Autonomic nervous system structures: structural and functional correlates. Introduction.
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Biomedical subjects
R D Yates
Publications and source records attributed to R D Yates.
Morphological observations of small granule-containing (chromaffin) cells in the celiac ganglion of the guinea pig, with emphasis on cell contacts.
Utilizing electron microscopic observation, several contacts between small, granule-containing cells (SGC) and postganglionic neurons (PGN) in the celiac ganglion of the guinea pig have been observed. A SGC in very close association with a PGN was seen to receive a distinct synaptic contact that contained many vesicles with dense cores. This contact was morphologically unlike cholinergic synapses previously reported on chromaffin cells. Because the SGC and PGN were clearly separated by a thin rim of satellite cell cytoplasm mutual to both cells, it is not known how or if the SGC would possibly exert a synaptic or paracrine effect on the PGN. Also, intraganglion SGC existed as large well-vascularized islands within the celiac ganglion. These intraganglion clusters sometimes contained more than 50 cells and perhaps could be considered to function as localized neuroendocrine components within the ganglion by secreting granule products into the nearby blood vessels for local or distant effects, although this certainly is not known. This work reports a unique synaptic ending upon a single-occurring SGC, which, in turn, closely approximates a ganglion neuron in a soma-somatic relationship. In addition, a very close association (but no actual contact) was observed between granule-containing processes, presumably emanating from the intraganglion clusters, and PGN. Whatever the function of ganglionic SGC may be, the exact relationship between SGC and PGN presumably would be of great interest and potential importance.
Animals↗
Synaptic morphology of substance P terminals on catecholamine neurons in the commissural subnucleus of the nucleus tractus solitarii in the rat.
The ultrastructure of substance P-containing nerve terminals synapsing on catecholamine neurons in the rat commissural subnucleus of the nucleus tractus solitarii (NTScom) was studied using a double immunocytochemical labeling technique. Although there were numerous tyrosine hydroxylase-immunoreactive (TH-I) somata present, substance P immunoreactive (SP-I) cell bodies were only occasionally found in the NTScom. At the light microscopic level, many SP-I terminals were seen closely associated with TH-I dendrites and somata. At the electron microscopic level, SP-I terminals synapsing on TH-I structures were also readily encountered. SP-I terminals contained small, clear, and predominantly spherical vesicles (32 +/- 4 nm diameter), as well as large dense-cored vesicles approximately 100 nm in diameter. Postsynaptic TH-I dendritic profiles of various calibers and somata were encountered. These postsynaptic TH-I structures often showed postsynaptic densities. The morphological features of the SP-TH synapses in the present study, that is, the size of synaptic vesicles and the presence of postsynaptic densities, are quite different from those of central carotid sinus afferent synapses reported in our previous study [Chen et al. (1992), J. Neurocytol., 21:137-147]. Therefore, most of the SP terminals of the SP-TH synapses in the NTScom appear not to originate from the carotid sinus afferents. SP-I second-order neurons of the carotid sinus afferent pathway [Chen et al. (1991), J. Auton. Nerv. Syst., 33:97-98] may be one of the possible sources of such terminals.
Afferent Pathways↗
Synaptic connections of central carotid sinus afferents in the nucleus of the tractus solitarius of the rat. II. Connections with substance P-immunoreactive neurons.
A combined transganglionic transport and immunocytochemical technique was used to study the synaptic morphology of central carotid sinus afferents and substance P-immunoreactive neurons in the commissural subnucleus of the nucleus of the tractus solitarius in rats. A large population of substance P-immunoreactive neurons (88.32%) were seen in close association with central carotid sinus afferents by light microscopy. However, many labelled central carotid sinus afferents appeared not associated with substance P-immunoreactive neurons in the nucleus of the tractus solitarius. Substance P-immunoreactive neurons were spindle, pear, or oval-shaped with a short axis ranging from 5 to 11 microns. Their long axis was oriented predominantly in a lateral-medial direction along the path of the central carotid sinus afferents from the solitary tract to the midline. Synaptic contacts between central carotid sinus afferents and substance P-structures, including dendritic profiles of different calibers and somas, were readily found by electron microscopy. Many central carotid sinus afferents were also found in synaptic contact with non-immunoreactive dendrites and somas. Appositions between central carotid sinus afferents and unlabelled axon terminals were common, but only in a few cases were morphological manifestations of synapses revealed. In the latter, the substance P-immunoreactive terminals appeared mostly presynaptic but postsynaptic ones were also encountered. Our data provide the evidence that some of the substance P-immunoreactive cells in the nucleus of the tractus solitarius are 2nd order neurons of the carotid sinus afferent pathway. The possibility that some of the substance P-immunoreactive neurons in the nucleus of the tractus solitarius may be interneurons and mediate carotid sinus afferent inputs to catecholaminergic neurons in the nucleus of the tractus solitarius is considered. Our findings also provide an anatomical substrate for a possible presynaptic modulatory role of central carotid sinus afferents on the inputs from other brain centers to the substance P-neurons in the nucleus of the tractus solitarius.
Afferent Pathways↗
Synaptic connections of central carotid sinus afferents in the nucleus of the tractus solitarius of the rat. I. An electron microscopic study.
A transganglionic transport technique was used to study the synaptic connections of the central carotid sinus afferents in the nucleus of the tractus solitarius of the rat by electron microscopy. The caudal part of the nucleus was profusely innervated. Labelled fibres extended to the contralateral nucleus, and to the ipsilateral dorsal motor nucleus of the vagus nerve, nucleus ambiguus, spinal nucleus of the trigeminal nerve and the area postrema. The labelled terminals were densely packed with clear, predominantly spherical vesicles about 50 nm in diameter and a few often swollen mitochondria. The terminals synapsed on dendrites of various calibres, spindle- or pear-shaped somal profiles with short axes lesser than 8 microns, and axon terminals. In axo-axonal synapses, most labelled terminals appeared to be presynaptic. Frequently, profiles of labelled terminals were in direct apposition with one another. The latter may represent the morphological substrate of the interaction between baro- and chemoreceptor inputs in the nucleus of the tractus solitarius and warrants further study. The present results indicate that in addition to direct inputs, the carotid sinus afferents are able to influence second-order neurons in the nucleus of the tractus solitarius indirectly through presynaptic modulation.
Afferent Pathways↗
Morphometric study of ventricular myocardial cells in the bat (Pipistrellus pipistrellus), hamster (Mesocricetus auratus) and Wistar rat.
A comparative morphometric study of ventricular myocardial cells of the West African insect-eating the Pipistrellus pipistrellus, the hamster and the rat revealed significant differences in volume fractions of mitochondria myofibrils, lipid bodies and T tubules. In the cells of the bat, mitochondria constitute 35% of cytoplasmic volume compared with 29 and 30% in the hamster and rat, respectively. Notably, crista density is much higher in the bat cells (3.58 x 10(5) cm-1) than in those of the hamster (2.59 x 10(5) cm-1) and of the rat (2.48 x 10(5) cm-1). Myofibril concentration is 40% in the bat, 53% in the hamster and 55% in the rat. There is greater numerical density of lipid bodies in the bat (212.27 x 10(9) cm-3) than in the hamster (139.20 x 10(9) cm-3) and in the rat (114.00 x 10(9) cm-3). The volume occupied by T tubules is 0.02 in the bat and hamster, and 0.009 in the rat. These differences suggest structural design for efficient metabolic activity in the bat which, among mammals, has high exercise tolerance.
Adaptation, Physiological↗
Fine structure of subendocardial (Purkinje) cells of the insect-eating bat (Pipistrellus pipistrellus).
Subendocardial cells of the right ventricular myocardium of the West African bat, Pipistrellus pipistrellus, were investigated at the ultrastructural level. The prominent features of these cells include a well-developed T-tubule system and numerous mitochondria with closely packed cristae. Additionally, the cells display large stores of lipid bodies. These unusual features confirm that Purkinje cells are heterogeneous in structural detail. From the paucity and poor structure of myofibrils of these cells, it is likely that the T-tubules may have a primary nutritional role in the regulation of electrolytes in an animal in which the cardiac cycle is particularly rapid. The well-developed mitochondria and the large stores of lipid bodies are appropriate for such active cells in which metabolism is probably of the aerobic type.
Animals↗
Mitotic cell division in the extraadrenal chromaffin system of various species.
Mitotic activity often has been reported in embryonic and fetal sympathetic neuroblasts, principal sympathoblasts, and primitive sympathetic cells in various species at different stages of development. Postnatal adrenal medullary cells also are known to undergo mitosis, but such dividing capabilities rarely have been observed in the true postnatal extraadrenal chromaffin system. Although few in number, this work nevertheless has clearly identified such cells in varying stages of the mitotic cycle in the young dog, Syrian hamster, mouse, rabbit, and rat. The dividing cells were noted in paraaortic chromaffin organs, paraganglia, and within the inferior mesenteric ganglion as well. They displayed the morphological character usually associated with their adrenal medullary catecholaminergic counterparts, including numerous dense-cored vesicles known to be the harbingers of catecholamines and various peptides. Nerve endings were not noticed upon the mitotic cells. The phenomenon of dividing extraadrenal chromaffin cells augments existing data and perhaps suggests that these cells are more endocrine than neural in type and subservient to the adrenal medulla in its classic endocrine function.
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Ultrastructure of the internodal myocardium in the rat.
Ultrastructural studies of the rat atrial myocardium reveal that the specialised myocardial cells can be distinguished from the usual atrial myocytes by their lack of specific atrial granules. On the basis of this distinction it has been shown that there is interposition of atrial myocardial tissue in the pathway between the two nodes and that there are no morphologically specialised internodal pathways. The atrial myocardial cells themselves exhibit variations in their content of cytoplasmic organelles such as myofibrils, T-tubules and sarcoplasmic reticulum but they all contain membrane-bound specific atrial granules.
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Substance P-like immunoreactivity in rat and cat carotid bodies: light and electron microscopic studies.
Substance P-immunoreactive (SP-1) structures in the carotid bodies of rats and cats were examined with the light and electron microscopes. In both species SP-I varicose nerve fibers were located singly in the interstitial connective tissue in close association with blood vessels. They were small unmyelinated fibers enveloped in a common Schwann cell sheath with other SP-negative fibers. Some of SP-I fibers contained large dense-cored granules and small clear vesicles in addition to microtubules and mitochondria and probably represented nerve fiber varicosities. The latter often were found incompletely invested by Schwann cell sheaths. SP-fibers were found occasionally in the envelopes of supporting cells at the periphery of parenchymal cell groups. However, none of the nerve terminals making synaptic contacts with glomus cells exhibited SP-like immunoreactivity. In cat carotid bodies some glomus cells showed moderate to intense SP-like immunoreactivity. The intense SP-I glomus cells displayed numerous dense-cored vesicles of 85 to 140 nm in diameter and frequently showed synaptic contacts with SP-negative nerve terminals. In rat carotid bodies we were unable to detect consistent SP-immunoreactivity in glomus cells. Our results do not favor the hypothesis that SP is a neurotransmitter/modulator in the chemoreceptor afferents synapsing on glomus cells in either the cat or rat carotid body. However our results support the hypothesis that SP in cat glomus cells may play a role in the modulation of chemoreceptor activity.
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Dopamine beta-hydroxylase-like immunoreactivity in the rat and cat carotid body: a light and electron microscopic study.
Immunocytochemical localization of dopamine beta-hydroxylase (DBH) was used to study the synthesis and storage sites of norepinephrine (noradrenaline) in the rat and cat carotid bodies. In the rat carotid body some parenchymal cells exhibited strong DBH-like immunoreactivity (DBH-I), while others displayed only faint DBH-I. In a typical parenchymal cell cluster, most cells with strong DBH-I were irregular in shape and appeared to partially surround those with weak DBH-I which usually were rounded in contour. In the cat carotid body most parenchymal cells showed a strong to moderate DBH-I. In both the rat and cat carotid bodies varicose nerve fibres with DBH-I were associated primarily with blood vessels. All autonomic ganglion cells examined, which were associated with the rat carotid body, showed DBH-I. Electron microscopy revealed that most DBH-I in the strongly positive cells of the rat carotid body was associated with dense granules (possibly corresponding to dense-cored vesicles of various sizes), although some was found in other sites. In oval cells with less DBH-I, reactivity resided in some of the large granules. In the cat carotid body the glomus cells contained more granules of various sizes and shapes than did those of the rat carotid body. Most of the cat glomus cell granules exhibited DBH-I activity. Our results indicate that some of glomus cells in the rat and most of the glomus cells in the cat contain DBH and therefore may be sites of norepinephrine synthesis.
Animals↗
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.
Acetylcholine↗
Autoradiographic localization of alpha-bungarotoxin-binding sites in the carotid body of the rat.
Radioiodinated alpha-bungarotoxin (alpha-Bgt) was used to localize alpha-Bgt-acetylcholine receptors in the carotid body of the rat. The gamma spectrometer analyses indicated a high uptake of [125I] alpha-Bgt in carotid bodies incubated in vitro (1.51 fmole per organ). Incorporation of the isotope was effectively blocked by pretreatment of carotid bodies with d-tubocurarine and unlabeled alpha-Bgt, but not by atropine. Light microscopic autoradiography showed a heavy labeling of some parenchymal cells. Electron-microscopic autoradiography revealed that labeling was localized along the interface between parenchymal cells, especially where their cytoplasmic processes engage in complex interdigitations. The silver grain counts on electron-microscopic autoradiographs suggest that labelings are preferentially associated with the plasma membrane of certain Type I cells. It is suggested that these Type I cells in the rat's carotid body probably are provided with nicotinic acetylcholine receptors on their plasma membranes.
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Age-related alterations in epicardial arteries of spontaneously hypertensive rats.
Proximal portions of the left coronary arteries were examined microscopically in aging female normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). The age-related intimal alterations in SHR were largely limited to endothelial cells, which demonstrated a proliferation of organelles (most notably Weibel-Palade bodies). In the media, degenerative alterations appeared to be most marked near the medio-adventitial junction. Compared to WKY and increasing with age, the media of the SHR epicardial artery demonstrated an accumulation of extracellular elements that included basement membrane-like material, collagen fibers and debris. Complex carbohydrates, as determined with the silver methenamine reaction, were noted to accumulate in a lamellar fashion. Smooth muscle cells demonstrated an age-related tendency (which was exaggerated in SHR) toward development of invaginations and irregular profiles. These observations indicate that age-related structural alterations in epicardial arteries of SHR are progressive, and they support the concept that structural alterations in SHR coronary arteries may represent accelerated aging phenomena.
Age Factors↗
An electron microscopic study of the baroreceptors in the internal carotid artery of the spontaneously hypertensive rat.
The carotid baroreceptor field of normotensive (NTR) and spontaneously hypertensive rats (SHR) examined in this study extends for about 0.5 mm along the length and about 1/3 to 1/2 of the circumference of the wall of the internal carotid artery opposite to the carotid body. The vascular wall of the baroreceptor field exhibits neither a marked dilation to form a carotid sinus nor histological differences in the intima and media compared to other parts of the carotid artery. Histologically the adventitia of the baroreceptor field is characterized by (1) an increased thickness and by less well developed elastic lamellae in comparison with other parts of the arterial wall, (2) a profuse blood and nerve supply, and (3) a richness of cellular elements. The presumptive baroreceptor terminals are localized in the inner 1/3 of the adventitia and display local enlargements that appear to show preferential association with the cell body or processes of the Schwann cell but not with other components of the adventitia. the enlargements are characterized by an accumulation of very densely packed mitochondria, and glycogen particles. No morphological alterations were noted in the baroreceptor terminals of SHR except for proliferated basal laminae that invest the terminals. Our work does not support the concept that resetting of the baroreceptors is due to degeneration of the terminals.
Animals↗
Brain aging in normotensive and hypertensive strains of rats. II. Ultrastructural changes in neurons and glia.
A variety of age-related changes occur in the structure of neurons in the cerebral cortex of Wistar-Kyoto and spontaneously hypertensive rats. The most marked alteration associated with increasing age was the deposition of lipofuscin pigment, primarily at the bases of apical dendrites of pyramidal neurons. While no strain-related differences in the amount of lipofuscin pigment were observed in the youngest (3 months) and in the aged (22-27 months) groups of rats, it appeared that hypertensive rats had larger pigment deposits at 12 months of age. At the ultrastructural level, neurons of the aged brains exhibited numerous nuclear invaginations and filamentous nuclear inclusions, increased amounts of Golgi complex and two types of cytoplasmic inclusions. The number of degenerative structures in the neuropil (membranous whorls, dystrophic axons and alterations in myelin sheaths) was also apparently increased in the aged brains. Neurofibrillary tangles were observed in dendritic processes of a 27-month-old Wistar-Kyoto rat. Glial cells accumulated distinctive pigment granules by which the three types of glia could be identified.
Age Factors↗
Effects of aging on the structural and permeability characteristics of cerebrovasculature in normotensive and hypertensive strains of rats.
This study demonstrates that markedly different patterns of age-related changes in blood pressure and body weight occur among normotensive Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats and spontaneously hypertensive rats (SHR). In addition, a variety of age-related structural alterations occurred in the walls of arterioles, capillaries, and venules of the frontal cortex. These changes include: (1) an increase in the thickness of the vascular wall by deposits of collagen and basal lamina which, in some cases, extended into the surrounding neuropil; (2) the presence of a flocculent material in the adventitia of intracerebral arterioles; (3) vesicular inclusions in perivascular macrophages, pericytes and smooth muscle cells which were labelled with i.v. administered horseradish peroxidase (HRP); (4) fragmentation of smooth muscle cells; and (5) accumulation of lipofuscin-like pigments in perivascular glial processes. The hypertensive rats exhibited these changes, but they were more advanced and more widely distributed throughout the cerebral cortex. The aged hypertensive rats occasionally had large bundles of 10 nm diameter, intermediate filaments in the endothelial cells. Whereas no change in blood-brain barrier permeability to HRP was observed in the aged normotensive rats, all age groups of the hypertensive rats exhibited increased permeability to HRP in the initial segment of penetrating arterioles in laminae I and II of the cerebral cortex.
Age Factors↗
Paraneurons and paraganglia: histological and ultrastructural comparisons between intraganglionic paraneurons and extra-adrenal paraganglion cells.
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Animals↗