1/13). There was no specific difference in terms of frequency and type of seizures, AED regimen and clinical performance. Membrane traffic of SVs within nerve terminals involves major Hydroxychloroquine clinical trial trafficking proteins that are common constituents of all SVs and small protein families containing several isoforms that are differentially expressed in different parts of the nervous

system, such as SV2 proteins. In this study, we report for the first time the distribution of the three SV2 isoforms, SV2A, SV2B and SV2C, in the hippocampus of controls and TLE patients. Only a few studies have analysed SV2A expression in the human hippocampus [9, 19], cerebral cortex [9, 39] and cerebellum [9]. In this study, TLE patients with HS showed reduced SV2A expression in hippocampal areas of neuronal/synaptic loss but increased expression in the IML when mossy fibre sprouting occurs. This compares well with previous observations by van Vliet et al. [19]. Similar observations have been

made in rat models of temporal epilepsy and it has been suggested that SV2A loss could contribute to epileptogenesis and pharmacoresistance [10, 15-18]. In contrast, no significant SV2A expression change Copanlisib in vivo was found within or around epileptogenic brain tumours [35], foci of cortical dysplasia and cortical tubers [39]. A recent prospective study indicates, however, that SV2A expression in tumour and peritumoural tissue correlates with clinical response to LEV and predicts LEV efficacy in these patients [40]. In the adult rodent brain, SV2B has a wide distribution, but with only some areas of restriction/exclusion, being barely detectable in the striatum and undetectable in the globus pallidus, cerebellar Purkinje cells, reticular nucleus of the thalamus, pars reticularis of the substantia nigra, and GCL in the hippocampus [3, 7]. This study shows that in human controls and TLE patients, SV2B distribution parallels synaptophysin and SV2A in the hippocampus, suggesting that most synapses contain both isoforms. The role of SV2B in epilepsy is unclear, as knockout SV2B−/− mice do not show an epileptic phenotype

and SV2B absence does not aggravate the phenotype of the SV2A deletion [2]. Like other SV2s, SV2B is not neurotransmitter specific but in one recent study, it was found to be associated preferentially with VGLUT-1 synaptic vesicles in the rat [7], a finding that contrasts with SV2B detection by in situ hybridization in both glutamatergic and GABAergic neurones [3] and also with our own findings. The preferential involvement of SV2A or SV2B in Ca2+-dependent vesicle exocytosis may be cell population specific as previous work has shown their differential distribution in neuronal and endocrine cells [3, 4, 21, 22, 41]. It may also reflect neurone maturation, as SV2B is not detected in the GCL in adult rats and mice although it is transiently expressed during development [3].