Axon terminals of the intrinsic neurons in the nucleus lateralis of the cerebellum an electron microscope study

Summary The large projection neurons of the lateral nucleus have long axons, which leave the cell mass in the superior cerebellar peduncle. These axons emit myelinated recurrent collaterals which have synaptic varicosities en passant. The varicosities are 2–5 m in diameter and contain round, agranular synaptic vesicles ranging between 280 and 480 Å with diameters of approximately 400 Å. The vesicles lie in a moderately dark axoplasmic matrix with a mean packing density of 281/m². The varicosities synapse through Gray's type 1 junctions with dendrites and thorns of large and small neurons. They constitute 22% of the total axonal population on dendrites of large neurons and 10% on dendrites of small neurons. The recurrent collateral system may provide a means for positive feedback to the same neuron and other neurons of the neuropil.The small neuron or interneuron has a short axonal plexus. The axon is myelinated, and is distinctive with a light axoplasmic matrix and varicosities containing elliptical synaptic vesicles. The vesicles are loosely dispersed with a mean population density of 44/m². These varicosities synapse through an intermediate type of junction upon the somata of certain large and small neurons and they consitute 14% and 22% of the axosomatic synapses respectively. They also make synapses on dendrites, constituting 12% and 25% of the total population of axons synapsing with dendrites of large neurons and those of small neurons respectively. It is suggested that these are the inhibitory interneurons of the lateral nucleus.The corticonuclear input through Purkinje axons is the dominant influence on the lateral nucleus neurons. This inhibitory input is considerably larger on the large neurons than on the small ones. It is speculated that the axosomatic synapses are inhibitory. Excitatory influences, through the collaterals of mossy and climbing fibers and the recurrent collaterals of the large intrinsic neurons, impinge upon the dendrites, where the axons of both Purkinje cells and interneurons also terminate.Supported in part by U.S. Public Health Service grants NS10536, NS03659, Training grant NS05591 from the National Institute of Neurological Diseases and Stroke, and a William F. Milton Fund Award from Harvard University.     

On certain fluorescent axon terminals containing granular synaptic vesicles in the cerebellar nucleus lateralis

Summary Thin, unmyelinated, green fluorescent fibers bearing fine beads or varicosities have been found in the neuropil and near blood vessels of the nucleus lateralis. In electron micrographs these fibers are identifiable as a class of axons, the CAT fibers, which contain large and small granular synaptic vesicles and agranular vesicles in their varicosities. There are two types of CAT fiber. 1) The CAT₁ terminals contain many large and elongated vesicles, 700–1700 Å in size, with dark, homogeneously dense centers; a few small granular vesicles each with an intensely osmiophilic particle, and small agranular vesicles. These terminals have not been seen in synaptic contact with other elements of the neuropil. 2) The CAT₂ terminals have a very thin unmyelinated connecting thread between small varicosities. The varicosities contain small agranular synaptic vesicles and small granular ones containing either a single dense particle, or an elliptical, intensely osmiophilic droplet flanked by lighter semicircular particles. Large granular vesicles, 750–950 Å each, with a variably dense center, are also found. These terminals form conventional axodendritic synapses with Gray's type 1 synaptic junctions and the subsynaptic specialization of Taxi, as well as synapses on thorns of spiny neurons.It is suggested that the CAT₁ and CAT₂ fibers may be the electron microscope equivalents of norepinephrine- and 5-hydroxytryptamine-containing fluorescent axons. These fibers probably have extrinsic origins since no fluorescent cells or perikarya with small or large granular vesicles have been found in the lateral nucleus. Their origins, however, are unknown. The proximity of these fluorescent fibers to blood vessels is discussed, and their functions are the subject of some speculation.Supported in part by U.S. Public Health Service grants NS10536, NS03659, Training grant NS05591 from the National Institute of Neurological Diseases and Stroke and a William F, Milton Fund Award from Harvard University.     

The cytology of neurons and their dendrites in the simple mammalian nucleus lateralis an electron microscope study

Summary Profiles of large neurons in the lateral nucleus range from 16 m to 35 m in diameter with dimpled nuclei, large Nissl bodies, and well developed Golgi apparatus. Two types of perikarya are distinguished, those that are smooth and those with irregular somatic and dendritic protuberances. About 86% of all large neuronal somata are covered with axosomatic synapses, predominantly with terminals of Purkinje axons and a few belonging to axons of the small neurons. The remaining 14% have no axosomatic synapses. The thick, fleshy dendrites of these cells are covered with terminals, the majority of which synapse directly upon the dendritic shaft. A few are present on spines. The initial segment of the large neuron is thick and robust and receives synapses upon its shaft or upon a spinous projection. The small neurons measure less than 12 m in diameter and have very lobulated nuclei in a sparse cytoplasm characterized by small Nissl bodies and a poorly elaborated Golgi apparatus. About 52% of all small neuronal somata bear no synapses whereas the remaining 48% are covered with axosomatic synapses, mainly from the axons of Purkinje cells and a few axons of other small cells. The slender long dendrites of both large and small cells bear synapses with six classes of axons in the neuropil. Synaptic protuberances of two varieties occur on the surfaces of both perikarya and dendrites, (a) dome-shaped ones capped with a pronounced asymmetrical synaptic junction and (b) ones with thin long necks and bulbous heads having synapses on both parts. Frond-like dendritic excrescences are borne on the processes of some small and large neurons and they are postsynaptic to many axon terminals clustered around them.Supported in part by U.S. Public Health Service Research grants NS10536, NS03659, Training grant NS05591 from the National Institute of Neurological Diseases and Stroke, and a William F. Milton Fund Award from Harvard University.     

Quantitative and ultrastructural study of ascending projections to the medial mammillary nucleus in the rat

Summary We analyzed the termination pattern of axons from the superior central nucleus and the ventral tegmental nucleus of Gudden within the medial mammillary nucleus (MM) in the rat. The neuropil of the MM consists of two classes of terminals, that is, terminals containing round synaptic vesicles and forming asymmetric synaptic contact, and terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact. The number of axodendritic terminals with round vesicles is almost equal to that of terminals with pleomorphic vesicles. Almost all axosomatic terminals contain pleomorphic vesicles with symmetric synaptic contact. Injection of WGA-HRP into the central part of the superior central nucleus permitted ultrastructural recognition of many anterogradely labeled terminals within the median region of MM. The labeled terminals contacted mainly intermediate (1–2 m diameter) and proximal dendrites (more than 2 m diameter) as well as the neuronal somata. Serial ultrathin sections of neurons of the median region of the MM revealed that 37% of the axosomatic terminals were labeled anterogradely. The pars compacta of the superior central nucleus had reciprocal connections with the median region of MM. The axon terminals from this nucleus occupied 53% of axosomatic terminals, and contacted mainly intermediate dendrites. Following injection of WGA-HRP into the ventral tegmental nucleus, many labeled terminals were found in the medial and lateral regions of MM. They contacted mainly intermediate dendrites as well as neuronal somata. In the medial region, 78% of axosomatic terminals contacting retrogradely labeled neurons were labeled anterogradely. All labeled terminals from these nuclei contained pleomorphic vesicles, and made symmetric synaptic contact.     

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.     

Identification of synapses formed in the cerebellar cortex by purkinje axon collaterals: an electron microscope study

Summary Purkinje axon collaterals and their synaptic terminals can be identified on the basis of three criteria: (1) They are the only myelinated axons of local elements, hence any myelinated axon persisting in chronically isolated folium is a Purkinje axon or its collateral; (2) They are the only known transfolial axons, so that axons and synapses found in the state of secondary degeneration after lesions placed into neighbouring folia of the cerebellar cortex are Purkinje axon collaterals and synapses; (3) The peculiar axonal tubular systems described by Andres (1965) are specific for Purkinje axons and their synaptic endings, which offers an additional clue for their identification. Using these three criteria numerous synapses of Purkinje axon collateral endings have been identified on the large Golgi neurons, both cell bodies and principal dendrites, and on the bodies of basket neurons. No evidence of the termination of Purkinje axon collaterals on other Purkinje cells could be detected.     

Phenylethanolamine N-methyltransferase-immunoreactive terminals synapse on adrenal preganglionic neurons in the rat spinal cord

Adrenergic neurons in the C1 region in the ventrolateral medulla oblongata send descending axons into spinal cord which terminate in thoracic and upper lumbar segments, overlapping the distribution of sympathetic preganglionic neurons. The present study was undertaken to determine whether adrenergic fibers synapse directly on preganglionic neurons which innervate the adrenal medulla and to examine the ultrastructure of these fibers during development. The ultrastructure and synaptology of adrenergic axons in the intermediolateral nucleus of mid-thoracic spinal cord were studied in 7-, 9-, 24-, 30-, 60-, and 90-day-old rats using immunocytochemical staining for phenylethanolamine N-methyltransferase, the epinephrine-synthesizing enzyme. Phenylethanolamine N-methyltransferase-immunoreactivity was observed in the cytoplasm of unmyelinated axonal varicosities and intervaricose segments in the neuropil of intermediolateral nucleus. Phenylethanolamine N-methyltransferase-immunoreactive synaptic boutons were filled with spherical electron-lucent vesicles and occasional larger dense-core vesicles. These boutons were observed to form symmetrical synaptic contacts with dendritic processes at all ages examined. Asymmetrical synapses on dendrites were also observed in adult rats. Axosomatic synaptic contacts were frequently observed in immature rats, but were never observed in adult rats. To determine whether adrenergic axons synapse on preganglionic neurons which project to the adrenal medulla, adrenal preganglionic neurons were retrogradely labeled with horseradish peroxidase and adrenergic axons were stained for phenylethanolamine N-methyltransferase-immunoreactivity. In young rats, phenylethanolamine N-methyltransferase-immunoreactive boutons were observed to form symmetrical axosomatic and axodendritic synaptic contacts with adrenal preganglionic neurons in intermediolateral nucleus. These contacts had already formed by postnatal day 7, the youngest age studied. In contrast, it was not possible to verify that adrenal preganglionic neurons receive adrenergic innervation in adult rats, since phenylethanolamine N-methyltransferase-immunoreactive boutons were only observed in contact with small diameter dendrites that were not retrogradely labeled by horseradish peroxidase. These studies demonstrate that adrenal preganglionic neurons receive adrenergic synapses prior to the first postnatal week. The initial synapses which form on preganglionic somata and proximal dendrites appear to reorganize late in development. It is suggested that these become more distally located as the dendritic tree matures. More generally, these observations suggest that adrenergic bulbospinal neurons are involved in central regulation of adrenal development and function.     

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.     

Fine structural survey of the intermediate subnucleus of the nucleus tractus solitarii and its glossopharyngeal afferent terminals

The intermediate subnucleus of the nucleus tractus solitarii (imNTS) receives somatosensory inputs from the soft palate and pharynx, and projects onto the nucleus ambiguus, thus serving as a relay nucleus for swallowing. The ultrastructure and synaptology of the rat imNTS, and its glossopharyngeal afferent terminals, have been examined with cholera toxin-conjugated horseradish peroxidase (CT-HRP) as an anterograde tracer. The imNTS contained oval or ellipsoid-shaped, small to medium-sized neurons (18.2×11.4 μm) with little cytoplasm, few cell organelles and an irregularly shaped nucleus. The cytoplasm often contained one or two nucleolus-like stigmoid bodies. The average number of axosomatic terminals was 1.8 per profile. About 83% of them contained round vesicles and formed asymmetric synaptic contacts (Gray’s type I), while about 17% contained pleomorphic vesicles and formed symmetric synaptic contacts (Gray’s type II). The neuropil contained small or large axodendritic terminals, and about 92% of them were Gray’s type I. When CT-HRP was injected into the nodose ganglion, many labeled terminals were found in the imNTS. All anterogradely labeled terminals contacted dendrites but not somata. The labeled terminals were usually large (2.69±0.09 μm) and exclusively of Gray’s type I. They often contacted more than two dendrites, were covered with glial processes, and formed synaptic glomeruli. A small unlabeled terminal occasionally made an asymmetric synaptic contact with a large labeled terminal. The large glossopharyngeal afferent terminals and the neurons containing stigmoid bodies characterized the imNTS neurons that received pharyngeal afferents.     

Ultrastructure of the central subnucleus of the nucleus tractus solitarii and the esophageal afferent terminals in the rat

The central subnucleus of the nucleus tractus solitarii (ceNTS) receives afferent projections from the esophageal wall and projects to the nucleus ambiguus, thus serving as a relay nucleus for peristalsis of the esophagus. Here we examine the synaptic organization of the ceNTS, and its esophageal afferents by using transganglionic anterograde transport of cholera toxin-conjugated horseradish peroxidase (CT-HRP). When CT-HRP was injected into the subdiaphragmatic esophagus, many anterogradely labeled terminals were found only in the ceNTS. The ceNTS was composed of round or oval-shaped, small neurons (14.7x8.7 micro m) containing sparse organelles and an irregularly shaped nucleus. The average number of axosomatic terminals was only 1.3 per section cut through the nucleolus. Most of them (92%) contained round vesicles and formed asymmetric synaptic contacts (Gray's type I), and a few (8%) contained pleomorphic vesicles and formed symmetric synaptic contacts (Gray's type II). All anterogradely labeled terminals contacted dendrites but not the neuronal somata. The labeled terminals were large (2.55+/-0.07 micro m) and exclusively Gray's type I. More than half of them (60%) contacted small dendrites (less than 1 micro m in diameter), and contained dense-cored vesicles. More than 40% of the labeled terminals contacted two to four dendrites, thus forming a synaptic glomerulus. Sometimes a labeled terminal that contacted an unlabeled terminal by an adherent junction was found within the glomerulus. The large terminals and these complex synaptic relations appeared to characterize the esophageal afferent projections in the ceNTS.     

GABAergic and pallidal terminals in the thalamic reticular nucleus of squirrel monkeys

The ultrastructure of synaptic terminals from the external segment of the globus pallidus and of other synaptic terminals positive for gamma-aminobutyric acid (GABA) was examined in the thalamic reticular nucleus (TRN) of squirrel monkeys. Two GABA-positive terminals types were commonly encountered within the TRN neuropil. The most common type of GABAergic terminals (F terminals) are filled with dispersed pleomorphic synaptic vesicles and clusters of mitochondria. These terminals establish multiple symmetric synapses upon the somata and dendrites of TRN neurons. The external pallidal terminals, labeled with WGA-HRP, arise from thinly myelinated axons and correspond to the medium to large F terminals. A less prevalent population of smaller GABAergic synaptic profiles was also identified. The synaptic profiles in this second group contain considerably fewer pleomorphic synaptic vesicles in small irregular clusters and fewer mitochondria, establish symmetric synapses, are postsynaptic to other axonal terminals, are presynaptic to dendrites and soma, and are unlabeled following pallidal injections of WGA-HRP.     

大鼠下丘脑弓状核突触的衰老性变化

用透射电镜结合体视学方法，对３月龄、１０月龄和３０～３４月龄大鼠弓状核突触进行了定性和定量研究。结果显示：老龄组大鼠神经毯呈萎缩变性相，大树突内脂褐素增多，小到中等大小的树突出现空泡变性、多泡体和膜被多层体等，棘萎缩减少；轴突终末内突触囊泡减少而大颗粒囊泡积聚，部分突触前、后膜变薄、缩短或间断，突触小球少见；轴－体、轴－树和轴－棘突触数减少，突触密度、突触连接带面密度和突触膜总长度降低，ＧｒａｙⅠ型和即Ⅱ型突触间隙增宽。上述结果表明，老年弓状核突触在数量、形态和结构上发生了衰老性改变，这是导致下丘脑神经内分泌衰老障碍的主要原因之一。     

Opioid neurons and pain modulation: an ultrastructural analysis of enkephalin in cat superficial dorsal horn

To clarify the circuitry through which opioid compounds modulate spinal and trigeminal nociceptive transmission, we have examined the synaptic associations formed by leucine-enkephalin-containing (enkephalin) neurons in the superficial dorsal horn of the cat. As described previously, punctate enkephalin immunoreactivity is concentrated in the marginal layer (lamina I) and in both the outer and inner layers of the substantia gelatinosa (lamina IIo and IIi). In colchicine treated cats, enkephalin perikarya are most numerous in lamina I and at the border between laminae I and II. Ultrastructural analysis reveals that enkephalin cells receive a diverse afferent input. The majority of afferent inputs are presynaptic to the enkephalin dendrites; few axosomatic synapses are seen. Among these presynaptic axonal profiles are unlabeled axons which resemble primary afferent terminals, including the characteristic central axonal varicosity. Enkephalin dendrites are also postsynaptic to enkephalin immunoreactive axons. Two types of enkephalin axonal profiles appear in the superficial dorsal horn. Class I profiles are only found in lamina I. These are large profiles which form few synapses; those synapses made are axodendritic. Class II enkephalin axons are smaller and are distributed in both layers I and II. While Class II axons most commonly form axo-dendritic synapses, they also form axo-axonic synapses with flat vesicle-containing profiles; the latter are generally presynaptic to the enkephalin terminals. Serial analysis further revealed that both the enkephalin and the flat vesicle-containing profile synapse onto a common dendrite. Although enkephalin axons frequently lie adjacent to round vesicle-containing profiles, anatomical evidence that opioid axons form synapses with this type of ending was not found. An additional type of enkephalin vesicle containing-profile is found in layer IIi; its morphological features do not clearly distinguish its axonal or dendritic origin. These endings are typically postsynaptic to unlabelled central endings, and provide minimal presynaptic input to other elements in the neuropil. Like some class II axons, these labelled profiles contain vesicles which cluster at the membrane immediately adjacent to unlabelled central axons. These results indicate that spinal enkephalin neurons receive a variety of synaptic inputs. These include inputs which may derive from primary afferent axons. Enkephalin neurons, in turn, influence nociceptive transmission predominantly through postsynaptic mechanisms. Finally, while we did not observe enkephalin terminals presynaptic in an axoaxonic relationship, the possibility that enkephalin neurons modulate the excitability of fine fiber nociceptive and nonnociceptive afferents via "nonsynaptic interactions" is discussed.     

The recurrent collaterals of Purkinje cell axons: A correlated study of the rat's cerebellar cortex with electron microscopy and the Golgi method

Summary Each Purkinje cell axon with its recurrent collaterals occupies a roughly triangular space in the folium, apex pointed towards the white matter and base against the Purkinje cell layer. The axon is smooth initially but develops distensions that become more obvious at twists and turns and at points where collaterals originate. These thin, finely beaded collaterals make characteristic acute angles with the axon from which they issue. The collaterals bifurcate further, their terminal branches becoming more varicose, intertwining with each other to form plexuses in the molecular and granular layers. These fiber plexuses are found in three locations: (1) the recurrent collateral plexus in the granular layer which synapses with dendrites and somata of deep Golgi II neurons; (2) the profuse infraganglionic plexus, boutons of which terminate in relation with the somata and dendrites of Purkinje cells and Lugaro cells, in addition to participating in other complex synaptic arrangements in the neuropil; (3) the sparse supraganglionic plexus which forms synapses with dendrites of Purkinje cells and occasionally with basket cells.In electron micrographs, terminals belonging to recurrent collaterals contain a mixture of neurofilaments, microtubules, and slender mitochondria with a loose array of flat, elliptical, and round synaptic vesicles embedded in a dark filamentous matrix. It is usual to find a cluster of boutons on the postsynaptic surface. Each synapse consists of several separate macular junctional complexes. The synaptic cleft is widened and contains a dense fibrous material while both pre- and postsynaptic components have very shallow, symmetrical filamentous densities adherent to the cytoplasmic surfaces of the membranes.It is suggested that recurrent collaterals from axons of Purkinje cells may provide a rapid monosynaptic feed-back mechanism for inhibitory control of Purkinje cell responses. These collaterals may also participate in a slower positive feed-forward circuit or resetting mechanism involving at least two synapses. The existence of this circuit is indicated by synapses on deep Golgi II neurons. The inhibition of Golgi II cells may depress their inhibitory activity on surrounding granule cells, thus resetting the mechanism for the subsequent responses to excitatory afferent input. Recurrent collateral inhibition also may aid in the disinhibition of Purkinje cells through the depression of basket cell activity.Supported by U.S. Public Health Service Research Grant NS03659 and Training Grant NS05591 from the National Institute of Neurological Diseases and Stroke.     

Noradrenergic and non-noradrenergic nerves containing small granular vesicles in Auerbach's plexus of the guinea-pig: evidence against the presence of noradrenergic synapses

The appearance and distribution of varicosities containing small granular vesicles in Auerbach's plexus of the guinea-pig ileum, distal colon and rectum has been studied with the electron-microscope. Two types of varicosity were recognised. The first type was located predominantly at the surface of the plexus and did not form synapses on intrinsic neurons. This type became labelled with 5-hydroxydopamine, a specific marker for noradrenergic axons, and was destroyed by 6-hydroxydopamine and extrinsic denervation, procedures which lead to degeneration of noradrenergic nerves in the gut. The second type formed axodendritic and axosomatic synapses on intrinsic neurons and the morphology of its synaptic vesicles differed subtly from that of the first type. The second type was unaffected by 5-hydroxydopamine, 6-hydroxydopamine, or extrinsic denervation. It is concluded that the two types of small granular vesicle-containing varicosities belong to different neurons and that the first type is noradrenergic. Noradrenergic varicosities do not, therefore, form synapses in Auerbach's plexus. This conclusion is in accord with the electrophysiological findings. The second type of small granular vesicle-containing varicosity is not noradrenergic although it was formerly thought to be so. It is intrinsic to the gut and is resistant to the serotoninergic neurotoxin, 5,6-dihydroxytryptamine.     

Ultrastructural features of neurons and synaptic contacts in the posterodorsal medial amygdala of adult male rats

The aim of the present study was to describe the ultrastructure of neurons (from eight animals) and to analyse the synaptic terminal distribution (from two animals) in the posterodorsal subnucleus of the medial amygdala (MePD) of adult male rats. Using transmission electron microscopy, it was possible to identify many spiny and aspiny dendrites, unmyelinated axonal bundles, single axonal processes, a few myelinated axons, blood vessels and glial processes in the neuropil. Axodendritic synapses were the most frequently observed (67.5%), appearing to be of either the inhibitory or the excitatory types. The presynaptic region contained round or flattened vesicles that occurred either singly or with dense-cored vesicles (DCVs). The dendrites often received many synapses on a single shaft, and axon terminals displayed synaptic contacts with one or more postsynaptic structures. Dendritic spines showed different morphologies and the synapses on them (23.1%) formed a single and apparently excitatory synaptic contact with round, electron-lucid vesicles alone or, less frequently, with DCVs. Inhibitory and excitatory axosomatic synapses (8.2%) and excitatory axoaxonic synapses (1.2%) were also identified. The present report provides new findings relevant to the study of the MePD cellular organization and could be combined with other morphological data in order to reveal the functional activity of this area in male rats.     

On the development of the cerebellum of the trout, Salmo gairdneri. IV. Development of the pattern of connectivity

Summary Synaptogenesis has been studied in the corpus cerebelli of the troutSalmo gairdneri, Richardson, 1836. The first synapses are observed in hatchlings and occur between parallel fibres and the shafts of Purkinje dendrites. Subsequently the axosomatic synapses of Purkinje axon collaterals on the neurons of the ganglionic layer appear, and finally the synapses made by climbing fibres and mossy fibres, and by stellate cell axons develop. Young synapses in the cerebellum of the trout resemble the mature structures so closely that the criteria for the identification of the latter can also be applied to the former. The number of parallel fibre synapses and of Purkinje axon collateral synapses increases considerably during development. Eurydendroid cells, the axons of which leave the cerebellum, receive an abundance of Purkinje axon collaterals on their somata and main dendritic trunks. Mossy fibre synapses are numerous in the granular layer. Climbing fibre contacts and synapses of stellate cell axons, both with Purkinje cells, are found occasionally. the following pattern of connectivity is proposed. The main input-output system is formed by the mossy fibres, the granule cells, the Purkinje cells and the eurydendroid cells. Additional pathways are formed by (1) the mossy fibres, granule cells and eurydendroid cells, and (2) the climbing fibres, Purkinje cells and eurydendroid cells. The afferent-efferent systems, mentioned above, are influenced by a number of internuncial elements: (1) The Golgi cells receive their input from the parallel fibres and contact with their axon collaterals the dendrites of granule cells. (2) Axon collaterals of Purkinje cells are in synaptic relation with Golgi cells. (3) Axon collaterals of Purkinje cells impinge upon the somata and main dendrites of other Purkinje cells. (4) Stellate cells, which derive their input from the parallel fibres, synapse with the dendrites and somata of Purkinje cells. The possible functional roles of all of these neuronal elements are discussed.     

Identification under the electron microscope of climbing fibers and their synaptic contacts

Summary An attempt is made to identify, under the electron microscope, the climbing fibers of the cerebellum (in the cat) and their synaptic contacts with Purkinje cells and other cortical neurons. — Two kinds of axonal profiles, having synaptic contacts with primary and secondary dendrites of Purkinje neurons, can be recognized: One being terminal fibers densely packed with neurofilaments, having mainly contacts de passage with the dendrite surface, with small accumulations of synaptic vesicles at the presynaptic side of the contact. The others are rather knob-shaped contacts filled with synaptic vesicles and poor in neurofilaments. In chronically isolated folia, in which only local neurons and their processes have survived, all filamentous profiles have disappeared while vesicular ones are not appreciably reduced in number. It is inferred from this, that the neurofilamentous profiles correspond to climbing fibers, whereas the vesicular ones could be the endings of outer stellate axons, recurrent Purkinje axon collaterals, or ascending basket axon collaterals. — Similar two kinds of axon-terminal profiles are found in synaptic contact with Golgi and basket cell bodies. As in chronically isolated folia only the vesicular profiles survive, it is inferred that the climbing fiber has axo-somatic terminals on Golgi cells and basket cells as well. Previous information of this kind, gained with the light microscope and with degeneration studies, is thus substantiated with the aid of the electron microscope. The vesicular presynaptic profiles on Golgi and basket neurons are in the first case certainly and in the second with high probability endings of recurrent Purkinje axon collaterals. — The few axosomatic synapses found on outer stellate neurons may also be terminals of climbing fibers, but degeneration evidence for this is not conclusive. — The observations are summarized and evaluated from the functional point of view in a diagram, with consideration to recent physiological information on the function of climbing fibers.     

三叉神经尾侧脊束核内P物质纤维终末的超微结构

目的　进一步探讨三叉神经尾侧脊束核内SP免疫反应阳性纤维在感觉传递中的可能作用。方法　SP采用免疫细胞化学方法和电子显微镜方法 ,观察大鼠三叉神经尾侧脊束核内SP阳性标记纤维的超微结构和突触联系。结果　SP轴突终末分布于树突间 ,这些轴突终末含有大量的透明小泡、少量大致密芯小泡和线粒体。经过秋水仙素处理后 ,可见到SP免疫反应阳性树突。多数SP轴突终末与非标记树突 ,以及个别SP轴突终末与SP树突形成轴 树突触。含SP的突触复合体较为多见 ,为会聚型。其中可见SP轴突终末与中心的非标记树突形成GrayⅡ型轴 树突触 ;另有非标记的轴突终末与中心SP树突形成 (扁平小泡形 )F型轴 树突触。结论　三叉神经尾侧脊束核接受多种纤维传入 ,SP纤维只是多种传入纤维中的一种。形态学证明 ,在痛调制活动中 ,三叉神经尾侧脊束核内有SP纤维构成的突触后抑制类型 (GrayⅡ )突触参与。