Essential fatty acids in visual and brain development

Essential fatty acids are structural components of all tissues and are indi spensable for cell membrane synthesis; the brain, retina and other neural t issues are particularly rich in long-chain polyunsaturated fatty acids (LC- PUFA). These fatty acids serve as specific precursors for eicosanoids, whic h regulate numerous cell and organ functions. Recent human studies support the essential nature of n-3 fatty acids in addition to the well-established role of n-6 essential fatty acids in humans, particularly in early life. T he main findings are that light sensitivity of retinal rod photoreceptors i s significantly reduced in newborns with n-3 fatty acid deficiency, and tha t docosahexaenoic acid (DHA) significantly enhances visual acuity maturatio n and cognitive functions. DHA is a conditionally essential nutrient for ad equate neurodevelopment in humans. Comprehensive clinical studies have show n that dietary supplementation with marine oil or single-cell oil sources o f LC-PUFA results in increased blood levels of DHA and arachidonic acid, as well as an associated improvement in visual function in formula-fed infant s matching that of human breast-fed infants. The effect is mediated not onl y by the known effects on membrane biophysical properties, neurotransmitter content, and the corresponding electrophysiological correlates but also by a modulating gene expression of the developing retina and brain. Intracell ular fatty acids or their metabolites regulate transcriptional activation o f gene expression during adipocyte differentiation and retinal and nervous system development. Regulation of gene expression by LC-PUFA occurs at the transcriptional level and may be mediated by nuclear transcription factors activated by fatty acids. These nuclear receptors are part of the family of steroid hormone receptors. DHA also has significant effects on photorecept or membranes and neurotransmitters involved in the signal transduction proc ess; rhodopsin activation, rod and cone development, neuronal dendritic con nectivity, and functional maturation of the central nervous system.