With the extracellular recording technique, the basal synaptic responses (population spike, PS) evoked by low frequency test stimulation in the dentate gyrus of anesthetized rats was recorded and the effects of (-) and (+) clausenamide(icv) on the PS and long-term potentiation (LTP) induced by tetanus (50 pulses at 200 Hz) were observed. The results showed that: (1) at a lower dose (1 nmol), (+) clausenamide showed no effect on either the basal PS or LTP, (-) clausenamide did not affect the basal PS but enhanced the magnitude of LTP. (2) At a higher dose (4 nmol), (-) clausenamide not only potentiated the basal PS but also dose-dependently augmented the magnitude of LTP. Meanwhile, (+) clausenamide did not affect the basal PS but attenuated the magnitude of LTP. These results suggest that the effects of clausenamide on the synaptic transmission in the dentate gyrus depend on its chirality. The potentiating effects of (-) clausenamide on synaptic transmission in hippocampus strongly support our previous behavioral and neurobiochemical studies on the nootropic action of (-) clausenamide.