Distribution of noradrenaline and of monoamine oxidase and catechol-O-methyltransferase activity in human foetal heart

Zusammenfassung Die Konzentration von Noradrenalin und die Aktivität der MAO und COMT wurde in verschiedenen Teilen des menschlichen foetalen Herzens bestimmt. Die Ventrikel der Herzen (bis zu 12 Wochen alt) waren sehr noradrenalinarm. Die COMT-Aktivität des rechten Vorhofs war bis zur Mitte der Schwangerschaft viel niedriger als die der übrigen Herzgebiete. Die COMT- und MAO-Aktivität im Gewebe des Spatium zwischen der Aorta und der Arteria pulmonalis lag ungefähr in der gleichen Grössenordnung wie die der Ventrikel.     

Lack of long-term cortical reorganization after macaque retinal lesions

Several aspects of cortical organization are thought to remain plastic into adulthood, allowing cortical sensorimotor maps to be modified continuously by experience. This dynamic nature of cortical circuitry is important for learning, as well as for repair after injury to the nervous system. Electrophysiology studies suggest that adult macaque primary visual cortex (V1) undergoes large-scale reorganization within a few months after retinal lesioning, but this issue has not been conclusively settled. Here we applied the technique of functional magnetic resonance imaging (fMRI) to detect changes in the cortical topography of macaque area V1 after binocular retinal lesions. fMRI allows non-invasive, in vivo, long-term monitoring of cortical activity with a wide field of view, sampling signals from multiple neurons per unit cortical area. We show that, in contrast with previous studies, adult macaque V1 does not approach normal responsivity during 7.5 months of follow-up after retinal lesions, and its topography does not change. Electrophysiology experiments corroborated the fMRI results. This indicates that adult macaque V1 has limited potential for reorganization in the months following retinal injury.     

Electronic tagging and population structure of Atlantic bluefin tuna

Electronic tags that archive or transmit stored data to satellites have advanced the mapping of habitats used by highly migratory fish in pelagic ecosystems. Here we report on the electronic tagging of 772 Atlantic bluefin tuna in the western Atlantic Ocean in an effort to identify population structure. Reporting electronic tags provided accurate location data that show the extensive migrations of individual fish (n = 330). Geoposition data delineate two populations, one using spawning grounds in the Gulf of Mexico and another from the Mediterranean Sea. Transatlantic movements of western-tagged bluefin tuna reveal site fidelity to known spawning areas in the Mediterranean Sea. Bluefin tuna that occupy western spawning grounds move to central and eastern Atlantic foraging grounds. Our results are consistent with two populations of bluefin tuna with distinct spawning areas that overlap on North Atlantic foraging grounds. Electronic tagging locations, when combined with US pelagic longline observer and logbook catch data, identify hot spots for spawning bluefin tuna in the northern slope waters of the Gulf of Mexico. Restrictions on the time and area where longlining occurs would reduce incidental catch mortalities on western spawning grounds.     

Trans-SNARE pairing can precede a hemifusion intermediate in intracellular membrane fusion

The question concerning whether all membranes fuse according to the same mechanism has yet to be answered satisfactorily. During fusion of model membranes or viruses, membranes dock, the outer membrane leaflets mix (termed hemifusion), and finally the fusion pore opens and the contents mix. Viral fusion proteins consist of a membrane-disturbing 'fusion peptide' and a helical bundle that pin the membranes together. Although SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes form helical bundles with similar topology, it is unknown whether SNARE-dependent fusion events on intracellular membranes proceed through a hemifusion state. Here we identify the first hemifusion state for SNARE-dependent fusion of native membranes, and place it into a sequence of molecular events: formation of helical bundles by SNAREs precedes hemifusion; further progression to pore opening requires additional peptides. Thus, SNARE-dependent fusion may proceed along the same pathway as viral fusion: both use a docking mechanism via helical bundles and additional peptides to destabilize the membrane and efficiently induce lipid mixing. Our results suggest that a common lipidic intermediate may underlie all fusion reactions of lipid bilayers.     

Rebuilt AAA + motors reveal operating principles for ATP-fuelled machines

Hexameric ring-shaped ATPases of the AAA + (for ATPases associated with various cellular activities) superfamily power cellular processes in which macromolecular structures and complexes are dismantled or denatured, but the mechanisms used by these machine-like enzymes are poorly understood. By covalently linking active and inactive subunits of the ATPase ClpX to form hexamers, here we show that diverse geometric arrangements can support the enzymatic unfolding of protein substrates and translocation of the denatured polypeptide into the ClpP peptidase for degradation. These studies indicate that the ClpX power stroke is generated by ATP hydrolysis in a single subunit, rule out concerted and strict sequential ATP hydrolysis models, and provide evidence for a probabilistic sequence of nucleotide hydrolysis. This mechanism would allow any ClpX subunit in contact with a translocating polypeptide to hydrolyse ATP to drive substrate spooling into ClpP, and would prevent stalling if one subunit failed to bind or hydrolyse ATP. Energy-dependent machines with highly diverse quaternary architectures and molecular functions could operate by similar asymmetric mechanisms.