Ultrastructural study on cell differentiation of the rabbit carotid body

The development of the carotid body in both fetuses from 13 to 30 days of gestation and newborn rabbits was studied by light and electron microscopy. The carotid body anlage first appeared as a cellular aggregation close to the ventral wall of the third branchial artery on the 14th day of gestation. Type-I cells were recognized as such by the presence of dense-cored vesicles in the cytoplasm on the 16th day of gestation, whereas cells destined to develop into Type-II cells became clearly distinguishable by their typical relationship to the Type-I cells on the 20th day of gestation. Afferent and efferent synapses as well as reciprocal-like synapses between Type-I cells and nerve endings were also observed in perinatal fetuses. Although cell differentiation was almost finished by birth, Type-I cells and their innervation did not seem to be fully matured. Thus, it was concluded that ultrastructurally, the rabbit carotid body during the fetal and perinatal periods was relatively inactive.     

Molecular and cellular mechanisms of the organogenesis and development of the mammalian carotid body

Despite significant advancements in understanding physiological properties of the carotid body, little attention has been paid to its organogenesis. This review addresses the molecular and cellular mechanisms underlying organogenesis of the carotid body in mammals. The carotid body consists of two types of cells, that is, glomus cells and sustentacular cells, that are derived from different origins. Glomus cells are derivatives of neural crest cells which form sympathetic ganglia. Sustentacular cells are derivatives of mesenchymal neural crest cells which colonize the third pharyngeal arch and form the wall of the third arch artery. Gene-targeting studies indicate that three elements are required for carotid body organogenesis: the carotid sinus nerve (CSN), third arch artery, and superior cervical sympathetic ganglion (SCG). The CSN sends sensory fibers and Schwann cells to the wall of the third arch artery. The third arch artery provides mesenchymal cells, which give rise to sustentacular cells. The nerve process from the SCG sends glomus cell progenitors into the carotid body primordium. The presence of stem cells in the adult carotid body was recently highlighted. The origin of stem cells, however, remains controversial. Based on embryonic development of the carotid body, this review proposes the origin of stem cells.     

A model for the embryological instruction of the branchial arteries

It is difficult to teach students about the embryological transformation of the branchial arteries. In mammals, six pairs of branchial arteries develop, but all are not present at the same embryological stage. The first, second, fifth and a part of right sixth branchial artery disappear early in embryological development. The remaining third, fourth and sixth branchial arteries mainly constitute the arterial system of the breast. The aorta and pulmonary trunk are derived from the truncus arteriosus. Because of the complexity of this developmental process, we have devised a user-friendly model in order to assist with educational presentations. In this model, the shrinkage of a vessel has been represented by inserting a wire inside of the hose representing the artery. Degenerated or disappearing parts of the vessel are removable by using hooks and Velcro tape. Branchial arteries, truncus arteriosus, aortic sac and dorsal arteries are represented by different colors. The descent of the heart is represented by the relational change between larynx and heart. Additionally we represented the vagus nerve and recurrent laryngeal nerve by using strings. The right vagus nerve can move dorsally and the left ventrally by rotating the digestive tract. The right recurrent laryngeal nerve can move superiorly to hook around the right subclavian artery, and left recurrent laryngeal nerve can hook around the ductus arteriosus formed by the left sixth branchial artery.     

Comparative embryology of the carotid body

Vertebrate carotid bodies and related structures (branchial arch oxygen chemoreceptors in fishes, carotid labyrinth in amphibians, chemoreceptors in the wall of the common carotid and its branches in birds) develop in embryos when neural crest cells, blood vessels, and nerve fibers from sympathetic and cranial nerve ganglia invade mesenchymal primordia in the wall of the 3rd branchial arch. This review focuses on literature published since the 1970s investigating similarities and differences in the embryological development of 3rd arch oxygen chemoreceptors, especially between mammals and birds, but also considering reptiles, amphibians and fishes.     

Reciprocal synapses between cholinergic axons and small granule-containing cells in the rat cardiac ganglion

Electron microscopy of the rat cardiac ganglion shows occurence of small granule-containing cells that form reciprocal synaptic junctions with cholinergic terminals. At the synaptic junctions which are from axon to granule-containing cell, the intraaxonal vesicles are clustered against the junctional axolemma, but dense-cored vesicles in the postynaptic cell do not cluster towards the membrane densities in these synapses. By contrast, the synaptic zone polarized in the opposite direction shows an absence of axonal vesicles in close proximity to the postsynaptic axolemma, but there is a marked aggregation of dense-cored vesicles towards the presynaptic specializations of granule-containing cells. The synaptic zones are multifocal rather than bifocal, and the minimal distance separating each synaptic zone is about 0.3 μ. These findings may indicate that cholinergic excitation of some or all granule-containing cells causes a reciprocal inhibition of one or more cholinergic terminals.     

Anomalous artery directly connecting the external and internal carotid arteries

An anomalous artery directly connecting the external with the internal carotid artery was encountered on the right side of a 68-year-old Japanese female cadaver. This anomalous artery (5 mm in diameter, 12 mm in length) branched out from the posterior aspect of the external carotid at the level of the origin of the lingual artery, ran obliquely upward posteriorly along the course of the hypoglossal nerve, and was confluent with the anterior aspect of the internal carotid artery. No other variations were found in the morphological aspects of, or in the anatomical relationships between, the carotid arteries and their surrounding structures on either side. The carotid body-like structure was observed at the carotid bifurcation and was innervated by small branches of the glossopharyngeal, the vagus and the sympathetic trunk. Embryologically, it is conceivable that this anomalous artery may have derived from the right second branchial arch artery, although there is no abnormality in other derivative structures of the second pharyngeal arch. There may have been no effect from this anomaly on the functions of the arterial blood flow and blood supply under normal circumstances in the present case, but this report may be of embryological significance and contribute some insight into the mechanisms of the formation of the carotid circulation systems.     

Light,fluorescence and electron microscopic studies of rabbit subclavian glomera

The subclavian glomera (aortic bodies) of young New Zealand white rabbits were studied with the light, fluorescence, and electron microscopes. Two cell types were identified: type I, granule-containing (chief) cells, and type II, agranular (sustentacular) cells. The type I cells possessed large nuclei, the normal complement of cytoplasmic organelles and numerous electron-opaque cytoplasmic granules. The type II cells were agranular with attenuated cytoplasmic processes which partially or completely ensheathed the type I cells. The glomera were well vascularized. Capillary endothelial cells contained numerous pinocytotic vesicles, but few fenestrae. Two profiles of nerve terminals were observed. One, apposing the type I cells, contained numerous electron-lucent vesicles, several dense-cored vesicles, mitochondria and possessed membrane specializations resembling those usually observed in synaptic zones. The other profile contained abundant mitochondria and a few electron-lucent and densecored vesicles. Structural specializations were not observed on the apposed membranes of these terminals or adjacent to type II cells. Fluorescence histochemistry revealed an intense yellow-green fluorescence in the glomera, which indicated the presence of biogenic amines, possibly primary catecholamines or an indolamine. The electron-opaque granules observed in the type I cells were believed to be the storage sites for these amines. The subclavian glomera were found to be morphologically similar to the carotid body which is a known chemoreceptor.     

Origins of substance P- and calcitonin gene-related peptide-containing nerves in the internal carotid artery of rat

An aggregation of substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing nerve cells (internal carotid mini-ganglion) is described at the junction between the greater superficial petrosal nerve and the internal carotid nerve close to the internal carotid artery. A retrograde tracer dye technique demonstrates that this ganglion and the trigeminal and superior vagal ganglia supply the internal carotid artery with SP/CGRP fibers at, above and below this level, respectively. Implications of this finding for cranial painful syndromes in man are discussed.     

Distribution of carotid body type I cells and other periadventitial type I cells in the carotid bifurcation regions of the cat

Summary The bilateral distribution of carotid body type I cells was investigated in five non-pedigree cats by serially sectioning the carotid bifurcation regions. Carotid body type I cells occurred bilaterally in close proximity to the wall of the occipital artery or one of its proximal branches, and less frequently the ascending pharyngeal artery within a division of connective tissue with defineable but irregular borders. Caudally, and separate from the principal mass of carotid body type I cells, isolated groups of periadventitial type I cells were found in seven out of ten specimens lying freely in the connective tissues around the occipito-ascending pharyngeal trunk and the origin of the occipital artery immediately rostral to the carotid bifurcation. Periadventitial type I cells were not observed at the level of the carotid bifurcation but on one occasion these cells were noted caudal to the carotid bifurcation lying adjacent to the wall of the rostral end of the common carotid artery. From our data on four specimens, reconstructions were made of the carotid body. The occurrence and significance of the periadventitial type I cells is discussed.     

The carotid body of the mini-pig

The bilateral distribution of carotid body type 1 and 11 cells was investigated in 3 mini-pigs by serially sectioning the carotid bifurcation regions. The majority of type 1 and 11 cells occurred bilaterally in close proximity to the wall of the occipital artery or one of its small proximal branches, the internal carotid artery and the common arterial trunk. A division of connective tissue surrounded the type 1 and 11 cells with defineable but very irregular borders and this combination of connective tissue and cells constituted the principal mass of the carotid body. In the majority of specimens the cells were diffusely arranged giving a fragmented appearance to the organ but in 2 specimens part of the carotid body was discrete, adopting an ovoid or crescent-shaped appearance over a limited rostral-caudal part of its extent. Arteries to the carotid body originated from the occipital arterial tree in the vicinity of the division of the common arterial trunk and less commonly from the common arterial trunk itself. A supplementary blood supply came from unidentified connective tissue arterioles. In 2 out of 6 specimens type 1 and 11 cells were associated with cervical nerve trunks. Periadvential type 1 and 11 cells were observed in one out of 6 specimens lying dorsal to the common arterial trunk. From our data on 6 specimens, three dimensional reconstructions were made of ventral views of the distribution of carotid body type 1 and 11 cells. On account of the diffuse arrangement of the mini-pig carotid body, morphometric analysis of the organ volume was not feasible.     

视神经管显微解剖学研究

目的　为视神经管减压术提供解剖学依据。方法　利用解剖学方法对 10 0个颅骨和 6 7个尸头视神经管口及四壁的结构与毗邻进行了观察和测量。结果　视神经管由蝶骨小翼两根与喋骨体构成 ,管自后内向前外斜行 ,分内、外、上、下四壁和颅、眶两口。其上壁、下壁、内侧壁、外侧壁的长度分别为 10 70±0 2 3mm ,6 2 5± 0 18mm ,9 6 7± 0 18mm ,7 91± 0 17mm。内侧壁向筛窦、蝶窦内突入形成视神经管隆凸。视神经在颅口处有硬脑膜压迹 ,视神经腹侧有眼动脉形成的压迹。结论　视神经管隆凸可作为确定视神经管位置的解剖标志。视神经管下壁和内侧壁与视神经、眼动脉、颈内动脉等结构毗邻 ,切除管壁时应注意保护邻近结构。     

经鼻入路蝶窦外侧壁和海绵窦内侧壁的显微解剖

目的　研究经鼻入路视角下蝶窦外侧壁和海绵窦内侧壁的显微解剖特征,为相关手术提供形态学依据。 方法　10例防腐尸颅按经鼻路径在显微镜下进行解剖,观测视神经、颈内动脉和蝶窦外侧壁的关系,测量前鼻棘与视神经管眶口、颈内动脉隆凸最凸点之间的距离,以及与鼻底平面的角度。 结果　颈内动脉和视神经在蝶窦外侧壁上形成隆凸,两者之间呈“＞”字形,前鼻棘与颈内动脉隆起最凸点之间的距离为（62.18±5.12）mm,与鼻底平面的夹角为（36.8±3.4）°,与视神经管眶口的距离为（69.24±3.95）mm,与鼻底平面的夹角（41.4±3.0）°。颈内动脉海绵窦段可分为鞍旁部和斜坡旁部,鞍旁部与垂体外侧壁关系最为密切,鞍旁部至中线的距离为（9.06±1.34）mm。海绵窦内侧壁由鞍旁部和蝶窦旁部组成。 结论　熟悉蝶窦外侧壁和海绵窦内侧壁的解剖学特点,对于术中定位,安全处理海绵窦病变有重要意义。     

Hes1 is required for the development of the superior cervical ganglion of sympathetic trunk and the carotid body

Hes1 gene represses the expression of proneural basic helix–loop–helix (bHLH) factor Mash1, which is essential for the differentiation of the sympathetic ganglia and carotid body glomus cells. The sympathetic ganglia, carotid body, and common carotid artery in Wnt1‐Cre/R26R double transgenic mice were intensely labeled by X‐gal staining, i.e., the neural crest origin. The deficiency of Hes1 caused severe hypoplasia of the superior cervical ganglion (SCG). At embryonic day (E) 17.5–E18.5, the volume of the SCG in Hes1 null mutants was reduced to 26.4% of the value in wild‐type mice. In 4 of 30 cases (13.3%), the common carotid artery derived from the third arch artery was absent in the null mutants, and the carotid body was not formed. When the common carotid artery was retained, the organ grew in the wall of the third arch artery and glomus cell precursors were provided from the SCG in the null mutants as well as in wild‐types. However, the volume of carotid body in the null mutants was only 52.5% of the value in wild‐types at E17.5–E18.5. These results suggest that Hes1 plays a critical role in regulating the development of neural crest derivatives in the mouse cervical region. Developmental Dynamics 241:1289–1300, 2012. © 2012 Wiley Periodicals, Inc.     

Postnatal maturation of neuroepithelial bodies and carotid body innervation: a quantitative investigation in the rabbit

The intrapulmonary airways contain oxygen-sensitive chemoreceptors which may be analogous to the arterial chemoreceptors: the neuroepithelial bodies (NEB). While the NEB are prominent in the neonatal lung, physiological studies indicate that the carotid bodies are still relatively inactive at birth. This points to an unequal degree of development of both during the early neonatal period. As a reflexogenic chemoreceptor function depends on a well-developed innervation, we undertook a comparative investigation of the development of the NEB and the carotid body glomus cell innervation. Two morphological aspects of the innervation of NEB and carotid body glomus cells were quantified in rabbits of different age groups. The total sectional area of intracorpuscular and intraglomerular nerve endings per NEB or glomus cell group, respectively, was measured and the area percentage of mitochondria and synaptic vesicles was determined. In the NEB, no significant difference in total sectional area of the nerve endings between the age groups was observed, while in the carotid body there was a significant increase in the adult age group. In addition, the area percentage of mitochondria and synaptic vesicles of the nerve endings did not change significantly with age in the NEB, while in the carotid body these increased and decreased, respectively, with age. These observations point to a shift from morphologically efferent nerve endings, rich in synaptic vesicles, to morphologically afferent nerve endings, rich in mitochondria. Our interpretation of these findings is that, at birth, the NEB innervation is more mature than the carotid body glomus cell innervation and that the latter matures at a later time than the former. These findings support the theory that the NEB may act as complementary chemoreceptors to the carotid body during the early postnatal period.     

蝶筛窦外侧壁应用解剖

观察５７具成人尸头标本蝶、筛窦外侧壁，以及同视神经管和颈内动脉的毗邻关系。眶板前下宽，后上窄，平均厚度为０．２ｍｍ。９３．８６％的视神经管内壁与蝶、筛窦外侧壁毗邻，且视神经管内蝶、筛窦内突出形成隆起的找率和程度同蝶、筛窦气代程度呈正相关。     

Constitution of the greater splanchnic nerve in the rat

The greater splanchnic nerve originating from the sympathetic ganglia between the 10th and 12th ribs on the dorsal thoracic wall passes through the diaphragm between its medial and lateral erura, to form the celiac plexus around the celiac trunk and superior mesenteric artery in the abdominal cavity. The nerve consists of about 10,000 of nerve fibers and of 25,000 of ganglion cells in its whole length of 2.5 cm; nerve fibers can be divided into myelinated fibers, accounting for less than 6% of total numbers, and unmyelinated fibers, which amount to more 90%. Special attention was not paid to the numerous ganglion cells in terms of their shapes, sizes, and cell organelles except for a small number of binucleate cells. However, the nerve contains remarkable synapses that connect between axon showing flat, elliptical, and cored vesicles and dendrite, between another type of axon having elliptical and cored vesicles and dendrite, and even between dendrite and cell body, in which synaptic vesicles are small spherical and elliptical. These facts can suggest that the greater splanchnic nerve contains more complex structure than has been hitherto described.     

The volume of the carotid body and periadventitial type 1 and type 2 cells in the carotid bifurcation regions of the pregnant and lactating cat

The bilateral distribution of carotid body type 1 cells was investigated in 2 pregnant cats at 95% full term and two lactating cats (2 and 4 d after parturition). Carotid body type 1 and 2 cells occurred bilaterally in close proximity to the occipital artery or one of its branches in a division of connective tissue with defineable but irregular borders. This combination of connective tissue and type 1 and 2 cells constituted the principal mass of the carotid body, which received its blood from the occipital and/or the ascending pharyngeal arteries. Using an interactive image analysis system, the area of the carotid body in each serial section was measured by accurately contouring its perimeter. The volume of the carotid body was calculated by multiplying the sum of the contoured areas of the serial sections by the thickness of the section. The volumes for the carotid bodies in pregnant cats ranged between 0.186 and 0.278 mm3 while the values in lactating animals lay between 0.287 and 0.356 mm3. Caudally and separate from the carotid body, isolated groups of periadventitial type 1 and 2 cells were found in 5 out of 8 specimens around the occipitoascending pharyngeal trunk, origin of the occipital artery, external carotid artery and rostral part of the common carotid artery. The volumes of the periadventitial type 1 and 2 cells were variable in pregnant and lactating cats.     

Ultrastructure of the primate carotid body: a morphometric study of the glomus cells and nerve endings in the monkey (Macaca fascicularis)

Summary The carotid body of the monkey (Macaca fascicularis) was studied at both the light and electron microscopic levels in an effort to provide a detailed quantitative characterization of this chemoreceptor organ in the primate. Structurally, the monkey carotid body was organized into lobules of from three to eight glomus cells (in section) and their ensheathing supporting cells. Interspersed among the lobules was abundant connective tissue stroma, fibroblasts and mast cells. Fenestrated capillaries, small arterioles and venules also permeated the organ. Each supporting cell partially ensheathed about three glomus cells and could be easily differentiated from glomus cells by their darker cytoplasmic staining, lack of dense-core vesicles and angular nuclear profile. Glomus cells exhibited an intense catecholamine histofluorescence and contained abundant dense-core vesicles. On the basis of dense-core vesicle size, shape and numerical density, four types of glomus cells were identified. The most common type (62% of all glomus cells) contained vesicles with an average diameter of 219 nm and a density of 8 vesicles per m² of cytoplasm. The second type possessed larger vesicles (264 nm in diameter) and accounted for about 14% of all glomus cells. A third type of glomus cell contained smaller (167 nm) and fewer (5 vesicles per m²) dense-core vesicles. The fourth type of glomus cell contained pleomorphic-shaped vesicles with a maximal diameter of 232 nm. Each of these last two types accounted for about 12% of all glomus cells. All four types of glomus cells were innervated, averaging 1.43 nerve endings per glomus cell (in sections). Nerve endings were primarily of the bouton-like variety averaging 2 m² in sectional area and containing 34.3 clear-core synaptic vesicles (average size 73.5 nm in diameter) per m² of cytoplasm. Of the 57 nerve endings examined in single sections, 16% displayed junctions typical of synaptic specializations and most of these were presynaptic to glomus cells. Glomus cell-glomus cell synapses were not observed. Based on these quantitative observations and on previous studies of carotid body cytoarchitecture in other laboratory species, it appears that the primate organ most closely resembles the cat carotid body, although several differences exist.     

Constrictor and compliance responses of some arteries to nerve or drug stimulation

1. The magnitude of the maximum constrictor response to nerve stimulation was measured in the saphenous, ear, inferior and superior mesenteric, renal and carotid arteries in the rabbit and corresponding arteries, except the ear and carotid, in the guinea-pig. The responses varied from an average rise of 350 mm Hg in the rabbit saphenous to almost no response in the rabbit carotid. The guinea-pig arteries gave consistently smaller responses than the rabbit. The response magnitude was unrelated to wall thickness or the presence of an active uptake mechanism for noradrenaline. The response did correlate with the density of adrenergic innervation, with the wall thickness to lumen ratio and with the function of the artery and the amount of connective tissue in its wall.2. The magnitude of the maximum constrictor response to noradrenaline and six other agonist drugs, acetylcholine, histamine, 5-HT, KCl, vasopressin and angiotensin II, was compared. In all arteries noradrenaline was the most powerful agonist. The maximum responses to nerve stimulation and to noradrenaline were compared. In the rabbit saphenous and ear arteries this ratio was almost 1, but in arteries such as the rabbit renal it fell below 0.5.3. Artery wall stiffness was measured from the pressure/volume relationship during distension of a closed length of artery. In a relaxed artery two components only were present, an early easily distended phase and a late relatively undistensible phase. Noradrenaline caused a third, early, very stiff phase to appear in the pressure/volume curves. This is probably due to contracted muscle. The increase in stiffness varied from 617% in the rabbit saphenous to 152% in the rabbit carotid. In conducting arteries such as the carotid the change in stiffness was a more sensitive index of noradrenaline action than vaso-constriction.4. During the measurement of wall stiffness stress relaxation was not noticeable in relaxed arteries but was prominent in arteries contracted by noradrenaline. Stress relaxation involved both the changes in wall stiffness and the ability to constrict and was reversible even in the continuing presence of agonist drugs.5. Nerve stimulation, even in arteries where its vasoconstrictor effects were equal to those of noradrenaline, gave only slight increases in artery wall stiffness, suggesting that even in these densely innervated arteries only a small fraction of the muscle is activated by nerve stimulation.     

Calcium handling by the cat carotid body--a pyroantimonate study

Subcellular regulation mechanisms of calcium concentrations related to oxygen sensing in the carotid body are unclear. In the present study, we investigated the ultrastructural distribution patterns of calcium in carotid body cells and its changes evoked by hypoxia. Carotid bodies were dissected from anesthetized cats exposed in vivo to normoxic or acute hypoxic conditions. We used the oxalate-pyroantimonate technique that yields an electron-opaque calcium precipitate. X-ray microanalysis and appropriate controls confirmed the presence of calcium in the precipitate. Calcium precipitates were found in all types of cells in carotid body parenchyma: chemoreceptor cells, sustentacular cells, and nerve endings. In normoxic chemoreceptor cells, the precipitate was localized in dense core vesicles, mitochondria, and nuclei, but rarely in the cytoplasm. The most apparent effect of hypoxia was disappearance of the precipitate from dense core vesicles and was associated with its appearance in the cytoplasm. The amount of precipitate throughout the carotid body parenchyma was decreased overall due to hypoxia. These results indicate the involvement of subcellular calcium trafficking in hypoxia-sensing in the carotid body. The redistribution pattern of granular calcium deposits from organelles to the cytoplasm of chemoreceptor cells agrees with biochemical data of calcium release from intracellular stores during hypoxia.