Cellular and Molecular NeuroscienceResearch PaperReduction of vesicle-associated membrane protein 2 expression leads to a kindling-resistant phenotype in a murine model of epilepsy

Our previous work has correlated permanent alterations in the rat neurosecretory machinery with epileptogenesis. Such findings highlighted the need for a greater understanding of the molecular mechanisms underlying epilepsy so that novel therapeutic regimens can be designed. To this end, we examined kindling in transgenic mice with a defined reduction of a key element of the neurosecretory machinery: the v-SNARE (vesicle-bound SNAP [soluble NSF attachment protein] receptor), synaptobrevin/vesicle-associated membrane protein 2 (VAMP2). Initial analysis of biochemical markers, which previously displayed kindling-dependent alterations in rat hippocampal synaptosomes, showed similar trends in both wild-type and VAMP2+/− mice, demonstrating that kindled rat and mouse models are comparable. This report focuses on the effects that a ∼50% reduction of synaptosomal VAMP2 has on the progression of electrical kindling and on glutamate release in hippocampal subregions. Our studies show that epileptogenesis is dramatically attenuated in VAMP2+/− mice, requiring both higher current and more stimulations to reach a fully kindled state (two successive Racine stage 5 seizures). Progression through the five identifiable Racine stages was slower and more variable in the VAMP2+/− animals compared with the almost linear progression seen in wild-type littermates. Consistent with the expected effects of reducing a major neuronal v-SNARE, glutamate-selective, microelectrode array (MEA) measurements in specific hippocampal subregions of VAMP2+/− mice showed significant reductions in potassium-evoked glutamate release. Taken together these studies demonstrate that manipulating the levels of the neurosecretory machinery not only affects neurotransmitter release but also mitigates kindling-induced epileptogenesis.

▶The v-SNARE, VAMP2, was reduced by 60% in hippocampal synaptosomes of VAMP2+/− mice compared with VAMP2+/+littermates. ▶Amygdala kindling was attenuated in VAMP2+/− vs. VAMP2+/+ mice, requiring a higher AD threshold and more stimuli. ▶Progression through kindling stages oscillated in VAMP2+/− vs. an almost linear progression seen in VAMP2+/+ littermates. ▶One month post-kindling there was increased ipsilateral 7SC and bilateral SV2, greater in VAMP2+/+ than VAMP2+/− hippocampus. ▶One month post-kindling there were reductions of KCl-evoked glutamate release in VAMP2+/− compared with VAMP2+/+ DG and CA3.