Abstract
Epilepsy affects approximately 50 million people worldwide, with 60% of adult epilepsies presenting an onset of focal origin. The most common focal epilepsy is temporal lobe epilepsy (TLE). The role of astrocytes in the presentation and development of TLE has been increasingly studied and discussed within the literature. The most common histopathological diagnosis of TLE is hippocampal sclerosis. Hippocampal sclerosis is characterized by neuronal cell loss within the Cornu ammonis and reactive astrogliosis. In some cases, mossy fiber sprouting may be observed. Mossy fiber sprouting has been controversial in its contribution to epileptogenesis in TLE patients, and the mechanisms surrounding the phenomenon have yet to be elucidated. Several studies have reported that mossy fiber sprouting has an almost certain co-existence with reactive astrogliosis within the hippocampus under epileptic conditions. Astrocytes are known to play an important role in the survival and axonal outgrowth of central and peripheral nervous system neurons, pointing to a potential role of astrocytes in TLE and associated cellular alterations. Herein, we review the recent developments surrounding the role of astrocytes in the pathogenic process of TLE and mossy fiber sprouting, with a focus on proposed signaling pathways and cellular mechanisms, histological observations, and clinical correlations in human patients.
Highlights
The definition of temporal lobe epilepsy (TLE) has not experienced significant revision since it was defined in 1985 by the International League Against Epilepsy (ILAE) as a condition characterized by recurrent, unprovoked seizures originating from the medial or lateral temporal lobe (ILAE, 1985)
TLE is further divided into mesial TLE and lateral TLE known as neocortical TLE, dependent on the structure in which epileptogenesis occurs (TellezZenteno and Hernandez-Ronquillo, 2011)
TLE patients who are refractory to antiepileptic drugs (AEDs) treatment may be candidates for surgical or neuromodulation treatments (Ladino et al, 2014). mesial TLE (mTLE) is one of the most common forms of epilepsy referred for surgical treatment (Tellez-Zenteno and Hernandez-Ronquillo, 2011)
Summary
The definition of temporal lobe epilepsy (TLE) has not experienced significant revision since it was defined in 1985 by the International League Against Epilepsy (ILAE) as a condition characterized by recurrent, unprovoked seizures originating from the medial or lateral temporal lobe (ILAE, 1985). HS is characterized by pyramidal cell loss within any of the 3 Cornu ammonis (CA) fields as well as hilus, which can be referred to as CA4, and is categorized into HS Types 1–3 (Blumcke et al, 2013). The phenomenon observed in HS termed mossy fiber sprouting is characterized by the granule cell axons projecting back into the molecular layer of the dentate gyrus (Cavarsan et al, 2018). We will briefly review the anatomy and histology of the human mesial temporal lobe (MTL) structures, with a focus on hippocampus This will be followed by discussion of common pathological findings of TLE, the current research related to the astrocytes role in TLE, mossy fiber sprouting, and clinical correlations
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