Abstracts

In the electroencephalogram (EEG) of WAG/Rij rats, a genetic model of absence epilepsy, two types of spike-wave-discharges (SWD) can be recorded: Type 1 SWD, bilateral generalized and Type 2 SWD, more local. Earlier it was established that all adult WAG/Rij rats show Type 1 SWD and that the pattern of inheritance obeys Mendelian rules. In the present experiment we studied the influences of strain and housing condition on the development and expression of Type 1 and Type 2 SWD. The strains were WAG/Rij and ACI rats, the latter strain has very few Type 1 SWD but a substantial number of Type 2 SWD. The environment was manipulated by housing the rats in an impoverished (IC) or enriched (EC) environment.
75 WAG/Rij and 80 ACI male rats were housed in an IC or EC environment from weaning until 6 months of age. At 3 months of age housing condition changed for half of the rats from IC to EC or vice versa, while for the other half it stayed the same. EC housing consisted of a group of 8-10 rats housed in a complex environment, and IC housing implied single housing in Makrolon type III cages. The EEG was recorded at 3 and again at 6 months of age. We analysed if strain or housing condition before 3 months of age or after 3 months of age had an influence on the number and the mean duration of Type 1 and Type 2 SWD.
We found that the number of Type 1 SWD was higher for WAG/Rij than for ACI rats. EC housing led to an increase in mean duration of Type 1 SWD in WAG/Rij rats only. Regarding Type 2 SWD we found that rats that were recently EC housed had a higher number of discharges than IC housed rats. Next, at 6 months of age WAG/Rij rats that were EC housed after 3 months of age had the highest number of Type 2 SWD of all groups. Finally, ACI rats had longer Type 2 SWD than WAG/Rij rats.
We could demonstrate that the development and expression of Type 1 and Type 2 SWD are differently influenced by strain and housing condition. The number of Type 1 SWD was influenced by strain while the number of Type 2 SWD was influenced by housing condition. But, whereas the mean duration of Type 1 SWD was influenced by housing condition, the mean duration of Type 2 SWD was strain dependent. Our data also revealed a genotype-environment interaction and a sensitive period for influences of housing condition on Type 2 SWD, inferred from the observation that only when WAG/Rij rats were EC housed after 3 month of age, they had more Type 2 SWD than rats from all other groups. In all, our data underline the different properties of Type 1 and Type 2 SWD, while a comparison with the literature suggests opposite effects of EC housing on absence and convulsive epilepsy.
[Supported by: Dutch Organization for Scientific Research (NWO), Grant 425-20-401]