Cluster dendritic

O. Srinivas, S. Radhika, N. M. Bandaru, S. K. Nadimpalli, and N. Jayaraman, Synthesis and biological evaluation of mannose-6-phosphate-coated multivalent dendritic cluster glycosides, Org. Biomol. Chem., 3 (2005) 4252-4257. 

Pyramidal Cell Modules Anatomically Defined Units Based on Apical Dendrite Clustering... 

Table 1 Center-to-center spacing of dendritic clusters in neocortex...

Fig. 1 Rat visual cortex sectioned in the vertical plane and labeled with an antibody to MAP2 to show the apical dendritic clusters arrows). Note the densely stained layer 1 beneath the pia, and the pale staining of the white matter. Scale bar = 100 (rm...

Apical Dendritic Clusters in the Neocortices of Other Animals... 

Another interesting variation in the clustering of apical dendrites occurs in the cat sensorimotor cortex. There it has been shown by Fleischhauer (1974) that in the posterior sigmoid gyrus the apical dendrites of the layer 5 pyramidal cells frequently bifurcate soon after they emerge from the large cell bodies. The secondary dendritic branches then run obliquely for a short distance and at the level of layer 3 they join secondary branches from other apical dendrites to form dendritic clusters... 

Fig. 4 (continued) Monkey primary visual cortex. Vertical sections labeled with an antibody to MAP 2. The illustration shows the apical dendritic clusters (arrows) arising from layer 5 pyramids and the bundles of apical dendrites (arrowheads) arising from layer 6a pyramidal cells. The locations of layers 4, 5, and 6 are indicated. From Peters and Sethares (1991). Scale bar = 100 p.m... 

The Spatial Arrangement and Connections of Apical Dendritic Clusters... 

Obviously, the question of the geometric distribution of dendritic clusters needs to be examined further, and any modular theory of cortical function based on the concept that the apical dendritic clusters are the axes of functional cortical modules, or minicolumns, has to take into account that there is biological variation in the composition of the modules, as shown by studies like those of Lev and White (1997) and Vercelli et al. (2004). 

Lohmann and Koppen (1995) have also shown that the dendritic clusters and the vertical axonal bundles in rat visual cortex originate from the same neurons, and that the axonal bundles and the dendritic clusters have similar center-to-center spacing. Recently Casanova et al. (2008) have concluded that in the human cortex the pyramidal cell arrays and the vertical bundles of myelinated axons have similar spacing. 

In addition to vertical bundles of myelinated axons, the cerebral cortex of monkeys (e.g., DeFelipe et al., 1990) and of humans (e.g., del Rio and DeFelipe, 1995) also contains vertically oriented bundles of unmyelinated axons that are referred to as horsetails. These horsetails are the axonal plexuses of the inhibitory double bouquet cells and can be demonstrated in monkey neocortex by immunolabeling with antibodies to calbindin and tachykinin. As shown by DeFelipe et al. (1990), in the monkey these axonal bundles are widespread and form a regular columnar system descending from layer 2 to layers 3-5. The bundles are most evident in tangential sections taken at the level of layer 3, where they can be seen to have a center-to-center spacing of 15-30 fim. In a later study of the calbindin labeled double bouquet cells in monkey striate cortex, Peters and Sethares (1997) showed that there is one double bouquet cell, and therefore one vertically oriented double bouquet cell axonal plexus, or horsetail, per pyramidal cell module (Fig. 7). Within layer 2/3 the double bouquet axons run alongside the apical dendritic clusters, while in layer 4C they are closely associated with the vertical myelinated axonal bundles. DeFelipe et al. (1989 1990) proposed that the axon terminals of the double bouquet cell synapse with the shafts and spines of basal dendrites and oblique shafts of apical dendrites of pyramidal cells, but the exact role of these vertical bundles of inhibitory axons is not known. It is likely that they constitute a vertical inhibitory system that acts upon pyramidal cells within the minicolumns. 

The only study in which both the disposition of dendritic clusters and of vertical arrays of neurons in the same cortical areas have been compared in the same cortical area is that of Gabbott (2003). He examined human prefrontal cortex using both MAP2 labeling to show dendritic clusters in sections cut parallel to the cortical... 

One reason why more studies like that of Gabbott (2003) have not been carried out is that most studies of the composition and dimensions of dendritic clusters and pyramidal cell modules have been carried out in mice, rats, cats, and rabbits, with a few studies in monkeys and only one in humans (see Table 1). In contrast all of the studies of the dimensions of minicolumns based on spacing of vertical strings of neurons in Nissl stained sections have been carried out in monkeys, ape, and human cortex (see Table 2). 

In a recent review article on the anatomy of autism Amaral et al. (2008) point out that in these studies by Casanova and his colleagues, only 14 cases of autism, 9 of which had seizures and at least 10 with mental retardation, have been examined for minicolumn pathology. Consequently, more studies using a greater number of autistic brains with fewer other complications need to be carried out before any definite conclusions can be reached about changes that can only be attributed to autism. It would also be appropriate to examine brains in which the apical dendritic clusters and myelinated axon bundles have been stained to confirm the sizes of the minicolumns as detected in digitized images from autistic brains. 

Eeldman ML, Peters A (1974) A study of barrels and pyramidal dendritic clusters in the cerebral cortex. Brain Res 77 55-76. 

Lev, DL, White EL (1997) Organization of pyramidal cell apical dendrites and composition of dendritic clusters in the mouse. Emphasis on primary motor cortex. Europ J Neurosci 9 280-290. 

The clean introduction of clusters onto the termini of polyphosphine dendrimers is a real challenge because of the current interest of dendritic clusters in catalysis and the mixtures usually obtained in thermal reactions of [Ru3(CO)i2] with phosphines.37 The diphosphine CH3(CH2)2N(CH2PPh2)2 (abbreviated P-P) was used as a simple, model ligand. The reaction between P-P and [Ru3(CO)i2] (molar ratio 1/1.05) in the presence of 0.1 equiv. [Fe p 6-C6Me6)] in THF at 20°C led to the complete disappearance of [Ru3(CO)i2] in a few minutes and the appearance of a mixture of chelate [P-P. Ru3(CO)i0], monodentate [P-P. Ru3(CO)n], and bis-cluster [P-P. (Ru3(CO)n 2]. These reactions were reported by Bruce et al. with simple diphosphines.38 On the other hand, the reaction of P-P with [Ru3(CO)i2] in excess (1/4) and only 0.01 equiv. [FeICp(r 6-C6Me6)] in THF at 20°C led, in 20 minutes, to the formation of the air-stable, light-sensitive bis-cluster [P-P. Ru3(CO)n 2] as the only reaction product. Given the simplicity of this characterization of the reaction product by 31P NMR and the excellent selectivity of this model reaction when excess [Ru3(CO)i2] was used, the same reaction between Reetz s dendritic phosphines,39 derived from DSM s dendritic amines,40 and... 

The nanocomposite of cross-linked ESO and supramolecular (/ )-12-hydroxystrearic acid (HSA) nanofibre was obtained by photo curing ESO/ HSA (10/1 weight ratio) at 100°C. The study revealed that dendritic clusters of HSA nanofibres are formed in the cross-linked ESO matrix. A thermal transition from the mesophase composed of supramolecular nanofibres to the isotropic state was observed at 67°C (A// = 22.6 Jg HSA), while the of crystalline HSA is 11.1°C (AH = 159 J g HSA).The tensile strength at 20°C of the ESO/HSA was 80% higher than that of photocured ESO without HSA. ... 

---