The in vivo activity of combinations of 5-azacytidine and cytidine on leukemia L-1210

Zusammenfassung Cytidin- oder Uridinzufuhr, bei an Leukämie L-1210 erkrankten Mäusen entweder 1 h vor oder gleichzeitig mit 5-Azacytidin verabreicht, bewirkt eine Herabsetzung der Toxizität von 5-Azacytidin, die sich in der Gewichtsveränderung und Verlängerung der Lebenszeit zeigt. Aufgrund der gefundenen zeitlichen Verhältnisse wird die Hypothese aufgestellt, dass Cytidin oder Uridin nur dann wirksam werden, wenn der Ort der metabolischen Vorgänge gleichzeitig mit 5-Azacytidin erreicht wird.     

A nonenzymic oxygen uptake and its implications in the assay of 4-hydroxyphenylpyruvate dioxygenase by an oxygen electrode

Summary The oxygen electrode provides a rapid, convenient assay for 4-hydroxyphenylpyruvate dioxygenase. However, due to the occurrence of a nonenzymic oxygen consumption when reducing agents were mixed witha,a-dipyridyl, its use is restricted to species which do not require reducing agents or necessitates the addition of catalase to the reaction mixture.     

Extensive halogen-mediated ozone destruction over the tropical Atlantic Ocean

Increasing tropospheric ozone levels over the past 150 years have led to a significant climate perturbation; the prediction of future trends in tropospheric ozone will require a full understanding of both its precursor emissions and its destruction processes. A large proportion of tropospheric ozone loss occurs in the tropical marine boundary layer and is thought to be driven primarily by high ozone photolysis rates in the presence of high concentrations of water vapour. A further reduction in the tropospheric ozone burden through bromine and iodine emitted from open-ocean marine sources has been postulated by numerical models, but thus far has not been verified by observations. Here we report eight months of spectroscopic measurements at the Cape Verde Observatory indicative of the ubiquitous daytime presence of bromine monoxide and iodine monoxide in the tropical marine boundary layer. A year-round data set of co-located in situ surface trace gas measurements made in conjunction with low-level aircraft observations shows that the mean daily observed ozone loss is approximately 50 per cent greater than that simulated by a global chemistry model using a classical photochemistry scheme that excludes halogen chemistry. We perform box model calculations that indicate that the observed halogen concentrations induce the extra ozone loss required for the models to match observations. Our results show that halogen chemistry has a significant and extensive influence on photochemical ozone loss in the tropical Atlantic Ocean boundary layer. The omission of halogen sources and their chemistry in atmospheric models may lead to significant errors in calculations of global ozone budgets, tropospheric oxidizing capacity and methane oxidation rates, both historically and in the future.     

A role for adult TLX-positive neural stem cells in learning and behaviour

Neurogenesis persists in the adult brain and can be regulated by a plethora of external stimuli, such as learning, memory, exercise, environment and stress. Although newly generated neurons are able to migrate and preferentially incorporate into the neural network, how these cells are molecularly regulated and whether they are required for any normal brain function are unresolved questions. The adult neural stem cell pool is composed of orphan nuclear receptor TLX-positive cells. Here, using genetic approaches in mice, we demonstrate that TLX (also called NR2E1) regulates adult neural stem cell proliferation in a cell-autonomous manner by controlling a defined genetic network implicated in cell proliferation and growth. Consequently, specific removal of TLX from the adult mouse brain through inducible recombination results in a significant reduction of stem cell proliferation and a marked decrement in spatial learning. In contrast, the resulting suppression of adult neurogenesis does not affect contextual fear conditioning, locomotion or diurnal rhythmic activities, indicating a more selective contribution of newly generated neurons to specific cognitive functions.     

Biogenic amine acetylation: No detectable circadian rhythm in whole brain homogenates of the insectOstrinia nubilalis

Summary With the biogenic amines tryptamine, dopamine, and octopamine as substrates, N-acetyltransferase activity shows no detectable circadian rhythm in homogenates of whole brains of the European corn borerOstrinia nubilalis (Lepidoptera: Pyralidae). The circadian clock of this insect may be fundamentally different from the N-acetyltransferase pacemaker in the pineal gland of vertebrates.