High-frequency oscillations and seizure-like discharges in the entorhinal cortex of the in vitro isolated guinea pig brain

- We studied HFOs in entorhinal cortex of the guinea pig whole brain preparation.
- 4AP SLEs are associated to ripples and BMI SLEs to fast ripples.
- Such difference could be due to their effect on GABAA receptor signaling.
- HFOs reveal differences that are not observed when analysing field potentials.

We analyzed the patterns of seizure-like activity and associated high-frequency oscillations (HFOs) induced by the K+ channel blocker 4-aminopyridine (4AP, 50 μM) or the GABAA receptor antagonist bicuculline methiodide (BMI, 50 μM) in the in vitro isolated guinea pig brain preparation. Extracellular field recordings were obtained from the medial entorhinal cortex (EC) using glass pipettes or silicon probes; 4AP or BMI were applied through the basilar artery. Ripples (80-200 Hz) or fast ripples (250-500 Hz) occurred at higher rates shortly before ictal events induced by 4AP or BMI, respectively. In addition, during the ictal period, ripples were mostly associated with 4AP-induced ictal events whereas fast ripples predominated during ictal discharges induced by BMI. Finally, ripples occurred at higher rates during the clonic phase of 4AP-induced ictal events compared to the tonic phase, while higher rates of fast ripples characterized the clonic phase in both 4AP- and BMI-induced ictal discharges. These differences in HFO occurrence presumably reflect the diverse action of these two convulsants on GABAA receptor signaling.