Phenytoin preferentially suppresses epileptiform activity in the superficial cortical layers of the cat.
Clinically, phenytoin is thought to be useful in controlling seizure activity by preventing it's spread from the focus to neighboring tissue. Experimentally, it has been suggested that phenytoin's principal action is no longer polysynaptic pathways with primary foci affected less than surrounding tissue. In this study, we present data confirming these basic experimental conclusions in foci induced in striate neocortical layer 4 of the cat. By using discrete penicillin microinjections strategically placed into this most penicillin-sensitive neocortical layer and recording simultaneously from several layers, we have been able to expand upon these conclusions by identifying this differential action at the interlaminar level. Epileptiform activity recorded from superficial laminae bordering layer 4, and into which layer 4's primary projections terminate, is suppressed preferentially by phenytoin. These superficial layers are also those that project into neighboring areas of the cat visual cortex. It would appear, then, that phenytoin begins protecting the cortex from seizure spread at the first synaptic termination into which this layer 4 primary focus projects. A discussion of the basic mechanisms of action that may be responsible for these results is also presented.
D000818:Animals; D002415:Cats / Q000502:physiology*; D002540:Cerebral Cortex / Q000187:drug effects*; D004569:Electroencephalography; D004827:Epilepsy / Q000139:chemically induced / Q000188:drug therapy* / Q000503:physiopathology; D010406:Penicillins; D010672:Phenytoin / Q000627:therapeutic use*
D010406:Penicillins; D010672:Phenytoin