There are several indications that HS plays an important contributing role in TLE. The aberrantly sprouted mossy fibers preferentially innervate glutamatergic granule cells, primarily creating a recurrent excitatory feedback circuitry, thus mossy fiber sprouting is believed to be an excitatory phenomenon (Buckmaster et al., 2002; Scharfman et al., 2003; Wuarin and Dudek, 1996). 12.4E and F) but also that nonselective cation-conducting transient receptor potential channels, L-type Ca2 + channels, and ryanodine receptors contribute to those slow oscillations (Govindaiah et al., 2018). After the seizure: 3.1. Mesial temporal sclerosis is the loss of neurons and scarring of the deepest portion of the temporal lobe and is associated with certain brain injuries. By contrast, in most surgical patients with poor seizure control, no hippocampal pathology or only mild damage can be demonstrated (e.g., amygdalar sclerosis) (Mathern et al., 1995; Miller et al., 1994). The new neurons also form abnormal connections, with abnormal growth of basal dendrites and sprouted mossy fibers resulting in recurrent excitatory loops (for a review see Kempermann, 2006). More common are complex partial seizures (CPSs) in which the patients lose consciousness and have sensory, mental, visceral, and somatomotor symptoms. Importantly, O-LM interneurons are critically involved in the generation of ictal discharges (Ziburkus et al., 2006), and group I metabotropic glutamate receptors contribute to vulnerability of hippocampal interneurons to excitotoxicity in seizures (Sanon et al., 2010). In rat primary hippocampal neurons, estrogen affects abnormal epileptiform bursting activity in a dose-dependent manner via modulation of the potassium channel Kv4.2 (Zhang et al., 2015). Mesial temporal lobe epilepsy (MTLE) is often discussed as a separate entity because it is quite distinct from its lateral counterpart in terms of etiology, semiology, imaging, and electrophysiologic characteristics. The relationship, if any, of mesial temporal sclerosis with febrile seizures is controversial, made all the more difficult due to the relative insensitivity of imaging and the difficulty in establishing whether a particular seizure was truly febrile. Recurrent excitation and the development of seizures have been associated with aberrant mossy fiber sprouting in Defelipe J, Fernández-gil MA, Kastanauskaite A et-al. Temporal lobe epilepsy is one of 20 different kinds of epilepsy. Together, these changes then pathologically rewire the network, as is particularly evident in HS (see Temporal lobe epilepsy) (Pitkanen and Lukasiuk, 2011). When restricted to only a small portion of cerebral gray matter, this pathologic electrical activity may not lead to clinical manifestations and is considered as an interictal epileptic abnormality. 12.3C for an example of PVBC in the dentate gyrus), surviving basket cells in TLE remain hypoactive, resulting in hyperexcitability in the dentate gyrus (also known as “the dormant basket cell hypothesis”), along with interneuron loss. When there is a single identifiable electrographic focus, these patients do well with removal of that focus (i.e., temporal lobectomy), achieving up to 66% long-term seizure freedom (Tellez-Zenteno et al., 2007 ). CA, cornu ammonis; DG, dentate gyrus; G, granule cell layer; ML, molecular layer of the dentate gyrus. Learn more. Mesial temporal lobe epilepsy is the most common of the medically refractory chronic epilepsies. Surgical resection is the gold standard treatment for drug-resistant focal epilepsy, including mesial temporal lobe epilepsy (MTLE) and other focal cortical lesions with correlated electrophysiological features. Note extensive axonal branching in the stratum lacunosum moleculare and soma with dendrites projecting horizontally in the stratum oriens. Moreover, inflammation and oxidative stress are able to increase the excitability of the network (Puttachary et al., 2015). The hypothesis on TLE development covers three phases: an initial precipitating insult of the brain, such as head trauma, status epilepticus, stroke, inflammation, or febrile seizures, initiates a cascade of events; a period of epileptogenesis during which several processes (either molecular or structural) occur; and chronic epilepsy characterized by the occurrence of recurrent seizures. MTS affects the hippocampus which is the brain region that is involved in memory formation and retrieval and the amygdala which is involved in emotional processing. During an epileptic seizure the normal asynchronous activity of cerebral neurons becomes abnormally synchronized, and the firing characteristics of individual cells take on various stereotypic features, especially bursting patterns. Experimental SE leads to extensive brain damage and behavioral disturbances, including cognitive deficits that might be much more severe than observed in MTLE patients. 81.3). Left mesial temporal sclerosis (MTS) Discussion. These interneurons are also known to be vulnerable to excitotoxicity in TLE (Fig. Temporal lobectomy is a surgical procedure to remove the brain tissue in the temporal lobe that is causing the seizures. Macroanatomy and microanatomy of the temporal lobe. The degree of mossy fiber sprouting correlates with the degree of neuronal loss (Cavazos and Cross, 2006), and both pathological factors seem to contribute to the intensification of chronic seizures (Gorter et al., 2001; Zhang et al., 2002). These highly coherent, yet functionally distinct brain circuits interact dynamically with each other in order to m … Although HS and mossy fiber sprouting are very often associated with TLE, there are patient studies (Spencer and Spencer, 1994) and experimental studies (Brandt et al., 2004; Longo and Mello, 1997, 1998; Romcy-Pereira and Garcia-Cairasco, 2003) showing that temporal lobe epileptogenesis can also occur without both processes taking place. Electroencephalography (EEG) has an important role in the diagnosis and classification of epilepsy. The intrahippocampal kainic acid (KA) mouse model of, Bouilleret et al., 1999; Langlois et al., 2010; Riban et al., 2002, Bouilleret et al., 1999; Riban et al., 2002, ). However, many of these patients have bilateral seizure foci, or develop contralateral foci after resection, and thereby remain refractory. Two to three weeks after KA injection, spontaneous recurrent hippocampal paroxysmal discharges (HPD) are observed, and persist for the life of the animal (Bouilleret et al., 1999; Langlois et al., 2010; Riban et al., 2002).