Some observations on the fine structure of the giant synapse in the stellate ganglk of the squid,Doryteuphis bleekeri

Summary The fine structure of the synapse between the second-order giant fibre and the third order-giant fibre of the squid Doryteuphis bleekeri was studied by means of electron microscope. In the synaptic region, the two giant fibres are arranged side by side. Many small processes from the third-order giant fibre penetrate the common sheath which separats the adjacent giant axons making synaptic contact with the second order giant axon.The contact surface consists of opposing two plasma membranes of adjacent axons separated by a narrow space of 20–30 m in width. The synaptic membranes are more electron dense and thicker than the other part of the axon membrane. The synaptic vesicles are concentrated exclusively in the presynaptic axon.The fine structural differences between giant synapse in the stellate ganglion of the squid and the giant-to-motor giant synapse of the crayfish were discussed.This work was supported by Grant Number B-3348 from the National Institutes of Health, United States Public Health Service, Department of Health, Education and Welfare.     

Ultrastructural study on the morphogenesis of the neuromuscular junction in the skeletal muscle of the chick

Summary The morphogenesis of the neuromuscular junction was examined at the ultrastructural level in the skeletal muscle of the lower limb of the chick. The fine structure of the neuromuscular junction of the adult fowl was essentially the same as that in other vertebrates; the junction consists of the axon terminal, the Schwann cell, and the muscle fiber. The first visible sign of neuromuscular junction formation, in embryos of 13 days in ovo, was the membrane thickening of the sarcolemma which develops into the postsynaptic membrane. The axons approaching the muscle fibers were incompletely ensheathed by a Schwann cell and contained vesicles. The subsequent differentiation of the junctional sarcoplasm, the axoplasm, and the Schwann cell cytoplasm takes place from 13 to 18 days in ovo and the junction nearly reaches maturity at around 20 days in ovo. The formation of complicated anastomoses and branching of the junctional infoldings seems to occur after hatching. These ultrastructural observations are in good agreement with histochemical findings (cholinesterase method) in terms of the chronology of the morphogenesis of the junction.This investigation was supported in part by U. S. Public Health Service Grant MH 12269-01, administered by Dr. Kazuo Ogawa. It was initiated on the suggestion of Prof. J. Nakai, Department of Anatomy, Faculty of Medicine, Tokyo University, and a part of it was performed in his laboratory. The author is greatly indebted to Prof. K. Ogawa, Department of Anatomy, Kansai Medical School, for his guidance and encouragement, and to Dr. S. Igarashi, Department of Anatomy, Tokyo University, for some technical advice.     

Synaptic relationships in the plexiform layers of carp retina

Summary The synaptic contacts made by carp retinal neurons were studied with electron microscopic techniques. Three kinds of contacts are described: (1) a conventional synapse in which an accumulation of agranular vesicles is found on the presynaptic side along with membrane densification of both pre- and postsynaptic elements; (2) a ribbon synapse in which a presynaptic ribbon surrounded by a halo of agranular vesicles faces two postsynaptic elements; and (3) close apposition of plasma membranes without any vesicle accumulation or membrane densification.In the external plexiform layer, conventional synapses between horizontal cells are described. Horizontal cells possess dense-core vesicles about 1,000 Å in diameter. Membranes of adjacent horizontal cells of the same type (external, intermediate or internal) are found closely apposed over broad regions.In the inner plexiform layer ribbon synapses occur only in bipolar cell terminals. The postsynaptic elements opposite the ribbon may be two amacrine processes or one amacrine process and one ganglion cell dendrite. Amacrine processes make conventional synaptic contacts onto bipolar terminals, other amacrine processes, amacrine cell bodies, ganglion cell dendrites and bodies. Amacrine cells possess dense-core vesicles. Ganglion cells are never presynaptic elements. Serial synapses between amacrine processes and reciprocal synapses between amacrine processes and bipolar terminals are described. The inner plexiform layer contains a large number of myelinated fibers which terminate near the layer of amacrine cells.This work was supported by an N.I.H. grant NB 05404-05 and a Fight for Sight grant G-396 to P.W. and N.I.H. grant NB 05336 to J.E.D. The authors wish to thank Mrs. P. Sheppard and Miss B. Hecker for able technical assistance. P.W. is grateful to Dr. G. K. Smelser, Department of Ophthalmology, Columbia University, for the use of his electron microscope facilities.     

Electron microscopy of degeneration in the lateral olfactory tract and plexiform layer of the prepyriform cortex of the rat

Summary The synaptic organization of the plexiform layer of the prepyriform cortex in the rat has been studied with the electron microscope both in the normal and after ipsilateral olfactory bulb removal. Survival times ranged from six hours to three months.In normal preparations synaptic contacts occur mainly on dendritic branches, spines or lateral projections. Gray's Type I contacts are most frequent and Type II contacts usually contain flattened vesicles after formalin fixation.Degeneration of the presynaptic bags begins within 24 hours after the lesion and some degenerated bags are still seen after three months survival. During this time degenerated bags are apparently removed by astroglia but the spine tips appear to be unaffected by the phagocytosis. Glia or other processes may come to occupy the denervated sites. The evidence for possible reestablishment of new contacts is considered.The severed axons show a characteristic mode of degeneration and at three months some appear to be phagocytosed by oligodendroglia which also contain lamellated inclusion bodies.This study represents a part of a thesis accepted in fulfillment of requirements for the degree of Doctor of Philosophy at the University of London (England), June 1966.This investigation was supported in part by a U.S. Public Health Service Fellowship NB 20-844 from the N.I.N.D.S. while the author was a postdoctoral fellow at the Anatomy Department, University College, London, England, and by grants NB 02896 and NB 04053 from the N.I.N.D.S. The author gratefully acknowledges this support and would also like to thank Professors J. Z. Young and E. G. Gray for encouragement and advice throughout the course of this study.     

Transganglionic regulation and fine structural localization of lectin-reactive carbohydrate epitopes in primary sensory neurons of the rat

Summary Light- and electron microscopic lectin histochemical studies showed that small dorsal root ganglion cells of the rat projecting to substantia gelatinosa Rolandi (Lamina II) contain terminal -d-galactose carbohydrate epitopes: while those projecting to Waldeyer's marginal zone (Lamina I) and the outer part of Lamina II contain terminal -d-galactose residues. These glycoconjugates are manufactured in the Golgi apparatus and transported to preterminal and terminal axoplasmic surface membranes. Both of the axolemmal carbohydrate moieties were shown to be subjected to transganglionic regulation, even though the effects of transganglionic degenerative atrophy become evident considerably later than the depletion of axoplasmic marker substances like fluoride resistant acid phosphatase and thiamine monophosphatase.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthdaySupported by research grants No. 527 from the Hungarian Ministry of Health and No. 05-065 from the Hungarian Academy of Sciences.     

On the alleged presence of non-argyrophile argentaffin cells in the human gastro-intestinal tract

Summary The relationship between the argentaffin and argyrophile cells of the human gastrointestinal tract has been studied, in foetal and adult material, by a technique involving the staining of sections first by an argentaffin method (Gomori-hexamine silver, Schmorl, Diazonium) and subsequently by an argyrophile method (Bodian). A comparison of the cells staining by the two methods shows that all argentaffin cells of the human gastrointestinal tract are also argyrophile and that there is no evidence to support the claim of Hellweg (1952) and of HamPerl (1952) regarding the presence of non-argyrophile argentaffin cells.W. H. O. fellow from the Department of Anatomy, Medical College, Rohtak, India. — I am very grateful to Professor J. D. Boyd and to the World Health Organisation for having made it possible for me to carry out this research at the Anatomy School, Cambridge. I am indebted to Dr. G. A. Gresham and his staff for their very willing cooperation in providing material from surgical resections. My thanks are also due to Mr. J. F. Crane for the photographs and to Mr. J. W. Cash and Mr. R. Smith for helpful discussions on staining techniques.     

Synaptic organization in the lateral geniculate nucleus of the monkey

Summary The synaptic organization in the lateral geniculate nucleus of the monkey has been studied by electron microscopy.The axon terminals in the lateral geniculate nucleus can be identified by the synaptic vesicles that they contain and by the specialized contacts that they make with adjacent neural processes. Two types of axon terminal have been recognized. The first type is relatively large (from 3–20 ) and contains relatively pale mitochondria, a great many vesicles and, in normal material, a small bundle of neurofilaments. These terminals have been called LP terminals. The second type is smaller (1–3 ), contains darker mitochondria, synaptic vesicles, and no neurofilaments. These have been called SD terminals.Both types of terminal make specialized axo-somatic and axo-dendritic synaptic contacts, but the axo-somatic contacts are relatively rare. In addition the LP terminals frequently make specialized contacts with the SD terminals, that is, axo-axonal contacts, and at these contacts the asymmetry of the membranes is such that the LP terminal must be regarded as pre-synaptic to the SD terminal.The majority of the synaptic contacts are identical to those that have been described previously (Gray, 1959 and 1963a) but, in addition, a new type of contact has been found. This is characterized by neurofilaments that lie close to the post-synaptic membrane, and by an irregular post-synaptic thickening. Such filamentous contacts have been found only where an LP terminal contacts a dendrite or a soma.The degeneration that follows removal of one eye demonstrates that the LP terminals are terminals of optic nerve fibres. The origin of the SD terminals is not known.The glial cells often form thin lamellae around the neural processes and tend to isolate synaptic complexes. These lamellae occasionally show a complex concentric organization similar to that of myelin.It is a pleasure to thank Prof. J. Z. Young for advice and encouragement and Dr. E. G. Gray for the considerable help he has given us. Dr. J. L. de C. Downer gave us much help with the care of the animals and with the operations. We also wish to thank Mr. K. Watkins for technical assistance and Mr. S. Waterman for the photography.     

The ultrastructure of human secretory ameloblasts

Summary The ultrastructure of secreting ameloblasts of deciduous teeth from a human foetus (crown-rump length 195 mm) was investigated. The ameloblasts demonstrate a formation of granules in a juxtanuclear Golgi complex. In the Tomes' process the granules are released either through the lateral plasma membrane into the intercellular space between the Tomes' processes or directly through the apical plasma membrane into the enamel.The human ameloblasts differ from non-human ameloblasts in having a non-oriented vesicular granular endoplasmic reticulum. Further, the majority of mitochondria are situated in the apical part of the ameloblast adjacent to the Tomes' process.We would like to thank chief-surgeon A. Christensen, Bispebjerg Hospital, Copenhagen for his help in acquiring foetal material. For technical assistance we would like to thank M. Balslev and U. Eberth, Anatomy Department A.     

Changes in nerve terminals and acini of the lacrimal gland and changes in secretion induced by autonomic denervation

Summary Nerve terminal alterations induced by superior cervical ganglionectomy and pterygopalatine ganglion lesions, and acinus cell alterations induced by the latter operation and by greater petrosal neurectomy, established that a majority of interstitial and all parenchymal nerve terminals of the lacrimal gland in monkeys were parasympathetic. These were shown to originate from neurones of the pterygopalatine ganglion. A minority of interstitial terminals were sympathetic and were distinguished from the remainder by the presence of small granular vesicles. The number of small granular vesicles was increased by iproniazid treatment.The production of serous but not of mucous secretion granules was shown to be dependent upon a functioning parasympathetic nerve supply. Lacrimal secretion was not appreciably altered by sympathectomy but was radically reduced by parasympathectomy.Nerve terminals were closely apposed to between 15 and 56% of capillary sections. Both parasympathetic and sympathetic terminals innervated capillaries.The various experimental results are used to postulate a peripheral control mechanism for lacrimal gland secretion involving only parasympathetic nerve terminals.The author expresses his appreciation to Professor R. Warwick for the use of facilities of the Anatomy Department, Guy's Hospital Medical School.     

Synapses in the cerebral ganglion of adult Ciona intestinalis

Summary Electron microscopy of the synaptic morphology of synapses in the cerebral ganglion of the adult ascidian (sea squirt) Ciona intestinalis reveals that the synapses are restricted to the central neuropil of the ganglion. Many of the synapses show a polarity of structure such that pre and post synaptic parts can be identified. The vesicles in the presynaptic bag are of two main diameters 80 and 30 nm respectively. The large vesicles have electron dense contents that vary both in their capacity and dimensions.The pre and postsynaptic membranes are more electron dense than the surrounding membranes, but they are only slightly thicker. Both the pre and post synaptic membranes have electron dense dots some 10 nm in diameter associated with their cytoplasmic surfaces. Sometimes the presynaptic membrane has larger peg-like projections between the vesicles. Associated with the post synaptic membrane are tubules some 10 nm in diameter. These tubules may be the dots cut obliquely.The synaptic cleft material is more electron dense than the surrounding intercellular material, and in it there is a dense line made up of granules about 3–5 nm in diameter. This dense line is usually mid way between the pre and post synaptic membranes, but may be nearer the postsynaptic membrane.No tight junctions between adjacent nerve process profiles have been observed.I wish to thank Professors J. Z. Young, F. R. S. and E. G. Gray for much advice and encouragement, also Dr. R. Bellairs for the use of electron microscope facilities and Mr. R. Moss and Mrs. J. Hamilton for skillful technical assistance.     

Axonal protrusions in the small multiple endings in the extraocular muscles of the rat

Summary A special type of myoneural junction has been observed in the extraocular muscles of the rat with electron microscopy. These axon terminals are derived from unmyelinated nerves and contain synaptic vesicles and mitochondria. The terminals are invested by teloglia cells and separated by a synaptic cleft of about 500 Å from a slow-type muscle fibre. From the nerve ending a pseudopod-like evagination projects into the muscle cell. The membranes of this evagination and the muscle cells are only separated by a narrow cleft of about 100 Å, which is devoid of the basement membrane-like material typical of ordinary myoneural junctions. The evagination contains fewer axonal vesicles than other regions of the terminal axoplasm and the postsynaptic part of the muscle plasma membrane in this special region does not exhibit the postsynaptic thickening characteristic of ordinary myoneural junctions.The author thanks ProfessorAntti Telkkä, M.D., Head of the Electron Microscope Laboratory, University of Helsinki, for permission to use the facilities of the laboratory.     

Elektronenmikroskopische Befunde zur Differenzierung der Rezeptorzellen und Bipolarzellen der Retina und ihrer synaptischen Verbindungen

Summary The differentiation of the bird's retina is described, paying special attention to the development of synapses and bipolar cells. The structural differentiation of receptor cells and bipolars, the topography and the time sequence of synaptic development has been studied in embryonic material ranging from 6 to 21 days of incubation.Due to the intimate interdigitation of opposing cell membranes in contact with each other, the formation of specialized contacts (synapses) occurs at selected places and shows special features. Their differentiation is characterized by a) accumulation of electrondense material close to the pre- and postsynaptic membrane, b) the presence of large numbers of synaptic vesicles initially perinuclear and moving later in the cytoplasmatic presynaptic processes, c) a special type of synaptic lamella surrounded by vesicles.

---

---

Ich danke der Deutschen Forschungsgemeinschaft und der Volkswagenstiftung für ihre Unterstützung, FräuleinCh. Kiele und FräuleinE. Möhring für die technische Assistenz.     

Effects of amphipathic drugs onl-[3H]glutamate binding to synaptic membranes and the purified binding protein

Four amphipathic molecules with known local anesthetic activity, dibucaine, tetracaine, chlorpomazine, and quinacrine, inhibited the binding ofl-[³H]glutamic acid to rat brain synaptic plasma membranes and to the purified glutamate binding protein. Neither haloperidol nor diphenylhydantoin had significant inhibitory effects on the glutamate binding activity of the membranes or of the purified protein. The amphipathic drugs apparently inhibitedl-[³H]glutamate binding to synaptic membranes by a mixed type of inhibition. The inhibitory activity of quinacrine on glutamate binding to the synaptic membranes was greater in a low ionic strength, Ca²⁺-free buffer medium, than in a physiologic medium (Krebs-Henseleit buffer). Removal of Ca²⁺ from the Krebs solution enhanced quinacrine's inhibition of glutamate binding. Quinacrine up to 1 mM concentration did not inhibit the high affinity Na⁺-dependentl-glutamate transport in these membrane preparations. The importance of Ca²⁺ in the expression of quinacrine's effects on the glutamate binding activity of synaptic membranes and the observed tetracaine and chlorpromazine-induced increases in the transition temperature for the glutamate binding process of these membranes, were indicative of an interaction of the local anesthetics with the lipid environment of the glutamate binding sites.     

Neuron–astrocyte interactions in the medial nucleus of the trapezoid body

The calyx of Held (CoH) synapse serves as a model system to analyze basic mechanisms of synaptic transmission. Astrocyte processes are part of the synaptic structure and contact both pre- and postsynaptic membranes. In the medial nucleus of the trapezoid body (MNTB), midline stimulation evoked a current response that was not mediated by glutamate receptors or glutamate uptake, despite the fact that astrocytes express functional receptors and transporters. However, astrocytes showed spontaneous Ca²⁺ responses and neuronal slow inward currents (nSICs) were recorded in the postsynaptic principal neurons (PPNs) of the MNTB. These currents were correlated with astrocytic Ca²⁺ activity because dialysis of astrocytes with BAPTA abolished nSICs. Moreover, the frequency of these currents was increased when Ca²⁺ responses in astrocytes were elicited. NMDA antagonists selectively blocked nSICs while D-serine degradation significantly reduced NMDA-mediated currents. In contrast to previous studies in the hippocampus, these NMDA-mediated currents were rarely synchronized.     

The fine structure of the synaptic membrane adhesions on Octopus synaptosomes

Summary Synaptosomes (nerve-ending particles), derived by homogenization and centrifugation fromOctopus andEledone brains, have been examined after OsO₄-fixation and PTA-staining, to determine the structure of the synaptic apparatus which holds together the synaptosomes and their postsynaptic processes. Both synaptic membranes are well-defined, with branching processes passing from the presynaptic membrane into the cytoplasm of the synaptosome, where synaptic vesicles apparently adhere to them. Small projections, with occasional web-like extensions, are seen along the cytoplasmic surface of the postsynaptic membrane. In transverse and oblique views of the cleft, bars are seen between the synaptic membranes. In frontal view, this part of the synaptic apparatus has a lattice arrangement of quadrilateral and pentagonal facets.A possible interpretation of these findings is discussed, and the functions of the synaptic apparatus are considered in the light of this.I am grateful to ProfessorsJ. Z. Young, F. R. S. andE. G. Gray for their advice and encouragement, and to Mr.S. Waterman for skilled photography.     

The fine structure of the endocardial endothelium

Summary The fine structure of the endocardium of the rat was studied at the level of the papillary muscles. In accordance with what is already known about endothelial cells of blood vessels, the occurrence of numerous vesicles underlying the plasma membrane was observed, indicating the pinocytotic activity of the endocardial endothelial cells.The plasma membrane, as in all other cells, consists of two electron-dense layers separated by a light interspace. However, after phosphotungstic acid staining, it appears as a thickened single band at the free cell surface. This characteristic feature decreases towards the lateral cell boundaries. Intensely stained are also clumps of material pinched off from the plasma membrane and released into the cavity.Assistant at the Department of Anatomy of the University, Torino, Italy (Dir.: Prof. F. Loretti). The author was awarded a grant from the Italian Consiglio Nazionale delle Ricerche for the present investigation.The author wishes to thank Mrs. Behrens and Miss Anhut for excellent technical assistance.     

Fine structural relation between the Sertoli cell and the differentiating spermatid in the human testis

Summary The structural relationship between the Sertoli cell and the developing spermatid was studied with the electron microscope. In the contact area of the Sertoli cell with the anterior part of the developing spermatid, a filamentous structure is observed. This structure consists of fine tubular filaments about 100 Å in diameter associated with dense material. The functional significance of the structure is discussed.Supported by Grant HD-00593-05 of National Institutes of Health, United States Public Health Service. The author is indebted to Dr. T. Katayama, Department of Urology, Chiba University, for supplying the materials.     

Special somatic spine synapses in the ciliary ganglion of the chick

Summary Somatic spine synapses modified with postsynaptic electron opaque materials were found in the axo-somatic ciliary ganglion synapse of the chick.A part of the postsynaptic cell body protrudes into the presynaptic calyciform ending as a somatic spine with about 1 in length and 0.15 in diameter, and forms the so-called synaptic complex with presynaptic process. Moreover, conspicuous electron opaque materials can be seen in the central axis of the spine, except for its end portion. Sometimes, these opaque materials are seen as arrayed dots.The morphological characteristics of the somatic spine synapses in this study are quite similar to that found in the habenula and interpeduncular nuclei of the cat (Milhaud and Pappas, 1966). the biological significance of which is obscure at present.This work was supported in part by grant from the Education Ministry of Japan.     

Ultrastructure of the developing gizzard epithelium in the chick embryo

Summary The fine structure of the gizzard epithelium is described at different stages in the development of the chick embryo. The elaborate apical processes, a characteristic feature, take part in secretion at thirteen days, but do not seem to have this function at nine and ten days. The formation of glands begins at thirteen days but the adult fine structure of the gland cells is not attained until hatching. The distinct surface layer present between thirteen and seventeen days may have a protective function. Acknowledgement. The author is grateful for research facilities provided by Professor G. M. Wyburn, Anatomy Department, The University of Glasgow.