SYNCHRONIZATION OF EPILEPTIFORM ACTIVITY BETWEEN CA1 AND CA3 HIPPOCAMPAL FIELDS UNDER SYNAPTIC AND NON-SYNAPTIC CONDITIONS IN RAT BRAIN SLICES

Abstract

Relevance. Over-synchronization of neuronal activity results in epileptic-like discharges that can lead to seizures and status epilepticus. Understanding mechanisms of neural net synchronization could provide new insights into the treatment of epileptic disorders.
 Objective: to compare the levels of synchronization between CA3 and CA1 hippocampal zones during epileptiform activity induced under synaptic and non-synaptic conditions.
 Materials and Methods. Transverse brain slices were obtained from 12-14 days old rats. For induction of epileptiform activity common pro-epileptic agents were used: bicuculline and 4-aminopiridine. Nonsynaptic epileptiform activity was induced by perfusion brain slices with low-Ca2+ and Cd2+-containing artificial cerebrospinal fluid (aCSF). Simultaneous extracellular recordings of field potentials were obtained from the CA3 and CA1 pyramidal cell layer with extracellular glass microelectrodes (2–3 MΩ). Signals were then low-pass filtered (kHz), amplified using a 2-channel differential amplifier M1800, digitized at 10 kHz using analog-to-digital converter. The level of synchronization between CA3 and CA1 was evaluated using cross-correlation analysis. 
 Results: Perfusion hippocampal slices with bicuculline and 4-aminopyridine induced epileptiform activity with high level of synchronization between CA3 and CA1 hippocampal zones. Removing Ca2+ from extracellular solution as well as adding CdCl2 to the perfusion aCSF induced epileptiform activity that was not synchronized between hippocampal CA3 and CA1 fields. 
 Conclusions: Synaptic interaction account for high level of CA3-CA1 synchronization induced by pro-epileptic agents bicuculline and 4-aminopiridine. Under non-synaptic conditions, local cellular interactions induce epileptiform activity with no synchronization between CA3 and CA1 hippocampal zones.