Fine structure of the carotid body of normal and anoxic cats

The effects of reserpine and hypoxia on the amine-storing granules of the hamster carotid body

The carotid bodies from control, reserpine-treated, and hypoxia-treated hamsters were fixed with phosphate-buffered glutaraldehyde and osmium tetroxide, s-Collidine-buffered osmium tetroxide, or phosphate-buffered glutaraldehyde followed by potassium dichromate incubation. Following glutaraldehyde-osmium tetroxide fixation no differences in density or population of the electron-opaque granules in the glomus cells of either control or experimental animals were observed. With s-Collidine-buffered osmium tetroxide and the glutaraldehyde-dichromate technique a marked decrease in density without an appreciable reduction in number of granules was noted after reserpine treatment, while in hypoxia-treated hamsters the density and population of the granules were not different from those of the controls. The results indicate that reserpine depletes the amines without granule disappearance and that hypoxia does not affect the amine content of the granules. It is suggested that following glutaraldehyde-osmium tetroxide double fixation, persistence of the density of the granules in reserpine-treated animals is due primarily to the nonamine content, and that the amines in the glomus cells are probably not directly involved in the respiratory reflex.

Ultrastructure of the carotid body of the goat

The carotid body of the goat was found to be a small oval or rounded parenchymatous organ. It was characterized by its profound vascularity. Delicate septa divided the parenchyma into small feebly defined lobules. Electron microscopy revealed that the parenchyma comprised type I cells, type II cells, nerve endings, axons and fenestrated dilated capillaries. Type I cells were characterized with electron dense-cored vesicles. They showed variations in size and concentration of the dense-cored vesicles and number of mitochondria. The possibility that these variations are reflections of different stages of activity is discussed. Type II cells were less numerous than type I cells, relatively small and devoid of dense-cored vesicles. They usually surrounded small groups of type I cells and associated nerve endings and axons. Presumptive afferent nerve endings characterized with many clear vesicles, occasional large granular vesicles and varying numbers of slender mitochondria, lay apposed to type I cells. Nerve endings of this kind showed afferent and efferent synaptic junctions with type I cells. Presumptive sympathetic efferent endings were occasionally seen within the lobules but never lay apposed to type I cells or afferent nerve ending.

Nerve branching and terminal arborizations in the carotid body of the cat. A light microscopic study following anterograde injury filling of carotid nerve axons with horseradish peroxidase

The terminal arborizations of carotid nerve axons within the carotid body of the cat were densely filled with horseradish peroxidase and studied under the light microscope. Two types of terminal arborizations were found in contact with glomus (type I) cells. The axons differed principally in the wealth of terminal swellings. The largest and most numerous type of arborization consisted of one to several clusters of terminals of variable size and shape arising from a single fiber and distributed in a rather ellipsoidal domain of about 9,000 microns 3 for each cluster. Thus, these arborizations might be in close relation with 20-60 glomus cells. The second type of arborization had substantially fewer terminal swellings, occupying a smaller volume and probably contacted significantly less glomus cells. Both kinds of axons had small rounded and large calyciform endings. The larger arborizations were derived consistently from larger fibers than those which produced the smaller arborizations. The results suggest that the carotid nerve axons generate two types of arborizations within the carotid body. Thus, glomus cells potentially can contact two classes of afferent fibers. The functional significance of a dual chemoreceptor innervation of the carotid body is discussed.

The effects of hypoxia on catecholamine dynamics in the rat carotid body

The catecholamine content of the rat carotid body was assayed using high performance liquid chromatography with electrochemical detection. The concentration of dopamine (DA) was found to predominate over that of norepinephrine (NE) by a small margin (31 pmol/carotid body pair DA; 23 pmol/carotid body pair NE). The turnover rates of carotid body DA and NE were determined from the time-dependent decline in their concentrations following the blockade of synthesis with alpha-methyl-p-tyrosine. Values were obtained (DA t 1/2 = 1.9 h; NE t 1/2 = 2.3 h) which suggested a rapid turnover of carotid body catecholamines. Exposure of rats to conditions of severe hypoxia (5% O2-95% N2) failed to significantly alter either the content or turnover of carotid body catecholamines. By contrast, the concentration of carotid body DOPAC, a reflection of DA utilization, was significantly elevated following hypoxic conditions. Further, in vivo tyrosine hydroxylase activity was assessed by measuring the accumulation of carotid body DOPA after inhibiting L-aromatic amino acid decarboxylase with NSD-1015. Basal tyrosine hydroxylase activity (approximately 14-16 pmol/carotid body pair/h) also was significantly increased by acute hypoxic exposure. These results, in part, suggest that rat carotid body DA may act as a neurotransmitter whose synthesis and release are coupled to stimulus demand.

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

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 micron 2 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 micron2) 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 micron2 in sectional area and containing 34.3 clear-core synaptic vesicles (average size 73.5 nm in diameter) per micron2 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.

The paraganglion supracardiale vagi: an intravagal paraganglion in the rat

In the Ham-Wistar rat, a paraganglion was found within the vagus nerve at the site of branching of the recurrent laryngeal nerve. Due to its location the name "paraganglion supracardiale vagi" is suggested. Fluorescence microscopy of the paragangkionic cells displays an intense yellow-green fluorescence indicating the presence of biogenic amines. Ultrastructurally, chief cells containing dense-core vesicles form three kinds of synaptic contacts (afferent, efferent and reciprocal) with enlarged. mitochondria-rich nerve endings.

Effects of low oxygen on the release of dopamine from the rabbit carotid body in vitro

1. Rabbit carotid bodies were pre-loaded with [(3)H]dopamine (DA) synthesized from [(3)H]tyrosine and then mounted in a vertical drop-type superfusion chamber which permitted simultaneous collection of released [(3)H]DA and recording of chemoreceptor discharge from the carotid sinus nerve.2. The time course of the spontaneous release of [(3)H]DA (superfusion with media equilibrated with 100% O(2)) in the presence of monoamine oxidase inhibitors exhibited two linear components, an initial steep phase followed after 3-4 hr by a later slower phase of release.3. When a 5 min low O(2) stimulus was delivered during the initial steep linear component of resting [(3)H]DA release, there was an abrupt increase in release, the magnitude of which was stimulus-dependent.4. The efflux of total radioactivity from the preparation declined exponentially with time; under resting conditions it was principally non-metabolized [(3)H]tyrosine. During stimulation, however the efflux increased, and 60-80% of the radioactivity could be attributed to [(3)H]DA.5. For a given low O(2) stimulus, the ratio of [(3)H]DA release during the stimulus period over that in the preceding control period remained approximately the same throughout a single experiment. Ratios for different low O(2) stimuli (50, 40, 30, 20, 10 and 0% O(2) in N(2)) yielded a parabolic relationship when plotted against stimulus intensity.6. Transection of the carotid sinus nerve or removal of the superior cervical ganglion 12-15 days prior to the experiment did not affect the release of [(3)H]DA at moderate stimulus intensities (superfusion with media equilibrated with 30% or 10% O(2) in N(2)) but both procedures significantly depressed release at the highest stimulus intensity (100% N(2)).7. Chemoreceptor discharge and [(3)H]DA release were simultaneously monitored in experiments using superfusion media free of monoamine oxidase inhibitors. In these experiments, the efflux of [(3)H]dihydroxyphenyl acetic acid (DOPAC) was also measured. The increase in peak chemosensory discharge was closely correlated with the increase in total release ([(3)H]DA + [(3)H]DOPAC) during stimulation with a series of low O(2) stimuli.8. Release of [(3)H]DA was almost completely abolished during superfusion with Ca(2+)-free, high Mg(2+) (2.1 mM) media, and the stimulus-related efflux of [(3)H]DOPAC was significantly reduced. However, chemoreceptor discharge was diminished by only 55%. These data are discussed with respect to their implications for DA as a chemosensory transmitter in rabbit carotid body.

Effects of hypoxia on catecholamine synthesis in rabbit carotid body in vitro

1. Unanaesthetized, unrestrained rabbits were exposed for 3 hr in a chamber to either air, hypoxic gas mixtures (10% or 14% O(2) in N(2)) or a hyperoxic gas mixture (50% O(2) in N(2)). The carotid bodies were then removed and incubated for 3 hr in modified Tyrode media equilibrated with 100% O(2) and containing either [(3)H]tyrosine or [(3)H]DOPA. The contents of [(3)H]DA and [(3)H]NA in the tissue were determined as described in the preceding paper.2. When [(3)H]DOPA was used as precursor, neither labelled dopamine (DA) or noradrenaline (NA) synthesis was increased in carotid bodies from rabbits exposed to 10% O(2) in N(2). Following exposure to 10% O(2) in N(2) and incubation with [(3)H]tyrosine, however, [(3)H]DA synthesis was increased by 72% above control (air) values while [(3)H]NA synthesis was unchanged. Less severe hypoxia, 14% O(2) in N(2), resulted in a smaller increase in [(3)H]DA synthesis, i.e. 53% above control value. Again, [(3)H]NA synthesis was unchanged. Similar experiments with the superior cervical ganglion involving exposure of the animals to either 10% or 14% O(2) in N(2) did not produce any change in the amounts of [(3)H]DA or [(3)H]NA synthesized from [(3)H]tyrosine when compared to control animals breathing air.3. Sympathectomy of the carotid body or transection of the carotid sinus nerve 12-15 days prior to hypoxic exposure (10% O(2) in N(2)) did not alter the increase in [(3)H]DA synthesis compared to normally innervated carotid bodies.4. Carotid bodies incubated with [(3)H]tyrosine for 2 hr in an alternating O(2)/N(2) sequence (5 min in media equilibrated with 100% O(2) followed by 3 min in media equilibrated with 100% N(2)) synthesized 37% more [(3)H]DA than control carotid bodies similarly exposed to an alternating O(2)/O(2) sequence. [(3)H]NA synthesis was unchanged. However, tissue levels of non-metabolized [(3)H]tyrosine were reduced by 19% in the carotid bodies exposed to the O(2)/N(2) sequence.5. Exposure of rabbits for 3 hr to 50% O(2) in N(2), followed by incubation of their carotid bodies in [(3)H]tyrosine, resulted in a 19% decrease in the absolute value for [(3)H]DA synthesis compared to control carotid bodies, but this difference was not significant (P > 0.05). However, [(3)H]NA synthesis was significantly reduced (51%; P < 0.05) in the hyperoxic carotid bodies. Similar experiments with the superior cervical ganglion showed that [(3)H]DA and [(3)H]NA synthesis were unchanged under control vs. hyperoxic conditions.6. Carotid bodies incubated with [(3)H]tyrosine for 3 hr, then transferred for 1 hr to unlabelled media equilibrated with 10% O(2) in N(2), released 81% more [(3)H]DA, and contained 38% less [(3)H]DA, than similarly treated carotid bodies exposed to 100% O(2). [(3)H]NA was not detectable in the media, and tissue levels of [(3)H]NA were the same in both hypoxic and control carotid bodies.

Transduction mechanisms in carotid body: glomus cells, putative neurotransmitters, and nerve endings

Carotid body chemoreceptors are activated by low PO2, high PCO2, acidity, increased temperature, and tonicity. These receptors are important in homeostasis and mediate their reflex effects on the CNS through sensory discharges of the carotid (sinus) nerve. The receptor complex is formed by glomus (type I) cells and carotid nerve endings, which, morphologically, appear to form a sensory synapse. The junction between glomus cells and nerve endings is enveloped by processes of sustentacular (type II) cells. The mechanisms of chemoreceptor transduction are complex; there is no agreement about the identity of the primary receptor element (glomus cell or nerve terminal) or what mechanisms are responsible for the onset of the sensory discharge in the carotid nerve. There is increasing evidence that integrity of the glomus cell is essential for normal transduction and that the receptor synapse described by morphologists may be functionally active. There is no conclusive evidence, however, that the glomus cell is the primary site of sensory transduction. Stimuli act on the glomus cell to release "transmitter" and/or "modulator" substances; but it is unknown if the released chemicals are directly responsible for the accompanying change in sensory impulse frequency or merely modify an already ongoing discharge. Interactions between glomus cells and nerves may be complicated enough to make it very difficult to resolve this question.

Ultrastructure of carotid body in rats living at a simulated altitude of 4300 metres

We studied the ultrastructure of the carotid body of three normal rats and three rats living in a hypobaric chamber at a pressure of 460 mm Hg for 27, 28 and 35 days respectively. The type I cells of the carotid bodies of our hypoxic rats were enlarged due to an increase in the volume of their cytoplasm. Many of their dense core vesicles were vacuolated and the core was displaced eccentrically to become adherent to the limiting membrane of the vesicle. The concentration and distribution of dense core vesicles remained unaltered and there were no obvious changes in the mitochondria, ribosomes or Golgi apparatus. There was pronounced capillary dilatation in the carotid bodies of all three rats exposed to chronic hypoxia. This change was accompanied by attenuation of capillary endothelial cells and increased frequency of endothelial fenestrations. There were no structural changes in the type II cells.

Intrapulmonary neuro-epithelial bodies in newborn rabbits. Influence of hypoxia, hyperoxia, hypercapnia, nicotine, reserpine, L-DOPA and 5-HTP

Neonatal rabbit neuro-epithelial bodies (NEB) were investigated under various experimental conditions with light microscopy, microspectrography, morphometry and electron microscopy. (1) Hypoxia causes a decreased amine fluorescence intensity and an increased secretory exocytosis of dense core vesicles (DCV). Otherwise the NEB appear structurally normal. (2) Hypercapnia also produces a decreased fluorescence and an increased exocytosis; ultrastructurally, however, the dense core of DCV fragmentizes. (3) Hyperoxia does not appear to affect significantly either fluorescence or exocytosis. (4) The uptake of biogenic amines such as 5-HTP and L-DOPA was demonstrated by fluorometry and electron microscopy. (5) Reserpine, on the other hand, provokes an amine depletion with a decrease of the NEB fluorescence and an ultrastructural palor of the DCV. (6) Intratracheally administered nicotine is accompanied by a decreased fluorescence and a distinct exocytosis of fragmented DCV. The reaction of NEB to hypoxia and hypercapnia suggests that these corpuscles could be intrapulmonary chemoreceptors (in addition to the classically known central and peripheral chemoreceptors), inducing a reflex reaction through the liberation of DCV at the corpuscular sensible nerve endings and via the CNS. In addition, they may subserve a local intrapulmonary effect by modulating directly the hypoxic and hypercapnic pulmonary vasoconstriction and thus the V/Q ratio.

Innervation of the carotid body of the adult rat. A serial ultrathin section analysis

The innervation of the carotid body of adult rats was studied by means of serial ultrathin sections. A single branching nerve fiber innervates 12 chief cells through several kinds of terminals (vesicle-containing, mitochondrial sack, and calyx-type) in en-passant and bouton forms.Two types of synaptic contacts between nerve terminals and chief cells are found; type 1 in which chief cells are postsynaptic, and type 2 in which chief cells are presynaptic. Since a single nerve fiber (possibly from the glossopharyngeal nerve) forms both types of synapses with type 2 predominating, the nerve fiber is considered basically sensory or centripetal. In addition to their synaptic connections with sensory nerve fibers, chief cells located in the periphery of this organ are in synaptic relation with dendrites of a few ganglion cells adjacent to these cells. Here the chief cells are presynaptic. A few synaptic contacts between two adjacent chief cells are seen, and so are direct contacts between thief cells and preganglionic efferent nerve fibers terminating on ganglion cells.

Studies of osmium deposits in the carotid body of the cat

Double aldehyde fixed carotid bodies and small pieces of vagus nerve of cats were incubated in 3 mM copper sulfate and 0.5 mM potassium ferricyanide in 0.05 M acetate buffer (pH 5.6) for 30 minutes at room temperature. Several modifications of this procedure were also attempted. Tissues were then postosmicated with 2% unbuffered osmium tetroxide and heated to 50-55 C for ten minutes. Under the electron microscope carotid body cells exhibited fine osmium deposits within cisternae of endoplasmic reticulum, saccula and vesicles of Golgi complex, and cristae of mitochondria. Intense osmium precipitation was also noted in the mitochondria of nerve endings. In addition, much more intense, more conspicuous and more localized reaction was noted in the intraperiod lines of the myelin sheath of nerves. Deposits here were rod-shaped, displaying considerable variation in length. These results are discussed in the light of previous findings on osmium deposits in various tissues. It was concluded that the osmium reaction is unspecific, and that histochemical methods employing hot osmium tetroxide to amplify enzymatic activities may therefore not be reliable.

The ultrastructure of the carotid body in chronically hypoxic rabbits

1. The ultrastructure of the carotid body in the rabbit has been examined by electron microscopy.2. A comparison was made between the ultrastructure of the carotid bodies in sea level rabbits, in rabbits which had been exposed to hypoxia equivalent to an altitude of 6000 m for 7 days and in rabbits which always had lived at an altitude of 4000-4300 m.3. We could not detect any difference in the ultrastructure between the two groups of hypoxic rabbits.4. When the hypoxic rabbits were compared with sea level rabbits there was a marked increase in the number of dense cored vesicles and mitochondria in the type I cells in the hypoxic rabbits. The Golgi region also appeared to be enlarged in the type I cells in the hypoxic rabbits.5. The finding suggests that in the rabbit the production of amines, probably dopamine, within the type I cells is increased during prolonged hypoxia which might explain the lowered ventilatory response to hypoxia observed in human high altitude residents.6. If the carotid bodies are organs of internal secretion the finding is compatible with an increased production of a hormone produced within the type I cells.

Chemoreceptor properties of glomus tissue found in the carotid region of the cat

1. ;Miniglomera' appearing as small masses of tissue with ample vascularization were found around the common carotid artery of the cat. Physiological, gross anatomical and electron microscopic studies were conducted on these tissues.2. The chemosensory function of each ;miniglomus' was evident from the behaviour of the afferent nerve fibres supplying the tissue: afferent responses became more active during asphyxia, when the blood flow through the tissue was reduced or blocked and when cyanide or ACh were applied. The afferent impulses became more infrequent during hyperventilation.3. Sensory frequency response curves constructed against percentage of inhaled O(2) showed that the impulses of single units increased in frequency with lowering of O(2) content of the inhaled gas.4. These miniglomera are innervated by afferent fibres emerging from the nodose ganglion; sometimes these fibres are contained in the aortic or common carotid baroreceptor nerves, but sometimes they emerge as independent nerves. None of the miniglomera are supplied by branches of the sinus nerve.5. The fine structure of the miniglomus is similar to that of the carotid body. The tissue contains two types of cells: glomus cells which contain dense cored granules, and sustentacular cells whose fine processes enclose the former. Membrane densifications occur where glomus cells lie adjacent to one another or where they are contacted by nerve terminals. Nerve fibres are common in the miniglomus but they contact glomus cells less frequently than in the carotid body.

Effects of sinus nerve stimulation on carotid body glomus cells

The sinus nerve or sympathetic trunk was stimulated unilaterally in one group of adult cats or Syrian hamsters while in another group the sinus nerve or sympathetic trunk was cut unilaterally and the animals were given reserpine. In a third group, atropine was administered prior to sinus nerve stimulation. All tissues were processed for the detection of primary monoamines. The carotid bodies on the operated sides were compared with those on the unoperated sides of the same animal in order to determine if amine depletion occurred following the experimental procedures. After sinus nerve stimulation alone, the density of the granules in the glomus cells was decreased, but changes were not noted in the granules following sympathetic nerve stimulation. Sinus nerve stimulation after atropine administration resulted in no change in granule density. Sinus nerve transection followed by reserpine treatment resulted in a greater decrease in granule density on the unoperated than on the operated side. Transection of the sympathetic components to the carotid body followed by reserpine injections resulted in a decrease in granule density in the glomus cells on both the operated and unoperated sides. These results suggest that the sinus nerve must be intact for reserpine to exert an effect and that the sinus nerve may contain efferent fibers which modulate amine secretion.

Electron microscopic and electrophysiological studies on the carotid body following intracranial section of the glossopharyngeal nerve

1. The innervation of carotid body Type I cells has been investigated in seventeen cats. At a sterile operation the glossopharyngeal and vagus nerve roots were cut intracranially on one side.2. From 1(1/2) to 378 days after the operation the carotid bodies were fixed in situ and prepared for electron microscopy. Nerve endings on Type I cells were found to degenerate with a prolonged time course. In each cat there was a decrease in the number of nerve endings on the operated side as compared with the non-operated side.3. Before the carotid bodies were fixed, recordings were made from chemoreceptor, and baroreceptor, afferent fibres in the sinus nerve on the operated side. The chemoreceptors responded in the usual way to changes in arterial O(2), CO(2) and pH; the injection of cyanide evoked a brisk response.4. It is concluded that the nerve endings on Type I cells are efferent rather than afferent and the cell bodies of their axons are probably in the brain stem.