Use Dependence of Presynaptic Tenacity

Abstract

Recent studies indicate that synaptic vesicles (SVs) are continuously interchanged among nearby synapses at very significant rates. These dynamics and the lack of obvious barriers confining synaptic vesicles to specific synapses would seem to challenge the ability of synapses to maintain a constant amount of synaptic vesicles over prolonged time scales. Moreover, the extensive mobilization of synaptic vesicles associated with presynaptic activity might be expected to intensify this challenge. Here we examined the ability of individual presynaptic boutons of rat hippocampal neurons to maintain their synaptic vesicle content, and the degree to which this ability is affected by continuous activity. We found that the synaptic vesicle content of individual boutons belonging to the same axons gradually changed over several hours, and that these changes occurred independently of activity. Intermittent stimulation for 1 h accelerated rates of vesicle pool size change. Interestingly, however, following stimulation cessation, vesicle pool size change rates gradually converged with basal change rates. Over similar time scales, active zones (AZs) exhibited substantial remodeling; yet, unlike synaptic vesicles, AZ remodeling was not affected by the stimulation paradigms used here. These findings indicate that enhanced activity levels can increase synaptic vesicle redistribution among nearby synapses, but also highlight the presence of forces that act to restore particular set points in terms of SV contents, and support a role for active zones in preserving such set points. These findings also indicate, however, that neither AZ size nor SV content set points are particularly stable, questioning the long-term tenacity of presynaptic specializations.

Synapsins Contribute to the Dynamic Spatial Organization of Synaptic Vesicles in an Activity-Dependent Manner

“…These data are in accordance with the finding that electrical stimulation has no influence on the mobility of single SVs in short timeframes (Kamin et al, 2010), although a more careful evaluation with longer timeframes and/or stimulation protocols might be required, because this issue is still debated (Fisher-Lavie et al, 2011). Nevertheless, our results indicate that the population of delocalized SVs observed in TKO synapses includes exocytosis-competent SVs.…”

“…Very recent findings render this result particularly relevant because SV redistribution within the same axon might be essential for the competitive strengthening/weakening of presynaptic efficacy and might improve pattern discrimination in dendritic networks (Herzog et al, 2011;Padamsey and Jeans, 2012). Through the mobilization/immobilization of SVs, Syns might locally regulate the plastic properties at single presynapses both acting as restrictors, by contributing with a resilient force to the tenacity of the terminal (Fisher-Lavie et al, 2011) and serving as integrators of presynaptic signaling in a phosphorylation-dependent manner .…”

Release properties of individual presynaptic boutons expressed during homosynaptic depression and heterosynaptic facilitation of the Aplysia sensorimotor synapse

“…It is therefore conceivable that because of internal gradients, the properties of presynaptic boutons may differ. Thus, the unequal distribution of organelles and molecules along a single neurite could account for the findings presented here (Fisher-Lavie et al, 2011). …”

Formation of Golgi-Derived Active Zone Precursor Vesicles

“…Initially, we verified that EGFP-fusion proteins of Bassoon, ELKS2, Munc13-1, and SV2 were appropriately localized within presynaptic boutons of synapses formed between neurons after 14 DIV (Bresler et al, 2004;Fisher-Lavie et al 2011; data not shown). These data indicate that the EGFP tags do not interfere with synaptic delivery.…”