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 wer e studied in layer II/III of 29-39-day-old rat primary visual cortex. Field potentials were evoked by stimulation of layer TV in slices from control ( CON) and dark-reared (DR) rats. Picrotoxin (PTX)-induced epileptiform activ ity was characterized by spontaneous and evoked epileptic field potentials (EFPs). The results showed that DR slices demonstrate greater susceptibilit y for induction of spontaneous EFP. PTX-induced changes in the characterist ics of evoked field potentials also showed higher tendency of DR animals to generate epileptiform activity. In both groups, field potentials consisted of pEPSP(1) (population excitatory postsynaptic potential 1, i.e., first n egativity) and pEPSP(2) (second negativity), respectively. There was no sig nificant difference between the characteristics of field potentials in CON and DR slices. PTX significantly increased amplitude and duration of pEPSP( 2), but it had no significant effect on pEPSP(1). Effects of PTX on pEPSP(2 ) were significantly higher in DR slices. It is concluded that visual depri vation results in a heightened potential in layer II/III of the rat visual cortex to generate PTX-induced epileptiform activity. (C) 1999 Elsevier Sci ence B.V. All rights reserved.