Brain metabolism dictates the polarity of astrocyte control over arterioles

Calcium signalling in astrocytes couples changes in neural activity to alterations in cerebral blood flow by eliciting vasoconstriction or vasodilation of arterioles. However, the mechanism for how these opposite astrocyte influences provide appropriate changes in vessel tone within an environment that has dynamic metabolic requirements remains unclear. Here we show that the ability of astrocytes to induce vasodilations over vasoconstrictions relies on the metabolic state of the rat brain tissue. When oxygen availability is lowered and astrocyte calcium concentration is elevated, astrocyte glycolysis and lactate release are maximized. External lactate attenuates transporter-mediated uptake from the extracellular space of prostaglandin E(2), leading to accumulation and subsequent vasodilation. In conditions of low oxygen concentration extracellular adenosine also increases, which blocks astrocyte-mediated constriction, facilitating dilation. These data reveal the role of metabolic substrates in regulating brain blood flow and provide a mechanism for differential astrocyte control over cerebrovascular diameter during different states of brain activation.     

No cold dust within the supernova remnant Cassiopeia A

A large amount (about three solar masses) of cold (18 K) dust in the prototypical type II supernova remnant Cassiopeia A was recently reported. It was concluded that dust production in type II supernovae can explain how the large quantities (approximately 10(8) solar masses) of dust observed in the most distant quasars could have been produced within only 700 million years after the Big Bang. Foreground clouds of interstellar material, however, complicate the interpretation of the earlier submillimetre observations of Cas A. Here we report far-infrared and molecular line observations that demonstrate that most of the detected submillimetre emission originates from interstellar dust in a molecular cloud complex located in the line of sight between the Earth and Cas A, and is therefore not associated with the remnant. The argument that type II supernovae produce copious amounts of dust is not supported by the case of Cas A, which previously appeared to provide the best evidence for this possibility.     

Mast cells as a source of both preformed and immunologically inducible TNF-alpha/cachectin

Tumour necrosis factor-alpha (TNF-alpha)/cachectin is a multifunctional cytokine that has effects in inflammation, sepsis, lipid and protein metabolism, haematopoiesis, angiogenesis and host resistance to parasites and malignancy. TNF-alpha was first described in activated macrophages, but certain mouse or rat mast cell populations (reviewed in refs 4,5) and some in vitro-derived human cells with cytochemical features of mast cells-basophils may also contain products similar to TNF-alpha. Here we present evidence that resident mouse peritoneal mast cells constitutively contain large amounts of TNF-alpha bioactivity, whereas cultured, immature mast cells vary in their TNF-alpha content. IgE-dependent activation of cultured or peritoneal mast cells induces extracellular release of TNF-alpha and augments levels of TNF-alpha messenger RNA and bioactivity. These findings identify mouse mast cells as an important source of both preformed and immunologically inducible TNF-alpha, and suggest that release of TNF-alpha by mast cells may contribute to host defence, the pathophysiology of allergic diseases and other processes dependent on TNF-alpha.