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PubMed1984

Dendritic development in human occipital cortical neurons.

Using quantitative techniques on rapid Golgi impregnations, the dendrites from neurons of visual cortex from 14 infants ranging in age from 20 weeks gestation to 7 years were assessed. Neurons in layers 3 and 5 were separately evaluated. The total dendritic length for all dendritic branches reached a maximum of 2800 microns for layer 3 neurons and 3400 microns for layer 5 neurons. At or before 40 weeks gestation, the dendritic tree of layer 3 neurons had reached 35% of the maximum compared with 55% of the maximum for layer 5 neurons. Dendritic branching occurred earlier in layer 5 and growth continued to be more advanced than in layer 3. After 40 weeks gestation in these layers no new branch orders were added to basal dendrites but 3 branch orders were added to apical dendrites. The determination of normal values for dendritic length, number of orders, and number of branches during early development provides a foundation for comparison of dendritic maturation in children with a variety of neurologic disorders.

Child↗

PubMed1987

Postnatal development of cell columns and their associated dendritic bundles in the lumbosacral spinal cord of the rat. II. The ventromedial cell column.

Postnatal formation of the ventromedial dendrite bundle (MDB) in the rat lumboscral cord was examined quantitatively with Golgi-Cox impregnation. At birth, dendrites of motoneurons in the MDB had not achieved their total length, and had not begun to form bundles. Dendrites projected from the soma in a radially symmetric fashion. At 5 days, dendritic shafts reoriented into the longitudinal plane, and by 10 days of age dendrite bundling was apparent. Between day 1 and 60, primary, secondary and tertiary dendrites from motoneurons in the MDB increased both in number and in length, and the MDB became more compact and intertwined. Dendritic growth and bundling was complete by two months of age. The dendritic spatial arrangement of the MDB, as well as the LDB, may provide an important anatomical substrate for receiving appropriate developing axonal inputs. In turn, it is likely that specific incoming axonal inputs that arrive in this cell column early in development may signal the redirection of dendrites of ventromedial motoneurons into the longitudinal plane.

Animals↗

PubMed1988

Regional difference in the dendritic morphology of dopamine cells in carp retina.

The dendritic morphology of dopamine (DA) cells in the inner plexiform layer of the retina of carp (body length, ca. 33 cm) was investigated by identifying their fluorescent cell bodies in isolated, aldehyde-fixed flat-mounts and injecting them iontophoretically with Lucifer yellow CH under microscopic control. Attention was paid to clarifying regional differences in their dendritic morphology. In the marginal zone within 0.25 mm from the retinal edge, the density of DA cells was extremely high (120 cells/mm2), their dendrites tended to extend in parallel with the retinal circumference, and the dendritic field size was small (2.5 X 10(-2) mm2). As the injection point was shifted centrally by steps, the dendrites of DA cells tended to extend toward the optic disc and subsequently toward the margin, finally forming a round or oval dendritic field for each cell. Concomitantly with such changes in the dendritic field, the cell density sharply decreased to about 30 cells/mm2, and the dendritic field size increased to 10 X 10(-2) mm2 in a zone 2-3 mm interior to the margin. However, the dendritic coverage factor was consistently about 3.0 over the entire retinal field. Such morphological changes observed sequentially from the retinal margin to the intermediate region represent a developmental course of DA cells in the carp retina.

Animals↗

PubMed1988

Dendritic and axonal distribution of the microtubule-associated proteins MAP2 and tau in the cerebellum of the nervous mutant mouse.

The fate of the different types of axons and dendrites in the nervous mutant mouse has been studied with antibodies raised against the two major microtubule-associated proteins, MAP2 and tau. These proteins are specific markers of dendrites and axons, respectively. (1) Immunoblot analysis of cerebellar extracts showed that MAP2 concentration is markedly reduced (by approximately 90%) in the adult mutant. A 60% decrease was already noticed at day 20 postnatal, i.e., when all the Purkinje cells are present in their normal location and in apparent normal number. (2) Immunohistochemical studies performed at an adult stage with anti MAP2 antibodies showed marked alterations in the shape of the dendrites of the rare surviving Purkinje cells present in the lateral sections of the cerebellum of the mutant. In the vermis, where 50% of the cells survive in adulthood, the MAP2 antibody revealed both clusters of cells with a normal density and an intricated and extensive pattern of dendritic arborization and isolated cells showing either an apparently normal or an altered dendritic tree. (3) At day 20 postnatal the same antibody revealed, in the lateral sections severe abnormalities of the dendrites of the Purkinje cells which were different from those seen in adulthood in the vermis. Thus, although few or any Purkinje cells are dead at this stage, a large proportion of them have already profound dendritic alterations. In contrast, in the vermis the Purkinje cells and their dendritic tree are undistinguishable at this stage from those of the unaffected normal mice. (4) Immunoblot and immunohistochemical studies performed with the anti Tau antibody suggested that the majority of the axonal fibers of the cerebellum were present both at day 20 postnatal and at later adult stages. This suggests that, although deprived of their postsynaptic targets these axons can survive for a long time after Purkinje cell death. However, an anti-neurofilament monoclonal antibody which stains specifically the axons of the basket cells, revealed an altered morphology of the basket cell nest in the regions devoid of Purkinje cells. (5) In conclusion the alterations in the morphology of dendrites seem to represent an early event of Purkinje cell degeneration and to be correlated with a marked decrease in expression of MAP2. It remains unclear, however, whether such changes in expression of MAP2 represent a primary effect of the mutation or if it is only a precocious result of Purkinje cell degeneration.

Animals↗

PubMed1991

Development of rostrocaudal dendritic bundles in rat thoracic spinal cord: analysis of cholinergic sympathetic preganglionic neurons.

Using monoclonal antibodies to choline acetyltransferase (ChAT) and glial fibrillary acidic protein (GFAP), we have analyzed the development of the dendritic bundles formed by cholinergic sympathetic preganglionic neurons (SPNs) in relationship to changes in the organization of glial fibers. In adult rat thoracic spinal cord, SPNs in the intermediolateral (IML) and central autonomic (CA) regions extend dendrites in both the mediolateral and rostrocaudal directions, forming a ladder-like pattern in horizontal sections of thoracic spinal cord. We report that, while the mediolateral dendrites form prenatally, the rostrocaudal dendritic bundles are not detected until at least a week later, during early postnatal life. The rostrocaudal dendrites develop rapidly during the first postnatal week, and achieve an adult-like pattern by postnatal day 14. The observed ontogenetic arrangements of dendritic bundles were correlated with the developing organization of astroglial processes with which they are intimately associated. While the appearance of mediolateral dendrites is consistent with the radial organization of glial in the embryonic spinal cord, the developmental time course of the rostrocaudal dendritic bundles coincides with the transformation of glial cells from this predominantly radial or transverse orientation to the randomly-oriented, stellate pattern of mature astrocytes. This temporal association suggests that ontogenetic changes in the organization of glial cells may contribute to the differential development of mediolateral and rostrocaudal dendritic patterns in the spinal cord.

Aging↗

PubMed1988

Overestimation of the electrical length of neuron dendrites and synaptic electrotonic attenuation.

The electrical (also termed electrotonic) length of dendrites is a key factor in determining the magnitude of the decay of a postsynaptic potential as it propagates from the dendrites to the soma. The average electrotonic length of dendrites in spinal, hippocampal, and red nucleus neurons have been estimated at 1.2 (range of 0.9-1.5), based on single (equivalent) cylinder models. Synaptic potentials evoked at the terminals of dendrites that are 1.2 space constants in length have been estimated to decay 50% during propagation to the soma, the lost energy being dissipated as heat. The present analysis was conducted because a 50% propagation loss seemed unlikely for such a widespread neuron function as passive dendritic propagation. The explicit and implicit assumptions of the cylinder model were reconsidered. It was found that the simplifying assumption of uniform dendritic electrotonic length has led to a three-fold overestimate of dendritic electrotonic length by previous investigators. The conclusion is that dendrites have a typical electrotonic length of 0.4 rather than 1.2, therefore resulting in a propagation loss of only 7% rather than 50% for distal dendritic synapses.

Dendrites↗

PubMed1983

Intracellular labelling of rat subthalamic neurones with horseradish peroxidase: computer analysis of dendrites and characterization of axon arborization.

Neurones of the rat subthalamic nucleus were identified by their response to cortical stimulation and then intracellularly labelled with horseradish peroxidase. After fixation, the brains were cut serially in sagittal plane and processed by the cobalt chloride-diaminobenzidine procedure. The morphology of nine of the twenty stained neurones strictly located inside the subthalamic nucleus is described by means of quantitative parameters following light-microscopic examination and three-dimensional computer reconstruction. They were all identified as Golgi type I neurones. The somata were ovoidal in shape. A mean of four dendritic stems arose from the soma and gave rise to a mean of 27 tips. The dendrites were thin with long and pedunculated spines. The dendritic fields were ellipsoidal in shape (100 x 600 x 300 micrometer) and were parallel to the principal plane of the nucleus. The dimensions of the dendritic fields are very close to those of the nucleus, and some dendrites cross its limits. The axons gave off two branches, one going caudally and the other rostrally. The caudal-going branch of the axon of one neurone, followed into the substantia nigra, divided into several collaterals coursing dorsoventrally. The rostral-going branch was never followed up to its termination. An intranuclear axonal collateral was observed in only one case. The present data are compared with those obtained from the primate subthalamic neurons. In spite of slight differences in the pattern of dendritic branching, the neurones are similar in both species. However, major differences in the internal organization of the dendritic fields are observed. Dendrites mixing with other neuronal populations were never observed in the primate. Moreover, the relative sizes of the dendritic fields and of the nucleus are strikingly different. This gives to the primate subthalamic nucleus specific and more precisely organized afferent connections.

Animals↗

PubMed1984

Tyrosine hydroxylase-immunoreactive boutons in synaptic contact with identified striatonigral neurons, with particular reference to dendritic spines.

Tyrosine hydroxylase-immunoreactive fibres in the rat neostriatum were studied in the electron microscope in order to determine the nature of the contacts they make with other neural elements. The larger varicose parts of such fibres contained relatively few vesicles and rarely displayed synaptic membrane specializations; however, thinner parts of axons (0.1-0.4 micron) contained many vesicles and had symmetrical membrane specializations, indicative of en passant type synapses. By far the most common postsynaptic targets of tyrosine hydroxylase-immunoreactive boutons were dendritic spines and shafts, although neuronal cell bodies and axon initial segments also received such input. Six striatonigral neurons in the ventral striatum were identified by retrograde labelling with horseradish peroxidase and their dendritic processes were revealed by Golgi impregnation using the section-Golgi procedure. The same sections were also developed to reveal tyrosine hydroxylase immunoreactivity and so we were able to study immunoreactive boutons in contact with the Golgi-impregnated striatonigral neurons. Each of the 280 immunoreactive boutons examined in the electron microscope displayed symmetrical synaptic membrane specializations: 59% of the boutons were in synaptic contact with the dendritic spines, 35% with the dendritic shafts and 6% with the cell bodies of striatonigral neurons. The dendritic spines of striatonigral neurons that received input from immunoreactive boutons invariably also received input, usually more distally, from unstained boutons that formed asymmetrical synaptic specializations. A study of 87 spines along the dendrites of an identified striatonigral neuron showed that the most common type of synaptic input was from an individual unstained bouton making asymmetrical synaptic contact (53%), while 39% of the spines received one asymmetrical synapse and one symmetrical immunoreactive synapse. It is proposed that the spatial distribution of presumed dopaminergic terminals in synaptic contact with different parts of striatonigral neurons has important functional implications. Those synapses on the cell body and proximal dendritic shafts might mediate a relatively non-selective inhibition. In contrast, the major dopaminergic input that occurs on the necks of dendritic spines is likely to be highly selective since it could prevent the excitatory input to the same spines from reaching the dendritic shaft. One of the main functions of dopamine released from nigrostriatal fibres might thus be to alter the pattern of firing of striatal output neurons by regulating their input.

Animals↗

PubMed1987

The dendrites of single brain-stem motoneurons intracellularly labelled with horseradish peroxidase in the cat. Morphological and electrical differences.

The geometrical differences between individual dendrites of a given motoneuron were investigated in the cat. We chose two brain-stem motoneurons involved in different motor activities. One abducens and one laryngeal motoneuron were selected from two series of experiments which had combined intracellular recording and horseradish peroxidase staining. Three-dimensional reconstructions were made using a computer-aided microscope to obtain high-resolution measurements from serial histological sections. Each dendrite was characterized by computer dissection. Comparisons between dendrites were made on the basis of the following parameters: spatial projections, length, diameters, tapering, branching pattern, daughter--branch ratio and branching power. The present findings show that each dendrite projects to specific terminal fields for both motoneurons and are different in the complexity of their geometry and branching structure. The consequences of this complexity for the cable properties of the motoneurons were analysed. The dendrites of the two motoneurons were partitioned into a series of contiguous regions deemed short enough to be considered an isopotential cylinder and the steady-state properties were calculated for each segment. The properties of each segment were then combined for each dendrite for the following parameters: electronic distance, somatopetal and somatofugal voltage attenuation, input resistance and charge transfer effectiveness ratio. The present results show significant differences in the electrical behaviour of individual dendrites. Branch-to-branch computation reveals low attenuation pathways between branches suggesting the possibility of local influences within the distal branches of the dendritic arborization. It is proposed that the individual dendrites of the motoneuron function as distinct channels and/or integrators for afferent inputs.

Abducens Nerve↗

PubMed1987

The dendrites of single brain-stem motoneurons intracellularly labelled with horseradish peroxidase in the cat. An ultrastructural analysis of the synaptic covering and the microenvironment.

Two laryngeal motoneurons intracellularly stained with horseradish peroxidase were studied ultrastructurally. The precise position of the ultrastructural observations made along the dendrites was obtained from the computer-reconstruction of the motoneurons in three dimensions. The shape and the size of the synaptic boutons, the percentage of membrane covered by bouton appositions and active zones, the number of boutons per 100 microns2 (packing density) were analysed on the soma and on the labelled dendrites at different distances from the soma up to 1000 microns. The results revealed no important regional differences in the mean length of synaptic apposition. The packing density was in the range of 9.3-14.9 boutons per 100 microns2 and was not correlated with the distance from the soma. The percentage apposition covering was higher on the soma and the proximal part of the dendrites than on the remaining part of the dendritic arborization. Close appositions between labelled dendrite and unlabelled somata and/or dendrites together with dendro-dendritic synapses suggested the possibility that the dendrites may be involved in local cell-to-cell communication. Microdendrites emerging from the soma or the proximal dendrites were contacted by synaptic boutons which may be more efficient as revealed by computation.

Animals↗

PubMed1993

Bi-stable dendrite in constant electric field: a model analysis.

Some neurons possess dendritic persistent inward current, which is activated during depolarization. Dendrites can be stably depolarized, i.e. they are bi-stable if the net current is inward. A proper method to show the existence of dendritic bi-stability is putting the neuron into the electric field to induce transmembrane potential changes along the dendrites. Here we present analytical and computer simulation of the bi-stable dendrite in the d.c. field. A prominent jump to a depolarization plateau can be seen in the soma upon initial hyperpolarization of its membrane. If a considerable portion of dendrites are parallel to the field it is impossible to switch off the depolarization plateau by changing the direction and the strength of the electric field. There is nothing similar in neurons with ohmic dendrites. The results of the simulation conform to the experimental observations in turtle motoneurons [Hounsgaard J. and Kiehn O. (1993) J. Physiol., Lond. (in press)]; comparison of the theoretical and the experimental results makes semi-quantitative estimation of some electrical parameters of dendrites possible. We propose modifications of the experiment which enable one to measure dendritic length constants and other parameters of stained neurons.

Dendrites↗

PubMed1993

Neonatal nerve injury causes long-term changes in growth and distribution of motoneuron dendrites in the rat.

Disruption of neuromuscular contact by nerve-crush during the early postnatal period results in the death of a large proportion of affected motoneurons. Increased activity and abnormal reflex responses are evident in those that survive. We have studied the aberrant dendritic morphology of surviving cells and have attempted to correlate the observed alterations in morphology with the above experimental findings. Motoneurons supplying the extensor hallucis longus muscles of the rat were retrogradely labelled with cholera toxin subunit-B conjugated to horseradish peroxidase. The dendritic tree of labelled cells was analysed in adult animals having undergone unilateral sciatic nerve-crush at birth. Unoperated control animals were also examined. Following nerve-crush at birth, total visible dendritic length was more than 30% smaller than control cells in the transverse plane. This decrease was confined largely to the medially directed segments of the dendritic field and appeared to be due to a reduction in dendritic branching combined with a failure to achieve the correct branch length. There was no overall change in total visible dendritic length in the longitudinal plane, but a reorientation of dendrites in favour of rostrodorsal regions was observed. There was no alteration in dendritic length in cells contralateral to the nerve injury. These results show that nerve injury during early postnatal development produces lasting changes in the distribution of motoneuron dendrites. The localized nature of these changes may explain the altered activity and induced death of motoneurons seen after neonatal nerve-crush.

Animals↗

PubMed1996

Autoradiographic localization of functional muscarinic receptors in the rat superior cervical sympathetic ganglion reveals an extensive distribution over non-synaptic surfaces of neuronal somata, dendrites and nerve endings.

Fast synaptic transmission in sympathetic ganglia is mediated by acetylcholine, acting on nicotinic receptors, yet muscarinic receptors are also present and are involved in the production of slow postsynaptic potentials. In order further to elucidate the role of muscarinic receptors in ganglionic transmission their distribution in the rat superior cervical sympathetic ganglion was investigated autoradiographically by use of the tritiated irreversible muscarinic ligand propylbenzilylcholine mustard. It was observed that this agent blocked the carbachol-evoked hydrolysis of inositol phospholipids in the ganglion and that this response to carbachol is itself inhibitable by selective muscarinic antagonists with a potency sequence which indicates involvement primarily of M1 receptors. Light microscope autoradiography showed that labelling inhibitable by atropine and by the M1-selective muscarinic antagonist pirenzepine was essentially confined to the margins of neuronal somata and regions of dendritic arborization, which include synaptic contacts. Quantitative electron microscope autoradiography showed that binding of the radioligand, of which approximately 70% was inhibitable by atropine and 68% by pirenzepine, was associated predominantly with surface membranes of neuronal somata, dendrites, other neurites (including axons and uncharacterized dendrites) and nerve terminal profiles, in the approximate ratios 95:85:52:45. Of the inhibitable binding over neuronal membranes in the ganglion little more than 3% was found to be synaptically located, and this involved para- or peri-synaptic regions of nerve terminal contacts rather than the specialized synaptic zone. About 5% of the inhibitable binding over neuronal membranes involved non-synaptic surfaces of nerve terminals and preterminal axon segments; almost 70% was distributed over non-synaptic surfaces of neuronal somata and dendrites, and about 21% upon other neurites. Binding sites were found not to be more highly concentrated at or adjacent to synapses than over other regions of neuronal surface membranes. About 50%, possibly more, of the binding on non-synaptic surfaces of nerve endings, and about 7% of binding upon dendritic membranes, was of non-M1, possibly M2 type, inhibitable by atropine but not by pirenzepine. Non-synaptic neuro-neuronal appositions, which involve dendrites and somata and often lie adjacent to synapses, showed rather more than twice the binding expected for each membrane individually; and neuronal membrane exposed to basal lamina lining ganglionic tissue spaces showed high levels of binding. Little inhibitable binding was seen over membranes of satellite and Schwann cells, or over cytoplasmic territories or ganglionic interstitial tissue. A model was constructed of the distribution of label, which showed that the observed results for total binding could be approximately matched by assuming the following relative densities of ligand binding sites: interstitial tissue space and supporting cells 1, soma cytoplasm 3, cytoplasm of dendrites, neurites and nerve terminals 4.5, surfaces of mesodermal elements 15, surfaces of neurites and nerve endings including sites of synapse 45, surfaces of dendrites 90, surfaces of neuronal somata 120, non-synaptic neuro-neuronal appositions 180. It is concluded that functional muscarinic receptors in this sympathetic ganglion, predominantly of the M1 type linked with slow depolarizations, but including some non-M1 receptors, are widely distributed over non-synaptic surfaces of the neuronal somata and dendrites and are not concentrated at synapses. Presynaptic autoreceptors are also present, of which half or more are of non-M1, possibly M2, type which might be inhibitory. The presence of M4 receptors is not excluded...

Animals↗

PubMed1981

Postnatal ontogenesis of hippocampal CA1 area in rats. I. Development of dendritic arborisation in pyramidal neurons.

Hippocampal pyramidal neurons (area CA1) in rats, 5, 10, 15, 24, 48 and 90 days old were studied by means of the Golgi-Cox impregnation. Using a video-computer microscope the development of dendritic arborisation was analysed and descriptive as well as quantitative data were obtained. During the suckling period (5 and 10 days) the basal dendrites, the main shaft and within the stratum moleculare branching terminal fibers of the apical dendrite were found to develop. At the weaning period (15 and 24 days) the development progressed with proliferation and ramification of the apical dendrite's lateral branches in the stratum radiatum and of its preterminal fibers branching in the stratum lacunosum. The lateral branches of the apical dendrite developed in a consequent order from the neuronal soma towards fissura hippocampi. Adult numbers of dendrites were set in first, followed by elongation and ramification of the fibers. The final number of segments was in the whole dendrite system, except of the main shaft, established before the maximum of the total dendritic length was reached. The afferent fibers termination upon the pyramidal neurons are known to be distinctly divided within the hippocampal layers. Step by step development of the individual groups of dendrites therefore probably eventuates the linkage of afferent fibers in a successive order.

Afferent Pathways↗

PubMed1995

Spatial synaptic integration in Purkinje cell dendrites.

Synaptic integration occurs within a framework of synaptic connections, and cell type-specific, intrinsic and transmitter-gated ion channels. These components are differentially distributed over the somato-dendritic membrane. Recent results from Purkinje cells and pyramidal cells exemplify some of these mechanisms of spatial synaptic integration. This paper focusses on the cerebellar Purkinje cell. In these neurons, the amplitude and distribution of single climbing fibre and parallel fibre EPSP-evoked Ca2+ influx were regulated by the transient outward, IA-like current in the distal (spiny) dendrites. The synaptically evoked Ca2+ influx was graded from a local response involving only a few terminal spiny dendrites to a propagated Ca2+ spike. The climbing fibre-evoked Ca2+ influx in the spiny dendrites was finely graded by parallel fibre-induced depolarization. Climbing fibre and parallel fibre-evoked Ca2+ influx elicited a short lasting afterhyperpolarization that affected subsequent dendritic Ca2+ influx. In addition, inhibitory synaptic input controlled dendritic Ca2+ influx. Interaction between information from different sources along the dendrites is thus controlled by intrinsic potassium conductances and IPSPs. Different electrophysiological properties are found in the cerebellar neurons. Thus, Golgi cells, stellate cells and granule cells seem to integrate on a shorter intrinsic timescale than do Purkinje cells, the output neuron of the cerebellar cortex. The specific mechanisms by which different types of presynaptic neurons specifically innervate a given dendritic compartment remain to be elucidated, but recent results provide some experimental evidence of a differential distribution of cell adhesion molecules between the axonal and the somato-dendritic membrane, suggesting one mechanism contributing to the ordered distribution of synapses during synaptogenesis.

Animals↗

PubMed2005

Development and maturation of Langerhans cells, spleen and bone marrow dendritic cells in TNF-alpha/lymphotoxin-alpha double-deficient mice.

Dendritic cells are key regulators of immunity and tolerance. TNF-alpha has manifold effects on dendritic cells. It is an indispensable ingredient in several dendritic cell generation protocols, especially in the human, and it is included in diverse maturation stimuli for dendritic cells. Mice deficient in various components of the TNF/lymphotoxin system (TNF-alpha, lymphotoxin-alpha and -beta, TNF receptors, combinations thereof) have profound defects in mounting immune responses to infections. The dendritic cell system in these mice has been incompletely studied to date. We therefore investigated dendritic cells from the epidermis (Langerhans cells), spleen and the bone marrow of mice double-deficient in TNF-alpha and lymphotoxin-alpha. We report that dendritic cells in these mice are grossly normal. Langerhans cells, spleen and bone marrow dendritic cells can develop and mature. Their expression of MHC II and CD86 is not impaired, and their T cell-stimulatory as well as antigen-processing capacity is comparable to their normal counterparts. Thus, the described defects in these mice appear to be due the lack of lymph nodes, the disturbed architecture of the spleen, and deranged chemokine production patterns, rather than to a profoundly altered dendritic cell system.

Animals↗

PubMed2004

Neuronal MAP2 mRNA: species-dependent differential dendritic targeting competence.

Providing the basis for local protein synthesis in dendritic microdomains, RNA transport in dendrites is thought to be underlying long-term neuronal plasticity. Dendritic RNA targeting mechanisms can therefore be expected to confer selective advantages in the evolution of complex neural systems. The question thus arises as to when and how dendritically targeted transcripts first acquired their targeting competence. To address this question, the dendritic targeting competence of MAP2 transcripts was examined in chicken, mouse and rat. In one approach, we established the somato-dendritic distribution of MAP2 transcripts in vivo. We found that in contrast to rodent MAP2 mRNAs, which are highly enriched in dendritic regions of the retina, chicken MAP2 transcripts are virtually absent from such areas and are rather confined to neuronal somata. In an independent line of investigation, we determined that a dendritic targeting element (DTE) corresponding to the mammalian MAP2 DTE is not contained in the 3' untranslated region (UTR) of avian MAP2 mRNA. The combined results indicate that in contrast to mammalian MAP2 transcripts, avian MAP2 mRNA is lacking dendritic targeting competence. The data thus suggest that the acquisition of such competence has likely been a relatively recent event in evolution.

Animals↗

PubMed2006

A new approach to reconstruction models of dendritic branching patterns.

Quantitative models for characterising the detailed branching patterns of dendritic trees aim to explain these patterns either in terms of growth models based on principles of dendritic development or reconstruction models that describe an existing structure by means of a canonical set of elementary properties of dendritic morphology, which when incorporated into an algorithmic procedure will generate samples of dendrites that are statistically indistinguishable in both canonical and emergent features from those of the original sample of real neurons. This article introduces a conceptually new approach to reconstruction modelling based on the single assumption that dendritic segments are built from sequences of units of constant diameter, and that the distribution of the lengths of units of similar diameter is independent of location within a dendritic tree. This assumption in combination with non-parametric methods for estimating univariate and multivariate probability densities leads to an algorithm that significantly reduces the number of basic parameters required to simulate dendritic morphology. It is not necessary to distinguish between stem and terminal segments or to specify daughter branch ratios or dendritic taper. The procedure of sampling probability densities conditioned on local morphological features eliminates the need, for example, to specify daughter branch ratios and dendritic taper since these emerge naturally as a consequence of the conditioning process. Thus several basic parameters of previous reconstruction algorithms become emergent parameters of the new reconstruction process. The new procedure was applied successfully to a sample of 51 interneurons from lamina II/III of the spinal dorsal horn.

Algorithms↗