Effects of 4-aminopyridine on sharp wave-ripples in rat hippocampal slices

Sharp wave-ripple complexes (SPW-Rs) are characterized by approximately 60 ms field potential transients superimposed by ripple oscillations of approximately 200 Hz. In chronic epileptic rodents and humans, faster ripples have been recorded showing frequencies of up to 500 Hz. In this study, we tested whether the blockade of K+ currents by 4-aminopyridine (4-AP) contribute to the generation of high-frequency ripples, as changes in K+ channel expression have been observed in chronic epileptic tissue. We showed that 4-AP significantly increased the amplitudes and incidence of induced SPW-Rs without significantly changing their ripple frequency. a-Dendrotoxin or BDS-I did not mimick these changes suggesting that 4-AP acts via Kv1.4 channels. Thus, the incidence of SPW-Rs, but not the ripple frequency is regulated by 4-AP-sensitive potassium currents.