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PubMed1979

Tangential orientation and spatial order in dendrites of cat auditory cortex: a computer microscope study of Golgi-impregnated material.

In the tangential plane (parallel to the pial surface) dendrites in the primary auditory cortex (A1) of cat were found to exhibit preferentially oriented growth. This was shown by means of a computer microscope study of Golgi-Cox stained neurons as seen in 100 micrometers and 300 micrometers thick tangential sections. Two techniques were used to represent the 3-dimensional structure of dendrites: the "dendritic stick" and the "dendritic trumpet". The former dismembers a dendrite into its individual segments; the latter considers a dendrite as an entity and represents it by its centroid, its moments and the spatial dispersionof its branches. Both statistical and Fourier analyses of the data show that within the tangential plane there is a significant and consistent orientation of the dendritic sticks in a dorso-ventral direction which seems correlated with the cortical isofrequency contours observed in electrophysiological maps of the A1 region. The dendritic trumpet analyses also show a distinctly non-random vertical distribution of pyramidal cell basal dendrites but not of stellate cell dendrites.

Animals↗

PubMed1975

Motoneuron dendrites: role in synaptic integration.

Dendrites constitute over 80 per cent of the receptive surface area in cat motoneurons. Calculations based on matched electrical and gemoetrical measurements in these neurons indicate that the specific resistance of dendritic membranes in resting motoneurons is at least 2,000 ohm-cm2. When the specific membrane resistance is this high, even the most distal dendritic synapses can contribute significantly to the depolarization of the soma, and hence influence the rate of action potential generation. However, dendritic membrane resistance depends strongly on the level of background synaptic activity. The conductance changes associated with excitatory synaptic activity on a dendrite can be great enough to reduce significantly both the excitatory synaptic driving potential and the effective membrane resistance on that dendrite, and thus greatly reduce the effectiveness of synapses on the dendrite. Inhibitory synaptic activity produces an even greater reduction in dendritic membrane resistance. Thus the relative effectiveness of dendritic synapses depends on the type, distribution, and intensity of background synaptic activity, as well as on dendritic geometry and resting membrane properties.

Action Potentials↗

PubMed1979

A raphe dendrite bundle in the rabbit medulla.

A Golgi-Cox, histofluorescence, and electron microscopic examination of the serotonergic raphe nuclei of the rabbit medulla has revealed a large, vertically-oriented midline dendrite bundle extending from the floor of the fourth ventricle to the ventral boundary of nucleus raphe pallidus. The bundle was confined to the medulla, and averaged 150-200 micrometer in width in the adult. This dendrite bundle received contributions from four major sources: (1) Dendrites of midline and paramedian neurons of nucleus raphe obscurus; (2) Dendrites of midline and paramedian neurons of nucleus raphe pallidus; (3) Shafts from tanycytes located on the midline floor of the fourth ventricle; and (4) Dendrites from neurons of the medullary reticular formation. Perikarya and dendrites of serotonergic raphe neurons frequently abutted tanycyte shafts, midline bhood vessels, and perikarya and dendrites of other raphe neurons. The tanycyte shafts extended from the floor of the fourth ventricle into the bundle, and often ran the entire length of the bundle, where they intertwined themselves among neurons and dendrites of the medullary raphe nuclei. This study suggests that neurons of the medullary raphe may be influenced by communication channels including dendro-dendritic contacts within the midline bundle, fourth ventricular cerebrospinal fluid-borne influences through tanycyte shafts, blood-borne influences through the direct neuronal-vascular relationship in the raphe, and traditionally described axonal contacts impinging upon raphe neurons. We suggest that the raphe neurons might act as both neurons and endocrine-neural transducer cells.

Animals↗

PubMed1979

Golgi studies on Purkinje cell development in the frog during spontaneous metamorphosis. II. Details of dendritic development.

The development of Purkinje cell dendrites was studied in the bullfrog from premetamorphic tadpoles to 10-week-old postmetamorphic frog-lets by the Golgi-Kopsch method. In this species two distinct patterns of arbor formation may be seen, which appear to be related to differences in the timing of initial dendritic development. In Purkinje cells that begin development in early tadpole stages, the dendritic tree is elaborated by continuous and concomitant growth and branching, a process by which the developing arbor expands in both height and width. Arbor formation in Purkinje cells that begin development in metamorphosing tadpoles proceeds in two separate steps. Initially, dendrites of such cells elongate, but form only a few poorly developed branches; only when the arbor reaches near-adult height does branching become extensive. Additional differences present in Purkinje cells are reflected in the paucity of growth cones and filopodia in the tadpole, and numerous filopodia and growth cones in the metamorphic period. An interesting feature of dendritic development in this species is a tendency to alter the arboreal domain by the formation of extra-arboreal dendrites, and possibly by the occasional resorbtion of other partially formed dendrites. The pattern of dendritic development in the frog is different than in mammals and is difficult to interpret. Such unusual development may be due to disturbances in the timing of the formation of Purkinje cell dendrites and of the establishment of the external granular layer (EGL).

Animals↗

PubMed1979

Morphometrical synaptology of Clarke cells and of distal dendrites in the nucleus dorsalis: an electron microscopic study in the cat.

The fine structural synaptology of large Clarke cells in L3 has been investigated from a morphometrical point of view in both normal and adult cats which received horseradish peroxidase (HRP) injections in the cerebellum. This marking method made it possible to distinguish small or distal dendrites of large Clarke cells from those of interneurons and the marginal cells of Clarke's column. A total of 1036 boutons was observed on the perikarya of 21 large Clarke cells; 81.9% (848/1036) were small-sized boutons, the cross-sectional areas of which ranged between 0.3 and 2.9 sq. micrometer, while 18.1% (186/1036) were giant boutons ranging between 3.0 and 8.0 sq. micrometer. From 1075 boutons on 17 primary dendrites of Clarke cells, 72.4% (778/1075) were small-sized boutons and 27.6% (297/1075) were giant boutons. From 1679 boutons contacting 366 distal or small HRP-labeled dendrites, 89.9% (1507/1679) were small boutons and 10.1% were giant boutons. The giant boutons were more frequently located on the proximal dendrites than on the cell bodies or small distal dendrites of Clarke cells. The proportion of S- and F-type boutons was different in 3 parts of large Clarke cells. F-type boutons were more frequent on soma (55.0% 570/1036) and primary dendrites (59.4%, 635/1075). S-type boutons outnumbered the F-type on small or distal dendrites (62.6%, 1952/1679). The S/F ratio seemed to increase from the cell body toward the distal dendrites. The results suggest that Clarke cells receive predominantly small S-type boutons since the total receptive area of the dendrites is supposed to exceed that of the cell body.

Animals↗

PubMed1978

Dendritic atrophy in the dentate gyrus of the senescent rat.

Quantitative electron microscopic analysis of the supragranular zone of the dentate gyrus molecular layer has shown that the number, volume fraction and surface area of dendritic shaft profiles are significantly decreased in senescent rats, relative to young adults. These modifications of dendritic morphology, which are not associated with age-related changes in dimensions of the molecular layer or in numbers of granule cells, may result from a decrease in the number and/or length of dendrites. In either case, the decreases in the number, volume fraction and surface area of dendritic shaft profiles found in the dentate gyrus of senescent rats signify an age-related atrophy of dendrites. Comparison of changes in the number and volume fraction of dendritic shaft profiles has demonstrated that age-related dendritic atrophy involves predominantly dendritic branches.

Aging↗

PubMed1976

The facial motor nucleus of the opossum: synaptic endings on dendrites.

The diameters of dendrites of large, medium and small neurons (Falls and King, '76) were measured from Golgi impregnations of the opossum facial motor nucleus in order to classify dendritic profiles sectioned in the transverse plane in electron micrographs. Three categories of dendrites are described: (1) proximal (4-7 mu in diameter); (2) intermediate (2-4 mu in diameter) and (3) distal (0.5-2 mu in diameter). The distribution of axodendritic synaptic endings was determined, recognizing that the neuronal source of individual dendritic profiles when seen in the transverse plane of section cannot be absolutely determined in view of the overlap in size of the dendrites issuing from the three types of neurons. Presynaptic terminals were categorized according to vesicle shape (spherical, pleomorphic or ellipsoidal), vesicle size, terminal size, junctional characteristics and post synaptic distribution. The vesicle size is expressed as a mean area (nm2) and was determined by using a cybergraphic tablet and a PDP-12 computer system. In any given plane of section, synaptic terminals cover most of the membrane of proximal dendrites and decrease in number as intermediate and distal dendrites are encountered. In Golgi impregnations four classes of afferent fibers which ramify among the dendrites of facial neurons can be distinguished. As yet, their sources have not been identified. Possible sites of origin for presynaptic profiles are discussed in the context of previous light microscopic findings.

Animals↗

PubMed1977

Dendritic spread of dorsal horn neurons in cats.

Observations of neurons in dorsal horn laminae IV-VI of the lumbosacral segments of Golgi-stained spinal cords in kittens and adult cats revealed laminar differences in dendritic architecture. Many neurons in lamina IV had dense, bushy dendritic fields. Lamina V contained, in addition to bushy cells similar in appearance to those of lamina IV, increasing numbers of neurons with radiating dendritic fields. Lamina VI was composed almost exclusively of neurons with radiating dendritic fields. These qualitative differences among laminae were accompanied by systematic variations in mean dendritic spread, which increased more than two-fold in adult cats between laminae IV and VI. A second gradient of dendritic spread was found within individual laminae: dendritic spread, particularly medial to lateral spread, increased for successively more lateral cells within a lamina. These differences in the spread of dendrites for neurons in different regions of the dorsal horn may be related to variations in the areas of peripheral receptive fields of dorsal horn neurons.

Age Factors↗

PubMed1979

Dendritic spikes in Purkinje cells of the guinea pig cerebellum studied in vitro.

Extracellular spikes were recorded simultaneously from dendrites and somata of Purkinje cells in thin cerebellar sections. Spontaneously occurring dendritic spikes were biphasic with the initial phase positive. Triphasic dendritic spikes with a large negative phase appeared during electrophoretic application of glutamate. In media containing procaine, tetrodotoxin, or high concentrations of KCl, negative dendritic spikes occurred whereas soma spikes were abolished. The negative dendritic spikes were suppressed by CoCl2 or MnCl2. Electrical stimulation elicited climbing fibre responses in somata and large negative waves in dendrites. Spikes of dendritic origin were different from those reflecting electrotonic spread of soma spikes. The relation between soma spikes and active dendritic spikes is discussed.

Animals↗

PubMed1977

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. IV. Terminations upon spiny dendrites.

The forms of the spiny dendrites in layer IV receiving degenerating thalamocortical axon terminals have been examined in serial thin sections. Reconstructions of segments of these dendrites show that the axon terminals synapse with both the dendritic spines and the dendritic shafts. No main shafts of apical dendrites of pyramidal neurons were found to synapse with the thalamic afferents, which are received mainly by spiny dendrites 1-2 micron in diameter, at least some of which appear to be the oblique branches of apical dendrites. The forms of these postsynaptic dendrites are so variable that is concluded they arise from more than one morphological type of neuron. The conclusion based on this and previous articles in the series is that most neuronal elements in layer IV which form asymmetric synaptic junctions are potential recipients of the thalamocortical afferents.

Animals↗

PubMed1978

Gap junctions between dendrites and somata of neurons in the primate sensori-motor cortex.

Gap junctions have been found infrequently between two dendrites or a dendrite and a cell soma in the deep layers of both the motor and somatic sensory cortices of the primate. At these junctions the outer leaflets of the plasma membranes of both profiles are intimately apposed with a gap of 2 nm between them which shows a structure of hexagonal subunits in tangential sections. These gap junctions occur mainly between the dendrites or dendrites and somata of large stellate cells but are also associated in some examples with a dendro-dendritic synapse and thus occur between large stellate dendrites and presynaptic dendrites; a desmosome may also occur in association with a gap junction and dendro-dendritic synapse. Gap junctions have been identified as sites of electrical transmission between cells in a number of sites and it is therefore suggested that some neurons in the sensori-motor cortex are electrotonically couples.

Animals↗

PubMed1977

Rapid dendritic atrophy following deafferentation: an EM morphometric analysis.

The nucleus laminaris (NL), a third-order brain stem auditory nucleus in birds, receives afferents to its dorsal dendrites from the ipsilateral nucleus magnocellularis (NM), while the ventral dendrites of NL neurons are innervated by axons from the contralateral NM via the crossed dorsal cochlear tract (CTrX). The CTrx was transected in young chickens and, 96 h later, NL was examined for cytological changes. A morphometric analysis of electron micrographs from lesioned and shamd axon terminals were localized almost entirely to the ventral neuropil region of NL. (2) The volume density of dendrite in the ventral region of NL of lesioned animals was reduced by 85% compared to both the dorsal dendritic region of the same animals and the ventral dendritic region of sham-operated control animals. (3) The frequency with which primary dendrites were encountered in the ventral neuropil of lesioned animals was 81% lower than sham-operated controls. (4) Frequently, there was an apparent reduction in the amount of rough endoplasmic reticulum, Golgi apparatus and cytoplasmic granularity in the deafferented part of the NL neurons. (5) The data indicate that the cytological integrity of dendritic processes cna be specifically, profoundly and very rapidly compromised by removing a significant proportion of their afferents, suggesting that a tonic influence may be exerted by the presynaptic terminals.

Animals↗

PubMed1977

Synthesis and transport of newly formed proteins in dendrites of rat hippocampal pyramid cells. An electron microscope autoradiographic study.

The synthesis and transport of newly synthesized proteins in dendrites of rat hippocampal pyramid cells were investigated. Labelled leucine was injected into the left lateral ventricle and the hippocampal region was processed for light and electron microscopic autoradiography. To differentiate between the silver grains originating from 'sedentary' or 'migratory' proteins, the radioactivity in dendritic areas free of ribosomes and rich in ribosomes was determined separately. Several conclusions were reached. (1) Protein synthesis in dendrites takes place mainly in the proximal parts although a slight synthetic activity can be observed along the whole dendritic tress as well. (2) Newly synthesized proteins are transported toward the distal dendritic region; the data obtained suggest that cisterns of the smooth endoplasmic reticulum and the microtubular system may be involved in this transport. (3) Two phases of dendritic transport may be distinguished; a fast phase with a rate of 100-200 mm/day and a slow phase with a rate of 2.8-10 mm/day. It also seems probable that the majority of the proteins newly synthesized in dendrites are transported by the slow phase.

Animals↗

PubMed1979

Postnatal dendritic development in the rabbit visual cortex.

Golgi preparations of rabbit visual cortex aged 1-25 days, as well as similar tissues from adults, were examined for the growth of the dendritic arbor, and in particular the development of dendritic spines. The layer 5 pyramidal neurons and layer 4 stellate neuron were chosen as representatives of larger classes of neurons in the visual cortex. It was determined that the growth of the dendritic arbor, determined by counts of total number of dendritic and total dendritic length, is quite similar for pyramidal and stellate neurons. Dendritic spine development, however, is more rapid in pyramidal neurons than in stellate. This disparity in the rate of dendritic spine development is discussed in the light of physiologic studies on the development of receptive field properties in the rabbit visual cortex.

Age Factors↗

PubMed1979

Distribution of thalamic input to different dendrites of a spiny stellate cell in mouse sensorimotor cortex.

A Golgi impregnated, gold-toned [2] spiney stellate cell from layer IV of mouse SmI cortex was reconstructed in three dimensions from serial thin sections to assess the apatial relationships of the synapses onto its dendrites. The distribution of thalamocortical (TC) synapses with the reconstructed dendrites is presented in this report. Thalamocortical axon terminals were labeled by lesion induced degeneration which, in mouse SmI cortex, may reliably indicate the numbers of thalamocortical axon terminals. Results indicate that thalamocortical synapses, which are distributed over most regions of the dendritic tree, are arranged in a regular, periodic fashion on parts of two of the reconstructed dendrites. In these regions, the necks of spines receiving thalamocortical input attach to the dendrite shaft at intervals of about 5 micrometers. In many other regions of the dendritic tree, two spines receiving thalamocortical synapses are separated by a similar interval. Further studies are expected to determine the extent to which dendrites of spiny stellate cells and of other kinds of cortical neurons are contacted in a periodic fashion by thalamocortical axon terminals.

Animals↗

PubMed1978

Light and electron microscopic investigation of the sensory dendrites in the epidermis of the foot of the snail, Helix pomatia L.

The fine structure of epithelial cells, supporting cells and the sensory dendrites running toward the surface between the former two was investigated in the epidermis of the foot of Helix pomatia. Cilia orienting in regular lines and possessing 9 + 2 tubular structure occur on the surface of the cylindrical epithelial cells lying on the basal lamina. The cilia terminate in basal bodies. The epithelial cells can first of all be characterized by a well-developed Golgi-apparatus and endoplasmic reticulum system as well as a developed tonofibrillar system. The supporting cells differ from the epithelial cells mainly in the poorly-developed tonofibrillar system and small number of cilia. Septate desmosome and zonula adherens are the common connecting structures between the cells composing the epithelium. According to the surface specialization, two types of sensory dendrites running toward the surface were distinguished: dendrites with and dendrites without cilia. On the surface of the former cilia with 9 + 2 tubular structure are randlomly distributed and are present in varying number. In their cytoplasm there are many mitochondria, few clear vesicles and multivesicular bodies. From the surface of the dendrites without cilia, microvilli of different diameter originate and sometimes a centriole was observed below the distal membrane. Their cytoplasm contains many clear vesicles, a well developed smooth endoplasmic reticulum system and few mitochondria. Comparing our results with literary data, we suppose that the differences between the two dendrite types in the presence and number of cilia as well as in the diameter of the microvilli show different forms of appearance of one type of dendritic terminal.

Animals↗

PubMed1978

Retinal ganglion cells in the crucian carp (Carassius carassius). II. Overlap, shape and tangential orientation of dendritic trees.

Ganglion cells were studied in methylene blue stained flat-mounted retinas. Three categories of cells are described: small (S) and large (L) ganglion cells in the main ganglion cell layer, and large ganglion cells (LD) with somata more or less displaced into the inner plexiform layer. These LD cells have two to four very thick primary dendrites and are identifiable as ganglion cells by their axons. An analysis of published data reveals that the large ganglion cells of the crucian carp (type L and LD) have several striking characteristics in common with the large ganglion cells of the dogfish, the frog and the cat: (1) they are selectively stained by methylene blue; (2) they comprise only 2-5% of all the ganglion cells; (3) the large cells can be divided into two or three subtypes, and within each subtype the dendritic trees usually cover the retinal surface with a two- or threefold overlap. New ganglion cells are formed from neuroblasts at the retinal margin and most dendrites first grow along this neuroblastic zone. Thus the main dendrites of the L and LD cells tend to be oriented parallel to the margin all around the periphery of a crucian carp retina. Independent of the size of the eye this parallel orientation disappears at the same relative distance from the margin (about one-third of the distance from the margin to the optic disc). If all L and LD cells are formed at the retinal margin and first develop oriented dendrites, we have to assume that the more randomly oriented dendritic trees in the central retina have undergone a reorganization.

Animals↗

PubMed1977

Methylazoxymethanol-induced aberrant Purkinje cell dendritic development.

Purkinje cell dendrites develop with a specific orientation and relationship to related neurons and glia. Their dendritic spine postsynaptic membrane specialization may, in turn, require a permanent presynaptic contact by parallel fibers. To determine whether changes in the surrounding cells influence the normal development of the cerebellar Purkinje cell dendrites and spine specializations, destruction on the differentiating cell layer was induced in the postnatal mouse by administration of methylazoxymethanol acetate (MAM) (0.05 micronl/gm body weight) at day zero. The Purkinje cells were examined by light and electron microscopy on the tenth postnatal day. The midsagittal surface area of the cerebellar vermis in treated animals was reduced by an average of 60%. MAM-induced granule cell depletion and Purkinje cell dislocation were observed by light microscopy. When compared to controls, examination following Golgi impregnation revealed random orientation of Purkinje cell apical poles, and multiple primary dendrites of reduced length with few branches, branchlets and spines. Vertical processes of Golgi epithelial (Bergmann) cells were obliquely directed, reduced in length and complexity in MAM-treated mice. Ultrastructural examination revealed naked Purkinje cell dendritic spine specializations in both groups. Although necrotic debris persisted in astrocytes and macrophages, degenerating presynaptic terminals were not found. This study suggests that permanent presynaptic contact by parallel fibers is not essential for spine development. Astrocytic reactions to injury, in association with the reduced folial expansion, may have contributed to the observed abnormalities and disorientation of the Purkinje cells. The data suggests that Purkinje cell dendritic development may be strongly influenced by changes in surrounding cells.

Animals↗