In TLE patients, SV2A and SV2B expression was decreased in areas of synaptic loss. SV2C, which is weakly expressed or absent in the hippocampus of controls, was overexpressed in 10/11 cases with classical MTS1A and mossy fibre sprouting but not in cases with other types of MTS. SV2C staining was located in the inner molecular

layer of the dentate see more gyrus and colocalized with dynorphin, ZnT3 and VGLUT1, suggesting selective expression in presynaptic glutamatergic Zn2+-rich terminals of abnormal sprouting fibres. SV2 expression patterns correlated with histological subtypes of MTS, but not with clinical features or therapeutic regimens in this patient cohort. In classical MTS1A, the expression of SV2 isoforms is altered with a marked decrease of SV2A and SV2B paralleling

synaptic loss and a selective increase of SV2C in sprouting mossy fibres. These findings suggest a different physiology of sprouting synapses and the possibility to target them with SV2C-specific strategies. Synaptic vesicle proteins 2 (SV2) are a small family of integral transmembrane glycoproteins that are localized to synaptic vesicles and appear to function as modulators of Ca2+-dependent exocytosis [1]. NVP-LDE225 Of the three known isoforms, SV2A is ubiquitously expressed in the rat brain [2, 3] while SV2B, although widely expressed, is undetectable in several groups of neurones in the hippocampus, central grey nuclei and cerebellum [3, 4]. SV2C has a much more restricted distribution being found mostly in the basal ganglia, midbrain and brainstem [5, 6]. Although SV2 isoforms are not neurotransmitter specific, their distribution has been reported to differ between glutamatergic and GABAergic synaptic vesicles [7]. SV2s also act as receptors for botulinum neurotoxins [8]. Both clinical and experimental data suggest that SV2 isometheptene proteins, and particularly SV2A, are involved in epilepsy [9, 10]. The anticonvulsant

activity of levetiracetam (LEV), a powerful antiepileptic drug (AED), has been linked to its ability to bind SV2A [9, 11]. More recently developed LEV analogues, such as brivaracetam and seletracetam, also bind to SV2A [12]. Moreover, SV2A−/− knockout mice have been shown to die early after birth due to severe spontaneous seizures [2, 13]. SV2A+/− animals display lower seizure thresholds in a number of models, reduced anticonvulsant efficacy of LEV as well as accelerated epileptogenesis [13, 14]. Furthermore, reduced SV2A expression has been reported in rodent models of temporal lobe epilepsy (TLE) [10, 15-18]. In the human, SV2A expression is reduced in the hippocampus of patients with TLE and hippocampal sclerosis (HS) [19].