Development of kindling and spontaneous seizures after massed stimulation of different loci in the rat piriform cortex

Massed electrical stimulation of the anterior piriform cortex (PC) in rats using short (5 min) interstimulus intervals has previously been reported to induce severe chronic epilepsy with spontaneous seizures and has thus proposed to represent a novel model of temporal lobe epilepsy. Ln the present study, we used this stimulation protocol to evaluate the frequency and severity of recurrent spontaneous seizures produced in this way. In addition to the locus in the anterior PC previously used for massed stimulation (MS), we also stimulated rats via a locus in the transition zone between anterior and posterior PC ("central PC"), which previously was found to be more sensitive to electrical stimulation than various other loci in the anterior or posterior PC. During MS (71 stimulations for 1 s each at twice afterdischarge threshold), focal and infrequent secondary generalized seizures occurred in both groups, but there was no consistent progressive increase in seizure severity with increasing number of seizures, possibly as a result of postictal inhibitory processes. Following MS, rats were restimulated after 1, 2, 4, and 7 weeks, using five stimuli at 5-min interstimulus periods at each retest period. Ln both PC-implanted groups, seizure severity and seizure duration progressively increased over the period of the retests, indicating a delayed development of kindling. Spontaneous seizures were only observed rarely, so that MS of the PC is certainly no effective means of producing recurrent spontaneous seizures. (C) 2000 Elsevier Science B.V. All rights reserved.