Date Available

7-10-2013

Year of Publication

2013

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Biology

First Advisor

Dr. Robin L. Cooper

Abstract

Glutamate is the main excitatory neurotransmitter in the CNS and at the neuromuscular junctions (NMJs) of invertebrate. The characteristic similarities to CNS glutamatergic synapses in vertebrate and the anatomical simplicity of invertebrate NMJs favor the investigation of glutamatergic synaptic functions in this system. This dissertation mainly aimed to physiologically separate two functional vesicle groups, the reserve pool (RP) and readily releasable pool (RRP) within presynaptic nerve terminals of Procambarus Clarkii and Drosophila melanogaster. This was addressed in part by blocking the vesicular glutamate transporter (VGlut) with bafilomycin A1. Various frequencies of motor nerve stimulation, exposure time, and concentration of bafilomycin A1 were examined. The low-output tonic opener NMJs in crayfish exposed to 4μM bafilomycin A1 and 20Hz continuous stimulation decreased the EPSP amplitude to 50% in ∼30min with controls lasting 3h. After activity and bafilomycin A1-induced synaptic depression, the EPSPs were rapidly revitalized by serotonin (5-HT, 1μM) in the crayfish preparations. The 5-HT action can be blocked almost completely with a PLC inhibitor, but partially with a cAMP activator. The higher output synapses of the larval Drosophila NMJ when stimulated at 1Hz or 5Hz and exposed to 4μM of bafilomycin A1 showed a depression rate of 50% within ∼10min with controls lasting ∼40min. After low frequency depression and/or exposure to bafilomycin A1 a burst of higher frequency (10Hz) can recruit vesicles from the RP to the RRP. Physiological differences in low- (tonic like) and high-output (phasic like) synapses match many of the expected anatomical features of these terminals, part of this dissertation highlights physiological differences and differential modulation and/or extent of the vesicles in a RP for maintaining synaptic output during evoked depression of the RRP in crayfish abdomen extensor preparation. With the use of bafilomycin A1, the tonic terminal is fatigue resistant due to a large RRP, whereas the phasic depresses rapidly upon continuous stimulation. Upon depression of the tonic terminal, 5-HT has a large RP to act on to recruit vesicles to the RRP; whereas, the phasic terminal, 5-HT can recruit RP vesicles to the RRP prior to synaptic depression but not after depression.

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