Visual deprivation increases capability of layer II/III for epileptiform activity in the rat visual cortical slices

Effects of visual deprivation on the induction of epileptiform activity were studied in layer II/III of 29-39-day-old rat primary visual cortex. Field potentials were evoked by stimulation of layer IV in slices from control (CON) and dark-reared (DR) rats. Picrotoxin (PTX)-induced epileptiform activity was characterized by spontaneous and evoked epileptic field potentials (EFPs). The results showed that DR slices demonstrate greater susceptibility for induction of spontaneous EFP. PTX-induced changes in the characteristics of evoked field potentials also showed higher tendency of DR animals to generate epileptiform activity. In both groups, field potentials consisted of pEPSP₁ (population excitatory postsynaptic potential 1, i.e., first negativity) and pEPSP₂ (second negativity), respectively. There was no significant difference between the characteristics of field potentials in CON and DR slices. PTX significantly increased amplitude and duration of pEPSP₂, but it had no significant effect on pEPSP₁. Effects of PTX on pEPSP₂ were significantly higher in DR slices. It is concluded that visual deprivation results in a heightened potential in layer II/III of the rat visual cortex to generate PTX-induced epileptiform activity. Copyright (C) 1999 Elsevier Science B.V.