Evoked responses in CA3 area to the mossy fibers stimulation were studied after low and high frequency tetanizations of the perforant path. Stimulations of perforant path with 10 and 100 Hz frequencies inducted depression testing through the same path. Subthreshold for potentiation of the mossy fibers inputs to the CA3 tetanization of the perforant path with 10 Hz frequency transformed to threshold one after previous tetanization of the perforant path with 100 Hz frequency. Tetanization of the mossy inputs to the CA3 with 10 Hz frequency leaded to potentiation whereas tetanization with frequency 100 Hz depressed the same inputs. High frequency tetanizations (100 Hz) of the perforant path with theta-rithm frequency stimulation basically depressed of the CA3 evoked responces to the mossy fiber stimulation.