1,721,699 research outputs found
Spatial and temporal patterns of neurogenesis in the embryo of the locust (Schistocerca gregaria)
No full textEmbryonic neurogenesis in the ventral nerve cord of the locust Schistocerca gregaria was studied using toluidine blue (TB) staining and birthdating of cells by incorporation of bromodeoxyuridine (BUdR). In the thorax, the neuroblasts (NBs) start dividing at the 28% stage and neurogenesis continues until 90%. In the abdomen, neurogenesis starts at about 30% and continues until 70%. Every NB appears to have its own fixed period of division before disappearing. Thus a specific spatial and temporal pattern of NB degeneration can be seen in every segment. This pattern is identical in each of the three thoracic ganglia. We have traced the fate of each of the original complement of NBs in the mesothoracic neuromere and specified the stage of development at which each NB ends its lineage and disappears. The abdominal segments A2 to A7 share an identical pattern of NB death, which is not comparable to the thoracic pattern. The progress of neurogenesis is marked by a gradual decrease in the number of NBs, with NBs in the thoracic ganglia persisting longer than their abdominal homologues. The differences between the thoracic and abdominal NBs are also reflected in the rates at which they divide, thoracic NBs dividing at almost twice the rate of the abdominal NBs
Inhibition of GABA uptake potentiates the effects of exogenous GABA on locust skeletal muscle
No full text1. Insect skeletal muscle is relatively insensitive to applied GABA, responses are elicited only when relatively high concentrations of GABA are used (>10?6M).2. Pretreatment of the muscle with the GABA uptake inhibitors nipecotic acid, ?-aminobutyric acid or ?-alanine increases the sensitivity of the muscle to GABA by as much as 1000-fold.3. The evidence suggests the existence of a GABA uptake mechanism in the insect neuromuscular system which could reside in glial cells
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Multi-Watt, diffraction-limited, CW and Q-switched, diode-end-pumped, double-clad waveguide lasers
No full textWe demonstrate that double-clad waveguides can be used to obtain multiWatt, CW and Q-switched, diffraction-limited output when end-pumped by broad-stripe diodes. The waveguide geometry is shown to be especially favourable for efficient laser operation of low gain and quasithree-level transitions. The performance of the Nd:YAG system at several operating wavelengths. The quasi-three-level 946 nm performance appears particularly impressive. The passively Q-switched Yb:YAG double-clad waveguide laser is demonstrated
Cloning and expression analysis of drosophila melanogaster extracellular Cu Zn SOD reveals sex specific variation
No full textAbstract: The superoxide dismutase (SOD) family of enzymes regulate reactive oxygen species by scavenging superoxide. In Drosophila homologues of two of the mammalian SODs, the intracellular (Sod1) and mitochondrial (Sod2) SODs, have been studied extensively indicating a link between SOD and ageing. Recently the sequence of a third Sod gene, homologous to both mammalian (Sod3) and C. elegans (Sod4) extracellular Sod, was identified in Drosophila and is also predicted to locate extracellularly (Sod3). We have cloned and sequenced this gene, identifying two gene products formed by alternative splicing. Here we report differential sex specific Sod3 expression patterns along with validation of a Sod3 hypomorph mutant. Furthermore, we indicate a functional role of Sod3 in protecting against H2O2 induced oxidative stress.<br/
The Nature of the Massive Young Stars in W75 N
No full textWe have observed the W75 N massive star forming region in SiO (J=2-1 and J=1-0) at 3"-5" resolution and in 6 cm, 2 cm, and 7 mm continuum emission at 1.4"-0.2" resolution. The abundance ratio of [SiO]/[H2]~5-7×10-11 is typical for what is expected in the ambient component of molecular clouds with active star formation. The SiO morphology is diffuse and centered on the positions of the ultracompact H II regions-no collimated, neutral jet was discovered. The ionized gas surrounding the protostars has emission measures ranging from 1 to 15×106 pc cm-6, densities from 0.4 to 5×104 cm-3, and derived spectral types of the central ionizing stars ranging from B0.5 to B2. Most of the detected sources have spectral indices that suggest optically thin to moderately optically thick H II regions produced by a central ionizing star. The spread in ages between the oldest and youngest early-B protostars in the W75 N cluster is 0.1-5×106 yr. This evolutionary timescale for W75 N is consistent with that found for early-B stars born in clusters forming more massive stars (M*>25Msolar)
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