Expression pattern of synaptic vesicle protein 2 (SV2) isoforms in patients with temporal lobe epilepsy and hippocampal sclerosis.

AIMS: Synaptic vesicle proteins 2 (SV2) are neuronal vesicles membrane glycoproteins that appear as important targets in the treatment of partial and generalized epilepsies. Therefore, we analysed the expression of SV2 isoforms in the hippocampus of patients with temporal lobe epilepsy (TLE). METHODS: SV2A, SV2B and SV2C immunostaining and QuantiGene branched DNA assay were performed on biopsies from 31 consecutive TLE patients with mesial temporal sclerosis (MTS) and compared with 10 autopsy controls. SV2 expression was further compared with Timm's staining, and synaptophysin, Zinc transporter 3 (ZnT3), dynorphin, vesicular glutamate transporter 1 (VGLUT1) and vesicular GABA transporter (VGAT) expression. RESULTS: 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 gyrus and colocalized with dynorphin, ZnT3 and VGLUT1, suggesting selective expression in presynaptic glutamatergic Zn(2+) -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. CONCLUSION: 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.

Induction of B1 bradykinin receptors in the kindled hippocampus increases extracellular glutamate levels: a microdialysis study.

A link between temporal lobe epilepsy (the most common epileptic syndrome in adults) and neuropeptides has been established. Among neuropeptides, the possible involvement of bradykinin has recently received attention. An autoradiographic analysis has shown that B1 receptors, which are physiologically absent, are expressed at high levels in the rat brain after completion of kindling, a model of temporal lobe epilepsy. Thus, the present work aimed at investigating the functional implications of this observation, by studying the effect of B1 receptor activation on extracellular glutamate levels in the kindled hippocampus. Microdialysis experiments have been performed in two groups of rats, control and kindled. Glutamate outflow has been measured under basal conditions and after chemical stimulation with high K+ (100 mM in the dialysis solution). Basal glutamate outflow in kindled animals was significantly higher than in controls. High K+-evoked glutamate outflow was also more pronounced in kindled animals, consistent with the latent hyperexcitability of the epileptic tissue. The B1 receptor agonist Lys-des-Arg9-BK induced an increase of basal and high K+-evoked glutamate outflow in kindled but not in control rats, and the selective B1 receptor antagonist R-715 prevented both these effects. Furthermore, R-715 significantly reduced high K+-evoked glutamate outflow when applied alone. These data suggest that the bradykinin system contributes to the modulation of epileptic neuronal excitability through B1 receptors.