Dendritic connectivity

FIGURE 1-22. The dendritic tree of a neuron can sprout branches, grow, and establish a multitude of new synaptic connections throughout its life. The process of making dendritic connections on an undeveloped neuron may be controlled by various growth factors, which act to promote the branching process and thus the formation of synapses on the dendritic tree. 

Hence, dendritic connection can be brought about by a combination of these regions. Regional combinations can thus be classified into three distinct types (1) outer sphere-outer sphere (2) outer sphere —inner sphere and (3) inner sphere-inner sphere. Each of these combinations can be employed either separately or in concert (Figure 9.4). 

Figure 9.4. Idealized models of dendritic connectivity a) outer sphere - outer sphere b) inner sphere - inner sphere and c) outer sphere - inner sphere.

Covalent dendritic connection can result from any standard synthetic transformation capable of forming a covalent bond. These include nucleophilic, electrophilic, ionic, radical, and carbenoid reactions. Elements effecting bond formation include metals, non-metals, and metaloids. 

In insects and arachnids, there are two main molting processes of the sensilla one which retains a dendritic connection between the old and the new sensillum, thus retaining the chemosensory function, and one where there is no such connection and the chemosensory function is presumably temporarily lost during the molt. The type without loss of chemosensory function is the more predominant one (Guse 1983). 

There are many possible dendritic connections to a nenron cell body. (From Campbell, N.A. et al.. Biology, 5th edn., Addison Wesley Longman, Menlo Park, CA, 1999. With permission.)... 

Aluminum has been suggested to be a risk factor in the pathogenesis of Alzheimer disease. In experimental work, aluminum significantly impairs dendritic connectivity within the rat hippocampus. When rats were fed pyridoxine for thirty days following aluminum injections the branch points in all areas of the hippocampus increased significantly (45). This effect might be due to the effect of pyridoxine on neurotransmitter and polyamine syntheses. 

E. Sreekumaran, T. Ramakrishna, T.R. Madhav, D. Anandh, B.M. Prabhu, S. Sulekha, P.N. Bindu, and T.R. Raju. Loss of dendritic connectivity in CAl, CA2 and CA3 neurons in hippocampus in rat under aluminum toxicity Antidotal effect of pyridoxine. Brain Res. Bull. 59 421-427 (2003). 

The human brain is comprised of many millions of interconnected units, known individually as biological neurons. Each neuron consists of a cell to which is attached several dendrites (inputs) and a single axon (output). The axon connects to many other neurons via connection points called synapses. A synapse produces a chemical reaction in response to an input. The biological neuron fires if the sum of the synaptic reactions is sufficiently large. The brain is a complex network of sensory and motor neurons that provide a human being with the capacity to remember, think, learn and reason. 

Tree like networks of nerve fiber called dendrites protrude outward from the neuron s cell body, or soma. Extending outward from the soma is also a long fiber called the axon that itself eventually branches out into a set of strands and sub strands. At the ends of these strands are the transmitting ends of communication junctions between nerve fibers called synapses. The receiving ends of these junctions exist both on dendrites and on the somas themselves. Each neuron is typically connected to several thousand other neurons. 

Langa and co-workers have prepared fullerodendrimers 18 and 19 in which the phenylenevinylene dendritic wedge is connected to a pyrazoHno [60] fullerene core rather than to a fulleropyrrolidine one as for 12-17 (Fig. 9) [44]. Preliminary photophysical investigations suggest that the efficient energy transfer from the excited antenna moiety to the pyrazolino [60] fullerene core is followed by an electron transfer involving the fullerene moiety and the pyrazoHne N atom. 

The cell bodies in lamina III are generally larger and less densely packed than those in the substantia gelatinosa. The main cell type of lamina III includes projection cells, which contribute to the SCT and postsynaptic dorsal column (PSDC). The dendrites of SCT cells are confined to lamina III and do not reach laminae I and IIo. However, those of PSDC are not flattened in the mediolateral plane and extend to laminae I and II, thus forming monosynaptic connections with small primary afferent fibres. 

GC) axon (Jia et al, 1999). The GC are the main inhibitory intemeurones, while the peri-glomerular cells can alter the probability of transmission at the first synapse. The olfactory inputs to the M/TCs have two ways in which they may be connected, via their primary dendrites, to a particular glomerulus. First, they may supply only one functional type as in MOE input [Fig. 5.14(a)], Second, they may supply two or more functional types [Fig. 5.14(b)]. The single connectivity type is found in the MOB, as the primary OR-M/TC... 

A potential source of structural imperfection is the rapid increase of reactive groups as growth is pursued. Their incomplete conversion leads to defects inside the molecule [27]. In convergent-iterative syntheses these problems are avoided by directing the dendritic growth from the surface inwards to a focal point. In a final step several dendrons are connected with a multifunctional core to yield the desired dendrimer (Fig. 9). 

Amongst the multitude of metals that could be employed as connecting units in dendritic macromolecular assembly, ruthenium is by far the most commonly... 

For instance, some time ago Newkome et al. reported the synthesis of ruthenium based dendrimers [170]. A dendrimer (80) with twelve peripheral terpyridine ligands was built around a central quaternary carbon-based core. In the final step complexation between the terminal ligand of the dendrimer and a terpyridinyl ruthenium chloride building block afforded the dodecaruthenium cascade molecule 80 (Fig. 35). Thus, preconstructed cores and dendritic fragments were linked by Ru2+ as the connecting unit and this mode of connectivity could be denoted by [—(Ru)—]. 

Practically all dendrimers [ 1 ] known today have cores with a few, typically three to six functional groups to which the corresponding number of dendrons (dendritic wedges) are attached. The fact that these dendrons are connected to one another by a small, almost dot-like molecule results in considerable steric congestion in the space around the core. This congestion is a unique structural feature and has one led to view dendrimers, specifically those of high genera-... 

Chung, Y. D., Zhu, J., Han, Y. and Kernan, M. J. nompA encodes a PNS-specific, ZP domain protein required to connect mechanosensory dendrites to sensory structures. Neuron 29 415-428,2001. 

Reid et al. [ 1.12] described the effect of 1 % addition certain polymers on the heterogeneous nucleation rate at-18 °C the rate was 30 times greater than in distilled, microfiltered water and at -15 °C, the factor was still 10 fold hogher. All added polymers (1 %) influenced the nucleation rate in a more or less temperature-dependent manner. However, the authors could not identify a connection between the polymer structure and nucleation rate. None the less it became clear that the growth of dendritic ice crystals depended on to factors (i) the concentration of the solution (5 % to 30 % sucrose) and (ii) the rate at which the phase boundary water - ice crystals moved. However, the growth was found to be independent of the freezing rate. (Note of the author the freezing rate influences the boundary rate). 

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