PROJECT SUMMARY/ABSTRACT
Inhibitory synapses are crucial for maintaining correct neuronal excitability, which is important for efficient
circuitry and proper brain function. Shifts in neuronal excitability have been implicated in a variety of neurological
disorders, including ischemia. Based on cell-type specific vulnerabilities, the oxygen and glucose deprivation
(OGD) observed in various brain regions including the hippocampus leads to differential effects that may alter
neuronal long-term function. The hippocampus is particularly a vulnerable brain region that experiences
either delayed cell-death in the CA1 region or resistance to delayed-cell death and shifts in long-term excitability
in the CA3 region. Cell-type specific synaptic alterations to neuronal populations may contribute to these
ischemic-induced changes. Even though alterations at excitatory synapses are well defined, our knowledge of
alterations at the inhibitory synapse remain elusive.
Inhibitory GABAA receptors (GABAARs) mediate the majority of fast synaptic inhibition in the brain. The
number of postsynaptic GABAARs influences inhibitory strength; therefore, GABAAR trafficking to and from
synaptic sites or the neuronal surface is an important regulator of overall inhibitory synaptic strength. During
OGD, GABAARs are downregulated from the neuronal surface in hippocampal neurons. Moreover, GABAAR
phosphorylation status influences the synaptic declustering or removal of receptors from the neuronal surface
during OGD in hippocampal neurons. However, mechanisms that regulate these differences in either synaptic
clustering or surface GABAAR expression following an ischemic insult in brain regions with varying susceptibilities
remain undefined.
In this project, I propose that GABAAR declustering and endocytosis mechanisms are differentially regulated
in distinct neuronal populations during OGD to influence GABAAR downregulation based on region-specific
vulnerability. Moreover, I hypothesize that these cell-type specific mechanisms drive increased neuronal
excitability during OGD due to increase synaptic declustering and decreased surface expression of
GABAARs in vulnerable neuronal populations. Based on this, I plan to investigate (i) mechanisms of synaptic
GABAAR declustering and surface downregulation in hippocampal pyramidal neurons following OGD (ii) probe
the temporal regulation to determine the sequential flow of events promoting GABAAR loss and (iii) use an in
vivo model of cerebral ischemia to compare cell-type specific mechanisms in CA1 and CA3 hippocampus that
may be differentially regulated based on neuronal susceptibility to OGD. Specifically, I plan to investigate the
role of phosphatases in regulating GABAAR phosphorylation state to promote GABAAR declustering and
endocytosis during OGD in both vulnerable neuronal populations. The results of this project will establish
mechanisms that are specific to GABAAR downregulation in vulnerable populations during OGD, providing novel
targets for future therapeutic intervention.
