Ultrastructure and morphometric parameters of glutamatergic synapses on nigrothalamic and unidentified neurons of the reticular zone of theSubstantia nigra in cats

Nigrothalamic neurons were identified into thesubstantia nigra by their retrograde labelling with horseradish peroxidase. Axon terminals that contain glutamate (the excitatory transmitter) were revealed immunocytochemically with an immunogold electron microscopic technique. Ultrastructural parameters (the large and small diameters of axon terminals, area of their profiles, coefficient of form of profiles, large and small diameters of synaptic vesicles) were analyzed in all 240 synapses under study. Synaptic contacts localized on both nigrothalamic and unidentified neurons belonged to three morphologically specific groups. Synapses of the groups I and III, according to classification by Rinvik and Grofova, were characterized by a symmetric type of synaptic contact and contained polymorphic synaptic vesicles. Contacts in group-II synapses were asymmetric, and respective terminals contained round vesicles. Among the studied synapses, 65.8% were classified as group-I contacts, 25.0% belonged to group II, and 9.2% belonged to group III. Glutamate-positive axon terminals formed predominantly group-II synapses; such connections constituted 70% of this group's synapses. Sixty percent of glutamate-positive synapses were localized on the distal dendrites and 23% on the proximal dendrites, while 17% of such synapses were distributed on the somata of nigral neurons. Such a pattern of distribution of glutamate-positive synapses was observed on both nigrothalamic and unidentified nigral neurons. About 7% of glutamate-positive synapses were formed by very large axon terminals containing round synaptic vesicles; yet, the contacts of these terminals were of a symmetric type. Twenty percent of group-I synapses, i.e., synapses considered inhibitory connections, were found to manifest a weak immune reaction to glutamate.Neirofiziologiya/Neurophysiology, Vol. 28, No. 6, pp. 285–295, November–December, 1996.     

The structure of the coeliac ganglion of a teleost fish Myoxocephalus scorpius

Summary In order to compare the structure of a teleost sympathetic ganglion with those of other vertebrates, light, fluorescence histochemical and electron microscopy were carried out on the coeliac ganglion of the scorpion fish, Myoxocephalus scorpius. In common with studies on other vertebrates, fluorescence histochemistry distinguished two cell types: a) principal neurones which exhibited low levels of specific catecholamine fluorescence and comprise the majority of neurones in the ganglia, and b) smaller intensely fluorescent cells, some of which had processes tens of micrometers long.With the electron microscope, the principal cells were seen to make axodendritic and axosomatic synapses with axons containing mainly 30 nm agranular vesicles at the synaptic site while in other vertebrates usually only one or other synaptic association is present.Both the somata and the processes of intensely fluorescent cells contain 300–600 nm diameter vesicles many of which have electron dense cores. These cells are also innervated by axons containing 30 nm agranular vesicles.     

Ultrastructure of sympathetic ganglion cells and granule-containing cells in the paracervical (Frankenhäuser) ganglion of the newborn rat

Summary A study was made of the ultrastructure of the paracervical (Frankenhäuser) ganglion of the newborn rat, using immersion fixation by glutaraldehyde (2.5%) followed by OsO₄ (1%), or KMnO₄ (3%) fixation. The cells containing dense—core vesicles were divided into three groups: (1) primitive sympathetic cells, (2) cells containing some dense-core vesicles 700–1100 Å in size and structurally resembling sympathetic neurons, called principal neurons, and (3) cells containing many dense-core vesicles with a larger, darker dense core, 800–2000 Å in diameter, called granule-containing cells. Using glutaraldehyde-osmium fixation, the principal neurons were further divided into dark and light cells on the basis of electron opacity of the cytoplasmic matrix. The granule-containing cells were believed to correspond to the small, intensely fluorescent cells (SIF-cells) previously described using the formaldehyde-induced fluorescence technique. On the basis of the amount of granules, the granulecontaining cells were classified as mature or maturing SIF-cells and as more primitive SIF-cells, and developing sympathicoblasts. The development of synapses in autonomic ganglia was discussed.Grant: The Finnish Medical Foundation.     

Electron microscope investigation of synapses,synapse-like structures,and possible sites of release of neurosecretory material in the buccal ganglia of Helix pomatia (Mollusca)

Summary In the buccal ganglia of Helix pomatia synapses and sites of possible release of neurosecretory material were investigated electron microscopically. There is one chemical synapse and one electrotonic synapse in the neuropile of the ganglion. No synapses could be detected in the buccal nerves, cerebro-buccal connectives, or in the buccal commissure. The synaptic cleft of the chemical synapse is about 25 nm wide and contains electron-dense material whereas the cleft of the electrotonic synapse is only 5 nm wide. The presynaptic fibre of the chemical synapse contains clear vesicles and dense core vesicles. The release sites of neurosecretory material are found at the initial segment of the axons, at perikarya of neurones, and at the perineurium of the ganglion. If the terminals are located at the plasmalemma of a nerve cell, these release sites are called synapse-like structures according to Roubos and Moorer-van Delft (1979). The synapse-like structures show all structural elements of synapses, except the 25 nm cleft containing dense material; the cleft is only 15–20 nm wide here like the normal cleft between neurones and glial cells or between two fibres. If the secretory material is released at the periphery through the perineurium the terminal is called synaptoid according to Scharrer (1970). In all cases, i.e. synapses, synapse-like structures, and synaptoids, clear vesicles were found in the axon terminal. This finding provides further evidence that clear vesicles always accompany the release of substances from axon endings.     

Neural pathways and innervation of cnidocytes in tentacles of sea anemones

Our previously published studies are here reviewed detailing neuro-cnidocyte synapses, demonstrating putative neurotransmitter substances, and identifying complex neural pathways in sea anemones. Synapses were traced to their contacts on nematocytes and spirocytes by transmission electron microscopy of serial thin sections of tentacles. In five animals, cells containing microbasic p-mastigophores had synapses with clear vesicles, whereas cells containing basitrichous isorhizas had synapses with dense-cored vesicles, providing preliminary evidence for a selectivity of neurotransmitter types for different nematocysts. Either clear or dense-cored synaptic vesicles were also present at neuro-spirocyte contacts. Antho-RFamide immunoreactivity occurred in some anthozoan synaptic vesicles and immunogold labeling of serotonin was found at a neuro-spirocyte synapse. Neural pathways included direct innervation of spirocytes by sensory cells, sequential neuro-neuro-spirocyte and neuro-neuro-nematocyte synapses and reciprocal synapses involving axons of both sensory cells and ganglion cells. Such synaptic patterns resemble neuro-effector pathways found in higher animals and lay to rest the independent effector hypothesis for cnidocyte discharge in tentacles of sea anemones.     

The effect of ageing on the SIF-cells in the hypogastric (main pelvic) ganglion of the rat

Summary The effect of ageing on SIF-cells was studied by the formaldehyde-induced fluorescence (FIF) method and by electron microscopy (EM). Microspectrofluorimetry was used to record emission spectra in FIF preparations. In newborn and in young adult (8–12 weeks) rats a single type of SIF-cell emitting greenish-yellow FIF was found while in aged rats a second type of SIF-cell emitting yellowish-brown granular FIF was also present. The intensity of the yellowish-brown FIF was lower than that of the greenish-yellow FIF. Also a few bright cytoplasmic fluorescent areas were occasionally found in some SIF-cells. The distribution of the SIF-cells through the ganglion did not change remarkably with age.In EM after glutaraldehyde-fixation in newborn and in young adult rats two types of small granule-containing (SGC) cells were distinguished according to the size of the dense cored vesicles, 1) 50–150 nm and 2) 50–250 nm. In aged rats, a third type of SGC-cells containing 50×250 nm elongated dense core vesicles could also be distinguished. After KMnO₄-fixation in newborn and in young adult rats the classification was identical with glutaraldehyde-fixation. In aged rats three types of storage granules were found after KMnO₄, 1) 100–300 nm empty vesicles and 2) 100–300 nm vesicles with small dense core, 3) 100–500 nm irregular in shape and filled with electron opaque material with a more dense core.     

Ultrastructure of the pineal organ of the killifish,Fundulus heteroclitus,with special reference to the secretory function

Summary The pineal organ of the killifish, Fundulus heteroclitus, was investigated by electron microscopy under experimental conditions; its general and characteristic features are discussed with respect to the photosensory and secretory function. The strongly convoluted pineal epithelium is usually composed of photoreceptor, ganglion and supporting cells. In addition to the well-differentiated photosensory apparatus, the photoreceptor cell contains presumably immature dense-cored vesicles (140–220 nm in diameter) associated with a well-developed granular endoplasmic reticulum in the perinuclear region and the basal process. These dense-cored vesicles appear rather prominent in fish subjected to darkness. The ganglion cell shows the typical features of a nerve cell; granular endoplasmic reticulum, polysomes, mitochondria and Golgi apparatus are scattered in the electron-lucent cytoplasm around the spherical or oval nucleus. The dendrites of these cells divide into smaller branches and form many sensory synapses with the photoreceptor basal processes. Lipid droplets appear exclusively in the supporting cell, which also contains well-developed granular endoplasmic reticulum and Golgi apparatus. Cytoplasmic protrusions filled with compact dense-cored vesicles (90–220 nm in diameter) are found in dark-adapted fish. The origin of these cytoplasmic protrusions, however, remains unresolved. Thus, the pineal organ of the killifish contains two types of dense-cored vesicles which appear predominantly in darkness. The ultrastructural results suggest that the pineal organ of fish functions not only as a photoreceptor but also as a secretory organ.We thank Dr. Grace Pickford for the fishes.     

Electron-microscopic analysis of adrenergic nerve endings in the cat caudal mesenteric ganglion

The ultrastructure of nerve endings of the cat caudal mesenteric ganglion was studied after fixation of the material with 4% lithium permanganate solution by Richardson's method in the modification of Hökfelt et al. [12]. This fixation method was shown to permit the demonstration of numerous adrenergic as well as cholinergic nerve endings. Four types of adrenergic organelles were distinguished in neurons of the ganglion: small and large granular vesicles 30–50 and 70–90 nm in diameter, respectively, a tubular reticulum with electron-dense contents, and small granular vesicles 15–20 nm in diameter. The localization of the adrenergic endings and their relations with other processes and cells of the caudal mesenteric ganglion were studied in detail. The problem of the origin and physiological role of adrenergic nerve endings in this ganglion is discussed.Institute of Physiology, Academy of Sciences of the Belorussian SSR, Minsk. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 86–92, January–February, 1980.     

Electrophysiological investigation of the conduction of excitation in the pterygopalatine ganglion of the cat

When responses in some nerves of the pterygopalatine ganglion of the cat in situ to stimulation of its other nerves were recorded it was found that most fibers passing through the ganglion are continuous sympathetic postganglionic fibers (at least three groups). Most of the parasympathetic preganglionic fibers forming synapses on neurons of the ganglion constitute a group of fibers with the same threshold of excitation. Intracellular recording from single neurons of the pterygopalatine ganglion showed that stimulation of the Vidian nerve evokes orthodromic spike potentials in some neurons of the ganglion with a short latent period, and in others with a long latent period (2.5–6.0 and 10–44 msec, respectively). Evidently only fast-conducting fibers terminate synaptically on most neurons of the ganglion and only slow-conducting fibers on some of them. Recording from intact nerves of the pterygopalatine ganglion revealed no tonic activity in them. Microelectrode recording from single neurons of the ganglion showed that either the frequency of generation of spike potentials is relatively low (1–3/sec) or such potentials are absent altogether.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 514–520, September–October, 1976.     

The neurohypophysis of the crested newt

Summary In the median eminence of the newt a medial region and two lateral regions are described.In cross section, the medial region appears to be made up of 1) an outer or glandular zone (Zone I) containing aldehyde-thionine-positive and negative nerve fibres and blood capillaries. Nerve fibres appear aligned in palisade array along the capillaries. 2) An inner zone (Zone II) made up of a) a layer of aldehyde-thionine-positive nerve fibres (fibrous layer) belonging to the preoptic hypophyseal tract and b) a layer of ependymal cells lining the infundibular lumen and reaching the blood vessels with their long processes.The lateral regions display a less pronounced stratification and aldehyde-thionine positive nerve fibres are nearly absent.A slender lamina (ependymal border) containing mainly aldehyde-thionine-positive nerve fibres and ependymal cells connects the median eminence to the pars nervosa.At the ultrastructural level, in the outer zone of the medial region at least 4 types of nerve fibres and nerve endings are identified:Type I nerve fibres containing granular vesicles of 700–1000 Å and clear vesicles (250–400 Å).Type II nerve fibres containing granular vesicles and polymorphous granules of 900–1300 Å and clear vesicles (250–400 Å).Type III nerve fibres containing dense granules of 1200–2000 Å and clear vesicles of 250–400 Å.Type IV nerve fibres containing only clear vesicles of 250–400 Å. In the inner zone too, all these nerve fiber types are found among ependymal cells, while the fibrous layer consists of nerve fibres containing granules of 1200–2000 Å in diameter.In the lateral regions Type I, Type II and Type IV nerve fibres and their respective perivascular terminals are found; axons containing dense granules (1200–2000 Å) are scanty. In these regions typical synapses between Type I nerve fibres and processes rich in microtubules are visible.The classification and functional significance of nerve fibres in the median eminence are still unsolved, but it may be assumed that nerve fibres of the medial region belong to both the preoptic hypophyseal and tubero hypophyseal tract, while the lateral regions are characterized by nerve fibres of the tubero hypophyseal tract. Peculiar specializations of the ependymal cells in the median eminence of the newt are also discussed.Work supported by a grant from the Consiglio Nazionale delle Ricerche.The authors are indebted to Mr. G. Gendusa and P. Balbi for technical assistance.     

Ultrastructural parameters of GABA-ergic and non-GABA-ergic synaptic contacts on neurons of the catsubstantia nigra

Nigrothalamic neurons were identified in the reticular part of thesubstantia nigra using labelling by the retrograde axonal transport of horseradish peroxidase. Nine parameters of the synaptic contacts (n=195) were analyzed, including the size and shape of terminals and size and type of synaptic vesicies. Sixty-six percent of axon terminals studied formed symmetric contacts and contained large polymorphic vesicles (group I). Two-thirds of these synapses were located on the distal dendrites, while one-third was distributed on the perikarya and proximal dendrites. Synapses of group II (29% of all synapses analyzed) exhibited asymmetric contacts and contained round agranular vesicles. Among these synapses, 79% were located on the distal dendrites, 19% were located on the proximal dendrites, and only 2% were located on the neuronal perikarya. Axon terminals of group III (5% of total population) exhibited symmetric contact and contained small polymorphic vesicles. High-resolution immunogold EM histochemistry indicated that 63% of the group-I axon terminals were GABA-positive. The majority of synapses on the labelled nigrothalamic neurons (21 contacts of 25) belonged to group I. Among these 21 synapses, 19 were axo-somatic and mostly GABA-positive. Within group II, 30% of synapses showed slightly expressed GABA-positivity.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 147–157, March–April, 1995.     

Developmental changes in synaptic formation in the hypothalamic arcuate nucleus of female rats

Summary The hypothalamic arcuate nucleus (ARCN) of female rats at 5, 20, 45 and 90 days of age was examined ultrastructurally. Axodendritic and axosomatic synapses were counted in 18,000 m² area of the ARCN in each brain. Axodendritic and axosomatic synapses in the ARCN of day 5 rats were very small in number. Axon terminals contained small spherical vesicles (SSVs, 40–60 nm in diameter). Occasionally large granular vesicles (LGVs, 75–130 nm in diameter) were found to coexist with SSVs in the endings. Pre- and postsynaptic membranes were thin. The ARCN at this age exhibited a large extracellular space which decreased with advancing age. In day 20 rats, axodendritic and axosomatic synapses increased in number up to about one-half of those of day 45 or day 90 animals. Synaptic vesicles increased in number and mitochondria were frequently encountered in the axon terminals. Pre- and postsynaptic membranes became thicker than those of day 5 rats. Further increase in the number of axodendritic and axosomatic synapses in the ARCN of day 45 rats was observed, and there were no significant difference in the morphology and incidence of synapses between day 45 and day 90 rats. Synaptic vesicles were numerous and pre- and postsynaptic membranes were thick. In tissue incubated with 5-hydroxydopamine (5-OH-DA) before fixation, small granular vesicles (SGVs, about 50 nm in diameter) which were labeled with 5-OH-DA were detected in a certain number of endings in all material taken from each age group, but the incidence of synapses containing SGVs was usually low. From these results, it can be proposed that an increase in the number of synapses in the ARCN is correlated with functional maturation of the ARC neurons. Acknowledgements. The authors wish to thank Prof. T. Kojima, Nihon University, for valuable suggestions during the initial stage of this study. This study was supported by grants from the Ministry of Education of Japan     

Synaptic organisation of the pelvic ganglion in the guinea-pig

Summary A semi-quantitative electron-microscopic study of neuronal cell bodies, nerve profiles and synapses in the anterior pelvic ganglia of the guinea-pig has been carried out following in vivo labelling of adrenergic nerve endings with 5-hydroxydopamine. Ganglion cells of three main types have been distinguished: 1) the majority (about 70%) not containing granular vesicles, probably cholinergic elements; 2) those containing large granular vesicles of uniform size (80–110 nm), with granules of medium density and prominent halos; and 3) those containing vesicles of variable size (60–150 nm), with very dense eccentrically placed granular cores. Some non-neuronal granule-containing cells were present, mainly near small blood vessels. Some 95% of the total axon profiles within the ganglia were cholinergic, the remaining 5% were adrenergic. However, 99% of synapses (i.e. axons within 50 nm of nerve cell membrane with pre-and post-synaptic specialisations) were cholinergic, and 1 % were adrenergic. Only three examples of nerve cell bodies exhibiting both cholinergic and adrenergic synapses were observed. Unlike the para-and prevertebral ganglia, the pelvic ganglia contained large numbers of axo-somatic synapses. As many as 20% of the nucleated neuronal cell profiles displayed two distinct nuclei.     

Layer by layer analysis of synaptic organization in the optic tectum of the prog

The distribution of axo-axonal and axo-dendritic synapses, nerve endings, and bodies of neurons by depth in the optic tectum ofRana temporaria L. was investigated under normal conditions and 6–9, 60, and 134 days after removal of the contralateral eye. Counting was carried out on long oriented sections examined in the electron microscope. In outer plexiform layer 9 the density of synapses was greatest near the surface of the tectum and decreased in the direction away from it; no inner sublayers with differing density of synapses could be distinguished. In the outer zone of layer 9 (to a depth of about 30 ) many axo-axonal synpases were discovered. Endings of myelinated optic fibers of large diameter ("dark" terminal degeneration) were widely distributed in the same layer. The density of axo-dendritic synapses in deep plexiform layer 5 was similar to that in layer 9. Many nerve endings containing granular vesicles as well as pale synaptic vesicles were found in layer 5 and neighboring zones.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 130–136, March–April, 1979.     

Acetylcholine estimate in glial cells of the cat spinal cord

Structures containing acetylcholinesterase were found in the motor nuclei of the cervical enlargement of the cat spinal cord by light and electron microscopy in material stained by the Karnovsky-Roots method. The specific response was observed not only in neurons of the motor nuclei, but also in some satellite cells, astrocytic glial cells, and Schwann cells. A positive reaction for acetylcholinesterase was found in some of the satellite cells located close to both cholinergic and noncholinergic neurons. As a result of electron microscopy, an electron-dense deposit of copper ferrocyanide was found on the structures of the nucleolus, on the surface of the inner and outer layers of the nuclear membrane, in the pores of the nuclear membrane, in the perinuclear space, and in the endoplasmic reticulum of the perikaryon of some satellite cells, as well as on the outer and inner surfaces of the cytoplasmic membrane of the Schwann cells.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev, Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 48–51, January–February, 1977.     

Observations on the ultrastructure of ganglion cells in the circumvallate papilla of rat and mouse

Ganglion cells in the circumvallate papilla of adult rodents are described as typical autonomic neurons. Some neurons are aggregated to form a discrete structure in the base of the papilla; others are scattered through the core, along the nerve bundles, and particularly near the dome. The term "circumvallate ganglion" is applied to the entire population. Satellite cells completely ensheathe each neuron. Preganglionic fibers, containing clear vesicles, synapse on the soma and stumpy dendrites of the neurons. Axons, containing dense-cored vesicles, are observed in close proximity to the neurons. However, these fibers do not establish true morphological synaptic contacts with the neurons. We have not observed serial or reciprocal synapses on or in the vicinity of the ganglion cells. The hypothesis that the axons of the circumvallate ganglion neurons act as parasympathetic vasodilators is indicated by the proximity of the two structures and by nerve terminations on the arteriole muscle cells. Direct modulation of taste transduction by these neurons is ruled out.     

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.     

Ultrastructure of interneuronal connections in the superior cervical sympathetic ganglion in cats

The structure of interneuronal synapses in the superior cervical sympathetic ganglion was studied in cats under normal conditions and after division of the cervical sympathetic nerves and removal of spinal ganglia T₁₂–L₂. A definite number of dendro-dendritic and dendro-somatic junctions is observed in the ganglion and most of them remained intact after operations of both types; they are probably synapses formed by dendrites of neurons located in the ganglion. Synapses of this sort participate in the formation of nest-like complexes, consisting of consecutive junctions of one neuron with several dendrites. The formation of such complexes may provide the anatomical basis for synchronization of rhythmic neuronal activity in the cellular glomeruli of the ganglion. The results of an ultrastructural study of dendro-dendritic junctions suggests that they are synaptic in nature. Some dendro-dendritic junctions underwent degeneration after both types of operation and are probably endings of neurons in spinal ganglia. Wide club-like structures, probably receptor endings, formed by dendrites of afferent neurons of spinal ganglia, also are found in the ganglion. These structures lie freely in the stoma of the ganglion or form contacts with axon terminals and dendrites of neurons located in the ganglion; some of them degenerate after removal of spinal ganglia T₁₂–L₂.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 3, pp. 299–306, May–June, 1981.     

Catecholaminergic innervation of the rat adrenal cortex

Summary The zona glomerulosa of the rat adrenal gland is innervated by catecholaminergic nerves. Using histofluorescence techniques, we observed catecholaminergic plexuses surrounding adrenal capsular and subcapsular blood vessels. Individual varicose nerve fibers that branched off these plexuses were distributed among adrenal glomerulosa cells. This innervation was permanently eliminated after neonatal sympathectomy with guanethidine or 6-hydroxydopamine, but was not affected by ligation of the splanchnic nerve or extirpation of the suprarenal ganglion. At the ultrastructural level, axonal varicosities were commonly observed in close proximity to glomerulosa cells and blood vessels. Nerve fibers and varicosities were found to contain small (30–60 nm) clear vesicles as well as large (60–110 nm) and small (30–60 nm) dense-cored vesicles. In tissue fixed for the dichromate reaction with or without pretreatment with the false transmitter 5-hydroxydopamine, many nerve terminals contained numerous small dense-cored vesicles which are thought to contain catecholamines. These results establish the anatomical substrate for the catecholaminergic innervation of the rat adrenal cortex.