Blood-brain barrier as a regulatory interface.

The blood-brain barrier (BBB) is an important component of the communication network that connects the central nervous system and peripheral tissues in the control of feeding-related behaviors. Specifically, the BBB acts as an interface that restricts and regulates the exchange of substances between the CNS and blood. Many of the eating-related peptides and regulatory proteins produced by peripheral tissues and with receptors in the brain have been found to cross the BBB. The consequences of BBB permeability to these substances can be viewed from various perspectives. Here, we briefly consider five views relating the BBB and eating. A view of physiologic integration emphasizes the BBB as a conduit that controls a humoral-dependent signaling between the CNS and peripheral tissues. A view of regulation emphasizes that the transporters for many of the eating-related hormones are themselves regulated by physiologic events. This means that blood-to-brain signaling across the BBB is state-dependent and adaptable to the needs of the organism. A view of pathologic dysfunction shows how dysregulation of BBB transporters can result in disease. Resistance to leptin caused by its decreased transport across the BBB in obesity is an example. An evolutionary view emphasizes how the role of the BBB in eating may have evolved and how adaptations to one set of eating conditions can result in maladaptations under other conditions. Finally, the implications of these views for drug development targeted at obesity or anorexia is explored. Overall, these views show the BBB is an integral part of the physiology of eating.