Migratory Reed Warblers Need Intact Trigeminal Nerves to Correct for a 1,000 km Eastward Displacement

Several studies have shown that experienced night-migratory songbirds can determine their position, but it has remained a mystery which cues and sensory mechanisms they use, in particular, those used to determine longitude (east–west position). One potential solution would be to use a magnetic map or signpost mechanism like the one documented in sea turtles. Night-migratory songbirds have a magnetic compass in their eyes and a second magnetic sense with unknown biological function involving the ophthalmic branch of the trigeminal nerve (V1). Could V1 be involved in determining east–west position? We displaced 57 Eurasian reed warblers (Acrocephalus scirpaceus) with or without sectioned V1. Sham operated birds corrected their orientation towards the breeding area after displacement like the untreated controls did. In contrast, V1-sectioned birds did not correct for the displacement. They oriented in the same direction after the displacement as they had done at the capture site. Thus, an intact ophthalmic branch of the trigeminal nerve is necessary for detecting the 1,000 km eastward displacement in this night-migratory songbird. Our results suggest that V1 carries map-related information used in a large-scale map or signpost sense that the reed warblers needed to determine their approximate geographical position and/or an east–west coordinate.     

Aminoguanidine inhibits caspase-3 and calpain activation without affecting microglial activation following neonatal transient cerebral ischemia

Microglial cells, the resident macrophages of the CNS, can be both beneficial and detrimental to the brain. These cells play a central role as mediators of neuroinflammation associated with many neurodegenerative states, including cerebral ischemia. Because microglial cells are both a major source of inducible nitric oxide synthase (iNOS)/nitric oxide (NO) production locally in the injured brain and are activated by NO-mediated injury, we tested whether iNOS inhibition reduces microglial activation and ischemic injury in a neonatal focal ischemia-reperfusion model. Post-natal day 7 rats were subjected to a 2 h transient middle cerebral artery (MCA) occlusion. Pups with confirmed injury on diffusion-weighted magnetic resonance imaging (MRI) during occlusion were administered 300 mg/kg/dose aminoguanidine (AG) or vehicle at 0, 4 and 18 h after reperfusion, and animals were killed at 24 or 72 h post-reperfusion. The effect of AG on microglial activation as judged by the acquisition of ED1 immunoreactivity and proliferation of ED1-positive cells, on activation of cell death pathways and on injury volume, was determined. The study shows that while AG attenuates caspase 3 and calpain activation in the injured tissue, treatment does not affect the rapidly occurring activation and proliferation of microglia following transient MCA occlusion in the immature rat, or reduce injury size.     

Kinetics of substrate recognition and cleavage by human 8-oxoguanine-DNA glycosylase

Human 8-oxoguanine-DNA glycosylase (hOgg1) excises 8-oxo-7,8-dihydroguanine (8-oxoG) from damaged DNA. We report a pre-steady-state kinetic analysis of hOgg1 mechanism using stopped-flow and enzyme fluorescence monitoring. The kinetic scheme for hOgg1 processing an 8-oxoG:C-containing substrate was found to include at least three fast equilibrium steps followed by two slow, irreversible steps and another equilibrium step. The second irreversible step was rate-limiting overall. By comparing data from Ogg1 intrinsic fluorescence traces and from accumulation of products of different types, the irreversible steps were attributed to two main chemical steps of the Ogg1-catalyzed reaction: cleavage of the N-glycosidic bond of the damaged nucleotide and β-elimination of its 3′-phosphate. The fast equilibrium steps were attributed to enzyme conformational changes during the recognition of 8-oxoG, and the final equilibrium, to binding of the reaction product by the enzyme. hOgg1 interacted with a substrate containing an aldehydic AP site very slowly, but the addition of 8-bromoguanine (8-BrG) greatly accelerated the reaction, which was best described by two initial equilibrium steps followed by one irreversible chemical step and a final product release equilibrium step. The irreversible step may correspond to β-elimination since it is the very step facilitated by 8-BrG.     

Alteration of the acetylcholine response by intra- and extracellular serotonin application in intracellularly perfused neurons ofLymnaea stagnalis

1. The effect of serotonin on the acetylcholine (ACh) response has been studied by means of voltage clamp and intracellular perfusion in unidentified isolated neurons from parietal and visceral ganglia of Lymnaea stagnalis. 2. In most cells studied serotonin added to the internal or external solution decreases the response to ACh. 3. In other neurons serotonin added to the intracellular solution increases the response to ACh; when it is added extracellularly it produces the opposite effect on the same cells. 4. The decreasing effect of serotonin on ACh currents is mimicked by cyproheptadine, an antagonist of serotonin receptors, and by the intracellular application of cyclic AMP (cAMP) forskolin. 5. The enhancing effect of intracellularly applied serotonin on ACh currents is blocked by cyproheptadine and is not obtained by the intracellular administration of cAMP and forskolin. In some cells the enhancing effect of serotonin appears after forskolin. 6. The results suggest a modulating effect of serotonin on cholinergic synaptic transmission in the nervous system of mollusks. The possible existence of intracellular serotonin receptors is discussed.     

A real-time study of the interaction of TBP with a TATA box-containing duplex identical to an ancestral or minor allele of human gene LEP or TPI

It is known that only a single-nucleotide substitution (SNP: a single nucleotide polymorphism) in the sequence of a TATA box can influence the affinity of the interaction of TBP with the TATA box and contribute to the pathogenesis of complex hereditary human diseases and sometimes may be a cause of monogenic diseases (for instance, β-thalassemia). In the present work, we studied the interaction of human TBP with a double-stranded oligodeoxyribonucleotide (ODN) 15 or 26 bp long identical to a TATA box of promoters of a real-life human gene, TPI or LEP, and labeled with fluorophores TAMRA and FAM. To analyze the interaction of TBP with a TATA box of an ancestral or minor allele (SNP in the TATA box) in real time, we used the stopped-flow method with detection of a Förster resonance energy transfer (FRET) signal. The nature of the resulting kinetic curves reflecting changes in the FRET signal (and therefore of DNA conformation during the interaction with TBP) pointed to a multistage mechanism of the formation of the TBP complex with the TATA-containing ODN. The results showed that with the increasing concentration and length of the ODN, heterogeneity of conformational changes (taking place during the first second of the interaction with TBP) in DNA also increases. In contrast to the initial nonspecific interaction, the subsequent phases strictly depend on TBP concentration: at the TBP:ODN ratio of 10:1, the velocity of change of the FRET signal increases approximately 100-fold.     

Structure and Origin of a Novel Dimeric Retroposon B1-dID

Here we describe a new short retroposon family of rodents. Like the primate Alu element consisting of two similar monomers, it is dimeric, but the left and right monomers are different and descend from B1 and ID short retroposons, respectively. Such elements (B1-dID) were found in the genomes of Gliridae, Sciuridae, Castoridae, Caviidae, and Hystricidae. Nucleotide sequences of this retroposon can be assigned to several structural variants. Phylogenetic analysis of B1-dID and related sequences suggests a possible scenario of B1-dID evolution in the context of rodent evolution. Received: 30 August 1999 / Accepted: 20 March 2000     

Geographic origin of human mitochondrial DNA: accommodating phylogenetic uncertainty and model comparison

Many biogeographic problems are tested on phylogenetic trees. Typically, the uncertainty in the phylogeny is not accommodated when investigating the biogeography of the organisms. Here we present a method that accommodates uncertainty in the phylogenetic trees. Moreover, we describe a simple method for examining the support for competing biogeographic scenarios. We illustrate the method using mitochondrial DNA sequences sampled from modern humans. The geographic origin of modern human mtDNA is inferred to be in Africa, although support for this hypothesis was ambiguous for data from an early paper.     

Effect of spacer attachment sites and pH-sensitive headgroup expansion on cationic lipid-mediated gene delivery of three novel myristoyl derivatives

The transfection activity and physicochemical properties of the dimyristoyl derivatives from three novel series of double-chained tertiary cationic lipids were compared. Two of the derivatives were constructed as isomers with different linkages of the same bis-(2-dimethylaminoethane) polar headgroup and hydrophobic chains to the diaminopropanol backbone, while the third was designed with a hydrophilic region containing only a single ionizable amine group. Such systematic molecular changes offer a great opportunity to delineate factors critical for transfection activity, which in this work include the intramolecular distance between the hydrophobic chains and pH-expandability of the polar headgroup. The physical studies comprised a variety of techniques, including pKa determination, Langmuir monolayer studies, fluorescence anisotropy, gel electrophoresis mobility shift assay, ethidium bromide displacement assay, particle size distribution, and zeta potential. These studies are crucial in the development of lipid-based gene delivery systems with improved efficacy. Physicochemical characterization revealed that a symmetric bivalent pH-expandable polar headgroup in combination with greater intramolecular space between the hydrophobic chains provide for high transfection activity through efficient binding and compaction of pDNA, increased acyl chain fluidity, and high molecular elasticity.     

Photophysics of nanographenes: from polycyclic aromatic hydrocarbons to graphene nanoribbons

Photosynthesis Research - Graphene quantum dots (GQDs) and nanoribbons (GNRs) are classes of nanographene molecules that exhibit highly tunable photophysical properties. There have been great...