Estrogen alters the acquisition of seizures kindled by repeated amygdala stimulation or pentylenetetrazol administration in ovariectomized female rats.

Ovariectomized female rats received estradiol (E2) replacement by means of subcutaneous silastic capsules (10% E2 in cholesterol). E2-replaced rats required fewer daily amygdala stimulations to develop fully kindled seizures as compared with ovariectomized rats implanted with cholesterol-only capsules. Other rats were injected with pentylenetetrazol (PTZ), 40 mg/kg i.p., every 48 h. E2-replaced rats showed a progressive increase in convulsive severity from minimal responses after the first injection to tonic convulsions after eight injections. Most rats without E2 replacement failed to progress past clonic convulsive responses after 22 injections. The results support a marked influence of E2 on seizure processes as demonstrated in two different models of seizure acquisition.