Why are most GABA agonists not effective antiepileptic drugs?

The role of the GABAergic system in the induction and control of seizures remains elusive despite considerable research. In this report, the action of GABA agonists and antagonists is investigated both iontophoretically and intravenously on the trigeminal nucleus model. This technique permitted us to differentiate the direct effect of these drugs on the trigeminal neurons from the action on neurons elsewhere in the central nervous system which impinge on the trigeminal neurons.