Absence seizures during pregnancy in WAG/Rij rats.

Spontaneously occurring spike-wave discharges (SWDs) and serum concentrations of ovarian steroid hormones were investigated before, during and after pregnancy in WAG/Rij rats, a rat strain with genetically determined absence seizures. Eight groups of rats were included in the assays of progesterone and estradiol: rats at diestrus, at various days of pregnancy and at lactating days. The number of SWDs in cortical EEG of WAG/Rij rats was decreased from the 3rd up to the 18th day of pregnancy and subsequently increased to control level. Thereafter, a new decrease was found 2-3 days after parturition. Serum concentration of progesterone was threefold increased at the 3rd day of pregnancy, remained elevated until the 18th day of pregnancy and returned to control values before delivery. Over measured days, estradiol was significantly elevated only at the 18th day of pregnancy. Results demonstrate that physiological conditions induced by the state of pregnancy lead to suppression of occurrence of SWDs. Changes in plasma progesterone concentration correspond to the changes in number of SWDs: an increased level of progesterone during pregnancy is accompanied by a decreased number of SWDs, while a decrease in circulating progesterone before parturition is paralleled by an increase of SWDs. Of interest, the relationship between SWDs and concentration of progesterone found during pregnancy is diametrically opposite to results obtained in acute administration studies of progesterone in nonpregnant animals.