Kindling‐induced asymmetric accumulation of hippocampal 7S SNARE complexes correlates with enhanced glutamate release

Abstract

SUMMARY Purpose To correlate kindling-associated alterations of the neurotransmitter secretory machinery, glutamate release in the trisynaptic hippocampal excitatory pathway, and the behavioral evolution of kindling-induced epileptogenesis. Method Neurotransmitter release requires the fusion of vesicle and plasma membranes; it is initiated by formation of a stable, ternary complex (7SC) of SNARE [soluble N-ethylmaleimide sensitive factor (NSF) attachment protein receptor] proteins. Quantitative Western blotting was used to monitor levels of 7SC and SNARE regulators [NSF, SV2 (synaptic vesicle protein 2)] in hippocampal synaptosomes from amygdala-kindled animals. Hippocampal synaptic glutamate release was measured in vivo with a unique microelectrode array (MEA) that uses glutamate oxidase to catalyze the breakdown of glutamate into a reporter molecule. Key Findings Ipsilateral hippocampal accumulation of 7SC developed with onset of amygdalar kindling, but became permanent only in animals stimulated to at least Racine stage 3; the ratio peaked and did not increase with more than two consecutive stage 5 seizures. Chronic 7SC asymmetry was seen in entorhinal cortex and the hippocampal formation, particularly in dentate gyrus (DG) and CA1, but not in the other brain areas examined. There was a strong correlation between asymmetric 7SC accumulation and increased total hippocampal SV2. Following a 30-day latent period, amplitudes of spontaneous synaptic glutamate release were enhanced in ipsilateral DG and reduced in ipsilateral CA3 of kindled animals; increased volleys of synaptic glutamate activity were seen in ipsilateral CA1. Significance Amygdalar kindling is associated with chronic changes in the flow of glutamate signaling in the excitatory trisynaptic pathway and with early but permanent changes in the mechanics of vesicular release in ipsilateral hippocampal formation.

Linking kindling to increased glutamate release in the dentate gyrus of the hippocampus through the STXBP5/tomosyn‐1 gene

“…There were significantly larger spontaneous peaks in the DG ipsilateral to the kindling electrode compared to all other brain regions except for the kindled, contralateral CA1. We previously observed similar spontaneous changes in kindled rats (Matveeva et al., 2011), indicating that heightened spontaneous synaptic glutamatergic activity in DG correlates with kindling in rodents and suggests it may be universal across species.…”

“…Here we show an increase in evoked and spontaneous glutamate release in the DG of the hippocampus in kindled mice. We have previously reported changes in DG glutamate dynamics in kindled animals (Matveeva et al., 2011, 2012). In fact, others have also found changes in the DG of the hippocampus using chemical and electrical kindling models (Popova, Aniol, Lazareva, Yu, & Gulyaeva, 2013; Sun et al., 2013).…”

“…This result was not as robust as our previous findings in several kindling models where we saw changes in these protein complexes in the hippocampi of both kindled rats and mice (Matveeva et al., 2007, 2011, 2012). In mice we observed minor, yet significant, increases in SV2 with minimal changes in NSF while observing more robust alterations in the 7SC (Matveeva et al., 2011). Ohno et al.…”

“…To normalize for protein loading the fluorescence intensity of all 7SC bands was standardized to the intensity of the syntaxin‐1 monomer as in Matveeva et al. (2011). The 7SC complex was then analyzed by comparing the relative ratio of protein from the ipsilateral hippocampus compared to the contralateral hippocampus (ipsilateral/contralateral) for both kindled genotypes using the following equation: [7SC ipsilateral/syntaxin‐1]/[7SC contralateral/syntaxin‐1].…”

Calcineurin/NFAT Signaling in Activated Astrocytes Drives Network Hyperexcitability in Aβ-Bearing Mice

“…Though most conspicuous around amyloid-␤ (A␤) deposits at late disease stages, activated glial cells (i.e., microglia and astrocytes) also appear at the outset of clinical symptoms (Carter et al, 2012;Schöll et al, 2015;Yokokura et al, 2016), suggesting that glial modulation strategies could slow the progression of AD. However, the phenotype of activated glial cells is very complex (Oberheim et al, 2012;Prokop et al, 2013;Pekny et al, 2014;Malm et al, 2015;Andreasson et al, 2016;Liddelow et al, 2017), and more work is required to elucidate their functional impact in neurodegeneration.…”