The chemokinetic effect of serum albumin

Summary Experiments performed by means of time lapse cinematography or the filter technique show that human serum albumin has marked chemokinetic effects on neutrophil cultured in Gey's solution. The average speed of the cells, as well as the proportion of neutrophils showing locomotion, is increased. Enhanced locomotion correlates with decreased attachment to the substratum as determined by morphological and functional criteria.We thank Mrs R. Graf and Miss M. Schuster for technical assistance. This work was supported by the Swiss National Science Fondation.     

The effect of aggregated γ-globulins on immune cytolysis: the role of complement

Zusammenfassung In einem aus Peritonealmastzellen, Antikörper und hitzelabilen Serumfaktoren bestehendenin vitro-System wird die Immunreaktion in Gegenwart von aggregiertem Human--Globulin gehemmt; aggregiertes bovines -Globulin hat dagegen keine derartige Wirkung.

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Supported by the Schweizerische Nationalfonds zur Förderung der wissenschaftlichen Forschung.     

Rapid leukocyte migration by integrin-independent flowing and squeezing

All metazoan cells carry transmembrane receptors of the integrin family, which couple the contractile force of the actomyosin cytoskeleton to the extracellular environment. In agreement with this principle, rapidly migrating leukocytes use integrin-mediated adhesion when moving over two-dimensional surfaces. As migration on two-dimensional substrates naturally overemphasizes the role of adhesion, the contribution of integrins during three-dimensional movement of leukocytes within tissues has remained controversial. We studied the interplay between adhesive, contractile and protrusive forces during interstitial leukocyte chemotaxis in vivo and in vitro. We ablated all integrin heterodimers from murine leukocytes, and show here that functional integrins do not contribute to migration in three-dimensional environments. Instead, these cells migrate by the sole force of actin-network expansion, which promotes protrusive flowing of the leading edge. Myosin II-dependent contraction is only required on passage through narrow gaps, where a squeezing contraction of the trailing edge propels the rigid nucleus.     

The amniote primitive streak is defined by epithelial cell intercalation before gastrulation

During gastrulation, a single epithelial cell layer, the ectoderm, generates two others: the mesoderm and the endoderm. In amniotes (birds and mammals), mesendoderm formation occurs through an axial midline structure, the primitive streak, the formation of which is preceded by massive 'polonaise' movements of ectoderm cells. The mechanisms controlling these processes are unknown. Here, using multi-photon time-lapse microscopy of chick (Gallus gallus) embryos, we reveal a medio-lateral cell intercalation confined to the ectodermal subdomain where the streak will later form. This intercalation event differs from the convergent extension movements of the mesoderm described in fish and amphibians (anamniotes): it occurs before gastrulation and within a tight columnar epithelium. Fibroblast growth factor from the extraembryonic endoderm (hypoblast, a cell layer unique to amniotes) directs the expression of Wnt planar-cell-polarity pathway components to the intercalation domain. Disruption of this Wnt pathway causes the mesendoderm to form peripherally, as in anamniotes. We propose that the amniote primitive streak evolved from the ancestral blastopore by acquisition of an additional medio-lateral intercalation event, preceding gastrulation and acting independently of mesendoderm formation to position the primitive streak at the midline.     

Morphology and dynamics of the upper cloud layer of Venus

Venus is completely covered by a thick cloud layer, of which the upper part is composed of sulphuric acid and some unknown aerosols. The cloud tops are in fast retrograde rotation (super-rotation), but the factors responsible for this super-rotation are unknown. Here we report observations of Venus with the Venus Monitoring Camera on board the Venus Express spacecraft. We investigate both global and small-scale properties of the clouds, their temporal and latitudinal variations, and derive wind velocities. The southern polar region is highly variable and can change dramatically on timescales as short as one day, perhaps arising from the injection of SO2 into the mesosphere. The convective cells in the vicinity of the subsolar point are much smaller than previously inferred, which we interpret as indicating that they are confined to the upper cloud layer, contrary to previous conclusions, but consistent with more recent study.     

Effects of neurochemical lesions restricted to spinal cord monoaminergic neurons on blood pressure and sympathetic activity of spontaneously hypertensive rats

Intraspinal (i.s.) injection of 6-hydroxydopamine or 5,7-dihydroxytryptamine in newborn spontaneously hypertensive rats (SHR) resulted, in the adult animal (30-week-old), in a marked decrease of spinal cord noradrenaline (NA) or 5-hydroxytryptamine (5-HT) levels, respectively. Since both neurotoxin- and vehicle-injected rats developed full hypertension and had similar plasma catecholamine concentrations, it is concluded that in SHR neither spinal cord NA nor 5-HT play a major role in development and maintenance of hypertension.     

α1-Adrenergic stimulation of ketogenesis and fatty acid oxidation is associated with inhibition of lipogenesis in rat hepatocytes

Summary The effect of norepinephrine on fatty acid synthesis (³H₂O incorporation into fatty acids), on fatty acid oxidation to CO₂ and on ketogenesis was studied in isolated hepatocytes of fed rats. After incubation with norepinephrine (50 M), lipogenesis was lower (5.7±1.1 nmoles³H₂O incorporated into fatty acids/mg dry weight/30 min) than in controls (7.5±1.7; n=6, p<0.02). In contrast, (1-¹⁴C) palmitate conversion into total ketone bodies was increased to 10.9±1.8 nmoles/mg/30 min with norepinephrine, vs 8.5±1.6 in controls (p<0.05), and more (1-¹⁴C) palmitate was converted to¹⁴CO₂ with norepinephrine than in controls (1.48±0.10 nmoles/mg/30 min vs 1.06±0.11, p<0.05). The inhibitory effect of norepinephrine on lipogenesis was abolished by addition of the ₁-receptor blocker prazosin, but not by ₂ or -blockers. The results demonstrate that the ketogenic effect of norepinephrine is coupled with an inhibitory effect on lipogenesis which may be explained by diminished activity of acetyl-CoA carboxylase, diminished formation of malonyl-CoA and decreased activity of carnitine palmitoyl transferase I.