Amino acid transmitters and the neural control of feeding and energy homeostasis

2016 Spring.Includes bibliographical references.Consuming the correct number of calories to maintain a healthy bodyweight is a delicate balancing act between intake and energy expenditure, and humans in modern society seem to have a keen knack for throwing the balance off-center. In the U.S. alone, more than 1/3 of adults are obese based on the body mass index scale, and $147 billion is the estimated annual medical cost for obesity in the United States. On the other end of the feeding spectrum, anorexia in the U.S. has been steadily rising since the 1960s, and has the highest mortality rate of any mental illness. While great strides have been made in understanding the neuronal regulation of energy balance, there is a need to more fully understand the homeostatic systems within the hypothalamus that are so powerful that they are able to drive individuals to poor health or death, often even in the face of consciously fighting their urges. Two groups of functionally opposed neurons contained within the arcuate nucleus of the hypothalamus, Neuropeptide Y / Agouti-related peptide (NPY/AgRP) and proopiomelanocortin (POMC) cells (the so-called first order feeding neurons), have been extensively studied for their roles in energy homeostasis—mostly through research into the peptides they are named after. There is clear evidence that peptides play an essential role for the function of NPY/AgRP and POMC cells, but what about simple amino acid transmitters? While it is known that GABA is packaged and released by NPY/AgRP cells and that this release is relevant to feeding behavior, there is still a dearth of information about this aspect of the circuitry, very much an area waiting to be mined. This study focuses on better understanding the functional release and relevance of amino acid transmitters packaged in both NPY/AgRP and POMC cell populations. Evidence is presented here for the conclusive release of both GABA and glutamate from POMC cells within intact circuitry. For NPY/AgRP neurons, evidence is presented for a shift in functional release of GABA from these neurons onto POMC cells depending on feeding state, corroborated by concurrent in situ hybridization experiments. Using a combination of electrophysiology and in situ hybridization approaches, evidence is also provided that mRNA levels of glutamate decarboxylase can act as a general proxy for functional GABA release. Altogether, these results indicate that amino acid transmitters play a significant role in first order feeding neuron physiology. Not only does this warrant further study on the significance of each transmitter alone and their purpose in comparison with the peptides released, but also the interplay between POMC cell and NPY/AgRP cell amino acid transmitters and their many shared downstream targets. Imbalances in proper glutamatergic and GABAergic signaling may significantly contribute to obesity, and advancing this area of study could lead to correcting those imbalances to restore healthy energy homeostasis

Nanoindentation of the a and c domains in a tetragonal BaTiO3 single crystal

Nanoindentation in conjunction with piezoresponse force microscopy was used to study domain switching and to measure the mechanical properties of individual ferroelectric domains in a tetragonal BaTiO3 single crystal. It was found that nanoindentation has induced local domain switching; the a and c domains of BaTiO3 have different elastic moduli but similar hardness. Nanoindentation modulus mapping on the a and c domains further confirmed such difference in elasticity. Finite element modeling was used to simulate the von Mises stress and plastic strain profiles of the indentations on both a and c domains, which introduces a much higher stress level than the critical value for domain nucleation

Probing the size and density of silicon nanocrystals in nanocrystal memory device applications

Structural characterization via transmission electron microscopy and atomic force microscopy of arrays of small Si nanocrystals embedded in SiO2, important to many device applications, is usually difficult and fails to correctly resolve nanocrystal size and density. We demonstrate that scanning tunneling microscopy (STM) imaging enables a much more accurate measurement of the ensemble size distribution and array density for small Si nanocrystals in SiO2, estimated to be 2-3 nm and 4 x 10^(12) - 3 x 10^(13) cm^(-2), respectively, in this study. The reflection high energy electron diffraction pattern further verifies the existence of nanocrystallites in SiO2. The present STM results enable nanocrystal charging characteristics to be more clearly understood: we find the nanocrystal charging measurements to be consistent with single charge storage on individual Si nanocrystals. Both electron tunneling and hole tunneling processes are suggested to explain the asymmetric charging/ discharging processes as a function of bias

Population dynamics of the raggedtooth shark (carcharias taurus) along the east coast of South Africa

This thesis develops the first open population model for any shark species worldwide using the Cormack-Jolly-Seber (CJS) model. In conjunction with a tagging study, five auxiliary studies were conducted to investigate stock structure, post-release mortality, tag shedding, and tag-reporting rates. The results from each of the studies were used to correct for any violations of the models assumptions to provide the first unbiased estimates of survival and abundance for the raggedtooth shark (Carcharias taurus) in South Africa. The C. taurus population exhibited complex stock structuring, by size and sex. Competitive shore anglers fished an estimated 37, 820 fishing days.year⁻¹ (95% C.I. = 28, 281 - 47, 359 days.year⁻¹) for sharks, and caught 1764 (95% C.I. = 321 – 3207) C. taurus. Although released alive, post-release mortality ranged from 3.85% for young-of-the-year sharks to 18.46% for adult sharks. Between 1984 and 2004, a total of 3471 C. taurus were tagged. In all, 302-tagged sharks (8.7%) were recaptured. Both juvenile ( 1.8 m TL) displayed philopatric behaviour for specific parts of their ranges, including gestating and parturition areas. Significant differences were observed in the percentage of recaptures between the different tag types, tagging programs, individual taggers and capture methods used to tag sharks. The annual tag retention rate for juvenile sharks, 94.19% (95% C.I. = 80.68% - 100.00%) was significantly higher than for adult sharks, estimated at 29.00% (95% C.I. = 6.76% - 64.39%). Tag reporting rates, from fishermen varied both spatially and temporally from 0.28 (95% C.I. = 0.00 – 0.63) to 0.77 (95% C.I. = 0.56 – 0.97). Associated tag wound damage and biofouling growth indicated that B-type tags were a suitable tag type for use on C. taurus, whereas C-type tags were not. The CJS bias-adjusted estimate for juvenile survival was 0.456 (95% C.I. = 0.367 – 0.516) and for adult sharks, 0.865 (95% C.I. = 0.795 – 0.915). From 1984 to 2004 the mean bias-adjusted population size for juvenile sharks was estimated at 3506 (95% C.I. = 2433 – 4350) and for adult sharks, 5899 (95% C.I. = 7216 – 11904). Trends in abundance over the 20-year study period indicated a stable, healthy population

Electrooptic Modulation in Thin Film Barium Titanate Plasmonic Interferometers

We demonstrate control of the surface plasmon polariton wavevector in an active metal−dielectric plasmonic interferometer by utilizing electrooptic barium titanate as the dielectric layer. Arrays of subwavelength interferometers were fabricated from pairs of parallel slits milled in silver on barium titanate thin films. Plasmon-mediated transmission of incident light through the subwavelength slits is modulated by an external voltage applied across the barium titanate thin film. Transmitted light modulation is ascribed to two effects, electrically induced domain switching and electrooptic modulation of the barium titanate index

Study of orientation effect on nanoscale polarization in BaTiO3 thin films using piezoresponse force microscopy

We have investigated the effect of texture on in-plane (IPP) and out- of plane (OPP) polarizations of pulsed-laser-deposited BaTiO3 thin films grown on Pt and La0.5Sr0.5CoO3 (LSCO) buffered Pt electrodes. The OPP and IPP polarizations were observed by piezoresponse force microscopy (PFM) for three-dimensional polarization analyses in conjunction with conventional diffraction methods using x-ray diffraction and reflection high energy electron diffraction measurements. BaTiO3 films grown on Pt electrodes exhibited highly (101) preferred orientation with higher IPP component whereas BaTiO3 film grown on LSCO/Pt electrodes showed (001) and (101) orientations with higher OPP component. Measured effective d(33) values of BaTiO3 films deposited on Pt and LSCO/ Pt electrodes were 14.3 and 54.0 pm/ V, respectively. Local piezoelectric strain loops obtained by OPP and IPP-PFM showed that piezoelectric properties were strongly related to film orientation

Nanoindentation of the \u3ci\u3ea\u3c/i\u3e and \u3ci\u3ec\u3c/i\u3e Domains in a Tetragonal BaTiO\u3csub\u3e3\u3c/sub\u3e Single Crystal

Nanoindentation in conjunction with piezoresponse force microscopy was used to study domain switching and to measure the mechanical properties of individual ferroelectric domains in a tetragonal BaTiO3 single crystal. It was found that nanoindentation has induced local domain switching; the a and c domains of BaTiO3 have different elastic moduli but similar hardness.Nanoindentationmodulus mapping on the a and c domains further confirmed such difference in elasticity. Finite element modeling was used to simulate the von Mises stress and plastic strain profiles of the indentations on both a and c domains, which introduces a much higher stress level than the critical value for domain nucleation

A Phase Diagram of Low Temperature Epitaxial Silicon Grown by Hot-wire Chemical Vapor Deposition for Photovoltaic Devices

We have investigated the low-temperature epitaxial growth of thin silicon films by hot-wire chemical vapor deposition (HWCVD). Using reflection high energy electron diffraction (RHEED) and transmission electron microscopy (TEM), we have found conditions for epitaxial growth at low temperatures achieving twinned epitaxial growth up to 6.8 µm on Si(100) substrates at a substrate temperature of 230°C. This opens the possibility of growing high quality films on low cost substrates. The H_2:SiH_4 dilution ratio was set to 50:1 for all growths. Consistent with previous results, the epitaxial thickness is found to decrease with an increase in the substrate temperature

Active plasmonic devices and optical metamaterials

We studied active near-infrared metamaterials based on phase transition of vanadium oxide thin films, asymmetrically coupled split-ring resonators for narrowing resonance line-widths , field effect modulation of plasmon propagation and 3D single layer, plasmonic negative-index metamaterials

Shark fishing effort and catch of the ragged-tooth shark Carcharias taurus in the South African competitive shore-angling fishery

In South Africa, Carcharias taurus is commonly known as the ragged-tooth shark or raggie. The species is also referred to as the sand-tiger shark in North America and as the grey-nurse shark in Australia. It is a long-lived species with an estimated longevity of up to 40 years (Goldman 2002). Female sharks reach sexual maturity at approximately 10 years (Goldman 2002), and they exhibit a biennial reproductive cycle (Branstetter and Musick 1994, Lucifora et al. 2002, G Cliff, Natal Sharks Board, unpublished data). Intra-uterine cannibalisation results in a maximum fecundity of two pups per litter after a gestation period of approximately 9–12 months (Bass et al. 1975, Gilmore et al. 1983). These life-history characteristics make this species particularly susceptible to overexploitation