Date of Award

1-1-2020

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Biological Sciences

Content Description

1 online resource (ii, 51 pages) : illustrations.

Dissertation/Thesis Chair

Gregory A Lnenicka

Committee Members

Ben Szaro, Paolo Forni

Keywords

Drosophila, Neuroplasticity, Myoneural junction

Subject Categories

Physiology

Abstract

Synaptic homeostasis is a specialized form of synaptic plasticity that maintains synaptic strength within normal parameters. The synapse must regulate its activity both during growth and in response to repeated stimulation. Much of the study of synaptic homeostasis has focused on presynaptic modifications to the quantal content. There is, however, evidence of postsynaptic regulation as an important form of synaptic homeostasis. To further investigate the ability of the synapse to make homeostatic modifications to its function we utilized the Drosophila neuromuscular junction (NMJ) as our model system. To examine the regulation of excitation at the NMJ during growth we observed the electrical properties of differently-sized muscle fibers (MFs) of 3rd instar larvae as well as their spontaneous excitatory postsynaptic potentials (minEPSPs) and currents (minEPSCs). We found that larger MFs had the lower input resistance and subsequently larger minEPSCs to produce consistent minEPSPs to MFs with higher input resistance. We also compared the same MFs during the 2nd and 3rd instar phases which also showed a compensatory increase of the minEPSC as the MF grew larger. To examine regulation of the NMJ in response to repetitive activity we stimulated the nerve repetitively and observed the spontaneous frequency thereafter. Following 60 seconds of 20Hz stimulation we observed a significant depression of the minEPSC that lasted for 90 sec post stimulation. This effect was shown to be calcium-dependent as modulating the bath saline or genetic expression of a Ca2+ buffer blocked this effect. This effect appears to be a postsynaptic silencing of the NMJ in response to prolonged stimulation that overlaps with a presynaptic enhancement of transmitter release as buffering of Ca2+ within the MF with the fast acting Ca2+ buffer BAPTA produced an increase in the minEPSC frequency. These two studies showed the ability of the NMJ to either increase or decrease synaptic strength in order during development or in response to activity in order to maintain synaptic homeostasis.

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