Excessive release of glutamate can cause many nervous system disorders. It has been reported that when a high dose of penicillin sodium is administered into the rat's brain, epilepsy, accompanied with glutamate elevation, will result. In this experiment, a low dose of penicillin sodium (1000 kIU/l) was microinjected into the rat's lateral ventricle to set up an overexcitation model, in which the concentration of ipsilateral hippocampal glutamate was monitored in vivo. by microdialysis-HPLC method as an indicator of the rat's excitatory state. Influences of sedative-hypnotic drugs on this model were verified by coadministration of diazepam or phenobarbital with Na-PCN intracerebroventricularly. In models, hippocampal glutamate concentration was elevated to 307% compared with its baseline level (p < 0.05), and this increase of glutamate was inhibited completely when different doses of diazepam or phenobarbital were administered (p < 0.05). The sedative effect of jujuboside A and trifluoperazine were then studied with this model. Jujuboside A (JuA) 0.1 g/l also reduced the glutamate level significantly (p < 0.05). Calmodulin antagonist trifluoperazine showed similar inhibitory effect as JuA, which may indicate that the effect of JuA is correlated with its anticalmodulin action. This model can be used to investigate the inhibitory effect of central nervous system drugs.