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Title: Response to aluminium at neutral pH in the freshwater snail Lymnaea stagnalis.
Author: Campbell, Morag Mackenzie.
ISNI:       0000 0001 3517 4594
Awarding Body: University of Manchester : University of Manchester
Current Institution: University of Manchester
Date of Award: 1998
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(1) The hypothesis underlying this research is that the bioavailability and toxicity of Al at neutral pH are dependent on its chemical form. Different compounds of Al may therefore have differential effects. The aim of the research presented in this thesis was to use the freshwater snail Lymnaea stagnalis (L.) to examine the effect of different Al compounds on water concentrations, bioaccumulation, behaviour and neuronal activity. Silicon is known to limit availability and ameliorate toxicity of AI. A further aim was therefore to investigate any changes in the response to Al in the presence of Si. (2) When Al was added as Al nitrate or Al lactate, Al water concentrations fell over 48 hours, probably as a result of hydroxyprecipitation. The presence of L. stagnalis caused a further reduction in Al water concentrations, even when loss of Al as a result of accumulation by the snails was taken into account. This increase in loss is suggested to be due to the presence of extracellular mucopolysaccharides secreted by the snails. Snails exposed to Al nitrate or Al lactate for 48 hours significantly accumulated AI. The gut is suggested to be the main route of uptake of Al and with snails accumulating Al as a result of ingesting insoluble AI. When Al was added as Al maltol, Al water concentrations remained high and accumulation by the snails was reduced. This suggests reduced bioavailability of Al when bound to maltol. The presence of Si increased the rate of loss of Al from the water column; however, this effect was masked in the presence of snails. The presence of Si had no significant effect on accumulation of Al by L. stagnalis. (3) Changes in the behaviour of L. stagnalis in response to exposure to Al nitrate, Al lactate and Al maltol (500 Jlgr1 ) were investigated. Depression of feeding behaviour and behavioural state score were observed after 2 to 14 days of continuous exposure, regardless of the form of AI. However, there was some evidence to suggest differences in the timing of behavioural changes depending on the Al compound to which snails were exposed. In some experiments behavioural changes in response to Al maltol occurred later than those in response to the other Al compounds. Differences in timing may be due to differences in bioavailability. The presence of Si ameliorated the toxic effects of Al on behaviour, although the concentration of Si was found to be critical. Concentrations of Si above 100 JlM protected against the toxic effects of Al on behaviour while concentrations below 100 JlM did not. (4) The effects of different Al compounds on the electrophysiological properties of an identified neuron (right parietal dorsal 1; RPD I) in the isolated CNS of L. stagnalis were examined. Extracellular addition of Al chloride or Al lactate (100 JlM) had marked and long lasting effects which included an increase or induction of irregular firing activity in the form of action potentials fired singly or in bursts. There was also an increase in the frequency and amplitude of synaptic inputs. These effects were accompanied by a slow depolarisation and changes in action potential shape and size. Extracellular addition of Al maltol (100 JlM) caused no significant changes. These differential effects are suggested to be due to differences in the bioavailability of the Al compounds. The presence of Si had no ameliorative effect on the electrophysiological changes produced in RPD 1 in response to Al lactate. (5) The results obtained in this study support the hypothesis that different Al compounds have differential effects. The results are discussed in relation to previous studies on Al toxicity and, in particular, to studies on the solution chemistry of the Al compounds used.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available