Poster abstracts

Poster number 82 submitted by Nidhi Devasthali

Neural stem cell-expressed excitatory amino acid transporter 1 supports normal hippocampal functioning

Nidhi Devasthali (Neuroscience Graduate Program), Bedri Parlar (College of Arts and Sciences), Elizabeth D. Kirby (Department of Psychology)

Abstract:
Glutamate is the primary excitatory neurotransmitter of the brain, and its presence in synapses is regulated to prevent excitotoxity. Most previous work on synaptic glutamate clearing has focused on astrocytic excitatory amino acid 2 (EAAT2), which transports glutamate from the extracellular space to inside the cell. In the dentate gyrus (DG) of the adult mouse hippocampus, neural stem cells (NSCs) abundantly express EAAT1 throughout their cell bodies, and likely in the terminals of their processes that wrap around and ensheathe glutamatergic synapses on dentate granule neurons. NSCs are primarily known to contribute to DG functioning by proliferating to give rise to functional neurons that integrate into existing hippocampal circuitry to support learning, memory, and affect regulation. Since NSC-EAAT1 likely has contact with synaptic glutamate, NSCs may clear synaptic glutamate and additionally contribute to DG functioning by maintaining low levels of activity hypothesized to underpin effective pattern separation. We therefore hypothesized that NSC-EAAT1 modulates DG functioning. To investigate this, we used CRISPR technology to generate a new EAAT1fl/fl mouse, in which a critical exon of EAAT1 was flanked by LoxP sites. Crossing EAAT1fl/fl mice with NestinCreERT2+/- mice yielded a tamoxifen sensitive NSC-specific knockout of the EAAT1 gene. Tamoxifen treated EAAT1fl/fl;NestinCreERT2+/- mice (cKO) showed significant loss of EAAT1 protein in NSCs compared to Cre-negative littermates (WT). cKO resulted in greater density of immunolabelling for cFos (detectable approx. 2 hrs after a neuron fires) in the granule cell layer at baseline and after a cognitive task compared to similarly treated WT mice. Additionally, cKO mice showed a trend for impaired hippocampus-dependent memory in a novel object location task compared to WT mice. Together, these findings suggest that NSC-EAAT1 is required to maintain sparse firing of granule neurons and may support hippocampal memory.

Keywords: neural stem cells, hippocampus, EAAT1