Chemogenetic silencing of the subiculum blocks acute chronic temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common form of medically-intractable epilepsy. Subicular hyperexcitability is frequently observed with TLE, presumably caused by impaired inhibition of local excitatory neurons. Here, we evaluated the effectiveness of silencing subicular pyramidal neurons to treat a rodent model of TLE. First, we generated a chronic TLE mouse model via initial intrahippocampal kainic acid (IHKA) injection. In the chronic state after first IHKA injection, behavioral seizures and histological abnormalities were reliably observed. We then injected an adeno-associated viral (AAV) vector carrying an inhibitory chemogenetic element, hM4D_i, directly into the subiculum. Eight weeks after the first IHKA injection, acute seizures were induced by giving a second dose of kainic acid (KA), which mimicked generalized tonic-clonic seizures. Herein, precise control over generalized tonic-clonic seizure onset was achieved via this two-step process. We found that chemogenetic suppression of subicular pyramidal neurons had a robust anti-epileptogenesis effect in this acute-chronic model of TLE. These data confirm a crucial role of the subiculum in the propagation of hippocampal seizures and highlight the potential for using subicular chemogenetic manipulation to treat generalized tonic-clonic seizures.