BR (2007) Astrocyte glycogen and brain energy metabolism. Glia 55:1263–1271

The brain contains glycogen but at low concentration com-pared with liver and muscle. In the adult brain, glycogen is found predominately in astrocytes. Astrocyte glycogen con-tent is modulated by a number of factors including some neurotransmitters and ambient glucose concentration. Com-pelling evidence indicates that astrocyte glycogen breaks down during hypoglycemia to lactate that is transferred to adjacent neurons or axons where it is used aerobically as fuel. In the case of CNS white matter, this source of energy can extend axon function for 20 min or longer. Likewise, during periods of intense neural activity when energy demand exceeds glucose supply, astrocyte glycogen is degraded to lactate, a portion of which is transferred to axons for fuel. Astrocyte glycogen, therefore, offers some protection against hypoglycemic neural injury and ensures that neurons and axons can maintain their function during very intense periods of activation. These emerging princi-ples about the roles of astrocyte glycogen contradict the long held belief that this metabolic pool has little or no functional significance. VC 2007 Wiley-Liss, Inc