There is now compelling evidence that axon terminals of principal cells fire ectopic action potentials (AP) during relevant network activity. We studied the involvement of parvalbumin expressing, perisomatic targeting interneurons in the propagation of ectopically initiated APs to the soma during oscillatory network activity in vitro. Kainate pressure application, field potential and whole cell recordings have been performed in areas CA1/CA3 of transgenic mice that expressed EGFP under the control of the parvalbumin promoter. Within a locally excited network, basket cells discharged on every gamma cycle and phase-locked to the field, whereas axo-axonic cells (AACs) showed very high frequency (~110 Hz) AP-firing during the gamma frequent field activity. Thus, AACs are likely to provide a high frequency patterned output to axon initial segments of principal cells. Both electrical activation of the monosynaptic inhibitory inputs to the principal cells and direct intrasomatic activation of ACCs with different frequencies (10–300 Hz) demonstrated the strongest suppression of antidromically-evoked population spikes in stratum pyramidale in the frequency range between 100–150 Hz. Thus, AACs can optimally suppress AP propagation to the parent soma in hippocampal principal cells and may thereby substantially affect their excitability.