The immunomorphologic analysis of innervation of chromaffin paraganglian cells of the mammalian arteries and heart

Innervation of chromaffin cells of paraganglia of the wall of mammalian large arterial vessels and heart (in rat, cat, and human) was studied by neuromorphological and immunohistochemical methods. There is established similarity in structure of specialized, "basket"-type nerve endings of the chromaffin cells (ChC) with pericellular nerve apparatuses of sympathetic and parasympathetic autonomic neurons. It is proposed to use immunohistochemical reaction for synaptophysin as method of selective detection of ChC of paraganglia and adrenal medulla. The conclusion is made that synaptophysin-positive terminals (SPPT) found on bodies of ChC and postganglionic neurons represent efferent, rather than afferent, synapses formed by myelinated axons of preganglionic fibers. It is suggested that ChC of paraganglia alongside with their characteristic endocrine function participate in complex mechanisms of chemoreceptor regulation of tissue homeostasis of mammalian blood vessels and heart.     

Increased numbers of extra-adrenal chromaffin cells in the abdominal paraganglia of senescent F344 rats: A possible role for the glucocorticoid receptor

Summary The increase in numbers of extra-adrenal chromaffin cells of abdominal paraganglia in senescent F344 rats was investigated by 5-bromo-2-deoxyuridine immunocytochemistry. A monoclonal antibody raised against 5-bromo-2-deoxyuridine was used to react with tissue-sections of paraganglia taken from 28-month-old animals given weekly injections of the thymidine analog over a 14-week period. No immunoreactivity was detected in the extra-adrenal chromaffin cells, whereas control sections of intestinal epithelium showed abundant immunoreactivity. Also, the profile for immunoreactivity of the glucocorticoid receptor in relation to age was compared between extra-adrenal and adrenal chromaffin cells, which share cytological characteristics, but not the increase associated with senescence. In the extra-adrenal chromaffin cells, the intensity of receptor immunostaining was unchanged, while in the adrenal chromaffin cells it decreased with age. These results indicate that hypertrophy of the paraganglia in aged F344 rats is not due to the proliferation of extra-adrenal chromaffin cells. Instead, they suggest that the chromaffin cell phenotype may be induced in pre-existing cells and that the expression of the glucocorticoid receptor has an intrinsic role in this change.     

Ultrastructural studies on the barrier properties of the paraganglia in the rat recurrent laryngeal nerve.

The permeability of blood capillaries in the paraganglia of the rat recurrent laryngeal nerve (RLN) was investigated by employing the ionic lanthanum tracer at ultrastructural level. Two types of blood capillaries, namely, fenestrated and nonfenestrated types, were observed in the rat RLN and its associated paraganglia (RLN paraganglia). A preferential distribution of fenestrated capillaries in the RLN paraganglia was noted. Nonfenestrated capillaries were distributed in the area of RLN devoid of paraganglia. Minute aberrant ganglia consisting of 4-8 neurons were frequently encountered in the rat RLN near the paraganglia. The capillaries in these neuronal areas were also nonfenestrated. The lanthanum tracer was limited within the vascular lumen, but not in the extravascular space, in the RLN proper and in the area of RLN paraganglia where the neurons were identified. In the RLN paraganglia, the tracer was located in the vascular lumen, extravascular space, periaxonal space of nerve fibers, and the intercellular space of the RLN paraganglionic cells. We concluded that (1) a blood-nerve barrier and a blood-ganglion (or blood-neuron) barrier exist in the area of RLN devoid of paraganglia, and (2) blood-paraganglion barrier and blood-nerve barrier were lacking in the rat RLN paraganglia.     

Development of adrenal chromaffin cells in Sf1 heterozygous mice

Adrenal medullary chromaffin cells are derivatives of the neural crest and are widely believed to share a common sympathoadrenal (SA) progenitor with sympathetic neurons. For decades, the adrenal cortical environment was assumed to be essential for channelling SA progenitors towards an endocrine chromaffin cell fate. Our recent analysis of steroidogenic factor 1(Sf1) −/− mice, which lack an adrenal cortex, has challenged this view: in Sf1 −/− mice chromaffin cells migrate to the correct “adrenal” location and undergo largely normal differentiation. In contrast to Sf1 homozygous mutants, heterozygous animals have an adrenal cortex, which, however, is smaller than in wildtype littermates. We show here that the Sf1 +/− adrenal cortical anlagen attract normal numbers of chromaffin progenitor cells into their vicinity by embryonic day 13.5 (E13.5). Two days later, however, only a few scattered cells with highly immature features have immigrated into the adrenal cortex, whereas the remainder form a coherent cell assembly ectopically located at the medial surface of the gland. These cells appear more mature than the scattered intracortical chromaffin progenitors and express the adrenaline synthesizing enzyme PNMT with a delay of 1 day in comparison with wildtype littermates. Nevertheless, chromaffin progenitor cells undergo a numerical reduction of approximately 30% by E17.5. Together, our data suggest that normal adrenocortical development is critical for the correct immigration of chromaffin progenitors into the cortical anlagen, for the timing of PNMT expression and for the regulation of chromaffin cell numbers.This work was supported by a grant from the Deutsche Forschungsgemeinschaft (SFB 488, TP A6).     

The ultrastructure of paraganglia associated with the inferior mesenteric ganglia in the guinea-pig

Summary The paraganglia of the inferior mesenteric ganglia in the guinea-pig are composed of small chromaffin cells containing an abundance of granule-containing vesicles. The chromaffin cells are almost completely surrounded by satellite cells. In areas in which satellite cell processes do not intervene, the membranes of adjacent chromaffin cells are closely apposed and often form specialized attachment zones. The paraganglia contain a dense capillary network, the endothelial cells of which are often extremely attenuated and show areas of fenestration. The processes of chromaffin cells approach close to the capillary walls and are often bare of satellite cells covering on the side facing the capillary. Evidence has been obtained for the exocytotic release of the contents of chromaffin cell vesicles into pericapillary spaces. Synapses of cholinergic and noradrenergic axons are seen on the chromaffin cells. The cholinergic axons degenerate when the praganglia are decentralized, but the noradrenergic axons, which appear to arise from the local inferior mesenteric ganglia, remain intact. The results suggest that the paraganglia have an endocrine function.     

Molecular markers of sympathoadrenal cells

Cells constituting the sympathoadrenal (SA) cell lineage originate from the neural crest and acquire a catecholaminergic fate following migration to the dorsal aorta. Subsequently, SA cells migrate to sites widely dispersed throughout the body. In addition to endocrine chromaffin and ”small intensely fluorescent” cells in adrenal glands and in extra-adrenal tissues such as the paraganglia, this lineage also includes neurones located in sympathetic ganglia and in the adrenal gland. It is widely assumed that these cells are all derived from the same precursors, which then differentiate along divergent pathways in response to different external stimuli. During embryonic differentiation, SA cells lose some of their early traits and acquire other distinguishing features. To help understand how the lineage diverges in terms of phenotype and function, this article examines the cellular expression of a variety of ”marker” proteins that characterize the individuals of the lineage. In particular, differences between adrenal medullary adrenergic and noradrenergic chromaffin cells in the expression of proteins, such as the neural adhesion molecule L1, the growth-associated protein GAP-43 and molecules involved in the secretory process, are emphasized. Factors that might differentially regulate such molecular markers in these cells are discussed. Received: 29 December 1998 / Accepted: 1 April 1999     

Monoamine storage in relation to cardiac regulation in the port jackson shark heterodontus portusjacksoni

Summary A study has been made of catecholamine stores that may be involved in cardiac regulation in the shark Heterodontus portusjacksoni. The anatomy of the anterior chromaffin bodies associated with the sympathetic chain is described. A fluoresent histochemical study shows that the chromaffin cells contain a monoamine, probably noradrenaline. The chromaffin cells have a fine structure comparable to that of chromaffin cells in other vertebrates. The heart is devoid of histochemically-demonstrable chromaffin cells or adrenergic nerve fibres, with the exception of a very sparse adrenergic innervation of the sinus venosus. It is argued that adrenergic control of the heart in Heterodontus might occur via amines released from the anterior chromaffin masses into the blood in the posterior cardinal sinus, which is then aspirated directly into the heart.     

Localization of cholinergic innervation and neurturin receptors in adult mouse heart and expression of the neurturin gene

Neurturin (NRTN) is a neurotrophic factor required during development for normal cholinergic innervation of the heart, but whether NRTN continues to function in the adult heart is unknown. We have therefore evaluated NRTN expression in adult mouse heart and the association of NRTN receptors with intracardiac cholinergic neurons and nerve fibers. Mapping the regional distribution and density of cholinergic nerves in mouse heart was an integral part of this goal. Analysis of RNA from adult C57BL/6 mouse hearts demonstrated NRTN expression in atrial and ventricular tissue. Virtually all neurons in the cardiac parasympathetic ganglia exhibited the cholinergic phenotype, and over 90% of these cells contained both components of the NRTN receptor, Ret tyrosine kinase and GDNF family receptor α2 (GFRα2). Cholinergic nerve fibers, identified by labeling for the high affinity choline transporter, were abundant in the sinus and atrioventricular nodes, ventricular conducting system, interatrial septum, and much of the right atrium, but less abundant in the left atrium. The right ventricular myocardium contained a low density of cholinergic nerves, which were sparse in other regions of the working ventricular myocardium. Some cholinergic nerves were also associated with coronary vessels. GFRα2 was present in most cholinergic nerve fibers and in Schwann cells and their processes throughout the heart. Some cholinergic nerve fibers, such as those in the sinus node, also exhibited Ret immunoreactivity. These findings provide the first detailed mapping of cholinergic nerves in mouse heart and suggest that the neurotrophic influence of NRTN on cardiac cholinergic innervation continues in mature animals.This study was supported by the National Heart, Lung, and Blood Institute (grant HL-54633).     

Structure of cells and nerve endings in abdominal vagal paraganglia of the rat

Summary The abdominal vagal paraganglia of the rat consist of small groups of cells, interspersed by blood vessels and nerve bundles and lying close to, or within, the vagus nerve or its branches. Each cell group consists of 2–10 Type I cells incompletely invested by 1–3 satellite cells. Type I cells are characterised by the presence of numerous dense-cored vesicles in their cytoplasm and may exhibit synaptic-like contact with each other.Small efferent nerve endings make synaptic contacts with Type I cells. Larger cup-shaped afferent nerve endings also make synaptic contacts of two kinds with Type I cells. Nerve-nerve synapses are often seen within or close to paraganglia.Attention is drawn to the close similarity of fine structure of abdominal vagal paraganglia, carotid body and small intensely fluorescent cells of the superior cervical ganglion in rats. Possible functional implications of this morphological similarity are discussed.     

Innervation of abdominal paraganglia: an ultrastructural study

Abdominal extra-adrenal chromaffin tissue, or paraganglia, was examined at the ultrastructural level to elucidate the innervation of this adrenal medullary homologue. Paraganglia display unmyelinated nerve fibers surrounded by Schwann cell cytoplasm. These nerves are separated from the paraganglion Type I (granule-containing) cells by cytoplasmic projections of paraganglion Type II (satellite) cells. However, serial sections show that the nerves eventually make synaptic contact with the Type I cell. At the axon-chromaffin cell junction, only the outer aspect of the nerve is covered by the satellite cell. The presynaptic endings contain numerous synaptic vesicles, mitochondria and glycogen particles. The vesicles are predominantly of the clear-cored variety, but a few possess centers which are elecron opaque. The pre- and postsynaptic membranes are separated bya subsynaptic space and occasionally exhibit the membranal densities usually associated with synaptic areas. These ultrastructural studies establish definite evidence that abdominal paraganglion cells are innervated.     

Heterogeneous distribution of neurocalcin-immunoreactive nerve terminals in the mouse adrenal medulla

Neurocalcin is a novel calcium-binding protein found in bovine brain tissue. We investigated immunoreactivity for neurocalcin in the mouse adrenal medulla using light and electron microscopy. The immunoreactivity was present in nerve fibers, nerve terminals, and ganglion cells in the adrenal medulla, but chromaffin cells, sustentacular cells, and Schwann cells were negative in reaction. Nerve bundles containing neurocalcin-immunoreactive fibers passed through the adrenal cortex and extended into the medulla. Immunopositive nerve fibers branched off and projected varicose terminals around the chromaffin cells. These varicose terminals contained small and large-cored vesicles and made synapses with the chromaffin cells. We performed paraformaldehyde-induced fluorescence-histochemical studies for catecholamine combined with immunohistochemical studies for neurocalcin. Neurocalcin-immunoreactive nerve terminals were more abundant at noradrenaline (fluorescent) cell-rich regions than at adrenaline (non-fluorescent) cell-rich regions. These results show that neurocalcin-immunoreactive nerves mainly innervate noradrenaline-containing chromaffin cells in the mouse adrenal medulla and that neurocalcin may regulate synaptic function in the nerve terminals. Received: 21 October 1996 / Accepted: 12 February 1997     

Enkephalin- and serotonin-like immunoreactivity in the aortico-pulmonary paraganglia of the white-belly opossumDidelphis albiventris (Marsupialia)

Summary Serial histological sections of the interatrial septum and basal heart vessels of the weaned and juvenile white-belly opossum (Didelphis albiventris) were obtained in order to study the presence of paraganglia and their content of regulatory peptides and serotonin. Paraganglion groups were mapped between the aorta and pulmonary arteries and close to the bifurcation of the pulmonary trunk and were found to contain cells with immunoreactivity to serotonin and to the neuroendocrine markers PGP 9.5 and NSE. When these paraganglia were tested for immunoreactivity to a battery of regulatory peptides, all were found to be positive for methionin-enkephalin, leucine-enkephalin and galanin. The hypothesis is raised that these peptides and serotonin, besides catecholamines, produced by these paraganglia may play a physiological role in the functions of the cardiovascular system of the white-belly opossum.Work supported by grants from FINEP and CNPq (Brazil).     

Calcitonin gene-related peptide (CGRP)-like immunoreactivity in scattered chromaffin cells and nerve fibers in the adrenal gland of rats

Summary The present immunohistochemical study reveals that a small number of chromaffin cells in the rat adrenal medulla exhibit CGRP-like immunoreactivity. All CGRP-immunoreactive cells were found to be chromaffin cells without noradrenaline fluorescence; from combined immunohistochemistry and fluorescence histochemistry we suggest that these are adrenaline cells. In addition, all CGRP-immunoreactive cells simultaneously exhibited NPY-like immunoreactivity. CGRP-chromaffin cells were characterized by abundant chromaffin granules with round cores in which the immunoreactive material was densely localized. These findings suggest the co-existence of CGRP, NPY and adrenaline within the chromaffin granules in a substantial number of chromaffin cells.Thicker and thinner nerve bundles, which included CGRP-immunoreactive nerve fibers, with or without varicosities, penetrated the adrenal capsule. Most of them passed through the cortex and entered the medulla directly, whereas others were distributed in subcapsular regions and among the cortical cells of the zona glomerulosa. Here the CGRP-fibers were in close contact with cortical cells. A few of the fibers supplying the cortex extended further into the medulla. The CGRP-immunoreactive fibers in the medulla were traced among and within small clusters of chromaffin cells and around ganglion cells. The CGRP-fibers were directly apposed to both CGRP-positive and negative chromaffin cells, as well as to ganglion cells. Immunoreactive fibers, which could not be found close to blood vessels, were characterized by the presence of numerous small clear vesicles mixed with a few large granular vesicles. The immunoreactive material was localized in the large granular vesicles and also in the axoplasm. Since no ganglion cells with CGRP-like immunoreactivity were found in the adrenal gland, the CGRP-fibers are regarded as extrinsic in origin. In double-immunofluorescence staining for CGRP and SP, all the SP-immunoreactive fibers corresponded to CGRP-immunoreactive ones in the adrenal gland. This suggests that CGRP-positive fibers in the adrenal gland may be derived from the spinal ganglia, as has been demonstrated with regard to the SP-nerve fibers.     

A Glutaraldehyde/Potassium Dichromate Tracing Method for the Localization and Preservation of Abdominal Extra-Adrenal Chromaffin Tissues

The present work introduces a method for the localization in situ of the abdominal paraganglia. After treating retroperitoneal tissue blocks with a near-neutral glutaraldehyde/ potassium dichromate solution following routine glutaraldehyde perfusion, intra- and extra-adrenal chromaffin tissues develop a pronounced brown color from the interaction of glutaraldehyde/potassium dichromate with amines. In this manner, visualization of the abdominal extra-adrenal chromaffin organs is enhanced at the same time that cellular ultrastructurr is preserved. Subsequent examination of the dichromate-reacted tissues with the electron microscope confirms that they represent the amine-rich paraganglia. This method offers an effective alternative to extensive sampling of plastic-embedded blocks for localizing peripheral chromaffin tissue and has been used to define the exact distribution of abdominal paraganglia in the rabbit.     

Light- and electron-microscopic demonstration of enkephalin-like immunoreactivity in paraganglia of the human urinary bladder

Summary The distribution of enkephalin-like immunoreactivity in paraganglia of the urinary bladder of adult humans was studied by use of immuno-electron microscopy. All paraganglionic cells were positively stained. Enkephalin-like immunoreactivity was located in chromaffin granules. Chromaffin cells in the paraganglia showed only few degenerative features, suggesting undisturbed function of the cells.     

Die Feinstruktur der peribronchialen Mikroparaganglien beim Meerschweinchen

Zusammenfassung Das Parenchym der peribronchialen Mikroparaganglien wird von zwei Zellarten aufgebaut: Chromaffine Zellen (Typ I-Zellen) und Hüllzellen (Typ II-Zellen).Die chromaffinen Zellen sind durch ihren reichen Gehalt an Vesikeln mit elektronendichtem Inhalt gekennzeichnet, deren Durchmesser 700–1300 Å beträgt. Markfreie Nerven ziehen an die Typ I-Zellen heran und bilden synaptische Kontakte aus. Die chromaffinen Zellen sind dabei der postsynaptische Teil der Verbindung. Die Hüllzellen entsprechen strukturell und funktionell den Schwannschen Zellen.Ein Mikroparaganglion wird von 10 bis 15 chromaffinen Zellen und deren Hüllzellen aufgebaut. Sie liegen dicht um fenestrierte Kapillaren, die von den Aa. bronchiales aus versorgt werden. Die Paraganglien sind von den Nervenzellen des peribronchialen Plexus durch dessen Perineurium getrennt. Selten findet man solitäre chromaffine Zellen innerhalb der Nervengeflechte. Es wird angenommen, daß die Paraganglien endokrine Funktionen erfüllen.

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The fine structure of the guinea pig peribronchial micro-paraganglia

Summary The parenchyma of peribronchial microparaganglia consists of two different cell types: chromaffin cells (type I-cells) and surrounding cells (type II-cells).The chromaffin cells contain numerous vesicles with electron dense content, their diameter ranging from 700 to 1,300 Å. Unmyelinated nerves form synapses with type I-cells. The surrounding cells structurally and functionally correspond to Schwann cells.A micro-paraganglion consists of ten to fifteen chromaffin cells and their satellite cells. They are situated close to fenestrated capillaries, which are supplied from the Aa. bronchiales. A perineurial sheath separates the paraganglia from the nerve cells of the peribronchial plexus. Single chromaffin cells are found seldom within the nervous plexus.The paraganglia are thought to have an endocrine function.

     

豚鼠胆囊SP免疫组织化学反应特点及电镜观察

研究采用ABC免疫组化方法及电镜观察发现;豚鼠胆囊含有SP免疫反应的神经元,神经纤维及肥大细胞,这些神经纤维束是被神经膜细胞完全或不完全包裹的无髓神经纤维。其神经纤维内含有的突触小泡形态大小不一。电镜下分可为3种类型;（1）以小型无芯小泡为主以及少量大型有芯小泡。（2）以小型有芯小泡为主以及少量无芯小泡和大型有芯小泡。（3）以大型有芯小泡为主以及少量小型无芯小泡。用SP免疫电镜组化方法观察。豚鼠胆囊的SP免疫反应阳性神经纤维内散在分布的突触小泡多为第3种。但在血管,淋巴管周围SP免疫反应阳性神经纤维内的突触小泡多为小型有芯小泡,胆囊除了受肾上腺素能神经支配外,尚受SP等肽能神经的支配。本研究对豚鼠胆囊SP免疫组织化学反应阳性神经纤维分布特点及神经纤维内突触小泡的超微结构特点进行了研究。     

Immunocytochemical identification of neuroendocrine markers in human cardiac paraganglion-like structures.

Paraganglion-like structures (PLS) containing chromaffin-positive cells have been reported to be present in the adult human heart. The present work was initiated in order to evaluate the density of these structures in the interatrial septum and to study the presence of immunoreactivity of their cells to NSE and PGP 9,5 antibodies, two neuroendocrine markers. Six hundred 6-microns paraffin serial sections were obtained from the upper third of the interatrial septum from six adult human hearts. From 2 to 12 paraganglia were found in each case, and their principal cells stained positively with NSE and PGP 9,5 antibodies. Depending on how these PLS related to other cardiac structures, four different types were identified: Type I - "True paraganglia" (located adjacent to ganglia or nerve fibers); Type II - "Free paraganglia" (immersed in the interatrial adipose tissue, without evident connection to other structures); Type III - "Intraganglionic paraganglia" (located within the nervous ganglia); Type IV - "Intramyocardic paraganglia" (small nests of immunoreactive cells closely related to myocardiocyte bundles). These cardiac paraganglia, which probably belong to the visceral-autonomic group, may have a role in the regulation of the cardiac function and in the adaptive mechanisms of the heart. Its is also possible that they originate functioning and non-functioning tumours.     

Monolayer co-culture of rat heart cells and bovine adrenal chromaffin paraneurons

Summary This paper describes a method for the preparation of co-cultures of rat heart cells and bovine adrenal chromaffin paraneurons. The most suitable condition for heart cell isolation was when a combination of paraneurons. The most suitable condition for heart cell isolation was when a combination of trypsin-DNAse I in Locke's solution was used for digestion. The best co-culture conditions were obtained when 10⁶ heart cells were plated on 7- to 8-d-old adrenal chromaffin paraneuron cultures containing 0.5×10⁶ cells per 35-mm diameter culture dishes. Measurements of DNA (heart cells and chromaffin paraneurons), monitoring of beating frequency (heart cells), and catecholamine (chromaffin paraneurons) levels and release indicated that both cell types remain viable and functional, for several weeks. Heart cells started their characteristic contractile activity 24 h earlier when plated either on viable or lysed chromaffin paraneurons, an effect apparently due to faster surface adhesion of heart cells. The beating frequency of heart cells increased after treatment of co-cultures with either noradrenaline or nicotine, with the latter agent acting indirectly through, the release of chromaffin paraneuron catecholamines. Propranolol produced a dose-related inhibition of the responses to either noradrenaline or nicotine, thus suggesting that the increase in myocyte's beating activity was mediated through β-receptors. Anti-myosin and anti-dopamine-β-hydroxylase immunostaining was used for cell type identification and for the demonstration of body-to-body and process-to-process contacts between adrenal chromaffin paraneurons and heart cells. This co-culture system will serve as a starting point of further studies directed to understand a) the influence of a cell type on the development and on the phenotypic characteristics of a second cell type and b) the interaction of cells derived from different organs and species. This study was supported by grant PG-20 from Medical Research Council of Canada and a grant from the Ontario Heart and Stroke Foundation. M. L. N. is a postdoctoral fellow of the MRC.     

Up-regulation of IL-1 receptor type I and tyrosine hydroxylase in the rat carotid body following intraperitoneal injection of IL-1β

It is well established that reciprocal modulation exists between the central nervous system and immune system. Interleukin (IL)-1β, a proinflammatory cytokine secreted at early stage of immune challenge, has been recognized as one of the informational molecules in immune-to-brain communication. However, how this large molecule is transmitted to the brain is still unknown. In recent years it has been reported that the cranial nerves, especially the vagus, may play a pivotal role in this regard. It is proposed that IL-1β may bind to its corresponding receptors located in the glomus cells of the vagal paraganglia and then elicit action potentials in the nerve. The existence of IL-1 receptor type I (IL-1RI) in the vagal paraganglia has been shown. The carotid body, which is the largest peripheral chemoreceptive organ, is also a paraganglion. We hypothesize that the carotid body might play a role similar to the vagal paraganglia because they are architectonically similar. Recently we verified the presence of IL-1RI in the rat carotid body and observed increase firing in the carotid sinus nerve following IL-1β stimulation. The aim of this study was to observe the changes in expression of IL-1RI and tyrosine hydroxylase (TH), a rate-limiting enzyme for catecholamine synthesis, in the glomus cells of the rat carotid body following intraperitoneal injection of IL-1β. The radioimmunoassay result showed that the blood IL-1β level was increased after the intraperitoneal injection of rmIL-1β (750 ng/kg) from 0.48 ± 0.08 to 0.78 ± 0.07 ng/ml (P < 0.05). Immunofluorescence and Western blot analysis showed that the expression of IL-1RI and TH in the rat carotid body was increased significantly following peritoneal IL-1β stimulation. In addition, double immunofluorescence labeling for TH and PGP9.5, a marker for glomus cells, or TH immunofluoresence with hematoxylin-eosin (HE) counterstaining revealed that a considerable number of glomus cells did not display TH immunoreactivity. These data provide morphological evidence for the response of the carotid body to proinflammatory cytokine stimulation. The results also indicate that not all of the glomus cells express detectable TH levels either in normal or in some abnormal conditions. Xi-Jing Zhang and Xi Wang are co-first authors.