Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Dendrites”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25Linked to original sources
PubMed1993

Synaptic integration in an excitable dendritic tree.

1. Compartmental modeling experiments were carried out in an anatomically characterized neocortical pyramidal cell to study the integrative behavior of a complex dendritic tree containing active membrane mechanisms. Building on a previously presented hypothesis, this work provides further support for a novel principle of dendritic information processing that could underlie a capacity for nonlinear pattern discrimination and/or sensory processing within the dendritic trees of individual nerve cells. 2. It was previously demonstrated that when excitatory synaptic input to a pyramidal cell is dominated by voltage-dependent N-methyl-D-aspartate (NMDA)-type channels, the cell responds more strongly when synaptic drive is concentrated within several dendritic regions than when it is delivered diffusely across the dendritic arbor. This effect, called dendritic "cluster sensitivity," persisted under wide-ranging parameter variations and directly implicated the spatial ordering of afferent synaptic connections onto the dendritic tree as an important determinant of neuronal response selectivity. 3. In this work, the sensitivity of neocortical dendrites to spatially clustered synaptic drive has been further studied with fast sodium and slow calcium spiking mechanisms present in the dendritic membrane. Several spatial distributions of the dendritic spiking mechanisms were tested with and without NMDA synapses. Results of numerous simulations reveal that dendritic cluster sensitivity is a highly robust phenomenon in dendrites containing a sufficiency of excitatory membrane mechanisms and is only weakly dependent on their detailed spatial distribution, peak conductances, or kinetics. Factors that either work against or make irrelevant the dendritic cluster sensitivity effect include 1) very high-resistance spine necks, 2) very large synaptic conductances, 3) very high baseline levels of synaptic activity, and 4) large fluctuations in level of synaptic activity on short time scales. 4. The functional significance of dendritic cluster sensitivity has been previously discussed in the context of associative learning and memory. Here it is demonstrated that the dendritic tree of a cluster-sensitive neuron implements an approximative spatial correlation, or sum of products operation, such as that which could underlie nonlinear disparity tuning in binocular visual neurons.

Animals↗
PubMed1999

Dendritic voltage-gated ion channels regulate the action potential firing mode of hippocampal CA1 pyramidal neurons.

The role of dendritic voltage-gated ion channels in the generation of action potential bursting was investigated using whole cell patch-clamp recordings from the soma and dendrites of CA1 pyramidal neurons located in hippocampal slices of adult rats. Under control conditions somatic current injections evoked single action potentials that were associated with an afterhyperpolarization (AHP). After localized application of 4-aminopyridine (4-AP) to the distal apical dendritic arborization, the same current injections resulted in the generation of an afterdepolarization (ADP) and multiple action potentials. This burst firing was not observed after localized application of 4-AP to the soma/proximal dendrites. The dendritic 4-AP application allowed large-amplitude Na(+)-dependent action potentials, which were prolonged in duration, to backpropagate into the distal apical dendrites. No change in action potential backpropagation was seen with proximal 4-AP application. Both the ADP and action potential bursting could be inhibited by the bath application of nonspecific concentrations of divalent Ca(2+) channel blockers (NiCl and CdCl). Ca(2+) channel blockade also reduced the dendritic action potential duration without significantly affecting spike amplitude. Low concentrations of TTX (10-50 nM) also reduced the ability of the CA1 neurons to fire in the busting mode. This effect was found to be the result of an inhibition of backpropagating dendritic action potentials and could be overcome through the coordinated injection of transient, large-amplitude depolarizing current into the dendrite. Dendritic current injections were able to restore the burst firing mode (represented as a large ADP) even in the presence of high concentrations of TTX (300-500 microM). These data suggest the role of dendritic Na(+) channels in bursting is to allow somatic/axonal action potentials to backpropagate into the dendrites where they then activate dendritic Ca(2+) channels. Although it appears that most Ca(2+) channel subtypes are important in burst generation, blockade of T- and R-type Ca(2+) channels by NiCl (75 microM) inhibited action potential bursting to a greater extent than L-channel (10 microM nimodipine) or N-, P/Q-type (1 microM omega-conotoxin MVIIC) Ca(2+) channel blockade. This suggest that the Ni-sensitive voltage-gated Ca(2+) channels have the most important role in action potential burst generation. In summary, these data suggest that the activation of dendritic voltage-gated Ca(2+) channels, by large-amplitude backpropagating spikes, provides a prolonged inward current that is capable of generating an ADP and burst of multiple action potentials in the soma of CA1 pyramidal neurons. Dendritic voltage-gated ion channels profoundly regulate the processing and storage of incoming information in CA1 pyramidal neurons by modulating the action potential firing mode from single spiking to burst firing.

4-Aminopyridine↗
PubMed2001

Dichotomy of action-potential backpropagation in CA1 pyramidal neuron dendrites.

In hippocampal CA1 pyramidal neurons, action potentials are typically initiated in the axon and backpropagate into the dendrites, shaping the integration of synaptic activity and influencing the induction of synaptic plasticity. Despite previous reports describing action-potential propagation in the proximal apical dendrites, the extent to which action potentials invade the distal dendrites of CA1 pyramidal neurons remains controversial. Using paired somatic and dendritic whole cell recordings, we find that in the dendrites proximal to 280 microm from the soma, single backpropagating action potentials exhibit <50% attenuation from their amplitude in the soma. However, in dendritic recordings distal to 300 microm from the soma, action potentials in most cells backpropagated either strongly (26-42% attenuation; n = 9/20) or weakly (71-87% attenuation; n = 10/20) with only one cell exhibiting an intermediate value (45% attenuation). In experiments combining dual somatic and dendritic whole cell recordings with calcium imaging, the amount of calcium influx triggered by backpropagating action potentials was correlated with the extent of action-potential invasion of the distal dendrites. Quantitative morphometric analyses revealed that the dichotomy in action-potential backpropagation occurred in the presence of only subtle differences in either the diameter of the primary apical dendrite or branching pattern. In addition, action-potential backpropagation was not dependent on a number of electrophysiological parameters (input resistance, resting potential, voltage sensitivity of dendritic spike amplitude). There was, however, a striking correlation of the shape of the action potential at the soma with its amplitude in the dendrite; larger, faster-rising, and narrower somatic action potentials exhibited more attenuation in the distal dendrites (300-410 microm from the soma). Simple compartmental models of CA1 pyramidal neurons revealed that a dichotomy in action-potential backpropagation could be generated in response to subtle manipulations of the distribution of either sodium or potassium channels in the dendrites. Backpropagation efficacy could also be influenced by local alterations in dendritic side branches, but these effects were highly sensitive to model parameters. Based on these findings, we hypothesize that the observed dichotomy in dendritic action-potential amplitude is conferred primarily by differences in the distribution, density, or modulatory state of voltage-gated channels along the somatodendritic axis.

Action Potentials↗
PubMed1976

[Quantitative study of dendritic tree of large (regular) pyramidal cells of lamina V in rat anterior cingular cortex].

At three month old male rats the dendritic trees of 36 large pyramidal cells in the Vth layer of the anterior cingulate cortex were analyzed quantitatively by means of the Golgi-Kopsch method. 12 pyramidal cells were localized at the medial border of the regio praecentralis (neocortex), 12 cells were localized in the adjacent mesoarchicortex, 12 cells were localized in the mesoarchicortex, which are three subregions of the anterior cingulate cortex. By means of a varianz-analysis the values of the three subregions were compared, in order to verify a supposed gradient of differentiation. 1. In the three subregions basal the number and the branching behaviour of the dendrites are greater than apical. The pyramidal cells of the neocortex and of the mesoneocortex have significantly more basal dendrites of the 1st, 2nd, 3rd, and 4th order than those of the mesoarchocortex. There are significantly more apical dendrites of the 1st and 2nd order at pyramidal cells of the neocortex compared with the two other subregions. 2. The total lengths of the dendritic branches are in proportion to the dendritic numbers of the corresponding orders. There are following tendencies for the three subregions: the number and length of apical dendrites decrease with the increasing number of order, basally, however, the number and length first increase and than decrease. 3. The total length of all basal dendrites of a pyramidal cell is largest in the mesoneocortex, than follows the neocortex, least values they find in the mesoarchicortex. There are significant differences between every one of the three subregions. The values of the total dendritic tree of a pyramidal cell (total dendritic length, total number of dendrites, volume of the dendritic tree, number of branching sites and free endings, total apical dendritic length) show significant differences between neocortex and mesoarchicortex as well as between mesoneocortex and mesoarchicortex. There are no significant differences between noecortex and mesoneocortex. The values of the total dendritic tree demonstrate that neocortex and mesoneocortex have a similar organization, while the lamina V-pyramidal cells of the mesoarchicortex indicate a significantly smaller and less branched dendritic tree.

Animals↗
PubMed1981

Distribution of dendrites from biventer cervicis and complexus motoneurons stained intracellularly with horseradish peroxidase in the adult cat.

The three-dimensional distribution of dendrites from the dorsal neck muscles biventer cervicis (BC) and complexus (CM) was examined in the adult cat using intracellular staining techniques. Motoneurons were electrophysiologically identified, stained with injection of horseradish peroxidase, and reconstructed from serial histological sections. The dendritic distributions of all motoneurons examined followed an orderly pattern. Many dendrites extended rostrally and caudally to form of complex parallel collection of dendrites in the ventromedial nucleus. Other dendrites projected dorsolaterally into the spinal accessory nucleus and lateral parts of lamina VII and VIII. Dorsomedial dendrites followed a path parallel to the medial border of the ventral horn are frequently terminated near the central canal. A new scattered dendrites were usually found directly dorsal to the soma in lamina VIII. This pattern of dendritic distribution differed distinctly from the dendritic distribution of motoneurons in other spinal regions. However, in all spinal regions, including the upper cervical spinal cord where BC and CM motoneurons were found, the pattern of dendritic distribution from different motoneurons was similar if their somata were located in the same region. For 15 motoneurons with well-stained dendrites, the mean rostral-caudal extent of the dendritic tree was 2,860 micrometers. The mean total dendritic length of three of these motoneurons measured 73,100 micrometers, almost four times larger than hindlimb motoneurons involved in planter reflexes. Despite the large size of the dendritic trees of BC and CM motoneurons, the surface areas of BC and CM cell bodies were smaller than most large hindlimb motoneurons. These quantitative differences in motoneuron dimensions may in turn be reflected by differences in the electrotonic properties of motoneurons in different motoneuron nuclei.

Animals↗
PubMed1984

Dendritic distribution of motoneurons innervating the three heads of the trapezius muscle in the cat.

The organization of the nuclei and dendritic architecture of motoneurons innervating the three heads of the trapezius muscle, clavotrapezius (CT), acromiotrapezius (AT), and spinotrapezius (ST), have been examined by using intracellular staining techniques. CT, AT, and ST motoneurons were found in the spinal accessory nucleus and were arranged in three overlapping subnuclei. CT motoneurons were primarily found in C2 and C3. In contrast, most AT motoneurons were found in C3, C4, and C5 and ST motoneurons were found in C4, C5, and the rostral parts of C6. Most dendrites of CT motoneurons, located in rostral C2, extended dorsally and many of these dendrites spread medially and laterally to encompass all of lamina VIII and the dorsolateral part of lamina VII. When viewed in the horizontal plane these motoneurons had a stellate appearance. The dendritic tree structure of CT motoneurons changed abruptly between rostral C2 and mid-C2. The majority of dendrites of CT motoneurons located in the central and caudal parts of C2 projected rostrally and caudally to form a complex bundle of dendrites in the motoneuron nucleus. Small numbers of dendrites were also found ventromedial and dorsal to the soma. The dendritic trees of CT motoneurons in C3 and C4 and AT and ST motoneurons located in C4 and the rostral parts of C5 also followed this fusiform distribution pattern. The dendritic trees of AT and ST motoneurons in caudal C5 were not fusiform but instead had a complex distribution pattern which consisted of dendrites projecting in several directions. Many dendrites projected rostrally and caudally, and in addition, there were major dendritic projections ventrolateral and dorsolateral to the soma. These results indicate that each head of the trapezius muscle is innervated by two structurally dissimilar groups of motoneurons which occupy different spinal segments. Trapezius motoneurons at the same segmental level, regardless of which head of the trapezius muscle they innervated, have similar dendritic trees whose structure differs from those of neighbouring dorsal neck muscle motoneurons in C2, C3, and C4. Thus, the organization of motoneuron dendritic trees appears to be governed by several factors including the muscle innervated by the motoneuron and the transverse and segmental position of the motoneuron's soma.

Animals↗
PubMed1987

Membrane area and dendritic structure in type-identified triceps surae alpha motoneurons.

The size and branching structure of the dendritic tree were studied in nine type-identified triceps surae alpha-motoneurons that were labeled intracellularly with horseradish peroxidase and reconstructed from serial sections in the light microscope. The average total membrane area (AN) for motoneurons of type S (slow-twitch) motor units was about 22% smaller than AN for cells of type F units (including both FF and FR motor unit types in this category) (480.1 X 10(3) microns 2 vs. 617.7 X 10(3) microns 2, respectively). Systematic correlations were found between stem dendrite diameter and three measures of dendritic size: dendrite membrane area, combined dendritic length, and number of terminations. All of these correlations were significantly different for the dendrites of F and S motoneurons. Power-function relations between stem diameter and dendritic membrane area were used to estimate AN for a sample of 79 type-identified motoneurons. Mean estimated AN values were significantly different for the F and S motoneuron groups, despite a large overlap in AN values between these groups. The branching structure of dendrites of F and S motoneurons also showed clear differences. Type S motoneuron dendrites showed less-profuse branching and a more-even radial distribution of branch points than found in type F cells. Examination of two forms of the "3/2 power rule" for the relation between the diameters of parent and daughter dendritic branches at branch points showed that the dendrites of type S motoneurons conform less well with the anatomical constraints necessary to represent binary branching trees as equivalent cylinders than do dendrites of type F cells. There was no systematic difference between F and S motoneuron dendrites in the degree of asymmetry of first-order daughter trees. The results overall indicate that the dendrites of F and S motoneuron groups are structurally different, giving rise to a systematic difference in AN between these groups. Such structural differences suggest that the F and S groups of alpha-motoneurons can be viewed as intrinsically distinct cell types and not just large vs. small variants of the same cell species.

Animals↗
PubMed1990

Dendritic morphology and development in the ferret medial superior olivary nucleus.

Dendritic morphology and development in the medial superior olivary nucleus of the ferret were studied using the Golgi method. In the adult ferret most medial superior olivary neurons had disk-shaped dendritic fields. These dendritic fields were oriented such that cells in a coronal plane of section appeared bipolar with major lateral and medial dendritic axes. In the horizontal plane the dendrites radiated about the soma. Dendrites of principal cells branched distally into tufts of numerous, tertiary processes that were beaded and thin. Peripheral cells in the fiber mantle encircling the nucleus were generally spindle-shaped or tripolar and lacked the tufted dendrites of principal cells. The dendrites of these peripheral cells coursed parallel to the nucleus both dorsoventrally and rostrocaudally. Horizontally oriented dendrites were observed even at birth for some cells in the medial superior olivary nucleus and bipolar dendritic fields were typical of most cells by the end of the second postnatal week. Dendrites of immature cells varied in caliber and radiated in all directions from the soma. Around postnatal days 8-10 transient appendages appeared on the soma and dendrites, first proximally and then more distally. These appendages persisted until the first postnatal month. Cell size and dendritic radius increased markedly during this same period. Postnatal days 28-30 were marked by the first appearance of tufts of tertiary dendritic branches. The tendril-like processes continued to increase in length until about the end of the second postnatal month.

Aging↗
PubMed1992

Changes in size and dendritic arborization patterns of adult cat spinal alpha-motoneurons following permanent axotomy.

This study was performed to analyse quantitatively the changes in dimensions and dendritic branching patterns of adult cat spinal alpha-motoneurons following permanent axotomy, i.e., in a situation in which the transected motoraxons are prevented from reinnervating their peripheral target muscle. After transection and ligation of the medial gastrocnemius nerve of adult cats, homonymous alpha-motoneurons were intracellularly labelled with horseradish peroxidase and subjected to quantitative light microscopic analyses. The cell bodies and proximal dendrites were studied at 3, 6, and 12 weeks after the axotomy. An initial increase in cell body size at 3 weeks was followed by a gradual return towards normal values. The mean diameter of the stem dendrites was decreased at all time periods studied, and the combined diameter of the stem dendrites was reduced at 12 weeks after the axotomy. Entire dendritic trees were reconstructed at 12 weeks postoperatively, and the regression equations describing the correlations between dendritic stem diameter, on one hand, and the size of the entire dendrite, on the other, were used to calculate the total dendritic length, volume, and membrane area of whole axotomized motoneurons. The dendritic branching patterns were also analysed. In comparison with normal medial gastrocnemius alpha-motoneurons, the dendritic membrane area and volume of the axotomized cells had decreased by 36% and 29%, respectively, at 12 weeks after the axotomy. This reduction in dendritic size was due to a loss of preterminal and terminal dendritic segments. Abnormal dendritic elongations were observed in 2 of 16 completely reconstructed dendrites.

Analysis of Variance↗
PubMed1992

Restorative effects of reinnervation on the size and dendritic arborization patterns of axotomized cat spinal alpha-motoneurons.

In a preceding paper [Brännström, et al. (1992) J. Comp. Neurol. 318:439-451] a marked reduction in dendritic size was observed in cat spinal motoneurons following permanent axotomy. The aim of the present study was to analyse the possible restorative effects of peripheral reinnervation on the size and dendritic branching patterns of cat spinal motoneurons which had been deprived of neuromuscular contact for an extended period of time. In adult cats the medial gastrocnemius (MG) nerve was transected and ligated. After 6 weeks the nerve was allowed to reinnervate its muscle through a nerve graft. With approximately 6 weeks needed for muscle reinnervation [Foehring, et al. (1986) J. Neurophysiol. 55:947-965], the MG motoneurons were devoid of neuromuscular contact for altogether about 12 weeks. Two years later reinnervated MG alpha-motoneurons were intracellularly labelled with horseradish peroxidase to allow quantitative analyses of the cell bodies and dendritic trees. Comparisons were made with previous data from normal and permanently axotomized MG motoneurons. The reinnervated motoneurons exhibited positive correlations between dendritic stem diameter, on one hand, and combined length, volume, membrane area, and number of end branches of the whole dendrite, on the other. By using the regression equations for these correlations, the total dendritic size of whole reinnervated motoneurons could be estimated. Such calculations showed that in comparison with the reduction in dendritic size found at 12 weeks after permanent axotomy (Brännström et al., see above), peripheral reinnervation caused the dendritic volume and membrane area to return to normal values. However, the values for combined dendritic length and number of dendritic end branches were still reduced by more than 25% as compared to the normal situation. The results indicate that following reinnervation of the target muscle, the axotomized motoneurons did not recover their original number of dendritic branches. The normalization of dendritic membrane area and volume was instead accomplished by two other mechanisms, namely an increase in dendritic diameters and an increased number of dendrites per neuron.

Animals↗
PubMed1993

A quantitative dendritic analysis of Wernicke's area in humans. II. Gender, hemispheric, and environmental factors.

This quantitative Golgi study extends our investigation of relationships between cortical dendrite systems in humans and higher cognitive functions. Here we examine the relationship between the basilar dendrites of supragranular pyramidal cells in Wernicke's area and selected intrinsic (i.e., gender and hemisphere) and extrinsic (i.e., education and personal history) variables. Tissue was obtained from 20 neurologically normal right-handers: 10 males (Mage = 52.2) and 10 females (Mage = 47.8). Several independent variables were investigated: GENDER (male, female), HEMISPHERE (left, right), and EDUCATION (less than high school, high school, and university). These were evaluated according to Total Dendritic Length, Mean Dendritic Length, and Dendritic Segment Count. A distinction was made between proximal (1st, 2nd, and 3rd order) and ontogenetically later developing distal (4th order and above) branches. There was significant interindividual variation in dendritic measurements, which roughly reflected individuals' personal backgrounds. Females exhibited slightly greater dendritic values and variability than males across the age range examined. On the whole, the left hemisphere maintained a slight advantage over the right hemisphere for all dendritic measures when all subjects were pooled, but these differences were not in a consistent direction across individuals. Education had a consistent and substantial effect such that dendritic measures increased as educational levels increased. Dendritic differences between independent variable levels were most clearly illustrated in the total dendritic length of 3rd and 4th order branches. Distal dendritic branches appeared to exhibit greater epigenetic flexibility than proximal dendrites. The present findings concur with environmental enrichment research results in animals and suggest that dendritic systems in humans function as a sensitive indicator of an individual's (a)vocational activities.

Adolescent↗
PubMed1994

Development of the dendritic fields of layer 3 pyramidal cells in the kitten's visual cortex.

The cat's visual cortex is immature at birth and undergoes extensive postnatal development. For example, cells of layers 2 and 3 do not complete migration until about 3 weeks after birth. Despite the importance of dendritic growth for synaptic and functional development, there have been few studies of dendritic development in the cat's visual cortex to correlate with numerous studies of functional and synaptic development. Accordingly, we used the Golgi method to study the development of the dendrites of layer 3 pyramidal cells in the visual cortex of a series of cats ranging in age from 2 days to 3 years. Blocks of visual cortex were impregnated by the Golgi-Kopsch method and sectioned in the tangential plane. Layer 3 pyramidal cells were drawn with a camera lucida and analyzed by Sholl diagrams and vector addition. In kittens < 1 week old, these cells were very immature, with only an apical dendrite and no basal dendrites. Basal dendrites appeared during the second week. By 2 weeks, all of the basal dendrites had emerged from the soma, but they had few branches and were tipped with growth cones. By 4 weeks, they had finished branching but continued to grow in length until, by 5 weeks, they reached their adult size. Examination of the basal dendritic fields in the tangential plane revealed that their dendritic fields were more elongated at 2 weeks than at later ages, perhaps because of their smaller size. The distribution of dendritic field orientations was uniform at all ages except 3 and 4 weeks, when there was a preponderance of fields oriented in the rostrocaudal direction. Because dendritic growth and branching occurred very rapidly over a period that precedes and overlaps with the peak periods of synaptogenesis and of sensitivity to the effects of early visual experience, they may depend on afferent visual activity. The early emergence of primary dendrites, however, suggests that this process is independent of afferent activity. The coincident timing of dendritic branching with the presence of dendritic growth cones suggests that branching may occur at growth cones.

Aging↗
PubMed2002

BMP-7 and excess glutamate: opposing effects on dendrite growth from cerebral cortical neurons in vitro.

Glutamate is an important regulator of dendrite development. During cerebral ischemia, however, there is massive release of glutamate reaching millimolar concentrations in the extracellular space. An early consequence of this excess glutamate is reduced dendrite growth. Bone morphogenetic protein-7 (BMP-7) a member of the transforming growth factor-beta (TGF-beta) superfamily has been demonstrated to enhance dendrite output from cerebral cortical and hippocampal neurons in vitro. However, it is not known whether BMP-7can prevent the reduced dendrite growth associated with excess glutamate or enhance dendrite growth after glutamate exposure. Therefore we quantified axon and primary, secondary, and total dendrite growth from embryonic mouse cortical neurons (E18) grown at low density in vitro in a chemically defined medium and exposed to glutamate (1 or 2 mM) for 48 h. Morphology and double immunolabeling (MAP2, NF-H) were used to identify cortical dendrites and axons after 3 DIV. In these short-term cultures, glutamate did not influence neuron survival. The addition of glutamate to cortical neurons, however, significantly attenuated dendrite output. This effect was mimicked by the addition of NMDA but not AMPA agonists and inhibited by the specific NMDA receptor antagonist MK-801. The reduction in dendrite growth mediated by excess glutamate was ameliorated by the administration of 30 or 100 ng/ml of BMP-7. In addition, when administered in a delayed fashion between 1 and 24 h after the initial glutamate exposure, BMP-7 was able to enhance dendrite growth, including primary dendrite number, primary dendrite length, and secondary dendritic branching. These findings demonstrate that BMP-7 can ameliorate reduced dendrite growth from cerebral cortical neurons associated with excess glutamate in vitro and are important because they may help explain why BMP-7 administration is associated with enhanced functional recovery in models of cerebral ischemia.

Animals↗
PubMed1985

The development of the dendritic organization of primary and secondary motoneurons in the spinal cord of Xenopus laevis. An HRP study.

During embryonic and larval development of the clawed toad, Xenopus laevis, two different populations of motoneurons appear in the spinal cord. In this study the development of primary motoneurons which innervate the axial musculature (used during embryonic locomotion) and of secondary motoneurons which innervate the extremity musculature (used for locomotion during metamorphosis and thereafter) was analyzed with horseradish peroxidase (HRP) as a neuronal marker. After application of HRP to the axial musculature (rostral five postotic myotomes) the first labeled primary motoneurons were found at stage 24/25. During development gradually more labeled neurons were observed. These primary motoneurons send their dendrites into the marginal zone (white matter). At first only dorsal and lateral dendrites develop (stages 25-33), followed by ventral dendrites (stage 37/38). Up till stage 48 the developing dendrites extend throughout the marginal zone. Hereafter the marginal zone increases particularly at the dorsolateral edge, a development which is not followed by the dendrites of the primary motoneurons. The dendrites of mature primary motoneurons (stages 58-62) occupy the ventral and ventrolateral parts of the marginal zone. At stage 48, shortly after the hindlimb bud arises (stage 46, early metamorphosis), the first neurons related to this developing extremity could be labeled in the ventrolateral part of the lumbar spinal cord. At first these secondary motoneurons bear only a few dorsal dendrites of which only the tips reache out in the adjacent white matter. Already at stage 50 these dorsal dendrites have invaded the whole dorsolateral part of the marginal zone. Also the first ventral dendrites were observed at this stage. Later, at stage 53/54 also some ventral dendrites have reached the white matter together with a few lateral dendrites. At these early metamorphic stages already some primary afferent fibers were found making contact with the dorsomedial dendrites. At stage 58 for the first time recurrent axon collaterals were found, which extend into the ventromedial part of the marginal zone. The development of motoneurons in the spinal cord seems to be characterized by two phases: (1) establishment of contacts between motoneurons and target muscles, and (2) subsequent formation of connections of these motoneurons with other nerve cells within the central nervous system. The dendrites of primary motoneurons follow the development of the marginal zone, while dendrites of secondary motoneurons develop into an already well developed marginal zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Relationship of Met-enkephalin-like immunoreactivity to vagal afferents and motor dendrites in the nucleus of the solitary tract: a light and electron microscopic dual labeling study.

Methionine (Met5)-enkephalin has been implicated in autonomic functions involving vagal reflexes within the nucleus of the solitary tract (NTS). We examined the light and electron microscopic relationships between neurons containing methionine (Met5)-enkephalin-like immunoreactivity (MELI) and vagal afferents and motor dendrites in the rat NTS. A polyclonal antibody raised against Met5-enkephalin and showing maximal cross-reactivity with this peptide was localized by immunoautoradiography. In the same sections, vagal afferents and motor neurons were identified by histochemical detection of anterogradely and retrogradely transported horseradish peroxidase (HRP). By light microscopy, the MELI was detected in perikarya distributed principally in the dorsomedial, intermediate and parasolitary subdivisions of the NTS. These subnuclei as well as medial and commissural divisions of the NTS also showed: (1) aggregates of silver grains thought to overlie terminals containing MELI, and (2) anterogradely transported HRP in varicose processes. Electron microscopic analysis of the dorsomedial NTS at the level of the area postrema established that MELI was detectable in perikarya, dendrites, and axon terminals. Most of the MELI was associated with large dense core vesicles (dcvs). These opioid terminals formed primarily symmetric synapses on proximal and asymmetric synapses on distal dendrites. Analysis of the dendritic targets of terminals containing MELI revealed that 13/222 were in synaptic contact with dendrites also containing MELI. The remainder of the terminals containing MELI either lacked recognized junctions or formed synapses with unlabeled dendrites. In comparison to the terminals containing MELI in the same series of sections, anterogradely labeled vagal terminals extensively formed asymmetric junctions with distal dendrites and spines. Of the observed anterogradely labeled terminals 6/84 formed synapses with dendrites containing MELI and 3/84 with dendrites containing retrogradely transported HRP. The remainder of the junctions were with dendrites lacking detectable immunoautoradiographic or HRP-labeling. The majority of the recognized synapses on labeled dendrites were at more proximal sites possibly reflecting more limited detection of both MELI and retrogradely transported HRP in smaller dendrites. However, the presence of even a few junctions at proximal sites on dendrites where synaptic transmission is known to be more effective suggests a potentially strong modulation of both opioid and vagal motor neurons by visceral afferents in the NTS. In addition to forming synapses on dendrites, both vagal afferents and terminals containing MELI showed frequent synaptic associations with unlabeled terminals, but not with each other. This finding suggests that the previously demonstrated opiate binding sites on vagal afferents is most likely attributed to other endogenous opiates.

Afferent Pathways↗
PubMed1982

The dendritic organization of the human spinal cord: the dorsal horn.

The human spinal cord was studied with the Golgi method from 26 weeks gestational age onto adult life. Impregnated neurons were analyzed morphometrically by an adaptation of Sholl's concentric circle method in order to specify dendritic geometry, ramification richness and branching pattern. Neurons were classified according to Rexed's laminar scheme, identified on adjacent Nisslstained sections. The following features were found to be characteristic of the dorsal horn laminae. Lamina I is formed of a uniform population of large, poorly ramified neurons. Their main dendritic domaine is disk-shaped in the tangential plane with a mean diameter of about 800 micrometers. Orthogonal, spiny dendrites penetrating into lamina II are numerous even in adult material. Four cell types, all lying in the sagittal plane, are found in lamina II. (1) "Islet cells' (about 30% of impregnated neurons) have a rostrocaudal, cylindrical dendritic domaine with a long axis of +/- 600 micrometers, a few scattered spines and a richly branched axonal network, confined to the dendritic territory. They are more numerous in the central part of lamina II. A few islet cells have two axons. (2) "Filamentous cells' (about 20%), so called because of their multiple filiform, spiny dendrites, are vertico-sagittally oriented. Their soma is located in inner or outer lamina II, their dendritic tree, trapezoïd of about 280 micrometers in height, being dorsal or ventral. The axon emits some collaterals in the vicinity of the dendritic tree, then it penetrates into lamina I or Lissauer's tract. (3) "Curly cells' (about 10%) have a complex, twisted, spine-rich dendritic tree. The dendritic domaine can be schematized by a sagittal disk with a diameter of about 200 micrometers, the cell body being eccentric. Curly cells are mainly found in outer lamina II. Their axon penetrates into lamina I or Lissauer's tract. (4) "Stellate cells' (about 40%) are multipolar neurons preferentially found in inner lamina II. They have straight, spine-poor dendrites, which cover a large (longest diameter ca. 500 micrometers), elliptical territory extending into laminae I and III. Their axon gives longitudinal collaterals to lamina II before penetrating deeply into laminae III and IV. Lamina III contains a mixed population of "antenna-like neurons' with a vertical, cone-shaped dendritic domaine and "radiate cells' characterized by a small, spherical territory. All lamina IV neurons are medium or large sized "antenna-like neurons' whose dorsally oriented, cone-shaped dendritic domaine may have a height of 1000 micrometers. It can be concluded that the dorsal horn of the human spinal cord has several distinct dendroarchitectonic features, different from those reported in animals. The possible functional implication of some dendritic features is examined and a laminar dendroarchitectonic scheme of the human cord is proposed as a morphological tool for future neuroanatomical and neuropathological studies.

Adult↗
PubMed2006

Dendritic morphogenesis of cerebellar Purkinje cells through extension and retraction revealed by long-term tracking of living cells in vitro.

Cerebellar Purkinje cells have the most elaborate dendritic trees among the neurons in the CNS. To investigate the dynamic aspects of dendritic morphogenesis of Purkinje cells, we performed a long-term analysis of living cells in cerebellar cell cultures derived from glutamate decarboxylase 67-green fluorescent protein mice. Most Purkinje cells had several primary dendrites during the 25-day culture period. Repeated observation of green fluorescent protein-expressing Purkinje cells over a period of 10-25 days in vitro demonstrated that not only extension, but also retraction of primary dendrites occurred during this culture period. Interestingly, both extension and retraction of primary dendrites were active between 10 and 15 days in vitro, and retraction of a primary dendrite occurred concomitantly with elongation of other primary dendrites in the same cell. Analysis of the morphological characteristics of the retracted primary dendrites demonstrated that shorter and less branched primary dendrites tended to retract. Furthermore, treatment with an inhibitor of calcium/calmodulin-dependent protein kinase II reduced the number of primary dendrites specifically during 5-15 days in vitro, the culture period when the extension and retraction of primary dendrites occurred actively. Blockade of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-type glutamate receptors also reduced the number of primary dendrites during the same culture period, while inhibition of glutamate transporters increased the number. These findings suggest that the final morphology of Purkinje cells is achieved not only through extension, but also through retraction of their dendrites, and that calcium/calmodulin-dependent protein kinase II and neuronal activity are involved in this dendritic morphogenesis.

Animals↗
PubMed2002

Natural killer and dendritic cell contact in lesional atopic dermatitis skin--Malassezia-influenced cell interaction.

The regulation of dendritic cells is far from fully understood. Interestingly, several recent reports have suggested a role for natural killer cells in affecting dendritic cell maturation and function upon direct contact between the cells. It is not known if this interaction takes place also in vivo, or if a potential interaction of natural killer cells and dendritic cells would be affected by allergen exposure of the dendritic cells. The yeast Malassezia can act as an allergen in atopic eczema/dermatitis syndrome, and induce maturation of dendritic cells. Our aims were to study the distribution of natural killer cells in the skin from atopic eczema/dermatitis syndrome patients with the emphasis on possible natural killer cell-dendritic cell interaction, and to assess whether the interaction of Malassezia with dendritic cells would affect subsequent interaction between dendritic cells and natural killer cells. A few scattered natural killer (CD56+/CD3-) cells were found in the dermis of healthy individuals and in nonlesional skin from atopic eczema/dermatitis syndrome patients. In lesional skin and in biopsies from Malassezia atopy-patch-test-positive skin, however, natural killer cells were differentially distributed and for the first time we could show close contact between natural killer cells and CD1a+ dendritic cells. Dendritic cells preincubated with Malassezia became less susceptible to natural-killer-cell-induced cell death, suggesting a direct effect imposed by Malassezia upon interaction of dendritic cells with natural killer cells. These findings indicate that natural killer cells and dendritic cells can interact in the skin and that Malassezia affects the interaction between natural killer cells and dendritic cells. Our data suggest that natural killer cells may play a role in regulating dendritic cells in atopic eczema/dermatitis syndrome.

Cell Communication↗