Synaptosomal-associated protein of 25 kDa (SNAP-25) is a SNARE protein that regulates neurotransmission by the formation of a complex with syntaxin 1 and synaptobrevin/VAMP2. SNAP-25 also reduces neuronal calcium responses to stimuli, but neither the functional relevance nor the molecular mechanisms of this modulation have been clarified. In this study, we demonstrate that hippocampal slices from Snap25 ؉/؊ mice display a significantly larger facilitation and that higher calcium peaks are reached after depolarization by Snap25 ؊/؊ and Snap25 ؉/؊ cultured neurons compared with wild type. We also show that SNAP-25b modulates calcium dynamics by inhibiting voltage-gated calcium channels (VGCCs) and that PKC phosphorylation of SNAP-25 at ser187 is essential for this process, as indicated by the use of phosphomimetic (S187E) or nonphosphorylated (S187A) mutants. Neuronal activity is the trigger that induces the transient phosphorylation of SNAP-25 at ser187. Indeed, enhancement of network activity increases the levels of phosphorylated SNAP-25, whereas network inhibition reduces the extent of protein phosphorylation. A transient peak of SNAP-25 phosphorylation also is detectable in rat hippocampus in vivo after i.p. injection with kainate to induce seizures. These findings demonstrate that differences in the expression levels of SNAP-25 impact on calcium dynamics and neuronal plasticity, and that SNAP-25 phosphorylation, by promoting inhibition of VGCCs, may mediate a negative feedback modulation of neuronal activity during intense activation. S ynaptosomal-associated protein of 25 KDa (SNAP-25) belongs to the SNARE superfamily of membrane proteins that participate in the regulation of neuronal exocytosis. SNAP-25 is present in two isoforms, a and b, resulting from alternative splicing of the exon 5 of the gene, which is differentially expressed during development. SNAP-25a is expressed at the embryonic stage, and SNAP-25b becomes the major isoform postnatally (1-3). SNAP-25 is anchored to the cytosolic face of membranes by palmitoyl side chains located in the central region of the molecule and contributes two ␣-helices to the exocytotic fusion complex, together with syntaxin-1 and synaptobrevin/ VAMP2 (4-5). SNAP-25 also interacts with the synaptic vesicle protein, synaptotagmin I (6), a major calcium sensor that regulates neurotransmitter release (7,8). Interaction of synaptotagmin with SNAP-25 is essential for the calcium-dependent triggering of membrane fusion (9) and for the control of fusion pore during the final steps of exocytosis (10). Furthermore, the C terminus of SNAP-25 is a target of G protein ␤-and ␥-subunits that mediate presynaptic inhibition (11). Therefore, SNAP-25 represents a multifunctional protein involved in the control of secretion by multiple interactions. Besides its well characterized role in regulating exocytosis, there is increasing evidence that SNAP-25 modulates various ion channels (12, 13). In particular, SNAP-25 physically interacts with different types of voltagegated calcium chann...

No abstract

No abstract

Our current knowledge of the structure, function, and diseases of the brain comes from direct examination of its substance. In the last centuries, only a few elite had managed to retrieve, gather, and preserve the elusive brain for their own research. The resulting brain collections, stored in formalin-filled jars or dried up in cabinets, served anatomical, neuropathological, anthropometric, ideological, and diagnostic purposes. In the 1960s, the first modern brain banks actively collecting and strategically preserving both diseased and healthy brains to be consequently distributed to the scientific community were instituted. In an era where state-of-the-art biochemical “Omic” studies and advanced metabolic and molecular neuroimaging exist, it is now, more than ever, that postmortem brain investigations must be performed. Only through the comparison and integration of postmortem neuropathological and biochemical findings and antemortem data from clinical, neuropsychological neuroimaging, and other biomarker examinations can we truly understand neurological disease mechanisms. Brain banks supplying brain specimens, antemortem information, and postmortem diagnosis are a major benefactor of brain research.

Seizure patterns identified in focal epilepsies caused by diverse etiologies are likely due to different pathogenic mechanisms. We describe here a novel, region-specific focal seizure pattern that mimics seizure activity observed in a subpopulation of patients submitted to presurgical monitoring with intracerebral electrodes. Distinctive seizure-like events (SLEs) are induced in the olfactory regions by acute treatment of both tangential brain slices and the isolated guinea pig brain with the potassium channel blocker 4-aminopyridine. Analysis of field potentials, intracellular activities, and extracellular potassium changes demonstrates that SLEs in the piriform cortex initiate in the superficial layer 1 lacking principal neurons with an activity-dependent increase of extracellular potassium. SLE progression (but not onset) does not require the participation of synaptic transmission and is mediated by diffusion of potassium to deep cortical layers. The novel seizure pattern here described is not observed in other cortical regions; it is proposed to rely on the peculiar organization of the superficial piriform cortex layers, which are characterized by unmyelinated axons and perisynaptic astroglial envelopes. This study reveals a sequence of ictogenic events in the olfactory cortex that were never described before in other cortical structures and supports the notion that altered potassium homeostasis and unmyelinated fibers may represent a potential vehicle for focal ictogenesis. We describe a novel seizure pattern peculiar of the olfactory cortex that resembles focal seizures with low-voltage fast activity at onset observed in humans. The findings suggest that network mechanisms responsible for seizure onset can be region specific.