Document Type

Thesis

Date of Award

12-1998

School/College

College of Science, Engineering, and Technology (COSET)

Degree Name

MS in Biology

First Advisor

Professor Yvonne Hogan

Abstract

Activity-dependent changes in synaptic efficacy of neurons seems to be important for the development of neuronal circuitry and for many forms of synaptic plasticity including memory and learning. Long-term depression (LTD) of synaptic transmission has been recognized in the brain as a mechanism for decreasing synaptic efficacy to modulate activity. In sympathetic ganglia, which is known to have a robust long-term potentiation (LTP), very little experimental work has been performed to explore the possibility of the presence of LTD. Preliminary experiments show that LTD can, in fact, be demonstrated in the superior cervical ganglia (SCG) of rat. Characterizing LTD in the rat ganglia was the first part of this project. Three different induction methods were used to obtain LTD. First, tetanic stimulation of 5 pulses! second for 15 minute (5Hz lIS min) with and without hexamethonium bromide (0.4mM) application. Second, tetanic stimulation at 3 pulses l second for 15 minute (3HzJ15 min) with hexamethonium bromide (0.4 mM) application. Third, paired pulses 2 tetanic stimulation composed of three repetitive separate trains ofO.5Hz for 400 seconds. LTO was obtained in 60% of the experiments by using the first induction method. In contrast, LTO was obtained only in 40% of the experiments by using the second method of induction, and in 33% of the experiments by using the third method of LTD induction. • « ';'- Two different drugs were used to characterize LTO in SeG of rat. Pretreatment of ganglia with the 5-hydroxytryptamin3 (5-HT1) receptor antagonist, (3-tropanyl)-IHindole- 3-carboxylic acid (Tropisetron; ICS, O.5J1M), blocked LTO induction. However, 'pretetanic and posttetanic administration of nitric oxide synthase inhibitor, n-nitro-Larginine (L-NOARG ), 20JiM or 50JiM has no effect on either LTD induction phase or maintenance phase. Based on these results, the following conclusions can be made; (1) LTO can be expressed in sympathetic ganglia in up to 6()01o of the experiments, (2) 5-HTl receptors might be involved in LTO induction phase, nevertheless, further testing is needed, (3) Nitric oxide is not required for the induction or the maintenance of LTD. The second part of this project was, to elucidate the role of carbon monoxide in long-term potentiation (LTP) of superior cervical ganglion of rats. When administered pre- and posttetanic stimulation, hemeoxygenase-2 enzyme (H0-2) inhibitor, Zinc protoporphyrin IX(Zn-PP9, 10J.1M), indicates that carbon monoxide was involved in the LTP induction but not in the maintenance phase.

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