Abstracts

There exists a general consensus that the variety of seizure types in TLE patients can be classified into two groups: hypersynchronous onset (HYP) and low voltage fast onset (LVF). Currently, it is not clear if corresponding seizure onset types exist in animal models of temporal lobe epilepsy. In this study, we compared seizure onsets in two rodent models of chronic epilepsy to determine the morphology of seizure onset. Kainic acid (0.4[micro]g/0.22[mu]l) was injected in the right CA3 area of posterior hippocampus of adult Wistar rats. Pilocarpine (25-30 mg/kg) was injected subcutaneously in a second group of rats. After the development of spontaneous seizures, microelectrodes (tungsten, 50 [mu]m) were implanted bilaterally in the hippocampus and entorhinal cortex for wide-band [italic]in vivo[/italic] EEG recording (0.1 Hz - 1kHz). Seizures were classified on the basis of morphological onset pattern, signal averaging and power spectral analysis. Seizures in the kainic acid group (n = 86, in 10 rats) were classified as either LVF (25%) or HYP (71%), with the remaining seizures (4%) falling into a third category, named [ldquo]Gradual[rdquo] because of their slower development. Signal averaging within each onset type revealed the presence of an Initial Slow Wave at onset in the LVF, but not at HYP, seizures. Of all HYP seizures, most (82.6%) were local and did not spread to other brain areas, while the remaining (17.4%) seizures generalized to both sides of the brain.
Seizures in the pilocarpine group (n =151, 4 animals) were classified visually as LVF (51%) or HYP (3.3%) onsets. Distinct from LVF and HYP, the remaining seizures (45.7%), exhibited high voltage fast activity (HVF) at onset. Signal averaging within each onset type revealed the presence of an Initial Slow Wave at onset in the LVF and HVF, but not at HYP, seizures. All seizures in the pilocarpine group generalized to both sides of the brain. These data indicate that two rodent models of chronic epilepsy exhibit seizures morphologically similar to those recorded patients with temporal lobe epilepsy. HVF and LVF seizures that exhibited a slow wave at onset were dominant in the pilocarpine model, while HYP onsets lacking a slow wave onset were more frequent in the KA rodent. The differences of seizure type ratio between may indicate that each model lends itself to the study of a particular onset pattern. Additionally, a useful relationship between the initial chemical insult, mechanism of seizure generation and morphological type of onset may exist. (Supported by NSF IGERT Neuroengineering Training Grant DGE-9972802; NIH grants NS-02808 and NS-33310.)