Nerve growth factor and Alzheimer's disease.

Alzheimer's disease is associated with a pronounced loss of the cholinergic neurons that form the ascending cholinergic projections of the basal forebrain. Even though the disease is also characterized by changes in other neuronal systems and by a high frequency of neuronal plaques and tangles, the cholinergic deficit seems to be a principal element responsible for the memory loss typical of Alzheimer's disease. This review summarizes findings in experimental animals which indicate that nerve growth factor (NGF), a well-characterized protein, acts as a neurotrophic factor for cholinergic neurons of the basal forebrain. NGF is present in the target areas of these cholinergic neurons and affects their survival, fiber growth, and expression of transmitter-specific enzymes. Furthermore, NGF is able to prevent the degeneration of cholinergic neurons in adult rats with experimental lesions mimicking the cholinergic deficit in Alzheimer's disease. These findings suggest that increasing the availability of NGF to human cholinergic cells might promote their survival in certain disease processes. Additional steps are discussed for establishing the possible involvement of NGF in the pathogenesis of Alzheimer's disease and the development of an effective therapy.