Deep brain stimulation (DBS) has shown great potential for treating various neurological disorders in clinic. However, the mechanisms of DBS are not clear yet. Regular DBS uses high frequency stimulation (HFS) of pulse sequences. The narrow pulses facilitate the activation of axon fibers most readily among all elements of a neuronal structure. Through the projection of axons, the effects of HFS can spread to downstream neurons. Therefore, to explore the mechanisms of DBS, we investigated the effects of axonal HFS on the downstream neurons in hippocampus, as it has been an important target for treating diseases such as epilepsy and dementia. One-minute HFS at 100 Hz was applied to the afferent fibers of hippocampal CA1 region (i.e., the Schaffer collaterals) in anesthetized rats. Single unit spikes of pyramidal cells and interneurons in the downstream CA1 region were recorded and analyzed. Firing rates of spikes, phase-locking values (PLV) between spikes and stimulation pulses, as well as spike latencies were calculated to quantify the changes of neuronal action potential firing during the HFS periods. Results showed that during the initial period of HFS, synchronized action potentials (i.e., population spikes, PS) generated in the population of neurons. During the late period of HFS (after the disappearance of PS events), both types of neurons continued to fire unit spikes with stable rates. However, the phase-locking relationship between spikes and stimulation pulses decreased gradually, while the latencies of spikes increased gradually. In addition, compared to interneurons, the unit spikes of pyramidal cells had smaller phase-locking values and longer latencies. These results indicate that prolonged axonal HFS can generate asynchronous activity in the downstream neurons. Partial block in axon conduction induced by high-frequency pulse stimulation might be one major cause underlying the phenomena. The present study provides important information for revealing the mechanisms of DBS.