Identification of penicillin diffusion at the onset of epileptogenesis in the cat striate cortex following differential laminar microinjection.
Diffusion patterns of 14C-labeled penicillin, resulting from microinjections into different neocortical laminae, were compared with simultaneous electrophysiologic monitoring of epileptogenesis across these laminae. Injections into layer IV produced response alterations quickly in all recorded layers even with penicillin confined to this granular cell layer. Supra- and infragranular layer injections also initiated epileptic response abnormalities, though much more slowly and only after penicillin had diffused into layer IV. Injections where penicillin diffusion was shown to be limited to either of the non-granular layers did not induce epileptogenesis. These results indicate not only that layer IV is the most penicillin-sensitive neocortical layer, but that (1) it is sufficient for epileptogenesis when initially injected and, that due to this heightened sensitivity, (2) it serves as a natural trigger for epileptiform response development in other layers when they are injected first. Neurochemical and neuromorphologic correlates within striate cortex are discussed in an attempt to identify the reason for this granule cell layer sensitivity to penicillin-induced epileptogenesis.
D000818:Animals; D002250:Carbon Radioisotopes; D002415:Cats; D004058:Diffusion; D004553:Electric Conductivity; D004827:Epilepsy / Q000139:chemically induced* / Q000503:physiopathology; D008845:Microinjections; D010400:Penicillin G / Q000008:administration & dosage / Q000378:metabolism*; D010775:Photic Stimulation; D014018:Tissue Distribution; D014793:Visual Cortex / Q000503:physiopathology*
D002250:Carbon Radioisotopes; D010400:Penicillin G