Degenerated boutons in the fundus striati (nucleus accumbens septi) after lesion of the parafascicular nucleus in the cat

Summary An attempt has been made to reveal which of the nine different types of synapses in the fundus striati, discriminated in a previous study, degenerate following experimental lesions in the parafasciculo-center median complex of the cat. Two types of synaptic contacts were found to be degenerated two days after the lesion was performed: (1) the axo-spinous type IV, characterized by densely-packed, small, round vesicles and a strong asymmetric thickening, and, (2) the axo-dendritic or axo-somatic type VII, again characterized by small, round vesicles in a dense accumulation and an asymmetric thickening. After two days of survival the original characteristics of the boutons could still be recognized in both types of synapses.A positive correlation exists between the location and extent of the coagulation foci in the parafascicular nucleus and the appearance of degenerated boutons in the fundus striati. Therefore, the conclusion that the parafasciculofundus neurons terminate as type IV or type VII boutons is entirely justified. Additionally, the role of the special types of boutons in the synaptic organization of the fundus striati has beeen discussed.Dr. J. W. Chung on leave of absence from the Department of Anatomy, Catholic Medical College, Seoul, KoreaHerrn Professor Dr. Drs. h. c. Wolfgang Bargmann zum 70. Geburtstag gewidmet     

Synapsoarchitechtonics of the parietal and acoustic regions of the cerebral cortex of cats]

The synapse architecture of the simcipital and auditory cortex of the cat (fields 7 and 22 after M. O. Gurevich and oth., 1929) was studied electron microscopically. In the both areas of the cortex there are much more axo-dendritic synapses that axo-somatic ones. In the upper layers the synapses are more often formed on small dendrites and thorns, while in layers IV-VI they often occur on the main trunks of large dendrites. The synapses on small branches and thorns of dendrites contain spherical vesicles, and the synapses on on large dendrites are formed by the terminals of two kinds-with flattened and spherical vesicles. The amount of axo-somatic synapses increases towards the lower layers of the cerebral cortes. The synapses on the soma and apical dendrites of the pyramid neurons always contain flattened vesicles; on the stellate neurons there occur perisynaptic terminals with sperical vesicles as well.     

Some observations on the fine structure of the corpus striatum of the rat brain

Summary The rat corpus striatum was perfused vitally with glutaraldehyde, immersed in OsO₄ and then observed under an electron microscope.Numerous small cells in the neostriatum show a simple cytoplasmic structure, while the large cells possess a complicated fine structure. These are differentiated under the elctron microscope into two kinds, which seem to have functional differences. The large pallidal cells containing much pale cytoplasm are covered with many varied axonal boutons from the cell body to the dendritic terminal making numerous axo-somatic or axo-dendritic trunk synapses. Numerous axo-dendritic, or spine synapses are recognized in the neostriatal neuropil.These numerous axon terminals, which belong to striatal nerve cells or other nuclei of the brain, are classified morphologically into several types. At least five types of synaptic vesicles are distinguished by their size or by the presence of fine dense granules on their membranes, and seem to be specific to the neostriatum.Many myelin interruptions and several kinds of glial cells in the corpus striatum are observed. Moreover, the ventricular wall of the caudate nucleus, namely, the ependyma, and two kinds of subependymal cells are described and discussed with reference to the subependymal layer.     

Electron microscopy of the arcuate nucleus of normal and 5-hydroxydopamine treated cats

The arcuate nucleus of normal cats and of cats treated with 5-hydroxydopamine (5-OHDA) was investigated by electron microscopy. The neurons of the arcuate nucleus were classified into three types, clear, intermediate and dark, according to their fine structure. The clear type contained numerous dense-cored vesicles and well developed cell organelles. All three types were frequently seen to be partially surrounded by glial processes. Many axo-somatic and axo-dendritic synapses mostly small in diameter were also observed around the neurons. Synaptic contacts were demonstrated between axon endings and axonal processes which contained elementary granules. After administration of 5-OHDA small and large dense-cored vesicles appeared in the nerve endings surrounding the neurons. The relationship between the dense-cored vesicles in the perikarya and dopamine was briefly discussed.     

Electron microscopic investigation of synaptic organization of the trochlear nucleus in cat

Summary Two distinct types of neuron in the cat trochlear nucleus (one large, one small) are described, the - and -motoneurons, respectively. Four types of terminals are observed which establish axo-dendritic synapses. Two of them (Types I and II) perform axo-somatic synapses as well. Terminals en passant (Types I and II) are predominant. The Type I terminal is long and slender with a characteristic distribution of the axoplasmic organelles and the unique feature of a relative narrowing of the synaptic cleft as compared to the width of the neighboring extracellular space. Its vesicle population is pleomorphic and a conspicuous glial barrier surrounds the synaptic zones. The Type II terminal differs slightly from Type I, revealing a wider synaptic cleft and lacking a characteristic distribution of the axoplasmic organelles. The type III terminal is rarely observed performing axo-somatic synapses, but is a common finding in the neuropil. Post-junctional dense bodies are often present in its axodendritic synapses. The Type IV nerve terminal performs axo-dendritic synapses and is characterized by a rich content of large granulated vesicles. Axo-axonal synapses are observed only very rarely.The synaptic organization of the feline trochlear nucleus is compared with the synaptic morphology of the oculomotor nuclei of inframammalian species (Waxman and Pappas, 1971). In addition to certain similarities (e.g., richness of synapses en passant), significant differences are encountered: the present study provides no morphological evidence for electrotonic transmission in the trochlear nucleus of cat.Preliminary report made at the Annual German Jahresversammlung der Anatomischen Gesellschaft, Lausanne, Switzerland, 1973.The authors wish to thank Professor R. Hassler for his valuable discussion. — Dr. W. B. Choi is on leave from the Department of Anatomy, Catholic Medical School, Seoul, Korea.     

Ontogeny of the mouse motor cortex. The polymorph layer or layer VI. A Golgi and electronmicroscopical study

Summary The development of neurons and their synapses of the mouse motor cortex has been studied from the first postnatal day up to an age of three weeks both electronmicroscopically and with the Golgi method. Special attention has been paid to the maturation of the different cell types in the sixth cortical layer and their dendritic organization within this layer.The polymorph layer is subdivided into two zones: an internal (VIb) and an external one (VIa). In these zones six different cell types can be identified both electronmicroscopically and with the Golgi method: large, small and inverted pyramidal cells in VIa; horizontal cells, star cells and small pyramidal cells in VIb.Spines of apical dendrites of large pyramidal cells in sublayer VIa can be detected as early as the 6th postnatal day. About the ninth day the basal dendrites as well show emerging spines. Somatic spines are found only on the large pyramidal cells and disappear slowly towards the end of the 3rd postnatal week.The small pyramidal cells show developing spines on their apical dendrite in the first half of the second postnatal week. The final density and distribution of spines is reached by the stem dendrites towards the end of the second week, by the basal dendrites during the third week. The maturation process of the improperly orientated neurons occurs in time in between the large and the small pyramidal cells.The axo-somatic synapses appear in general at a later date than the axo-dendritic ones. In the horizontal cells axo-somatic synapses are visible already at the seventh postnatal day.At the end of the first week especially in layer VIb many immature neurons with an ovoid or round nucleus are present having little if any endoplasmic reticulum organised as ergastoplasm.Towards the end of the second week however most neurons in the polymorph layer have a well developed endoplasmic reticulum.Electronmicroscopical pictures reveal in outgrowing dendrites many enlargements filled with vesicles, these correspond to the varicosities seen in Golgi pictures. At nine days postnatally the first myelinated fibres appear.Aided by grant (R-209-67) from the United Cerebral Palsy Research and Educational Foundation, New York.     

Ultrastructural organization of the neuropil in layer I of the cat cerebral cortex

The ultrastructure of layer I in the middle ectosylvian gyrus (area 22) of the cat's cerebral cortex was investigated. Beneath the subpial astrocytic layer most of the neuropil in layer I was shown to be occupied by nerve fibers and their terminals, terminal branches, dendritic spines, and astrocytic processes surrounding them. More than 90% of the presynaptic terminals contained spherical synaptic vesicles. The predominant types of interneuronal junctions are axo-spinous and axo-dendritic synapses of asymmetrical type. Presynaptic terminals, which contain flattened and pleomorphic synaptic vesicles, take part in the formation of all symmetrical junctions, accounting for 6% of the total number of synapses. Large polymorphic outgrowths filled with vacuoles — so-called multivacuolar sacs — are described. These structures were invaginated into varicose expansion of the terminal branches of apical dendrites of pyramidal neurons. They are shown to be outgrowths of presynaptic terminals. Dependence of synaptic function on the shape of the synaptic vesicles is examined.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 15, No. 1, pp. 50–55, January–February, 1983.     

Synaptic interactions of luteinizing hormone-releasing hormone (LHRH) neurons in the guinea pig preoptic area

Previous studies from many laboratories have failed to demonstrate a significant synaptic input to luteinizing hormone-releasing hormone (LHRH) neurons in the rodent or primate hypothalamus/preoptic area. Having now developed immunocytochemical procedures that result in excellent ultrastructural preservation as well as in retention of antigenicity (Silverman AJ: J Comp Neurol 227:452, 1984), we have reinvestigated the question of the organization of the synaptic arrangements of LHRH neurons in the medial preoptic area of the guinea pig. Afferent inputs to these LHRH neurons include several varieties of axo-somatic and axo-dendritic synapses. Presynaptic terminals contain either round clear vesicles or a mixture of round and flattened vesicles. Most of these terminals, especially when serial sections are examined, contain dense-core granules. Well-defined synaptic clefts are evident and postsynaptic densities can be identified for asymmetrical connections. However, the presence of reaction product in the postsynaptic structure makes it difficult to categorize symmetrical terminals. In addition to these classical inputs, LHRH neurons also enter into complex heterodox synaptic relationships with their neighbors, including somato-dendritic and dendro-dendritic synapses in which the LHRH neuron can be either the pre- or postsynaptic element. These results suggest that complex synaptic relationships might account for the multiple levels of regulation of neurohormone release.     

The fine structure of the dorsal column nucleus and the nucleus of bischoff of the python (Python reticulatus)

Three types of neuronal perikaryal profiles were identified in the dorsal column nucleus and the nucleus of Bischoff of the python (Python reticulatus). Type I neuronal profiles are large (diameters 12–20 μm) with a deeply indented uncleus. The cisterns of rough endoplasmic reticulum (rER) are mostly randomly dispersed. Axosomatic synapses are few. Type II neuronal profiles (9–11 μm) have a smooth, round, or slightly oval nucleus. Several small stacks of rER are present. Type III neuronal profiles (8–10 μm) have little cytoplasm. The nuclear margin is irregular but not deeply infolded. The rER usually consists of a single long perinuclear ribosome-studded cistern. Two types of astrocytic profiles have been identified. Both types contain abundant filaments. Type I astrocytes are large cells, and the nucleus is very irregular in shape. Type II astrocytes are smaller and are found among the myelinated axons in the dorsal funiculus. Two classes of axon terminals have been identified. One class contains round synaptic vesicles (R profiles) and the other flattened vesicles (F profiles). Some R profiles are small (SR profiles), others are large (LR profiles). Some R profiles also contain a few large, dense-cored vesicles. The R and F profiles establish axodendritic and axoaxonal synapses, some of which are located in the synaptic glomeruli and others in the extraglomerular neuropil. In most of the axoaxonal synapses, the presynaptic element is an F profile and the post synaptic element an LR profile. Occasionally, LR profiles are presynaptic to F profiles. The findings in the python are compared with those of the dorsal column nuclei of the rat, cat, and monkey.     

Electron microscopic examination of the orexin immunoreactivity in the dorsal raphe nucleus

The ultrastructure and the synaptic relationships of the orexin-A-like immunoreactive fibers in the dorsal raphe nucleus were examined with an immunoelectron microscopic method. At the electron microscopic level, most of the immunoreactive fibers, a varicosity appearance at the light microscopic level, were found as axon terminals. The large dense-cored vesicles contained in the immunoreactive axon terminals were the most intensely immunostained organellae. These axon terminals were often found to make synapses. While the axo-dendritic synapses were usually asymmetric in appearance, the axo-somatic synapses were symmetric. Orexin-A-like immunoreactive processes with no synaptic vesicles were also found. These processes often received asymmetric synapses. With less frequency, the synapses were found between the orexin-like immunoreactive processes. The results suggest that the orexin peptides are stored in the large dense-cored vesicles; the orexin-containing fibers may have influences on the physiological activities of the dorsal raphe nucleus through direct synaptic relationships.     

Electron-microscopic studies on developing intramural ganglia of the small intestine in human and rabbit fetuses.

Electron-microscopic studies were made on the appearance of synapses in the intramural ganglion (Auerbach) and findings were correlated with the onset and development of intestinal peristalsis in 6- to 30-week-old human and rabbit fetuses from the 12th day after conception until birth. At stage I, in which the small intestine shows no indication of a muscle layer or spontaneous peristalsis, primitive synapses containing several clear vesicles and a few cored vesicles are seen on neuroblasts and their processes (dendrites). At stage II, in which the circular muscle is developed and bidirectional peristalsis occurs, synaptic profiles can be classified into 3 types. Type 1 is the most numerous but seldom shows membrane specificity on the synaptic portion. Types 2 and 3 have small flattened vesicles and small round vesicles, respectively. They are further characterized by thickening of snyaptic membranes and aggregation of small clear vesicles associated with the presynaptic membrane. At stage III, the longitudinal muscle layer develops in the small intestine. At this stage, nerve terminals containing mainly cored vesicles have been observed and classified into types 4 and 5, according to their morphology. At stage IV, antiperistalsis no longer occurs and type 6 nerve terminals in the intramural ganglia can be recognized by their densely packed, large-cored vesicles. The possible physiological significance of the nerve terminals has been discussed.     

The nucleus of the basal optic root in the pigeon: an electron microscope study

The ultrastructure of the nucleus of the basal optic root in an avian species (Columba livia) was investigated. The ectomamillary nucleus (EMN) in which terminates the basal optic tract reveals three types of neurons: 1) small round neurons bearing a scanty cytoplasm in organelles, 2) medium-sized neurons, spindle-shaped with a dense population of organelles and 3) large multipolar neurons with well developed perikaryal elements. Some of these neurons have their inner plasma-membrane which fuse to make junctional zones alternating between attachment plates and gap junctions. The analysis of the neuropil displays four types of vesicle-containing profiles (VCP), Type I VCP, identified as optic terminals, are numerous (49%), contain round vesicles (500-550 A) and establish Gray type I contacts principally with dendrites. They also participate in serial and triadic arrangements. Type II VCP have lighter hyaloplasm and are less numerous (6,7%). Rounded vesicles (450-500 A) with a clear content synapse also with Gray type I active zones on dendrites. Some of these profiles have the peculiarity of both a chemical and electrical transmission known as mixed synapses. Type III VCP are larger and contain a mixed population of rounded and flattened vesicles which synapse according to Gray type II. Type IV VCP are characterized by a light hyaloplasm where the microtubules are a predominant organelle. Their active zones are also of Gray type II.     

Ciliated neurons and different types of synapses in anterior hypothalamic nuclei of reptiles

Summary The magnocellular paraventricular and supraoptic nuclei and the parvocellular preoptic and periventricular nuclei have been studied by light and electron microscopy in Emys orbicularis, Lacerta agilis and Elaphe longissima. The ultrastructure of cerebrospinal fluid (CSF)-contacting neurons was described in the preoptic and periventricular nuclei of Emys and Lacerta species. Single 9×2+0 cilia similar to those of the CSF-contacting dendritic terminals were found on perikarya of non CSF-contacting nerve cells, in all four investigated nuclei. The cilia project from funnel-like invaginations of the perikarya into the intercellular space. In the neurons of the nuclei studied, granular vesicles were found, their size being mainly 1,600 Å in the paraventricular nucleus, about 1,800 Å in the supraoptic nucleus, 1,100 Å in the periventricular nucleus and 800 Å, or up to 1,250 Å in the preoptic nucleus. In general, the neurons possess synapses of the axo-somatic, axo-somatic spine, axo-dendritic and axo-dendritic spine types. In the supraoptic nucleus, multiple interdigitated synapses were observed. Presynaptically, either synaptic vesicles only, or synaptic vesicles and dense core vesicles of different sizes (600 to 800 Å, about 1,100 Å, 1250 Å, and up to 2,000 Å) were found. It is discussed whether the above described 9×2+0 cilia may represent some kind of hypothalamic sensory structure that earlier physiological studies postulated to exist. The ciliated hypothalamic perikarya are considered by the authors to be a more differentiated form of the CSF-contacting neurons. The different types of synapses indicate multilateral connections of the nerve cells of the nuclei studied.Dedicated to Prof. Dr. Berta Scharrer on the occasion of her 70th birthday     

Immunolocalization of choline acetyltransferase in 2 types of efferent synapses of the organ of Corti

The efferent (olivo-cochlear) innervation of the organ of Corti was studied using a monoclonal antibody against choline acetyltransferase (ChAT). In the inner spiral bundle (ISB), below the inner hair cells (IHCs), the anti-ChAT immunoreactivity was observed within unvesiculated fibers and vesiculated varicosities. Unreactive varicosities, at least as numerous as the immunoreactive ones, were also detected. Both types of vesiculated varicosities synapsed with the dendrites of the primary auditory neurons (afferent fibers) connected to the IHCs. At the outer hair cell (OHC) level, nearly all the vesiculated terminals making axo-somatic synapses with the OHCs were anti-ChAT immunoreactive. Only few terminals synapsing with the OHCs were unreactive. These findings allowed the differentiation of at least three types of efferent synapses in the organ of Corti. In the ISB, a first population of axo-dendritic synapses seems to be cholinergic whereas a second population might use another neurotransmitter. At the OHC level, our results support the hypothesis that acetylcholine is the neurotransmitter of nearly all the large axo-somatic synapses. The rare unreactive axo-somatic synapses could constitute a fourth and minor type of efferent synapse. Thus, it would be helpful to subclassify the efferent innervations of the organ of Corti according to their neurochemical nature. A re-evaluation of the whole body of available electrophysiological data would be also necessary, as until now, acetylcholine was considered as being the only efferent cochlear neurotransmitter.     

Light and electron microscopic studies of slowly adapting abdominal stretch receptors of the American river crayfish Orconectes limosus (RAF)]

The slowly adapting abdominal stretch receptors of Orconectes limosus (RAF) have been investigated morphologically; 1. Despite their variety of size and shape all slowly adapting receptor neurons show common characteristic features which in addition distinguish them clearly from the fast adapting receptor neuron type SN2. The slightly globular cells have always several dendrites (often 4-6). They originate apical or lateral to the neuron, are oriented mainly longitudinal to the muscle fibres and are brodly ramified. The fine dendrites form a 3-dimensional fibrilar network. 2. The structure and distribution of the connective tissue in the "intertendon" of the muscle receptor organ correspond to the dendrite ramification; In this area, some muscle fibres end direktly at tendon-like connective tissue structures, but a number of different fibres run uninerruptedly through the whole muscular fascicle. 3. The perikaryon of every sensory neuron shows 2 "cytoplasm types" which are clearly distinguishable one against the other. A characteristic feature of the granular-lamellar neuroplasm that closely surrounds the nucleus are many flat vesicles of the granular endoplasmatic reticulum, accumulations of free ribosomes, numerous mitochondria and Golgi fields. The fibril-rich neuroplasm on the contrary contains only few mitochondria, but very many neurofilaments, here and there also neurotubuli. It projects directly into the dendrites and neuritek. Cell bodies, axon and dendrites are surrounded alternatingly by sheath cells and connective tissue of collagenous nature. The innermost layer of the coat cells borders directly on the neuron membrane. Finer dendrites are enclosed by nothing more but a thin layer of sheath cell plasm and intercellular substance. The dendrite terminals are either stored directly in connective tissue ground substance or border immediately on the sarcoplasm. 5. The axo-dendritic or axo-somatic synapses, respectively, contain numerous ellipsoidal (250-350 X 400-500 A), but also many spherical, vesicles. Some vesicles have a slightly larger diameter (700-900 A) and contain an electron-dense core. The synaptic gap measures 150 to 200 A. The neuromuscular (supposedly excitatory) synapses are filled much lighter with vesicles as compared with those just mentioned, which show a relatively unique form and size (nearly all spherical, phi 400-500 A). There are less vesicles with an electron-dense centre. On the average, the synaptic gap is broader (200-250 A) and the contact zone is larger. Apart from these, terminals could be observed in the dendritic ramification area, too, resembling the axo-dendritic and axo-somatic ones, respectively. 6. Finer dendrite branches contain vesicles differing slightly from those mentioned above as far as shape and size are concerned. Their diameters vary between 500 and 1 000 A. "Dense bodies" could be observed sporadically in these vesicles.     

Effect of visual deafferentiation on the ultrastructure of synapses of the rat visual cortex.]

Electron microscopic study and quantitative analysis of the visual cortex synapses in 14, 30 and 60-day-old rats were performed after bilateral enucleation of newly-forn rats. A great amount of synapses of other functional systems was shown to be functioning in the area striata in addition to the synapses formed by specific visual afferents. Alterations in the synapses of the area striata of blind rats are developing gradually, achieving the greatest pronouncement in 60-day-old rats. These changes develop according to the type of atrophic process in connection with dysfunction. The atrophic alterations of the synapses were found both in axo-somatic and axo-dendritic synapses on the dendrite trunks and on the thorns. The alterations of synapses being concentrated in layer IV. The quantitative ratio of different kinds of atrophied synapses in the cross-section of the visual cortex was different suggesting the following conclusion about the distribution of the visual afferents. In layers I and III the visual afferents formed mostly axon-thorn contacts and less amount of axo-somatic and axo-dendritic synapses on the dendrite trunks. In layer IV they mainly formed axo-somatic and axo-thorn synapses and less amount of axo-dendritic ones on the dendrite trunks. In layers V and VI they mainly contact with the dendrite trunks and with the nervous cell bodies and more rarely with thorns.     

Cerebrospinal fluid-contacting neurons,ciliated perikarya and “peptidergic” synapses in the magnocellular preoptic Nucleus of teleostean fishes

Summary The magnocellular preoptic nucleus of fishes (Anguilla anguilla, Amiurus nebulosus, Cyprinus carpio, Carassius auratus, Ctenopharyngodon idella, Cichlasoma nigrofasciatum) has been studied by light and electron microscopy.Two kinds of neurons were found: a) large, electron-dense, Gomori-positive cells with moderate acetylcholinesterase (AChE) positivity which contain granulated vesicles of 1400 to 2200 Å (in average 1600 to 1800 Å), and b) small, strongly AChE-positive, electron-lucent neurons containing granulated vesicles of 900 to 1200 Å. The nerve cells are supplied with axo-somatic and axo-dendritic synapses. These are formed by axon terminals containing either 1. synaptic vesicles of 500 Å, or 2. synaptic vesicles of 500 Å and dense-core vesicles of 600 to 800 Å, or 3. synaptic vesicles of 600 Å and granulated vesicles of up to 1100 Å, or 4. synaptic vesicles of about 400 Å and granulated vesicles of up to 1800 Å. The presence of peptidergic and numerous other synapses shows the complexity of the organization and afferentation of the magnocellular preoptic nucleus.In the eel, both types of nerve cells form dendritic terminals within the cerebrospinal fluid (CSF). These CSF contacting dendrites are supplied with 9×2+0 cilia. In the other species investigated, only some large neurons build up intraventricular endings. The ependymofugal process of the CSF contacting neurons enters the preoptic-neurohypophysial tract.Perikarya of both the large and the small cells may give rise to single, paired or multiple 9×2+0 cilia extending into the intercellular space. The number of CSF contacting neurons is reciprocal to the number of perikarya with intercellular cilium. These latter cells may represent modified, more differentiated forms of the CSF contacting neurons. We think that atypical cilia protruding into the intercellular space may have the same significance for the intercellular fluid as the cilia of the intraventricular dendrites of the CSF contacting neurons for the CSF.Dedicated to Prof. Dr. W. Bargmann on the occasion of his 70th birthday.     

Cytology of large neurons in the guinea pig dorsal cochlear nucleus contacting the inferior colliculus

Large neurons in the dorsal cochlear nucleus of the guinea pig which project to the inferior colliculus were identified after injections of the neural tracer WGA-HRP. Retrograde labelled cells (pyramidal and giant neurons) in the dorsal cochlear nucleus were glycine and GABA immunonegative and showed a similar ultrastructure. Between 30 and 60% of their perimeter was covered by axo-somatic boutons, most of which (>50%) contained pleomorphic synaptic vesicles. Other boutons (about 40% of total) contained flat vesicles and few (5-6%) contained round vesicles, a characteristic of the excitatory cells innervating the inferior colliculus. Immunogold-cytochemistry, coupled to silver intensification, showed that more than 50% of axo-somatic pleomorphic boutons and over 90% of boutons containing flat and pleomorphic vesicles store glycine. Rare WGA-HRP labelled axo-somatic boutons containing flat-pleomorphic vesicles were seen on pyramidal and giant neurons. This suggests that a few inhibitory collicular terminals contact the excitatory large neurons in the dorsal cochlear nucleus.     

Synaptic morphology of the carotid body of the domestic fowl

Efferent and reciprocal synapses have been demonstrated in the carotid body of the domestic fowl (Gallus gallus domesticus). Synapses were also found with purely afferent morphology, but were probably components of reciprocal synapses. The general morphology of the endings suggested the presence of two types of axon, afferent axons making reciprocal and perhaps afferent synapses with Type I cells, and efferent axons making efferent synapses with Type I cells. A few axo-dendritic synapses were also found. The dense-cored vesicles associated with the afferent components of reciprocal synapses and with the possible true afferent synapses varied in diameter and core but could belong to one population of pre-synaptic vesicles. These observations are consistent wtih a new theory for the carotid body receptor mechanism. This proposes a spontaneously discharging afferent axon inhibited by an inhibitory transmitter substance released by the Type I cell via the "afferent" component of its reciprocal synapse, the "efferent" component inhibiting this release. Besides this chemoreceptor modulation of its afferent axon, the Type I cell may also have a general secretory function.     

Synaptic organisation of the pelvic ganglion in the guinea-pig

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