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Investigation into the molecular basis of diabetes-induced erectile dysfunction was carried out on corpus cavernosum tissue from control and streptozotocin (STZ)-induced diabetic rats. Increased expression of endothelial nitric oxide synthase (eNOS) and increased nitrosative stress was found in the diabetic penile tissue. Diabetic neuropathy is associated with a failure in axonal regeneration. In vitro axon growth, guidance and regeneration model systems were used to study both the intrinsic nature of diabetic DRG neurones to grow and respond to guidance cues, but also to study the supportive properties of the diabetic nerve environment for axon regeneration. Cyclic Adenosine-3’5-Monophosphate (cAMP) signalling is compromised in diabetic DRG neurones. Increasing cAMP in diabetic neurones reduced the deficit in neurite growth and reversed the aberrant response of diabetic neuronal growth cones to the cAMP-dependent trophic factor, nerve growth factor (NGF). Diabetic neurones display reduced expression of Exchange protein activated by cAMP (Epac), a downstream effector of cAMP. Specifically activating Epac also rescued the abnormal turning responses of diabetic DRG neurones. Impaired axonal regeneration in diabetes has been, in part, attributed to delayed Wallerian degeneration. Using the cryoculture bioassay, it was shown that during regeneration the peripheral nerve environment, of both control and diabetic rats are equally supportive for axon growth. In summary, this is the first study to imply that specific signalling mechanisms, involving the cAMP-Epac pathway, may be compromised in neurones from diabetic rats, which contribute towards reduced neurite growth and abnormal responses to axon guidance cues.

In this thesis we show that Saturn’s magnetopause and bow shock oscillate with a period near that of planetary rotation that we term the ‘magnetospheric period’. In our first study, using two Cassini orbits as exemplars, we demonstrate that Saturn’s magnetopause oscillates at the magnetospheric period in response to changes in the magnetospheric pressure. The change in internal pressure required to produce such oscillations, which typically correspond to a ~10% change in the boundary radius, is estimated to be ~30-40% of the unperturbed background pressure. In our second study we develop a simple theoretical model of motion through an oscillating planar boundary that is equally applicable to the magnetopause and the bow shock. In our third study we use data from ~40 Cassini orbits to conduct a first systematic investigation of the magnetospheric period magnetopause oscillations. We show that boundary oscillation events are highly organized by the phase of the magnetic oscillations in the ‘core’ region of the magnetosphere. When radial propagation is accounted for, the phase of maximum outward boundary displacement is found to be directly related to the phase of the density maximum in the Enceladus torus. The boundary oscillation amplitude is estimated to be ~1.2 Saturn radii, but is occasionally as great as ~4-5 Saturn radii. In our fourth study we use data from 35 Cassini orbits that crossed both the magnetopause and the bow shock to provide first evidence for magnetospheric period bow shock oscillations. We find that the oscillations are significantly organized by the phase of the ‘core’ magnetosphere magnetic oscillations, though the degree of organization is less than for the magnetopause. The bow shock and magnetopause are found to oscillate approximately in phase within a phase uncertainty of about ± 25° and to have similar oscillation amplitudes.

This thesis describes the construction and analysis of a cosmid library specific for the human Y chromosome. The purpose of preparing such a library is to provide a source of ordered overlapping clones for use in the identification of genes, analysis of chromosome structure, and perhaps, as a starting point for the sequencing of the chromosome. Approximately 2,000 cosmid clones containing inserts derived from human DNA have been identified in a library prepared from a somatic cell hybrid containing the Y chromosome as the only human material. These clones have been analysed in two principal ways. Firstly, hybridisation to various characterised DNA fragments has identified cosmids containing known repeat elements and single copy DNA sequences which have been previously assigned to regions of the chromosome by deletion mapping. Secondly, a unique 'fingerprint' has been produced for each clone; band patterns of Hint I digestion products separated by polyacrylamiae gel electrophoresis have been analysed by computer to detect overlapping clones. A significant proportion of the chromosome is represented in this way.

Dental caries is a dynamic process rather than a diagnosis. It is therefore inappropriate to cite an exact 'threshold' at which interventive operative dental care becomes the 'correct' treatment option. This thesis explored this problem by applying decision theory to one diagnostic test for caries - namely the bitewing radiograph. Fifteen 'mock' dentitions were assembled, using materials of similar radiodensity to oral structures. A number of cariously involved teeth were included in these dentitions. Radiographs were taken using a standardised technique to ensure that the quality and density of the simulated radiographs were as similar as possible to those taken 'in vivo'. Twenty dental practitioners each made 360 treatment decisions based on these bitewing radiographs. Subsequently the teeth were serially sectioned, examined histologically, and the extent of any caries in each tooth was recorded and correlated with the visual appearance of the tooth surfaces. The dentists' decisions were then subjected to Receiver Operator Characteristic (ROC) and Kappa analysis. The work described also explored the value placed on various tooth-states by the population. By using the available literature and the results of the two studies described above, a decision tree was constructed which permitted examination of the expected values of treatment decisions. This decision analysis allowed recommendations to be made concerning the setting of treatment thresholds. The first part of the study showed that the microscopic, radiographic and visual appearances of a tooth were not always directly related to one another. The analysis of the dentists' decisions indicated that individual practitioners have differing views about the importance of sensitivity and specificity, and therefore have different thresholds at which they institute treatment. These values and attitudes influenced the treatment decisions made to a greater extent than the dentists' views about the depth of lesion needing restoration. The decision analysis indicated that, for the sample populations of dentists and patients investigated, the detectability of caries on bitewing radiographs was not great enough to warrant their routine use as diagnostic tools. The treatment thresholds held by the group of dentists in the study were inappropriate in relation to the utilities for dental health held by the population examined. This study has highlighted the importance of three methods of evaluating diagnostic tests. It has shown that the values dentists place on the outcomes of their decisions affect their treatment thresholds more profoundly than lesion depth. Therefore restorative treatment thresholds should be reviewed and appropriate training given so that dental diagnostic skills are improved and clinical decisions made according to the values that patients hold.

Intracellular microelectrodes were used in conjunction with ion substitution, agonists and inhibitors of known transport processes and diuretic hormone (DH), to investigate the mechanisms whereby ions cross the basal and apical cell membranes of the Malpighian tubules of Locusta migratoria, and their endocrine control. Values for basal, apical and transepithelial potentials in control saline were -70.4 + 0.9 mV, -76.1 ± 1.5 mV and +5.5 ± 1.3 mV (lumen positive), respectively (n=73).Ion substitution experiments, involving K(^+), Na(^+) and CI(^-) in the bathing medium, indicated that the basal membrane is more permeable to K(^+) than Na(^+) and CI(^-). Ion flux studies suggest that CI(^-) entry across the basal membrane is not by direct cotransport with K(^+), nor Na(^+). Some CI(^-) entry also appears to be stimulated under conditions of high K(^+)(_o). Crude corpus cardiacum (CC) preparations with DH activity effected ca. 150% increase in tubular fluid secretion above basal secretion in vitro, and ca. 106% and 335% increase in net transepithelial Na(^+) and Cl(^-) movement from bathing medium to lumen above basal flux, respectively. Treatment of tubules with CC extract also resulted in a significant increase in levels of the intracellular second messengers, cAMP and the Ca(^2+)-mobilizing Inositol 1,4,5- trisphosphate. Ion substitution experiments using dibutyryl cAMP suggest that cAMP stimulates an apical cation pump, whilst having no effect on Cl(^-) conductance. Cytochemical localization and membrane separation techniques used in conjunction with biochemical analyses indicate the presence of (Na(^+)+K(^+))-ATPase on the basolateral membranes, and HCO(_3)- stimulated ATPase on both the basolateral and apical membranes. The results referred to above are discussed, and a hypothetical model is proposed to describe the endocrine control of ion movements across the two cell membranes mediated by changes in intracellular cAMP and Ca(^2+).

The characteristics of photosynthesis and inorganic carbon accumulation were investigated in two species of marine intertidal macroalgae: Porphyxa umbilicalis and Ulva lactuca. Both species have a similar mid-intertidal location, although P. umbilicalis grows on bare rock faces while U. 1actuca-is found submersed-in rock pools. The similar morphology of the species allows a direct comparison of both the gas exchange and the light response characteristics. For P. umbilicalis-the low light compensation and saturation points are comparable to the light requirements of shade adapted terrestrial plants. Photosynthetic capacity is greater-in seawater although the efficiency of light utilization is no higher than that in air. In the summer population, however, the photosynthetic response is reduced. In the absenceof-any corresponding effect on the the light requirements, this-can be related in part to seasonal variation in the-total chlorophyll concentration. Even after acclimation the summer-population can be photoinhibited by periods of excess PAR. P. umbilicalis is capable of using both HC03 and C02 as a substrate for photosynthesis. The maximum photosythetic capacity is greater in air, and corresponds to a higher affinity-for'C02. The gas exchange characteristics are 02-insensitive indicating low photorespiratory activity in this species. The-suppression of RuBPc-oxygenase may be attributable, to-an effective method of inorganic carbon uptake. The mechanism in P. umbilicalis involves the diffusive uptake of C02, supplied directly or by the Carbonic Anhydrase (CA) dependent catalysis of HC03-, external to the plasma membrane. An intracellular CA maintains the rate of transfer of inorganic carbon to the site C02 fixation in the chloroplast. U. 1actuca shows very similar light response characteristics to those of P. umbilicalis. The low light-requirements are the same as for the summer population, while the decrease in the Vmax of the response is again independent of an effect on the photosynthetic efficiency. The change in the capacity corresponds to a seasonal variation in the total chlorophyll content and corresponding ratio of chlorophyll a: b. Photoinhibition of the photosynthetic response significantly alters the characteristics of the light response, even though this species has the ability to maintain efficient rates of carbon fixation. In U. 1actuca the mechanism of inorganic carbon accumulation involves the direct uptake of both HC03- and C02, independent of any external CA activity. C02 will diffuse across the plasma membrane, while HC03- must be actively transported. Internal CA activity modifies the photosynthetic capacity of this species although more than one possible location is proposed for this enzyme. The difference in the characteristics of photosynthesis and inorganic carbon accumulation may be determined by the specific habitat of the two species. P. umbilicalis, more often exposed, shows a greater photosynthetic efficiency in air and a higher affinity for C02. In contrast, the photosynthetic system in U. 1actuca appears to be adapted to longer periods of submersion. In relation to the inorganic carbon accumulating mechanism, there is evidence that those marine intertidal macroalgae more often exposed have a greater affinity for C02, dependent to a degree on the activity of an external CA.