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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

An investigation into the neuroprotective properties of melatonin

Southgate, Garrick Steven January 1999 (has links)
Until the beginning of this decade the neurohormone, melatonin, had been considered as little more than a tranquillising hormone, responsible for regulating certain circadian and circannual rhythms. In the last eight years, a whole new dimension to melatonin’s role in biological organisms has emerged. In 1991 it was discovered [1,2] that melatonin exhibited antioxidant properties. Since then, many researchers [3,4] have found melatonin to be a powerful free radical scavenger and antioxidant. In the present study, the ability of melatonin to offer neuroprotection against glutamate, N-methyl-D-aspartate (NMDA), quinolinic acid (QA) and kainic acid (KA) (collectively referred to as the glutamate receptor agonists) was investigated. It was first shown that stress causes an increase in circulating glucocorticoid concentrations, which resulted in an increase the number of glutamate receptors on synaptic membranes in rat brain homogenate. Melatonin acted to reduce the number of glutamate receptors present on the synaptic membranes, implying that melatonin has neuroprotective properties, as overstimulation of the glutamate receptors leads to excitotoxicity and neurodegeneration. Further investigations showed that the glutamate receptor agonists induce neurodegeneration in primary neuronal cell cultures. Both co-treatment and posttreatment with melatonin against the glutamate receptor agonists, increased neuronal cell viability in a dose dependent manner. Melatonin also appeared to offer protection against quinolinic acid-induced neurodegeneration following intrahippocampal injections of quinolinic acid. The mechanism whereby melatonin offered this protection was investigated. The glutamate receptor agonists caused an increase in intracellular calcium concentrations, which is known [5] to be responsible for initiating the excitotoxic response. Melatonin had no effect on regulating intracellular calcium concentrations Additional studies indicated that melatonin was effective at scavenging superoxide radicals. Production of superoxide radicals was induced by the glutamate receptor agonists in primary neuronal cultures. Superoxide radicals induce lipid peroxidation, which involves the destruction of lipid membranes by chain reactions. By acting as an antioxidant, melatonin was able to reduce quinolinic acid-induced lipid peroxidation in rat brain homogenate, in a dose dependent manner. Melatonin was also effective at reducing lipid peroxidation induced by the glutamate receptor agonists in primary neuronal cultures. Melatonin therefore appeared to be offering neuroprotection by removing superoxide radicals and inhibiting lipid peroxidation. It had been reported [6] that melatonin inhibits nitric oxide synthase activity. This enzyme produces the free radical, nitric oxide, and can also produce superoxide radicals. Melatonin was able to reduce nitric oxide synthase activity in a dose dependent manner. This is a novel method of neuroprotection, as melatonin was now acting as an enzyme regulator. The results obtained demonstrate that melatonin offers neuroprotection against glutamate induced excitotoxicity, by removing free radicals and preventing lipid peroxidation. The neurohormone offers further protection by decreasing the activity of enzymes that aid in the neurotoxic cascade. Melatonin is the most potent naturally occurring free radical scavenger in the body [3]. During aging, the serum concentrations of melatonin decrease [7]. During the senescence of life, free radical damage to the body is at its highest [8], while at the same time melatonin concentrations are at their lowest. Melatonin therefore shows potential for the treatment of diseases and disorders that exhibit an excitotoxic pathology.
2

The occurrence and metabolism of melatonin /

Fellenberg, A. J. January 1983 (has links) (PDF)
Thesis (Ph. D.)--University of Adelaide, Dept. of Obstetrics and Gynaecology, 1987. / Includes bibliographical references (leaves 89-118).
3

Cellular and molecular studies on pigment-granule translocation in Xenopus laevis melanophores

Teh, Muy-Teck January 2000 (has links)
No description available.
4

Melatonin secretion and excretion : a clinical study focusing on factors and disease states which might influence melatonin /

Wikner, Johan, January 1900 (has links)
Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 6 uppsatser.
5

Comparative morphological and biochemical study of the pineal complex in geckos /

Moyer, Robert Walter. January 1998 (has links) (PDF)
Thesis (Ph.D.)--University of Adelaide, Dept. of Anatomical Sciences, 1998. / Copies of author's previously published articles inserted. Bibliography: leaves 161-187.
6

The evaluation of melatonin as a possible antidepressive

Skene, Debra Jean January 1980 (has links)
Melatonin, a hormone of the pineal gland, was evaluated in a variety of animal models of depression. Measurements of the frog righting reflex and rat locomotor activity showed that low doses of melatonin have a serotonin-like potentiating effect following monoamine oxidase inhibition. High doses of melatonin caused a reduction in the duration of rat immobility in the Porsolt model of depression and exerted a chlorpromazine-like effect on conditioned avoidance behaviour. In view of the indoleamine hypothesis of depressive disorders, the possibility of melatonin being a potential antidepressive is discussed and it is concluded that melatonin might be useful in the treatment of "agitated" depressions
7

Melatonin and anticancer therapy : interactions with 5-Fluorouracil /

Cassim, Layla. January 2007 (has links)
Thesis (Ph.D. (Pharmacy)) - Rhodes University, 2008.
8

An investigation into the neuroprotective effects of melatonin in a model of rotenone-induced neurodegeneration /

Kadanthode, Rubina John. January 2003 (has links)
Thesis (M. Sc. (Pharmacy))--Rhodes University, 2004.
9

Melatonin receptors in the rat uterus

Zhao, Hang, 趙航 January 2000 (has links)
published_or_final_version / Physiology / Doctoral / Doctor of Philosophy
10

Melatonin receptors in the rat epididymis

Li, Li, 李莉 January 1998 (has links)
published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

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