Effects of four common anticonvulsants on the high pressure nervous syndrome in the rat.

This study reports results from experiments designed to test common, clinically useful anti-convulsants for their effectiveness, if any, against the high pressure nervous syndrome (HPNS) in rats. Phenytoin, carbamazepine, phenobarbitone, or diazepam were administered orally to rats before compression. Endpoints used to assess the progression of the HPNS were T1, T3, and T5 (onset of, continuous, and severe tremor), myoclonus, and seizures. Of the four drugs tested, only phenobarbitone increased the onset pressure for tremor and seizures by: T1 33%; T3 11%; T5 14%; seizures 10%. Neither phenytoin, carbamazepine, nor diazepam had any significant effect on any of the endpoints studied. High dose chronic pretreatment with phenytoin also had no effect on the HPNS. These data suggest that conventional anticonvulsant treatment would be of limited value for HPNS in man, and the lack of effect also suggests that HPNS seizures are of an unusual type.