Cold streams in early massive hot haloes as the main mode of galaxy formation.

Massive galaxies in the young Universe, ten billion years ago, formed stars at surprising intensities. Although this is commonly attributed to violent mergers, the properties of many of these galaxies are incompatible with such events, showing gas-rich, clumpy, extended rotating disks not dominated by spheroids. Cosmological simulations and clustering theory are used to explore how these galaxies acquired their gas. Here we report that they are 'stream-fed galaxies', formed from steady, narrow, cold gas streams that penetrate the shock-heated media of massive dark matter haloes. A comparison with the observed abundance of star-forming galaxies implies that most of the input gas must rapidly convert to stars. One-third of the stream mass is in gas clumps leading to mergers of mass ratio greater than 1:10, and the rest is in smoother flows. With a merger duty cycle of 0.1, three-quarters of the galaxies forming stars at a given rate are fed by smooth streams. The rarer, submillimetre galaxies that form stars even more intensely are largely merger-induced starbursts. Unlike destructive mergers, the streams are likely to keep the rotating disk configuration intact, although turbulent and broken into giant star-forming clumps that merge into a central spheroid. This stream-driven scenario for the formation of discs and spheroids is an alternative to the merger picture.

A model of inositol compartmentation in astrocytes based upon efflux kinetics and slow inositol depletion after uptake inhibition.

Intracellular compartmentation of inositol was demonstrated in primary cultures of mouse astrocytes, incubated in isotonic medium, by determination of efflux kinetics after "loading" with [3H]inositol. Three kinetically different compartments were delineated. The largest and most slowly exchanging compartment had a halflife of approximately 9 hr. This slow release leads to retention of a sizeable amount of pre-accumulated inositol in the tissue 24 hr after the onset of uptake inhibition, as confirmed by the observation that the inositol uptake inhibitor fucose caused a larger inhibition of unidirectional inositol uptake than of inositol pool size, measured as accumulated [3H]inositol after 24 hr of combined exposure to the inhibitor and the labeled isotope. Based upon the present observations and literature data, it is suggested that the large, slowly exchanging compartment is largely membrane-associated and participating in signaling via the phosphatidylinositide second messenger system, whereas inositol functioning as an osmolyte is distributed in the cytosol and located in one or both of the compartments showing a faster release.

Chronic treatment of human astrocytoma cells with lithium, carbamazepine or valproic acid decreases inositol uptake at high inositol concentrations but increases it at low inositol concentrations.

Inositol uptake was measured at concentrations of 25, 40 and 50 microM in human astrocytoma cell cultures treated for 1-3 weeks with pharmacologically relevant concentrations of LiCl, valproic acid or carbamazepine as well as in control cultures that had not been treated with any drug. After at least 2 weeks of treatment, each of these 3 conventional anti-bipolar drugs increased the uptake significantly at 25 microM inositol, had no effect at 40 microM, and decreased it at 50 microM inositol. Reduction of the drug concentrations by 50% abolished the stimulation of uptake at 25 microM inositol by lithium and valproic acid and reduced that by carbamazepine. These findings may contribute to an understanding of the mechanisms of action for anti-bipolar medication, and explain the controversy in the literature whether or not brain inositol is reduced after chronic administration of lithium.