Glycogen brain metabolism

Weghuber, D., M. Mandl, M. Krssak, M. Roden, P. Nowotny, A. Brehm, M. Krebs, K. Widhalm and M.G. Bischof, 2007 Characterization of hepatic and brain metabolism in young adults with glycogen storage disease type 1 a magnetic resonance spectroscopy study.Am J Physiol Endocrinol Metab. 293, El378-384. 

The main source of brain energy metabolism is the continuous availability of glucose from the blood. To some extent, energy can be derived from glycogen, stored in astrocytes. Neurons also use lactate as an energy source, even under normoxic conditions. During neuronal activation, lactate may even be the... 

H, receptors in brain slices can also stimulate glycogen metabolism [5] and can positively modulate receptor-linked stimulation of cAMP synthesis. The activation of brain cAMP synthesis by histamine is a well studied phenomenon that reveals a positive interaction between histamine receptors [35]. When studied in cell-free preparations, this response shows characteristics of H2, but not H receptors. When similar experiments are performed in brain slices, however, both receptors appear to participate in the response. Subsequent work showed that H receptors do not directly stimulate adenylyl cyclase but enhance the H2 stimulation, probably through the effects of calcium and PKC activation on sensitive adenylyl cyclase iso forms (see Ch. 21). 

Hormones and neuronal activity affect brain glycogen metabolism 538... 

Glycogen and its enzymes are compartmentalized. Glycogen granules are only present in astrocytes of adult animals but are found in both astrocytes and neurons of immature animals. Of the enzymes involved in glycogen metabolism, glycogen phosphorylase is found in astrocytes only. Under steady-state conditions, it is probable that less than 10% of phosphorylase in brain is in the unphosphorylated b form (requiring AMP). This form is probably not very active at the low AMP concentrations present when intracellular glucose is sufficient to maintain ATP synthesis. Brain phosphorylase b kinase is activated indirectly by cAMP and by the molar concentrations... 

Hormones and neuronal activity affect brain glycogen metabolism. Glycogen is affected by hormones endogenous to the brain including vasoactive intestinal peptide and noradrenaline, as well as circulating hormones, such as insulin [61, 63, 64]. The mechanism whereby insulin exerts an effect on glycogen metabolism in brain has not been determined [63]. Glycogen metabolism in brain, unlike in other tissues, is controlled locally, due to differential local metabolic rates. 

The astrocyte-neuron lactate shuttle hypothesis is controversial. In recent years the possibility that lactate, formed within the brain and released by astrocytes, is an important neuronal substrate both for energy and incorporation into neurotransmitters has been the subject of many studies and considerable controversy. There is evidence that suggests transient release of lactate in human brain on stimulation [48,8,88], Little is known about the highly active metabolism that takes place in the many elaborate, lamellar distal processes of astrocytes dispersed through the neuropil and interacting with an estimated >100,000 synapses [82, and references therein]. However, it is well established that astrocytes do respond to neuronal activity [89], For example, in the isolated mouse optic nerve preparation, upon stimulation, astrocytic glycogen... 

Cruz, N. F. and Dienel, G. A. High glycogen levels in brains of rats with minimal environmental stimuli implications for metabolic contributions of working astrocytes. J. Cereb. Blood Flow Metab. 22 1476-1489, 2002. 

Swanson, R. A. Physiologic coupling of glial glycogen metabolism to neuronal activity in brain. Can. J. Physiol. Pharmacol. 70 S138-S144,1992. 

Oz, G., Henry, P. G., Seaquist, E. R. etal. Direct, noninva-sive measurement of brain glycogen metabolism in humans. Neurochem. Int. 43 323-329, 2003. 

Hydrocephaly decreases in weight of brain, lung, liver, and kidney decreases in liver glycogen, kidney proteins and alkaline phosphatase and disrupted brain DNA and protein metabolism (Kav-lock et al. 1982)... 

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