The effect of sodium valproate on extracellular GABA and other amino acids in the rat ventral hippocampus: an in vivo microdialysis study.

We report the effects of i.p. administration of sodium valproate (VPA) on extracellular concentrations of various amino acids in the rat ventral hippocampus studied using in vivo microdialysis, followed by HPLC with fluorometric detection. At the doses used (100, 200 and 400 mg/kg), VPA had no effect on extracellular aspartate, glutamine and taurine, whilst inducing a small, but not statistically significant increase in glutamate at 200 and 400 mg/kg. In contrast, VPA administration produced a biphasic effect on extracellular GABA levels which was dependent on the dose used. At 100 mg/kg, VPA reduced GABA concentrations by 50% when compared to basal. 200 mg/kg VPA had virtually no effect, whilst 400 mg/kg VPA raised extracellular GABA levels to 200% of basal. The results are discussed in relation to the known pharmacological and anticonvulsant actions of VPA.