Experimental models in the study of epileptogenesis

Abstract

Epilepsy is a chronic neurological disease characterized by spontaneous recurrently occurring epileptic seizures as a consequence of abnormal, excessive and synchronous neuronal activity in the brain. Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy in adults, being characterized by hippocampal sclerosis, reactive gliosis, neurodegeneration, and synaptic reorganization. Animal models of TLE based on the administration of convulsive agents trigger a status epilepticus (SE) that progresses towards the occurrence of spontaneous recurrent seizures. Among these models are those induced by the systemic administration of pilocarpine or by intrahippocampal injection of kainic acid, both being characterized by 3 clearly defined phases: (i) acute SE seizures; (ii) latent period and (iii) occurrence of recurrent spontaneous seizures. These models not only reproduce most of the neuropathological TLE features but also allow for the identification of biomarkers of epileptogenesis and potential pharmacological targets. The use of neuroimaging techniques such as positron emission tomography (PET) with the radiotracer 18F-Fluorodeoxyglucose (18F-FDG) identifies brain hypometabolism in the latent period that not only localizes the epileptic focus but is also an biomarker of early diagnosis. Other neuroimaging techniques allow for detecting, among others, biomarkers of neuroinflammation, alterations in the permeability of the blood-brain barrier and astrocytic activation, all of them associated with epileptogenesis. Finally, the use of chemogenetics through DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) technology in murine models leads to targeted modulation of astrocytic activity, being a novel tool that considers the contribution of the astrocytes role in brain metabolic alterations in epileptogenesis.