Abstract
During the past 2 y the leptin field has continued to expand rapidly (from 600 to >2000 citations currently in the MEDLINE database), extending leptin biology into areas well beyond feeding behavior and energy metabolism. For example, there is a growing body of literature linking leptin with the regulation of reproductive function and on the potential involvement of leptin in puberty onset, pregnancy, lactation, and infertility associated with energy restriction and low body adiposity (1). Leptin has also been implicated in roles as diverse as the regulation of the immune system (2) and respiratory function (3). In addition, ongoing studies are clarifying the central nervous system (CNS) mechanisms by which leptin exerts its effects on energy balance (4) as well as suggesting important actions for leptin in regulating peripheral metabolic fluxes (5).