Brain energy expenses

Alexandre Blais Alexandre.Blais at
Fri Sep 1 21:11:09 EST 2000

"Richard L. Hall" wrote

> In normal function brain energy consumption must be essentially
> constant.  Why?  There are no energy stores in the brain and
> consequently the brain extracts energy moment by moment from the
> blood.

Just my humble contribution to the trend, as I read that glycogen could serve as
an energy reservoir in the brain. But this may be only unverified hypotheses :"
Physiologic coupling of glial glycogen metabolism to neuronal activity in brain.
Can J Physiol Pharmacol 1992;70 Suppl:S138-44
Brain glycogen is localized almost exclusively to glia, where it undergoes
continuous utilization and resynthesis. We have shown that glycogen utilization
increases during tactile stimulation of the rat face and vibrissae. Conversely,
decreased neuronal activity during hibernation and anesthesia is accompanied by a
marked increase in brain glycogen content. These observations support a link
between neuronal activity and glial glycogen metabolism. The energetics of
glycogen metabolism suggest that glial glycogen is mobilized to meet increased
metabolic demands of glia rather than to serve as a substrate for neuronal
activity. An advantage to the use of glycogen may
 be the potentially faster generation of ATP from glycogen than from glucose.
Alternatively, glycogen could be utilized if glucose supply is transiently
insufficient during the onset of increased metabolic activity. Brain glycogen may
have a dynamic role as a buffer between the abrupt increases in focal metabolic
demands that occur during normal brain activity and the compensatory changes in
focal cerebral blood flow or oxidative metabolism." End of quote

 And also:"

Acta Physiol Scand 1999 Dec;167(4):275-84. The role of astrocytes and
noradrenaline in neuronal glucose metabolism
In the classical model the energy requirements during neuronal activation are
provided by the delivery of additional glucose directly into the extracellular
compartment that results from the increase in local cerebral blood flow (rCBF).
The present review proposes that astrocytes play a key role in the response to
neuronal activation. Arginine for the synthesis of NO, which has a major role in
the increase in rCBF, is released from astrocytes in response to stimulation of
astrocytic glutamate receptors. The increased delivery of glucose by the blood
stream enters astrocytes, where some of it is converted to glycogen. During
neuronal activation there is a decrease in extracellular glucose owing to
increased utilization followed by a delayed increase; this results from
stimulation of astrocytic beta-adrenergic receptors, which leads to a breakdown
of glycogen and the export of glucose." End of quote

Alexandre Blais

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