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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↗

PubMed1976

[Quantitative studies on the dendritic spine distribution on the lamina-5 pyramidal cells in the anterior gyrus cinguli of the rat].

At three months old male rats the spine-distribution of the main dendrite and of the apical and basal dendrites of 36 lamina V-pyramidal cells of the regio cingularis (anterior cingulate cortex) was analyzed (from every subregion -- neocortex, mesoneocortex, mesoarchicortex -- 12 neurons). 1. The limbic pyramidal neurons show the same spine-distribution at their main dendrite as neocortical neurons of other brain regions and other mammal-species do: after an initial segment with poor spines only there follows an rapid increase of the spine-values with an amount at a range of 150 mum from the perikaryon, thereafter spine-values decrease continuously and slowly up the branching into the terminal bundle. 2. Basal and apical lateral dendrites however show another spine-distribution: basally there is an increase of the spine-values from the 1st up to the 3rd order, followed by a decrease at subsequent orders. Apically spine-density decreases from the 1st up to the 4th order. 3. The spine-distribution at the parts of the dendritic tree is discussed as a general biological sign of pyramidal cells. 4. The total number of spines of lamina V-pyramidal cells in the regio cingularis (anterior cingulate cortex) is less than those in the sensomotoric cortex and in the hippocampus, which corresponds with the lower differentiation of the limbic cortex. 5. By means of a variance-analysis the pyramidal spine-values of the three subregions were compared: concerning the total number of spines of a pyramidal neuron there are significant differences between the three subregions; the values are in the ratio of 3 to 2 to 1 (Regio praecentralis agranularis, 2461; mesoneocortex, 1664; mesoarchicortex, 800). The significantly least spine-density of all parts of the dendritic tree you can find in lamina V-pyramidal cells of the mesoarchicortex. 6. The equality of the basal and apical spine-values in the mesoneocortex is due to less specialization of these neurons. 7. The spine-values for a single dendritic field (EDF) show the differences between the limbic subregions clearly: there are significant differences between the three subregions concerning not only the number of spines but also the spine-densities apically and basally.

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↗

PubMed1978

Dendro-dendritic and reciprocal synapses in the primate motor cortex.

Dendro-dendritic synapses have been observed infrequently in the deep layers of the motor cortex. The presynaptic dendrites are of a varicose type and themselves receive a considerable density of synapses both of the asymmetric and symmetrical type. The ultrastructure of the dendro-dendritic synapse itself shows the typical arrangement of presynaptic and postsynaptic membrane densities, often with presynaptic dense projections, and the membrane specialization is of the symmetrical type. There is the usual cleft containing electron-dense material between the presynaptic and postsynaptic profiles. The synaptic vesicles occur in a small cluster confined to a region close to the presynaptic membrane specialization; some of the vesicles are flattened and were shown by tilt analysis to be of the discoid type. Two examples were found of reciprocal dendro-dendritic synapses, both components being of the symmetrical type. A single axon terminal may make a synapse on to both dendrites involved in a dendro-dendritic synapse.

Animals↗

PubMedDate not supplied

The effects of postnatal lead exposure on Purkinje cell dendritic development in the rat.

Rat pups, suckled by mothers maintained after parturition on a diet containing 4% lead acetate, were killed at 30 days and their cerebella examined. The blood lead was greatly increased in these animals (258.20 +/- 6.72 micrograms/100 ml) as compared with controls (4.75 +/- 0.75 micrograms/100 ml) and their mean body weight was reduced by 28%. Cerebellar weight, however, remained unchanged. Histologically the vermis showed vacuolation of the white matter and an increase in the size of Purkinje cell bodies. The total number of Purkinje and granule cells and their densities were unchanged except in animals with encephalopathy when these parameters were reduced. Network analysis of the dendritic trees of Purkinje cells indicated a 34.8% reduction in total dendritic length, due to reduction in total segment number and in the length of distal segments. Dendritic density and the frequency of trichotomous branching were unchanged by the experimental treatment. The density of dendritic spines over the periphery of the network was normal. The topology of the dendritic trees of Purkinje cells was abnormal in that branching patterns deviated from the normal pattern generated by random terminal growth. These results suggest that lead causes changes in Purkinje cell metabolism which reduce the rate of dendritic growth and cause abnormal branching. It remains to be determined whether these are direct effects or secondary to the vascular changes known to occur in the cerebellum during lead intoxication.

Animals↗

PubMed1975

Vestibular nystagmus and teleost oculomotor neurons: functions of electrotonic coupling and dendritic impulse initiation.

1. Nystagmus in the horizontal plane is evoked in fish by mechanical stimulation of the ampulla of the horizontal semicircular canal or by electrical stimulation of the nerve from this canal. The movements are conjugate and the slow phase is away from the side of stimulation. 2. Medial rectus motoneurons were recorded from intracellularly, during nystagmus. During the slow phase (induced by ipsilateral stimulation), impulses arise abruptly from the base line and appear to arise at a distance from the cell body. During the fast phase (evoked by contralateral stimulation), impulses appear to arise from large PSPs that must be generated at or near the cell body. 3. In the curarized fish, stimulation of the nerve from the contralateral horizontal canal evokes spikes that arise from large EPSPs and that are blocked relatively easily by hyperpolarizing currents. Stimulation of the nerve from the ipsilateral horizontal canal evokes spikes that arise abruptly from the base line and that are much more difficult to block by hyperpolarizing currents. Little if any underlying PSP is observed when these impulses are delayed or blocked. Thus impulses evoked by stimulation of contralateral and ipsilateral side are initiated near to and far from the cell soma, respectively. 4. If impulses evoked by contralateral stimulation fail to excite the cell body due to injury, antidromic spikes are not occluded. Thus contralateral stimulation initiates impulses in the dendrites. 5. Cell bodies of neighboring motoneurons are coupled electrotonically, and graded antidromic stimulation evokes graded depolarizing potentials which result from electrotonic spread of spike activity from adjacent neurons. These depolarizing potentials are adequate to excite the cells in the presence of a background EPSP evoked by contralateral canal stimulation. In this manner coupling tends to synchronize cells during the fast phase of the nystagmus. 6. Antidromic responses of neighboring cells fail to interact with dendritic inputs to a particular cell, although indirect evidence indicates antidromic spikes invade the impulse-initiating regions in the dendrites. Thus coupling between dendrites is negligible and dendritic inputs can mediate the smoothly graded movements of the slow nystagmic phase. Coupling between somata is too weak to cause significant interaction between dendritically evoked impulses (unless the cell bodies are depolarized by EPSPs). 7. Rhythmic firing can be recorded in a single presynaptic fiber corresponding to either the slow or the fast phase of nystagmus, but not to both. Oculomotor neurons appear to be "relay cells" that, during the fast phase of the nystagmus receive a synchronized synaptic input which is initiated in a higher level command nucleus.

Animals↗

PubMed2026

Myeloid Dendritic Cell Counts and Coronary Heart Disease: a Bidirectional Mendelian Randomization Study.

BACKGROUND: Coronary heart disease (CHD) remains a leading cause of morbidity and mortality worldwide, with immune and inflammatory mechanisms playing important roles in its pathogenesis. Dendritic cells (DCs) are key regulators of immune responses; however, the relationship between specific DC subsets and CHD risk remains incompletely understood. METHODS: This study conducted a bidirectional two-sample Mendelian randomization (MR) analysis using publicly available genome-wide association study (GWAS) summary statistics to investigate the potential associations between circulating dendritic cell traits and CHD. Genetic instruments for myeloid dendritic cells (Myeloid DCs) and plasmacytoid dendritic cells (Plasmacytoid DCs), including both absolute counts and relative proportions, were obtained from immune cell GWAS datasets. Summary statistics for CHD were derived from a large European-ancestry population. Multiple MR methods were applied, and sensitivity analyses were performed to assess the robustness of the findings and potential pleiotropic effects. RESULTS: Nominal associations between genetically predicted Myeloid DC counts and CHD risk were observed in the MR-Egger and weighted median analyses, whereas the inverse variance weighted analysis demonstrated no significant association. These nominal associations did not remain statistically significant after correction for multiple testing. No significant associations were observed for Plasmacytoid DC counts or for the relative proportions of either DC subset. Reverse MR analyses were inconclusive due to wide confidence intervals, precluding meaningful inference regarding a causal effect of CHD on DC-related traits. Sensitivity analyses revealed no substantial heterogeneity or horizontal pleiotropy. CONCLUSIONS: This bidirectional MR study explored the potential relationships between circulating dendritic cell traits and CHD risk. Although nominal associations involving Myeloid DC counts were observed in secondary MR analyses, no robust evidence supporting an association remained after correction for multiple testing. Further studies using larger datasets and functional approaches are warranted to clarify the role of dendritic cells in CHD.

Humans↗

PubMed1979

Scanning and transmission electron microscopy of intraventricular dendrite terminals of hypothalamic cerebrospinal fluid contacting neurons in Triturus vulgaris.

A scanning (SEM) and transmission electron microscopic (TEM) study of the ventricular wall of the hypothalamus of Triturus vulgaris was performed with special regard to the intraventricular dendrite terminals of the cerebrospinal fluid (CSF) contacting neurons of the preoptic area (magnocellular and parvocellular preoptic nuclei), the infundibular lobe (anterior periventricular nucleus, infundibular nucleus), and the paraventricular organ. In the preoptic area and infundibular lobe, the terminals were knob-like or club-shaped, of various sizes (diameter about 0,5 to 3,0 micrometer) and located immediately above the ependyma. Ultrastructurally, they may contain dense-core vesicles of varying sizes. The CSF contacting dendrite endings of the paraventricular organ built up a supraependymal labyrinthic layer which could be divided into a rostral crest-like part and a caudal flat and broad division. In both parts, three main types of terminals of various size and shape could be distinguished: a) ramifying, b) elongated, and c) bulb-like dendrite endings which also differed by their TEM structure. The bulk-like terminals, first of all the small ones, originated from the distal part of the nucleus of the organ (nucleus organi paraventricularis) while the other two types took their origin from its intra- and subependymal part. In all areas investigated, each intraventricular dendrite ending gave rise to a solitary cilium (type 9 X 2 + 0). It differed from the ependymal kinocilia by both SEM and TEM characteristics. In the paraventricular organ, the neuronal cilia were hidden inside, or below the supraependymal layer of terminals. There were intraventricular axons which formed synapses on CSF contacting dendrite endings of both parts of the paraventricular organ. Free intraventricular neurons, further ependymal areas heavily or scarcely ciliated, were described. The CSF contacting dendrite terminals were predominantly present near ventricular recesses and in regions where the ependyma was scarcely ciliated.

Animals↗

PubMed1978

[Ultrastructure of the dendrites of neurons of the brain stem reticular formation in acute hypoxic hypoxia].

In 45 adult rats (Wistar strain) neuronal dendrites of the reticular formation were studied electron microscopically at an acute hypoxic hypoxia. Structural changes in neurons of the reticular formation, were demonstrated to begin, as a rule, in the terminal portions of the dendrites. Dystrophic and destructive changes in dendrites are always more pronounced than in the pericaryon and are not infrequently they terminate in destruction of cytoplasmic islets. Submicroscopic changes in the dendrites are classified according to the dynamics of their development. Taking into consideration a specific role of the neuronal dendrites of the reticular formation under certain physiological conditions, it is possible to conclude that dendritic damage is of major importance in functional disturbance of the reticular formation at hypoxic hypoxia.

Acute Disease↗

PubMed1978

Effects of dark rearing on dendritic spines in layer IV of the mouse visual cortex. A quantitative electron microscopical study.

The effect of visual deprivation on dendritic spines in the visual cortex layer IV of 19 days old mice was studied with the electron microscopy. From the serial ultrathin sections of the selected dendrites bearing spines the author has calculated the volume and surface area of dendritic spines, and also the surface area of their synaptic zones. Employing statistical methods he has demonstrated that visual deprivation produced a retarded development of some dendritic spines in dark reared mice. The fact that the smallest dendritic spines cannot be seen with the light microscope while the number of such small spines is larger in the dark reared mice can well explain the apparent reduction in the number of dendritic spines in deprived animals studied in Golgi impregnated material.

Animals↗

PubMed1979

A quantitative investigation of spine and dendrite development of neurons in visual cortex (area 17) of Macaca nemestrina monkeys.

In a previous Golgi study (Lund et al., '77) which examined the development of the macaque monkey striate cortex (area 17) it was observed that the dendrites of neurons within the visual cortex show a marked increase in the number of spines on their surface during the first eight weeks of postnatal life. The qualitative observation was also made that all neurons then showed a marked decrease in spine numbers by the time the animal was adult. Since these spines are known to be sites of synaptic contact, changes in their numbers may reflect changes in synapse populations on these neurons. This study examines quantitatively spine frequency and total dendritic development of Golgi impregnated neurons in monkeys ranging in age from 145 days gestation to adult. Four cell types were studied: spiny stellate neurons from laminae IVCalpha and IVCbeta and pyramidal neurons with soma in either lamina IIIB or upper lamina VI. After consideration of possible sources of variation in spine numbers several conclusions are made: (1) Dendritic spine development appears to be a tightly controlled process both in terms of actual numbers of spines on a neuron at any one age and in the rate of change of spine frequency. (2) The neurons populations examined all show a gradual increase in spine numbers up to eight weeks of age. (3) At least two different trends are found in spine population maturation after the eight week point: (A)-the spine population may remain constant at the eight week level for same period of time or (B)-there may be a rapid decline in spine numbers following the eight week peak. (4) There is a suggestion that those neurons associated with direct input, or early stages in the relays, from the parvocellular geniculate laminae show trend B, while those associated with magnocellular input, or later order combined relays within the cortex, show trend A. (5) Different parts of a single pyramidal neuron dendrite may show either trend A or trend B, depending on the lamina location of the dendritic segment considered. (6) All neurons show spine population decreases between nine months of age and adult (5-7 years) suggesting continuing long term maturational changes.

Animals↗

PubMed1977

Monoaminergic synapses, including dendro-dendritic synapses in the rat substantia nigra.

Intraventricular administration of 1 or 2 mg of the osmiophilic "false transmitter" 5-hydroxydopamine (5-OHDA) was used to label monoamine storage and release sites in the rat substantia nigra. Vesicles containing unusually dense cores indicative of the presence of the marker were seen forming from the Golgi apparatus in the cell bodies of medium-sized neurons of the substantia nigra, pars compacta, and from smooth endoplasmic reticulum in the dendrites of those neurons and in small unmyelinated axons of unknown origin. In serial sections, both axons and dendrites containing synaptic vesicles marked with 5-OHDA were seen to form synapses "en passage" in pars compacta, and some presynaptic dendrites containing vesicles filled by the marker were also observed to form contacts with dendrites in pars reticulata. The only identified postsynaptic elements engaging in monoaminergic synapses in the substantia nigra were dendrites of medium-sized pars compacta neurons.

Animals↗

PubMed1976

Fulminant Purkinje cell death following axotomy and its use for analysis of the dendritic arborization.

Young and adult cats were operated upon and a number of the vermal cerebellar folia were either transected with a vertical incision or isolated by a horizontal cut. In the proximity of the lesion, Purkinje cell bodies and their dendritic trees became stainable with the Fink-Heimer method. Electron microscopy of the silver stained sections show that the argyrophilic Purkinje neurons undergo an electron dense type of degeneration. Stellate cell dendrites adjacent to the degenerating Purkinje trees are normal, suggesting that the cause of cell death is axotomy close to the perikaryon rather than direct injury. The retrograde Purkinje cell degeneration is fulminant since it is evident 6 hours after the lesion. In Fink-Heimer stained sections the entire dendritic tree is impregnated 1-3 days after the lesion. 4-10 days post-operatively, the flattened dendritic tree becomes fragmented and is partially phagocytized. The silver stained arborizations are approximately 280 mu in width and have an uneven thickness (8-16 mu). In longitudinal and horizontal silver stained sections of lesioned cerebellar folia, uninterrupted fields of degenerating Purkinje cell arborizations can be seen, suggesting that the arborizations overlap. The overlap was demonstrated in electron micrographs of single degenerating arborizations surrounded by normal dendritic trees. The degree of overlap varies with the thickness of the arborization and is in the order of 1-2 mu. This approach indicates that each Purkinje tree occupies an exclusive sheet of molecular layer 8 mu thick and may overlap for as much as 2 mu on each side with neighboring trees. The average thickness of the Purkinje tree is approximately 12 mu.

Animals↗

PubMed1977

Dendritic bottlenecks of crustacean motoneurons.

Cobalt-labelled fast flexor motoneurons of the crayfish (Procambarus) were studied by electron microscopy after treatment with diaminobenzidine. The neurons were traced into the abdominal ganglion to locations at which they made contacts with the lateral giant fibres of the nerve cord. Fine secondary dendritic branches extended from the primary dendrites of the fast flexor motoneurons to the lateral giant fibre. These fine branches had bottlenecks at various places along their lenghts and also at their junctions with primary dendrites. Chemical synapses occurred at the bottlenecks and at other locations on the fine branches. It is postulated that chemical synapses at dendritic bottlenecks could act to modify the effectiveness of the excitatory drive provided by the lateral giant fibres to the fast flexor motoneurons, most likely by 'gating' electrical signals conveyed by the fine dendrites.

Animals↗

PubMed1975

The morphometry of the branching pattern in dendrites of the visual cortex pyramidal cells.

An analysis has been made of the three-dimensional branching structure for the basal and apical dendrites of cortical neurons in an adult rabbit. The real branching angles of basal dendrites and apical oblique branches are in the same range, but differ from those of the apical main shaft. Therefore, several different parts of the apical dendrite have to be distinguished on anatomical grounds, coincident with the presynaptic areas distinguished in the literature. The bifurcations of basal dendrites are essentially symmetrical. The mode of outgrowth, however, is non-symmetrical. Redirection of dendrites will, therefore, occur. This redirection is often not complete, so that a large variability of branching angles results. The possible significance of the observed symmetry is discussed.

Animals↗

PubMed1979

The ventral dendritic arbor of marginal (lamina I) neurons in the adult primate spinal cord.

The ventral (gelatinosal) dendritic arbor of marginal neurons taken from lumbosacral cord was examined in Golgi preparations from adult Macaque monkey and adult Squirrel monkey where neurons were filled with horseradish peroxidase (HRP) via secondary diffusion. Based on morphological criteria two types of marginal neurons were found which give rise to a substantial ventral dendritic arbor. These dendrites penetrate the depth of lamina II and some extend well into lamina III. The cell bodies are medium to large in size and confined to the medial half of lamina I. Marginal neurons located in the lateral half of the marginal layer lack gelatinosal dendrites and are characterized instead by numerous interstitial dendrites.

Animals↗