The hormone insulin controls the metabolism of glucose, fats, and proteins.
Alterations in insulin production and response can lead to type II
diabetes, a disorder that affects more than 100 million people worldwide. A
growing body of evidence has suggested that insulin signaling may also play
an important role in the central nervous system. Bruning et al. (p. 2122;
see the Perspective by Schwartz) have separated the brain action of insulin
from its other actions by creating mice that are selectively deficient in
the brain insulin receptor. Mutant mice showed modest diet-induced obesity
and insulin resistance as well as a significant reduction in fertility, the
latter attributable to impaired hypothalamic regulation of luteinizing
hormone. These findings may enhance understanding of the complex metabolic
disorders often associated with type II diabetes.