The Role of Insulin as a Satiety Factor in the Central Nervous System

Abstract

This chapter discusses the role of insulin as a satiety factor in the central nervous system (CNS). One potential problem with a theory suggesting that insulin interacts with the CNS is that most of the brain is known not to require insulin for glucose uptake and utilization. However, a number of experiments have recently demonstrated the presence of specific insulin receptors or binding sites within discrete brain regions, suggesting that insulin does indeed interact with the brain. These receptors have been found mainly in areas of the brain with a reduced blood–brain barrier, that is, the circumventricular organs, including parts of the ventral hypothalamus. The finding that individual neurons in the ventral hypothalamus respond to the direct application of insulin is consistent with the demonstration of insulin receptors there. It has been found that some neurons that respond directly to the iontophoretic application of insulin and others in which the response to glucose is modified by the simultaneous application of insulin. The paucity of reports of immunohistochemically identified insulin in the brain of mammals and the lack of demonstration of c-peptide or mRNA for insulin in the brain has led to question the concept that insulin is synthesized within the brain.