Enhanced excitability of the hippocampal CA2 region and its contribution to seizure generation in a mouse model of temporal lobe epilepsy

ABSTRACT The hippocampal CA2 region, an area important for social memory, has been suspected to play a role in temporal lobe epilepsy (TLE) because of its resistance to the degeneration observed in neighboring CA1 and CA3 regions in both human and rodent models of TLE. However, little is known about whether alterations in CA2 properties serve to promote seizure generation or propagation. Here we have used the pilocarpine-induced status epilepticus (PILO-SE) model of TLE to explore the role of CA2. Ex vivo electrophysiological recordings from acute hippocampal slices revealed a set of coordinated changes that enhance CA2 intrinsic excitability, reduce CA2 local inhibitory input, and increase CA2 excitatory output to its major CA1 synaptic target. Moreover, selective silencing of CA2 pyramidal cells using a chemogenetic approach caused a significant decrease in the frequency of spontaneous seizures. These findings provide the first evidence that CA2 actively contributes to TLE seizure activity and may thus be a promising therapeutic target.