Endocrinology. 1992 Aug;131(2):662-8.
Estradiol selectively regulates agonist binding sites on the N-methyl-D-aspartate receptor complex in the CA1 region of the hippocampus.
Estradiol alters cognitive function and lowers the threshold for seizures in women and laboratory animals. Both of these activities are modulated by the excitatory neurotransmitter glutamate in the hippocampus. To assess the hypothesis that estradiol increases the sensitivity of the hippocampus to glutamate activation by increasing glutamate binding sites, the densities of N-methyl-D-aspartate (NMDA) agonist sites (determined by NMDA displaced glutamate), competitive antagonist sites (CGP 39653), noncompetitive antagonist sites (MK801) as well as the non-NMDA glutamate receptors for kainate and AMPA (using kainate and CNQX, respectively) were measured using autoradiographic procedures. Two days of estradiol treatment increased the density of NMDA agonist, but not of competitive nor noncompetitive NMDA antagonist binding sites exclusively in the CA1 region of the hippocampus. The density of noncompetitive NMDA antagonist sites, however, was decreased in the dentate gyrus by estradiol treatment. Ovarian steroids had no effect on the density of kainate or AMPA receptors in any region of the hippocampus examined. These data indicate that the agonist and antagonist binding sites on the NMDA receptor/ion channel complex are regulated independently by an as yet unidentified mechanism, and that this regulation exhibits regional specificity in the hippocampus. The increase in NMDA agonist sites with ovarian hormone treatment should result in an increase in the sensitivity of the hippocampus to glutamate activation which may mediate some of the effects of estradiol on learning and epileptic seizure activity.
Epilepsia. 1985 May-Jun;26(3):252-7.
Comparative effects of estradiol benzoate, the antiestrogen clomiphene citrate, and the progestin medroxyprogesterone acetate on kainic acid-induced seizures in male and female rats.
Nicoletti F, Speciale C, Sortino MA, Summa G, Caruso G, Patti F, Canonico PL.
We have investigated the comparative effects of estradiol benzoate (EB), the antiestrogen clomiphene citrate (CC), and the progestin medroxyprogesterone acetate (MPA) on seizures induced by systemic injection of kainic acid (15 mg/kg i.p.) in male and female rats. Subcutaneous administration for 10 days of EB (10 micrograms/kg) or high doses of CC (50 mg/kg) significantly potentiated kainate-induced seizures, with this effect being more pronounced in male animals. Doses of 2.5 mg/kg of CC potentiated kainate-induced seizures in male rats but were ineffective in female rats. Low doses of CC (0.5 mg/kg) exhibited a mild anticonvulsant effect in both sexes. Repeated administration of MPA (2.5 mg/kg) partially protected female animals against kainate-induced seizures; in male animals, MPA induced a 30% increase in the seizure severity score, although the difference from the score of control male rats was not significant. These data suggest that sex steroids influence kainate-induced seizures in a sex-dependent manner and that the effects of the antiestrogen CC are dose dependent. This should be taken into account in view of a possible use of CC and MPA in hormonal therapy for seizure disorders.
Epilepsia. 2000 May;41(5):510-5.
Estradiol facilitates kainic acid-induced, but not flurothyl-induced, behavioral seizure activity in adult female rats.
This study was designed to determine whether previously demonstrated increases in hippocampal axospinous synapse density and NMDA receptor function induced by estradiol are paralleled by increased susceptibility to limbic (kainic acid induced) or generalized (flurothyl induced) behavioral seizures.
Kainic acid was injected systemically to ovariectomized adult female rats treated with either estradiol or oil vehicle. The latencies to each of five stages of seizure-related behaviors (staring, wet-dog shakes, head waving and chewing, forelimb clonus, rearing, and falling) were recorded for each animal. Flurothyl was administered by inhalation to ovariectomized adult female rats treated with estradiol alone, estradiol followed by short-term progesterone, or oil vehicle. The latencies to each of three stages of seizure-related behaviors (first myoclonic jerk, forelimb clonus, wild running and bouncing) were recorded for each animal.
Estradiol treatment decreased the latency to seizure-related behaviors induced by kainic acid, but neither estradiol alone nor estradiol followed by progesterone had any effect on flurothyl-induced seizure-related behaviors.
The same estradiol treatment paradigm known to induce structural and functional changes in the excitatory circuitry of the hippocampus facilitates the progression of kainic acid-induced seizures, which are known to involve the hippocampus, but has no effect on flurothyl-induced seizures. The lack of an effect of estradiol alone or estradiol followed by progesterone on flurothyl-induced seizures indicates that estradiol’s effects on seizure susceptibility do not result from increased neuronal excitability throughout the brain, but rather involve action within the limbic system. The data suggest that structural and functional changes in hippocampal circuitry induced by estradiol may contribute to increased susceptibility to limbic seizure activity.
Epilepsy Res. 1993 May;15(1):47-52.
Patterns of seizure occurrence in catamenial epilepsy.
Herkes GK, Eadie MJ, Sharbrough F, Moyer T.
The pattern of seizure occurrence was analysed over 44 menstrual cycles in 12 epileptic women who considered they had menstrually related seizures. Two peaks in the daily seizure rate were apparent. A significant increase in seizures occurred during the days of menstrual flow and the two days preceding it, with a second peak in the four days at midcycle. The lowest seizure rate was in the late phase of the menstrual cycle. Daily salivary progesterone levels were assayed in 11 women, and 12 ovulatory and eight anovulatory cycles were identified on this basis. No increase in seizures occurred at midcycle if ovulation did not occur, but the perimenstrual increase took place irrespective of ovulatory status.