Chronic epileptogenicity following focal status epilepticus

We examined chronic epileptogenicity in the perforant path stimulation model of focal status epilepticus. After 24 h of perforant path stimulation, every stimulation elicited multiple population spike discharges, and this phenomenon persisted more than 2-3 months after stimulation. Short (10-100 ms) interstimulus interval-dependent paired-pulse inhibition was almost completely lost right after stimulation, but recovered progressively over the following month. Long (200-1000 ms) interstimulus interval-dependent paired-pulse inhibition decreased, and in spite of a partial recovery, remained significantly reduced 4 weeks after stimulation. Frequency-dependent paired-pulse inhibition was lost immediately after stimulation. One month later, inhibition at 2 Hz remained significantly reduced, although in individual rats recovery ranged from poor to complete. Input/output response curves showed increased population spike amplitude but no change of the slope of excitatory postsynaptic potentials. 3-4 weeks after stimulation, spontaneous generalized motor convulsions were observed in half of the stimulated rats. In all of the stimulated rats, the kindling phenomenon was significantly accelerated compared with non-stimulated controls, and class 5 convulsions were elicited in 3.3 +/- 1.0 trials in stimulated rats, against 11.0 +/- 2.5 trials in controls.