The laminar sensitivity of cat striate cortex to penicillin induced epileptogenesis.

By utilizing the microinjection of low nanoliter volumes of convulsant drug and recording from the injection site, we have been able to electrophysiologically identify a layer of cat striate cortex that is most sensitive to the epileptogenic effects of penicillin. This band encompasses cortical depths of approximately 1000-1250 micrometers when the smallest volumes of penicillin are injected. Comparable penicillin injections made either superficial to or deeper than this were not as effective in producing epileptiform alterations in normal activity. Histochemical marks made at the site of these injections have identified cortical cytoarchitectonic layer IV as the site of maximal neocortical penicillin sensitivity. The vulnerability of layer IV to penicillin epileptogenesis may be related to certain distinctive anatomic features of this layer.