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PubMed1992

Dendritic morphology of pyramidal neurones of the visual cortex of the rat. IV: Electrical geometry.

Features of the dendritic morphology of pyramidal neurones of the visual cortex of the rat that are relevant to the development of models of their passive electrical geometry were investigated. The sample of 39 neurones that was used came from layers 2/3 and 5. They had been recorded from and injected intracellularly with horseradish peroxidase (HRP) in vitro as part of a previous study (Larkman and Mason, J. Neurosci 10:1407, 1990). These cells had been reconstructed and measured previously by light microscopy. The relationship between the diameters of parent and daughter dendrites during branching was examined. It was found that most dendrites did not closely obey the "3/2 branch power relationship" required for representation of the dendrites as single equivalent cylinders. Estimates of total neuronal membrane area ranged from 27,100 +/- 7,900 microns2 for layer 2/3 cells to 52,200 +/- 11,800 microns2 for thick layer 5 cells. Dendritic spines contributed approximately half the total membrane area. Both neuronal input resistance and the ratio of membrane time constant to input resistance were correlated with neuronal membrane area as measured anatomically. The relative electrical lengths of the different dendrites of individual neurones were investigated, by using simple transformations to take account of the differences in diameter and spine density between dendritic segments. A novel "morphotonic" transformation is described that represents the purely morphological component of electrotonic length. Morphotonic lengths can be converted into electrotonic lengths by division by a "morphoelectric factor" ([Rm/Ri]1/2). This procedure has the advantage of separating the steps involving anatomical and electrical parameters. These transformations indicated that the dendrites of the apical terminal arbor were much longer electrically than the basal or apical oblique dendrites. In relative electrical terms, most apical oblique trees arose extremely close to the soma, and terminated at similar distances to the basals. These results indicate that the dendrites of these pyramidal cells cannot be represented as single equivalent cylinders. The electrotonic lengths of the dendrites were calculated by using the electrical parameters specific membrane capacitance (Cm), intracellular resistivity (Ri), and specific membrane resistivity (Rm). Conventional values were assumed for Cm (1.0 muFcm-2) and Ri (100 omega cm), but three different Rm values were used for each cell. Two of these were within the conventionally accepted range (10,000-20,000 omega cm2), while the third value was an order of magnitude higher, in line with some recent evidence from modeling and whole-cell recording studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Dendritic co-stratification of ON and ON-OFF directionally selective ganglion cells with starburst amacrine cells in rabbit retina.

The morphology, dendritic branching patterns, and dendritic stratification of retinal ganglion cells have been studied in Golgi-impregnated, whole-mount preparations of rabbit retina. Among a large number of morphological types identified, two have been found that correspond to the morphology of ON and ON-OFF directionally selective (DS) ganglion cells identified in other studies. These cells have been characterized in the preceding paper in terms of their cell body size, dendritic field size, and branching pattern. In this paper, the two kinds of DS ganglion cell are compared in terms of their levels of dendritic stratification. They are compared with each other and also with examples of class III.1 cells, defined in the preceding paper with reference to our previous studies. Studies employing computer-aided, 3D reconstruction of dendritic trees, as well as analysis of a pair of ON DS and ON-OFF DS ganglion cells with overlapping dendritic trees show that the two types of DS ganglion cell partly co-stratify in the middle of sublamina b (stratum 4). The report that some ON DS ganglion cells extend a few dendrites into sublamina a is confirmed. The study of pairs of ON-OFF DS ganglion cells and starburst amacrine cells with overlapping dendritic trees reveals a precise co-stratification of these two cell types, and many points of close apposition of starburst boutons with ON-OFF DS ganglion cell dendrites in both sublaminae of the inner plexiform layer (IPL). This is confirmed by high-resolution light microscopy and by electron microscopy. It is possible to conclude, therefore, that ON DS are also partly co-stratified with type b starburst (cholinergic) amacrine cells, and are apparently also partly co-stratified with type a starburst amacrine cells, when occasional dendrites rise to that level. The co-stratification of the two kinds of DS ganglion cell is consistent with the sharing of some inputs in common, including some cone bipolar cell inputs. The co-stratification of both with starburst amacrine cells agrees with the physiological demonstration of the powerful pharmacological effects upon ON and ON-OFF DS ganglion cells reported for cholinergic agonists. The major difference in the dendritic stratification of bistratified ON-OFF DS ganglion cells and generally unistratified ON DS ganglion cells is consistent with the bisublaminar organization of ON and OFF pathways in the IPL. The problem of occasional branches of ON DS cells in sublamina a is discussed in terms of a threshold for OFF responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Dendritic remodelling of retinal ganglion cells during development of the rat.

Investigation of the morphology of ganglion cells in the cat retina has shown that a remarkable reduction in the number of dendritic spines and branches occurs during development of the alpha and beta cell classes. To learn whether dendritic remodelling represents a generalized mechanism of mammalian retinal ganglion cell development, we have examined the morphology of ganglion cells in the retina of the developing rat. The present study has concentrated on type II cells, which retain a great number of dendritic spines and branches in the adult and comprise a large proportion of the population of rat retinal ganglion cells. To reveal fine dendritic and axonal processes, Lucifer yellow was injected intracellularly in living retinae maintained in vitro. Size and complexity of the dendritic trees were found to increase rapidly during an initial stage of development lasting from late fetal life until approximately postnatal day 12 (P12). Dendrites and axons of immature ganglion cells expressed several transient morphological features comprising an excessive number of dendritic branches and spine-like processes, and short, delicate axonal sidebranches. The following developmental stage was characterized by a remarkable decrease in the morphological complexity of retinal ganglion cells and a slowed growth of their dendritic fields. The number of dendritic branches and spines of types I and II retinal ganglion cells declined after P12 to reach a mature level by the end of the first postnatal month. Thus, even cells that retain a highly complex dendritic tree into the adult state undergo extensive remodelling. These results suggest that regressive modifications at the level of the dendritic field constitute a generalized mechanism of maturation in mammalian retinal ganglion cells.

Animals↗

PubMed1994

Morphology of developing rat genioglossal motoneurons studied in vitro: changes in length, branching pattern, and spatial distribution of dendrites.

The aim of this study is to describe the postnatal change in dendritic morphology of those motoneurons in the hypoglossal nucleus that innervate the genioglossus muscle. Forty genioglossal (GG) motoneurons from four age groups (1-2, 5-6, 13-15, and 19-30 postnatal days) were labeled by intracellular injection of neurobiotin in an in vitro slice preparation of the rat brainstem and were reconstructed in three-dimensional space. The number of primary dendrites per GG motoneuron was approximately 6 and remained unchanged with age. The development of these motoneurons from birth to 13-15 days was characterized by a simplification of the dendritic tree involving a decrease in the number of terminal endings and dendritic branches. Motoneurons lost their 6th-8th order branches, in parallel with an elongation of their terminal dendritic branches maintaining the same combined dendritic length. The elongation of terminal branches was attributed to both longitudinal growth and the apparent lengthening caused by resorption of distal branches. The elimination of dendritic branches tended to increase the symmetry of the tree, as revealed by topological analysis. Later, between 13-15 days and 19-30 days, there was a reelaboration of the dendritic arborization returning to a configuration similar to that found in the newborn. The length of terminal branches was shorter at 19-30 days, while the length of preterminal branches did not change, suggesting that the proliferation of branches at 19-30 days takes place in the intermediate parts of terminal branches. The three-dimensional distribution of dendrites was analyzed by dividing space into six equal volumes (hexants). This analysis revealed that GG motoneurons have major components of their dendritic tree oriented in the lateral, medial, and dorsal hexants. Further two-dimensional polar analysis (consisting of eight sectors) revealed a reconfiguration of the tree from birth up to 5-6 days involving resorption of dendrites in the dorsal, dorsomedial, and medial sectors and growth in the lateral sector. Later in development (between 13-15 days and 19-30 days), there was growth in all sectors, but of a greater magnitude in the dorsomedial, medial, and dorsolateral sectors.

Animals↗

PubMed1994

Dendritic development of dentate granule cells in the absence of their specific extrinsic afferents.

Dendrites and spines are postsynaptic structures that develop in association with presynaptic fibers. Recent studies have shown that granule cells of the fascia dentata survive in slice cultures and differentiate in a manner known from in situ studies. However, all extrinsic afferent fibers are absent under culture conditions. In the present study, we study whether dendrites and spines of granule cells in slice cultures differentiate normally, although they are not contacted by their normal layer-specific afferents. Slices of hippocampus were prepared from rat pups at the day of birth. After 5, 10, 15, and 20 days of incubation, granule cells in these cultures were Golgi impregnated. For comparison, perfusion-fixed hippocampal sections of 5-, 10-, 15-, and 20-day-old rats were impregnated the same way. Our results show that the total density of spines on granule cell dendrites in culture increased as in perfusion-fixed animals. However, after 20 days of incubation, the absolute number of dendritic spines on cultured neurons was reduced because of a reduction of peripheral dendrites. This reduction was accompanied by an increase in the number of stem dendrites originating from the perikaryon. The density of spines on these proximal dendrites was larger in cultured granule cells than in controls. Our results suggest that the lack of major extrinsic (entorhinal) afferents that normally terminate on peripheral granule cell dendrites causes retraction of these dendrites. At the same time, there is growth of proximal dendritic portions. Proximal dendrites are targets of associational fibers, which are known to sprout under these culture conditions.

Animals↗

PubMed1995

Comparison of the topology and growth rules of motoneuronal dendrites.

The complexity, shape, and branching modes of the dendrites of spinal motoneurons were compared in cat, rat, and frog using topological analysis and growth models. The complexity of motoneuronal dendrites, measured as the mean number of terminal segments, varied significantly among samples and was related to contractile properties of innervated motor units. Despite this variation, all mature motoneurons having a mean number of terminal segments per dendrite greater than ten (up to 24.3) exhibited a narrow range of values of coefficients describing the symmetry of tree shapes (0.42-0.47). This implies low variability in the topological shape of motoneuronal dendrites of different animals. This similarity of tree shapes proved to be a result of the similarity of growth rules. The growth of the dendrites could be described to a first approximation by a two-parameter (Q and S) model called the QS model and by a multitype Markovian model. The estimation of parameters of the QS model, in which parameter Q is related to the probability of branching of intermediate segments, revealed that Q was equal or close to 0, implying that branching of dendrites is restricted to terminal segments. The estimates of the parameter S, which describes whether the probability of branching increases (S < 0) or decreases (S > 0) exponentially with segment order, were positive. This was in agreement with the results of estimation of probabilities of branching provided by the Markovian model, which showed that the branching probabilities decreased with segment order in an exponential manner in most of the neurons studied. The QS and Markovian models involve different assumptions about the sequence and timing of branching events, and selection of the best model can provide insight into details of dendritic outgrowth. Extensive simulation of tree outgrowth using a Markovian model revealed significant differences between stimulated trees and real dendrites, particularly with regard to variability of the number of terminals and to symmetry. In contrast, the QS model provided a good fit to the mean values and standard deviations of basic topological parameters. This model is adequate to describe the shape of mature motoneuronal dendrites. It implies that dendritic branches have many opportunities to bifurcate during the whole time of development and that bifurcating potency of a branch is a function of the number and position of other branches of that dendrite. Combined with analysis of metrical properties such as lengths of segments, the QS model can assist in a quantitative analysis of development and plasticity.

Animals↗

PubMed1991

Antigen presentation by dendritic cells provides optimal stimulation for the production of interleukin (IL) 2, IL 4 and interferon-gamma by allogeneic T cells.

Previous studies have shown that dendritic cells are the most potent inducers of T cell proliferation in vitro and that this is reflected in the release of interleukin (IL) 2 into culture supernatants during dendritic cell-T cell interaction. However, the role of the dendritic cells, and, indeed, of the antigen-presenting step, has not yet been explored with respect to other T cell-derived cytokines, in either a qualitative or relative fashion. In this study, therefore, we have examined the comparative role of different antigen-presenting cells (APC) as inducers of T cell cytokine release in allogeneic responses. We have confirmed that dendritic cells are the most effective inducers for IL2 and have shown that this is true not only in primary alloresponses, but also in alloresponder T cells maintained for extended periods and then rechallenged. Dendritic cells were also the most potent inducers of IL3 and interferon-gamma (IFN-gamma) in primary cultures. No IL4 was demonstrable irrespective of the type of presenting cells used, and both tissue macrophages and dendritic cells can induce synthesis of IL6. Likewise, in secondary alloresponses both dendritic cells and to a lesser extent tissue macrophages induce release of IL3, no IL4 is detectable, and activated macrophages and B cells raise IFN-gamma levels in the supernatants albeit to a lower concentration than that seen when dendritic cells are used as stimulators. The results were similar in the tertiary alloresponse except that (a) IL4 was now detectable in the supernatants but only where dendritic cells had been used as APC, and (b) both resting and activated macrophages induced IL2 and IFN-gamma. By the eighth cycle of allostimulation there is negligible IL2. Dendritic cells, tissue macrophages and activated B cells constitute a hierarchy of APC for IL3, IFN-gamma and IL4. These findings therefore demonstrate the role of dendritic cells as potent in vitro inducers of IL3, IL4 and IFN-gamma synthesis as well as of IL2.

Animals↗

PubMed2003

Maturation of granule cell dendrites after mossy fiber arrival in hippocampal field CA3.

Most granule neurons in the rat dentate gyrus are born over the course of the first 2 postnatal weeks. The resulting heterogeneity has made it difficult to define the relationship between dendritic and axonal maturation and to delineate a time course for the morphological development of the oldest granule neurons. By depositing crystals of the fluorescent label Dil in hippocampal field CA3, we retrogradely labeled granule neurons in fixed tissue slices from rats aged 2-9 days. The results showed that all labeled granule cells, regardless of the age of the animal, exhibited apical dendrites. On day 2, every labeled neuron had rudimentary apical dendrites, and a few dendrites on each cell displayed immature features such as growth cones, varicosities, and filopodia. Some cells displayed basal dendrites. By day 4, the most mature granule neurons had longer and more numerous apical branches, as well as various immature features. Most had basal dendrites. On days 5 and 6, the immature features and the basal dendrites had begun to regress on the oldest cells, and varying numbers of spines were present. On day 7, the first few adult-like neurons were seen: immature features and basal dendrites had disappeared, all dendrites reached the top of the molecular layer, and the entire dendritic tree was covered with spines. These data show that dendritic outgrowth occurs before, or concurrent with, axon arrival in the CA3 target region, and that adult-like granule neurons are present by the end of the first week.

Aging↗

PubMed2005

Maturation of dendritic architecture: lessons from insect identified neurons.

The highly complex geometry of dendritic trees is crucial for neural signal integration and the proper wiring of neuronal circuits. The morphogenesis of dendritic trees is regulated by innate genetic factors, neuronal activity, and external molecular cues. How each of these factors contributes to dendritic maturation has been addressed in studies of the developing nervous systems of animals ranging from insects to mammals. This article reviews our current knowledge and understanding of the role of afferent input in the establishment of the architecture of mature dendritic trees, using insect neurons as models. With these model systems and using quantitative morphometry, it is possible to define the contributions of intrinsic and extrinsic factors in dendritic morphogenesis of identified neurons and to evaluate the impact of dendritic maturation on the integration of identified neurons into functional circuits subserving identified behaviors. The commonly held view of dendritic morphogenesis is that general structural features result from genetic instructions, whereas fine connectivity details rely mostly on substrate interactions and functional activity. During early dendritic maturation, dendritic growth cone formation produces new branches at all dendritic roots. The second phase is growth cone independent and afferent input dependent, during which branching is limited to high order distal dendrites. During the third phase, activity-dependent synaptic maturation occurs with limited or subtle remodeling of branching.

Animals↗

PubMed2003

Dendritic cells transfected with interleukin-12 and pulsed with tumor extract inhibit growth of murine prostatic carcinoma in vivo.

BACKGROUND: The induction of anti-tumor immune response by injection of dendritic cells loaded with specific antigen or transduced with genes encoding tumor-specific antigens have been studied in animal models and have shown promising anti-tumor effects. The impact of different routes of administration of dendritic cells on their anti-tumor effects is uncertain. METHODS: We examined the effect of injection of cloned dendritic cells, which were stably transfected with IL-12 and exposed to an extract of murine RM-9 prostate carcinoma cell antigens on tumor growth in vivo. The cloned dendritic cells were injected intramuscularly, subcutaneously, or intraperitoneally into C57BL/6 mice. Seven days later, the mice were inoculated subcutaneously with 100,000 RM-9 cells. The sizes of the resulting tumors were measured every 3 days. RESULTS: Compared with the wild type dendritic cells, the IL-12-transfected dendritic cells delayed tumor engraftment by 7 days (P=0.04), and reduced tumor growth by up to 80% (P=0.02). Among the three routes of injection, intramuscular injection was most effective. In contrast to wild type dendritic cells, IL-12-transfected dendritic cells induced infiltration of mononuclear cells into the tumors, and induced apoptosis and necrosis of tumor cells. Injection of IL-12-transfected dendritic cells also significantly delays tumor growth in the preexisting RM-9 tumors. CONCLUSIONS: We conclude that antigen-exposed, IL-12-transfected dendritic cells have potential as an immunotherapy for prostate carcinoma. Routes of administration of dendritic cells are critical for maximal anti-tumor effect.

Animals↗

PubMed1988

Dendritic development and preferential growth into synaptogenic fields: a quantitative study of Golgi-impregnated spinal motor neurons.

Branching patterns of dendrites may be modulated by the way in which dendritic growth cone filopodia come into initial synaptic relationships with afferent axons. This synaptotropic hypothesis of dendritic branching predicts that dendritic growth will be directed preferentially into regions containing numerous prospective presynaptic elements. The developing mouse spinal cord provides a natural experiment to test this prediction, because synapses are found exclusively within the marginal zones bordering the motor columns during the early (E11-14) period of synaptogenesis. During this time, therefore, most motor dendritic growth would be expected to be directed laterally or ventrally into the marginal zones, whereas internally directed growth should become more prevalent later, when synaptogenesis begins to take place within the intermediate zone, i.e., the motor columns proper. A computer-assisted three dimensional reconstruction system has been used to test these expectations in Golgi preparations of developing mouse (C57BL/6J) spinal cords ranging in age from E13 through P1. Mean dendritic lengths and branch densities are significantly greater for marginal zone dendrites than for intermediate zone dendrites at early ages (E13-14), but there are no significant differences in these measures at later stages of development (P0,1). These findings are interpreted as meaning that motor dendritic growth is initially biased into the marginal zone by synaptogenic afferents and that this preferential distribution is progressively lost as synapses develop within the intermediate zone to attract or to stabilize internally directed dendritic growth. Thus the findings of this study are consistent with predictions of the synaptotropic hypothesis of dendritic branching.

Animals↗

PubMed1996

Dendritic remodeling of dentate granule cells following a combined entorhinal cortex/fimbria fornix lesion.

This study examined the time course of dendritic reorganization of dentate granule neurons of the hippocampus following the loss of input from both the fimbria fornix (FF) and the entorhinal cortex (EC). We used the Golgi-Cox stain to assess the morphology of dentate granule neurons at six postlesion time points (4, 8, 14, 30, 45, and 60 days) and dendritic measures included total dendritic length, number of segments, number of branch points, and spine density. We found that as early as 4 days postlesion, total dendritic length and number of segments were significantly decreased with the greatest change occurring in the distal parts of the dendritic arbor located in the outer molecular layer of the dentate gyrus. Dendritic measures related to segment number and dendritic length returned to 70% of intact values by 30 days postlesion and were not significantly different from unlesioned rats at 45 and 60 days postlesion. In contrast, the recovery of spine density was transient. Spine density in the outer molecular layer of the dentate gyrus decreased by 60% at 4 days postlesion and returned to 87% of intact values by 30 days postlesion. However, there was a second loss of dendritic spines along the distal portion of the dendrite between 30 and 60 days postlesion. These data provide evidence that the ability of granule neurons to recover a dendritic morphology similar to that of unlesioned rats is impaired following the combined EC/FF lesion and that the "secondary loss" of dendritic spine density on granule neurons may significantly limit the chances of the hippocampus reforming a synaptic circuitry that could lead to functional recovery after the EC/FF lesion.

Animals↗

PubMed1999

OP-1 enhances dendritic growth from cerebral cortical neurons in vitro.

Osteogenic protein-1 (OP-1), a member of the transforming growth factor-beta (TGF-beta) superfamily, has been demonstrated to stimulate dendrite growth from sympathetic neurons in culture. However, it is not known whether OP-1 affects dendrite growth from central nervous system neurons. Therefore we quantified axon and primary, secondary, and total dendritic growth from embryonic mouse cortical neurons (E 18) grown in vitro in a chemically defined medium. Morphology and double immunolabeling (MAP2, NF-H) were used to identify cortical dendrites and axons after 3 days in vitro. Cell morphology, neuron survival, and axon length were similar under all experimental conditions. The number of primary dendrites also was similar; however, the length of primary dendrites and the length and number of secondary dendrites were significantly increased by the addition of OP-1 to the culture medium. This increase in dendrite growth was dose-dependent; maximal dendritic growth was observed after the addition of 30-100 ng/ml of OP-1 to the culture medium. Specific support of dendrite growth was not observed when neurons were exposed to other members of the TGF-beta superfamily. These findings demonstrate that OP-1 selectively increases dendrite growth from cerebral cortical neurons in vitro.

Animals↗

PubMed2002

Enhanced dendritic cell antigen presentation in RNA-based immunotherapy.

BACKGROUND: Dendritic cells pulsed with mRNA provide a unique approach to tumor immunotherapy. We hypothesized that increased mRNA transfection efficiency and dendritic cell maturation would improve antigen processing and presentation as well as T-cell costimulation, resulting in enhanced induction of antimelanoma immune responses. METHODS: Immature monocyte-derived dendritic cells were transfected with mRNA by passive pulsing, lipofection, or electroporation. Dendritic cells were either left untreated or matured using the double-stranded RNA poly(I:C). T-Cell cultures were generated by stimulation of naïve T-cells with each set of dendritic cells. Specific antigen presentation and specific effector T-cell generation were analyzed by an IFN-gamma release Elispot assay. RESULTS: Greatest intracellular green fluorescent protein was observed by flow cytometry following dendritic cell electroporation with green fluorescent protein mRNA. DC presentation of Mart-1/Melan A peptide, as measured by Elispot assay using a specific T-cell clone, was greatest following transfection with Mart-1/Melan A mRNA by electroporation. Maturation of dendritic cells further improved antigen presentation regardless of transfection technique. Specific Mart-1/Melan A effector T cells were produced after culture of naïve T cells with dendritic cells that were electroporated with Mart-1/Melan A mRNA and then matured, but not for dendritic cells that remained immature. CONCLUSIONS: Efficient mRNA transfection by electroporation as well as dendritic cell maturation results in increased levels of Mart-1/Melan A antigen presentation and enhanced production of antigen-specific effector T cells. This combination of strategies may be used to enhance immune responses to RNA-based dendritic cell vaccines.

Antigen Presentation↗

PubMed1986

Vesicle-containing dendrites in the nucleus raphe dorsalis of the cat. A serial section electron microscopic analysis.

The nucleus raphe dorsalis of the cat was examined by serial section electron microscopy and the presence of vesicle-containing dendrites is reported. Such dendrites were divided into two classes according to their synaptic contact. Dendrites containing round and/or pleomorphic vesicles associated with a clear synaptic specialization which was generally intermediate between a Gray's type I or II were classified as presynaptic dendrites. These presynaptic dendrites were presynaptic to conventional dendrites and dendritic spines. In addition, some profiles containing a sparse population of vesicles which may be dendritic in nature were observed involved in serial synaptic arrangements. A second class of dendrites were characterized by the presence of vesicles which were never found associated with any synaptic membrane specialization. Commonly, the vesicles were densely packed and associated with unusual densities. Serial section analysis of these densities showed that they were not presynaptic dense projections. We suggest that the existence of vesicle-containing dendrites in the nucleus raphe dorsalis of the cat constitute the morphological support for the dendritic release of neurotransmitters.

Animals↗

PubMed1991

Statistical evaluation of dendritic growth models.

A mathematical model (Kliemann, W. 1987. Bull. math. Biol. 49, 135-152.) that predicts the quantitative branching pattern of dendritic tree was evaluated using the apical and basal dendrites of rat hippocampal neurons. The Wald statistic for chi 2-test was developed for the branching pattern of dendritic trees and for the distribution of the maximal order of the tree. Using this statistic, we obtained a reasonable, but not excellent, fit of the mathematical model for the dendritic data. The model's predictability of branching pattern was greatly enhanced by replacing one of the assumptions used for the original method "splitting of branches for all dendritic orders is stochastically independent", with a new assumption "branches are more likely to split in areas where there is already a high density of branches". The modified model delivered an excellent fit for basal dendrites and for the apical dendrites of hippocampal neurons from young rats (30-34 days postpartum). This indicates that for these cells the development of dendritic patterns is the result of a purely random and a systematic component, where the latter one depends on the density of dendritic branches in the brain area considered. For apical dendrites there is a trend towards decreasing pattern predictability with increasing age. This appears to reflect the late arrival of afferents and subsequent synaptogenesis proximal on the apical dendritic tree of hippocampal neurons.

Animals↗

PubMed2003

Quantitative analysis of the dendritic architectures of single jaw-closing and jaw-opening motoneurons in cats.

Little is known about the dendritic architectures of trigeminal motoneurons innervating antagonistic muscles. Thus, the aim of the present study was to provide a quantitative description of jaw-closing (JC) and jaw-opening (JO) alpha motoneurons and to determine geometrical similarities and differences of the dendritic tree between the two. Seven JC alpha motoneurons and four JO alpha motoneurons were intracellularly labeled with horseradish peroxidase (HRP) in the cat and quantitatively analyzed with a computer-assisted three-dimensional system. The dendritic tree of JC alpha motoneurons was confined within the JC motor nucleus, despite locations of the cell body. In contrast, JO alpha motoneurons generated extensive extranuclear dendrites in the reticular formation. The branching pattern of proximal dendritic segments was simpler in the JC than in the JO alpha motoneurons. Despite these differences, the mean values of dendritic parameters examined per neuron were not different between the two kinds of alpha motoneurons, and the stem dendrite diameter was positively correlated with several dendritic parameters in a linear manner. The present study provides new evidence that underlying design principles of the geometry of the dendritic tree are not concerned with the differences in configuration and branching pattern of the dendritic tree of trigeminal alpha motoneurons innervating antagonistic muscles. In addition, we estimated the number of excitatory and inhibitory synapses covering dendrites of single JC alpha motoneurons.

Animals↗

PubMed1998

Geometry-induced features of current transfer in neuronal dendrites with tonically activated conductances.

The impact of dendritic geometry on somatopetal transfer of the current generated by steady uniform activation of excitatory synaptic conductance distributed over passive, or active (Hodgkin-Huxley type), dendrites was studied in simulated neurons. Such tonic activation was delivered to the uniform dendrite and to the dendrites with symmetric or asymmetric branching with various ratios of branch diameters. Transfer effectiveness of the dendrites with distributed sources was estimated by the core current increment directly related to the total membrane current per unit path length. The effectiveness decreased with increasing path distance from the soma along uniform branches. The primary reason for this was the asymmetry of somatopetal vs somatofugal input core conductance met by synaptic current due to a greater leak conductance at the proximal end of the dendrite. Under these conditions, an increasing somatopetal core current and a corresponding drop of the depolarization membrane potential occurred. The voltage-dependent extrasynaptic conductances, if present, followed this depolarization. Consequently, the driving potential and membrane current densities decreased with increasing path distance from the soma. All path profiles were perturbed at bifurcations, being identical in symmetrical branches and diverging in asymmetrical ones. These perturbations were caused by voltage gradient breaks (abrupt change in the profile slope) occurring at the branching node due to coincident inhomogeneity of the dendritic core cross-section area and its conductance. The gradient was greater on the side of the smaller effective cross-section. Correspondingly, the path profiles of the somatopetal current transfer effectiveness were broken and/or diverged. The dendrites, their paths, and sites which were more effective in the current transfer from distributed sources were also more effective in the transfer from single-site inputs. The effectiveness of the active dendrite depended on the activation-inactivation kinetics of its voltage-gated conductances. In particular, dendrites with the same geometry were less effective with the Hodgkin-Huxley membrane than with the passive membrane, because of the effect of the noninactivating K(+)-conductance associated with the hyperpolarization equilibrium potential. Such electrogeometrical coupling may form a basis for path-dependent input-output conversion in the dendritic neurons, as the output discharge rate is defined by the net current delivered to the soma.

Animals↗