Nutrients as trophic factors in neurons and the central nervous system: Role of retinoic acid

In multicellular organisms, death, survival, proliferation, and differentia tion of a given cell depend on signals produced by neighboring and/or dista nt cells, resulting in the coordinated development and function of the vari ous tissues. In the nervous system, control of cell survival and differenti ation is achieved through the action of a distinct group of polypeptides co llectively known as neurotrophic factors. Recent findings support the view that trophic factors also are involved in the response of the nervous syste m to acute injury. By contrast, nutrients are not traditionally viewed as p otential trophic factors; however, there is increasing evidence that at lea st some influenced neuronal differentiation. During development the brain i s responsive to variations in nutrient supply, and this increased sensitivi ty or vulnerability of the brain to nutrient supply may reappear during neu ronal repair, a period during which a rapid membrane resynthesis and reesta blishment of synthetic pathways occur. To further evaluate the potential of specific nutrients to act as pharmacologic agents in th repair of injured neurons, the effects of retinoic acid, an active metabolite of vitamin A, a nd its role as a trophic factor are discussed. This literature review is in tended to provide background information regarding the effect of retinoic a cid on the cholinergic phenotype and the differentiation of these neurons a nd to explain how it may promote neuronal repair and survival following inj ury.