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Graduation Term
Spring 2026
Degree Name
Master of Science (MS)
Department
School of Biological Sciences
Committee Chair
Wolfgang Stein
Committee Co-Chair
Allison Harris
Committee Member
Ben Sadd
Abstract
Spreading Depression (SD) is a neuropathology that causes a temporary neuronal shutdown across the brain. SD is fundamental across many species including mammals, birds, and insects. However, the SD-initiation and propagation mechanisms are still unclear. Several studies suggest that neuronal hyperactivity is a major contributor to SD initiation, acting through and influencing extracellular potassium and neurotransmitter accumulation. Voltage-gated sodium and potassium channels have been suggested to play a key function in determining the neuronal state during SD.
This MS thesis explores the contribution of neuronal activity and voltage-gated potassium channels in cooling-induced SD. I use Drosophila melanogaster larvae expressing fluorescent calcium and voltage sensors pan-neuronally to observe SD and measure the larvae's susceptibility to it, using the SD initiation threshold temperature.
To reduce neuronal activity, I first bath-applied GABA (γ-Aminobutyric acid), a neurotransmitter known to increase synaptic inhibition. GABA was applied to activate GABA receptors, which increases membrane conductance to chloride ions (Cl⁻) and shifts the membrane potential towards more negative values, increasing the threshold required to trigger action potential. As a result, GABA application postponed SD initiation and thus also lowered SD threshold temperature. When action potentials were completely blocked with Tetrodotoxin, a blocker of voltage-gated sodium channels, SD was completely abolished. In contrast, blocking GABAA receptors induced SD already at room temperature and eliminated the inhibitory effect of GABA on SD threshold, suggesting that GABA's actions are mediated by GABAA receptors. Together these data indicate that action potentials are a necessary component to initiate cooling-induced SD and that high neuronal activity favors SD initiation.
To test the effect of induced-neuronal hyperactivity, I applied the voltage-gated potassium blockers 4-aminopyridine (4-AP) and Tetraethylammonium (TEA). Both blockers were selected to target transient A-type (IA) and delayed rectifier (IK) currents, respectively. Blocking the potassium outflow current aimed to prevent the membrane potential’s ability to return to its negative resting potential during repolarization. I found that blocking the IA potassium current evoked SD spontaneously, while blocking the IK current did not. Furthermore, to establish a state of maximum neuronal hyperactivity, I chemically blocked both currents IA and IK to eliminate the overall potassium outflow current. Surprisingly, this dual blockade of potassium outflow current reduced the neuronal activity and increased the threshold to elicit SD, suggesting that reducing potassium accumulation in the extracellular space impacts the neuronal activity and SD evocation. Collectively, potassium current blockers influence the neuronal activity and SD initiation threshold and pinpoint distinct roles of different voltage-gated potassium channels during SD events.
Access Type
Thesis-ISU Access Only
Recommended Citation
Al Mokbil, Mohammad, "Understanding the Initiation Mechanisms of Spreading Depression: The Roles of Neuronal Hyperactivity and Potassium Dynamics" (2026). Theses and Dissertations. 2272.
https://ir.library.illinoisstate.edu/etd/2272