Dendritic Bundles Research Articles

Neurotrophin-3 Is Involved in the Formation of Apical Dendritic Bundles in Cortical Layer 2 of the Rat

Apical dendritic bundles from pyramidal neurons are a prominent feature of cortical neuropil but with significant area specializations. Here, we investigate mechanisms of bundle formation, focusing on layer (L) 2 bundles in rat granular retrosplenial cortex (GRS), a limbic area implicated in spatial memory. By using microarrays, we first searched for genes highly and specifically expressed in GRS L2 at postnatal day (P) 3 versus GRS L2 at P12 (respectively, before and after bundle formation), versus GRS L5 (at P3), and versus L2 in barrel field cortex (BF) (at P3). Several genes, including neurotrophin-3 (NT-3), were identified as transiently and specifically expressed in GRS L2. Three of these were cloned and confirmed by in situ hybridization. To test that NT-3–mediated events are causally involved in bundle formation, we used in utero electroporation to overexpress NT-3 in other cortical areas. This produced prominent bundles of dendrites originating from L2 neurons in BF, where L2 bundles are normally absent. Intracellular biocytin fills, after physiological recording in vitro, revealed increased dendritic branching in L1 of BF. The controlled ectopic induction of dendritic bundles identifies a new role for NT-3 and a new in vivo model for investigating dendritic bundles and their formation.

Virtual Fly Brain: An image-linked ontology of the Drosophila Brain

Event Abstract Back to Event Virtual Fly Brain: An image-linked ontology of the Drosophila Brain David Osumi-Sutherland1*, Mark Longair2 and J. Douglas Armstrong2 1 University of Cambridge, United Kingdom 2 University of Edinburgh, School of Informatics, United Kingdom Introduction:Drosophila neuro-anatomical data is scattered across a large, diverse literature dating back over 75 years and a growing number of community databases. Lack of a standardized nomenclature for neuro-anatomy makes comparison and searching this growing data-set extremely arduous. Common criteria for classification of neurons include: which tracts their axons fasciculate in; which neuropil domains they innervate; their morphology; their function; their circuit position; what neurotransmitter they release; their lineage. Large amounts of data pertaining to these classifications exist, but have not been standardized or integrated in any queriable resource.A recent standardization effort [1] has produced a segmented, 3D model of gross Drosophila brain anatomy annotated with a controlled vocabulary. We are formalizing this to produce an image-linked ontology that will provide a substrate for defining neuronal types in according to where fasciculation and innervation patterns. Neuronal types are also classified in the ontology according to neurotransmitter released, lineage and function. The resulting ontology provides both a vocabulary for annotation and a means for integrative queries of neurobiological data. Results: General mereological relationships (part-hood, connectedness) are useful in defining relations between neuronal classes and gross anatomy, but are not sufficient to capture biologically important details (e.g.- fasciculation, innervation). We are developing relations to capture this information. For example: fasciculates_with - relation between a neuron and an axonal or dendritic bundle that its axon or dendrite is part of (implies mereological overlap [2])innervates - relation between a neuron and a structure in which it has a synapse (implies mereological overlap [2]).We are also developing methods to record neurotransmitter released (classified according to the chemical ontology, CHEBI) and function (classified according to gene ontology biological process terms) and systems for asserted classification of neurons according to morphology and circuit position. We are recording lineage using existing relations. Future Aims:In collaboration with FlyBase, the combined ontology and image data will provide the basis for an web-based, image-linked query system for Drosophila neuro-anatomical data and related genetic data. INCF-09-133-edit INCF-09-133

Eccles’s Psychons Could Be Zero-Energy Tachyons

This paper suggests that mental units called psychons by Eccles could be tachyons defined theoretically by physicists sometime ago. Although experiments to detect faster-than-light particles have not been successful so far, recently, there has been renewed interest in tachyon theories in various branches of physics. We suggest that tachyon theories may be applicable to brain physics. Eccles proposed an association between psychons and what he called dendrons which are dendrite bundles and basic anatomical units of the neocortex for reception. We show that a zero-energy tachyon could act as a trigger for exocytosis (modeled by Friedrich Beck as a quantum tunneling process), not merely at a single presynaptic terminal but at all selected terminals in the interacting dendron by momentarily transferring momentum to vesicles, thereby decreasing the effective barrier potential and increasing the probability of exocytosis at all boutons at the same time. This is consistent with the view of tachyons, which treats them as strictly non-local phenomenon produced and absorbed instantaneously and non-locally by detectors acting in a coherent and cooperative way.

Dendrodendritic and dendrosomatic contacts between oculomotor and trochlear motoneurons of the frog, Rana esculenta

Gaze fixation requires very fast movements of the eye during body displacement. The morphological and physiological background of the very fine and continuous tuning of gaze fixation is not yet fully understood. In a previous study we have shown that the dendrites of oculomotor neurons form bundles which invade the trochlear nucleus, and vice versa, trochlear dendritic bundles invade the oculomotor nucleus. Earlier physiological observations demonstrating electrotonic coupling between dendrites of spinal motoneurons in the frog suggest a similar mechanism between the oculomotor and trochlear motoneurons. We studied a possible morphological basis of gaze fixation. The experiments were carried out on common water frogs, Rana esculenta. The trochlear and oculomotor nerves were cut, and their proximal stumps were labeled simultaneously with different retrograde fluorescent tracers. Using confocal laser scanning microscope we detected a large number of close contacts in both nuclei, the majority of them were dendrodendritic apposition. The distance between the adjacent profiles suggested close membrane appositions without intercalating glial or neuronal elements. At the ultrastructural level, the dendrodendritic and dendrosomatic contacts did not show any morphological specialization; the long membrane appositions may provide ephaptic interactions between the neighboring profiles. This electrotonic coupling between the oculomotor and trochlear nerve motoneurons may promote the co-activation of the muscles responsible for vertical eye movements.

Synaptic Connections between Layer 5B Pyramidal Neurons in Mouse Somatosensory Cortex Are Independent of Apical Dendrite Bundling

Rodent somatosensory barrel cortex is organized both physiologically and anatomically in columns with a cross-sectional diameter of 100-400 microm. The underlying anatomical correlate of physiologically defined, much narrower minicolumns (20-60 microm in diameter) remains unclear. The minicolumn has been proposed to be a fundamental functional unit in the cortex, and one anatomical component of a minicolumn is thought to be a cluster of pyramidal cells in layer 5B (L5B) that contribute their apical dendrite to distinct bundles. In transgenic mice with fluorescently labeled L5B pyramidal cells, which project to the pons and thalamus, we investigated whether the pyramidal cells of a cluster also share functional properties. We found that apical dendrite bundles in the transgenic mice were anatomically similar to apical dendrite bundles previously proposed to be part of minicolumns. We made targeted whole-cell recordings in acute brain slices from pairs of fluorescently labeled L5B pyramidal cells that were located either in the same cluster or in adjacent clusters and subsequently reconstructed their dendritic arbors. Pyramids within the same cluster had larger common dendritic domains compared with pyramids in adjacent clusters but did not receive more correlated synaptic inputs. L5B pyramids within and between clusters have similar connection probabilities and unitary EPSP amplitudes. Furthermore, intrinsically bursting and regular spiking pyramidal cells were both present within the same cluster. In conclusion, intrinsic electrical excitability and the properties of synaptic connections between this subtype of L5B pyramidal cells are independent of the cell clusters defined by bundling of their apical dendrites.

Unusual Patch-Matrix Organization in the Retrosplenial Cortex of the reeler Mouse and Shaking Rat Kawasaki

The rat granular retrosplenial cortex (GRS) is a simplified cortex, with distinct stratification and, in the uppermost layers, distinct modularity. Thalamic and cortical inputs are segregated by layers and in layer 1 colocalize, respectively, with apical dendritic bundles originating from neurons in layers 2 or 5. To further investigate this organization, we turned to reelin-deficient reeler mouse and Shaking rat Kawasaki. We found that the disrupted lamination, evident in Nissl stains in these rodents, is in fact a patch-matrix mosaic of segregated afferents and dendrites. Patches consist of thalamocortical connections, visualized by vesicular glutamate transporter 2 (VGluT2) or AChE. The surrounding matrix consists of corticocortical terminations, visualized by VGluT1 or zinc. Dendrites concentrate in the matrix or patches, depending on whether they are OCAM positive (matrix) or negative (patches). In wild-type rodents and, presumably, mutants, OCAM(+) structures originate from layer 5 neurons. By double labeling for dendrites (filled by Lucifer yellow in fixed slice) and OCAM immunofluorescence, we ascertained 2 populations in reeler: dendritic branches either preferred (putative layer 5 neurons) or avoided (putative supragranular neurons) the OCAM(+) matrix. We conclude that input-target relationships are largely preserved in the mutant GRS and that dendrite-dendrite interactions involving OCAM influence the formation of the mosaic configuration.

Combing and self-assembly phenomena in dry films of Taxol-stabilized microtubules.

Microtubules are filamentous proteins that act as a substrate for the translocation of motor proteins. As such, they may be envisioned as a scaffold for the self-assembly of functional materials and devices. Physisorption, self-assembly and combing are here investigated as a potential prelude to microtubule-templated self-assembly. Dense films of self-assembled microtubules were successfully produced, as well as patterns of both dendritic and non-dendritic bundles of microtubules. They are presented in the present paper and the mechanism of their formation is discussed.

Interconnected Network of Ganglion-Like Neural Cell Spheres Formed on Hydrozoan Skeleton

Identifying scaffolds supporting in vitro reconstruction of active neuronal tissues in their 3-dimensional (3D) conformation is a major challenge in tissue engineering. We have previously shown that aragonite coral exoskeletons support the development of neuronal tissue from hippocampal neurons and astrocytes. Here we show for the first time that the porous aragonite skeleton obtained from bio-fabricated hydrozoan Millepora dichotoma supports the spontaneous organization of dissociated hippocampal cells into highly interconnected 3D ganglion-like tissue formations. The ganglion-like cell spheres expanded hundreds of microns across and included hundreds to thousands of astrocytes and mature neurons, most of them having only cell-cell and no cell-surface interactions. The spheres were linked to the surface directly or through a neck of cells and were interconnected through thick bundles of dendrites, varicosity-bearing axons, and astrocytic processes. Thus, M. dichotoma exoskeleton is a novel scaffold with the unprecedented ability to support a highly ordered organization of neuronal tissue. This unexpected organization opens new opportunities for neuronal tissue regeneration, because the spheres resemble in vivo nervous tissue having high volume of cells associated primarily through cell-cell rather than cell-matrix interactions.

Microanatomy in 21 day rat brains exposed prenatally to cocaine

We examined cell minicolumns, apical dendrite bundles, and inhibitory interneurons, in prefrontal and somatosensory cortex of 21-day-old rat brains exposed to cocaine during fetal development. Cell columns and apical dendrite bundles were found to be narrower, or closer together, in all three areas following in utero cocaine exposure. The inter-rater reliability among different observers was R2=0.89. The number of cells stained for glutamic acid decarboxylase (GAD) was not significantly different in the prenatal cocaine exposed group compared to saline controls. The present data suggests that recreational doses of cocaine administered intravenously in early pregnancy, have the capacity to modify the maturation of the ontogenetic cell column.

Zinc-rich transient vertical modules in the rat retrosplenial cortex during postnatal development

The rat retrosplenial cortex is part of a heavily interconnected limbic circuit, considered to have an important role in spatial memory. Interestingly, the granular retrosplenial cortex has an exceptionally distinct system of dendritic bundles, originating from callosally projecting pyramidal neurons in layer II. These can be detected as early as postnatal day 5; and, although their functional significance remains to be elucidated, the existence of these bundles makes the granular retrosplenial cortex an attractive model system for a wide range of development and functional investigations. Here, we report four results concerning the development of modularity in the granular retrosplenial cortex in rats as investigated by neurochemical markers associated to cortico-cortical and thalamo-cortical connections. Emphasis is placed on zinc, an activity-related substance associated with glutamatergic, non-thalamic terminations. 1) Zinc shows a transient strong expression during early postnatal development, but later than the appearance of the upper layer bundles (at postnatal day 5). By postnatal day 11 to postnatal day 15 staining for zinc achieved its most complex pattern; such that layer I had an elaborate organization both in the tangential and radial dimensions. Three sublaminae were distinguished (layers Ia–c): a superficial, thin tier (Ia) with patchy, moderate staining which periodically intruded into the underlying layer Ib (“funnel” modules), a middle band of variable width and light staining (Ib), and a deep, thin band with heavy and patchy staining (Ic) which, at rostral levels, spread upward into layer Ib (as “dome-like” modules). 2) At postnatal day 15, immunohistochemical methods showed that layers Ia, b zinc-funnels were co-localized with glutamate receptor subunits 2/3, GABA receptor type A α1 subunit and the thalamo-cortical marker, vesicular glutamate transporter 2. Layer Ic and the zinc dome-like modules were co-labeled for the cortico-cortical marker, vesicular glutamate transporter 1 and calretinin. 3) The spatial coincidence between zinc funnels in layers Ia, b and vesicular glutamate transporter 2 was further investigated by electron microscopy, which demonstrated co-localization of zinc and vesicular glutamate transporter 2 in synaptic boutons. The unusual co-localization of zinc and thalamo-cortical terminations was confirmed by retrograde transport of zinc to neurones in the anterodorsal thalamic nucleus at postnatal day 9 and postnatal day 13, and can thus be considered a transient zinc expression in thalamo-cortical boutons. This was not observed at postnatal day 28 or later. 4) After postnatal day 18, zinc staining started to fade in all layers. Before postnatal day 21, the heavy staining for zinc in the domes had completely disappeared. Zinc staining in layer Ia and the funnels virtually disappeared after postnatal day 28. A transient expression of zinc is reported in at least one other cortical area (layer IV of barrel cortex from postnatal day 5 to postnatal day 14, maximal at postnatal days 9–11). We conclude that the transient expression of zinc can occur in both limbic and sensory areas, and that down-regulation of zinc in cortical modules might be related to synaptic plasticity and remodeling during development.

Development of Postural Muscles and Their Innervation

Control of posture is a prerequisite for efficient motor performance. Posture depends on muscles capable of enduring contractions, whereas movements often require quick, forceful muscle actions. To serve these different goals, muscles contain fibers that meet these different tasks. Muscles with strong postural functions mainly consist of slow muscle fibers with a great resistance against fatigue. Flexor muscles in the leg and arm muscles are mainly composed of fast muscle fibers producing relatively large forces that are rapidly fatigable. Development of the neuromuscular system continues after birth. We discuss in the human baby and in animal experiments changes in muscle fiber properties, regression from polyneural into mononeural innervation, and developmental changes in the motoneurons of postural muscles during that period. The regression of poly-neural innervation in postural muscles and the development of dendrite bundles of their motoneurons seem to be linked to the transition from the immature into the adult-like patterns of moving and postural control.

Morphological changes of the soleus motoneuron pool in chronic midthoracic contused rats

This study investigated the morphological features of the soleus motoneuron pool in rats with chronic (4 months), midthoracic (T 8) contusions of moderate severity. Motoneurons were retrogradely labeled using unconjugated cholera toxin B (CTB) subunit solution injected directly into the soleus muscle of 10 contused and 6 age- and sex-matched, normal controls. Morphometric studies compared somal area, perimeter, diameter, dendritic length, and size distribution of labeled cells in normal and postcontusion animals. In normal animals, motoneurons with a mean of 110.4 ± 5.2 were labeled on the toxin-injected side of the cord (left). By comparison, labeled cells with a mean of 93.0 ± 8.4 (a 16% decrease, P = 0.006) were observed in the chronic spinal-injured animals. A significantly smaller frequency of very small (area, approximately 100 μm 2) and medium (area, 545–914 μm 2) neurons, and a significantly higher frequency of larger (area, >914 μm 2) neurons was observed in the labeled soleus motoneuron pools of injured animals compared with the normal controls. Dendritic bundles in the contused animals were composed of thicker dendrites, were arranged in more closely aggregated bundles, and were organized in a longitudinal axis (rostrocaudal axis). Changes in soleus motoneuron dendritic morphology also included significant decrease of total number of dendrites, increased staining, hypertrophy of primary dendrites, and significant decreased primary, secondary, and tertiary branching. The changes in size distribution and dendritic morphology in the postcontusion animals possibly resulted from cell loss and transformation of medium cells to larger cells and/or injury-associated failure of medium cells to transport the immunolabel.

High-resolution mapping of neuronal activity by thallium autometallography

Different methods are available for imaging neuronal activity in the mammalian brain with a spatial resolution sufficiently high to detect activation patterns at the level of individual functional modules such as cortical columns. Severe difficulties exist, however, in visualizing the different degree of activity of each individual neuron within such a module, and mapping neuronal activity with a spatial resolution of single axons has remained impossible thus far. Here, we present a novel method for mapping neuronal activity that is able to visualize activation patterns with light and electron microscopical resolution. The method is based on the tight coupling of neuronal activity and potassium (K +) uptake. We have injected Mongolian gerbils with the K + analogue thallium (Tl +), stimulated the animals with pure tones of different frequencies and analyzed, by an autometallographic method, the Tl + distribution in the auditory cortex (AC). We find tonotopically organized columns of increased Tl +-uptake in AC. Within columns, the spatial patterns of neuronal activity as revealed by thallium autometallography are highly elaborated. Tl +-uptake differs in different layers, sublayers, and cell types, being especially high in large multipolar inhibitory interneurons in layer IV. A prominent feature of the columnar activation pattern is the presence of vertical modules of minicolumnar dimensions. Clusters of layer Vb pyramidal cells and their apical dendrite bundles are clearly visible in the center of the columns.

Aspects of the organization of neurons and dendritic bundles in primary somatosensory cortex of the rat.

In order to analyze some aspects of the spatial organization in the primary somatosensory cortex of the rat, we have reconstructed the positions of bundles of apical dendrites and neurons in a cortical prisms measuring 0.5 mm x 0.4 mm x cortical thickness, with special reference to a hypothetical columnar organization. Complete series of semithin (0.65 microm) sections were cut, tangentially from the pial surface down to the white matter, stained and digitizalized into a computer and represented as a stack of 2D images. The mean neuron density (N(V)-value) was (60 x 10(3) +/- 15 x 10(3)) neurons/mm3. The mean number of neurons beneath 1 mm2 of cortical surface (NC-value) was (113 x 10(3) +/- 8 x 10(3)) neurons/mm2. Well-defined bundles of apical dendrites emanating from layer V pyramidal cells were observed. The bundles consisted of 3-12 (mean 5 +/- 2) dendrites. The dendrites within a bundle converged while ascending towards the pial surface and reached a maximal close packing in layer IV. Superficially, the packing density decreased again. The mutual positions of the dendrites within the bundles shifted only slightly along their course towards the pial surface. The occurrence of bundles in tangential sections through layer IV was about 190 bundles/mm2 and the average number of neurons per bundle was estimated at approximately 600. However, when calculating Voronoi-diagrams, the number of neurons, which with this mathematical technique, is ascribed to each of the reconstructed dendritic bundles, varied between 200 and 1000. The possibility that the dendritic bundles are centers in cortical cell modules is discussed.

Some thoughts on cortical minicolumns.

Although a columnar geometry is one of the defining features of cortical organization, major issues regarding its basic nature, key features, and functional significance remain unclear and often controversial. This review is intended to survey some of the basic anatomical features of columnar organization, and in particular the smaller scale dendritic minicolumns. One motive was simply to clarify what seem to be differences in terminology, where "minicolumn" can be used to refer to vertical rows of cells, pyramidal cell modules, or apical dendritic bundles. A second aim was to review anatomical details which over the years have tended increasingly to be overlooked. A third aim was to expand on recent results concerning the border of layers 1 and 2 as a specialized zone with its own micromodular organization. Views on columnar organization have arguably been heavily influenced by a desire for general principles; but re-examination of the complex underlying features may be both timely and worthwhile. We point out that what are defined as dendritic bundles do not extend through the full cortical thickness and are not strictly repetitive, but rather display significant inter- and intra-areal variation.

Somatodendritic minicolumns of output neurons in the rat visual cortex

The apical dendrites of the pyramidal neurons of the cerebral cortex form radial bundles in all species and areas. Using microtubule-associated protein (MAP)2 immunostaining and Voronoi tessellation analysis in the rat visual cortex, we obtained objective criteria to define dendritic bundles in tangential sections: in supragranular layers of the rat visual cortex we found bundles of 6-6.4 dendrites, at a density of 1929 bundles/mm(2) and a centre-to-centre distance of 27 micro m. Using lipophilic tracers to label different pyramidal cell populations, based on the same criteria as in MAP2-immunostained material, we found that in the rat visual cortex the bundles consist of neurons with specific targets. Neurons projecting to the ipsi- or contralateral cortex form bundles together and with neurons projecting to the striatum, but not with those projecting to the superior colliculus, dorsal division of the lateral geniculate nucleus or through the cerebral peduncle. The latter neurons form bundles with neurons projecting to the striatum. Thus, the cerebral cortex is organized in minicolumns of output neurons visible at the earliest ages studied (P3), which might have a higher probability of being interconnected than those outside.

Region Specific Micromodularity in the Uppermost Layers in Primate Cerebral Cortex

A micromodularity specific to the uppermost cortical layers, layers 1 and 2, is demonstrated in primates. This is most pronounced as patches of zinc-positive (Zn+) terminations, preferentially in the pre-Rolandic and limbic areas. The upper layer modularity can frequently be demonstrated by parvalbumin-immunoreactive (PV-ir) GABAergic terminations and by bundles of apical dendrites. Double-labeling or alternate section analysis shows that PV-ir and Zn+ terminations co-mingle at the layer 1,2 border and appear to coincide with dendritic bundles, proposed to originate from layer 2 pyramidal neurons. This model is basically similar to the prominent wall-and-hollow honeycomb organization in rat visual cortex. The organization of the PV-ir and dendritic components, however, is more difficult to define in primate than in rat. Moreover, the micromodularity is not uniform across areas. In some areas (motor and limbic), the modularity can be visualized by both zinc and PV. In other areas (i.e. primary sensory, sensory associational and prefrontal areas 46 and 8), although PV immunohistochemisty shows a periodic distribution, there is no detectable Zn+ modularity. These results add to the evidence for the complexity of layers 1 and 2 and raise the possibility that patches of Zn+ terminations correspond to zones of area-specific zinc-related plasticity. This might figure in the context of top-down or feedback influences, as often associated with layer 1.

Parvalbumin positive dendrites co-localize with apical dendritic bundles in rat retrosplenial cortex.

The granular retrosplenial cortex in rats, involved in learning and memory, has a highly modular organization in layer 1. Apical dendrites of layer 2 pyramidal neurons form bundles, which correspond to patchy thalamic input. Here, we demonstrate that dendrites of parvalbumin-immunoreactive (PV-ir) GABAergic neurons in layers 2/3 also form bundles, and that these co-localize in layer 1 with the apical dendritic bundles, as verified by double immunofluorescence for PV and microtuble-associated protein. Deeper, at the border of layers 1/2, the PV-ir bundles merge into a honeycomb-like structure, with walls consisting of PV-ir neuropil. Compartmentalization in layers 1/2 is characteristic of other periallocortical structures. Further work is necessary to determine whether these specializations may be specifically related to learning and memory.

Development of dendritic bundles of pyramidal neurons in the rat visual cortex

The apical dendrites of pyramidal neurons in the cerebral cortex form vertical bundles whose distribution and density vary across species and areas. To understand their relationships with cortical columns, we labeled retrogradely neurons from the white matter underlying the visual cortex with 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) at P3 and P10 and with biotinylated dextran amine at P30. We also mapped the distribution of apical dendrites in tangential sections, immunostained for microtubule-associated proteins (MAP2). Their composition and distribution were studied with Neurolucida and NeuroExplorer software. The apical dendrites of pyramidal neurons formed different bundle types: at P3 we found bundles formed (a) by neurons located in cortical plate; (b) by layer V neurons; and (c) by upper layer V neurons and cortical plate neurons. At P10, the amount of supragranular neurons participating in the bundles increased. The inter-dendritic and inter-bundle distances increased with age. These findings confirm that dendritic bundles are present in the rat visual cortex early in development and are formed by neurons belonging to different cortical layers. The existence of different types of bundles relative to the layer of location of their parent neurons suggests that they are heterogeneous from each other in nature and in the pattern of connectivity.

Types of neurons and some dendritic patterns of basolateral amygdala in humans — a Golgi study

Classification of the neurons in the human basolateral amygdala is performed on preparations impregnated by the Golgi technique. Three different neuronal types are found in the nuclei of the basolateral amygdala: Type I--Pyramidal cells, with numerous dendritic spines and two subtypes (slender and squat); Type II--Modified pyramidal cells, sparsely spinous with rare dendritic spines and two subtypes (single apical and double apical) and; Type III--Non-pyramidal cells, with few dendritic spines and three subtypes (bipolar, multipolar and gliaform). The analysis of the primary dendritic branches pointed out the occasional presence of dendritic bundles (fascicular dendritic arrangement) with their predomination in the parvicellular division of the basal nucleus and paralaminar nucleus. Additionally, the presence of dendrodendritic contacts, indicated by light microscopy, was also found in the parvicellular division of the basal nucleus and especially in the paralaminar nucleus.