Organizational actions of metabolic hormones.

Brain development is a complex and dynamic process, and many environmental factors have been found to influence the normal development of neural pathways. Cumulative evidence suggests that metabolic hormones that regulate the hypothalamic circuits that control energy homeostasis function in much the same way that sex steroids act on sexually dimorphic circuits. For example, although the effects of the adipocyte-derived hormone leptin were originally thought to be limited to the neural control of energy homeostasis in adult animals, it is now becoming increasingly clear that leptin can also determine patterns of neurogenesis, axon growth, and synaptic plasticity in the developing hypothalamus. More recent studies have also extended the role of the metabolic hormones ghrelin and insulin in various aspects of brain development. Examining how metabolic hormones control hypothalamic development will help our understanding of the developmental origin of adult metabolic diseases and, hopefully, improve our ability to predict adverse outcomes.