Ultrastructural study of ascending projections to the lateral mammillary nucleus of the rat

Summary We examined the synaptic organization of ascending projections from the pars ventralis of the dorsal tegmental nucleus of Gudden (TDV) and the laterodorsal tegmental nucleus to the lateral mammillary nucleus (LM). The LM neuropil consists of terminals containing pleomorphic synaptic vesicles and forming symmetric synaptic contact, and terminals containing round synaptic vesicles and forming asymmetric synaptic contact. They make up 63% and 37%, respectively, of all axodendritic terminals. All axosomatic terminals contain pleomorphic vesicles and make symmetric contact. Following injection of WGA-HRP into the TDV, many anterogradely labeled terminals and retrogradely labeled cells are found in the LM. Labeled terminals contact mainly proximal (more than 2 m diameter) and intermediate (1–2 m diameter) dendrites. Serial ultrathin sections of the LM show that 55% of axosomatic terminals are labeled anterogradely. Following injection of WGA-HRP into the laterodorsal tegmental nucleus, many anterogradely labeled terminals are found in the LM, but no retrogradely labeled cells are present. Labeled terminals contact mainly distal (less than 1 m diameter) and intermediate dendrites as well as somata. In the LM neurons, 46% of axosomatic terminals are labeled anterogradely. All labeled terminals from these nuclei contain pleomorphic vesicles and make symmetric synaptic contact. These results indicate that almost all axosomatic terminals come from the TDV and the laterodorsal tegmental nucleus, which send inhibitory inputs to the lateral mammillary nucleus.     

Synaptic organization of afferent projections to the supramammillary nucleus of the rat

We studied the fine structure of afferent terminals from the preoptic area, the nucleus of the diagonal band of Broca, the infralimbic cortex and the laterodorsal tegmental nucleus within the supramammillary nucleus (SUM) using the anterograde tracing method of horse-radish peroxidase conjugated with wheat germ agglutinin (WGA-HRP). Injection of WGA-HRP into the preoptic area permitted ultrastructural recognition of many anterogradely labeled terminals in the SUM. Almost all labeled terminals (99%) contained clear round synaptic vesicles and formed asymmetric synaptic contacts (Gray's type I). About 86% of labeled terminals from the nucleus of the diagonal band were asymmetric (Gray's type I), whereas 14% contained pleomorphic synaptic vesicles and formed symmetric synaptic contacts (Gray's type II). Almost all labeled terminals from the infralimbic cortex were located in the ventral part of the SUM, and 95% of labeled terminals were Gray's type I. The majority of labeled terminals (90%) from the laterodorsal tegmental nucleus were Gray's type I, and the remaining (10%) were Gray's type II. The percentage of labeled terminals with dense-cored vesicles was very high in terminals from the preoptic area (70%), and low in terminals from the infralimbic cortex (19%). Labeled terminals in all cases contacted mainly intermediate-sized dendrites (0.5–1.0 m diameter). All cases had only a few labeled axosomatic terminals. The cases of injections into the preoptic area and the diagonal band nucleus had some reciprocal connections at the ultrastructural level.     

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.     

Direct synaptic projections to the myenteric ganglion of the rat subdiaphragmatic esophagus from the dorsal motor nucleus of the vagus

We have examined the ultrastructure of the myenteric ganglion of the subdiaphragmatic esophagus and determined whether the ganglion neurons receive direct projections from the dorsal motor nucleus of the vagus (DMV) using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) as an anterograde tracer. The neurons (22.2 microm x 13.3 microm) of myenteric ganglion in the esophagus contained dark cytoplasm having many free ribosomes, mitochondria, and an oval nucleus, and received only a few axon terminals contacting somata. All axon terminals formed asymmetric synaptic contacts with dendrites or somata. Approximately 85% of the axon terminals contacting dendrites and about 50% of the axon terminals contacting somata contained pleomorphic vesicles, while the rest contained round synaptic vesicles. When WGA-HRP was injected into the DMV, anterogradely labeled fibers and terminals were found in the myenteric ganglia. The WGA-HRP labeled terminals were large (1.97 microm) and contained round clear vesicles and small granular vesicles. These labeled terminals contacted exclusively the small dendrites, but not the somata. These results suggest that the DMV neurons project directly to the myenteric ganglion neurons and regulate the esophageal muscles via the ganglion neurons.     

Monosynaptic inputs from the nucleus tractus solitarii to the laryngeal motoneurons in the nucleus ambiguus of the rat

The cricothyroid (CT) and the posterior cricoarytenoid (PCA) muscles in the larynx are activated by the laryngeal motoneurons located within the nucleus ambiguus; these motoneurons receive the laryngeal sensory information from the nucleus tractus solitarii (NTS) during respiration and swallowing. We investigated whether the neurons in the NTS projected directly to the laryngeal motoneurons, and what is the synaptic organization of their nerve terminals on the laryngeal motoneurons using the electron microscope. When wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the NTS after cholera toxin subunit B-conjugated HRP (CT-HRP) was injected into the CT muscle or the PCA muscle, the anterogradely WGA-HRP-labeled terminals from the NTS were found to directly contact the retrogradely CT-HRP-labeled dendrites and soma of both the CT and the PCA motoneurons. The labeled NTS terminals comprised about 4% of the axosomatic terminals in a section through the CT motoneurons, and about 9% on both the small (PCA-A) and the large (PCA-B) PCA motoneurons. The number of labeled axosomatic terminals containing round vesicles and making asymmetric synaptic contacts (Gray’s type I) was almost equal to that of the labeled terminals containing pleomorphic vesicles and making symmetric synaptic contacts (Gray’s type II) on the CT motoneurons. The labeled axosomatic terminals were mostly Gray’s type II on the PCA-A motoneurons, while the majority of them were Gray’s type I on the PCA-B motoneurons. These results indicate that the laryngeal CT and PCA motoneurons receive a few direct excitatory and inhibitory inputs from the neurons in the NTS. Accepted: 2 June 2000     

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.     

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.     

Immunohistochemical localization of substance P and substance P receptor (NK1) in the olivary pretectal nucleus of the rat

The olivary pretectal nucleus (OPN) is the first central nucleus in the pupillary light reflex arc (PLR). Substance P (SP) is a neuropeptide present in the OPN. The present immunohistochemical study, performed at the ultrastructural level, aimed to determine the synaptic localization of SP and SP receptor in the OPN. Three types of SP-positive terminals were found. The most abundant type was of retinal origin, characterized by electron-lucent mitochondria and round vesicles, organized in glomerular structures, making asymmetric synaptic contacts with dendrites, and profiles containing pleomorphic vesicles, also making synaptic contacts with dendrites. The second type of SP-immunoreactive terminal contained electron-dense mitochondria and pleomorphic vesicles. This type made symmetric synaptic contacts and may originate from the ventral part of the lateral geniculate nucleus. The third type of SP-immunoreactive terminals contained electron-dense mitochondria, clear round vesicles, and made an asymmetric synaptic contact. This type originates from the contralateral OPN. SP receptors of the NK1 subtype were revealed to be on dendrites and were part of the glomerular-like arrangement. On account of the present observations, it can be concluded that retinal projections to the OPN use SP as a neuromodulator and synapse on NK1 receptor-containing dendrites of large neurons projecting to the Edinger-Westphal nucleus. Since SP also modulates the parasympathetic component of the PLR, we postulate that SP plays a modulating role in all components of the PLR.     

Synaptic organization of the nucleus raphe dorsalis of the cat

Summary This electron microscopic study describes the different types of synaptic terminals found in the nucleus raphe dorsalis of the adult cat. Serial section analysis was used extensively to confirm the nature of the synaptic contact established by the various classes of terminals.Five different classes of terminals are identified according to the shape and packing density of the synaptic vesicles and type of contact they establish. The most common class (RDI-type) contains densely packed, round, agranular synaptic vesicles and establishes asymmetrical synaptic contacts. A second class (RDII-type) also contains spherical synaptic vesicles, but establishes symmetrical synaptic contacts with dendrites of all sizes. Most of the terminals in these two classes contain a few dense-cored synaptic vesicles, but a small sub-group contains many dense-cored vesicles. A third, less frequent, class (RSI-type) contains sparsely packed spherical synaptic vesicles and the majority of these terminals have asymmetrical contacts. A fourth terminal class contains pleomorphic synaptic vesicles (P-type), contacts dendrites of all sizes, and usually establishes symmetrical synaptic contacts. Finally, boutons thought to be the vesicle-filled excrescences of dendrites (postsynaptic dendrites) are found and in some cases the dendritic origin of these profiles was confirmed by serial sectioning. Such boutons containing pleomorphic vesicles are presynaptic to other such dendrites as well as conventional dendrites, and are postsynapticto the other terminal types described.Somata within the nucleus exhibit somatic spines but receive few synaptic contacts. Most axo-somatic terminals contain either round or pleomorphic vesicles and have postsynaptic thickenings intermediate to the symmetric and asymmetric types.     

Ultrastructure and synaptic relations of neural elements containing glutamic acid decarboxylase (GAD) in the perigeniculate nucleus of the cat

Summary The perigeniculate nucleus of the cat (PGN) was examined at light and electron microscopic levels after immunocytochemical labeling for the gamma-aminobutyric acid (GABA) synthesizing enzyme, glutamic acid decarboxylase (GAD). In light microscopic sections, virtually all perikarya were found to be labeled (GAD+), as well as proximal dendrites, fibres and punctiform elements. Cells in the thalamic reticular nucleus (TRN) dorsal to PGN were also labeled. Ultrastructural analysis of PGN showed immunoreactivity in all somata, in dendrites and in the following vesicle containing profiles: 1.) F1 terminals, which are characterized by large size, dark mitochondria, and pleomorphic vesicles. These terminals form symmetrical synaptic contacts with somata, somatic spines and with dendrites of GAD+ PGN cells. 2.) F2 terminals, which are smaller than F1 terminals, contain also pleomorphic vesicles and frequently make serial synapses of the symmetric type with other F2 terminals. Presumably, F1 terminals are formed by collaterals of PGN-cell axons and F2 terminals by vesicle containing dendrites of PGN cells. Terminals devoid of immunoreactivity included: 1.) RLD terminals characterized by large size, round vesicles, dark mitochondria, and by asymmetric synaptic contacts with somata, especially with somatic spines, and with dendrites of GAD+ perigeniculate neurons; 2.) RSD terminals, characterized by small size, round vesicles and dark mitochondria, which make asymmetric synapses with GAD+ dendrites of medium and small size; 3.) Multivesicular (MV) terminals with variably shaped vesicles including dense core vesicles synapsing on GAD+ dendrites. There are reasons to believe that RSD terminals belong to corticofugal axons and RLD terminals to collateral axons of LGN relay cells. The origin of MV terminals remains to be determined. The GABAergic nature of the PGN cells conforms with the presumed function of these cells as mediators of inhibition of LGN relay cells. The complex synaptic relations observed between GAD+ elements in the PGN would allow for reciprocal inhibition between perigeniculate cells.Supported in part by NIH grants EY02877 to V.M. Montero and HD 03352 to the Waisman Center     

大鼠中脑导水管周围灰质－中缝大核－三叉神经脊束核尾侧亚核通路的电镜研究

用ＰＨＡ－Ｌ顺行追踪和ＨＲＰ逆行追踪结合的方法，在电镜下观察到来自中脑导水管周围灰质的ＰＨＡ－Ｌ顺行标记轴突终末与中缝大核向三叉神经脊束核尾侧亚核投射的ＨＲＰ逆行标记神经元形成以非对称性为主的轴树突触。另外，发现顺行标记的轴突终末也与中缝大核内其它神经元之间形成多种突触联系。本研究结果首次在突触水平证明了中脑导水管周围灰质中缝大核－三叉神经脊束核尾侧亚核的间接通路，同时又发现中脑导水管周围灰质下行投射的终末与中缝大核内的神经元成分之间还形成比较复杂的突触联系，并对之进行了讨论。     

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.     

大鼠三叉神经脊束核尾侧亚核-臂旁核-丘脑间接联系的研究

目的 观察臂旁核（ＰＢＮ）内向丘脑腹后内侧核（ＶＰＭ）投射神经元和三叉神经脊束核尾侧亚核（Ｖｃ向旁核投射纤维和终末的分布,以及两者之间的突触联系。方法 ＨＲＰ逆行追踪与生物素警聚糖胺（ＢＤＡ）顺行追踪相结合的双标技术,标记结果分别在光镜或电镜下观察。结果 将ＨＲＰ注入ＶＰＭ后,在光镜下可见ＨＲＰ逆标神经元主要位于同侧的臂旁外侧核,Ｋｏｌｌｉｋｅｒ－Ｆｕｓｓ（ＫＦ）核和臂旁内侧核。将ＢＤＡ注入Ｖｃ后     

Cholinergic and non-cholinergic neurons in the rat pedunculopontine tegmental nucleus

Summary Choline acetyltransferase immunhistochemistry was employed at light and electron microscopic levels in order to determine the distribution of cholinergic neurons in two subdivisions of the rat pedunculopontine tegmental nucleus that were previously defined on cytoarchitectonic grounds, and to compare the synaptic inputs to cholinergic and non-cholinergic somata in the subnucleus dissipatus, which receives major input from the substantia nigra. Large cholinergic neurons were found in both the pars compacta and the pars dissipata of the pedunculopontine nucleus. However, they were intermingled with non-cholinergic neurons and did not respect the cytoarchitectural boundaries of the nucleus. Ultrastructural study showed that all cholinergic neurons in the subnucleus dissipatus exhibited similar features. The majority had large somata (largest diameter 20 m) containing abundant cytoplasmic organelles and nuclei displaying a few shallow invaginations. Synaptic terminals on the cholinergic cell bodies were scarce and unlabeled boutons containing spherical synaptic vesicles and establishing asymmetric synaptic junctions were the dominant type. In contrast, the non-cholinergic neurons presented prominent differences in the size of their somata as well as in the distribution of axosomatic synapses. Two almost equally represented classes of non-cholinergic neurons which are referred to as large (largest diameter 20 m) and small (largest diameter <20 m) were recognized. Large non-cholinergic cell bodies were ultrastructurally similar to the cholinergic ones, but they received rich synaptic input by unlabeled nerve terminals which contained pleomorphic vesicles and were engaged in symmetric synaptic junctions. Small non-cholinergic cell bodies were characterized by deeply invaginated nuclei surrounded by a narrow rim of cytoplasm, and were often found near or in direct apposition to the cholinergic somata. Their major input consisted of axosomatic boutons containing round synaptic vesicles. These results demonstrate that cells in the pedunculopontine tegmental nucleus are differentiated with regard to their axosomatic synaptic inputs which may influence their firing properties. Furthermore, they support previous suggestions that nigral afferents may be preferentially distributed to a subpopulation of the pedunculopontine neurons.Abbreviations cp cerebral peduncle - CG central gray - CNF cunei-form nucleus - LPB lateral parabrachial nucleus - ml medial lemn-iscus - MPB medial parabrachial nucleus - me5 mesencephalic tri-geminal tract - Me5 nucleus of the mesencephalic tract of the trige-minal nerve - Mo5 motor trigeminal nucleus - PPNc pedunculo-pontine nucleus, subnucleus compactus - PPNd pedunculopontinenucleus subnucleus dissipatus - rs rubrospinal tract - RPo pontinereticular nucleus, oral portion - RR retrorubral nucleus - RRF re-trorubral field - scp superior cerebellar peduncle - SNr substantianigra, pars reticulata - SPTg subpeduncular tegmental nucleus - 3n oculomotor nerve     

Substance P immunoreactivity in the rat interpeduncular nucleus: synaptic interactions between substance P-positive profiles and choline acetyltransferase- or glutamate decarboxylase-immunoreactive structures.

The subnuclear and synaptic distribution of substance P immunoreactivity was examined in the rat interpeduncular nucleus at the light and electron microscope level. The nucleus possessed a prominent substance P-immunoreactive axonal plexus in the lateral and dorsomedial subnuclei, and in the dorsal cap of the rostral subnucleus. The density of substance P-immunoreactive axons in the remaining subnuclear divisions was sparse to moderate. Terminals of immunoreactive axons contained spherical vesicles and formed asymmetric contacts on dendritic processes exclusively. Immunoreactive neurons, restricted to the rostral subnucleus, possessed long, sparsely branched dendrites. Unlabelled terminals containing either spherical or pleomorphic vesicles contacted substance P-immunoreactive dendritic profiles. Axodendritic and axosomatic synapses containing substance P immunoreactivity pre- and postsynaptically were not observed. Ultrastructural evidence for synaptic relationships between substance P-containing profiles and those containing either choline acetyltransferase or glutamate decarboxylase was obtained by means of double antigen immunohistochemistry. Terminals of fasciculus retroflexus axons stained for choline acetyltransferase immunoreactivity formed asymmetric synaptic contacts with substance P-immunoreactive dendritic profiles. Few substance P-positive dendrites in the rostral subnucleus received terminals possessing glutamate decarboxylase activity. Unlabelled terminals containing either spherical or pleomorphic vesicles contacted substance P- and glutamate decarboxylase-immunoreactive dendritic profiles simultaneously. Terminals possessing either substance P or glutamate decarboxylase immunoreactivity formed synaptic contacts with dendritic processes of neurons in the lateral subnucleus. Many of the neurons within this subnuclear division contained glutamate decarboxylase. This study provides direct evidence of synaptic relationships between choline acetyltransferase-immunoreactive axons and substance P-immunoreactive dendritic profiles, and between substance P-positive axons and glutamate decarboxylase-immunoreactive dendrites. These findings reveal that two types of transmitter-specific axons of the fasciculus retroflexus innervate neuronal populations of the interpeduncular nucleus stained immunohistochemically for either substance P or glutamate decarboxylase.     

Ultrastructure of the gracile nucleus projection to the dorsal accessory subdivision of the cat inferior olive

Summary This study examined the termination pattern within the dorsal accessory subdivision of the cat inferior olive of axons arising from the gracile nucleus. The gracile terminals were labeled by anterograde transport of wheat germ agglutinin complexed to horseradish peroxidase and visualized with tetramethyl benzidine. Gracile terminals were found to contain round synaptic vesicles and form asymmetric synaptic contacts. Of particular interest was the finding that gracile axons, like axons from the spinal cord, terminate primarily outside of synaptic glomeruli. Yet most of the gracile terminals did not synapse on isolated dendritic elements. Rather, the majority contacted distal dendrites which directly contacted other dendritic elements, forming simple complexes termed dendritic thickets. Typically the dendritic thickets were composed of two or three dendrites that received input from more than one round vesicle-containing synaptic terminal. Only one terminal per thicket was labeled by injections in the gracile nucleus. This clustering of pre-and postsynaptic elements within the thickets provides opportunities for many of the same interactions allowed by synaptic glomeruli, in particular divergence and convergence of information.     

GABAergic innervation of rat abducens motoneurons retrogradely labelled with HRP: quantitative ultrastructural analysis of cell bodies and proximal dendrites

Summary In this quantitative electron microscopic study we investigated the distribution of GABA axon terminals on rat abducens motoneurons by combining retrograde labelling of motoneurons with post-embedding immunodetection of GABA. We analysed the synapses on 13 cell bodies and 60 proximal dendritic profiles distributed along the entire rostro-caudal extent of the nucleus. For each of these two compartments, we analysed 1754 and 1176 axon terminals in contact with 6042 and 3299 m of postsynaptic membrane. The axon terminals were classified as Sv-type (containing spherical vesicles) or Pv-type (containing pleomorphic vesicles). The GABAergic terminals contained pleomorphic vesicles and established mainly symmetrical synaptic contacts. Their apposition lengths were greater than those of unlabelled terminals. On cell bodies, the percentage of GABAergic synaptic covering varied from 2.5% to 14.1% and the synaptic frequency of GABAergic axon terminals varied from 0.6% to 8.9%. These two parameters were significantly correlated with the diameter of the motoneurons. The percentage of synaptic covering and synaptic frequency were smaller on dendrites of small motoneurons than on those of large ones. The proximal dendrites of small motoneurons had a lesser GABAergic innervation than large ones. The total synaptic covering and frequency were smaller on somata than on dendrites. However, the percentage of synaptic covering by GABA terminals was higher on cell bodies than on proximal dendrites.     

The adrenergic innervation of the rat central amygdaloid nucleus: a light and electron microscopic immunocytochemical study using phenylethanolamine N-methyltransferase as a marker

Using immunocytochemistry of phenylethanolamine N-methyltransferase for light and electron microscopy, investigations were carried out to document the morphology of adrenergic afferents innervating the rat central amygdaloid nucleus and to analyse the manner in which contacts with neurons of the nucleus are formed. With the light microscope, dense terminal plexus of phenylethanolamine N-methyltransferase-immunoreactive axons with typical large boutons (diameter>1 m) were found in the medial central nucleus, extending into its ventral subdivision and the adjacent intra-amygdaloid portion of the bed nucleus of the stria terminalis. Electron microscopy of the medial central nucleus showed phenylethanolamine N-methyltransferase-immunoreaction product in the cytoplasm of intervaricose axons and boutons. Large adrenergic boutons contained numerous small clear vesicles and, occasionally, large dense-cored vesicles. In serial sections, most boutons formed synaptic contacts. Synapses of immunoreactive terminals were mainly of the asymmetric type and localized preferentially on medium sized to small dendrites and dendritic spines. Structures postsynaptic to adrenergic boutons were often additionally contacted by non-labelled terminals. The study gives evidence that adrenergic afferents exert a direct synaptic influence on medial central nucleus neurons. The peripheral localization of the majority of adrenergic synapses, their asymmetric configuration, and the presence of non-adrenergic synapsing terminals in their immediate vicinity indicate that the major component of the adrenergic input is of an excitatory nature, and is integrated with innervation from other sources.Abbreviations BNST _i Intra-amygdaloid portion of the bed nucleus of the stria terminalis - CL lateral central amygdaloid nucleus - CLc lateral capsular central amygdaloid nucleus - CM medial central amygdaloid nucleus - CN central amygdaloid nucleus - CV ventral central amygdaloid nucleus - DAB diaminobenzidine - EM electron microscopy - ir immunoreactive - LM light microscopy - NPY neuropeptide tyrosine - PBS phosphate buffered saline - PFA paraformaldehyde - PNMT phenylethanolamine N-methyltransferase     

The synaptic organization of terminals traced from individual labeled retino-geniculate axons in the cat

Individual retino-geniculate axons in the dorsal lateral geniculate nucleus of the cat were filled with horseradish peroxidase and studied with both the light and electron microscope. A procedure was followed which allowed us to identify the size, shape and arrangement of particular terminal swellings by light microscopy and then to study their patterns of synaptic contacts with the electron microscope. Many of the labeled terminals in laminae A and Al have the same fine structural features as retino-geniculate terminals that have been described previously. They are large, contain round synaptic vesicles and pale mitochondria, and are the central processes in glomeruli where they form asymmetric contacts with dendrites and terminals containing pleomorphic synaptic vesicles. Other terminals have the same cytological features but are quite small and are not the central processes in glomeruli. Some of these small terminals form simple axo-dendritec contacts while others participate in very large glomeruli containing several terminals from a single retino-geniculate axon. These different patterns of synaptic contacts made by different terminals can be found on branches of a single axon and correspond to the variations in terminal arbors described in the preceding paper (MASON & ROBSON, 1978).