo and in cell culture

Diethylnitrosamine is known to cause squamous cell carcinoma and adenocarcinoma of the lung in Syrian golden hamsters. Sections of lungs obtained from hamsters treated with the systemic carcinogen diethylnitrosamine showed a significant increase in the number of argyrophilic cells of neuroepithelial bodies. The hyperplastic response was retained at least 4 weeks after cessation of treatment. To examine whether these affected cells exhibited enhanced survival in vitro, lung cells were dissociated with Pronase and grown in culture. After 7 days, argyrophilia, dense-cored vesicles, and corticotropin-like immunoreactivity were observed in many of the cells derived from hamsters treated for 5 or 8 weeks. These findings suggest that the endocrine-like cells of neuroepithelial bodies are affected by diethylnitrosamine as evidenced by a numerical increase in vivo and by the properties exhibited by cells in vitro. The relationship of this diethylnitrosamine-induced reaction to bronchial carcinoid tumors or small-cell carcinoma of the lung remains to be established.

Neuroepithelial bodies in the lung of the tree frog, Hyla arborea L. A scanning and transmission electron microscopic study

The endocrine-like cells (ELC), which together with nerve endings form the neuroepithelial bodies, are located on primary and secondary septa in the non-ciliated epithelium of the lung of Hyla arborea. ELC protrude markedly toward the lumen of the lung and are surrounded by pneumocytes, which separate ELC from the lumen by thin cytoplasmic processes. ELC possess a light cytoplasm containing two types of granules: (i) numerous small granules, 50-110 nm in diameter, and (ii) single large granules, 290-860 nm in diameter. Numerous nerve fibers, often forming synaptic junctions, can be observed in contact with ELC.

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

We have investigated morphologic and histochemical characteristics of serotonin-containing epithelial cells in tracheas from adult rabbits, using the Falck-Hillarp freeze-dried formaldehyde vapor technique. An intracellular formaldehyde-induced fluorescent substance was identified as serotonin by microspectrofluorometric techniques. Fluorescence microscopy and subsequent histochemical staining of the same sections demonstrated that serotonin-containing cells were argentaffin-, argyrophil-, and ferric ferricyanide-positive. The serotonin-containing epithelial cells were more numerous in ventral than in dorsal aspects of trachea. The number of detectable fluorescent cells was reduced after reserpine administration but was not affected by injecting the amine precursor L-dihydroxyphenylalanine (L-DOPA). The emission peak of the fluorophore was not significantly shifted after L-DOPA injections. The cells may regulate tracheobronchial-pulmonary function by releasing serotonin or other as yet unidentified biologically active substances.

Endocrine-like cells in the lungs of the newt, Triturus alpestris Laur

Endocrine-like cells (ELC) scattered in the basal part of the ciliated epithelium were identified in the lungs of the newt, Triturus alpestris. These ELC have a clear cytoplasm containing large amounts of secretory vesicles (69-180 nm in diameter), especially in their basal parts, but do not display formaldehyde-induced fluorescence. The ELC may be associated with nerve fibres.

Ultrastructural and histological study of 11 bronchial carcinoids. Evidence for different types

Seven of eleven bronchial carcinoids investigated showed cells with small granules resembling P cells which have already been described in human fetal and adult lung; two of these P cell tumours showed distinctive paraganglioid features. One tumour showed peculiar ultrastructural findings resembling closely those previously reported by Black (1969) in a so called "pulmonary oncocytoma". Three remaining cases showed large secretory granules resembling those of type 3 cells already described by Hage (1973b) in bronchial carcinoids; one of these tumours produced large amounts of 5-hydroxytryptamine (5HT). It is concluded that, on cytological grounds, at least two types of tumours can be distinguished among bronchial carcinoids, i.e. P cell and type 3 cell tumours. Moreover, two varieties of P cell carcinoids have been recognized, showing either the less frequent and more distinctive paraganglioid structure or the more common trabecular structure.

Primary oat-cell carcinoma of the larynx

A primary oat-cell carcinoma of the larynx in a 63-year-old man is reported. The oat-cell pattern appeared intermingled at one edge with a squamous carcinoma. The origin of this mixed tumour is considered together with the literature of extrapulmonary carcinomas having an oat-cell pattern.

PAS-lead hematoxylin as a stain for small-granule endocrine cell populations in the lungs, other pharyngeal derivatives and the gut

Epithelial cells of the several subtypes that comprise the small-granule cell population of the respiratory system are little studied, partly because adequate silver, monoamine fluorescence and other specific light microscopical preparations have been more difficult to obtain than in the gut and other organs possessing diffuse endocrine systems. Periodic acid-Schiff (PAS) in combination with MacConaill-Solcia's lead hematoxylin has in our hands proven dependable for routine staining of serial 2-micrometer glycol methacrylate sections used in mapping the distributions of these cells along the airway. In lungs of mice, hamsters, kittens, and fetal rabbits, typical small-granule cells stain weakly or not at all with lead hematoxylin alone, hence are easily overlooked. PAS adds to the cytoplasm a diffuse magenta coloration; and because it is diastase-resistant, less brilliant than that of mucus but more so than bronchiolar cell secretions, and finer textured than lysosomal staining of other cells present, the effect is to highlight small-granule cells whether solitary or in clusters. Additional PAS staining of basement membranes and lead hematoxylin staining of cilia enhance the combined stain's resolving power. In thyroid gland, parafollicular cells stand out boldly against follicular elements; in small intestine, hematoxylin-positive endocrine cells are well differentiated from absorptive, mucous, and Paneth cells that surround them. Using a complementary monoamine fluorescence technique on plastic sections of lungs from control and 5-hydroxytryptophan-pretreated animals prior to staining, we can show that fluorescent epithelial cells are identical with those stained by PAS-lead hematoxylin.

Differentiation of two types of endocrine cells which take up amine precursors using their capacity to take up the fluorescent dihydroisoquinoline derivative of dopamine

A study was made of the accumulation of the strongly fluorescent 2-carboxymethyl-6,7-dihydroxy-3,4-dihydroisoquinolinium compound (2-Carb. Me-DIQ) derived from the condensation reaction of dopamine with glyoxylic acid in endocrine cells possessing the capacity to take up and store biogenic monoamine precursors. Thin-layer chromatographic studies of urine showed that 2-Carb. Me-DIQ was metabolized into two strongly fluorescent metabolites, possessing at least one hydroxyl group in the phenol moiety of the molecule, which were excreted in urine together with the parent compound. Histochemical observations, however, indicated that the tissue fluorescence showing maximal emission at 480 nm was due to 2-Carb. Me-DIQ. Generally, the injection of 2-Carb. Me-DIQ induced a strong fluorescence in those tissue components possessing the extraneuronal uptake mechanism of catecholamines. In the endocrine cells strong fluorescence was seen in the pineal glandular cells and in some cells of the pars distalis of the hypophysis, of which some cells also took up DL-5-HTP, as was seen following formaldehyde vapour treatment. No accumulation of 2-Carb. Me-DIQ was observed in the pancreatic islet cells, the C cells of the thyroid gland or the tracheal enterochromaffin-like cells. These findings lead to the conclusion that biogenic monoamines in the cells of the pars distalis of the hypophysis might use the phenolic moiety of the molecule to bind to some intracellular receptor. Thus, the pars distalis cells may have an intracellular binding mechanism for biogenic monoamines that is different from other endocrine cells showing the uptake and storage of biogenic monoamines. On the other hand, the findings gave further support to the suggestion that in the pancreatic islet cells, the thyroidal C cells and the tracheal enterochromaffin-like cells biogenic monoamines are stored by a mechanism in which the basic, positively charged amino group of biogenic monoamines is bound electrostatically to the anionic, negatively charged carboxyl group of a hormone storage granule. The pars distalis cells and the pineal glandular cells seemed to take up amines and amine derivatives in a similar manner. This suggests that in the pars distalis cells, too, biogenic monoamines have an active metabolism and possibly some regulative role in hormone synthesis and/or secretion.