[Increase in extracellular levels of serotonin and amino acids in the rat brain following cyanide-induced energy failure].

We studied the effects of ATP depletion on neurotransmitter release in the rat brain using the microdialysis method. Ringer's solution containing 2 mM sodium cyanide (NaCN) was perfused into the hippocampus and striatum for 60 min via a microdialysis probe, and changes in serotonin (5-HT) and amino acids (glutamate, aspartate and taurine) levels in dialysates were investigated. NaCN perfusion induced a transient 3.9-fold increase in 5-HT levels in the hippocampal dialysate. Amino acid levels in dialysates also increased during NaCN perfusion, but differently in the striatum and hippocampus (glutamate: 1.3- and 2.4-fold, taurine: 2.3- and 1.3-fold, respectively). Perfusion of Ca(2+)-free Ringer's solution remarkably suppressed the NaCN-induced increase in 5-HT but not the increases in amino acid levels. Depolarization by 100 mM KCl perfusion could induce increases in 5-HT and amino acids in dialysates at 3 hr after NaCN perfusion similarly with that of control. These findings indicate that the sensitivity of nerve terminals to energy failure are different between neurons containing different neurotransmitters and also between brain regions, and suggest that this regionally different sensitivity of amino acid neurons might be involved in the underlying mechanism of the localized vulnerability to transient ischemia.