Regulation of Leydig Cell Function by Prolactin, Growth Hormone and Luteinizing Hormone

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72585/1/j.1365-2605.1978.tb00026.x.pd

Thermodynamics of natural images

The scale invariance of natural images suggests an analogy to the statistical mechanics of physical systems at a critical point. Here we examine the distribution of pixels in small image patches and show how to construct the corresponding thermodynamics. We find evidence for criticality in a diverging specific heat, which corresponds to large fluctuations in how "surprising" we find individual images, and in the quantitative form of the entropy vs. energy. The energy landscape derived from our thermodynamic framework identifies special image configurations that have intrinsic error correcting properties, and neurons which could detect these features have a strong resemblance to the cells found in primary visual cortex

Imaging Spectroscopy for Extrasolar Planet Detection

Coronagraphic imaging in combination with moderate to high spectral resolution may prove more effective in both detecting extrasolar planets and characterizing them than a standard coronagraphic imaging approach. We envisage an integral-field spectrograph coupled to a coronagraph to produce a 3D datacube. For the idealised case where the spectrum of the star is well-known and unchanging across the field, we discuss the utility of cross-correlation to seek the extrasolar planet signal, and describe a mathematical approach to completely eliminate stray light from the host star (although not its Poisson noise). For the case where the PSF is dominated by diffraction and scattering effects, and comprises a multitude of speckles within an Airy pattern typical of a space-based observation, we turn the wavelength dependence of the PSF to advantage and present a general way to eliminate the contribution from the star while preserving both the flux and spectrum of the extrasolar planet. We call this method `spectral deconvolution'. We illustrate the dramatic gains by showing an idealized simulation that results in a 20-sigma detection of a Jovian planet at 2 pc with a 2-m coronagraphic space telescope, even though the planet's peak flux is only 1% that of the PSF wings of the host star. This scales to detection of a terrestrial extrasolar planet at 2 pc with an 8-m coronagraphic Terrestrial Planet Finder (TPF) in ~7 hr (or less with appropriate spatial filtering). Data on the spectral characteristics of the extrasolar planet and hence on its atmospheric constituents and possible biomarkers are obtained naturally as part of this process.Comment: 62 pages 27 figures accepted for publication in Ap

Are biological systems poised at criticality?

Many of life's most fascinating phenomena emerge from interactions among many elements--many amino acids determine the structure of a single protein, many genes determine the fate of a cell, many neurons are involved in shaping our thoughts and memories. Physicists have long hoped that these collective behaviors could be described using the ideas and methods of statistical mechanics. In the past few years, new, larger scale experiments have made it possible to construct statistical mechanics models of biological systems directly from real data. We review the surprising successes of this "inverse" approach, using examples form families of proteins, networks of neurons, and flocks of birds. Remarkably, in all these cases the models that emerge from the data are poised at a very special point in their parameter space--a critical point. This suggests there may be some deeper theoretical principle behind the behavior of these diverse systems.Comment: 21 page

Colic: Idiopathic, Excessive, Infant Crying

Infantile colic is a common and frustrating condition for parents and health care practitioners. A commonly held belief is that the condition is benign and only results in transient loss of parental sleep; however, a detailed study of the recent literature and clinical studies suggests that not all colic abates without residual consequences. In this article, we outline current understanding of the condition and suggest methods of intervention. In addition, we focus on the potential effect of colic on infant attachment; the later growth and development of the once-colicky child; the evidence that supporting and refuting commonly held beliefs, and areas of intervention

Testicular responsiveness to human chorionic gonadotrophin in growth hormone deficient pre-pubertal boys: lack of effect of replacement therapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74977/1/j.1365-2605.1982.tb00246.x.pd

Dissociation of lutropin-induced loss of testicular lutropin receptors and lutropin-induced desensitization of testosterone synthesis

The relationship between changes in testicular lutropin receptors, as measured by specific binding of 125I-labeled human chorionic gonadotropin, and testosterone synthesis in response to lutropin (testicular responsiveness) was studied in intact and hypophysectomized rats. Administration of a single 200-[mu]g dose of ovine lutropin to intact rats results at 3 days in a 58% decrease in lutropin receptors associated with a parallel decrease in testicular responsiveness. A single 30-[mu]g dose of lutropin to intact rats resulted in a comparable decrease in lutropin receptors with a transient increase in testicular responsiveness. Rats receiving twice-daily injections of 15 [mu]g lutropin for 10 days exhibited a 48% decrease in lutropin receptors by day 3 which persisted during the 10-day treatment period, but was accompanied by a progressive increase in testicular responsiveness to lutropin. Hypophysectomy resulted in an 80% loss of receptors and a 72% loss in responsiveness 7 days after surgery. Daily treatment with lutropin initiated immediately following surgery resulted in a further dose-dependent decrease in lutropin receptors and a dose-dependent increase in testicular responsiveness. Loss of lutropin receptors was not due to occupancy of the receptor by exogenous lutropin. These studies demonstrate a dissociation between the negative regulation of lutropin receptors and testicular responsiveness to lutropin. Furthermore, the studies in hypophysectomized rats indicate that lutropin is the only hormone essential for maintenance of steroidogenesis and that this is independent of lutropin receptor concentration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22603/1/0000152.pd