Effect of anticonvulsants on thalamic afterdischarge in rats and cats

Effects of anticonvulsants were determined on thalamic afterdischarge in gallamine-immobilized cats and d-tubocurarine-immobilized rats in order to clarify the participation of anticonvulsants in the thalamus. Thalamic afterdischarge was induced by electrical stimulation of cat nucleus centralis lateralis and rat nucleus reticularis at 50 Hz, 1 msec for 4 sec. In cats, diphenylhydantoin, carbamazepine, phenobarbital, and diazepam raised afterdischarge threshold, and shortened its duration induced at twice the threshold voltage. Trimethadione and dipropylacetate raised the threshold, but did not change the duration. In rats, diphenylhydantoin, phenobarbital, and diazepam raised the threshold, and shortened the duration with comparable dose ranges used for cats. Dipropylacetate and acetazolamide raised the threshold, although did not change the duration except for shortening action with a higher dose of dipropylacetate. Trimethadione was without effect. These results suggest that the depressive effect of anticonvulsants on the thalamus is, at least in part, associated with control of the epilepsies.