Structural Characteristics and Stellar Composition of Low Surface Brightness Disk Galaxies

We present UBVI surface photometry of a sample of low surface brightness (LSB) disk galaxies. LSB disk galaxies are fairly well described as exponential disks with no preferred value for either scale length, central surface brightness, or rotational velocity. Indeed, the distribution of scale lengths is indistinguishable from that of high surface brightness spirals, indicating that dynamically similar galaxies (e.g., those with comparable Rv^2) exist over a large range in surface density. These LSB galaxies are strikingly blue. The complete lack of correlation between central surface brightness and color rules out any fading scenario. Similarly, the oxygen abundances inferred from HII region spectra are uncorrelated with color so the low metallicities are not the primary cause of the blue colors. While these are difficult to interpret in the absence of significant star formation, the most plausible scenario is a stellar population with a young mean age stemming from late formation and subsequent slow evolution. These properties suggest that LSB disks formed from low initial overdensities with correspondingly late collapse times.Comment: Astronomical Journal, in press 45 pages uuencoded postscript (368K) including 9 multipart figures also available by anonymous ftp @ ftp.ast.cam.ac.uk /pub/ssm/phot.uu CAP-30-210442962983742937

Preclinical models of stress and environmental influences on binge eating

Preclinical models cannot explain all of the complex internal and external factors that influence eating behaviors in humans. Still, they represent an essential tool to investigate the underlying neuro- and psychobiology implicated in disorders that are associated with binge eating. Several environmental conditions induce aberrant feeding behavior on calorie-dense food in animal models of binge eating. Various kinds of stress (acute or chronic), the combination of repeated cycles of food restriction and refeeding plus stress, food deprivation, and limited access to palatable food have been used to elicit binge-like eating episodes to model human behaviors. Animal studies have revealed the involvement of different neurotransmitter pathways, especially dopamine, opioids, CRF, serotonin, orexin, and GABAergic systems in binge-like eating. They may aid in the ultimate goal of identifying novel, safe, and effective therapeutic targets