Structure of synapes in the supraoesophageal ganglion of the water beetle (Dytiscus marginalis).

1. Light- and electron microscopic investigations prove that synapses, without any exception, are confined to the neuropil. 2. Under the light-microscope, synapses display the shape of terminal boutons at the ends of the nerve fibres; in some cases they appear as smaller or larger plates. Electron microscopic investigations suggest that also varicosities of nerve fibres can be regarded as synapses, though these might have possible arisen from axoplasmatic peristalsis. 3. Electron microscopically the overwhelming majority of the synapses are axodendritic contacts; axo-axonic contacts occur less often. 4. The generally accepted characteristics of synapses are defective. Membrane thickenings and intersynaptic spaces are missing. Accordingly, synapses in the supraoesophageal ganglion of the water beetle differ markedly from those described in Vertebrates. 5. Synaptic vesicles sometimes fill the axoplasm of the nerve fibre completely. In other cases, clusters of synaptic vesicles can be seen, on both sides of the contact. 6. Synaptic vesicles are mixed with neurosecretory granules. Synaptic vesicles may appear also in the dendrites.     

Two different types of dynorphin-A-immunoreactive terminals in rat substantia nigra

Summary The opioid peptide dynorphin A (1–17) is the third transmitter identified in the striatonigral projection, the other two being gamma-aminobutyric acid (GABA) and substance P. The ultrastructural features of the dynorphinergic terminals in substantia nigra/pars reticulata were studied using pre-embedding immunocytochemistry with the classical peroxidase-antiperoxidase-diaminobenzidine-method; these features were compared with GABAergic boutons visualized with an immunogold method. Two distinct types of dynorphin-A-immunoreactive boutons could be identified: (1) type A (81%) possessing characteristics similar to the GA-BAergic nerve endings in this region, i.e., large pleomorphic vesicles and symmetric synaptic contacts, (2) type B (19%) displaying asymmetric synaptic zones and small, mostly round vesicles. These results are in agreement with physiological studies suggesting a dual action of dynorphin A in substantia nigra.     

Synapses in the rat substantia nigra

The composition and organization of the input to the rat substantia nigra were studied with the electron microscope. Four distinct types of synaptic boutons were described. The first contained small (381 A), clear synaptic vesicles. The second type contained the small, clear vesicles and several large, dense-core vesicles. The third ending contained large, dense-core vesicles and larger (581 A) clear vesicles. The fourth ending, found on the axon hillock and other terminal boutons, contained slightly elongated, clear synaptic vesicles. The presence of these four boutons was discussed in light of the known afferent input and neurochemical composition of the substantia nigra.     

Effects of frontal motor cortex ablation on the ultrastructure of cat substantia nigra

3,4 and 5 days after the removal by suction of the left motor and premotor cortex in cats, the presence of ultrastructural changes in the substantia nigra was investigated. Whereas after 3 days dark bouton degeneration was rare, after 4- and 5-day survival it was regularly found for a distinct type of synapse containing in its bouton densely packed small round vesicles and possessing an asymmetric synaptic junction with a dendrite. Often these darkly degenerated boutons contained dense bodies which were also observed in the same type of synapse not yet exhibiting a dark axoplasm. Various inclusions, especially glycogen depots, were present in these boutons suggesting that they were in the process of degeneration. The glial reaction was comparatively severe. In addition, darkly shrunken dendrites contacted both, by intact and by altered boutons were frequently encountered as well as single degenerated neuronal perikarya. The nature of this effect, i.e. whether transneuronal or retrograde, could not be clarified. All these alterations were found bilaterally after the unilateral cortex ablation, and were confined to the substantia nigra pars compacta along its whole anterior-posterior extent. In the pars reticulata, solely traversing myelinated axons in the process of degeneration were observed. Thus, the results are in agreement with the older studies and with evidence from primates demonstrating that the substantia nigra receives a bilateral projection from the motor and premotor cortex.     

The fine structure of the neurons in the rat substantia nigra

Three distinct neurons were identified in the substantia nigra of the rat using Golgi, light, and electron microscopic techniques. A large neuron, found in the pars reticulata, is characterized by well-developed RER, a tubular cytoplasmic inclusion, and somatic and dendritec thorns. A medium-sized neuron, found in the pars compacta, has an eccentric nucleus, distinct Nissl bodies, and an inclusion composed of whorls of concentric cisternae. A small neuron, found in both nigral regions, contains a highly invaginated nucleus, fibrous nuclear inclusion, and paucity of cytoplasmic organelles. Its axon synapses around other nigral dendrites. The presence of these neurons was correlated with the efferent projections and function of the substantia nigra.     

Immunohistochemical evidence for different pathways immunoreactive to substance P and calcitonin gene-related peptide (CGRP) in the guinea-pig stellate ganglion

The colocalization of immunoreactivities to substance P and calcitonin gene-related peptide (CGRP) in nervous structures and their correlation with other peptidergic structures were studied in the stellate ganglion of the guinea pig by the application of double-labelling immunofluorescence. Three types of fibre were distinguished. (1) Substance P⁺/CGRP⁺ fibres, which sometimes displayed additional immunoreactivity for enkephalin, constituted a small fibre population of sensory origin, as deduced from retrograde labelling of substance P⁺/CGRP⁺ dorsal root ganglion cells. (2) Substance P⁺/CGRP^– fibres were more frequent; some formed baskets around non-catecholaminergic perikarya that were immunoreactive to vasoactive intestinal polypeptide (VIP). (3) CGRP⁺/substance P^– fibres were most frequent and were mainly distributed among tyrosine hydroxylase (TH)-immunoreactive cell bodies. The peptide content of fibre populations (2) and (3) did not correspond to that of sensory ganglion cells retrogradely labelled by tracer injection into the stellate ganglion. Therefore, these fibres are throught to arise from retrogradely labelled preganglionic sympathetic neurons of the spinal cord, in which transmitter levels may have been too low for immunohistochemical detection of substance P or CGRP. CGRP-immunoreactivity but no substance P-immunolabelling was observed in VIP-immunoreactive postganglionic neurons. Such cell bodies were TH-negative and were spared by substance P-immunolabelled fibre baskets. Retrograde tracing with Fast Blue indicated that the sweat glands in the glabrous skin of the forepaw were the targets of these neurons. The streptavidin-biotin-peroxidase method at the electron-microscope level demonstrated that immunoreactivity to substance P and CGRP was present in dense-cored vesicles of 50–130 nm diameter in varicosities of non-myelinated nerve fibres in the stellate ganglion. No statistically significant difference in size was observed between vesicles immunolabelled for substance P and CGRP. Immunoreactive varicosities formed axodendritic and axosomatic synaptic contacts, and unspecialized appositions to non-reactive neuronal dendrites, somata, and axon terminals. Many varicosities were partly exposed to the interstitial space. The findings provide evidence for different pathways utilizing substance P and/or CGRP in the guinea-pig stellate ganglion.     

Types, numbers and distribution of synapses on the dendritic tree of an identified visual interneuron in the brain of the locust

The descending contralateral movement detector (DCMD), an identified descending interneuron in the brain of the locust Schistocerca gregaria has been investigated by using light and electron microscopy. We describe the fine structure, distribution and numbers of synapses that it receives from another identified brain neuron, the lobular giant movement detector (LGMD), and from unidentified neurons. The DCMD dendrites emerging from the integrative segment vary in form and number between individuals and sexes but always form a flattened dendritic domain. The arborizations and the integrative segment appear to be exclusively postsynaptic. Two types of synaptic contacts (Type 1 and 2) onto the DCMD can be discerned as having either round (Type 1) or pleiomorphic synaptic vesicles (Type 2) and by large (Type 1) or small (Type 2) subsynaptic appositions. Contact zones of Type 1 synapses are smaller than those of Type 2. LGMD-synapses are of Type 1 and occur intermingled with presynaptic sites of unidentified units. Some branches of the DCMD receiving input from unidentified units are devoid of contacting LGMD processes. Synapses of both types are randomly distributed over the DCMD integrative segment and at fibres with similar sizes.Type 1 synapses are much more frequent than Type 2 synapses and their number is negatively correlated with fibre diameter. For a whole DCMD dendritic arborization, a total of 8500 active zones of chemical synapses has been calculated, including a minimum of 2250 LGMD-synapses and about 1000 Type 2 synapses. The DCMD may thus receive a considerable amount of input from as yet unidentified neurons.     

Distribution of synaptic boutons in the mesencephalic trigeminal nucleus of the rat--a quantitative electron-microscopical study.

The distribution of synapses and synaptic bouton types in the mesencephalic trigeminal (Me5) nucleus was examined in a quantitative electron-microscopical study. Of 588 terminal boutons that were counted in the compact caudal part of the Me5 nucleus, less than 8% formed synapses on the somata of the predominantly unipolar Me5 neurons. About 79% formed synapses on fibres located between the Me5 somata, while about 13% of the vesicle-containing terminals had no clear synaptic specialization. All of these non-synaptic terminals were G type boutons, with pleomorphic and large characteristic dense-core vesicles. Approximately 60% of the axosomatic synapses were of the S type, containing spherical vesicles and an asymmetrical or symmetrical synaptic specialization. About 20, respectively 15% of the axosomatic synapses, were of the F, respectively P type; both are symmetrical synapse types containing either a majority of flat or pleomorphic vesicles. Less than 10% of the axosomatic synapses were of the G type. Although some proportional differences were noted, an almost similar bouton type distribution pattern was found for the axodendritic synapses suggesting that the axosomatic and axodendritic synapses in the Me5 nucleus are part of the same afferent fibre plexus covering the Me5 nucleus.     

Electron microscopic study of the substantia nigra and the strio-nigral projection in the rat

Summary The normal ultrastructure of rat substantia nigra was investigated. Special attention was paid to the different types of boutons, and the mode of termination of the striatonigral connection was examined. Two different types of nigra neurons with deep nuclear membrane indentations were observed. The synaptic organization of rat substantia nigra is very complex. Six types of boutons, with many characteristics, could be differentiated: pleomorphicvesicle boutons (40%), elongated-vesicle boutons (10%), small-round-vesicle boutons (10%), large-round-vesicle boutons (20%), clear-terminal (15%) and dense-core-vesicle boutons (about 5%). Vesicle-containing dendrites were observed entering dendro-dendritic synapses. One to four days after large unilateral striatal lesions were made, a great number of degenerating boutons were seen in the ipsilateral substantia nigra, while the contra-lateral substantia nigra was entirely free of degeneration. The newly defined pleomorphic-vesicle boutons were found almost exclusively in the process of degeneration. The neuronal origin of the other bouton types is discussed.On leave of absence from Anatomical Institut, Semmelweis University, Budapest.     

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.     

Presynaptic dendrites and dendro-dendritic synapses in the superior tubercles of the rat quadrigeminum]

The types of dendro-dendritic synapses and their participation in the synaptic, organization of superficial layers of the quadrigeminum superior tubercles were studied electron microscopically. In addition to simple forms of dendro-dentritic synapses the reciprocal dendro-dendritic synapses were revealed. Presynaptic dendrites formed the synaptic fields and glomerules of the superficial grey layer. The terminals of optical, cortical fibres from the visual cortex and other types of terminals terminated on presynaptic dendrites.     

Fine structure of nerve-melanophore contacts in the angelfish Pterophyllum scalare

Contacts between small unmyelinated nerve fibres and dermal melanophores of the angelfish, Pterophyllum scalare, exhibit several features characteristic of synapses, including small synaptic vesicles and dense core vesicles, a narrow synaptic cleft, electron-dense material at the postsynaptic membrane (cell membrane of the melanophore) and, occasionally, presynaptic densities. An analysis of serial thin sections shows that the synapses described here represent varicosities of an otherwise more or less straight nerve fibre. A single axon thereby may form several en passant synapses with a single melanophore. It is suggested that the synaptic contacts described here not only represent sites of transmitter release but also play a role as sites of firm attachment between nerves and melanophores which guarantee a stable arrangement of nerve fibres and melanophores.Supported by the Deutsche Forschungsgemeinschaft     

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.     

Three-dimensional microanatomy of perineuronal proteoglycan nets enveloping motor neurons in the rat spinal cord

Summary. Spinal motor neurons possess reticular coats of extracellular matrix proteoglycans on their somata and proximal dendrites. In order to define the anatomical background of the network, spatial relationships of the perineuronal proteoglycans with synaptic boutons and astrocyte processes were analyzed in rat motor neurons by TEM after histochemical detection of the substances with cationic iron colloid, and by SEM after exposure of the cytoarchitecture with NaOH maceration. Narrow intercellular channels filled with proteoglycan were found to extend along the surface of the neurons to form a homogeneous network of a mesh size of about 1 µm. The system of perineuronal channels consisted of two parts: a primary intervaricose net which meandered among synaptic boutons on the surface of the motor neuron, and secondary subvaricose nets which irrigated interfaces between larger boutons and the neuron. No elements in the perineuronal cytoarchitecture coincided with the meshwork of proteoglycan, indicating the involvement of postsynaptic factors in the distribution of the substance. Thin astrocyte processes surrounding the neurons formed a distinct network with heterogeneous meshes corresponding to boutons of various sizes. The perineuronal glial nets extended their surface area in contact with the intervaricose nets of proteoglycan by complex cellular interdigitations. The subvaricose nets of proteoglycan compartmentalized multiple synapses on large boutons, suggesting an involvement in the division of the synapses during development.     

Motor Axon Synapses on Renshaw Cells Contain Higher Levels of Aspartate than Glutamate

Motoneuron synapses on spinal cord interneurons known as Renshaw cells activate nicotinic, AMPA and NMDA receptors consistent with co-release of acetylcholine and excitatory amino acids (EAA). However, whether these synapses express vesicular glutamate transporters (VGLUTs) capable of accumulating glutamate into synaptic vesicles is controversial. An alternative possibility is that these synapses release other EAAs, like aspartate, not dependent on VGLUTs. To clarify the exact EAA concentrated at motor axon synapses we performed a quantitative postembedding colloidal gold immunoelectron analysis for aspartate and glutamate on motor axon synapses (identified by immunoreactivity to the vesicular acetylcholine transporter; VAChT) contacting calbindin-immunoreactive (-IR) Renshaw cell dendrites. The results show that 71% to 80% of motor axon synaptic boutons on Renshaw cells contained aspartate immunolabeling two standard deviations above average neuropil labeling. Moreover, VAChT-IR synapses on Renshaw cells contained, on average, aspartate immunolabeling at 2.5 to 2.8 times above the average neuropil level. In contrast, glutamate enrichment was lower; 21% to 44% of VAChT-IR synapses showed glutamate-IR two standard deviations above average neuropil labeling and average glutamate immunogold density was 1.7 to 2.0 times the neuropil level. The results were not influenced by antibody affinities because glutamate antibodies detected glutamate-enriched brain homogenates more efficiently than aspartate antibodies detecting aspartate-enriched brain homogenates. Furthermore, synaptic boutons with ultrastructural features of Type I excitatory synapses were always labeled by glutamate antibodies at higher density than motor axon synapses. We conclude that motor axon synapses co-express aspartate and glutamate, but aspartate is concentrated at higher levels than glutamate.     

Light and electron microscopic autoradiography of substantia nigra of rat after intraventricular administration of tritium labelled norepinephrine,dopamine, serotonin and the precursors

Summary In autoradiographies of substantia nigra in rat, it has been observed that after intraventricular injections of ³H-dopamine and ³H-norepinephrine respectively the silvergrains are accumulated in nigra neurons and their dendritic branches. The incorporation was more pronounced in the case of ³H-norepinephrine than ³H-dopamine. This seems to indicate that exogenous norepinephrine may have stronger affinity to nigra neurons and their dendrites than exogenous dopamine. In addition, some ³H-dopamine and ³H-norepinephrine labelled nerve terminals were observed in axo-dendritic synapses. In contrast to these data, ³H-5HTP and ³H-5HT administration showed almost all silver grains accumulated in the neuropil when observed in light microscopic autoradiography. Electron micrographs further reveal that the incorporation of ³H-5HTP and ³H-5HT was mostly within axo-dendritic boutons with more frequent dense core vesicles. These data again strongly suggest that substantia nigra receives a large number of serotoninergic fibres forming axo-dendritic synapses which may play an important role in modulation of substantia nigra function.Dr. Parizek was on leave of absence from the Charles University, Faculty of Medicine, Hradec Králové, Czechoslovakia.     

Acetylcholinesterase activity at the synapses of presynaptic boutons with presumed alpha-motoneurons in chicken ventral horn. Light- and electron-microscopic studies

Acetylcholinesterase (AChE) activity at the synapses of presynaptic boutons on presumed alpha-motoneurons in the chicken ventral horn was studied histochemically at the light- and electron-microscope levels. At the light-microscope level, many dot-like AChE-active sites were observed on the soma and dendrites of presumed alpha-motoneurons. On electron microscopy, reaction products for AChE activity were observed mainly in the synaptic clefts of the four kinds of presynaptic boutons: (1) S type boutons, (2) boutons containing small, spherical, dense cored vesicles (diameter range, 60-105 nm) and spherical, clear vesicles, (3) boutons containing medium-sized, spherical, dense cored vesicles (65-115 nm) and spherical, clear vesicles, and (4) boutons containing large, spherical, dense cored vesicles (80-130 nm) and spherical, clear vesicles. In the light of previous physiological and biochemical studies, the present results suggest the possibility that each of these presynaptic boutons which are AChE-active in their synaptic clefts may contain acetylcholine, substance P, or enkephalins which acts as a neurotransmitter or modulator.     

Ultrastructural study of neurotensin immunoreactivity in the superficial laminae of the dorsal horn of the rat

Neurotensin immunoreactivity was identified in cell bodies, dendrites, spines, axons, terminals and varicosities in superficial laminae of rat spinal cord with the electron microscope. Unlabeled terminals synapsed with neurotensin-immunoreactive cell bodies, dendrites and spines. Presynaptic terminals contained round or pleomorphic vesicles and generally made symmetrical contacts with medium-sized neurotensin-containing dendrites in outer lamina II, and asymmetrical or symmetrical contacts with large and small dendrites and spines in inner lamina II. Neurotensin immunoreactive axons were unmyelinated, and their terminals were presynaptic to unlabeled dendrites and spines in laminae I and II. Terminals contained small, round, clear vesciles (31 nm) and occasional large granular vesicles (78 nm). Contacts in outer lamina II were evenly distributed among dendrites of various sizes and spines, whereas the majority of labeled terminals in inner lamina II made contacts onto small dendrites and spines. These findings indicate that neurotensin effects in rat spinal cord are mediated by axodendritic synapses, and that neurotensin cells at the inner and outer borders of lamina II contact dendrites of efferent neurons or other interneurons in the dorsal horn.     

Light- and electron-microscopic study of synaptic connections in the paracervical ganglion of the female rat: special reference to calcitonin gene-related peptide-, galanin- and tachykinin (substance P and neurokinin A)-immunoreactive nerve fibers and terminals

Nerve fibers and varicosities in the pelvic paracervical ganglia (PG) are immunoreactive for the neuropeptides calcitonin gene-related peptide, galanin, and the tachykinins substance P and neurokinin A. Many of these fibers and varicosities are capsaicin-sensitive, originate in dorsal root ganglia and, thus, are considered to be primary afferent fibers. Numerous immunoreactive varicosities are pericellular to principal neurons in the PG. The present study examines the ultrastructure of calcitonin gene-related peptide-, galanin-, substance P-, and neurokinin A-immunoreactive nerve fibers and varicosities in the ganglia to determine their relationships to principal neurons and their synaptic connectivity. Paracervical ganglia of female rats were processed for light-microscopic immunohistochemistry using antisera against synapsin I, as a nerve terminal marker, and microtubule-associated protein-2 to define soma and dendrites. The rationale for performing this co-immunohistochemical analysis was to reveal the relationship between nerve endings and principal neurons. Synapsin I endings were predominantly axosomatic with fewer being axodendritic. Other ganglia were processed for electron-microscopic immunohistochemistry using both standard immunogold and peroxidase-anti-peroxidase procedures. Unmyelinated fibers and varicosities immunoreactive for calcitonin gene-related peptide, galanin, and the tachykinins were routinely observed in the interstitium between neuron somas. Numerous immunoreactive axon profiles were present in small groups that were ensheathed by Schwann cells. Immunoreactive fibers and varicosities were also observed within the satellite-cell sheath of the neuron soma and often intimately associated with the membrane of the soma, somal protrusions, or with the proximal part of a dendrite. Membrane specializations, indicative of synaptic contacts, between the fibers and the principal neurons were observed. It is suggested that these peptide-immunoreactive sensory fibers and varicosities are involved in regulation of activity in the PG.     

人胚DA能神经元移植于帕金森氏病猴模型的TH免疫细胞化学的研究

为了对人胚黑质ＤＡ神经元移植治疗ＰＤ人的临床应用作出客观评估,将８－１２周人胚黑质细胞移植到用ＭＰＴＰ诱发的偏侧ＰＤ猴新纹状体内。实验动物分别存活２个月、５个月和１年后,用ＴＨ免疫细胞化学方法对被移植的人胚ＤＡ细胞的存活和与宿主间的突触联系进行检查。在光镜下可见被移植侧的新纹状体内有ＴＨ阳性细胞,它们成小群散在分布,每小群有３－１０个细胞。ＴＨ阳性细胞的轴突延伸到整个新纹状体,树突呈现出正常发育过