Adrenalectomy,ovarian HCG-binding and the onset of female puberty in the rat

Summary The delay of puberty onset in female rats adrenalectomized before the 25th day of age is due neither to changes in the number of ovarian HCG-receptors nor to an altered hormone affinity of these receptors. It is assumed that glucocorticoids act on an intracellular level, in the ovarian cells, possibly by alterations of cyclic AMP-dependent phosphodiesterase activity.This work was supported in part by the Deutsche Forschungsgemeinschaft (SFB 46). Purified HCG was a gift of Schering AG, Berlin-West. We thank Mrs Margarete Lindig for assistance and Mrs Ursula Frigewski for secretarial help.     

Rain, winds and haze during the Huygens probe's descent to Titan's surface

The irreversible conversion of methane into higher hydrocarbons in Titan's stratosphere implies a surface or subsurface methane reservoir. Recent measurements from the cameras aboard the Cassini orbiter fail to see a global reservoir, but the methane and smog in Titan's atmosphere impedes the search for hydrocarbons on the surface. Here we report spectra and high-resolution images obtained by the Huygens Probe Descent Imager/Spectral Radiometer instrument in Titan's atmosphere. Although these images do not show liquid hydrocarbon pools on the surface, they do reveal the traces of once flowing liquid. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing are of a dry riverbed. The infrared reflectance spectrum measured for the surface is unlike any other in the Solar System; there is a red slope in the optical range that is consistent with an organic material such as tholins, and absorption from water ice is seen. However, a blue slope in the near-infrared suggests another, unknown constituent. The number density of haze particles increases by a factor of just a few from an altitude of 150 km to the surface, with no clear space below the tropopause. The methane relative humidity near the surface is 50 per cent.     

Polysaccharide aggregation as a potential sink of marine dissolved organic carbon

The formation and sinking of biogenic particles mediate vertical mass fluxes and drive elemental cycling in the ocean. Whereas marine sciences have focused primarily on particle production by phytoplankton growth, particle formation by the assembly of organic macromolecules has almost been neglected. Here we show, by means of a combined experimental and modelling study, that the formation of polysaccharide particles is an important pathway to convert dissolved into particulate organic carbon during phytoplankton blooms, and can be described in terms of aggregation kinetics. Our findings suggest that aggregation processes in the ocean cascade from the molecular scale up to the size of fast-settling particles, and give new insights into the cycling and export of biogeochemical key elements such as carbon, iron and thorium.     

Oscillatory responses in cat visual cortex exhibit inter-columnar synchronization which reflects global stimulus properties

A fundamental step in visual pattern recognition is the establishment of relations between spatially separate features. Recently, we have shown that neurons in the cat visual cortex have oscillatory responses in the range 40-60 Hz (refs 1, 2) which occur in synchrony for cells in a functional column and are tightly correlated with a local oscillatory field potential. This led us to hypothesize that the synchronization of oscillatory responses of spatially distributed, feature selective cells might be a way to establish relations between features in different parts of the visual field. In support of this hypothesis, we demonstrate here that neurons in spatially separate columns can synchronize their oscillatory responses. The synchronization has, on average, no phase difference, depends on the spatial separation and the orientation preference of the cells and is influenced by global stimulus properties.