Brain-like structures

It is still discussed in the literature whether so-called prion rods isolated from infectious brains (for which amyloid-like structure has been shown) correspond to the structure of the infectious form and/or the structure of the neurotoxic form of PrP. It is also under discussion whether filaments observed in diseased brains (so-called scrapie associated fibers) are similar to prion rods (reviewed in Weissmann, 2005). 

In inherited forms of prion diseases, a mutation in the gene encoding PrP produces a change in one amino acid residue that is believed to make the conversion of PrPG to PrPSc more likely. A complete understanding of prion diseases awaits new information about how prion protein affects brain function. Structural information about PrP is beginning to provide insights into the molecular process that allows the prion proteins to interact so as to alter their conformation (Fig. 2). 

Muneoka KT, Takigawa M. 5-Hydroxytiyptamine7 (5-HT7) receptor immuno-reactivity-positive stigmoid body -like structure in developing rat brains. Int Dev Neurosci 2003 21 133-143. 

Figure 4.1. Tlie vasculai blood-brain barrier tliree levels of complexity. The upper panel illustrates tlie brain endotlielial cell. Tliis is tlie functional and anatomical site of botli banier function and of saturable and non-saturable mechanisms of passage. The major modifications allowing botli banier function and selective penetration of substances ai e indicated. Tlie middle panel illustrates otlier cell types and sti uc-tures important in BBB function. Pericytes are embedded in a basement membrane and asti ocytes foim a net-like structure over tlie capillary bed. Botli cell types are in paracellular communication witli tlie brain endotlielial cells. Pericytes and asti ocytes to some extent oppose each o tilers effects on BBB functions. Tlie lower panel illusti ates tlie neurovasculai unit, a concept, tliat emphasizes inlegration of peripheral, BBB, and centi al inleractions.

A possible drawback to the use of antibodies for the treatment of toxicity is the possibility of anti-idiotypes being produced against the monoclonal antibody binding site. These antibodies could potentially mimic drug-like structural features necessary for binding to a receptor. However, antibodies do not cross the blood-brain barrier in significant amounts and studies to date have not found this to be a problem, especially when Fab fragments are used. 

Amantadine is a primary amine, with a pKa of 10.8, and most of the drug is in the protonated form at physiologic pH. Nevertheless, the drug may enter the brain because of its cage-like structure that not only increases its lipophilicity but also precludes its catabolism by oxidative enzymes metabolism studies have shown that amantadine is excreted in the urine unchanged. 

Dipeptidylaminopeptidase, which produces the dipeptide Tyr-GIy on hydrolysis of enkephalins, was first reported to be present in rat brain [112], The enkephalin-hydrolysing aminopeptidase and DAP activity in monkey brain was separated by Hazato et al. [113] who showed that DAP activity was unaffected by either bestatin or puromycin but was inhibited in the presence of metal chelators. This indicated that DAP was a metalloenzyme. DAP was originally reported to be a membrane-boimd enzyme since it was found in the membrane fraction of rat brain homogenate [112], but further studies with the enzyme isolated from calf-brain striatum showed that DAP is not membrane-bound, but was present in the membrane fractions due to occlusion in vesicle-like structures [65]. 

R. Simantov, S.H. Snyder, Morphine-like peptides in mammalian brain isolation, structure elucidation, and interactions with the opiate receptor, Proc. Nad. Acad. Sci. U.S.A 73 (1976) 2515-2519. 

An organ like the stomach or the brain contains structures within it such as arteries, nerves and other specialised components. These components, which contain cells of a similar kind, are referred to as tissues. So we have nervous tissue, arterial tissue, muscular tissue and so on making up specialised organs which have a specific function. (The stomach, for example, is concerned with the first stage in the digestive process.)... 

Polyaniline (PANI) represents one of the most cited examples of nanostructured polymers, due to its outstanding electronic properties and technological applications that have promoted a wide number of studies and publications. Although a variety of different and peculiar morphologies have been reported, such as brain like [92], cauliflowers [93], nanoflakes, nanospheres and nanorods [94], chrysan-fhemum flower-like [95], plate-like structures and flower-like superstructures [96],... 

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