Figure 2.  Past and present perspectives on the role of the dentate gyrus (DG) in temporal lobe epilepsy (TLE). A. Past views. A simplified schematic of the DG in TLE is shown with the major layers on the left (MOL, molecular layer; GCL, granule cell layer; HIL, hilus). Glutamatergic neurons are green; GABAergic neurons are red. In TLE, hilar MCs and SOM cells are reduced (dotted lines). The axons of GCs sprout in the epileptic brain and innervate dendrites in the MOL (SPROUT). B. Present views. An updated schematic shows that some MCs and SOM cells are lost in TLE. In addition to reactive astrocytes in the hilus, there are microglia, reflecting new appreciation of the diverse roles of glia and inflammation. New branches of blood vessels emerge because of new appreciation of angiogenesis in TLE. There are progenitors (IMM for immature) in the area next to the GCL which can divide in adulthood, giving rise to new GCs. Ectopic GCs (EGC) arise in the hilus. They contribute to sprouting that previously had been considered to be a characteristic only of cells in the GCL. Immature GCs arise from progenitors that are mainly beneath the GCL but can be in the hilus.55 Many types of GABAergic neurons (red) are added to the diagram because of the greater understanding that they normally are present. GABAergic neurons are named using a different classification system. PV (parvalbumin) or perisomatic-targeting neurons replace the term basket cells; HIPP cells replaces SOM cells.