Abstracts

Several rat strains have been studied extensively and are well-known as genetic models of absence epilepsy. Less well-known is the fact that many common laboratory rat strains frequently express spike-wave discharges (SWDs) in a similar fashion. These SWDs are usually 6-9 Hz, and are associated with motor arrest of the animal. Generally, SWDs tend to be more frequent and longer in duration as the animals grow older. To our knowledge, however, no study in Long Evans rats has included a detailed observation of SWDs and how SWD expression changes throughout their lifetime.
Previously, we reported that cortical infarction by middle cerebral artery / common carotid artery occlusion results in a significant reduction in the frequency and duration of SWDs compared to sham-operated control animals (Kelly et al, 2006). In this study, we sought to extend these observations to gain a better understanding of the timecourse of SWDs and the effect of lesion-associated changes on their expression in these animals., Five Long Evans rats lesioned by MCA/CCAO and four Long Evans sham-operated controls were intermittently monitored by video-EEG over a six-month period as previously reported (Kelly et al, 2006). Fifty-hour samples were then chosen from each animal[apos]s EEG record and visually reviewed for the presence of SWDs. The time and date of each SWD observed was documented, as well as the duration of the event. Preliminary results were obtained by plotting SWD data on a timeline for analysis by linear regression., Preliminary results in control rats indicate that in 4 of 4 animals (100%) SWDs tend to increase in frequency of occurrence as the animal grows older. The average duration of SWDs tended to increase with age in 2 of 4 animals (50%), while decreasing in the other 2 animals (50%). Preliminary results in lesioned animals show a trend toward both greater frequency of occurrence and longer duration of SWDs in 2 of 5 (40%) of animals, and a decrease in both frequency of occurrence and duration in 2 of 5 animals (40%). One animal (20%) showed an increase in the frequency of occurrence, but a decrease in the average duration of SWDs., Since 7 of the 9 animals included in this study showed a trend toward an increase in the frequency of occurrence of SWDs over the six-month monitoring period, these studies appear to be consistent with reports of an aging-related increase in SWD expression in other rat strains. Changes in average duration of SWDs over time appear to be variable animal to animal. No reported changes in SWD expression are clearly related to the lesion., (Supported by RFA 01-07-26 to KMK.)