Emerging roles of insulin-like growth factor-I in the adult brain.

All tissues in the body are under the influence of insulin-like growth factor-I (IGF-I). Together with insulin, IGF-I is a key regulator of cell metabolism and growth. IGF-I also acts in the central nervous system, where it affects many different cell populations. In this brief review, we discuss the many roles of IGF-I in the adult brain, and present the idea that diseases affecting the brain will perturb IGF-I activity, although more refined studies at the molecular and cellular level are needed before we can firmly established this possibility. We also suggest that under normal physiological conditions IGF-I may play a significant role in higher brain functions underlying cognition, and may serve a homeostatic role during brain aging. Among newly emerging issues, the effects of IGF-I on non-neuronal cells within the nervous system and their impact in brain physiology and pathology are becoming very important in understanding the biology of this peptide in the brain.