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Volume 17, Number 24,
Issue of December 15, 1997
pp. 9448-9457
Endogenous Monocarboxylates Sustain Hippocampal Synaptic Function
and Morphological Integrity during Energy Deprivation
Received May 6, 1997; revised Sept. 9, 1997; accepted Sept. 30, 1997.
Yukitoshi Izumi1,
Ann
M. Benz1,
Hiroshi Katsuki1, and
Charles F. Zorumski1, 2
Departments of 1 Psychiatry and
2 Neurobiology, Washington University School of Medicine,
St. Louis, Missouri 63110
The ability to fuel neurons via glycogenolysis is believed to be an
important function of glia. Indeed, the slow, rather than immediate,
depression of synaptic transmission in hippocampal slices during
exogenous glucose deprivation suggests that intrinsic energy reservoirs
help to sustain neurotransmission. It is believed that glia fuel
neighboring neurons via diffusible monocarboxylates such as pyruvate
and lactate, although a role for glucose has been proposed also. Using
-cyano-4-hydroxycinnamate (4-CIN) to inhibit monocarboxylate
transport and cytochalasin B (CCB) to inhibit glucose transport, we
examined the role of glucose and monocarboxylates in supporting the
functional and morphological integrity of hippocampal neurons during
glucose deprivation. Although 200 µM 4-CIN failed to
depress EPSPs supported by 10 mM glucose, pretreatment with
4-CIN accelerated the depression of EPSPs during glucose deprivation.
4-CIN also accelerated the decline in glucose-supported EPSPs after
administration of 50 µM CCB, whereas CCB failed to alter
the slow decay of pyruvate-supported EPSPs during pyruvate deprivation.
4-CIN did not alter the morphology of pyramidal neurons in the presence
of 10 mM glucose but produced significant damage during
glucose deprivation or CCB administration. These results suggest that
endogenous monocarboxylates rather than glucose maintain neuronal
integrity during energy deprivation. Furthermore, EPSPs supported by
2-3.3 mM glucose were sensitive to 4-CIN, suggesting that
endogenous monocarboxylates are involved in maintaining neuronal function even under conditions of mild glucose deprivation.
Key words:
hippocampus;
energy metabolism;
glucose transport;
pyruvate;
lactate;
neuroglial interactions
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