The effects of temperature on vesicular supply and release in autaptic cultures of rat and mouse hippocampal neurons

Abstract

Membrane fusion plays a central role in the synaptic vesicle cycle. While many of the pre- and postfusion events have been investigated at room temperature, few researchers have investigated these processes at more physiologically relevant temperatures. We have used autaptic cultures of hippocampal neurons to investigate changes in the size and refilling rate of the readily releasable pool (RRP) of synaptic vesicles brought about by an increase in temperature from 25 to 35 degrees C. We have also examined temperature-dependent changes in spontaneous and action potential (AP)-evoked release as well as the fraction of the RRP that is released during an AP. Although we found a threefold increase in the refilling rate of the RRP at the higher temperature, there was no apparent change in the size of the RRP with increased temperature. Moreover, we observed a slight but significant decrease in the quanta released during an AP. This increased refilling rate and decreased release probability resulted in a reduction of both the degree and time course of synaptic depression during high frequency stimulation at the higher temperature. This reduction in synaptic depression was accompanied by an increased maintenance of the synchronous component of release during high frequency stimulation. These findings indicate that the dynamics of vesicular supply and release in hippocampal neurons at room temperature are significantly different at near physiological temperatures and could affect our present understanding of the way in which individual neurons and networks of neurons process information.

Limit on the Role of Activity in Controlling the Release-Ready Supply of Synaptic Vesicles

“…For example, the rate at which vesicles leave the RRP without undergoing exocytosis has been shown to be slow compared with the rate of pool filling (Murthy and Stevens, 1999). This, along with other observations Wesseling, 1998, 1999b;Pyott and Rosenmund, 2002), implies that the pool has a fixed size and is not instead in some steady-state equilibrium with a larger reserve pool (the reverse reaction would formally be a negligible component of ␤). An additional rate-limiting element in the synaptic vesicle exocytic/endocytic cycle plays a role during more extensive use (Stevens and Wesseling, 1999b).…”

“…The identity of the molecular machinery that limits how quickly vesicles are prepared for exocytosis remains obscure, although it seems to be enzymatic in nature Wesseling, 1998, 1999b;Pyott and Rosenmund, 2002) and may be related to biochemical priming that takes place during or after physical docking to the active zone (Kawasaki et al, 1998). During extended periods of synaptic activity, a second rate-limiting process also plays a role in a longer-lasting form of synaptic depression that may be related to depletion of the reserve pool of vesicles or to some other rate-limiting element in the exocytic/endocytic cycle (Stevens and Wesseling, 1999b).…”

Synaptic vesicle dynamics in mouse rod bipolar cells

“…However, both membrane retrieval and pool refilling rates have been reported to be temperature-sensitive (Pyott & Rosenmund 2002;Kushmerick et al, 2006;Rendon & von Gersdorff 2007). Thus, it is conceivable that at physiological temperature, both membrane recovery and pool refilling in the mouse rod bipolar cell may be even faster than reported here.…”

An essential role for vesicular glutamate transporter 1 (VGLUT1) in postnatal development and control of quantal size

“…Microisland cultures of mouse postnatal-day-0 hippocampal neurons were prepared according to published procedures (22). Experiments were performed with hippocampal neurons between day in vitro 10 and 20, except for FM1-43 imaging experiments, for which neurons were assayed on day in vitro 15-24 according to published protocols (23).…”

“…Recordings of miniature EPSCs (mEPSCs) were done in the presence of 300 nM tetrodotoxin, and for subtraction of noise, 3 mM kynurenic acid was applied. Exogenous GABA and kainate were applied at concentrations of 30 M. Data acquisition and analyses were done as described (22), with values expressed as mean Ϯ SE. Statistical significance of the release probability was assessed by an unpaired Kolmogorov-Smirnov test.…”