The brain uses fatty acids to synthesize the complex fat molecules that form neuronal and glial cell membranes. This process is more active in growing animals than in adults. The brain synthesizes some fatty acids from smaller molecules, but their uptake from the circulation is also an important source, and is the only source for certain fatty acids (the essential fatty acids, which cannot be manufactured in the body). The details of the uptake process are not well understood.
From the nutritional perspective, diet influences essential fatty acid availability to brain, with potentially important functional consequences. In almost all mammals, there are two essential fatty acids: linoleic acid and a-linolenic acid (termed polyunsaturated fatty acids; PUFAs). In the nervous system (as elsewhere), linoleic and a-linolenic acids are incorporated into phospholipid molecules, and inserted into cellular membranes, where they influence membrane fluidity and membrane-associated functions (e.g., the functionality of receptors and transporters). In addition, the linoleic acid in membrane lipids can be released and converted into arachidonic acid, a key precursor in the synthesis of prostaglandins and leuko-trienes, families of important signaling molecules. a-Linolenic acid can be converted into docosahex-anoic acid, a molecule found in very large amounts in the rods and cones of the retina, and in nerve terminal membranes in brain. Docosahexanoic acid is thought to be a key component of photo-transduction, and has been demonstrated to have important effects on vision. Dietary modifications in essential fatty acid intake might therefore be expected to influence membrane functions in brain, leading to alterations in brain function (as has been demonstrated for vision).
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