Enhanced activity of GABA receptors inhibits glutamate release induced by focal cerebral ischemia in rat striatum.

Cerebral ischemia causes an excess release of glutamate, which can injure neurons. The striatum is one of the important regions vulnerable to hypoxia and ischemia. Using push-pull perfusion technique, we investigated the regulatory role of gamma-aminobutyric acid (GABA) and its receptors in modifying the amount of glutamate in rat striatum with ischemia. Perfusion with exogenous GABA (1 mM) inhibited cerebral ischemia-induced glutamate release by as much as 47%. We further characterized relative roles of subtype receptors of GABA on glutamate release by using pharmacological tools. While baclofen (500 microM), a GABA(B) receptor agonist, suppressed ischemia-induced glutamate release by 52%, GABA(B) receptor antagonist saclofen (500 microM) failed to produce a significant increase of glutamate release. The GABA(A) receptor agonist muscimol (500 microM) also reduced by 38% the release of glutamate induced by cerebral ischemia but the GABA(A) receptor antagonist bicuculline (500 microM) had very little effect. The present study demonstrates that the excessive release of glutamate or the overly activated glutamate receptor, triggered by cerebral ischemia, can be down-regulated by exogenous GABA or by increased activity of GABA receptors, especially the presynaptic GABA(B) receptors, which might be one of the important mechanisms to protect against striatum neuronal damage from over stimulation by excessive glutamate during ischemia.