Showing papers in "Journal of Neurocytology in 1976"

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. I. General description.

Abstract: Lesions were made in the lateral geniculate nucleus of the rat and the consequent degeneration in area 17 of the cerebral cortex was studied by light and electron microscopy. These lesions produced prominent degeneration of axon terminals in layer IV extending into layer III and a much lesser amount in layers I and VI. The darkened degenerating axon terminals forming asymmetric synaptic junctions and were frequently surrounded by hypertrophied astrocytic processes. These terminals appeared to be disposed randomly, forming no discernible patterns. In layer IV 83% of the synapsing, degenerating terminals formed junctions with dendritic spines, 15% with dendritic shafts, and 2% with neuronal perikarya. The dendritic shafts and neuronal perikarya appeared to belong to spine-free stellate cells. The dendrites giving rise to the spines receiving degenerating axon terminals could not be identified, for most of the spines appeared as isolated profiles that could not be traced back to their dendritic shafts. One example of a degenerating axon terminal synapsing with an axon initial segment was encountered. Small, degenerating myelinated axons were prevalent in layers VI, V and IV, but were only infrequent in the supragranular layers. These results are compared with those obtained in other studies of thalamocortical projections.

Morphometric analysis of rat superior cervical ganglion after axotomy and nerve growth factor treatment

Abstract: The changes in neuronal number, cell body size and nuclear size have been followed for 12 weeks after postganglionic axotomy of the rat superior cervical ganglion. Axotomy was carried out at 6 days post partum and treatment with nerve growth factor (NGF) was from 6-21 days. During normal development there is a 30% decrease in the number of neurons in the superior cervical ganglion; axotomy increases the loss of cells resulting in a 90% decrease by 28 days post partum. The normal decrease is prevented and the enhanced loss of cells after axotomy is decreased by administration of NGF. Thus the increased number of cells observed after NGF administration appears to be due to the survival of cells that otherwise would have degenerated. NGF causes a rapid enlargement of both the cell bodies and the nucleus in the normal and axotomized ganglia. This increase in size rapidly reverses after cessation of treatment. These changes in cell size may account for the previously observed changes in cell profile number with NGF. There is a large increase in the number of non-neuronal cells during normal development and axotomy prevents this increase. NGF treatment results in a 6 fold increase in the number of non-neuronal cells and it is suggested that these are required to support the massive fibre outgrowth that occurs in NGF treated ganglia. It is concluded that these results are consistent with a physiological role for NGF as the trophic substance supporting adrenergic neurons making the appropriate contact with their target cell.

Intramembranous particle distribution at the node of Ranvier and adjacent axolemma in myelinated axons of the frog brain

Abstract: The plasma membrane of myelinated axons in the frog brain has been examined by the freeze-fracture technique. The cytoplasmic leaflet of the axolemma contains numerous randomly distributed particles in nodal and internodal regions but relatively fewer particles in the axoglial junctional portion of the paranodal region. Particle distribution is even less uniform in the outer leaflet of the axolemma, which contains a low concentration of particles in the internodal region and a relatively high concentration at the node of Ranvier (approximately 1200 particles mum-2). The nodal particles tend to be larger than most intramembranous particles, approaching 200 A diameter. The paranodal region of the leaflet is virtually devoid of such particles except in the narrow helical 'groove' which faces extracellular clefts between terminating glial processes. In places this pathway widens to form 'lakes' up to approximately 0.3 mum2 area which contain large numbers of large particles resembling those at the node. The concentration of particles at the node is in the same range as the concentration of sodium channels estimated to be in this region and it is suggested on the basis of their location and concentration that these particles represent ionophores. The distribution of particles in the paranodal region suggests that the large intramembranous particles do not have free access to the axoglial junctional portion of the membrane and therefore the movement of such particles along the paranodal region of the membrane may occur primarily in the membrane of the 'groove' spiraling through this portion of the axolemma. Such a restriction in surface area for particle movements on either side of the node of Ranvier could result in trapping of particles at the node and thus contribute to their concentration in the nodal axolemma.

Potential of Schwann cells from unmyelinated nerves to produce myelin: a quantitative ultrastructural and radiographic study.

Abstract: In adult mice, most fibres in the cervical sympathetic trunk (CST) are unmyelinated whereas a large proportion of sural nerve fibres are myelinated. This study of nerve grafts in syngeneic mice was designed to determine if Schwann cells originating from the unmyelinated CST would produce myelin when in contact with regenerating axons of the sural nerve. Quantitative microscopy of triated thymidine-labelled CST segments grafted to unlabelled sural nerve stumps revealed that, one month after grafting, previously unmyelinated grafts contained many myelinated fibres. By phase and electron microscope radioautography, nearly 40% of the myelin-producing cells in the reinnervated graft were shown to have originated in the unmyelinated CST. These findings indicate that Schwann cells originating from unmyelinated fibres are able to differentiate into myelin producing cells.

The ultrastructure of Auerbach's plexus in the guinea-pig. II. Non-neuronal elements

Abstract: The ultrastructural features of non-neuronal cells associated with Auerbach's plexus in the stomach, ileum and colon of the guinea-pig have been examined. Apart from Schwann, mast and interstitial or fibroblast-like cells, two other cell types are described that do not appear to have been reported previously. Of these two cell types, one was found external, but close to, the plexus and contained large granular vesicles. The other cell type contained numerous glycogen-like granules, was situated close to or within axon bundles and had processes that extended within and peripheral to nerve bundles as well as being close to smooth muscle cells. Although axon varicosities were opposed to both the processes and cell body of the second type of cell, synaptic-like contacts were not observed.

Precision of reinnervation of original postsynaptic sites in frog muscle after a nerve crush.

Abstract: Regenerating neuromuscular junctions in the cutaneous pectoris muscle of the frog were examined by light and electron microscopy up to three months after crushing the motor nerve. The aim was to determine the precision of reinnervation of the original synaptic sites. More than 95% of the original postsynaptic membrane is recovered by nerve terminals and little, if any, synaptic contact is made on other portions of the muscle fibre surface. Even after prolonged denervation when the Schwann cells have retracted from 70-80% of the postsynaptic membrane, regenerating terminals return to and cover a large fraction of it. Although synapses are confined to the original synaptic sites, the pattern of innervation of muscle fibres is altered in several ways: (a) regenerating axon terminals can fail to branch leaving small stretches of postsynaptic membrane uncovered; (b) two terminal branches can lie side by side over a stretch of postsynaptic membrane normally occupied by one terminal; and (c) after growing along a stretch of postsynaptic membrane on one muscle fibre, terminals can leave it to end either in extracellular space or on the postsynaptic membrane of another fibre. Altogether the results demonstrate a strong and specific affinity between the original synaptic sites and regenerating nerve terminals.

Morphological aspects of the elimination of polyneuronal innervation of skeletal muscle fibres in newborn rats.

Abstract: The ultrastructure of neuromuscular junctions of rat soleus muscles 1–40 days postnatally was examined for possible morphological correlates of the transient polyneuronal innervation which is present in newborn rats. Several vesicle-laden profiles of terminal axons are seen to contact each muscle fibre up to 8 days postnatally. Axon terminals often lie close together, without Schwann cell intervention. Between days 8 and 16 the number of profiles of terminals on each muscle fibre is reduced, and both Schwann cells and ridge-like extensions of muscle fibre cytoplasm intervene between and separate axon terminals. No signs of degenerating intramuscular axons or axon terminals could be found. It is suggested that the redundant terminals are eliminated by retraction into the parent axons. This process is apparently accomplished without any morphological signs of degeneration.

A method to correct adequately for the change in neuronal size when estimating neuronal numbers after nerve growth factor treatment.

Abstract: A method is described to compute the correct distribution of nuclear diameters in thick sections of superior cervical ganglia of rats from the observed distribution of nuclear profiles. This method is applicable to the problem of correcting for the differing diameters of cells observed after treatment with nerve growth factor (NGF). It overcomes the errors due to the failure to count small fragments of nuclei too thin to be seen and the multiple counting of nuclei in more than one section. It has been shown that the changes in number of neurons after NGF treatment were not as large as previously supposed. An estimate of the volume occupied by the cell bodies suggests that the numbers calculated here are correct.

Intercellular junctions in the reticular lamina of the organ of Corti

Abstract: Junctions between the cells in the reticular lamina of the organ of Corti were examined in thin sections and after freeze-fracturing to find a structural basis for the large ionic differences between the endolymph and perilymph. The apices of the cells in the reticular lamina are joined by a band of tight junctions spaced at 140 A intervals. Beneath this apical band the organization of the tight junctions depends on whether they join a supporting cell and a hair cell, or two supporting cells. At hair cell junctions with supporting cells, there is an extensive labyrinth of tight junctions enclosing lengthy, tortuous passages whose walls are composed of either multiple parallel or single junctions. At appositions between two supporting cells, maculae or fasciae occludentes lie immediately beneath the apical bands of closely spaced tight junctions, near the top of the zonulae adherentia which are characteristic of appositions between supporting cells. The complexes of tight junctions, or zonulae occludentes, between extralaminar supporting cells differ from those in the reticular lamina. The extralaminar cells are joined by a band of four to seven branching, anastomotic tight junctions. Thus, these junctions are like zonulae occludentes in other tissues. The novel organization of the tight junctions in the reticular lamina, different from those between the extralaminar supporting cells, suggests a special role for these junctions in the reticular lamina. Two sizes of gap junctions link, and presumably couple, supporting cells in the reticular lamina.

Organization of crustacean neuropil. I. Patterns of synaptic connections in lobster stomatogastric ganglion.

Abstract: The stomatogastric ganglion of the lobster consists of about thirty neurons, mainly large monopolar cells, which have been well characterized physiologically. This paper presents an anatomical description of this ganglion, emphasizing synaptic connections in the neuropil. The neuron cell bodies are located on the dorsal surface of the ganglion. They send processes into the underlying neuropil mass. The neuropil is differentiated into two regions: a core of coarse neuropil consists of large heavily ensheathed processes; a surrounding region of fine-textured synaptic neuropil consists of smaller unsheathed processes. Synapses are found only in synaptic neuropil, not in the core of coarse neuropil. Synaptic contacts, about one million in the entire neuropil, are easily recognized by a set of criteria including presynaptic vesicles and pre- and postsynaptic membrane specializations. Most synaptic contacts involve at least three neural processes, usually one pre- and two postsynaptic elements. Synapses are clustered onto irregular swellings or varicosities on neural processes. These varicosities make both pre- and postsynaptic contacts. Three different types of presynaptic profile are recognized. Pyloric dilator, ventricular dilator and lateral posterior gastric neurons belong to type A with clear irregular synaptic vesicles. Lateral pyloric, pyloric, anterior median and dorsal gastric neurons belong to type B with larger clear round vesicles. Many unidentified fibres, presumably stomatogastric nerve afferents, belong to type C with both small clear irregular vesicles and also large dense-core vesicles. The synaptic vesicle types are tentatively correlated with neurotransmitters: type A with acetylcholine, type B with an unknown transmitter, possibly glutamate, and type C with dopamine. The distribution of synaptic contacts on the processes of identified neurons reconstructed from serial sections is presented in the following paper.

Organization of crustacean neuropil. II. Distribution of synaptic contacts on identified motor neurons in lobster stomatogastric ganglion.

Abstract: Identified neurons in the stomatogastric ganglion of the lobster were examined and reconstructed by serial section electron microscopy. Each motor neuron consists of a soma, a primary process leading directly from the soma to the motor axon which leaves the ganglion, and a group of secondary processes which branch from the primary process and ramify within the neuropil. Synapses are found only on small processes in the synaptic neuropil, never on the primary processes or on larger secondary processes in the coarse neuropil. Nearly every secondary process of every neuron examined makes both pre- and postsynaptic contacts. Hence these neurons are not polarized into distinct pre- and postsynaptic regions but have both input and output distributed over each of the secondary processes in the neuropil. The connection between a specific pair of neurons is also distributed over several branches of both the pre- and the postsynaptic neurons. The restriction of synapses to the more distal portions of the secondary processes suggests that no single contact or localized group of contacts can exert an overriding influence on the neuron by virtue of an especially advantageous position. The close proximity of input and output on most secondary processes suggests that synaptic input may be capable of directly influencing output without the intervention of action potentials. The distribution of specific synapses over several branches of both pre- and postsynaptic neurons suggests that each neuron functions as a whole without differentiation into specialized branches.

Altered patterns of innervation in frog muscle after denervation.

Abstract: The pattern of reinnervation of muscle fibres after a nerve crush was examined in the cutaneous pectoris muscle of the frog by microscopy and electrophysiology. Normally, about 16% of the muscle fibres are innervated by more than one motor neuron. Two months after reinnervation, about 50% of the fibres are polyneuronally innervated and this high incidence persists for at least seven months. The total number of neurons reinnervating the muscle, as well as the number of muscle fibres comprising the muscle, are normal. However, nerve fibres sprout branches at the site of the crush, and, therefore, the number of axons entering the muscle is greater than normal. Regenerating axons contact muscle fibres precisely at the original synaptic sites and the terminal branches from different axons that end on the same muscle fibre often run side by side occupying stretches of original postsynaptic membrane normally covered by one terminal. Our findings indicate that the amount of synaptic contact during regeneration is limited by the amount of original postsynaptic membrane and that any number of axons that reach vacant portions of original postsynaptic membrane can make synaptic contact with it.

Cytological organization of the dorsal lateral geniculate nuclei in mutant anophthalmic and postnatally enucleated mice

Abstract: The dorsal lateral geniculate nuclei (dLGN) of anophthalmic and early postnatally enucleated mice were studied to determine the role retinal fibres play in the differentiation of postsynaptic target structures. Cell counts indicate that retinal fibres are necessary for the development and maintenance of the normal number of dLGN neurons and glia. This retinal fibre dependence is greater for animals enucleated on postnatal day 3 than for animals with a congenital absence of optic axons. Golgi analysis reveals, however, that the lack of retinal fibres does not preclude the development of the thalamo-cortical and intrinsic types of dLGN neuron.

Microtubules in synapses of the retina

Abstract: Using a new method, microtubules can be seen running up to, and lying in close relationship with, the synaptic ribbons in the outer and inner plexiform layers of the frog retina. In the inner plexiform layer microtubules can be seen running up to the terminal membrane in the non-ribbon synapses. Unlike non-ribbon C.N.S. synapses (frog and rat) processed by the same method, there is no clear association between synaptic vesicles and microtubules in the approach regions.

Prenatal development of Bergmann glial fibres in rodent cerebellum.

Abstract: The external granular and molecular layers in the foetal cerebellar cortex of mice and rats were examined by electron microscopy for the presence of Bergmann glial fibres. Morphologically distinct Bergmann fibres were observed at embryonic day E 15 in the mouse and at E 17 in the rat. Even at prenatal stages of development these fibres have a considerable degree of cytological differentiation which permits their identification as glial elements. The glial fibres contain numerous microfilaments, some smooth endoplasmic reticulum, a few mitochondria and scant free ribosomes. They penetrate the molecular and external granular layers radially and terminate with endfeet at the cerebellar surface. The proliferative cells of the external granular layer possess cytoplasmic processes which are oriented randomly, do not have endfeet, and are morphologically distinct from the Bergmann fibres with which they intermingle. In conclusion, immature Bergmann glial cells are present well before birth in the rodent cerebellum.

Neonatal neuronal loss in rat superior cervical ganglia: retrograde effects on developing preganglionic axons and Schwann cells.

Abstract: Beginning prenatally and during the first week after birth, there is normally a loss of axons in rat cervical sympathetic trunk. To test the hypothesis that this spontaneous axonal loss represents a natural process whereby an excessive number of immature preganglionic axons in the cervical sympathetic trunk adapts to the neuronal population in the superior cervical ganglion, the number of nerve cells in the superior cervical ganglion was reduced in newborn rats by administration of nerve growth factor antiserum, 6-hydroxy-dopamine or postganglionic axotomy. Quantitative ultrastructural studies of these animals at later stages of development revealed that, with each method, the number of preganglionic axons and Schwann cells was reduced to nearly one-third of normal. These findings indicate that the superior cervical ganglion plays an important role in the development of the cervical sympathetic trunk. Removal of ganglionic cells causes a retrograde loss of preganglionic fibres. This process probably represents an exaggeration of the normal mechanism for elimination of redundant axons. Because the changes in axonal numbers are associated with similar reductions in the number of Schwann cells, it can also be concluded that postnatal Schwann cell proliferation is influenced by axonal populations.

The ultrastructure of the sheath around chronically implanted electrodes in brain.

Abstract: Insulated, bipolar stainless steel electrodes were chronically implanted in various regions of the cat brain and the long-term structural changes in the tissue surrounding the electrodes were studied by light and electron microscopy. A sheath surrounded and separated the electrode from normal grey or white matter. A layer of foreign body giant cells of variable thickness was formed adjacent to the electrode. This layer was attenuated in some places so that it was unrecognizable by light microscopy. The bulk of the sheath structure consisted of collagen fibrils, leptomeningeal cells and hypertrophied astrocytes. Areas consisting of modified leptomeningeal cells with long thin processes we designated as spongy areas. These have not been previously reported using the electron microscope. Glycogen bodies were seen in leptomeningeal cells. Astrocytes became greatly enlarged and were more numerous in and around the sheath. Oligodendrocytes contained lamellar bodies, and direct continuity was shown between a lamellar body and an adjacent myelin sheath. Myelin was seen in abnormal sites (around oligodendrocytes and neurons) and in unusual configurations. Neuronal changes near the sheath included whorls and stacks of modified endoplasmic reticulum and the presence of cytoplasmic nucleolus-like bodies. Reactive, regenerative and degenerative axons were observed. Blood vessels were more numerous in the sheath and surrounding tissue than normal. Perivascular spaces were prominent even around capillaries and often plasma cells and monocytes were in these spaces. As compared to normal tissue the extracellular space is noticeably increased. Electrodes passing through ventricles were surrounded with a sheath covered with ependymal cells. This sheath was comparable in structure to the sheath present around the electrode in other locations.

Aspects of cortical organization related to the geometry of neurons with intra-cortical axons.

Abstract: Using the Golgi method, cells with intra-cortical axons in the visual cortex of young mice were classified according to defined geometrical axonal shapes. This study principally describes a computer technique and its application to the study of neuronal morphology. Neurons were converted in a sequence of three-coordinate points which were stored in digital form on magnetic tape. From the stored data and total real length in space of dendrites and axons was obtained and the results compared in two groups of mice raised under different conditions. Preliminary observations show short axonal lengths in mice raised in darkness. Using Eulerian coordinate transformations, reconstructions of individual neurons and of groups of several neurons and fibres were obtained by generating displays of different views after rotation around the horizontal axis. Reconstructed pictures were compared with their corresponding original drawings in order to describe particular aspects of cortical organization.

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. II. Terminations upon neuronal perikarya and dendritic shafts.

Abstract: The forms of dendrites in layer IV receiving degenerating thalamocortical axon terminals directly on their shafts were examined in serial thin sections. Reconstructions showed these dendrites varied in thickness between 2.5 and 0.5 μm. They had essentially smooth contours and rarely showed evidence of protrusions or spines. They were further characterized by the presence of many synapses along their shafts. Only about one in 12 of these synapses was formed by degenerating thalamocortical axon terminals. These smooth dendrites emerged from neuronal perikarya that also received degenerating axon terminals which formed asymmetric synaptic junctions. Such cell bodies bore both symmetric and asymmetric synaptic junctions, and not all of the latter were caused to degenerate after a thalamic lesion. These postsynaptic neurons appeared to be of two kinds, ones with thin dendrites that often contained closely packed microtubules, and others with thicker dendrites that emerged from the poles of oval perikarya.

Ventral horn synaptology in the rat.

Abstract: The synaptology of the normal ventral horn of the rat was studied. Presynaptic boutons were classified as S (spherical vesicles), F (flattened vesicles), and G (predominance of 700–1200 A granular vesicles). In addition, Cf, Cs, M, and T synaptic complexes were defined and quantitated. Synaptology was studied on α-motoneuron somata, α-motoneuron primary dendrites, peripheral dendrites and interneuron somata. In addition, organelles were quantified for the pre- and postsynaptic members of the synaptic complex. All counts were made on coded material and these data were analyzed statistically. Motoneuron somata had significantly more (P < 0.01) F (58%) than S (33%) boutons. This was also the case for the motoneuron primary dendrite (P < 0.01; F, 61%; S, 37%). The small dendrites had more (P < 0.05) S (56%) than F (44%) boutons. More Cf bulbs (P < 0.01) were found on motoneuron somata (9%) than on motoneuron primary dendrites (2%) or interneuron somata (3%). The C complex presynaptic bouton contained spherical (Cs) or flattened (Cf) synaptic vesicles which were attributed to the fixation employed. Cf bulbs were not observed on small dendrites. G bulbs were observed (< 1%) only on small dendrites. M bulbs were not observed on any postsynaptic structure. The boutons of the motoneuron primary dendrites (15% of total afferents) and peripheral dendrites (14% of total afferents) were frequently branched whereas there was significantly (P < 0.01) less branching of boutons on motoneuron and interneuron somata. Small postsynaptic subsurface cisterns were associated with boutons of both the S and F type on all structures. In addition, these cisterns were observed in motoneuron somata (4%) and interneuron somata (2%) without an accompanying bouton. C postsynaptic organelles were observed in motoneuron somata (3%) and primary dendrites (1%) with an overlying neuroglial cell process and no presynaptic bouton. The synaptology of the rat ventral horn is comparable to that in the cat and monkey. However, M (R) and P bulbs were not observed in the rat. This could be due to the sampling method which indicated that synapses with less than 1% occurrence fall at the level of statistical resolution in quantitative electron microscopy. The presence of postsynaptic specialization usually associated with presynaptic boutons with no presynaptic component may be a reflection of the dynamics of normal bouton renewal in the rat ventral horn.

Non-innervated sense organs of the lateral line: development in the regenerating tail of the salamander Ambystoma mexicanum.

Abstract: New lateral line organs (neuromasts) are formed in regenerating tails of the larvae of a urodele, the axolotl (Ambystoma mexicanum), even in the absence of the lateral line nerve, as confirmed by electron microscopic examination. The non-innervated organs are similar to normal innervated organs. The hair cells are polarized in opposite directions, and despite the lack of nerve endings, contain synaptic bodies, which in normal innervated organs are found in relation to afferent boutons.

Olfactory epithelium of Necturus maculosus and Ambystoma tigrinum.

Abstract: The morphological study presented here provides a general description of the elements of the olfactory epithelium in the mud puppy and tiger salamander, and gives evidence about their dynamic activity and interrelationships. There are morphological indications of local bursts of reduplication and a continual line of differentiation of receptor cells from basal cell progenitors through stages of mature development to senescence (indicated by the accumulation of pigment granules) and cell death and disposal (by expulsion of pycnotic cell nuclei and by phagocytosis by macrophages). The supporting cells probably play several roles: a secretory role which supplements the activity of Bowman's glands, a minor insulating role in which some dendrites are shielded from the surrounding milieu, and a skeletal role in which they facilitate the efficient displacement of dendrites. The dendrites are regularly arranged in organized relationships with one another and are for the most part in direct apposition, separated only by a 200 A intercellular gap, thus suggesting the possibility of functional interrelationships. This study emphasizes the fact that efficient planning of experimental investigations must include knowledge and consideration of the thickness of the particular olfactory epithelium under study. It also suggests that because of the large receptor-cell size, the mud puppy and/or tiger salamander would make good model systems for single cell recording. Further, the olfactory epithelia of these species are suggested as favorable targets for studies of the aging process in nerve cells.

On the occurrence of Schwann cells within the normal central nervous system.

Abstract: The presence of Schwann cells and P.N.S. myelin are reported in subpial areas of apparently normal spinal cord from one control rabbit, two experimental rabbits and one experimental guinea pig. These P.N.S. elements exerted no adverse effects upon local C.N.S. components. The occurrence of ectopic Schwann cells in the normal C.N.S. has also been reported elsewhere in studies on normal human spinal cord tissue. The propensity for Schwann cells to reside in the normal C.N.S. of several species makes it necessary for experiments and hypotheses on the aetiology of Schwann cell invasion into the abnormal C.N.S. to take the present phenomenon into consideration.

Junctional subsurface organs in frog sympathetic ganglion cells.

Abstract: Subsurface cisternae in frog sympathetic ganglion cells were studied and shown to have similar features to those of the C.N.S. A number of special features were, however, revealed by high resolution microscopy. Highly flattened subsurface cisternae occurred in close proximity to the ganglion cell membrane and formed structures comparable to gap junctions. These subsurface cisternae appeared to be elongated plates (about 0.3 × 2.5 μm) specifically restricted to the area of the ganglion cell membrane adjacent to nerve endings, although often with the intervention of a thin satellite sheath. Thus they have been termed here ‘Junctional subsurface organs’, although the nerve terminals opposing them did not show any synaptic specialization. The Junctional subsurface organ was often accompanied by closely arrayed endoplasmic reticulum and/or mitochondria. Where the Junctional subsurface organ intervened between plasma membrane and endoplasmic reticulum or mitochondria, faint particles appeared to traverse both sides and bridge the narrow spaces to the opposing plasma membrane and endoplasmic reticulum or mitochondria. The possible functional significance of the Junctional subsurface organs is discussed.

The fine structure of synapses in relation to the large spherical neurons in the anterior ventral cochlear of the cat.

Abstract: The fine structure of synapses in relation to the large spherical neurons, the principal neurons in the anterior ventral cochlear nucleus (AVCN) of the cat, was studied. Axo-somatic synapses were classified into three types based on their size and shape and the distribution of synaptic vesicles. Axo-dendritic synapses were also classified into three types with respect to synaptic contact, cytoplasmic densities associated with the pre- and postsynaptic membranes and the shape of the synaptic vesicles. Mossy fibre-like endings and preterminal axons containing dense-core vesicles were observed in this study. Serial or triadic synapses were also found in cat AVCN. We occasionally found a nematosome in the cytoplasm of the principal neuron.

Peripheral nerve glycoproteins and myelin fine structure during development of rat sciatic nerve

Abstract: Developmental changes in relative amounts of peripheral nerve proteins and glycoproteins have been correlated with the degree of morphological myelination at various ages during the first 25 postnatal days in rat sciatic nerve. At birth there is virtually no major myelin glycoprotein (P0), but there is a protein which migrates to the same point on sodium dodecyl sulphate (SDS) polyacrylamide gels as the small myelin basic protein (P2). During the time myelin is being formed in the nerve, the P0 protein increases and the P2 protein appears to decrease in relative amount in the nerve. The accumulation of P0 protein in the nerve correlates extremely well with the degree of myelination in sciatic nerve.

Ultrastructure of the terminals of an identified 5-hydroxytryptamine-containing neurone marked by intracellular injection of radioactive 5-hydroxytryptamine.

Abstract: The axons and terminal processes of an identified 5-hydroxytryptamine-containing neurone were located for study with the electron microscope. Tritiated 5-hydroxytryptamine was injected into the neurone's cell body, and after allowing time for the radioisotope to pass along the processes of the neurone, tissue was examined by electron microscope autoradiography. Terminal processes were observed at approximately 1 cm from the injected cell body, in areas of the nervous system where previous electrophysiological work had shown the presence of postsynaptic neurones. Dense-cored vesicles of mean diameter 100 nm were observed in the axons and terminal processes of the neurone. The terminal processes also contained aggregates of clear vesicles of mean diameter 65 nm. Structures resembling lysosomes, which were frequently labelled, were present in the axons of the neurone. No membrane specializations associated with typical synapses were observed.

The termination of thalamo-cortical fibres in the visual cortex of the cat.

Abstract: An electron microscopic study has been made of the site and mode of termination of thalamo-cortical fibres in area 17 of the visual cortex of the cat. Thalamo-cortical fibres had been selectively interrupted 4–5 days before perfusion of the brain. In agreement with previous studies, degenerating axon terminals were found in layer I, in the deep part of layer III, and in layer IV of the cortex. In addition, a few degenerating thalamo-cortical axon terminals were found making synapses upon spines and small dendrites in layer VI. Two examples were seen of degenerating axon terminals making axo-dendritic synapses upon dendrites in continuity with their cell bodies. These neurons were not large stellate cells and were probably pyramidal.

The effect of the local anaesthetic bupivacaine on the muscle spindle of rat.

Abstract: The effects of a long-lasting local anaesthetic, bupivacaine, in combination with hyaluronidase, on the intrafusal muscle fibres of adult rat muscle spindles have been investigated by light and electron microscopy. Necrotic changes in the axial bundle are present within 4 h of the combined drug injection and are widespread by 2 days. The equatorial nucleation of the spindle is lost owing to the necrosis of the myonuclei. Satellite cells, however, appear to survive these changes, even where the underlying muscle fibres are grossly necrotic. Sensory nerve terminals undergo necrosis during this period and plate-type fusimotor nerve terminals withdraw from the degenerating muscle fibres. Macrophage infiltration and early regeneration of the axial bundle is apparent by the third day. Myoblasts first appear at the periphery of the affected muscle fibres, but decrease in number as regeneration proceeds. By the end of the third week, regeneration of the muscle component is complete and re-innervating fusimotor nerve terminals established. The encapsulated regions of the spindle remain abnormal, without recognizable bags or chains of nuclei, although the muscle fibres differ both in size and ultrastructure. Regenerating sensory axons make contacts with the intrafusal bundle that differ in their configuration and ultrastructure from normal terminals. The production of enucleated spindles is discussed in the light of the morphogenetic influences of the spindle nerve terminals, as well as the possible use of such a model in discovering the function of nuclear bags and nuclear chains.

Electron microscopic observations of the mesencephalic nucleus of the fifth nerve in the Selachian brain.

Abstract: The mesencephalic nucleus of the trigeminal nerve (mes V) in the brain of the skate (Raja oscellata) was studied by electron microscopy. Mes V neurons are large (40–80 μm diameter) and are located in the periventricular grey matter. Their perikaryal cytoplasm is rich in Golgi apparatus, small mitochondria, rough endoplasmic reticulum, polysomes and bundles of neurofilaments. A striking feature is the presence of masses of glycogen granules, at times surrounded by membrane wrappings and lysosomal bodies.