The mormyrid brainstem--II. The medullary electromotor relay nucleus: an ultrastructural horseradish peroxidase study

The medullary relay nucleus of the mormyrid weakly electric fish Gnathonemus petersii is a stage in the command pathway for the electric organ discharge. It receives input from the presumed command or pacemaker nucleus and projects to the electromotoneurons in the spinal cord. Its fine structure and synaptology were investigated by electron microscopy. The origin of the terminals contacting the cell membrane of the neurons of this nucleus was determined by horseradish peroxidase (HRP) injections into different brain structures, namely into the bulbar command- and mesencephalic command-associated nuclei. Twenty-five to thirty large cells of about 45 micron in diameter constitute the medullary electromotor relay. Each cell has a kidney-shaped, lobulated nucleus, a large myelinated axon with a short initial segment and several long, richly arborizing primary dendrites. Many, if not all, cells are interconnected with large somatosomatic or dendrosomatic, dendrodendritic and dendroaxonic gap junctions. These junctions often occur in serial or triadic arrangements. The relay cells receive large club endings as well as small boutons. The club endings are found mainly on the soma and primary dendrites and are morphologically mixed synapses. The boutons are characterized by synapses which are only chemical and are distributed all over the cell membrane, but with a definitely higher frequency on secondary dendrites and more distal parts of dendritic processes. Horseradish peroxidase injections into the mesencephalic command-associated nucleus reveal a large number of labelled boutons on the secondary dendrites of the relay cells. Injections into the bulbar command-associated nucleus label the same type of boutons as mesencephalic injections, but also label club endings on relay cell soma and primary dendrites. The results support the conclusion made on the basis of previous light microscopical observations that boutons originate from the bulbar command-associated nucleus, whereas the club endings issue from the presumed pacemaker nucleus (nucleus c). The club endings of the bifurcating axons of this nucleus are labelled by retro- and anterograde transport of horseradish peroxidase; the bifurcating axons project simultaneously to the bulbar command-associated nucleus and the medullary relay nucleus.     

Synaptic organization of the dorsal lateral geniculate nucleus in the adult hamster

Summary The synaptic organization of the sector of the dorsal lateral geniculate nucleus has been examined by electron microscopy in normal adult hamsters and in adult hamsters subjected to unilateral eye enucleation or intravitreal injection of horseradish peroxidase.Two types of neuropil are apparent. Islands of complex neuropil partially enclosed by astrocyte processes (synaptic glomeruli) are surrounded by a sea of simpler non-glomerular neuropil. The latter is dominated by small axon terminals with spherical synaptic vesicles and Gray type 1 axodendritic contacts (SR-boutons) and also contains axon terminals with flattened synaptic vesicles (F-boutons). The glomerular neuropil contains (i) exclusively postsynaptic dendrites and dendritic protrusions of presumptive projection cells; (ii) pre- and postsynaptic pleomorphic-vesiclecontaining P-boutons (interpreted as appendages of the dendrites of interneurons); (iii) large axon terminals containing spherical synaptic vesicles and large pale mitochondria (R-boutons) which were experimentally identified as retinal terminals and which are presynaptic to both projection cell dendrites and P-boutons at Gray type 1 contacts; (iv) F-boutons (minority component). F-boutons and P-boutons are presynaptic to both projection cell dendrites and P-boutons and P-boutons are the intermediate elements of various serial synapses including triplet (triadic) synapses. Medium-large terminals with spherical synatpic vesicles and dark mitochondria (RLD-boutons) which were commonly invaginated by dendritic spines of projection cells in small glomerulus-like formations were also identified. The origin of RLD-boutons is unknown but SR-boutons probably derive chiefly from ipsilateral visual cortex and possibly also from superior colliculus, and non-glomerular F-boutons probably originate in the ipsilateral thalamic reticular nucleus.No differences in synaptic organization were found between the part of the nucleus which receives uncrossed retinal input and the part which receives crossed input, nor were differences seen in the size, fine structure or relationships between the terminals of identified crossed and uncrossed retinal axons.     

Synaptology of the command (pacemaker) nucleus in the brain of the weakly electric fish, Sternarchus (Apteronotus) albifrons

The high frequency electric emission of the weakly electric fish Sternarchus (Apteronotus) albifrons depends on the pacemaker activity of a specific brainstem nucleus located in the ventral part of the rhombencephalic reticular formation. The general morphology and fine structure of this nucleus has been investigated, with particular reference to its synaptic connections.Three neuronal components could be distinguished in the nucleus; namely large cells of 80–100 μm diameter, small cells of 30–50 μm diameter and bundles of thin, myelinated fibres. These elements are embedded in a network of thick myelinated fibres. The large cells have a few small and short dendrites whereas the small neurons have long branching dendrites. Large and small neurons possess thick myelinated axons, but only those of the latter show branching patterns and send collaterals which have intranuclear courses only. Two types of synaptic terminals have been found on both neurons: large club endings exclusively with gap junctions and small bouton-like terminals with polarized chemical synapses. Serial semi-thin and ultra-thin sections revealed that the large club endings belong to the pacemaker cells, whereas the small terminals are found in the thin myelinated axons of extranuclear origin.The findings indicate that the small neurons are connected 1) to each other and 2) to the large neurons, by way of their large myelinated axons. Both, small (pacemaker) as well as large (relay), neurons receive chemical synapses from myelinated fine fibers probably originating from higher encephalic centers. Thus, electric organ discharge rhythm can be modulated at the level of pacemaker as well as of the relay cells. No somatosomatic, dendrodendritic or dendrosomatic connections were found between large, small or large and small cells.     

大鼠丘脑前核内海马下托复合体谷氨酸能传入终末与皮质投射神经元的突触联系

目的 探讨大鼠丘脑前核-海马下托复合体神经元环路的突触结构及谷氨酸分布特征.方法 应用HRP束路追踪结合包埋后胶体金免疫电镜技术.结果 在丘脑前核内,可见HRP顺行标记的海马下托复合体传入轴突终末,终末多为卵圆形,内含圆形透亮突触小泡和数个线粒体.其做为突触前成分与HRP标记的树突或非HRP标记的树突形成非对称性突触.在谷氨酸胶体金免疫反应切片上,胶体金颗粒标记胞体、树突、轴突终末等.HRP标记的轴突终末和一些非HRP标记的与突触后成分形成非对称性突触的轴突终末(Gray Ⅰ型)内,胶体金颗粒密度明显大于背景(胞体、树突、Gray Ⅱ型轴突终末等)的胶体金颗粒密度.其平均胶体金颗粒密度为突触后树突的3倍多,为对称性轴突终末(Gray Ⅱ型)的6倍多.在两张邻近的连续切片,γ-氨基丁酸(GABA)胶体金免疫反应切片上,GABA胶体金颗粒浓重标记Gray Ⅱ型轴突终末,背景标记极少;而非对称性轴突终末(Gray Ⅰ型)胶体金颗粒标记极弱.谷氨酸胶体金免疫反应切片上,Gray Ⅱ型轴突终末胶体金颗粒标记极弱.GABA阳性轴突终末与HRP标记的树突形成对称性突触,在同一树突上可见GABA能轴突终末形成的对称性突触和其他轴突终末形成的非对称性突触.结论 丘脑前核内来自海马下托复合体投射神经元的轴突终末是谷氨酸能的;来自海马下托复合体皮质投射神经元轴突终末,在丘脑前核与投射至海马下托皮质的神经元树突形成非对称性轴-树突触.     

Fine distribution of substance P-like immunoreactivity in the dorsal nucleus of the vagus nerve in cats

The ultrastructure of substance P (SP)-immunoreactive elements in the cat dorsal motor nucleus of the vagus nerve was examined using pre- and post-embedding immunocytochemical procedures. Substance P-like immunoreactivity was observed in axon terminals and axon fibres which were mostly unmyelinated. Quantitative data showed that at least 16% of axon terminals contained SP. Their mean diameter was larger than that of their non-immunoreactive counterparts. Most (83%) SP-containing terminals were seen to contact dendrites but some were observed adjoining soma or entirely embedded in the cytoplasm of vagal neurons (4.5%). Only 0.5% were observed to contact soma of internuerons. A few immunoreactive axon terminals (4%) were observed in contact with non-immunoreactive axon terminals. Round agranular vesicles and numerous dense core vesicles were visible in most SP-containing axon terminals (84.6%). The immunogold procedure showed the preferential subcellular location of SP to be dense core vesicles. In 32.4% of cases, SP-containing terminals were involved in synaptic contacts that were generally of the asymmetrical Gray type 1 and mainly apposed dendrites. The theoretical total of synaptic contacts was 74.5% and this suggests the existence of weak non-synaptic SP innervation involving approximately 25% of SP-containing axon terminals. No axo-axonic synapses were observed in the dorsal vagal nucleus. These results support the hypothesis that SP found in the dorsal vagal nucleus originates partly from vagal afferents and is involved in direct modulation of visceral functions mediated by vagal preganglionic neurons.     

A GABA immunocytochemical study of rat motor thalamus: light and electron microscopic observations.

A light and electron microscopic study of GABA-immunoreactive neurons and profiles in the ventroanterior-ventrolateral and ventromedial nuclei of rat dorsal thalamus was conducted using antiserum raised against GABA. Less than 1% of the neurons in these motor-related nuclei exhibited GABA immunoreactivity, confirming previous reports that these nuclei are largely devoid of interneurons. Immunoreactive neurons in the ventral anterior-ventral lateral complex and ventromedial nucleus were bipolar or multipolar in shape, and tended to be smaller than non-immunoreactive neurons. GABA immunoreactivity in the neuropil consisted of labeled axon terminals and myelinated and unmyelinated axons, and was lower in the ventral anterior-ventral lateral complex and ventromedial nucleus than in neighboring thalamic nuclei. The density of neuropil immunolabeling was slightly higher in ventral anterior-ventral lateral complex than in ventromedial nucleus. GABA-immunoreactive axon terminals, collectively termed MP boutons for their medium size and pleomorphic vesicles (and corresponding to "F" profiles of some previous studies of thalamic ultrastructure), formed symmetric synapses and puncta adhaerentia contacts predominantly with large and medium-diameter (i.e. proximal) non-immunoreactive dendrites. Approximately 12 and 18% of boutons in the ventral anterior-ventral lateral complex and ventromedial nucleus, respectively, were GABA-immunopositive. Many of these immunoreactive profiles probably arose from GABAergic neurons in the thalamic reticular nucleus, substantia nigra pars reticulata and entopeduncular nucleus. Two types of non-immunoreactive axon terminals were distinguished based on differences in morphology and synaptic termination sites. Boutons with small ovoid profiles and round vesicles that formed prominent asymmetric synapses onto small-diameter dendrites were observed. Mitochondria were rarely observed within these boutons, which arose from thin unmyelinated axons. These boutons composed approximately 82 and 74% of boutons in the ventral anterior-ventral lateral complex and ventromedial nucleus, respectively, and were considered to arise predominantly from neurons in the cerebral cortex. In contrast, boutons with large terminals that contained round or plemorphic vesicles and formed multiple asymmetric synapses predominantly with large-diameter dendrites were also observed. Puncta adhaerentia contacts were also common. Mitochondria were numerous within large boutons with round vesicles, which arose from myelinated axons. Many of the large boutons were likely to have originated from neurons in the cerebellar nuclei. Approximately 6% of the boutons in the ventral anterior-ventral lateral complex and 8% in ventromedial nucleus were of the large type.(ABSTRACT TRUNCATED AT 400 WORDS)     

Ultrastructural identification of cholinergic neurons in the external cuneate nucleus of the gerbil: acetylcholinesterase histochemistry and choline acetyltransferase immunocytochemistry

Summary Using acetylcholinesterase histochemical and choline acetyltransferase immunocytochemical localization methods, this study has provided conclusive evidence for the existence of cholinergic neurons in the external cuneate nucleus of gerbils. By light microscopy, both acetylcholinesterase and choline acetyltransferase labelling was confined to the rostral portion of the external cuneate nucleus. Ultrastructurally, acetylcholinesterase reaction products were found in the nuclear envelope, cisternae of rough endoplasmic reticulum and Golgi saccules of some somata and large dendrites as well as in the membranes of small dendrites, myelinated axons and axon terminals. These neuronal elements were also stained for choline acetyltransferase; immunoreactivity was associated with nuclear pores, nuclear envelope, perikaryal membrane and all the membranous structures within the cytoplasm. Of the total choline acetyltransferase-labelled neuronal profiles analysed, 79% were myelinated axons, 15% dendrites, 4% somata and 2% axon terminals. The immunostained axon terminals consisted of two types containing either round (Rd type; 62.5%) or pleomorphic (Pd type; 37.5%) vesicles. Both were associated directly with choline acetyltransferase-positive dendrites. In contrast to the paucity of choline acetyltransferase-labelled axon terminals, numerous choline acetyltransferase-positive myelinated axons were present. It may thus be hypothesized that most, if not all, of the external cuneate nucleus cholinergic neurons are projection cells; such cells may give rise to axonal collaterals which synapse onto their own dendrites for possible feedback control. Choline acetyltransferase-positive dendrites were contacted by numerous unlabelled presynaptic boutons, 60% of which contained round or spherical synaptic vesicles (Rd boutons) and 40% flattened vesicles (Fd boutons), suggesting that these neurons are under strong inhibitory control. The preferential concentration of cholinergic components in the rostral external cuneate nucleus may be significant in the light of the highly organized somatotopy in the external cuneate nucleus and its extensive efferent projections to medullary autonomic-related nuclei. Our results suggest that the cholinergic neurons may be involved in somatoautonomic integration.     

Synaptology of the medullary command (pacemaker) nucleus of the weakly electric fish (Apteronotus leptorhynchus) with particular reference to comparative aspects

Summary The general organization and synaptology of the medullary command (pacemaker) nucleus (MCN) was investigated in the high frequency weakly electric fish, Apteronotus leptorhynchus. This study was undertaken in order to establish differences and similarities between the MCN of A. leptorhynchus and that of the closely related species, Apteronotus albifrons which has been studied previously. The basic morphology and synaptology of the MCN in A. leptorhynchus is similar to that of A. albifrons. The MCN of A. leptorhynchus consists of large (relay) and small (pacemaker) cells; both cell types receive synaptic input or large club endings with electrotonic gap junctions and bouton-like terminals with polarized chemical synapses. Club endings originate from thick meyelinated fibres belonging to the small (pacemaker) cells, whereas the bouton-like terminals issue from thin myelinated fibers of extranuclear origin. Via their club endings, the small (pacemaker) cells are connected both to each other and to the large (relay) cells. Besides the similarities, there are distinct and characteristic differences between the MCN of the two species, which mainly concern the synaptology of the nucleus. In A. leptorhynchus, the large (relay) cells possess long dendritic processes, covered exclusively with bouton-like terminals; the axon initial segment of large (relay) cells receives boutons, in addition to club endings. Small (pacemaker) cells have short dendritic protrusions receiving input from club endings and boutons; furthermore, the small pacemaker cells axon initial segment receives both club endings and bouton-like terminals. These differences are discussed in terms of the functional organization of the MCN in certain gymnotoids and draw attention to the fact that the morphological and ultrastructural aspects of the central command of the electric organ discharge reveal several differences not only between different gymnotoid fish (Apteronotus and Eigenmannia) but also between closely related species such as A. albifrons and A. leptorhynchus.     

Anterograde tracer study on the nucleus geniculatus dorsalis and its internal synaptic structure in chick brain

In the present study the terminals of retinal fibres and those of internal layer cells in ventral geniculate nucleus of chicks were labelled with the anterograde tracer biotinylated dextran amine. The tracer showed the connections from the internal cell layers of ventral geniculate nucleus to the medial part of the dorsal lateral geniculate nucleus. The labelled retinal terminals were located exactly in the lateral part of nucleus. The labelled terminals in the two parts of the nucleus were analysed with the electron microscope and showed a different synaptic organisation in the two parts of the dorsal lateral geniculate nucleus. In the lateral part, two kinds of synaptic glomeruli were found mostly in the vicinity of large dendrites, which are proximal dendrites of projection neurons. One type is a simple glomerulus containing a large dendrite, a large optic terminal and a large and/or series of asymmetrical synapses surrounded by glial processes. The other type is a complex synaptic unit with several pre- and postsynaptic components, among them synapses of GABA-positive axon terminals and/or dendraxons. No glomeruli were found in the medial part of the nucleus. In the medial part of the lateral geniculate nucleus, the terminals of internal layer cell axons established asymmetrical synapses with dendrites. Often, a large terminals and large dendritic profiles established serial asymmetrical synapses. GABA-positive myelinated fibres entered and ramified in both parts of the dorsal lateral geniculate nucleus, and GABA-positive terminals were seen to form synapses on the same dendrite near to the asymmetrical contacts. To our knowledge, this is the first report of the connection from ventral geniculate internal layer cells to the dorsal lateral geniculate nucleus in the chick.     

An ultrastructural study of the lateral reticular nucleus in the rat

Summary A systematic study of the normal synaptic patterns within the lateral reticular nucleus (LRN) of the rat revealed various synaptic relationships. Two types of axon terminals were identified according to the morphology of the synaptic vesicles contained within them. Axon terminals with round vesicles established asymmetrical synaptic contacts with the somata and all areas of the dendritic trees including somatic and dendritic appendages. Pleomorphic-vesicle terminals established symmetrical synaptic contacts on somata and their appendages and on all sizes of dendrites and their appendages. Both round and pleomorphicvesicle terminals were infrequently seen to synapse upon the somata and proximal dendrites. The round-vesicle terminals outnumbered the pleomorphic-vesicle terminals on the dendritic trees. Terminals of the en passant type were also common throughout the LRN. Both round and pleomorphic-vesicle terminals were observed simultaneously contacting the soma and one or more dendritic profiles, or two different dendritic profiles. Synaptic configurations (glomeruli) were also observed in all three divisions of the nucleus. They consisted of a large, central, round-vesicle terminal contacting a number of small-calibre dendritic processes. This arrangement was surrounded by one or more sheets of glial lamellae. Puncta adherentia were observed on the apposed membranes of adjacent cells, adjacent dendrites and adjacent axon terminals.     

Catecholamine-containing axon terminals in the hypoglossal nucleus of the rat: an immuno-electronmicroscopic study

Summary A correlative light and electron microscopic investigation was undertaken to determine the morphology and distribution of catecholamine (CA)-containing axon terminals in the hypoglossal nucleus (XII) of the rat. This was accomplished immunocytochemically with antibody to tyrosine hydroxylase (TH). The major findings in this study were the following: 1) Immunoreactive profiles were found throughout XII and included unmyelinated axons, varicosities, axon terminals and dendrites; 2) Nonsynaptic immunoreactive profiles (preterminal axons, varicosities) were more frequently observed (55.2%) than synaptic profiles (43.5%); 3) CA-containing axon terminals ending on dendrites were more numerous (71.8%) than those synapsing on somata (25.4%) or nonlabeled axon terminals (2.7%); 4) The morphology of labeled axon terminals was variable. Axodendritic terminals typically contained numerous small, round agranular vesicles, a few large dense-core vesicles and were associated with either a symmetric or no synaptic specialization, axosomatic terminals were often associated with a presynaptic membrane thickening or a symmetric synaptic specialization and contained small, round and a few elliptical-shaped vesicles, while axoaxonic synapses formed asymmetric postsynaptic specializations; and 5) CA-positive dendritic processes were identified in XII. These findings confirm the CA innervation of XII, and suggest a complex, multifunctional role for CA in controlling oro-lingual motor behavior.     

大鼠中脑导水管周围灰质腹外侧区5-羟色胺样、P物质样和亮氨酸-脑啡肽样免疫反应阳性亚微结构的电镜观察

本文用免疫电镜技术研究了大鼠中脑导水管周围灰质腹外侧区内5-HT样、SP样和L-ENK样的免疫反应阳性亚微结构。5-HT样免疫反应阳性的胞体较多,常见5-HT样阳性树突与阴性轴突终末形成多为非对称性的轴-树突触;偶见阳性轴突终末与阴性树突以及阴性轴突终末与阳性胞体分别构成轴-树和轴-体突触.SP样阳性胞体数目较少,可见少量含多形性小泡的阴性轴突终末与之形成轴-体突触;由阴性轴突终末与阳性树突所形成的轴-树突触最常见;阳性轴突终末与阴性胞体和阳性树突分别构成轴-体突触和轴-树突触。L-ENK样阳性胞体数目也较少,L-ENK样阳性树突与阴性轴突终末所形成的轴-树突触最多见,可见L-ENK样阳性胞体与阴性轴突终末构成轴-体突触;偶见阳性轴突终末与阴性树突形成轴-树突触。上述各种突触均主要含圆形小泡,有时有少量扁平小泡、椭圆形小泡和颗粒囊泡。     

Substance P neuronal organization in the median region of the interpeduncular nucleus of the cat: an electron microscopic analysis

The localization of substance P-like immunoreactivity in the interpeduncular nucleus using the peroxidase-antiperoxidase technique, revealed that the median region of the interpeduncular nucleus was one area rich in substance P-like immunoreactive processes. The ultrastructural characteristics of these substance P-like immunoreactive processes and their organization within the middle zone of the median region of the interpeduncular nucleus was studied. Substance P-like immunoreactivity was found in the perikaryon of small neurons, and in proximal and small dendrites. The substance P-like immunoreactive cell bodies and proximal dendrites receive a variety of unlabeled synaptic terminals. The immunoreactive small dendrites usually formed the central component of a "rosette"-like formation with unlabeled terminals. A few immunoreactive small unmyelinated axons and boutons were also present in the neuropil. The substance P-like immunoreactive boutons contained mainly small round vesicles with some large dense-core vesicles. These substance P-like immunoreactive boutons were presynaptic to unlabeled dendritic profiles, and frequently to substance P-like immunoreactive dendritic profiles. They were also seen in apposition to unlabeled boutons. Substance P-like immunoreactive boutons were not found to synapse with the crest-like dendritic processes in this part of the interpeduncular nucleus. It is suggested on the basis of morphological features, that some of the unlabeled terminals synapsing on substance P-like immunoreactive dendrities, may be cholinergic in nature.     

Neural elements containing glutamic acid decarboxylase (GAD) in the dorsal lateral geniculate nucleus of the rat; immunohistochemical studies by light and electron microscopy

Immunoreactive constituents of the dorsal lateral geniculate nucleus of adult albino rats were examined by light- and electron-microscopy, using the unlabelled antibody enzyme method, following treatment of brain slices with a purified antibody to glutamic acid decarboxylase. The neuropil of the dorsal lateral geniculate nucleus displayed a conspicuous granular immunoreactivity. In addition, the antibody was bound to a class of small neurons of characteristic morphology. These cells possessed few (commonly 2-4) sparsely branched, long dendrites from some of which immunoreactive appendages were traced. Many cells were bipolar in form, and the dendrites of some appeared to be preferentially orientated. The immunoreactive cells closely resembled intrinsic interneurons characterized in previous Golgi studies of this nucleus. By electron-microscopy, immunoreactive presynaptic elements were present both in the extraglomerular neuropil and in the synaptic glomeruli. The former were axon terminals containing flattened synaptic vesicles and making Gray type II axo-dendritic synaptic contact; they appeared to correspond to axon terminals whose origin in the thalamic reticular nucleus has been established in previous studies, but it is possible that some were axon terminals of intrinsic interneurons. The immunoreactive glomerular components also contained flattened vesicles, were presynaptic to presumptive projection cell dendrites, postsynaptic to retinal axon terminals, and participated in triplet (triadic) and other complex synaptic arrangements. They corresponded in all respects to the synaptic portions of the complex dendritic appendages of intrinsic interneurons, identified and characterized in previous studies. The finding that there are high levels of glutamic acid decarboxylase in the cell bodies, dendritic shafts and dendritic appendages of intrinsic interneurons in the dorsal lateral geniculate nucleus of the rat, and in the axon terminals of fibres projecting to this site from the thalamic reticular nucleus, allows us to conclude that the inhibitory inputs to the geniculo-cortical projection cells from both of these sources are probably mediated by gamma-aminobutyric acid.     

Neuronal and synaptic organization of the centromedian nucleus of the monkey thalamus: a quantitative ultrastructural study, with tract tracing and immunohistochemical observations

Summary The ultrastructure of the centromedian nucleus of the monkey thalamus was analysed qualitatively and quantitatively and projection neurons, local circuit neurons, and synaptic bouton populations identified. Projection neurons were mostly medium-sized, with oval-fusiform or polygonal perikarya, few primary dendrites, and frequent somatic spines; local circuit neurons were smaller. Four basic types of synaptic boutons were distinguished: (1) Small- to medium-sized boutons containing round vesicles (SR) and forming asymmetric contacts, identified as corticothalamic terminals. (2) Heterogeneous medium-sized boutons with asymmetric contacts and round vesicles, similar to the so-called large round (LR) boutons, which were in part of cortical origin. (3) Heterogeneous GAD-positive small- to medium-sized boutons, containing pleomorphic vesicles and forming symmetric contacts (F1 type), which included pallidothalamic terminals. (4) Presynaptic profiles represented by GAD-positive vesicle-containing dendrites of local circuit neurons. Complex synaptic arrangements, serial synapses and triads with LR and SR boutons engaging all parts of projection neuron dendrites and somata, were seen consistently, whereas classical glomeruli were infrequent. LR and SR boutons also established synapses on dendrites of local circuit neurons. F1 boutons established synapses on projection neuron somata, dendrites and initial axon segments. Compared to other previously studied motor-related thalamic nuclei, differences in synaptic coverage between proximal and distal projection neuron dendrites were less pronounced, and the density of synapses formed by local circuit dendrites on projection neuron dendrites was lower. Thus, compared to other thalamic nuclei, the overlap of different inputs was higher on monkey centromedian cells, and centromedian inhibitory circuits displayed a different organization.     

猫丘脑腹后内侧核内三叉丘系纤维终末的超微结构及其突触联系

本文采用顺行溃变法对猫丘脑腹后内侧核内发自三叉神经尾侧脊束核的三叉丘系纤维终末的超微结构及其突触联系进行了研究。在电灼损毁三叉神经尾侧脊束核四天后 ,在电镜下发现丘脑腹后内侧核内的三叉丘系终末存在三种溃变形式 ,即 :电子致密型溃变 ,电子透明型溃变及神经微丝型溃变 ,以电子致密型溃变终末最为常见。溃变的三叉丘系终末常较大 ,含有大量密集的圆形无颗粒小泡 ,在丘脑腹后内侧核内主要形成不对称型轴—树突触 ,多数溃变轴终末还参与形成以树突为中心的汇聚型突触复合体     

弓状核内神经紧张素能神经元与神经肤Y能神经元关系的免疫电镜双标记研究

用包埋前免疫电镜PAP双标记技术,对大鼠下丘脑弓状核内的神经紧张素(NT)和神经肽Y(NPY)的分布进行了超微结构研究。先用DAB法显示NPY免疫反应。然后用钼酸铵-TMB法显示NT免疫反应,再经DAB-氯化钴稳定后作免疫电镜包埋。结果:在弓状核内,NPY免疫反应产物呈电子密度高的颗粒状或絮状沉淀,弥漫分布于核周质的细胞器和基质、树突的微管周围、轴突的小透亮囊泡周围。NT免疫反应产物则为致密的针状或块状,散在分布于核周质、树突和轴突内。两者极易分辨。NPY能和NT能神经结构在弓状核内呈交错分布,彼此关系密切。含NPY的树突和轴突与免疫反应阴性轴突形成突触连接;含NT的胞体和树突与免疫反应阴性轴突形成突触连接。此外,NPY阳性轴突末梢还与NT阳性树突形成对称性轴-树突触。本研究结果为下丘脑NT能神经元的肽能突触调节提供了又一新的超微结构依据。     

Synaptic connections of morphologically identified and physiologically characterized large basket cells in the striate cortex of cat

Neurons were studied in the striate cortex of the cat following intracellular recording and iontophoresis of horseradish peroxidase. The three selected neurons were identified as large basket cells on the basis that (i) the horizontal extent of their axonal arborization was three times or more than the extent of the dendritic arborization; (ii) some of their varicose terminal segments surrounded the perikarya of other neurons. The large elongated perikarya of the first two basket cells were located around the border of layers III and IV. The radially-elongated dendritic field, composed of beaded dendrites without spines, had a long axis of 300-350 microns, extending into layers III and IV, and a short axis of 200 microns. Only the axon, however, was recovered from the third basket cell. The lateral spread of the axons of the first two basket cells was 900 microns or more in layer III and, for the third cell, was over 1500 microns in the antero-posterior dimension, a value indicating that the latter neuron probably fulfills the first criterion above. The axon collaterals of all three cells often branched at approximately 90 degrees to the parent axon. The first two cells also had axon collaterals which descended to layers IV and V and had less extensive lateral spreads. The axons of all three cells formed clusters of boutons which could extend up a radial column of their target cells. Electron microscopic examination of the second basket cell showed a large lobulated nucleus and a high density of mitochondria in both the perikarya and dendrites. The soma and dendrites were densely covered by synaptic terminals. The axons of the second and third cells were myelinated up to the terminal segments. A total of 177 postsynaptic elements was analysed, involving 66 boutons of the second cell and 89 boutons of the third cell. The terminals contained pleomorphic vesicles and established symmetrical synapses with their postsynaptic targets. The basket cell axons formed synapses principally on pyramidal cell perikarya (approximately 33% of synapses), spines (20% of synapses) and the apical and basal dendrites of pyramidal cells (24% of synapses). Also contacted were the perikarya and dendrites of non-pyramidal cells, an axon, and an axon initial segment. A single pyramidal cell may receive input on its soma, apical and basal dendrites and spines from the same large basket cell.(ABSTRACT TRUNCATED AT 400 WORDS)     

Synaptic terminals in the dorsal lateral geniculate nucleus from neurons of the thalamic reticular nucleus: A light and electron microscope autoradiographic study

(³H)-proline was injected in the caudodorsal part (visual segment) of the thalamic reticular nucleus to study its projection to the dorsal lateral geniculate nucleus. This was done by autoradiographic tracing of anterograde axonal transport of tritium at the light- and electron microscopic level. The results of the light-microscope autoradiography show that connections of the thalamic reticular nucleus are distributed along lines of projections in the dorsal lateral geniculate nucleus, indicating a retinotopic arrangement of this projection. The results of the electron microscope autoradiography provide direct evidence that axons of cells in the thalamic reticular nucleus terminate in the dorsal lateral geniculate nucleus as synaptic boutons that contain flattened synaptic vesicles, dark mitochondria and establish symmetrical synapses with perikarya and with proximal, intermediate and distal dendrites. They do not take part in intraglomerular synapses (as boutons with pleomorphic synaptic vesicles do) and are not postsynaptic to other vesicle-containing boutons in the dorsal lateral geniculate nucleus.The present results, taken in conjunction with physiological studies that have shown postsynaptic inhibitory effects of the thalamic reticular nucleus on dorsal lateral geniculate nucleus relay cells in the rat, establish a correlation of an inhibitory synapse with the presence of flattened synaptic vesicles in the corresponding synaptic boutons. Also, the observation that thalamic reticular nucleus terminals in the dorsal lateral geniculate nucleus avoid forming synapses with boutons containing pleomorphic vesicles, believed to be synaptic processes of interneurons, is indicative that the inhibitory effects are exerted monosynaptically on geniculate relay cells.