Increase in the stimulation-induced overflow of glutamate by fluoroacetate, a selective inhibitor of the glial tricarboxylic cycle.

Fluoroacetate is known to be taken up selectively by glia, where after forming fluorocitrate, it inhibits the tricarboxylic acid cycle. Since uptake into glia has a major role in the inactivation of synaptically released glutamate, the effect of fluoroacetate on the overflow of glutamate evoked by electrical field stimulation in slices of rat hippocampus was investigated. In agreement with previous reports, 1 mM fluoroacetate reduced the release and content of glutamine, but increased only slightly the overflow of glutamate induced by stimulation. If, however, 0.5 mM glutamine was added to the superfusion fluid, fluoroacetate nearly tripled the overflow of glutamate evoked by electrical field stimulation. The large glutamate overflow due to field stimulation in the presence of fluoroacetate was fully Ca2+ -dependent. Results confirm the major role of glia in the inactivation of glutamate. The absence of such an uptake may contribute to the in vivo convulsive effect of fluoroacetate.