Date of Degree

2-2022

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Itzhak Mano

Committee Members

Jonathan Levitt

Chris Li

Jeremy Dittman

Alexander Sobolevsky

Subject Categories

Biology | Genetics | Molecular and Cellular Neuroscience

Keywords

C. elegans, glutamate, glutamate transporter, glutamate signaling, neuroscience, perfusion, GCaMP, iGluSnFR

Abstract

As the major excitatory neurotransmitter in the mammalian brain, Glutamate (Glu) is critical for normal neuronal physiology. Disruption in Glu clearance results in hyper-stimulation of glutamatergic circuits, potentially leading to excitotoxic neurodegeneration. The canonical model of brain connectivity describes glutamatergic synapses as well insulated and enveloped by glia. These glia express Glu Transporters (GluTs) which work to clear Glu following synaptic activity. However, critical areas of the brain such as the mammalian hippocampus display poor synaptic isolation, which may result in Glu spillover between adjacent synapses and subsequent loss of circuit specificity. How accurate signal transmission is achieved in these glia-deprived areas remains unclear. We approach this question using the C. elegans system, which faces the same dilemma as the mammalian hippocampus. Using a combination of behavioral assays and imaging of transgenic animals expressing Ca2+-sensitive reporter GCaMP or Glu-sensitive reporter iGluSnFR, we demonstrate a combined role of synaptic location and pharyngeal pulsatility in efficient Glu clearance of the nerve ring. We find that perfusion of Glu-rich interstitial fluid plays a vital role in GluT-mediated synaptic clearance, shown in our experiments where we induce paralysis of pharyngeal and head muscles to inhibit local movement. This study provides novel insights to mechanisms of effective Glu clearance in the absence of glia, a feature shared between nematodes and vital areas of the mammalian brain. Investigating novel mechanisms of Glu clearance can inform us in seeking candidate targets for therapeutic interventions in brain ischemia, and potential ways of manipulating brain pulsations and heart rate to promote clearance of solutes and aggregates (such as amyloid β) in patients to slow the onset of Alzheimer’s disease and other neuropathies.

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