EXTRACELLULAR GLUCOSE-CONCENTRATION IN MAMMALIAN BRAIN - CONTINUOUS MONITORING OF CHANGES DURING INCREASED NEURONAL-ACTIVITY AND UPON LIMITATION IN OXYGEN-SUPPLY IN NORMOGLYCEMIC, HYPOGLYCEMIC, AND HYPERGLYCEMIC ANIMALS
Ia. Silver et M. Erecinska, EXTRACELLULAR GLUCOSE-CONCENTRATION IN MAMMALIAN BRAIN - CONTINUOUS MONITORING OF CHANGES DURING INCREASED NEURONAL-ACTIVITY AND UPON LIMITATION IN OXYGEN-SUPPLY IN NORMOGLYCEMIC, HYPOGLYCEMIC, AND HYPERGLYCEMIC ANIMALS, The Journal of neuroscience, 14(8), 1994, pp. 5068-5076
The concentration of extracellular glucose in anesthetized rat brain w
as measured continuously with two types of substrate-specific microele
ctrodes in a number of physiological and pathological conditions. Extr
acellular glucose level increased in hyperglycemia and decreased in hy
poglycemia, paralleling the changes in blood sugar. Increased neuronal
activity and in particular spreading depression, evoked triphasic alt
erations in extracellular glucose concentration: an initial rapid fall
was followed by an equally swift overshoot above the baseline and a s
ubsequent return to it. Limitation in O-2 supply led to a decline in e
xtracellular content of glucose: respiration with 5% O-2 reduced the l
evel by 7-20% and that with 3% O-2 by 75-85%. Decreases to undetectabl
e concentrations were seen in ischemia despite the use of an oxygen-in
sensitive microglucose sensor. Restoration of oxygen supply to the bra
in was accompanied by increases in extracellular glucose content above
the original normoxic level, which returned to baseline values after
10-15 min. In hyperglycemic animals ischemia-induced leakage of K+ was
delayed while the rate of recovery to control levels after restitutio
n of blood flow was enhanced. It is concluded that continuous monitori
ng of glucose with glucose-specific microelectrodes provides a new and
important insight into brain energy metabolism.