Ultrastructure of the human carotid body. A perspective on the mode of chemoreception

Expression of the cellular prion protein by mast cells in the human carotid body

Prion diseases are fatal neurologic disorders that can be transmitted by blood transfusion. The route for neuroinvasion following exposure to infected blood is not known. Carotid bodies (CBs) are specialized chemosensitive structures that detect the concentration of blood gasses and provide feedback for the neural control of respiration. Sensory cells of the CB are highly perfused and densely innervated by nerves that are synaptically connected to the brainstem and thoracic spinal cord, known to be areas of early prion deposition following oral infection. Given their direct exposure to blood and neural connections to central nervous system (CNS) areas involved in prion neuroinvasion, we sought to determine if there were cells in the human CB that express the cellular prion protein (PrPC), a characteristic that would support CBs serving as a route for prion neuroinvasion. We collected CBs from cadaver donor bodies and determined that mast cells located in the carotid bodies express PrPC and that these cells are in close proximity to blood vessels, nerves, and nerve terminals that are synaptically connected to the brainstem and spinal cord.

General Morphology of the Mammalian Carotid Body

The carotid body (CB) is the main peripheral arterial chemoreceptor that registers the levels of pO2, pCO2 and pH in the blood and responds to their changes by regulating breathing. It is strategically located in the bifurcation of each common carotid artery. The organ consists of "glomera" composed of two cell types, glomus and sustentacular cells, interspersed by blood vessels and nerve bundles and separated by connective tissue. The neuron-like glomus or type I cells are considered as the chemosensory cells of the CB. They contain numerous cytoplasmic organelles and dense-cored vesicles that store and release neurotransmitters. They also form both conventional chemical and electrical synapses between each other and are contacted by peripheral nerve endings of petrosal ganglion neurons. The glomus cells are dually innervated by both sensory nerve fibers through the carotid sinus nerve and autonomic fibers of sympathetic origin via the ganglioglomerular nerve. The parasympathetic efferent innervation is relayed by vasomotor fibers of ganglion cells located around or inside the CB. The glial-like sustentacular or type II cells are regarded to be supporting cells although they sustain physiologic neurogenesis in the adult CB and are thus supposed to be progenitor cells as well. The CB is a highly vascularized organ and its intraorgan hemodynamics possibly plays a role in the process of chemoreception.

History and Recent Progress in Carotid Body Studies

This chapter describes the history of the carotid body (CB) and the subsequent research on its structure and function. The chronological development of ideas about its anatomical structure as a ganglion, the first descriptions of its glandular nature as a ball of highly vascular tissue (glomus), the discovery of its neural crest origin and relevant embryological views as a true paraganglion toward a more conclusive understanding of its sensory nature as a chemoreceptor for chemical changes in blood have been consistently demonstrated. The knowledge of the CB neurochemistry, physiology and pathophysiology has progressed immensely in the past century and a large and compelling body of evidence for the presence of a neurogenic niche in the CB has accumulated over the last two decades, thus underlying its function and possibility for the development of cell replacement therapies.

Immunohistochemical Characteristics of the Human Carotid Body in the Antenatal and Postnatal Periods of Development

The evolutionary and ontogenetic development of the carotid body is still understudied. Research aimed at studying the comparative morphology of the organ at different periods in the individual development of various animal species should play a crucial role in understanding the physiology of the carotid body. However, despite more than two centuries of study, the human carotid body remains poorly understood. There are many knowledge gaps in particular related to the antenatal development of this structure. The aim of our work is to study the morphological and immunohistochemical characteristics of the human carotid body in the antenatal and postnatal periods of development. We investigated the human carotid bodies from 1 embryo, 20 fetuses and 13 adults of different ages using samples obtained at autopsy. Immunohistochemistry revealed expression of βIII-tubulin and tyrosine hydroxylase in the type I cells and nerve fibers at all periods of ontogenesis; synaptophysin and PGP9.5 in the type I cells in some of the antenatal cases and all of the postnatal cases; 200 kDa neurofilaments in nerve fibers in some of the antenatal cases and all of the postnatal cases; and GFAP and S100 in the type II cells and Schwann cells in some of the antenatal cases and all of the postnatal cases. A high level of tyrosine hydroxylase in the type I cells was a distinctive feature of the antenatal carotid bodies. On the contrary, in the type I cells of adults, the expression of tyrosine hydroxylase was significantly lower. Our data suggest that the human carotid body may perform an endocrine function in the antenatal period, while in the postnatal period of development, it loses this function and becomes a chemosensory organ.

Cellular properties and chemosensory responses of the human carotid body

The carotid body (CB) is the major peripheral arterial chemoreceptor in mammals that mediates the acute hyperventilatory response to hypoxia. The CB grows in response to sustained hypoxia and also participates in acclimatisation to chronic hypoxaemia. Knowledge of CB physiology at the cellular level has increased considerably in recent times thanks to studies performed on lower mammals, and rodents in particular. However, the functional characteristics of human CB cells remain practically unknown. Herein, we use tissue slices or enzymatically dispersed cells to determine the characteristics of human CB cells. The adult human CB parenchyma contains clusters of chemosensitive glomus (type I) and sustentacular (type II) cells as well as nestin-positive progenitor cells. This organ also expresses high levels of the dopaminotrophic glial cell line-derived neurotrophic factor (GDNF). We found that GDNF production and the number of progenitor and glomus cells were preserved in the CBs of human subjects of advanced age. Moreover, glomus cells exhibited voltage-dependent Na(+), Ca(2+) and K(+) currents that were qualitatively similar to those reported in lower mammals. These cells responded to hypoxia with an external Ca(2+)-dependent increase of cytosolic Ca(2+) and quantal catecholamine secretion, as reported for other mammalian species. Interestingly, human glomus cells are also responsive to hypoglycaemia and together these two stimuli can potentiate each other's effects. The chemosensory responses of glomus cells are also preserved at an advanced age. These new data on the cellular and molecular physiology of the CB pave the way for future pathophysiological studies involving this organ in humans.

Carotid body paraganglioma. Diagnosis and treatment by angiography

Paraganglioma is a rare neoplasia of neural crest origin. It most commonly arises in carotid body, jugular bulb, tympanic plexus on the promontory, and along the vagal nerve pathway or anywhere along the paraganglia pathway. This review describes our experience of cervical paraganglioma. Although there is no consensus in the literature on preoperative angiographic embolization, we think angiography is the gold standard in the diagnosis and treatment of paraganglioma. A small paraganglioma probably does not usually require preoperative embolization because the risks may exceed the benefits. But angiography is mandatory in the diagnosis and treatment of large highly vascular paragangliomas. Imaging of the vascular map of the tumor, that is only possible by angiography, will help the neurosurgeon evaluate the real extension of the neoplasia and chose treatment modalities. Embolization is performed to decrease operative bleeding, shorten the surgery timing and avoid cranial nerve deficit. Cemal Umit Isik et al. studied four brothers with familial paragangliomas noting unexplained concomitant thyroid functional disorders in their patients. Because of the pedigree they thought this may have been a coincidence. Our reported case, unrelated to the Turkish family, also had hypothyroidism suggesting that the relation between paraganglioma and thyroid dysfunction may not be merely a coincidence.

Familial paraganglioma

Paragangliomas are unusual tumors that are sometimes familial. We treated a family who exhibited multiple head and neck paragangliomas (HNPGs) and pheochromocytomas. The purpose was to determine the clinical characteristics of paragangliomas with familial history and to define a better standardized proceeding in the management of these tumors. Patients diagnosed with head and neck paragangliomas and identified retrospectively through clinical otolaryngology practices were given a medical and family history questionnaire. We studied a family who exhibited familial paragangliomas. This relationship was examined by reviewing the medical records of family members with verified tumors, carrying out neck computed tomography or magnetic resonance imaging on their relatives to look for tumors that had been unrecognized in the past. All patients underwent a complete head and neck examination. The initial evaluation usually included CT and/or MRI. Computed tomography and magnetic resonance imaging contributed additional information about tumor extension. Angiography was performed in every patient with carotid body tumor, with one undergoing therapeutic embolization to reduce the tumor size. Eleven tumors were identified in four patients with a familial history. Familial disease was initially determined by pedigree analysis. Four patients with a median age of 31 years (range: 25-42) underwent surgery. Median follow-up was 5 years (range 2-14); carotid angiography provided essential mainstays for the definite diagnosis. All patients underwent successful surgical resection of the tumor after the appropriate preoperative preparation. There were no perioperative deaths or hemiplegia. Three patients had bilaterality carotid body paragangliomas. One patient had three paragangliomas, and two patients had bilateral carotid body paragangliomas associated with pheochromocytoma. Clinically functioning tumors and malignant tumors were not identified, and none of the patients died after surgery. During follow-up, none of the patients developed recurrence or metastatic disease. The carotid body paraganglioma (CBPG) and glomus vagale manifested as asymptomatic neck masses. The clinical pheochromocytomas typically present with uncontrolled hypertension. In conclusion, paragangliomas are rare, with multicentricity being more common in patients with a familial history. In patients with familial paragangliomas, high-resolution computed tomography and magnetic resonance imaging are recommended for early screening and contributed additional information about the tumor extension and definitive treatment. Early surgery is recommended to minimize major risks.

Weibel-Palade bodies as a storage site of calcitonin gene-related peptide and endothelin-1 in blood vessels of the rat carotid body

BACKGROUND

The vasculature of the carotid body has been considered to play a role in the regulation of blood flow into this organ. This light and electron microscope immunocytochemistry deals with endothelium-dependent vasomotion by vasodilatory calcitonin gene-related peptide (CGRP) and vasoconstrictive endothelin-1 (ET-1).

METHODS

After adult male rats were perfused with a solution of periodate-lysine-paraformaldehyde through the left ventricle, the carotid artery bifurcations were isolated and utilized for light and electron microscope immunolabelings with CGRP and ET-1 primary antisera.

RESULTS

By light microscope immunocytochemistry, immunoreactions to CGRP were seen along the endothelium of the carotid body artery (CBA) and its branches, and those of ET-1 were observed along the endothelium of the intralobular capillaries in addition to the above vessels. By immunoelectron microscopy, immunoreactive gold particles of CGRP and ET-1 were identified in the rough endoplasmic reticulum (rER) and in the Weibel-Palade (WP) bodies of endothelial cells of the CBA and its branches. Colocalization of both immunoreactive gold particles was observed in the same WP body. Immunoreactive gold particles of CGRP were also identified in the rER, Golgi apparatus, and specific granules of the dark glomus cells.

CONCLUSIONS

Conceivably, CGRP and ET-1 are synthesized in the rER of these endothelial cells and are stored in the WP bodies for the autoregulation of blood flow.

Vagal nerve complex in normal development and sudden infant death syndrome

BACKGROUND

Although the pathogenesis of sudden infant death syndrome (SIDS) is not understood, one of the major hypotheses is that a subtle defect in respiratory circuitry is an important underlying factor. The vagus nerve is a critical component of respiratory control, but its neuroanatomic complexity has limited its investigation in human disease.

METHODS

Correlating developmental studies on different parts of the vagus nerve allows a more comprehensive assessment of its maturation process. Comparison of the normal developing vagus nerve with nerves examined in SIDS patients suggests alterations in the nucleus tractus solitarius and dorsal vagal nucleus as well as in the peripheral vagus nerve.

RESULTS AND CONCLUSIONS

The persistence of dendritic spines and lack of appropriate axonal growth implies delays in vagal maturation. Since nodose ganglia can be examined in vitro from autopsy material, perturbation to this system can be explored to evaluate further the mechanism involved in terminal vagal maturation. Although the reason for the delayed vagal maturation in SIDS is not apparent, the presence of astrogliosis in the region of the vagal nuclei is consistent with an exposure to hypoxic-ischemic events some time before death.

Ultrastructure and immunohistochemistry of the coronary chemoreceptor in human and canine hearts

Ultrastructure of the coronary chemoreceptor that causes a hypertensive reflex was studied immunohistochemically in human and canine hearts. Both cytologic and histologic features were similar in human beings and dogs, consisting of chief cells, sustentacular cells, Schwann cells, nerve fibers, blood vessels, and connective tissue. Three or four chief cells were typically surrounded by one Schwann cell, making a glomoid cluster about 20 microns across. Volume fractions of chief cells compared to capillaries were about 1:2 in dog and 1:4 in human chemoreceptors. Abundant osmiophilic dense granules filled the chief cells. Complex junctions between nerve fibers, chief cells, and sustentacular cells or Schwann cells exhibited a characteristic fine structure. Immunohistochemically, serotonin reactivity was observed mainly in the vicinity of junctions between nerve endings and chief cells, but some large granules in chief cells also stained positively. These new morphologic findings provide further support for the probable role of serotonin in the activation of the cardiogenic hypertensive chemoreflex in both human and canine hearts.

An ultrastructural study of spontaneous cell death in a mouse mastocytoma with particular reference to dark cells

The morphology and frequency of the various types of cell death occurring spontaneously in a mouse mastocytoma growing as intramuscular nodules were investigated. In addition to necrosis and apoptosis, which have been well documented in malignant neoplasms in the past, a third morphological pattern of cell death, the formation of dark cells, was observed. Necrosis first appeared in confluent patches about 5 days after tumour inoculation, and these increased in size as the tumours grew. Apoptosis, on the other hand, was present at all stages of tumour growth, and remained at a reasonably constant level. Dark cells were first observed at about 6 days, and increased in numbers thereafter. Dark cells were characterised by overall cellular condensation and gross swelling of mitochondria. Their cytoplasm became squeezed out between adjacent cells and then fragmented. Remnants of dark cells were eventually phagocytosed and degraded by macrophages. The distribution of dark cells in the tumours suggested that crowding and compression may contribute to their development.

Two types of glomus cell in the rat carotid body as revealed by alpha-bungarotoxin binding

Horseradish peroxidase (HRP)-conjugated alpha-bungarotoxin (alpha Bgt) was used to localize alpha Bgt-acetylcholine receptor sites in the rat carotid body. Two types of glomus cell were differentiated on the basis of the staining of their plasma membranes by the conjugate: type A, devoid of staining or only partly stained; and type B, exhibiting staining over the entire cell surface. The parts of type A glomus and supporting cells stained were always in direct apposition to type B glomus cells. It is concluded that type B glomus cells are possibly the only cell types exhibiting specific binding sites of alpha Bgt. Other morphological characteristics and quantitative studies indicated that the type A and type B glomus cells presented in this study were equivalent to those described in the rat carotid body by other investigators (McDonald & Mitchell, 1975). alpha Bgt-HRP staining facilitated the observation of the distribution pattern of glomus cells in the parenchyma: type A glomus cells were arranged in groups and often showed polarity toward neural elements and sinusoidal capillaries; and clusters of type B glomus cells were frequently situated in a demilune -like fashion over groups of type A glomus cells. Because of differences in morphology, synaptology, alpha Bgt-binding affinity, and polarity toward the blood vessels, we propose that type A and type B glomus cells in the rat carotid body represent functionally distinct cell types.

Dark cell proliferation in carotid body hyperplasia

The histopathology of the enlarged carotid bodies, in both qualitative and quantitative terms, is described in two cases. One was in a woman of 80 years with systemic hypertension and the other in a man of 72 years with pan-acinar emphysema complicated by chronic hypoxaemia. In both instances there was generalized hyperplasia of sustentacular cells, perhaps with involvement of Schwann cells and fibrocytes, with superimposed focal proliferation of dark or 'pyknotic' variants of chief cells. The functional significance of both froms of tissue response in the carotid bodies is speculated upon.

Nonfunctional paraganglioma of the larynx: clinical and pathological considerations

Paraganglioma of the larynx is a rare neoplasm. A review of the 16 previously reported cases in English medical literature is presented along with the details of an additional case. The tumor was analyzed by light and electron microscopy. The anatomy and embryology of the laryngeal paraganglia and controversies in nomenclature are discussed. Hoarseness, pain, dysphagia, and neck mass are the cardinal symptoms of this neoplasm; other clinical characteristics are reviewed. Partial laryngectomy and excision via lateral pharyngotomy and extralaryngeal approaches are the most commonly employed methods of treatment. More aggressive therapy including radical neck dissection, total laryngectomy, and radiation therapy have been used for malignancies.

Malignant carotid body paraganglioma: light and electron microscopic study of the tumor and its metastases

A right carotid body paraganglioma (CBP) was removed from a 30-year-old female after finding metastases to cervical lymph nodes. The tumor and its metastases were studied by light and electron microscopy to determine the neoplastic cell type. Light microscopy confirmed the presence of chief cells but was inadequate alone to exclude sustentacular cells. By electron microscopy, only chief cells were found in both the primary and secondary tumors. This is the first report of an ultrastructural study of a metastasis from a malignant CBP. From our observation, we suggest that CBP be defined as a proliferation of chief and sustentacular cells. Electron microscopy is essential to determine the cell types present and thereby help classify the lesion as a tumor or hyperplasia of the carotid body.

The neuroendocrine nature of the glomus cells: an experimental, ultrastructural, and histochemical tissue culture study

Although the carotid body is an established chemoreceptor, there is considerable evidence also for its possessing a secretory function. While adrenergic neuroendocrine cells of neuroectodermal derviation exist in the central and autonomic nervous systems, the exact histogenesis of the mammalian carotid body is unsettled. The normal human carotid body and glomus jugulare tumor have been grown in tissue culture and their constituent cells have been observed to transform from epithelial to neuronoid appearing cells with extensive dendritic processes. This conversion has been further enhanced by the addition of nerve growth factor, a polypeptide specific for neural tissue. Electron microscopy confirmed that these culus cell. Histofluorescence revealed that these in vitro cells continued to synthesize and store biogenic monoamines in culture. Comparison of the morphologic, ultrastructural and histochemical features of the glomus cell with established neuroendocrine cells (central nervous system neurons, sympathetic ganglia cells, chromaffin cells) shows striking similarities. On the basis of these findings it is concluded that the glomus cell is a modified neuron of neural crest origin. The embryology, electron microscopy and histochemistry of the carotid body and related glomera and their tumors are reviewed.

Microspectrography of formaldehyde and fluorescamine-induced fluorescence in rabbit pulmonary neuroepithelial bodies: demonstration of a new, probably polypeptide intracytoplasmic substance

The microspectrographic analysis of the fluorescence emitted by NEB's in gaseous formaldehyde-fixed lung tissue, posttreated with fluorescamine, revealed the presence of numerous primary amino groups which are clearly different from the serotonin identified in our earlier studies and correspond to a new, probably a polypeptide intracytoplasmic substance.

Chief cell hyperplasia in the human carotid body at high altitudes; physiologic and pathologic significance

The area occupied by parenchymal cells, in sections comprising the entire half of the surface of the carotid body, is significantly greater in people born and living at 14,350 feet than in those at sea level. The enlargement and increase in weight of the carotid bodies observed at high altitudes can thus be attributed to hyperplasia of parenchymal tissue. The proliferated cells have the morphology of type I chief cells and display marked vacuolation and depletion of yellow-green, naturally fluorescing, bioamine containing granules. Although unimportant variations in size and weight in relation to age occurred at sea level, it was found that the magnitude of the carotid body enlargement increased with age at high altitudes. The augmented carotid body size and weight in relation to age at high altitudes are associated with progressive chemoreceptor insensitivity. The physiologic and pathologic significance of these findings is discussed.

So-called "minute pulmonary chemodectoma": a tumor not related to paragangliomas

Twenty-six cases of so-called "minute pulmonary chemodectoma" are presented. The patient population showed a marked female preponderance, and there appeared to be an association of the lesion with pulmonary injury from a variety of causes including cardiac failure, chronic bronchitis and emphysema, and thromboemboli. Half the cases had multiple tumors. Microscopically, the tumors consisted of nests of cells in the interstitial tissue near small veins. Argentaffin and argyrophil stains failed to demonstrate cytoplasmic granules in any case. By electron microscopy, the nests were composed of large cells with broadly interdigitating processes connected by many well-formed desmosomes. The cytoplasm was filled with numerous 60-A filaments. The Golgi apparatus was prominent, while other organelles were sparse. No secretory granules were identified. It is concluded that the fine structure and lack of silver-positive granules are inconsistent with the morphology of previously reported paragangliomas, but that there is a resemblance at the light and electron microscopic level to meningeal arachnoed cells and the cells of meningiomas.

Post-mortem size and structure of the human carotid body

The weights of the carotid bodies have been measured in an unselected group of 40 successive cases coming for routine necropsy. Although the mean weight of the carotid bodies was higher in those subjects with emphysema or Pickwickian syndrome, this difference did not reach a level of statistical significance. Nevertheless, in a group of two patients with cor pulmonale and one with the Pickwickian syndrome the mean weight of the carotid bodies was significantly higher than that of the rest. Such observations would be consistent with enlargement of the glomic tissue in response to chronic hypoxia. In addition to these observations there was a significant correlation between the size of the carotid bodies and the weights of the left and right ventricles separately, while there was a substantially higher correlation between the weights of the carotid bodies and the combined weights of the two ventricles. Should such a correlation be determined by a causative link between these two measurements, a new metabolic role of glomic tissue will have to be considered. The histology of the carotid bodies was studied and differential cell counts were carried out in 21 cases. Enlargement of the carotid bodies was not accompanied by any change in the differential cell count, except that in one case with `cor pulmonale' and large carotid bodies areas of hyperplasia showed a predominance of the dark variety of type 1 (chief) cell.

Chemodectoma in relation to the aortic arch (aortic body tumour). A clinical report

Tumours of the aortic body in man are relatively rare and were first described in 1950. Aortic bodies are found in the region of the base of the heart and great vessels, are thought to be of neuroepithelial origin, and have a role in maintenance of circulatory homoeostasis. A clinical report is presented of a benign aortic body tumour which was removed surgically from a 61-year-old woman.