CHARACTERIZATION OF EPILEPTIFORM FIELD POTENTIALS RECORDED IN THE IN-VITRO PERIRHINAL CORTEX OF AMYGDALA-KINDLED EPILEPTOGENESIS

The perirhinal cortex (PRC) has recently been reported that the excita tory role of this area is important for the generation and the propaga tion of kindled seizures. In the present study, we investigated the ex tracellular electrophysiological properties of the circuitry which con tribute to the propagation of seizures in the PRC, and examined the hy pothesis that amygdala-kindling changes the electrophysiological natur e of the rat PRC slice in vitro. Field potentials elicited in the PRC had extended duration (> 200 ms, most congruent to 1 s) with overlying spike components. The potentials showed strong synchronizing effect g overned by an all-or-none rule. Although spontaneous epileptiform disc harges that were equivalent in appearance to synaptically-activated fi eld potentials were observed in the PRC of both amygdala-kindled and c ontrol rats, the number of slices showing spontaneous activity was sig nificantly larger in the kindled group than in the control group (chi( 2)-test, P < 0.01). The occurrence of tetanus-induced afterdischarges in kindled rats was significantly higher than in control rats (chi(2)- test, P < 0.01). The afterdischarge durations of control slices were g enerally short and the afterdischarges did not consist of the typical 'tonic-clonic' phases. However, the occurrence of the electrographical seizure in the high K+ ACSF were not affected by amygdala-kindling op eration. These results indicate that amygdala-kindling lowers the thre shold for transsynaptic excitability and enhances the synchronized act ivity of the PRC induced by episodic proconvulsive manipulations such as tetanus stimulation.