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.     

An electron microscopic study of the normal synaptic relationships and early degenerative changes in the rat olfactory tubercle

Summary The olfactory tubercle of the rat was studied by electron microscopy both in the normal and after ipsilateral olfactory bulb ablation at survival times of from 14 hours to seven days. Particular emphasis was placed on synaptic structures and their changes following the lesion. Normal synapses are similar to those described in previous studies and presynaptic profiles are of at least three types. Types-A and -B contain round vesicles and form asymmetrical contacts and type-C profiles contain flattened vesicles and form symmetrical contacts.There appear to be two major types of degenerative changes. The electron-lucent type predominates at early survival times and is seen first at 14 hours. These profiles show an early reduction in numbers of vesicles with mitochondrial swelling followed by shrinkage of the profile. These profiles become increasingly electron-dense at later survival times. The second major type of degenerating profile is initially electron-dense. The earliest changes in these profiles are an increased axoplasmic density and increased microtubular density and clumping without apparent loss of vesicles. These profiles also become progressively more electron-dense at longer survival times. The observations are discussed in relation to previous reports.This study represents a part of a thesis (C. A. Anderson) for the Doctor of Medicine degree, University of Washington School of Medicine. It was supported by PHS grants NS 04053, NS 02896 and NS 09678 from the N.I.N.D.S., National Institutes of Health. The authors gratefully acknowledge this support.     

The organization of the substantia gelatinosa rolandi in the cat lumbosacral spinal cord

Summary The organization of the substantia gelatinosa and adjacent lamina III in cat lumbo-sacral spinal cord has been studied by light and electron microscopical techniques in normal cord and following dorsal root section.The substantia gelatinosa (lamina II of Rexed) is characterized by bundles of small, non-myelinated axons, principally oriented longitudinally. The substantia gelatinosa cells are small, spindle shaped, with a cytoplasm generally devoid of Nissl substance. There are extensive axo-dendritic and axo-axonal contacts within the substantia gelatinosa and less frequent axo-somatic contacts.Larger marginal cells oriented horizontally on the surface of the substantia gelatinosa and containing Nissl substance are also seen.Lamina III is somewhat similar to the substantia gelatinosa, but lacks the complex bundles of non-myelinated axons.Following dorsal root section, heavy degeneration is seen by light and electron microscopy in lamina III, but is rarely seen in the substantia gelatinosa. It is concluded that the substantia gelatinosa and lamina III are distinct anatomically and therefore may differ functionally.The possible physiological role of the substantia gelatinosa is discussed.This work was supported by a Special Fellowship 2F11 NB 1140 02 NSRB from the National Institute of Neurological Diseases and Blindness, United States Public Health Service.The author is indebted to Dr. E. G.Gray for his excellent advice. I thank Dr. R. W. Guillery, Dr. L. E. Westeum and Dr. B. G. Cragg for their assistance, and Prof. J. Z. Young, F. R. S. for his kind suggestions. I also wish to thank Mr. S. Waterman for the photography.     

Electron microscope observations of some peripheral synapses in the sensory pathway of the sucker of Octopus vulgaris

Summary A synaptic axo-dendritic linkage is described between primary receptors lying in the epithelia of the sucker of Octopus and encapsulated nerve cells found near the rim of the sucker in the subepithelial connective tissue. These synapses are postulated to perform a drastic reduction of inputs between the primary receptors of the order of more than ten thousand and the subjacent encapsulated nerve cells of the order of some hundreds. The morphology of these cells as well as that of the synaptic structures are described from electron microscope studies. Aknowledgement. This work was done at University College London, while I was in receipt of a Medical Research Council grant.I am deeply indebted to Prof. J. Z. Young F. R. S. for support and criticism, and to Dr. E. G. Gray for advice and discussion. My thanks are due to Mr. A. Aldrich for the photographs.     

The fine structure of the retinal plexus in Octopus vulgaris

Summary The plexiform layer of the octopus retina was investigated by means of electron microscopy. The axonic processes of visual cells contain closely packed microtubules, 300 Å in diameter, running parallel to one another along the long axis of the processes. Visual cells also send out a large number of thin axon collaterals. Each of them forms presynaptic knobs with numerous clear vesicles along their course. These are assumed to be concerned with the reciprocal communication between visual cells. Nerve endings with dense-cored vesicles form synaptic contacts with visual cells. The visual cells show some spherical protrusions into the perivascular spaces.Octopuses, captured off the coast of Onagawa (Miyagi-ken, Japan) in autumn of 1963 and 1964, were offered for this research through the kindness of Dr. Kyoji Tasaki, Assistant Professor of Physiology in Tohoku University School of Medicine.I wish to thank Professor Toshiyuki Yamamoto for his encouragement and suggestions throughout all stages of this work, and also Mr. Masae Kato for his technical assistance in drawing.     

Interneuronal synapses in the local ganglia of the cat urinary bladder.

The interneuronal synapses of the urinary bladder in the cat were studied by electron microscopy. The great majority of the fibres containing vesicles are found within the ganglia occurring in the trigonum area. Morphologically differentiated synaptic contacts could be observed on the surface of the local neurons and between the different nerve processes. The presynaptic terminals can be divided into three types based on a combination of synaptic vesicles. Type I terminals, presumably cholinergic synaptic terminals, contain only small clear vesicles of 40-50 nm in diameter. Type II terminals, presumably adrenergic terminals, are characterized by small granulated vesicles of 40-60 nm in diameter. Type III terminals, probably of local origin, contain a variable number of large granulated vesicles of 80-140 nm in diameter. Occasionally, a single nerve fibre contacted several (two or four) other nerve processes forming a typical synapse. In other cases, on one nerve cell soma or on other nerve processes there are two or three different-type nerve terminals establishing synapses. It might be inferred from these observations that convergence and divergence can occur in the local ganglia and that cholinergic and adrenergic synaptic terminals can modulate the ganglionic activity. However, a local circuit also can play an important role in coordinating the function of the bladder.     

Degeneration in the parvocellular portion of the lateral geniculate nucleus of the cebus monkey

Summary The synaptology of the Cebus lateral geniculate nucleus (LGN) was studied after varying (3–15 days) periods of survival following unilateral and bilateral eye enucleations. Part of the material was processed with the Glees and Nauta techniques for light microscopy while the rest was processed for electron microscope observation. The study revealed a variety of degenerated terminals in the parvocellular portion of the LGN and allowed the differentiation of the retinal from the extraretinal terminals. The most frequent synaptic type of retinal origin is a glomerular large central terminal (up to 20 long) which makes axodendritic and axoaxonic synaptic contacts with geniculate dendrites and peripheral small terminals. Simple axodendritic and axosomatic terminals of retinal and extraretinal origin were also found. The early changes affecting the geniculate neurons and astrocytes during the degenerative process are described.These results are discussed in relation to: 1) previous work on the LGN synaptology of cats and macaques; 2) the physiology of the LGN; 3) the phagocytic role of astrocytes; 4) the general problem of degeneration in the central nervous system. In addition, a correlation between the light and electron microscope observations is attempted.Work supported by Grants from the National Council to Combat Blindness, Inc. N.Y., U.S.A. (Fight for Sight Grant-in-Aid-G-340), the AF-AFOSR Grant No. 963/67-68, and the Consejo Nacional de Investigaciones Cientificas y Técnicas, Buenos Aires, Argentina.The authors acknowledge the continuous advice and encouragement received from Prof. E. de Robertis throughout all the phases of the project. The expert technical assistance of Miss E. di Matteo, Mr. A. Sáenz and Mr. R. Castelli is also gratefully acknowledged.     

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 reorganization of the hypophysial stalk following hypophysectomy in the teleost Porichthys notatus Girard

Summary Porichthys notatus has a long infundibular stalk, measuring 3 to 5 mm. The third ventricle extends into the stalk as a long infundibular funnel.In several hypophysectomised specimens the proximal cut end of the stalk enlarged to form a round or oblong body, having axonal endings with AF-positive material, glial elements, and blood sinuses. This suggests that in the absence of the pituitary the cut end of the stalk is reorganised into a neurohypophysis-like organ.The regenerated stalk seems to have the essential components for neurohypophysial function; axonal endings for the storage of secretory products, and related blood vessels for the release of the stored principles.This work was supported by the Population Council of the Rockefeller Institute, New York. I am thankful to Dr. R. L. Fernald, Director of the Friday Harbor Marine Biological Laboratories, University of Washington, for providing collection and laboratory facilities. I am indebted to Dr. Aubrey Gorbman, Department of Zoology, University of Washington for the generous hospitality in his laboratory and encouragement, which made this work possible. Material support in part for this research was received from U. S. P. H. S. grant NB 04887 awarded to Dr. A. Gorbman.     

Synaptic patterns in the dorsal lateral geniculate nucleus of the monkey

Summary Synaptic junctions are found in all parts of the nucleus, being almost as densely distributed between cell laminae as within these laminae.In addition to the six classical cell laminae, two thin intercalated laminae have been found which lie on each side of lamina 1. These laminae contain small neurons embedded in a zone of small neural processes and many axo-axonal synapses occur there.Three types of axon form synapses in all cell laminae and have been called RLP, RSD and F axons. RLP axons have large terminals which contain loosely packed round synaptic vesicles, RSD axons have small terminals which contain closely packed round vesicles and F axons have terminals intermediate in size containing many flattened vesicles.RLP axons are identified as retinogeniculate fibers. Their terminals are confined to the cell laminae, where they form filamentous contacts upon large dendrites and asymmetrical regular synaptic contacts (with a thin postsynaptic opacity) upon large dendrites and F axons. RSD axons terminate within the cellular laminae and also between them. They form asymmetrical regular synaptic contacts on small dendrites and on F axons. F axons, which also occur throughout the nucleus, form symmetrical regular contacts upon all portions of the geniculate neurons and with other F axons. At axo-axonal junctions the F axon is always postsynaptic.Supported by Grant R 01 NB 06662 from the USPHS and by funds of the Neurological Sciences Group of the Medical Research Council of Canada. Most of the observations were made while R. W. Guillery was a visiting professor in the Department of Physiology at the University of Montreal. We thank the Department of Physiology for their support and Mr. K. Watkins, Mrs. E. Langer and Mrs. B. Yelk for their skillful technical assistance.     

Development of the myoneural junction in the rat

Summary The structure of the myoneural junction in the striated muscle of rat embryos and postnatal rats was studied by electron microscopy in order to assess at ultrastructural level the roles of neuronal and muscular elements and the sequence of events resulting in the formation of a functionally mature synaptic organization.From the observations it is concluded that the axon terminals enveloped by Schwann cells contain vesicles prior to apposition of the prospective synaptic membranes. Subsequently, subsarcolemmal thickening of the postsynaptic membrane takes place after the synaptic gap has been formed by disappearance of the teloglial cell from between the synaptic membranes but before the primary synaptic cleft in the strict sense is formed. Secondary synaptic clefts are formed later, when the primary synaptic cleft is regular in width, by local finger-like invaginations of the postsynaptic membrane, which thereafter expand basally, in a plane transverse to the axis of the axon terminal, to resemble flattened flasks. The junction is formed between multinucleated muscle cells and multiple axons, which at first lie side by side and later, when formation of adult-type secondary synaptic clefts is in progress, become separated by folds of the sarcoplasm and the teloglia. In extraocular muscles of adult rats the sarcoplasmic reticulum is closely associated with the postjunctional sarcoplasm.In the light of earlier observations on the development of contractibility after nerve stimulation, cholinesterase histochemistry and muscle fibre physiology, these observations are interpreted to indicate that functional differentiation of the myoneural synapse results from induction by the motor axon and that the association of the sarcoplasmic reticulum with the postjunctional sarcoplasm in adult extraocular muscles is related to modified fibre physiology.The author wishes to thank Prof. Antti Telkkä, M.D., Head of the Electron Microscope Laboratory, University of Helsinki, for placing the electron microscopic facilities at his disposal.     

Electron microscopic study on the innervation of the pancreas of the domestic fowl

Summary The innervation of the pancreas of the domestic fowl was studied electron microscopically. The extrapancreatic nerve is composed mostly of unmyelinated nerve fibers with a smaller component of myelinated nerve fibers. The latter are not found in the parenchyma. The pancreas contains ganglion cells in the interlobular connective tissue. The unmyelinated nerve fibers branch off along blood vessels. Their synaptic terminals contact with the exocrine and endocrine tissues. The synaptic terminals can be divided into four types based on a combination of three kinds of synaptic vesicles. Type I synaptic terminals contain only small clear vesicles about 600 Å in diameter. Type II terminals are characterized by small clear and large dense core vesicles 1,000 Å in diameter. Type III terminals contain small clear vesicles and small dense core vesicles 500 Å in diameter. Type IV terminals are characterized by small and large dense core vesicles. The exocrine tissue receives a richer nervous supply than the endocrine tissue. Type II and IV terminals are distributed in the acinus, and they contact A and D cells of the islets. B cells and pancreatic ducts are supplied mainly by Type II terminals, the blood vessels by Type IV terminals.This work was supported by a scientific research grant (No. 144017) and (No. 136031) from the Ministry of Education of Japan to Prof. M. Yasuda     

Synaptology of three peptidergic neuron types in the central nucleus of the rat amygdala

The synaptology of neurotensin (NT)-, somatostatin (SS)- and vasoactive intestinal polypeptide (VIP)-immunoreactive neurons was studied in the central nucleus of the rat amygdala (CNA). Three types of axon terminals formed synaptic contacts with peptide-immunoreactive neurons in the CNA: Type A terminals containing many round or oval vesicles; Type B terminals containing many pleomorphic vesicles; and Type C terminals containing fewer, pleomorphic vesicles. Peptide-immunoreactive terminals were type A. All three types of terminals formed symmetrical axosomatic and asymmetrical axodendritic contacts. However, type B and peptide-immunoreactive terminals frequently formed symmetrical axodendritic synaptic contacts. VIP-immunoreactive terminals also formed asymmetrical axodendritic contacts. SS- and NT-immunoreactive terminals commonly formed symmetrical contacts on SS- and NT-immunoreactive cell bodies, respectively. VIP-immunoreactive axon terminals were postsynaptic to nonreactive terminals. Type B terminals appeared more frequently on VIP neurons than on NT or SS neurons.     

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.     

Structure and function of the parapodial cirri of the polynoid polychaete,Harmothoë

Summary Structural and physiological studies indicate a sensory and secretory function for parapodial cirri. A cirrus is composed of a neuronal core containing synapses, enveloped by a stroma, an epithelium and a cuticle bearing ciliated papillae enclosing projections of subcuticular somata from which fibers pass into the core. The cuticle contains microvilli and canals associated distally with 470 Å granules appearing at all seasons in both sexes. One type of stromal cell produces PAS+ granules, and the nuclei of several types contain dense strands 250 Å in diameter. Upon electrical stimulation of the parapodial nerve, a PAS+ secretion appears on the ventral cirrus. The presence of synapses in the core reopens the problem of peripheral sensory confluence in polychaetes.The author thanks G. A. Horridge and members of the Gatty Marine Laboratory and the Zoology Department of the University of St. Andrews for assistance, and is especially appreciative of J. Stevenson's photographic services. This investigation was supported by a Public Health Service Fellowship IF2 NB20, 539-01 from the Institute of Neurological Diseases and Blindness.     

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.     

Evidence for the existence of monoamine neurons in the central nervous system

Summary With the help of the highly specific and sensitive fluorescence method of Falck and Hillarp together with the histochemical and pharmacological criteria for the specificity of the fluorescence reaction convincing evidence has been obtained that the fine, varicose nerve fibres observed in a vast number of regions in the mammalian central nervous system (mouse, hamster, rat, guineapig, rabbit, cat), which exhibit a green or yellow fluorescence, contain primary catecholamines and 5-HT respectively. Strong support has been given for the view that CA fibres showing a rapid recovery after administration of -MMT contain DA, while those showing a slow recovery contain NA.There is little doubt that the monoamine-containing fibres in the brain represent the terminal ramifications of axons belonging to specific monoamine neurons and that they are true synaptic terminals. They seem to make their contacts via the varicosities which have extremely high concentrations of amines and in all probability represent the presynaptic structures, specialized for synthesis, storage and release of the amines. The central monoamine terminals thus have the same characteristic appearance as the adrenergic synaptic terminals in the peripheral nervous system.All the data strongly support the view that the specific central neurons giving rise to the terminals are monoaminergic, i.e. function by releasing their amines from the synaptic terminals. Consequently, DA, NA and 5-HT seem to be central neurotransmitters.Not only the median eminence but also the nuc. caudatus putamen, tuberculum olfactorium, nuc. accumbens and the small circumscribed areas medial to nuc. accumbens contain very fine (partly sublightmicroscopical) CA terminals. These areas react to treatment with reserpine, nialamide-dopa and -MMT in the same way and since the nuc. caudatus putamen and tuberculum olfactorium are known to have a high DA content it seems likely that abundant DA terminals are accumulated in these special areas.The Following Abbreviations are Used CA Catecholamine - DA Dopamine - dopa 3.4-Dihydroxy-phenylalanin - NA Noradrenaline - A Adrenaline - 5-HT 5-Hydroxytryptamine - -MMT -Methyl-meta-tyrosine - MAO Monoamine oxidase For generous supplies of drugs the author is indebted to the following companies: Swedish Ciba, Stockholm, Sweden (reserpine); Swedish Pfizer, Stockholm, Sweden (nialamide); Abbott Research Laboratories, Chicago, USA. (MO 911). This study has been supported by a Public Health Service Grant (NB 02854-04) from the National Institute of Neurological Diseases and Blindness and by grants from the Knut and Alice Wallenberg Foundation, and the Swedish Medical Research Council.     

GABA-immunohistochemistry as a label for identifying types of local interneurons and their synaptic contacts in the antennal lobes of the American cockroach

Summary Synaptic contacts between GABA-immunoreactive neurons, antennal receptor fibers and non-GABA-immunoreactive neurons in the glomerular neuropil of the antennal lobes have been identified by means of a combination of (i) immunohistochemical labeling and (ii) labeling of afferent fibers of the antenna by experimentally induced degeneration. Characteristic contacts of these neurons are: a) Serially arranged polysynaptic contacts between degenerated antennal fibers, GABA-immunoreactive neurons and non-GABA-immunoreactive neurons. b) Monosynaptic contacts between degenerated antennal fibers and non-GABA-immunoreactive neurons. c) Reciprocal synaptic contacts between immunostained and non-stained neurons and synaptic contacts between individual GABA-immunoreactive neurons. d) Synaptic output contacts of GABA-immunoreactive neurons with degenerated antennal fibers.GABA-immunoreactive neuron profiles in the glomeruli are assigned to multiglomerular local interneurons (Distler 1989a); non-immunolabeled profiles may be assigned to projection neurons and other not yet identified interneurons.     

GABA-immunohistochemistry as a label for identifying types of local interneurons and their synaptic contacts in the antennal lobes of the American cockroach

Synaptic contacts between GABA-immunoreactive neurons, antennal receptor fibers and non-GABA-immunoreactive neurons in the glomerular neuropil of the antennal lobes have been identified by means of a combination of (i) immunohistochemical labeling and (ii) labeling of afferent fibers of the antenna by experimentally induced degeneration. Characteristic contacts of these neurons are: a) Serially arranged polysynaptic contacts between degenerated antennal fibers, GABA-immunoreactive neurons and non-GABA-immunoreactive neurons. b) Monosynaptic contacts between degenerated antennal fibers and non-GABA-immunoreactive neurons. c) Reciprocal synaptic contacts between immunostained and non-stained neurons and synaptic contacts between individual GABA-immunoreactive neurons. d) Synaptic output contacts of GABA-immunoreactive neurons with degenerated antennal fibers. GABA-immunoreactive neuron profiles in the glomeruli are assigned to multiglomerular local interneurons (Distler 1989a); non-immunolabeled profiles may be assigned to projection neurons and other not yet identified interneurons.     

Mapping of experimental axon degeneration by electron microscopy of golgi preparations

Summary For the mapping of the terminal area of transected axons within the central nervous system, electron microscopy has recently been adopted. A greater accuracy is thereby obtained than with silver impregnation and light microscopy, since it becomes possible to determine the kinds of structure (soma, dendrites, spines) with which the degenerating boutons establish synaptic contact. In the present study this technique was extended by Golgi impregnation of such material with the aim of making possible classification of the postsynaptic neuron. A few days after transection of a pathway (commissural fibres to the hippocampus being used as a model in this study) the brain was fixed by perfusion with phosphate buffered formalin with sucrose. This was followed by immersion in an osmium tetroxide-potassium dichromate mixture (Dalton's fixative without sodium chloride) later replaced by a solution of silver nitrate. Satisfactory Golgi impregnation of nerve cells and processes was obtained. By careful trimming, and reembedding of selected areas, blocks for ultramicrotomy could be obtained which contained only one type of impregnated cell, e.g., hippocampal pyramidal cells.The relation of basal dendrites of such cells to degenerating boutons of commissural fibres was studied. Numerous examples of contact between degenerating boutons and spines belonging to the basal dendrites were seen. Although the Golgi precipitate obscured the postsynaptic substance in the spines, a number of features at the sites of contact were considered strong indication that many of the contacts were synapses and not merely the result of random juxtaposition. This combined procedure is supposed to be applicable to other problems and to other parts of the nervous system as well.This study was supported in part by Grant NB 02215 from the National Institute of Neurological Diseases and Blindness, U.S. Public Health Service. This ais is gratefully acknowledged. The author is indebted to Mrs. J. L. Vaaland and Mr. B. V. Johansen for valuable technical assistance.