Abstracts

The latent period is usually considered to be a seizure-fee interval between an epileptogenic injury and the development of chronic seizures. If the chronic seizures occur at a stable frequency, then post-injury seizure probability can be considered a step function. We hypothesize 1) post-injury seizure probability is a continuous function and that at some point the seizure frequency goes through an exponential growth phase, and 2) that seizures tend to occur in clusters throughout the period of continuously increasing seizure frequency., We obtained nearly continuous electroencephalographic recordings using radiotelemetry in adult rats for 100 days after kainate-induced status epilepticus (n=9)., In all 9 kainate-treated rats the seizures continuously increased with time after a mean latent period of 8 days, and all rats experienced an exponential increase in the seizure frequency at variable times after the latent period. A frequency histogram of the inter-seizure intervals throughout the period of seizure progression shows a distinct peak of intervals occurring at very short times. An analysis of the inter-seizure interval distribution compared to both a Poisson distribution and matched randomly generated intervals shows that the inter-seizure interval distribution is significantly different from a Poisson and random distribution., Seizure frequency continuously increases as a function of time after injury, suggesting that progressive molecular and cellular changes underlying seizure generation (e.g., axon sprouting and increased recurrent excitation) are steadily increasing with time after the injury. The exponential increase in seizure probability may reflect nonlinearities in the network response to steady increases in sprouting (see abstract by Swiercz et al.). These data also indicate that spontaneous seizures tend to occur in clusters throughout the period of increasing seizure frequency., (Supported by NIH.)