In a continuing effort to develop a noninvasive means of monitoring glucose levels using the aqueous humor of the eye, a dual wavelength system has been developed in order to show that varying birefringence, similar to what is seen with a moving cornea, can be compensated. In this paper a dual wavelength, closed-loop, system was designed and a model was developed to extract the glucose concentration information. The system and model were tested using various concentrations of glucose in a birefringent test cell subject to motion artifact. The results show that for a static, non-moving sample, glucose can be predicted to within 10 mg/dl for the entire physiologic range (0-600mg/dl) for either laser wavelength (523nm or 635nm). In the presence of moving birefringence, each individual wavelength produced standard errors on the order of a few thousand mg/dL. However, when the two wavelengths are combined into the developed model, this error is less than 20mg/dL. The approach shows that multiple wavelengths can be used to drastically reduce the error in the presence of a moving birefringent sample. This research also shows promising preliminary results that the error is less than 25mg/dl in presence of a motion induced cornea birefringence artifact in NZW rabbits’ eyes.

No description available.

Clinical guidelines dictate that frequent blood glucose monitoring in diabetic patients is critical towards proper management of the disease. Although, several different types of glucose monitors are now commercially available, most of these devices are invasive, thereby adversely affecting patient compliance. To this end, optical polarimetric glucose sensing through the eye has been proposed as a potential noninvasive means to aid in the control of diabetes. Arguably, the most critical and limiting factor towards successful application of such a technique is the time varying corneal birefringence due to eye motion artifact. In the first part of this research, we describe a birefringent ocular model along with a geometric ray tracing scheme to serve as a tool towards better understanding of the cornea’s birefringence properties. The simulations show that index-unmatched coupling of light is spatially limited to a smaller range when compared to index-matched situation. Polarimetric measurements on rabbits’ eyes indicate relative agreement between the modeled and experimental values of corneal birefringence. In addition, the observed rotation in the plane of polarized light for multiple wavelengths demonstrates the potential for using a dual-wavelength polarimetric approach to overcome the noise due to time-varying corneal birefringence. These results will ultimately aid in the development of an appropriate eye coupling mechanism for in vivo polarimetric glucose measurements. The latter part of the dissertation focuses on design and development of a dual wavelength optical polarimeter. The described system utilizes real-time closed-loop feedback based on proportional-integral-derivative (PID) control, which effectively reduced the time taken by the system to stabilize while minimizing the effect of motion artifact, which appears as common noise source for both the wavelengths. Glucose measurements performed in both in vitro and ex vivo conditions demonstrate the sensitivity of the current system. Finally, in vivo results in rabbits indicate that dual-wavelength polarimetry has the potential to noninvasively probe glucose through the anterior chamber of the eye.

No description available.

Diabetes mellitus is a potentially lethal disease that affects 7.6 percent of American people. In the US, it is recognized as the 6th leading cause of death. Failure to control blood glucose levels (BGL) in patients with either type of diabetes can lead to other serious complications as well, such as loss of limb, blindness and other health problems. Controlling and monitoring the BGL in post-op and intensive care patients in the hospital is also vital to their health. Currently the most reliable method of monitoring BGL is through an invasive procedure which monitors the amount of glucose in blood directly. A non-invasive glucose sensor would drastically improve the treatment of sensitive patients, and serve to improve the quality of diabetic patients' lives. This glucose sensor is strongly based upon the mercury sensor developed by F.E. Hernandez and his colleagues. Glucose is used as a reducing agent to reduce mercury from Hg2+ to Hg0, which will form amalgams with the gold nanorods in solution. The change in aspect ratio of gold nanorods leads to a change in the UV-Visible spectrum of the solution. The blue shift seen was measured and correlated with the glucose concentration of the system. The system was then tested varying conditions such as pH, temperature, gold nanorod concentration, and mercury concentration. A preliminary study of the kinetics of the reaction was also done. The results showed a limit of detection of 1.58x10-13 and a linear dynamic range covering the concentrations of human tear glucose levels that are currently cited in the literature.

Animal and human studies have consistently demonstrated that recurrent hypoglycaemia (RH) blunts both hormonal and behavioral counter regulatory responses (CRR) to further episodes of hypoglycaemia. It is now well established that the brain is involved in regulating whole-body glucose homeostasis, including the CRR to hypoglycaemia. The aim of the current study was to investigate if adaptations occur, following RH, which are intrinsic to glucose-sensing neurons in the absence of synaptic/glial inputs or signals from the periphery. Utilising the GT1-7 hypothalamic mouse cell line as an in vitro model of homogenous glucose-excited neurons, the current study has demonstrated that recurrent low glucose exposure reprograms intracellular metabolism towards a “hypometabolic state”. This result occurs in conjunction with an attenuated ability of the cells to hyperpolarise in response to low glucose and a reduction in the sensitivity of the KATP channel to activation by MgADP. In an attempt to reverse the changes observed in KATP channel activity, the SUR1-selective KATP channel opener, NN414, was applied chronically to GT1-7 cells. However, chronic KATP channel activation severely reduced channel conductance and sensitivity to activation by MgADP and further NN414 application. These results suggest that chronic activation of the KATP channel leads to the induction of a negative feedback mechanism to reduce channel activity. This may be in an attempt to maintain neuronal membrane potential within a physiological range. These results also suggest activation of central KATP channels during RH may be driving the resulting defective CRR. However, adaptations in metabolism following RH may also be altering the function of central KATP channels.

Metabolic coupling between glial cells and neurons is essential for neuronal function. It is a well-conserved and vital feature of the bilaterian nervous system as well. Under normal and adverse conditions, glial cells act as a major metabolic hub fueling neuronal oxidative metabolism by producing lactate or ketone bodies. I now ask the question of whether such metabolic coupling is only necessary for preserving brain homeostasis or if it could also have implications in decision making such as food choice behavior. Choosing an appropriate food source is key for the survival of an organism. Carbohydrates are the preferred source of energy and thus evaluation of their nutritive content is essential. Several studies have demonstrated that Drosophila melanogaster larvae and adults, as mammals, can distinguish between nutritious and non-nutritious carbohydrates independent of their taste. Two groups of neurons, Diuretic Hormone 44 (Dh44)-expressing neurons and gustatory receptor 43a (Gr43a)-expressing neurons, have been implicated in postprandial sugar sensing in adult flies. Gr43a- expressing neurons are narrowly fine-tuned for sensing fructose in both adults and larvae. Nonetheless, in the larva, central nervous system (CNS) Gr43a neurons have been shown to act as the main sugar sensor. This raises the question of how CNS fructose-sensing neurons are involved in sensing non-fructose dietary sugars. To decipher this post-ingestive mechanism, I used frustrated total internal reflection (FTIR) - based larval tracking to investigate larval food choice behavior. The results present in this thesis suggest that besides Gr43a-expressing neurons, glial cells are indispensable for sensing nutritive non-fructose dietary sugars such as glucose and sorbitol. I show that post-ingestive carbohydrate sensing involves carbohydrate conversion into fructose locally in the glial cells. Glia-derived fructose then enables Gr43a-dependent postprandial carbohydrate sensing in the CNS and drives carbohydrate preferences with the help of the downstream signalling peptide corazonin. Thus, in post-ingestive carbohydrate sensing, the glial cells act as a master metabolite sensor and provide a fructose stimulus to neurons to regulate behavior.:Table of Contents Abstract 1 Zusammenfassung 2 1. Introduction 3 1.1. External Nutrient Sensing in mammals and Drosophila melanogaster 4 1.1.1. Taste detection in mammals 4 1.1.2. Taste detection in Drosophila melanogaster 6 1.1.3 Sweet and Umami Taste in mammals 8 1.1.4. Sweet Sensing in Drosophila melanogaster 8 1.1.5. Bitter Taste in mammals 9 1.1.6. Bitter Sensing in Drosophila melanogaster 9 1.1.7. Sour, Carbonation, Fatty acid and Salty taste in mammals 9 1.1.8. Amino acid, Fatty acid and Salt Sensing in Drosophila melanogaster 10 1.2 Post-ingestive nutrient sensing in mammals and Drosophila melanogaster 11 1.2.1. Post-ingestive amino acid sensing in mammals 11 1.2.2. Post-ingestive amino acid sensing in Drosophila melanogaster 12 1.2.3. Post-ingestive lipid sensing in mammals 13 1.2.4. Post-ingestive carbohydrate sensing in mammals 13 1.2.4.1. The role of the nervous system in post-ingestive carbohydrate sensing mammals 16 1.2.5. Post-ingestive carbohydrate sensing in Drosophila melanogaster 16 1.2.5.1. The role of the nervous system in post-ingestive carbohydrate sensing in flies 18 1.2.5.2. The role of the nervous system in post-ingestive carbohydrate sensing in larvae 19 1.3 The cellular architecture of the larval nervous system 20 1.3.1 The Blood-brain barrier (BBB) and carbohydrate transport 23 1.4 Aim of study 25 2. Experimental Procedures 26 2.1 Materials 26 2.1.1 Chemicals 26 2.1.2 Media 27 2.1.3 Buffer and Solution 27 2.1.4 Antibodies 28 2.1.5 Flystocks 29 2.2 Methods 33 2.2.1 Fly genetics 33 2.2.1.1 Maintenance and crosses 33 2.2.2 Immunohistochemistry & Microscopy 33 2.2.2.1 Immunohistochemistry of larval filets 33 2.2.2.2 Confocal Microscopy 33 2.3 Experimental Design 34 2.3.1 Studying food choice in Drosophila larvae 34 2.3.1.1 Concept 34 2.3.1.2 Experimental setup 36 2.3.1.3 Analysis 36 2.3.1.4 MATLAB Script 38 3. Results 40 3.1. Frustrated total internal reflection based two-choice assay (TCA) 40 3.1.1 Investigating larval sugar preference 40 3.2 The role of diuretic hormone 44 (Dh44) neurons in post-ingestive glucose sensing in third instar larvae 47 3.2.1 Immunohistochemical analysis of Dh44 in third instar larval brains 47 3.2.2 Role of Dh44 in glucose sensing 49 3.3 The role of gustatory receptor 43a (Gr43a) neurons in post-ingestive nutritive carbohydrate sensing in third instar larvae 51 3.3.1 Immunohistochemical analysis of Gr43a in third instar larval brains 51 3.4. Investigating the role of polyol pathway in post-ingestive carbohydrate sensing 56 3.4.1 Identifying the key polyol pathway enzyme in Drosophila melanogaster 56 3.4.2 Examining RNAi mediated neuronal and glial knockdown of polyol pathway enzymes in postprandial sugar sensing 57 3.4.2.1 CG9436 57 3.4.2.2 CG6084 and CG10863 60 3.4.2.3 Sodh-2 66 3.5 Determining the glia subtypes vital for conducting polyol pathway 69 3.6 The role of the blood brain barrier (BBB) in post-ingestive carbohydrate sensing 74 4. Discussion 80 4.1. Gr43a is the only sugar sensor in Drosophila larvae 80 4.2. Polyol Pathway is crucial for glucose and sorbitol sensing 82 4.3. Glia, the master metabolic sensor 84 4 4. Transport over BBB: a prerequisite for postprandial carbohydrate sensing85 4.5. Proposed model for larval post-ingestive nutritive carbohydrate sensing... 86 5. References 89 6. Abbreviation List 100 7. Appendix 103

Abstract Light scattering diagnostics of turbid media containing both structural and dynamic inhomogeneities is currently of significant importance. One of the important directions in modern light scattering diagnostics is the development of methods for probing biological media with visible- and near-infrared radiation allowing for visualization of the biotissue structure. Optical methods for studying the biotissue structure and characterization of its optical properties are very promising and have been rapidly developing during the past decade. The present work is aimed at improving and discovering new potentials of currently existing methods of laser diagnostics of biological tissues containing both structural and dynamic inhomogeneities. In particular, the feasibilities of spatially resolved reflectometry and time-of-flight techniques for the problem of noninvasive determination of glucose level in human blood and tissues were examined both numerically and experimentally. The relative sensitivities of these methods to changes in glucose level were estimated. Time-of-flight technique was found to be more sensitive. The possibilities of Doppler optical coherence tomography for imaging of dynamic inhomogeneities with high resolution were considered. This technique was applied for the first time for the imaging of complex autowave cellular motility and cytoplasm shuttle flow in the slime mold Physarum polycephalum. The effect of multiple scattering on the accuracy of the measured flow velocity profiles for the case of single flow and for the case of the flow embedded into the static medium with strong scattering was studied. It was shown that this effect causes significant distortion to the measured flow velocity profiles and it is necessary to take this into account while making quantitative measurements of flow velocities.

Une alimentation riche en protéines entraîne une importante diminution de la prise alimentaire, chez l’homme et l’animal, par rapport à une alimentation classique (riche en hydrates de carbones). Les précédents travaux du laboratoire chez le rat montrent que le mécanisme implique une induction de la production intestinale de glucose libéré dans la veine porte. Il s’ensuit un signal qui transite au cerveau via le nerf vague et se traduit par un effet anorexigène. Le régime protéique induit en fait une redistribution de la production endogène de glucose au profit du rein et de l’intestin chez le rat, et au profit de l’intestin et du foie chez la souris. L’effet anorexigène des protéines est présent également chez les souris, confirmant un rôle tout particulier de l’intestin, et du signal glucose portal, dans ce phénomène de satiété. Nos résultats montrent d’ailleurs que le signal glucose portal n’est pas impliqué dans l’augmentation de la production rénale de glucose induite par le régime protéique qui est observée uniquement chez le rat. Les mesures effectuées chez des rats nourris par différents régimes protéiques indiquent l’implication de mécanismes propres à la nature des protéines qui reste à déterminer. De plus nous avons mesuré une augmentation de la sensibilité à l’insuline de la production endogène de glucose chez le rat nourri par le régime protéique. Des études plus approfondies chez la souris devraient permettre de comprendre les mécanismes impliqués. Nos expériences suggèrent par ailleurs que le système mélanocortinergique ne serait pas impliqué dans l’effet anorexigène du régime à long terme mais pourrait constituer un élément important de contre-régulation face à l’hypophagie sévère temporaire provoquée par le changement de régime / Protein feeding is known to decrease hunger and subsequent food intake in animals and humans. Previous data point out the connection between the central nervous system and the intestinal glucose production in the central inhibitorycontrol of food intake by protein feeding. Our study demonstrates that protein feeding induces redistribution of endogenous glucose production to the kidney and intestine in rats and to the intestine and liver in the mouse. Anorexigenic effect of protein diet exists in both animal models, confirming a specific role of the intestine in this satiety phenomenon. Moreover, portal glucose sensing is not involved in the induction of renal glucose production by protein feeding that is only observed in rats. Measurement in rat fed with different protein diets suggest a role of the nature of the protein or structure, but proper mechanisms remain to be clarified. Moreover, protein feeding potentiates the endogenous glucose production suppression by insulin. Some additional studies have to be performed to find the mechanisms that are implicated. Our experiments suggest that the melanocortinergic system wouldn’t be involved in the longterm anorexigenic effect of protein feeding but could constitute an important counter-regulatory pathway against the temporary hypophagia induced by diet change

The central nervous system (CNS) melanocortin signaling pathway plays a critical role in the regulation of metabolism. However, the regulatory effects of CNS melanocortin signaling on hepatic lipid metabolism and fatty liver disease have not been well established. Although the activity of the CNS melanocortin system is regulated by metabolic signals, the mechanism for this regulation is not fully understood. Variants of the FTO (fat mass and obesity-associated) gene are associated with obesity and FTO is expressed in the hypothalamic neurons including proopiomelanocortin (POMC) neurons. Therefore, it is hypothesized that hypothalamic FTO plays a role in the regulation of metabolism by mediating the effect of metabolic signals on hypothalamic melanocortinergic neurons, and that impairments in this regulation may cause metabolic impairments including obesity and fatty liver disease. Intracerebroventricular (i.c.v.) treatment with SHU9119, a melanocortin antagonist, increased hepatic lipid accumulation and the expression of genes encoding lipogenic enzymes in lean mice. Conversely, i.c.v. treatment with MTII, a melanocortin agonist, reduced the expression of hepatic lipogenic genes in association with reduction in body weight in ob/ob mice, a mouse model of fatty liver disease. Immunohistochemical analysis demonstrated that Fto is co-expressed in both POMC and agouti-related protein (AgRP) neurons in the mouse hypothalamus. Fto mRNA and protein expression was reduced by fasting and increased by glucose treatment in nutritionally important hypothalamic nuclei. Fasting-induced reduction in hypothalamic Fto expression was observed in both lean wild-type and obese ob/ob mice, while the stimulatory effect of glucose on hypothalamic Fto expression was absent in ob/ob mice. These findings support the hypothesis that central melanocortin signaling regulates hepatic lipid metabolism in part by regulating de novo lipogenesis. Impairments in the central melanocortin signaling lead to the development of hepatic steatosis, while enhanced melanocortin signaling may be beneficial in reversing abnormal hepatic lipid metabolism in fatty liver disease (Poritsanos et al., 2008). These findings also support the hypothesis that Fto is expressed in the hypothalamic melanocortinergic neurons and is regulated by metabolic signals involving changes in CNS glucose availability and/or glucose action. Impairments in this regulation may cause metabolic impairments including obesity and fatty liver disease.