Effects of anticonvulsant drugs on 4-aminopyridine-induced seizures in mice.
The K+ channel blocker 4-aminopyridine (4-AP) causes epileptiform activity in in vitro preparations and is a potent convulsant in animals and man. In mice, 4-AP produces behavioral activation, clonic limb movements and wild running, followed by tonic hindlimb extension and death (ED97, 13.3 mg/kg, s.c.). We evaluated the ability of a series of anticonvulsant drugs to protect against 4-AP-induced seizures using lethality as the endpoint. Drugs with a phenytoin-like profile of activity were protective with ED50 values (all in mg/kg, i.p.) of 34.4 for phenytoin, 18.6 for carbamazepine, 26.9 for felbamate, and 41.5 for zonisamide. Phenobarbital and valproate also protected against 4-AP-induced seizures and lethality (ED50s, 30.6 and 301, respectively). In contrast the NMDA antagonists (+/-)-CPP and (+)-MK-801 were inactive as were the GABA enhancers diazepam, vigabatrin and tiagabine; the antiabsence drug ethosuximide; and the L-type Ca2+ channel blocker nimodipine. We conclude that drugs like phenytoin which block seizure spread are effective antagonists of seizures induced by K+ channel blockade. Drugs with specific actions on other cellular targets may be weak or inactive, presumably because they are unable to attenuate the spread of intense (non-NMDA receptor mediated) excitation evoked by 4-AP.
Yamaguchi
S
S
Neuronal Excitability Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
Rogawski
M A
MA
D015761:4-Aminopyridine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D001522:Behavior, Animal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D011930:Reaction Time; D012640:Seizures / Q000139:chemically induced* / Q000517:prevention & control
D000927:Anticonvulsants; D015761:4-Aminopyridine