Insulin in the Brain: A Hormonal Regulator of Energy Balance*

EARLY studies of brain glucose metabolism established the axiom that insulin is not required for utilization of glucose by the central nervous system (CNS) (1). A corollary to this concept was the belief that circulating insulin is incapable of crossing the bloodbrain barrier (BBB) and is therefore without effects in the brain. While the first of these tenets remains unchallenged, the second has been subjected to detailed scrutiny for over a...