Shedding light on the role for astrocytic D-serine on NMDAR activation
Dunphy, Jaclyn.
2019
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Astrocytes release
signaling molecules at synapses in a process known as gliotransmission, but how this
impacts synaptic physiology over time is unclear. In this report we explore the impact
of gliotransmission on synaptic activity by attenuating vesicular release with both
molecular genetic and optogenetic approaches. First we show that astrocytes release
D-serine in a wakefulness-dependent ... read moremanner. Transgenic mice with attenuated
gliotransmission do not exhibit wakefulness-dependent changes in D-serine throughout the
day. D-serine is an obligate co-agonist of the N-methyl D-aspartate receptor (NMDAR) and
saturation of the co-agonist site influences learning performance throughout the day.
Second, we discovered that hippocampal astrocytes sense wakefulness-dependent activity
of septal cholinergic fibers through alpha 7 nicotinic acetylcholine receptors
(α7nAChRs), which drives D-serine release. Third, we revealed that encenicline, an
α7nAChR agonist that was in Phase III clinical trials for schizophrenia and
Alzheimer's disease enhances NMDAR activation. Fourth, we used a light-activated
"singlet oxygen generator" (miniSOG) fused to vesicle-associated membrane proteins
(VAMPs) to acutely impair vesicular release from astrocytes on demand. Upon illumination
with blue light, miniSOG produces radical oxygen species, which inactivates the fused
protein. VAMP2 and VAMP3 were inactivated with light, and we found that we could impair
D-serine release from astrocytes on demand. We demonstrate that acute inactivation of
either VAMP2 or VAMP3 in astrocytes decreased NMDA receptor saturation. This is the
first time such precise spatial and temporal control over vesicular release from
astrocytes in situ has been reported. This method of acute inactivation of
gliotransmission selectively impairs the release of some signaling molecules (D-serine)
but not others (ATP/adenosine). And fifth, we developed a modified contextual fear
conditioning paradigm to test fear learning both before and after an experimental
manipulation in the same mice. Although in vivo illumination of the hippocampus for the
purposes of inactivating gliotransmission prior to fear training did not significantly
decrease the amount of time spent freezing, our modified two-context fear conditioning
paradigm could be used to test the effects of acute manipulations on fear learning in
the same animals. We conclude that astrocytes tune the gating of NMDARs to vigilance
state, and we demonstrate that this process can be manipulated in transgenic mice with
attenuated gliotransmission, or on demand with miniSOG-fusion proteins. Future work
could use these tools to investigate the role for gliotransmission in vivo and
investigate the role of astrocyte signaling in
real-time.
Thesis (Ph.D.)--Tufts University, 2019.
Submitted to the Dept. of Neuroscience.
Advisor: Philip Haydon.
Committee: Chris Dulla, Jamie Maguire, Thomas Biederer, Daniel Jay, and Daniel Mulkey.
Keyword: Neurosciences.read less - ID:
- 6m312252d
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