Repeated administration of triiodothyronine enhances the susceptibility of rats to isoniazid- and picrotoxin-induced seizures.

In an experimental condition of hyperthyroidism, obtained by repeated administration of triiodothyronine in adult rats (100 micrograms/kg/day, sc for 7 consecutive days), there is an increased susceptibility to the convulsant effect of isoniazid (300 mg/kg, ip) and picrotoxin (4 mg/kg, ip). On the other hand, the characteristics of brain [3H] flunitrazepam binding sites are not modified. These data afford further experimental evidence of the influence of thyroid hormones on brain function.