Polymers, catalysts and nanostructures a hybrid approach to biomolecule detection
- Authors: Frith, Kelly-Anne
- Date: 2009
- Subjects: Polymers , Nanostructured materials , Biomolecules , Tryptophan , Melatonin , Electrodes , Electrochemistry , Tryptophan oxygenase
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3980 , http://hdl.handle.net/10962/d1004039 , Polymers , Nanostructured materials , Biomolecules , Tryptophan , Melatonin , Electrodes , Electrochemistry , Tryptophan oxygenase
- Description: The main goals in electroanalytical sensing are towards improved sensitivity and selectivity, or specificity, of an analyte. There are several approaches to achieving these goals with the main approach being modification of an electrode surface with synthetic or natural catalysts (enzymes), polymers and also utilisation of nanostructured materials. At present, there is a strong movement towards hybrid sensing which couple different properties of two or more surface modification approaches. In this thesis, a range of these surface modifications were explored for analysis and detection of two main analytes: the amino acid, tryptophan (Trp); and, the neurotransmitter, dopamine (DA). Specifically, this thesis aimed to utilise these methods to enhance the sensitivity and selectivity for Trp over an interferent, the indoleamine, melatonin (Mel); and, DA over the vitamin, ascorbic acid (AA). For Trp detection, immobilisation of an enzyme, Tryptophanase (Trpase) resulted in poor selectivity for the analyte. However, enhanced sensitivity and selectivity was achieved through pH manipulation of the electrolyte medium at a Nafion®-modified electrode surface for both Trp and Mel. At pH 3.0, the Mel and Trp anodic peak potentials were sufficiently resolved allowing for an LOD of 1.60 and 1.62 nM,respectively, and permitting the accurate analysis of Trp in a dietary supplement containing Mel. Multi-walled carbon nanotubes (MWCNTs) suspended in Nafion® exhibited further increases in the signal responses of these analytes at pH 3.0 and 7.4 with minimal change in the resolution of the anodic peaks. A lower sensitivity was, therefore, observed at the Nafion® and MWCNT modified electrode compared to the Nafion®-modified electrode at pH 3.0 with LODs of 0.59 and 0.80 nM exhibited for Trp and Mel, respectively. Enhanced selectivity for Trp in the presence of Mel can be achieved with MWCNTs in the presence of metallotetrasulphonated phthalocyanines (MTSPcs) particularly at pH 3.0, owing to cation exchange effects. However, the lack of sensitivity towards Trp, and even Mel, at this CoTSPc and MWCNT modified electrode remains a drawback. For DA, detection at the MWCNT and Nafion® surface resulted in improved sensitivity over that of both the bare electrode (613.0 nM) and the Nafion® modified electrode (1045.1 nM) with a calculated LOD of 133.9 nM at this layer. Furthermore, improvements in the selectivity of DA were achieved at the Nafion® and MWCNT modified electrode as exclusion of AA (150 μM) was achieved. At the MWCNT and CoTSPc surface, AA was excluded up to 130 μM with sensitivity for DA extending as low as 14.3 nM, far greater than observed for Trp and Mel. These concentrations are well within physiological concentration ranges and represent the most significant solution yet in terms of AA exclusion and enhanced sensitivity for DA. An examination of the surface layering by impedance spectroscopy and atomic force microscopy indicates that the success of the hybrid sensor utilising CoTSPc and MWCNTs lay in improved dispersion of MWCNTs and improved electron transfer kinetics, facilitated by the net charge of the materials present. This thesis, thus, showed the utility of a judicious selection of synthetic and biological catalysts, polymers and carbon nanomaterials towards a hybrid approach to the electrochemical sensing of Trp, Mel, DA and AA with focus on sensitivity and selectivity of these analytes.
- Full Text:
- Date Issued: 2009
- Authors: Frith, Kelly-Anne
- Date: 2009
- Subjects: Polymers , Nanostructured materials , Biomolecules , Tryptophan , Melatonin , Electrodes , Electrochemistry , Tryptophan oxygenase
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3980 , http://hdl.handle.net/10962/d1004039 , Polymers , Nanostructured materials , Biomolecules , Tryptophan , Melatonin , Electrodes , Electrochemistry , Tryptophan oxygenase
- Description: The main goals in electroanalytical sensing are towards improved sensitivity and selectivity, or specificity, of an analyte. There are several approaches to achieving these goals with the main approach being modification of an electrode surface with synthetic or natural catalysts (enzymes), polymers and also utilisation of nanostructured materials. At present, there is a strong movement towards hybrid sensing which couple different properties of two or more surface modification approaches. In this thesis, a range of these surface modifications were explored for analysis and detection of two main analytes: the amino acid, tryptophan (Trp); and, the neurotransmitter, dopamine (DA). Specifically, this thesis aimed to utilise these methods to enhance the sensitivity and selectivity for Trp over an interferent, the indoleamine, melatonin (Mel); and, DA over the vitamin, ascorbic acid (AA). For Trp detection, immobilisation of an enzyme, Tryptophanase (Trpase) resulted in poor selectivity for the analyte. However, enhanced sensitivity and selectivity was achieved through pH manipulation of the electrolyte medium at a Nafion®-modified electrode surface for both Trp and Mel. At pH 3.0, the Mel and Trp anodic peak potentials were sufficiently resolved allowing for an LOD of 1.60 and 1.62 nM,respectively, and permitting the accurate analysis of Trp in a dietary supplement containing Mel. Multi-walled carbon nanotubes (MWCNTs) suspended in Nafion® exhibited further increases in the signal responses of these analytes at pH 3.0 and 7.4 with minimal change in the resolution of the anodic peaks. A lower sensitivity was, therefore, observed at the Nafion® and MWCNT modified electrode compared to the Nafion®-modified electrode at pH 3.0 with LODs of 0.59 and 0.80 nM exhibited for Trp and Mel, respectively. Enhanced selectivity for Trp in the presence of Mel can be achieved with MWCNTs in the presence of metallotetrasulphonated phthalocyanines (MTSPcs) particularly at pH 3.0, owing to cation exchange effects. However, the lack of sensitivity towards Trp, and even Mel, at this CoTSPc and MWCNT modified electrode remains a drawback. For DA, detection at the MWCNT and Nafion® surface resulted in improved sensitivity over that of both the bare electrode (613.0 nM) and the Nafion® modified electrode (1045.1 nM) with a calculated LOD of 133.9 nM at this layer. Furthermore, improvements in the selectivity of DA were achieved at the Nafion® and MWCNT modified electrode as exclusion of AA (150 μM) was achieved. At the MWCNT and CoTSPc surface, AA was excluded up to 130 μM with sensitivity for DA extending as low as 14.3 nM, far greater than observed for Trp and Mel. These concentrations are well within physiological concentration ranges and represent the most significant solution yet in terms of AA exclusion and enhanced sensitivity for DA. An examination of the surface layering by impedance spectroscopy and atomic force microscopy indicates that the success of the hybrid sensor utilising CoTSPc and MWCNTs lay in improved dispersion of MWCNTs and improved electron transfer kinetics, facilitated by the net charge of the materials present. This thesis, thus, showed the utility of a judicious selection of synthetic and biological catalysts, polymers and carbon nanomaterials towards a hybrid approach to the electrochemical sensing of Trp, Mel, DA and AA with focus on sensitivity and selectivity of these analytes.
- Full Text:
- Date Issued: 2009
An investigation into the neuroprotective effects of melatonin in a model of rotenone-induced neurodegeneration
- Authors: Kadanthode, Rubina John
- Date: 2004
- Subjects: Melatonin , Nervous system -- Degeneration -- Treatment , Rotenone
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3763 , http://hdl.handle.net/10962/d1003241 , Melatonin , Nervous system -- Degeneration -- Treatment , Rotenone
- Description: Parkinson’s disease, one of the most common neurodegenerative disorders associated with ageing, is characterised by abnormal and profound loss of nigrostriatal dopaminergic neurons. The cause of Parkinson’s disease is unknown, but epidemiological studies suggest an association with pesticides and other environmental toxins, and biochemical studies implicate oxidative damage and mitochondrial impairment, particularly at the level of complex I enzyme. Recently, rotenone, a commonly used organic pesticide and a classical inhibitor of mitochondrial complex I has been reported to reproduce the specific features of Parkinson’s disease in rodents. The mitochondrial respiratory chain is one of the most important sites of reactive oxygen species production under physiological conditions. Toxic free radicals have been implicated in a variety of neurodegenerative diseases as well as ageing itself. Melatonin, a secretory product of the pineal gland is a multifaceted free radical scavenger and natural antioxidant. In the present study, the neuroprotective effects of melatonin against the environmental neurotoxin, rotenone was investigated. Initial studies showed that inhibition of mitochondrial complex I enzyme by rotenone induced superoxide radical generation. Melatonin, administered to the rat in vivo and in vitro was able to offer neuroprotection by curtailing the production of superoxide radicals induced by rotenone. Mitochondria, being the major target of rotenone, the effects of melatonin were investigated at the mitochondrial level. Melatonin was able to increase the electron transport chain activity thus preventing the respiratory inhibition by rotenone. The pineal hormone also counteracted the action of rotenone on complex I enzyme. These results suggest melatonin’s ability to potentially limit the free radical generation and thereby modulate the mitochondrial functions. The detection and measurement of lipid peroxidation is the evidence most frequently cited to support the involvement of free radical reactions in toxicology and in human disease. Melatonin also offered significant protection in vivo and in vitro against rotenone induced lipid peroxidation. Since iron plays a major role in oxidative damage and in the progression of Parkinson’s disease, the effect of melatonin on both rotenone and iron induced lipid peroxidation was investigated, the results of which show that melatonin affords protection and this was suggested to be due to its interaction with the rotenone-iron complex that might have formed. Electrochemical studies were further used to characterise the interactions between melatonin, rotenone and iron (III). Melatonin was shown to bind with iron and thus reducing their toxicity. Histological studies were undertaken to assess the effects of melatonin on rotenone induced toxicity on the dopaminergic neurons in the rat brain. Rotenone treated brains showed extensive neuronal damage whereas with melatonin less damage was observed. Rotenone induces apoptosis via reactive oxygen species production and apoptotic cell death has been identified in PD brains. Furthermore, the apoptotic cell death was detected and quantified by the TUNEL staining. Rotenone treated sections showed signs of apoptosis whereas with melatonin, less apoptotic damage was observed. The findings of this study indicate that the neurohormone, melatonin may protect against rotenone-induced neurodegeneration. Since melatonin production falls substantially during ageing, the loss of this antioxidant is theorized to be instrumental in the degenerative processes associated with advanced age. Considering how devastating diseases such as Parkinson’s disease, are to a patient and the patient’s families, the discovery of protective agents are a matter of urgency. Further investigations using the pesticide model will help to determine the involvement of environmental exposure in the pathogenesis of human diseases as well as to test therapeutic strategies for the treatment of such diseases.
- Full Text:
- Date Issued: 2004
- Authors: Kadanthode, Rubina John
- Date: 2004
- Subjects: Melatonin , Nervous system -- Degeneration -- Treatment , Rotenone
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3763 , http://hdl.handle.net/10962/d1003241 , Melatonin , Nervous system -- Degeneration -- Treatment , Rotenone
- Description: Parkinson’s disease, one of the most common neurodegenerative disorders associated with ageing, is characterised by abnormal and profound loss of nigrostriatal dopaminergic neurons. The cause of Parkinson’s disease is unknown, but epidemiological studies suggest an association with pesticides and other environmental toxins, and biochemical studies implicate oxidative damage and mitochondrial impairment, particularly at the level of complex I enzyme. Recently, rotenone, a commonly used organic pesticide and a classical inhibitor of mitochondrial complex I has been reported to reproduce the specific features of Parkinson’s disease in rodents. The mitochondrial respiratory chain is one of the most important sites of reactive oxygen species production under physiological conditions. Toxic free radicals have been implicated in a variety of neurodegenerative diseases as well as ageing itself. Melatonin, a secretory product of the pineal gland is a multifaceted free radical scavenger and natural antioxidant. In the present study, the neuroprotective effects of melatonin against the environmental neurotoxin, rotenone was investigated. Initial studies showed that inhibition of mitochondrial complex I enzyme by rotenone induced superoxide radical generation. Melatonin, administered to the rat in vivo and in vitro was able to offer neuroprotection by curtailing the production of superoxide radicals induced by rotenone. Mitochondria, being the major target of rotenone, the effects of melatonin were investigated at the mitochondrial level. Melatonin was able to increase the electron transport chain activity thus preventing the respiratory inhibition by rotenone. The pineal hormone also counteracted the action of rotenone on complex I enzyme. These results suggest melatonin’s ability to potentially limit the free radical generation and thereby modulate the mitochondrial functions. The detection and measurement of lipid peroxidation is the evidence most frequently cited to support the involvement of free radical reactions in toxicology and in human disease. Melatonin also offered significant protection in vivo and in vitro against rotenone induced lipid peroxidation. Since iron plays a major role in oxidative damage and in the progression of Parkinson’s disease, the effect of melatonin on both rotenone and iron induced lipid peroxidation was investigated, the results of which show that melatonin affords protection and this was suggested to be due to its interaction with the rotenone-iron complex that might have formed. Electrochemical studies were further used to characterise the interactions between melatonin, rotenone and iron (III). Melatonin was shown to bind with iron and thus reducing their toxicity. Histological studies were undertaken to assess the effects of melatonin on rotenone induced toxicity on the dopaminergic neurons in the rat brain. Rotenone treated brains showed extensive neuronal damage whereas with melatonin less damage was observed. Rotenone induces apoptosis via reactive oxygen species production and apoptotic cell death has been identified in PD brains. Furthermore, the apoptotic cell death was detected and quantified by the TUNEL staining. Rotenone treated sections showed signs of apoptosis whereas with melatonin, less apoptotic damage was observed. The findings of this study indicate that the neurohormone, melatonin may protect against rotenone-induced neurodegeneration. Since melatonin production falls substantially during ageing, the loss of this antioxidant is theorized to be instrumental in the degenerative processes associated with advanced age. Considering how devastating diseases such as Parkinson’s disease, are to a patient and the patient’s families, the discovery of protective agents are a matter of urgency. Further investigations using the pesticide model will help to determine the involvement of environmental exposure in the pathogenesis of human diseases as well as to test therapeutic strategies for the treatment of such diseases.
- Full Text:
- Date Issued: 2004
An investigation into the possible neuroprotective role of melatonin in copper-loading
- Authors: Parmar, Paresh H
- Date: 2001
- Subjects: Melatonin , Copper , Nervous system -- Degeneration -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3783 , http://hdl.handle.net/10962/d1003261
- Description: Copper is an extremely toxic metal in biological systems and thus, its availability to the system, must be effectively and efficiently controlled. Copper is vital for life, as it is essential for critical enzymes in biological systems. It is free copper in the biological systems that is toxic, as free copper induces free radical generation, which disrupts lipid membranes, interacts with DNA causing mutations, and eventually leads to cell death. Wilson’s disease is a inherited copper disease, which results in hepatolenticular disease. Copper is unable to be excreted, and thus accumulates, eventually spilling over into the bloodstream from the liver, and “poisons” the patient. The Wilson’s disease patient leads a short life, due to neurological and hepatological problems. There is no cure for Wilson’s disease, only chelation therapy using potent chelators such as penicillamine and EDTA. Zinc, in high doses, can be used to compete with copper absorption. This has proved to be the only successful therapy at present. This study investigates the possible use of melatonin as a copper binder/chelator. Melatonin has been shown to interact with copper in vitro. By binding/chelating to copper, melatonin may inhibit copper-induced free radical generation, and thus prevent copper from interacting with DNA to cause mutations and act as a cytotoxin. In vivo studies on copper (2mg/kg) administered for 2-weeks and 6-weeks were carried out on Wistar rats. The potential of melatonin (12mg/kg) to prevent copper-induced cellular damage was investigated. The results indicate that melatonin does not protect the lipid membranes from copper-induced lipid peroxidation. In vitro investigations using 1mM, 5mM and 10mM copper and 5mM melatonin, show that melatonin prevents copper-induced lipid peroxidation at a copper concentration of 1mM (p<0.001). The 5mM and 10mM copper induces less lipid peroxidation, compared to the 1mM copper. It has been reported that metal ions, antioxidants and chelating agents can influence peroxide decomposition during the assay. Melatonin (5mM) administration does not significantly prevent copper-induced lipid peroxidation at 5mM and 10mM copper. It is possible that due to melatonin’s relatively low concentration, it is unable to inhibit lipid peroxidation induced by the copper. The chemical nature of the interaction between melatonin and copper was also investigated, using NMR, IR and electrochemistry techniques. The NMR and IR techniques show that melatonin coordinates with Cu²⁺ and not Cu¹⁺, at the carbonyl group of melatonin. The electrochemistry experiments using cyclic voltammetry and adsorptive stripping voltammetry, show that melatonin forms a strong bond with Cu¹⁺. Cu²⁺ prefers binding to oxygen, and that is clearly seen in the NMR and IR. Cu¹⁺ prefers binding to nitrogen and then oxygen, and this is seen in the electrochemistry, as Cu¹⁺ is forced to bind through one of the nitrogens on the melatonin. Previously, it has been shown that melatonin binds/chelates with Cu²⁺. Histochemical investigations show that copper administration for 2-weeks and 6-weeks, causes extensive mitochondrial damage in liver and kidney’s proximal convoluted tubule epithelium cells. Melatonin (12mg/kg) co-administration with copper for 2-weeks and 6-weeks did not significantly protect the mitochondria from copper-induced damage. Copper-specific stains (rhodanine, silver sulphide and rubeanic acid) were used to stain liver, brain and kidney tissue samples. Rhodanine and silver sulphide were equally sensitive in staining copper in the 2-week samples, but not at all in the 6-week samples. This could not be explained. Rubeanic acid was ineffective in all samples tested. Thus, it appears that specific copper stains cannot be used in making a definitive diagnosis in cases of copper overload, and that specific copper stains do not always correlate with a high concentration of copper present in tissues. Pineal organ culture was used to determine the effect of copper administration on pineal indole synthesis. Exogenous (³H) tryptophan was administered to the pineal organ cultures, and the level of (³H) pineal indoles synthesised, were measured. Pineals from 2-week and 6-week copper/melatonin treated animals exhibited paradoxical 5- methoxytryptophol (ML) levels, as compared to the 2-week and 6-week copper treated animals. The 2-week copper/melatonin administered animals, showed a decrease in the ML level (p<0.01), and the copper/melatonin administered for 6-weeks, showed an increase in the ML levels (p<0.01). This indicates that melatonin interacts with the HIOMT enzyme. Pineals from 6-week copper/melatonin treated animals, as compared to the 6-week copper treated animals, showed an increase in N-acetylserotonin levels. This indicates that melatonin prevents the inhibition of the NAT enzyme. The final experiment was to determine in vitro, the effect of Cu²⁺ and Cu¹⁺ administration, on mitochondrial electron transport chain. Rat liver homogenate was incubated with and solutions of Cu²⁺ (10mM) and Cu¹⁺ (10mM) and melatonin (10mM). Cu²⁺ administration caused an inhibition of the electron transport at t=0 and t=60, whereas Cu¹⁺ administration at t=0 caused an inhibition of electron transport, but at t=60, Cu¹⁺ administration stimulated electron transport. Melatonin administered with Cu²⁺, resulted in an inhibition of the electron transport chain at t=0 and t=60. The findings of this study indicate that melatonin might have a potentially beneficial effect in copper overloading, by binding/chelating copper.
- Full Text:
- Date Issued: 2001
- Authors: Parmar, Paresh H
- Date: 2001
- Subjects: Melatonin , Copper , Nervous system -- Degeneration -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3783 , http://hdl.handle.net/10962/d1003261
- Description: Copper is an extremely toxic metal in biological systems and thus, its availability to the system, must be effectively and efficiently controlled. Copper is vital for life, as it is essential for critical enzymes in biological systems. It is free copper in the biological systems that is toxic, as free copper induces free radical generation, which disrupts lipid membranes, interacts with DNA causing mutations, and eventually leads to cell death. Wilson’s disease is a inherited copper disease, which results in hepatolenticular disease. Copper is unable to be excreted, and thus accumulates, eventually spilling over into the bloodstream from the liver, and “poisons” the patient. The Wilson’s disease patient leads a short life, due to neurological and hepatological problems. There is no cure for Wilson’s disease, only chelation therapy using potent chelators such as penicillamine and EDTA. Zinc, in high doses, can be used to compete with copper absorption. This has proved to be the only successful therapy at present. This study investigates the possible use of melatonin as a copper binder/chelator. Melatonin has been shown to interact with copper in vitro. By binding/chelating to copper, melatonin may inhibit copper-induced free radical generation, and thus prevent copper from interacting with DNA to cause mutations and act as a cytotoxin. In vivo studies on copper (2mg/kg) administered for 2-weeks and 6-weeks were carried out on Wistar rats. The potential of melatonin (12mg/kg) to prevent copper-induced cellular damage was investigated. The results indicate that melatonin does not protect the lipid membranes from copper-induced lipid peroxidation. In vitro investigations using 1mM, 5mM and 10mM copper and 5mM melatonin, show that melatonin prevents copper-induced lipid peroxidation at a copper concentration of 1mM (p<0.001). The 5mM and 10mM copper induces less lipid peroxidation, compared to the 1mM copper. It has been reported that metal ions, antioxidants and chelating agents can influence peroxide decomposition during the assay. Melatonin (5mM) administration does not significantly prevent copper-induced lipid peroxidation at 5mM and 10mM copper. It is possible that due to melatonin’s relatively low concentration, it is unable to inhibit lipid peroxidation induced by the copper. The chemical nature of the interaction between melatonin and copper was also investigated, using NMR, IR and electrochemistry techniques. The NMR and IR techniques show that melatonin coordinates with Cu²⁺ and not Cu¹⁺, at the carbonyl group of melatonin. The electrochemistry experiments using cyclic voltammetry and adsorptive stripping voltammetry, show that melatonin forms a strong bond with Cu¹⁺. Cu²⁺ prefers binding to oxygen, and that is clearly seen in the NMR and IR. Cu¹⁺ prefers binding to nitrogen and then oxygen, and this is seen in the electrochemistry, as Cu¹⁺ is forced to bind through one of the nitrogens on the melatonin. Previously, it has been shown that melatonin binds/chelates with Cu²⁺. Histochemical investigations show that copper administration for 2-weeks and 6-weeks, causes extensive mitochondrial damage in liver and kidney’s proximal convoluted tubule epithelium cells. Melatonin (12mg/kg) co-administration with copper for 2-weeks and 6-weeks did not significantly protect the mitochondria from copper-induced damage. Copper-specific stains (rhodanine, silver sulphide and rubeanic acid) were used to stain liver, brain and kidney tissue samples. Rhodanine and silver sulphide were equally sensitive in staining copper in the 2-week samples, but not at all in the 6-week samples. This could not be explained. Rubeanic acid was ineffective in all samples tested. Thus, it appears that specific copper stains cannot be used in making a definitive diagnosis in cases of copper overload, and that specific copper stains do not always correlate with a high concentration of copper present in tissues. Pineal organ culture was used to determine the effect of copper administration on pineal indole synthesis. Exogenous (³H) tryptophan was administered to the pineal organ cultures, and the level of (³H) pineal indoles synthesised, were measured. Pineals from 2-week and 6-week copper/melatonin treated animals exhibited paradoxical 5- methoxytryptophol (ML) levels, as compared to the 2-week and 6-week copper treated animals. The 2-week copper/melatonin administered animals, showed a decrease in the ML level (p<0.01), and the copper/melatonin administered for 6-weeks, showed an increase in the ML levels (p<0.01). This indicates that melatonin interacts with the HIOMT enzyme. Pineals from 6-week copper/melatonin treated animals, as compared to the 6-week copper treated animals, showed an increase in N-acetylserotonin levels. This indicates that melatonin prevents the inhibition of the NAT enzyme. The final experiment was to determine in vitro, the effect of Cu²⁺ and Cu¹⁺ administration, on mitochondrial electron transport chain. Rat liver homogenate was incubated with and solutions of Cu²⁺ (10mM) and Cu¹⁺ (10mM) and melatonin (10mM). Cu²⁺ administration caused an inhibition of the electron transport at t=0 and t=60, whereas Cu¹⁺ administration at t=0 caused an inhibition of electron transport, but at t=60, Cu¹⁺ administration stimulated electron transport. Melatonin administered with Cu²⁺, resulted in an inhibition of the electron transport chain at t=0 and t=60. The findings of this study indicate that melatonin might have a potentially beneficial effect in copper overloading, by binding/chelating copper.
- Full Text:
- Date Issued: 2001
The effects of melatonin on the testis, epididymis and sperm physiology of the Wistar rat
- Authors: Gwayi, Noluzuko
- Date: 2001
- Subjects: Rats as laboratory animals , Rats -- physiology , Spermatozoa , Melatonin , Testis , Epididymis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5681 , http://hdl.handle.net/10962/d1005366 , Rats as laboratory animals , Rats -- physiology , Spermatozoa , Melatonin , Testis , Epididymis
- Description: Melatonin is a product of the pineal gland and is postulated to play an antigonadotropic role in the reproductive system of mammals. The reproductive system of non-seasonally breeding mammals is believed to be not as responsive to melatonin treatment as that of seasonally breeding mammals. Recently, there has been increasing support from in vivo and in vitro studies, for the hypothesis that melatonin has negative effects on sperm physiology, especially on sperm motility. High and/or low seminal concentrations of melatonin have been associated with abnormalities in human sperm motility and concentration. In this study, I examined the effects of melatonin on the testis, epididymis and sperm physiology, using in vivo and in vitro experiments, in a non-seasonally breeding mammal. Treatment, in vivo, with exogenous melatonin for six weeks did not inhibit testosterone production or spermatogenesis, nor did it affect the mass of the testes and epididymides at dissection, the concentration the morphology of speimatozoa. However, melatonin in vivo had a small, but significant negative effect on sperm motility and sperm motility index. In vitro incubation of spermatozoa Fith melatonin reduced the percentage (%) of forward progressive movement (fpm), increased the % reduction in fpm, reduced the vigor or quality of sperm motility, reduced the sperm motility index, and delayed and/or prolonged the transition of one pattern of sperm motility to the subsequent patterns. Melatonin increased the pH of the culture medium, and the increased pH, and the ethanol utilized as a solvent for melatonin, both negatively affected all the sperm motility parameters that were assessed in my study. The effects of ethanol increased with time, and the effects of pH increased with both time and increasing pH. Melatonin in vitro did not inhibit capacitation and the acrosome reaction, but it delayed the onset and the progression of capacitation and the acrosome reaction. These results suggest that while melatonin did not inhibit spermatogenesis in the Wistar rat, it may influence sperm motility. Therefore, the presence of high concentrations of melatonin in the reproductive fluids may inhibit sperm motility. With further detailed research, melatonin may have a potential use as a contraceptive drug.
- Full Text:
- Date Issued: 2001
- Authors: Gwayi, Noluzuko
- Date: 2001
- Subjects: Rats as laboratory animals , Rats -- physiology , Spermatozoa , Melatonin , Testis , Epididymis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5681 , http://hdl.handle.net/10962/d1005366 , Rats as laboratory animals , Rats -- physiology , Spermatozoa , Melatonin , Testis , Epididymis
- Description: Melatonin is a product of the pineal gland and is postulated to play an antigonadotropic role in the reproductive system of mammals. The reproductive system of non-seasonally breeding mammals is believed to be not as responsive to melatonin treatment as that of seasonally breeding mammals. Recently, there has been increasing support from in vivo and in vitro studies, for the hypothesis that melatonin has negative effects on sperm physiology, especially on sperm motility. High and/or low seminal concentrations of melatonin have been associated with abnormalities in human sperm motility and concentration. In this study, I examined the effects of melatonin on the testis, epididymis and sperm physiology, using in vivo and in vitro experiments, in a non-seasonally breeding mammal. Treatment, in vivo, with exogenous melatonin for six weeks did not inhibit testosterone production or spermatogenesis, nor did it affect the mass of the testes and epididymides at dissection, the concentration the morphology of speimatozoa. However, melatonin in vivo had a small, but significant negative effect on sperm motility and sperm motility index. In vitro incubation of spermatozoa Fith melatonin reduced the percentage (%) of forward progressive movement (fpm), increased the % reduction in fpm, reduced the vigor or quality of sperm motility, reduced the sperm motility index, and delayed and/or prolonged the transition of one pattern of sperm motility to the subsequent patterns. Melatonin increased the pH of the culture medium, and the increased pH, and the ethanol utilized as a solvent for melatonin, both negatively affected all the sperm motility parameters that were assessed in my study. The effects of ethanol increased with time, and the effects of pH increased with both time and increasing pH. Melatonin in vitro did not inhibit capacitation and the acrosome reaction, but it delayed the onset and the progression of capacitation and the acrosome reaction. These results suggest that while melatonin did not inhibit spermatogenesis in the Wistar rat, it may influence sperm motility. Therefore, the presence of high concentrations of melatonin in the reproductive fluids may inhibit sperm motility. With further detailed research, melatonin may have a potential use as a contraceptive drug.
- Full Text:
- Date Issued: 2001
Serotonin-melatonin interactions in acetaminophen and N,N-dimethylformamide toxicity
- Anoopkumar-Dukie, Shailendra
- Authors: Anoopkumar-Dukie, Shailendra
- Date: 2000
- Subjects: Serotonin , Acetaminophen , Melatonin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3898 , http://hdl.handle.net/10962/d1003957 , Serotonin , Acetaminophen , Melatonin
- Description: Acetaminophen and N,N-dimethylformamide (DMF) are compounds which are extremely toxic to the liver. Acetaminophen is a drug which is well known for its analgesic and antipyretic properties. However, the abuse potential of this agent as a non-narcotic analgesic in alcoholics is well known. It is also the leading cause of overdose in England. DMF toxicity results mainly from occupational exposure. At present there are no known reports of an antidote for DMF poisoning, while N-acetylcysteine, the antidote for acetaminophen poisoning, is known to produce adverse effects. The present study evaluates the potential of melatonin as an antidote for acetaminophen and DMF poisoning. This study also investigates the mechanism underlying acetaminophen addiction and abuse. Initial studies involved in vitro techniques in an attempt to remove the complexities of organ interactions. The photodegradation studies, using ultraviolet (UV) light, revealed that melatonin accelerates the rate of acetaminophen degradation in the presence of air, and reduces the rate of degradation in the presence of nitrogen. This study also revealed that melatonin is rapidly degraded in the presence of air, following UV irradiation. The effect of DMF on hydroxyl radical generation was also determined. DMF was shown to act as a free radical scavenger, rather that a generator of free radicals. The in vitro studies were followed by lipid peroxidation determination. DMF (0.4ml/kg and 0.8ml/kg) did not produce any significant increases in lipid peroxidation in the liver. Three different doses of acetaminophen (30mg/kg, 100mg/kg, and 500mg/kg) were administered to rats for seven days. Acetaminophen (500mg/kg) was shown to significantly increase (p<0.05) lipid peroxidation in the liver. Melatonin (2.5mg/kg) was not able to significantly reduce the damage. The lower doses of acetaminophen (30mg/kg and 100mg/kg) did not increase lipid peroxidation. Electron microscopy studies showed that DMF adversely affects the liver, and in particular, the endoplasmic reticulum. Co administration of melatonin (2.5mg/kg) was able to reduce the damage. Further experiments need to be performed before an accurate assessment can be made on the ability of melatonin as an antidote for DMF and acetaminophen poisoning. Several experiments were done in an attempt to uncover the biochemical mechanism underlying acetaminophen addiction and abuse. The first experiment targeted the liver enzyme tryptophan-2,3-dioxygenase (TDO). This enzyme is the major determinant of tryptophan levels in vivo. Acetaminophen administration (100mg/kg for three hours) was shown to significantly inhibit (p<0.05) the activity of TDO, indicating increased peripheral levels of tryptophan. This experiment was followed up with determination of brain serotonin and pineal melatonin. Brain serotonin was determined using the ELISA technique. Melatonin was estimated using this technique as well as with pineal organ culture. Acetaminophen administration (100mg/kg for three hours) significantly increased (p<0.05) brain serotonin levels. Using organ culture where exogenous (3H) tryptophan is metabolised to (3H) melatonin, acetaminophen (100mg/kg for three hours) was shown to significantly increase (p<0.05) pineal melatonin concentrations. However, the ELISA technique did not reveal any changes in endogenous pineal melatonin levels. The final experiment was the determination of urinary 5-hydroxyindole acetic acid (5- HIAA), the major metabolite of serotonin, following acetaminophen administration (100mg/kg for three hours). Acetaminophen was shown to significantly reduce 5-HIAA levels (p<0.05) suggesting reduced catabolism of serotonin. The findings of this study indicate that acetaminophen mimics the actions of an antidepressant. This compelling finding has important clinical implications, and needs to be examined further.
- Full Text:
- Date Issued: 2000
- Authors: Anoopkumar-Dukie, Shailendra
- Date: 2000
- Subjects: Serotonin , Acetaminophen , Melatonin
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3898 , http://hdl.handle.net/10962/d1003957 , Serotonin , Acetaminophen , Melatonin
- Description: Acetaminophen and N,N-dimethylformamide (DMF) are compounds which are extremely toxic to the liver. Acetaminophen is a drug which is well known for its analgesic and antipyretic properties. However, the abuse potential of this agent as a non-narcotic analgesic in alcoholics is well known. It is also the leading cause of overdose in England. DMF toxicity results mainly from occupational exposure. At present there are no known reports of an antidote for DMF poisoning, while N-acetylcysteine, the antidote for acetaminophen poisoning, is known to produce adverse effects. The present study evaluates the potential of melatonin as an antidote for acetaminophen and DMF poisoning. This study also investigates the mechanism underlying acetaminophen addiction and abuse. Initial studies involved in vitro techniques in an attempt to remove the complexities of organ interactions. The photodegradation studies, using ultraviolet (UV) light, revealed that melatonin accelerates the rate of acetaminophen degradation in the presence of air, and reduces the rate of degradation in the presence of nitrogen. This study also revealed that melatonin is rapidly degraded in the presence of air, following UV irradiation. The effect of DMF on hydroxyl radical generation was also determined. DMF was shown to act as a free radical scavenger, rather that a generator of free radicals. The in vitro studies were followed by lipid peroxidation determination. DMF (0.4ml/kg and 0.8ml/kg) did not produce any significant increases in lipid peroxidation in the liver. Three different doses of acetaminophen (30mg/kg, 100mg/kg, and 500mg/kg) were administered to rats for seven days. Acetaminophen (500mg/kg) was shown to significantly increase (p<0.05) lipid peroxidation in the liver. Melatonin (2.5mg/kg) was not able to significantly reduce the damage. The lower doses of acetaminophen (30mg/kg and 100mg/kg) did not increase lipid peroxidation. Electron microscopy studies showed that DMF adversely affects the liver, and in particular, the endoplasmic reticulum. Co administration of melatonin (2.5mg/kg) was able to reduce the damage. Further experiments need to be performed before an accurate assessment can be made on the ability of melatonin as an antidote for DMF and acetaminophen poisoning. Several experiments were done in an attempt to uncover the biochemical mechanism underlying acetaminophen addiction and abuse. The first experiment targeted the liver enzyme tryptophan-2,3-dioxygenase (TDO). This enzyme is the major determinant of tryptophan levels in vivo. Acetaminophen administration (100mg/kg for three hours) was shown to significantly inhibit (p<0.05) the activity of TDO, indicating increased peripheral levels of tryptophan. This experiment was followed up with determination of brain serotonin and pineal melatonin. Brain serotonin was determined using the ELISA technique. Melatonin was estimated using this technique as well as with pineal organ culture. Acetaminophen administration (100mg/kg for three hours) significantly increased (p<0.05) brain serotonin levels. Using organ culture where exogenous (3H) tryptophan is metabolised to (3H) melatonin, acetaminophen (100mg/kg for three hours) was shown to significantly increase (p<0.05) pineal melatonin concentrations. However, the ELISA technique did not reveal any changes in endogenous pineal melatonin levels. The final experiment was the determination of urinary 5-hydroxyindole acetic acid (5- HIAA), the major metabolite of serotonin, following acetaminophen administration (100mg/kg for three hours). Acetaminophen was shown to significantly reduce 5-HIAA levels (p<0.05) suggesting reduced catabolism of serotonin. The findings of this study indicate that acetaminophen mimics the actions of an antidepressant. This compelling finding has important clinical implications, and needs to be examined further.
- Full Text:
- Date Issued: 2000
An investigation into the anxiolytic properties of melatonin in humans
- McCallaghan, Johannes Jacobus
- Authors: McCallaghan, Johannes Jacobus
- Date: 1999
- Subjects: Melatonin , Pineal gland -- Secretions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3772 , http://hdl.handle.net/10962/d1003250 , Melatonin , Pineal gland -- Secretions
- Description: The purpose of this project was to investigate the role of melatonin in the pathophysiology of anxiety in humans. The literature study confirmed the intimate relationship between serotonin and melatonin. Melatonin is not only able to act as an agonist (in physiological concentrations) and an antagonist (at higher concentrations) on serotonin receptors but via control of brain pyridoxal kinase activity might have an effect on GABA, serotonin, dopamine and norepinephrine synthesis. A clinical trial to investigate melatonin's effect on anxiety in humans was conducted as a pilot study. Thirty patients complaining of anxiety participated in a liN of 1" double blind placebo controlled trial. During the experiment each subject was thus exposed to melatonin and a placebo for a week at a time on two occasions. During the first phase of the experiment, (Pair '1) patients showed a statistically significant reduction in their anxiety levels during the first period (P1P1), which was not the case during the second period (P1P2). The improvement however continued during the second phase of the experiment (Pair 2) so that there was also a statistically significant improvement during P 2 P 2 (Period 2 / Pair 2) when placebo was administered. It could not conclusively be shown that melatonin was responsible for the improvement in the patients' anxiety. The explanation for these results suggests thelt the improvement was due to a: 1) placebo effect throughout, 2) psychotherapeutic effect due to contact with a clinician, 3) melatonin induced phase shift in the patient's endogenous melatonin response curve, 4) combination of all 3 options. This pilot study lays the groundwork for a much more exhaustive study in which the melatonin of the patients is determined before melatonin is administered, the role of the clinician is clarified and the most appropriate time for melatonin administration is sought .
- Full Text:
- Date Issued: 1999
- Authors: McCallaghan, Johannes Jacobus
- Date: 1999
- Subjects: Melatonin , Pineal gland -- Secretions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3772 , http://hdl.handle.net/10962/d1003250 , Melatonin , Pineal gland -- Secretions
- Description: The purpose of this project was to investigate the role of melatonin in the pathophysiology of anxiety in humans. The literature study confirmed the intimate relationship between serotonin and melatonin. Melatonin is not only able to act as an agonist (in physiological concentrations) and an antagonist (at higher concentrations) on serotonin receptors but via control of brain pyridoxal kinase activity might have an effect on GABA, serotonin, dopamine and norepinephrine synthesis. A clinical trial to investigate melatonin's effect on anxiety in humans was conducted as a pilot study. Thirty patients complaining of anxiety participated in a liN of 1" double blind placebo controlled trial. During the experiment each subject was thus exposed to melatonin and a placebo for a week at a time on two occasions. During the first phase of the experiment, (Pair '1) patients showed a statistically significant reduction in their anxiety levels during the first period (P1P1), which was not the case during the second period (P1P2). The improvement however continued during the second phase of the experiment (Pair 2) so that there was also a statistically significant improvement during P 2 P 2 (Period 2 / Pair 2) when placebo was administered. It could not conclusively be shown that melatonin was responsible for the improvement in the patients' anxiety. The explanation for these results suggests thelt the improvement was due to a: 1) placebo effect throughout, 2) psychotherapeutic effect due to contact with a clinician, 3) melatonin induced phase shift in the patient's endogenous melatonin response curve, 4) combination of all 3 options. This pilot study lays the groundwork for a much more exhaustive study in which the melatonin of the patients is determined before melatonin is administered, the role of the clinician is clarified and the most appropriate time for melatonin administration is sought .
- Full Text:
- Date Issued: 1999
An investigation into the neuroprotective properties of melatonin
- Authors: Southgate, Garrick Steven
- Date: 1999
- Subjects: Melatonin
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3900 , http://hdl.handle.net/10962/d1003959
- Description: 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.
- Full Text:
- Date Issued: 1999
- Authors: Southgate, Garrick Steven
- Date: 1999
- Subjects: Melatonin
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3900 , http://hdl.handle.net/10962/d1003959
- Description: 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.
- Full Text:
- Date Issued: 1999
Pineal-adrenal gland interactions in search of an anti-stressogenic role for melatonin
- Authors: Van Wyk, Elizabeth Joy
- Date: 1993
- Subjects: Pineal gland -- Secretions , Melatonin , Adrenal glands , Pineal gland -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4054 , http://hdl.handle.net/10962/d1004115 , Pineal gland -- Secretions , Melatonin , Adrenal glands , Pineal gland -- Research
- Description: The multiple functions of the pineal gland have been collectively interpreted as constituting a general anti-stressogenic role. The adrenal glands play a central role in maintaining homeostasis. The major neuroendocrine consequence of long-term stress is elevated circulating glucocorticoid levels. In this study, the effect of chronic, oral hydrocortisone treatment on pineal biochemistry was investigated in male Wi star rats of the albino strain. The results show that seven days of oral hydrocortisone treatment endows the pineal gland with the ability to increase melatonin synthesis in organ culture. The increase is accompanied by a rise in NAT activity, cyclic AMP levels and enhanced specific binding to the pineal B-adrenergic receptors. It appears that hydrocortisone sensitizes the pineal gland to stimulation by B-adrenergic agonists. thus rendering the pineal more responsive to B-adrenergic agonists. Further studies were directed at demonstrating an anti-stressogenic function for the pineal gland by investigating whether the principal pineal indole, melatonin. could protect against the deleterious effects of elevated. circulating drocortisone levels. The results show that chronic, oral hydrocortisone treatment significantly increases liver tryptophan pyrrolase activity. The catabolism of tryptophan by tryptophan pyrrolase is an important determinant of tryptophan availability to the brain, and therefore, brain serotonin levels. The findings show that melatonin inhibits basal and hydrocortisone-stimulated liver tryptophan pyrrolase apoenzyme activity in a dose-dependent manner. This inhibition suggests that melatonin may protect against excessive loss of tryptophan from circulation and against deficiencies in the cerebral serotinergic system which are associated with mood and behavioural disorders. It was shown that another deleterious effect of chronic hydrocortisone treatment is a significant increase in the number of glutamate receptors in the forebrain of male Wistar rats. The increase in receptor number observed in this study is probably due to an increase in the synthesis of glutamate receptors and is associated with a marked reduction in the affinity of the glutamate receptors for glutamate. possible to demonstrate an receptor number or the For practical reasons, it was not effect of melatonin on either glutamate affinity of glutamate receptors for glutamate in rat forebrain membranes. In view of the neurotoxic effect of glutamate in the eNS, the functional significance of recently described glutamate receptors in the pineal gland was investigated. The results show that 10-4 M glutamate significantly inhibits the isoprenaline-stimulated synthesis of N-acetylserotonin and melatonin in organ culture when the pineal glands were pre-incubated with glutamate for 4 hours prior to stimulation with isoprenalin and when glutamate and isoprenaline were administered together in vitro. GABA, a glutamate metabolite could not mimic the decrease in isoprenalinestimulated melatonin, and it is likely that the observed effects were directly attributed to glutamate. Incubation of the pineal gland with 10-4 M glutamate in organ culture did not affect HIOMT activity in pineal homogenates, but significantly elevated both basal and isoprenaline-stimulated NAT activity. It was concluded that glutamate only inhibits melatonin synthesis in intact pineal glands and not in pineal homogenates. The present study has provided further support for an interaction between the pineal and the adrenal glands. There is an ever increasing likelihood that melatonin is an anti-stressogenic hormone and that the pineal gland may have a protective role to play in the pathology of stress-related diseases.
- Full Text:
- Date Issued: 1993
- Authors: Van Wyk, Elizabeth Joy
- Date: 1993
- Subjects: Pineal gland -- Secretions , Melatonin , Adrenal glands , Pineal gland -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4054 , http://hdl.handle.net/10962/d1004115 , Pineal gland -- Secretions , Melatonin , Adrenal glands , Pineal gland -- Research
- Description: The multiple functions of the pineal gland have been collectively interpreted as constituting a general anti-stressogenic role. The adrenal glands play a central role in maintaining homeostasis. The major neuroendocrine consequence of long-term stress is elevated circulating glucocorticoid levels. In this study, the effect of chronic, oral hydrocortisone treatment on pineal biochemistry was investigated in male Wi star rats of the albino strain. The results show that seven days of oral hydrocortisone treatment endows the pineal gland with the ability to increase melatonin synthesis in organ culture. The increase is accompanied by a rise in NAT activity, cyclic AMP levels and enhanced specific binding to the pineal B-adrenergic receptors. It appears that hydrocortisone sensitizes the pineal gland to stimulation by B-adrenergic agonists. thus rendering the pineal more responsive to B-adrenergic agonists. Further studies were directed at demonstrating an anti-stressogenic function for the pineal gland by investigating whether the principal pineal indole, melatonin. could protect against the deleterious effects of elevated. circulating drocortisone levels. The results show that chronic, oral hydrocortisone treatment significantly increases liver tryptophan pyrrolase activity. The catabolism of tryptophan by tryptophan pyrrolase is an important determinant of tryptophan availability to the brain, and therefore, brain serotonin levels. The findings show that melatonin inhibits basal and hydrocortisone-stimulated liver tryptophan pyrrolase apoenzyme activity in a dose-dependent manner. This inhibition suggests that melatonin may protect against excessive loss of tryptophan from circulation and against deficiencies in the cerebral serotinergic system which are associated with mood and behavioural disorders. It was shown that another deleterious effect of chronic hydrocortisone treatment is a significant increase in the number of glutamate receptors in the forebrain of male Wistar rats. The increase in receptor number observed in this study is probably due to an increase in the synthesis of glutamate receptors and is associated with a marked reduction in the affinity of the glutamate receptors for glutamate. possible to demonstrate an receptor number or the For practical reasons, it was not effect of melatonin on either glutamate affinity of glutamate receptors for glutamate in rat forebrain membranes. In view of the neurotoxic effect of glutamate in the eNS, the functional significance of recently described glutamate receptors in the pineal gland was investigated. The results show that 10-4 M glutamate significantly inhibits the isoprenaline-stimulated synthesis of N-acetylserotonin and melatonin in organ culture when the pineal glands were pre-incubated with glutamate for 4 hours prior to stimulation with isoprenalin and when glutamate and isoprenaline were administered together in vitro. GABA, a glutamate metabolite could not mimic the decrease in isoprenalinestimulated melatonin, and it is likely that the observed effects were directly attributed to glutamate. Incubation of the pineal gland with 10-4 M glutamate in organ culture did not affect HIOMT activity in pineal homogenates, but significantly elevated both basal and isoprenaline-stimulated NAT activity. It was concluded that glutamate only inhibits melatonin synthesis in intact pineal glands and not in pineal homogenates. The present study has provided further support for an interaction between the pineal and the adrenal glands. There is an ever increasing likelihood that melatonin is an anti-stressogenic hormone and that the pineal gland may have a protective role to play in the pathology of stress-related diseases.
- Full Text:
- Date Issued: 1993
The evaluation of melatonin as a possible antidepressive
- Authors: Skene, Debra Jean
- Date: 1980
- Subjects: Melatonin , Antidepressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3728 , http://hdl.handle.net/10962/d1001465
- Description: 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
- Full Text:
- Date Issued: 1980
- Authors: Skene, Debra Jean
- Date: 1980
- Subjects: Melatonin , Antidepressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3728 , http://hdl.handle.net/10962/d1001465
- Description: 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
- Full Text:
- Date Issued: 1980
- «
- ‹
- 1
- ›
- »