Dickinson, Keith (1987) Receptor mechanisms in olfaction. PhD thesis, University of Warwick.

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Abstract

This thesis is a study of receptor-mediated events occurring in olfaction. Potential enzymes involved in olfactory transduction were investigated using standard biochemical techniques, and an investigation of the fatty acid receptor/s was attempted using psychophysical methods.

1. Other investigators in olfaction have recently demonstrated an odorant modulated adenylate cyclase in the frog. We have shown that tissue preparations from the rat have high levels of the enzyme adenylate cyclase. This activity was stimulated in the presence of odorants by up to two times the basal value. The concentrations of odorants used were in the range expected to be physiologically relevant. Both basal and stimulated adenylate cyclase were inhibited by μM calcium ion. Tissue preparations from brain showed no odorant activation. Guanylate cyclase was present at a tenth the concentration of adenylate cyclase and showed no odorant simulation.

2. There are no studies in the literature characterising the cyclic nucleotide phosphodiesterases in olfactory tissue. The Sutherland criteria require the presence of a cyclic nucleotide phosphodiesterase (PDE) in olfactory tissue, if cyclic AMP is to be a second messenger in olfaction. It is possible that olfactory PDE is directly regulated by a receptor, as is found in vision. It is important, therefore, that the PDE’s in olfactory tissue are characterised.

Tissue preparations of the rat and sheep were shown to have high levels of cyclic nucleotide phosphodiesterase. The activities were not stimulated in the presence of physiologically relevant concentrations of odorants; inhibition of these activities by odorants was not significantly different from that of brain homogenates. Characterisation of the phosphodiesterase isoenzymes separated by DEAE chromatography established that they resembled the isoenzymes characterised from other tissues. The evidence presented indicates that olfactory tissue does not resemble visual tissue, which has a receptor-linked phosphodiesterase. All evidence suggests that PDE’s in olfactory tissue serve to return cyclic nucleotide concentrations to resting levels after stimulation. The observation that the Type 1 (calcium/calmodulin stimulated) phosphodiesterase is present in high concentrations in olfactory tissue suggests that calcium ion concentration in vivo may be an important regulator of phosphodiesterase activity.

3. The threshold values of various short chain fatty acids, of high purity, were determined using human subjects. The results were one order of magnitude greater than found by Amoore (1970) but showed a similar group trend. Descriptive analysis was also performed on these acids by generating a series of descriptors sufficient to discriminate between the acids. Analysis of the results by principal component analysis yielded a three dimensional map that showed the acids clustering into four groups. These four groups could indicate the presence of four receptors. Attempts to demonstrate structure-activity relationships between the thresholds, and descriptive analysis results with various physical and chemical parameters, failed. This was probably due to the interaction of the acids with more than one receptor.

So far, the lack of success in identifying olfactory receptors by researchers has meant that investigations of olfactory receptors have had to be done using psychophysical techniques such as those used in this report. It will probably not be known if these methods are useful for identifying receptors, until the receptors can be purified and characterised biochemically.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QP Physiology
Library of Congress Subject Headings (LCSH):	Smell -- Physiological aspects, Olfactory receptors, Cyclic nucleotides, Adenylate cyclase, Cellular signal transduction
Official Date:	October 1987
Dates:	Date Event October 1987 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dodd, G. H.
Sponsors:	Agricultural and Food Research Council (Great Britain) ; Unilever (Firm)
Format of File:	pdf
Extent:	x, 158 leaves : illustrations, charts
Language:	eng

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