We investigated the effect of injection of a local anesthetic, tetracaine, into the ipsilateral basolateral amygdala (BLA) on long-term potentiation (LTP) in the medial perforant path-dentate gyrus granule cell synapses of anesthetized rats. The dentate gyrus synaptic potential evoked by low frequency test stimulation did not change following tetracaine injection into BLA. However, when tetanic stimulation (30 pulses at 60 Hz) was applied 10 min after tetracaine injection, the magnitude of LTP was significantly attenuated in a dose-dependent manner. Injection of tetracaine after tetanic stimulation did not affect the established LTP. The small LTP observed in the BLA-lesioned rats was regarded as the BLA-independent component of LTP, which was not affected by tetracaine injection. These results suggest that neuron activities in the ipsilateral BLA are partly required for the induction of LTP in the dentate gyrus in vivo.