We investigated the changes in the levels of amino acids during high frequency stimulation (HFS) of the anterior nucleus of the thalamus (ANT) in epileptic rats, which had seizures induced by unilaterally stereotactic administration of kainic acid (KA). Thirty-six adult male Wistar rats were divided into three groups: the KA-stim group (KA rats received ipsilateral ANT stimulation), the ICA-sham group (KA rats received sham stimulation) and the control group, which underwent stereotactic administration of saline and received ipsilateral ANT stimulation. Microdialysis probes were unilaterally lowered into the CA3 region of the hippocampus, but probes were implanted bilaterally in the ICA-stim group. The concentrations of glutamate (Glu), taurine (Tau), aspartate (Asp) and gamma-aminobutyric acid (GABA) in the dialysate samples were determined by high-performance liquid chromatography. The concentrations of Glu, Asp and Thu in the hippocampi of KA rats were significantly higher than that found in control rats; however, no difference in the concentrations of GABA were found. In the ipsilateral hippocampi (KA-injected) of rats in the ICA-stim group, stimulation of the ANT caused decreases in concentrations of Glu and Asp, an increase in the concentration of GABA and no significant change in the concentration of Thu. Unilateral ANT stimulation did not influence the amino acids in the contralateral hippocampus. In control rats, extracellular Tau significantly increased during and after stimulation. This study demonstrated that unilateral ANT stimulation inhibited the hyperactivation of the excitatory process and promoted the inhibitory process in the ipsilateral hippocampus of KA rats. (C) 2012 Elsevier B.V. All rights reserved.