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Mild metabolic stress is sufficient to disturb the formation of pyramidal cell ensembles during gamma oscillations

Elzoheiry, Shehabeldin

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Abstract

Gamma oscillations are associated with several higher cognitive functions; selective attention, memory formation, and sensory perception. Gamma oscillations represent a balanced fast interplay between excitation and inhibition. Inhibition provides temporal windows for excitatory cells to fire in synchrony. Whether excitation or inhibition requires more energy is still unknown. Disturbances of gamma oscillations occur rapidly during metabolic stress. However, the underlying mechanisms are not fully understood. In this study, we performed calcium imaging (CamKII.GCaMP6f) to explore the presence of pyramidal cell ensembles in rat hippocampus and challenge them metabolically. Using a low concentration of rotenone we achieved a mild metabolic stress condition. The stress level results in suppressing gamma oscillations without being terminated. We found that (1) synchronized activity is significantly reduced before observing a reduction in the overall activity of pyramidal cells. (2) Pyramidal cells recruited in ensembles formation tend to be more active upon mild stress. We performed spike sorting and found that (3) slowspiking units are more active upon mild metabolic stress. Furthermore, (4) power of gamma oscillations was reduced without changes in the firing of fast-spiking units. These findings suggest that ensemble formation is highly vulnerable to metabolic stress, and disturbances occur likely because of functional alterations in the presynaptic compartment of fast-spiking units. This reveals a plausible mechanism for altered cognitive functions during mild metabolic stress conditions.

Document type: Dissertation
Supervisor: Bading, Prof. Dr. Hilmar
Place of Publication: Heidelberg
Date of thesis defense: 28 October 2019
Date Deposited: 11 Nov 2019 13:27
Date: 2019
Faculties / Institutes: The Faculty of Bio Sciences > Dean's Office of the Faculty of Bio Sciences
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