Generation of sharp wave-ripple complexes (SPW-R) within hippocampal area CA3 was induced by repeated stimulation of orthodromic as well as antidromic pathways of adult rat hippocampal brain slices. SPW-R originated in CA3 and propagated throughout the hippocampus. Intracellular recordings showed that their induction involves time-dependent changes in interactions between clusters of neurons in the CA3 associational network. In about 50 percent of recorded CA3 pyramidal cells synaptic input during SPW-R caused an EPSP generation followed by 1–4 action potentials whereas the remaining cells responded with a compound IPSP. Blocking GABAA-mediated inhibition during SPW-R activity led to a gradual transition of SPW-R into prolonged hypersynchronous bursts within area CA3. In comparison to stimulus-induced SPW-R the SR-95531-mediated bursts showed a significantly higher amplitude, duration and frequency content as well as >10-fold higher increases in [K+]o. Intracellular recordings of all recorded cells during GABAA receptor blockade showed that the bursts were characterized by a large, prolonged depolarization envelop giving rise to 20–40 action potentials. Applying the the gap junction blocker mefloquine during hypersynchronous network activity largely reduced fast ripple oscillations (~300 Hz) without blocking recurrent bursts.