The flash-evoked afterdischarge (FEAD) is a self-sustained burst of wave-and-spike complexes recorded from occipital cortex in the rat and other animals in response to a single light flash. On the basis of behavioral experiments and studies employing single doses of
antiepileptic drugs, FEAD has been proposed as a model of the
absence seizure. In order to test the validity of FEAD as an
absence seizure model, the present experiments determined dose-response relationships for the suppression of FEAD by six
antiepileptic drugs with established clinical profiles. It was found that
phenobarbital,
ethosuximide, and
trimethadione suppressed FEAD in a dose-related manner, and that
ethosuximide was approximately three times as potent as
trimethadione.
Mephenytoin produced a maximal reduction of FEAD of only 30 to 40%, which was not dose-related. Neither
phenytoin nor
acetazolamide suppressed FEAD. The results obtained with
ethosuximide,
trimethadione, and
phenytoin are qualitatively similar to their
therapeutic effects in
absence epilepsy. The FEAD model failed, however, to unequivocally predict the therapeutic efficacy of
mephenytoin or
acetazolamide. In this respect, it is similar to the
metrazol seizure model. It is concluded that FEAD is a valid
absence seizure model with a pharmacological predictive value that is at least as good as the
metrazol model.