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Neurosteroid‐induced enhancement of short‐term facilitation involves a component downstream from presynaptic calcium in hippocampal slices

Neurosteroid‐induced enhancement of short‐term facilitation involves a component downstream from... We used Magnesium Green AM to measure Ca2+ transients in Schaffer collateral presynaptic terminals simultaneously with postsynaptic field potentials (fEPSPs) to investigate the mechanism of neurosteroid enhancement of short‐term synaptic facilitation. Measurement of (Ca2+)i, isolated to presynaptic events, using the fluorescence ratio (ΔF/F0) demonstrated that at a constant stimulus intensity there was no change in the excitability of presynaptic fibres between paired stimuli or between ACSF and 1 μm pregnenolone sulphate (PREGS). Paired‐pulse facilitation (PPF) was correlated with residual Ca2+ ((Ca2+)res), and there was an additional increase in the ∫ΔF/F0 for the (Ca2+)res‐subtracted response to the second of paired stimuli, resulting primarily from a slowing of the decay time constant. In addition to the role of presynaptic (Ca2+)res in PPF, we observed a decrease in EC50 and a greater maximum for Hill function fits to fEPSP versusΔF/F0 during the second of paired responses. The enhancement of fEPSP PPF by PREGS did not result from an increase of ΔF/F0. The data presented here support a PREGS‐induced increase in presynaptic glutamate release from the second, but not the first, of a pair of stimuli for a given presynaptic (Ca2+) because: (a) there is actually a decrease in the ∫ΔF/F0 of the (Ca2+)res‐subtracted second response over that seen in ACSF; (b) PREGS causes no change in presynaptic Ca2+ buffering; and (c) there is a decrease in EC50 and an increase of ymax in the Hill function fits to ΔF/F0versus fEPSP data. We hypothesize that PREGS enhances short‐term facilitation by acting on the Ca2+‐dependent vesicle release machinery and that this mechanism plays a role in the cognitive effects of this sulphated neurosteroid. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

Neurosteroid‐induced enhancement of short‐term facilitation involves a component downstream from presynaptic calcium in hippocampal slices

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References (55)

Publisher
Wiley
Copyright
© 2006 The Journal of Physiology © 2006 The Physiological Society
ISSN
0022-3751
eISSN
1469-7793
DOI
10.1113/jphysiol.2006.118505
pmid
16931546
Publisher site
See Article on Publisher Site

Abstract

We used Magnesium Green AM to measure Ca2+ transients in Schaffer collateral presynaptic terminals simultaneously with postsynaptic field potentials (fEPSPs) to investigate the mechanism of neurosteroid enhancement of short‐term synaptic facilitation. Measurement of (Ca2+)i, isolated to presynaptic events, using the fluorescence ratio (ΔF/F0) demonstrated that at a constant stimulus intensity there was no change in the excitability of presynaptic fibres between paired stimuli or between ACSF and 1 μm pregnenolone sulphate (PREGS). Paired‐pulse facilitation (PPF) was correlated with residual Ca2+ ((Ca2+)res), and there was an additional increase in the ∫ΔF/F0 for the (Ca2+)res‐subtracted response to the second of paired stimuli, resulting primarily from a slowing of the decay time constant. In addition to the role of presynaptic (Ca2+)res in PPF, we observed a decrease in EC50 and a greater maximum for Hill function fits to fEPSP versusΔF/F0 during the second of paired responses. The enhancement of fEPSP PPF by PREGS did not result from an increase of ΔF/F0. The data presented here support a PREGS‐induced increase in presynaptic glutamate release from the second, but not the first, of a pair of stimuli for a given presynaptic (Ca2+) because: (a) there is actually a decrease in the ∫ΔF/F0 of the (Ca2+)res‐subtracted second response over that seen in ACSF; (b) PREGS causes no change in presynaptic Ca2+ buffering; and (c) there is a decrease in EC50 and an increase of ymax in the Hill function fits to ΔF/F0versus fEPSP data. We hypothesize that PREGS enhances short‐term facilitation by acting on the Ca2+‐dependent vesicle release machinery and that this mechanism plays a role in the cognitive effects of this sulphated neurosteroid.

Journal

The Journal of PhysiologyWiley

Published: Nov 1, 2006

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