Prominent Spikes Research Articles

Activity-Dependent Control of Neuronal Output by Local and Global Dendritic Spike Attenuation

Neurons possess elaborate dendritic arbors which receive and integrate excitatory synaptic signals. Individual dendritic subbranches exhibit local membrane potential supralinearities, termed dendritic spikes, which control transfer of local synaptic input to the soma. Here, we show that dendritic spikes in CA1 pyramidal cells are strongly regulated by specific types of prior input. While input in the linear range is without effect, supralinear input inhibits subsequent spikes, causing them to attenuate and ultimately fail due to dendritic Na(+) channel inactivation. This mechanism acts locally within the boundaries of the input branch. If an input is sufficiently strong to trigger axonal action potentials, their back-propagation into the dendritic tree causes a widespread global reduction in dendritic excitability which is prominent after firing patterns occurring in vivo. Together, these mechanisms control the capability of individual dendritic branches to trigger somatic action potential output. They are invoked at frequencies encountered during learning, and impose limits on the storage and retrieval rates of information encoded as branch excitability.

Genetic evaluation of growth of Kenya Boran cattle using random regression models

Data consisting of 18 884 weight records collected from 1273 Boran cattle from birth to 24 months of age were used to estimate covariance functions and genetic parameters for growth of Boran cattle using random regression (RR) models under a situation of small herd size and inconsistent recording. The RR model fitted quadratic Legendre polynomials of age at recording for additive genetic and permanent environmental effects. Genetic variance increased from birth, reaching an asymptotic value at 455 days and was maximum at 525 days of age after which it gradually dropped. Permanent environmental variance increased throughout the trajectory. Estimates of temporary environmental variance were heterogeneous across ages. Direct heritability and permanent environmental variance as a proportion of phenotypic variance fluctuated greatly during the early ages but later stabilized at intermediate to later ages; the estimates ranged from 0.11 to 0.33 and from 0.18 to 0.83, respectively. Genetic correlation estimates were positive, ranging from 0.10 to unity. The estimates declined with increasing in lag between the age points. Phenotypic correlation pattern was erratic between early ages, negatively low (-0.02) between the extreme data points and moderate to highly positive (>0.50) between intermediate and later points, with prominent spikes along the diagonal. It is concluded that RR models have potential for modelling growth of Boran cattle, notwithstanding conditions of small herd sizes and inconsistent recording.

MEG source estimation from mesio-basal temporal areas in a child with a porencephalic cyst

A child whose left temporal lobe contained mesial, anterior and basal structures but lacked superio-lateral cortex had intractable epilepsy secondary to a porencephalic cyst. Magnetoencephalography (MEG) shows equivalent current dipoles (ECDs) as dipole modeling for temporal lobe epilepsy rather than in an exact location. We hypothesized that the magnetic fields generated by the epileptic discharges in mesio-basal temporal areas could be detected by MEG without interference from the superio-lateral temporal cortices. We analyzed MEG spikes using single dipole analysis and synthetic aperture magnetometry (SAM), and compared with EEG spike topography. Two MEG ECDs corresponding to T3 spikes localized to the anterior mesio-basal temporal region with vertical orientation. Sixteen MEG ECDs corresponding to T5 spikes localized to the middle to posterior mesio-basal temporal region with vertical orientation. SAM revealed maximum current density at hippocampus and anterior fusiform gyrus for T3 spikes, and at posterior hippocampus and fusiform gyrus for T5 spikes. Vertically oriented ECDs were obtained without superio-lateral temporal cortices because of temporo-parieto-occipital porencephalic cyst. The absence of superio-lateral temporal cortices, prominent temporal EEG spikes, less prominent MEG spikes, and mesio-basal SAM spikes indicated that the vertically oriented ECDs were projected directly from the mesio-basal temporal region.

Photometry of particulate surfaces at extremely small phase angles

We present results of goniometric photometry of different samples at extremely small phase angles using a new laboratory setup with a laser light source ( λ=0.63 μm). No opposition effect of carbon soot is found in the range 0.008–1.5°; whereas, MgO deposits and very disperse porous SiO 2 powder demonstrate a narrow brightness spike of significant amplitude. We find a strong dependence of phase curve slope in the range on albedo when studying mixtures of white chalk and carbon soot. These measurements as applied to interpretation of opposition effect observed for Kuiper belt objects suggest that the albedo of these objects cannot be small. Size particle separates of olivine reveal prominent opposition spikes independent of the particle size. Spherical particles with a diameter near 50 μm show significant differences in their scattering behavior depending on whether they form a monolayer or thick particulate surfaces. The latter show a sharp opposition surge unlike the monolayer. Except for the monolayer of spheres, no particulate surface in our measurements yet exhibits phase curve rounding as the phase angle approaches zero.

Electron Tomography of Nascent Herpes Simplex Virus Virions

Cells infected with herpes simplex virus type 1 (HSV-1) were conventionally embedded or freeze substituted after high-pressure freezing and stained with uranyl acetate. Electron tomograms of capsids attached to or undergoing envelopment at the inner nuclear membrane (INM), capsids within cytoplasmic vesicles near the nuclear membrane, and extracellular virions revealed the following phenomena. (i) Nucleocapsids undergoing envelopment at the INM, or B capsids abutting the INM, were connected to thickened patches of the INM by fibers 8 to 19 nm in length and < or =5 nm in width. The fibers contacted both fivefold symmetrical vertices (pentons) and sixfold symmetrical faces (hexons) of the nucleocapsid, although relative to the respective frequencies of these subunits in the capsid, fibers engaged pentons more frequently than hexons. (ii) Fibers of similar dimensions bridged the virion envelope and surface of the nucleocapsid in perinuclear virions. (iii) The tegument of perinuclear virions was considerably less dense than that of extracellular virions; connecting fibers were observed in the former case but not in the latter. (iv) The prominent external spikes emanating from the envelope of extracellular virions were absent from perinuclear virions. (v) The virion envelope of perinuclear virions appeared denser and thicker than that of extracellular virions. (vi) Vesicles near, but apparently distinct from, the nuclear membrane in single sections were derived from extensions of the perinuclear space as seen in the electron tomograms. These observations suggest very different mechanisms of tegumentation and envelopment in extracellular compared with perinuclear virions and are consistent with application of the final tegument to unenveloped nucleocapsids in a compartment(s) distinct from the perinuclear space.

Light backscatter by surfaces composed of small spherical particles

We present measurements of phase angle curves of intensity and degree of linear polarization of powdery surfaces at two spectral bands centered near 0.44 and 0.63 microm. Three powder samples consisting of nonabsorbing spherical particles of sizes comparable with the wavelengths 0.5, 1.0, and 1.5 microm were examined. The particulate surfaces were measured in the phase angle range of 0.2 degrees-50 degrees by two different photometers and/or polarimeters. At small phase angles, powdery samples consisting of spherical particles (having very high albedo that resulted in significant multiple scattering) showed prominent features that corresponded to single-particle scattering. These features became more prominent after compressing the surfaces when we changed the packing density of the powders from 0.29 to 0.48. Noticeable differences were observed between polarimetric curves corresponding to different wavelengths. All the samples demonstrated prominent opposition intensity spikes at phase angles <2 degrees likely caused by the coherent backscatter enhancement due to multiple scattering within the particulate surface. The intensity phase curves at these two wavelengths were similar. The photopolarimetric measurements may have broad applications to the interpretation of photometry, spectroscopy, and polarimetry of the ice regoliths of high albedo satellites.

Geochronology of the khondalite belt of Trivandrum Block, Southern India: Electron probe ages and implications for Gondwana tectonics

In a comprehensive U–Pb electron microprobe study of zircon and monazite from the khondalite belt of Trivandrum Block in southern Kerala, we present age data on five key metapelite locations (Nedumpara, Oottukuzhi, Kulappara, Poolanthara and Paranthal). The rocks here, characterized by the assemblage of garnet–sillimanite–spinel–cordierite–biotite–K–feldsapr–plagiocalse–quartz–graphite, have been subjected to granulite facies metamorphism under extreme thermal conditions as indicated by the stability of spinel + quartz and the presence of mesoperthites that equilibrated at ultrahigh-temperature (ca. 1000 °C) conditions. The oldest spot age of 3534 Ma comes from the core of a detrital zircon at Nedumpara and is by far the oldest age reported from this supracrustal belt. Regression of age data from several spot analyses in single zircons shows “isochrons” ranging from 3193 ± 72 to 2148 ± 94 Ma, indicating heterogeneous population of zircons derived from multiple provenance. However, majority of zircons from the various localities shows Neoproterozoic apparent ages with sharply defined peaks in individual localities, ranging between 644–746 Ma. The youngest zircon age of 483 Ma was obtained from the outermost rim of a grain that incorporates a relict core displaying ages in the range of 2061–2543 Ma. The cores of monazites also show apparent older ages of Palaeo-Mesoproterozoic range, which are mantled by late Neoproterozoic/Cambrian rims. The oldest monazite core has an apparent age of 2057 Ma. Extensive growth of new monazite during latest Neoproterozoic to Cambrian–Ordovician times is also displayed by grain cores with apparent ages up to 622 Ma. The homogeneous core of a sub-rounded monazite grain yielded a maximum age of 569 Ma, markedly younger than the 610 Ma age reported in a previous study from homogenous and rounded zircon core from a metapelite in Trivandrum Block. These younger ages from abraded grains that have undergone fluvial transport are interpreted to indicate that deposition within the khondalite belt was as young as, or later than, this range. Probability density plots indicate that majority of the monazite grain population belong to Late Proterozoic/Cambrian age (ca. 560–520 Ma) with major peaks defining sharp spikes in individual localities. The age data presented in this study indicate that the metasediments of the Trivandrum Block sourced from Archaean and Paleo-Mesoproterozoic crustal fragments that were probably assembled in older supercontinents like Ur and Columbia. The largest age population of zircons belong to the Neoproterozoic, and are obviously related to orogenies during the pre-assembly phase of Gondwana, possibly from terrains belonging to the East African Orogen. Several prominent age spikes within the broad late Neoproterozoic–Cambrian age range displayed by monazites denote the dynamic conditions and extreme thermal perturbations attending the birth of Gondwana. Our study further establishes the coherent link between India and Madagascar within the East Gondwana ensemble prior to the final assembly of the Gondwana supercontinent.

The spatial clustering of X-ray selected AGN and galaxies in the Chandra Deep Field South and North

We investigate the spatial clustering of X-ray selected sources in the two deepest X-ray fields to date, namely the 2 Ms Chandra Deep Field North (CDFN) and the 1 Ms Chandra Deep Field South (CDFS). The projected correlation function w(rp), measured on scales ∼0.2−10 h −1 Mpc for a sample of 240 sources with spectroscopic redshift in the CDFN and 124 sources in the CDFS at a median redshift of ¯ z ∼ 0.8 is used to constrain the amplitude and slope of the real space correlation function ξ(r) = (r/r0) −γ . The clustering signal is detected at high confidence (> 7σ) in both fields. The amplitude of the correlation is found to be significantly different in the two fields, the correlation length r0 being 8.6 ± 1.2 h −1 Mpc in the CDFS and 4.2 ± 0.4 h −1 Mpc in the CDFN, while the correlation slope γ is found to be flat in both fields: γ = 1.33 ± 0.11 in the CDFS and γ = 1.42 ± 0.07 in the CDFN (a flat Universe with Ωm = 0. 3a ndΩΛ = 0.7 is assumed; 1σ Poisson error estimates are considered). The correlation function also has been measured separately for sources classified as AGN or galaxies. In both fields AGN have a median redshift of ¯ ∼ 0. 9a nd am edian 0.5−10 keV luminosity of ¯ Lx ∼ 10 43 erg s −1 , i.e. they are generally in the Seyfert luminosity regime. As in the case of the total samples, we found a significant difference in the AGN clustering amplitude between the two fields, the best fit correlation parameters being r0 = 10.3 ± 1.7 h −1 Mpc, γ = 1.33 ± 0.14 in the CDFS, and r0 = 5.5 ± 0.6 h −1 Mpc, γ = 1.50 ± 0.12 in the CDFN. In the CDFN, where the statistics are sufficiently high, we were also able to measure the clustering of X-ray selected galaxies, finding r0 = 4.0 ± 0.7 h −1 Mpc and γ = 1.36 ± 0.15. Within each field no statistically significant difference is found between soft and hard X-ray selected sources or between type 1 and type 2 AGN. After having discussed and ruled out the possibility that the observed variance in the clustering amplitude is due to observational biases, we verified that the extra correlation signal in the CDFS is primarily due to the two prominent redshift spikes at z ∼ 0.7 reported by Gilli et al. (2003). The high (5−10 h −1 Mpc) correlation length measured for the X-ray selected AGN at z ∼ 1i n the twoChandra Ms fields is comparable to that of early type galaxies at the same redshift. This is consistent with the idea that, at z ∼ 1, AGN with Seyfert-like luminosities might be generally hosted by massive galaxies.

Co-Replication of a Reovirus and a Polydnavirus in the Ichneumonid Parasitoid Hyposoter exiguae

A recently established colony of the ichneumonid parasitoid, Hyposoter exiguae, was found to carry both a reovirus (HeRV) and a polydnavirus (HePDV). Morphogenesis of these viruses was observed in all cells comprising the ovarian calyx epithelium, apparently without detrimental effect to the parasitoid. While polydnavirus replication in H. exiguae was restricted to the calyx region, HeRV was detected in ovarioles, oviducts, midguts, malpighian tubules, and accessory glands associated with the male reproductive system. In addition, HeRV was able to infect the fat body of parasitized host larvae and to establish a persistent infection in vitro. Electron microscopy revealed that both viruses were released into the calyx fluid compartment exclusively by budding, a phenomenon rarely observed among the Reoviridae; HeRV envelopes thus obtained, however, appeared to be subsequently shed within the oviducts. HeRV particles were concentrated to near homogeneity by differential centrifugation; mature virions consisted of seven to eight structural polypeptides and 10 dsRNA genome segments. Prominent spikes were observed at the vertices of icosahedral core particles. Most, but not all, individuals comprising the H. exiguae colony appeared to be infected with HeRV, suggesting a commensal relationship between wasp and virus; however, while this association is of obvious benefit to the virus, it seems unlikely that any advantage accrues to the parasitoid which carries it.

Integrated stratigraphy of the Waitakian‐Otaian Stage boundary stratotype, Early Miocene, New Zealand

The base of the type section of the Otaian Stage at Bluecliffs, South Canterbury, is recognised as the stratotype for the boundary between the Waitakian and Otaian Stages. Principal problems with the boundary are the restriction of existing bioevent proxies to shelf and upper slope environments and its uncertain age. These topics are addressed by a multidisplinary study of a 125 m section about the boundary, which examines its lithostratigraphy, depositional setting, biostratigraphy, correlation, and geochronology. The lower siltstone lithofacies (0–38.5 m) was deposited at upper bathyal depths (200–600 m) in a marginal basin which was partially sheltered from fully oceanic circulation by a submarine high and islands. The site was covered by cool‐temperate water and was probably adjacent to the Subtropical Convergence. This unit is succeeded by the banded lithofacies (38.5–106 m) and the upper siltstone lithofacies (basal 19 m studied). Paleodepth probably declined up‐sequence, but deposition at shelf depths is not definitely indicated. A cyclic pattern of abundance spikes in benthic and planktonic foraminifera commences 9 m above base and extends to 73 m in the banded lithofacies. Oxygen isotope excursions (up to 2.08%o) in Euuvigerina miozea and Cibicides novozelandicus are greatest within the interval containing the abundance spikes. The stage boundary occurs in the banded lithofacies at the highest abundance spike (73 m). Although condensed intervals might affect the completeness of the section, they are not associated with sedimentary discontinuities, and we consider that the section is suitable as a biostratigraphic reference. Spores, pollens, dinoflagellates, calcareous nannofossils, foraminifera, bryozoans, and ostracods are preserved near the boundary, but molluscs principally occur higher, in the shallower upper siltstone lithofacies. Siliceous microfossils are rare. There is considerable scope for further biostratigraphic research. The primary event marking the boundary at 73 m is the appearance of the benthic foraminifer Ehrenbergina marwicki. This is a distinctive and widely distributed event but is restricted to shelf and upper bathyal environments. Supplementary events in planktonic foraminifera and calcareous nannofossils were researched. Highest occurrences of Globigerina brazieri and G. euapertura are recorded at 47 and 58 m. There is a marked decline in relative abundance of Paragloborotalia spp. at 62 m. Helicosphaera carteri becomes more abundant than H. euphratis between 56 and 87 m. These events are not exact proxies for the boundary but they may usefully indicate proximity to it. They occur in the interval of prominent spikes in foraminiferal abundance. The Waitakian‐Otaian boundary is dated at 21.7 Ma by strontium isotopes. Stable primary remanence could not be determined in a pilot paleomagnetic study of Bluecliffs specimens. However, specimens trended towards reversed polarity, and remagnetisation great circle analysis will allow directions to be calculated in future collections.

The age and distribution of mantle heterogeneity along the Mid-Atlantic Ridge (31–41°N)

New trace element and isotopic data for basalts from the mid-Atlantic ridge between 31 and 41°N allow a better description of the geochemical gradient south of the Azores triple junction, and the systematics of mantle source heterogeneity. There is a long wavelength enrichment in incompatible trace elements and isotopes associated with the Azores hot spot that extends from the Kurchatov fracture zone near 41°N to the Hayes fracture zone near 33°N. Superimposed on this gradient are local spikes of enrichment, the most prominent being the anomaly near the Oceanographer Fracture Zone (NOFZ). The Oceanographer anomaly spike is reflected modestly in the morphology of the ridge axis, but is not obviously related to a plume. The isotopic data alone are consistent with involvement of subcontinental material, but the samples do not contain the negative Nb–Ta anomalies which are usually associated with the presence of continental material in the mantle source. Away from the prominent enrichment spikes associated with the Azores and Oceanographer fracture zone, there are systematic relationships in this region between parent/daughter element ratios and isotope ratios. The Pb, Sr and Nd isotope systems all give apparent ages in the range 100 Ma to 300 Ma, with the age increasing with likely parent/daughter fractionation during melting (U/Pb < Rb/Sr < Sm/Nd age). Monte Carlo simulations of an enrichment event in a depleted heterogeneous mantle at 250 Ma produce results that correspond well with the observations for all three isotopic systems. Since this age also corresponds to the pre-opening of the North Atlantic, it raises the possibility that some of the heterogeneity in this region is associated with shallow level mantle heterogeneity resulting from the rifting of Gondwanaland rather than from interaction with mantle plumes. The data may also reflect a mean mixing time for the heterogeneities in the upper mantle source. Sr isotope systematics reveal correlations in a 87Sr/ 86Sr versus 87Rb/ 86Sr plot, which are geographically controlled. Data points from 10–24°N samples and data points from 31–38°N samples (excluding NOFZ samples) plot on two offset trends of similar slope. Irrespective of the origin of the isotopic variations, these data require end member depleted mantle with distinct isotopic characteristics. Depleted sources with low 87Rb/ 86Sr (0.005–0.04) and low (La/Sm) N (<0.5), have 87Sr/ 86Sr values that vary between 0.70215 and 0.7029. Therefore the depleted mantle source of N-MORB is not a homogeneous reservoir, but shows isotopic variations almost as large as the differences between generic depleted mantle (0.7025) and the enriched Atlantic plumes. Creation of a very heterogeneous depleted mantle in terms of isotopic composition needs to be included as a constraint on models of mantle mixing and convection.

Native display of complete foreign protein domains on the surface of hepatitis B virus capsids.

The nucleocapsid of hepatitis B virus (HBV), or HBcAg, is a highly symmetric structure formed by multiple dimers of a single core protein that contains potent T helper epitopes in its 183-aa sequence. Both factors make HBcAg an unusually strong immunogen and an attractive candidate as a carrier for foreign epitopes. The immunodominant c/e1 epitope on the capsid has been suggested as a superior location to convey high immunogenicity to a heterologous sequence. Because of its central position, however, any c/e1 insert disrupts the core protein's primary sequence; hence, only peptides, or rather small protein fragments seemed to be compatible with particle formation. According to recent structural data, the epitope is located at the tips of prominent surface spikes formed by the very stable dimer interfaces. We therefore reasoned that much larger inserts might be tolerated, provided the individual parts of a corresponding fusion protein could fold independently. Using the green fluorescent protein (GFP) as a model insert, we show that the chimeric protein efficiently forms fluorescent particles; hence, all of its structurally important parts must be properly folded. We also demonstrate that the GFP domains are surface-exposed and that the chimeric particles elicit a potent humoral response against native GFP. Hence, proteins of at least up to 238 aa can be natively displayed on the surface of HBV core particles. Such chimeras may not only be useful as vaccines but may also open the way for high resolution structural analyses of nonassembling proteins by electron microscopy.

The cataclysmic variable period gap: still there

We consider a recently proposed alternative explanation of the CV period gap in terms of a revised mass-radius relation for the lower main sequence. We show that no such thermal equilibrium relation is likely to produce a true gap. Using population synthesis techniques we calculate a model population that obeys the claimed equilibrium mass-radius relation. A theoretical period histogram obtained from this population shows two prominent period spikes rather than a gap. We consider also recent arguments suggesting that the period gap itself may not be real. We argue that, far from demonstrating a weakness of the interrupted braking picture, the fact that most CV subtypes prefer one side of the gap or the other is actually an expected consequence of this model.

Evidence for retrovirus infections in green turtles Chelonia mydas from the Hawaiian islands

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 31:1-7 (1997) - doi:10.3354/dao031001 Evidence for retrovirus infections in green turtles Chelonia mydas from the Hawaiian islands Rufina N. Casey1, Sandra L. Quackenbush1, Thierry M. Work2, George H. Balazs3, Paul R. Bowser1, James W. Casey1,* 1Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA2U.S. Geological Survey, Biological Resources Division, National Wildlife Health Center, Honolulu Field Station, Honolulu, Hawaii 96850, USA3National Marine Fisheries Service, Southwest Fisheries Science Center, Honolulu Laboratory, Honolulu, Hawaii 96822-2396, USA *Addressee for correspondence. E-mail: jwc3@cornell.edu Apparently normal Hawaiian green turtles Chelonia mydas and those displaying fibropapillomas were analyzed for infection by retroviruses. Strikingly, all samples were positive for polymerase enhanced reverse transcriptase (PERT) with levels high enough to quantitate by the conventional reverse transcriptase (RT) assay. However, samples of skin, even from asymptomatic turtles, were RT positive, although the levels of enzyme activity in healthy turtles hatched and raised in captivity were much lower than those observed in asymptomatic free-ranging turtles. Turtles with fibropapillomas displayed a broad range of reverse transcriptase activity. Skin and eye fibropapillomas and a heart tumor were further analyzed and shown to have reverse transcriptase activity that banded in a sucrose gradient at 1.17 g ml-1. The reverse transcriptase activity purified from the heart tumordisplayed a temperature optimum of 37°C and showed a preference for Mn2+ over Mg2+. Sucrose gradient fractions of this sample displaying elevated reverse transcriptase activity contained primarily retroviral-sized particles with prominent envelope spikes, when negatively stained and examined by electron microscopy. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of gradient-purified virions revealed a conserved profile among 4 independent tumors and showed 7 prominent proteins having molecular weights of 116, 83, 51, 43, 40, 20 and 14 kDa. The data suggest that retroviral infections are widespread in Hawaiian green turtles and a comprehensive investigation is warranted to address the possibility that these agents cause green turtle fibropapillomatosis (GTFP). Green turtle · Reverse transcriptase · Retrovirus · Fibropapillomatosis · Electron microscopy Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 31, No. 1. Publication date: October 28, 1997 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1997 Inter-Research.

Late Jurassic climate and its impact on carbon cycling

The climate of the Late Jurassic has been characterized by high atmospheric CO 2 levels and by a monsoonal rainfall pattern. In this study we traced the evolution of the global carbon cycle through the Late Jurassic with the help of carbonate carbon isotope stratigraphy. The Oxfordian-Tithonian δ 13C curve is marked by one major positive carbon isotope excursion with an amplitude Δδ 13 C > 1.0‰ (Middle to Late Oxfordian) and a second, minor positive excursion with an amplitude Δδ 13 C < 1.0‰ (Late Kimmeridgian). The Early Kimmeridgian and Early Tithonian δ 13C-values fluctuate around δ 13 C = +2‰±0.3‰ and contrast with the less positive δ 13C-values of Early Oxfordian and Late Tithonian age ( δ 13 C = +1‰±0.5‰ ). A comparison of the Late Jurassic carbonate carbon isotope curve with the occurrence of organic-rich sediments suggests that not only fluctuations in organic carbon burial but also in carbonate carbon burial had an impact on the C-isotope record. The Oxfordian C-isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level. However, episodes of enhanced organic carbon burial during the Kimmeridgian and Early Tithonian are not reflected by prominent spikes in the C-isotope record. Favourable conditions for carbonate platform growth at a time of high global sealevel may have resulted in the stabilisation of the C org/C carb burial ratio and hence maintained the δ 13C record at steady but relatively positive values. The Middle and Late Tithonian C-isotope values drop below δ 13 C = +1.5‰ . A similar shift to less positive C-isotope values was recognized in other C-isotope records from the Tethys and Atlantic Oceans and reflects a decrease in the C org/C carb burial ratio possibly related to a reorganisation of the global climate system. Globally widespread marine black shale-mature quartzose sandstone assemblages suggest that the relative efficiency of the Late Jurassic carbon pumps was controlled by weathering, erosion and runoff causing widespread marine eutrophication. Eutrophication favoured the organic carbon pump but it diminished the carbonate-platform growth potential. The monsoonal rainfall distribution pattern may explain why Late Jurassic carbonate platforms experienced less severe growth crises than Early Cretaceous carbonate platforms.

SHAPES AND FREE ENERGIES OF MOLTEN SODIUM CLUSTERS

The shell-correction method is formulated to calculate the shapes and free energies of hot alkali clusters. The equilibrium shapes of Na clusters with mass 50–700 are calculated by minimizing simultaneously with respect to two deformation parameters. For T=700°K strong deviations from spheroidal shape including reflection asymmetric shapes are found to survive in the center of the open shells. The second derivative of calculated free energy correlates with the derivative of the experimental cluster abundances, showing prominent spikes related to the change between spherical and deformed shape.

Time-Lapse Confocal Imaging of Calcium Dynamics in Starfish Embryos

During fertilization and cleavage, embryos undergo transient rises in their intracellular free calcium levels that are postulated to provide essential signals enabling normal development to proceed. In order to analyze the spatiotemporal patterns and possible biological significance of these calcium transients, time-lapse confocal microscopy was used to monitor starfish embryos during normal development and following experimental manipulations that disrupted cleavage and/or the release of calcium ions from internal stores in the embryo. For such analyses, oocytes were co-injected with dextran-conjugated forms of the calcium-sensitive fluorochrome calcium green (CG) and the calcium-insensitive dye rhodamine (Rh) for dual-channel confocal ratioing. Based on CG/Rh ratioed images obtained every 15 sec far the first few hours of development, no prominent calcium spikes were typically evident at the onset of the first cell cycle as hormone-treated oocytes resumed maturation and underwent germinal vesicle breakdown (GVBD). Subsequently, fertilizations of post-GVBD oocytes caused a single prolonged calcium wave that reached relatively uniform amplitudes throughout the ooplasm. Within 90 min after fertilization, most starfish zygotes began to display clusters of repetitive calcium oscillations that typically—but not invariably—preceded nuclear envelope breakdown, anaphase onset, and the formation of the first cleavage furrow. Rapidly decaying calcium oscillations continued through at least the first five cleavages in specimens that developed into normal blastulae, and unlike fertilization-induced calcium waves, such spikes tended to be more pronounced in the cortical cytoplasm during early cleavages. Thus, three different types of calcium dynamics—no marked transients, a single nonoscillating wave, and repetitive oscillations—were observed as normally developing starfish underwent prefertilization maturation, fertilization, and cleavage, respectively, suggesting that the spatiotemporal patterns of calcium spiking can change during starfish early development. In specimens microinjected with colchicine, calcium transients were also visible in the absence of cell divisions, indicating that calcium spiking can be uncoupled from cytokinesis. To assess whether calcium fluxes are required for normal development, oocytes were also treated with haparia to black calcium release mediated by inositol 1,4,5-trisphosphate (IP 3). Injections of heparin, but not the control molecule de-N-sulfated heparin, caused abnormal fertilization-induced calcium dynamics in a does-dependent fashion and typically abolished marked postfertilization calcium oscillations and normal cleavage. Based on correlative studies using caged IP 3, heparin interfered with IP 3-mediated calcium release, suggesting that such release is involved in the production of the free calcium elevations that occur in normally developing starfish embryos.

Physiological subgroups of nonpyramidal cells with specific morphological characteristics in layer II/III of rat frontal cortex

Physiological and morphological properties of nonpyramidal cells in layer II/III of frontal cortex of young rats were studied in vitro by whole-cell recording and intracellular staining with biocytin. Layer II/III nonpyramidal cells could be divided into four subgroups by their firing patterns in response to depolarizing current pulses and their patterns of dendritic and axonal arborizations. (1) Fast-spiking (FS) cells (35% of the total sample) showed an abrupt episode of nonadapting repetitive discharges of shorter-duration action potentials. FS cells had local and horizontal axonal arbors which did not enter layer I. This type of FS cell was immunoreactive for parvalbumin and included some basket cells. Three chandelier cells were identified as FS cells, although one chandelier cell was not identified as an FS cell. (2) Late-spiking (LS) cells (11%) exhibited slowly developing ramp depolarizations near threshold. LS cells were neurogliaform cells. (3) Low-threshold spike (LTS) cells (5%) had prominent low-threshold spikes when stimulated from hyperpolarizations. The main axons of LTS cells ascended, and the collaterals entered into layer I. (4) The remaining cells [regular-spiking nonpyramidal (RSNP) cells] (49%) could not be categorized into the above three subgroups. In some RSNP cells depolarizing pulses from hyperpolarizations induced fast depolarizing notches with small amplitude. RSNP cells had vertically elongated axonal fields, extending from layer I to V, sometimes to layer VI. This subgroup included double bouquet cells and bipolar cells. Each subgroup with a different firing mode may differentially contribute to neocortical laminar and columnar circuitry.

The Structure of Human Parvovirus B19 at 8 Å; Resolution

Empty capsids of the human parvovirus B19, self-assembled in a baculovirus expression system, have been crystallized in a cubic space group P2,3 with a = 362 Å. In spite of extensive purifications, the crystals diffract X-rays to only 8.0 Å resolution. Diffraction data were collected using oscillation photography with synchrotron radiation. The orientations of the particles in the unit cell were determined with a self-rotation function and their positions were obtained with an R-factor search using the known homologous canine parvovirus (CPV) structure. The resultant phases were improved by electron density averaging and solvent flattening to include all the terms between 23.0 and 8.0 Å resolution. The central eight-stranded antiparallel β-barrel, common to many viruses, is situated similarly in B19 with respect to the icosaheral symmetry axes to that observed for feline panleukopenia virus (FPV) and CPV. However, the surface structure of B19 is significantly different from the other known parvoviruses. The most striking difference is that B19 lacks the prominent spikes on the threefold icosahedral axes observed in FPV and CPV. This spike region contains residues involved in host recognition and antigenicity for the latter viruses, showing that there are major differences between subgroups of autonomous parvoviruses.

Coronavirus immunogens

Coronaviruses (CV) infect a variety of livestock, poultry and companion animals. They belong to at least five antigenic groups. CV cause localized infections of the respiratory and/or intestinal tracts, with the exception of feline infectious peritonitis virus (FIVP) and hemagglutinating encephalomyelitis (HEV) which cause systemic infections. The enteropathogenic CV infect the villous enterocytes resulting in villous atrophy leading to malabsorptive diarrhea. Several CV (bovine CV-BCV, porcine respiratory CV-PRCV, infectious bronchitis virus-IBV) cause respiratory disease. Current evidence indicates that protection against enteric and respiratory CV infections is mediated by passive or active immunity at the primary site of CV replication. Maternal vaccination approaches to induce passive immunity include the use of inactivated and modified live viral vaccines. Modified live viruses and a Ts mutant CV (FIPV) are also used as oral or intranasal vaccines to induce active mucosal immunity. The success of these vaccines in the field is often compromised by a number of potential problems. Coronaviruses are spherical, enveloped viruses, ranging from 80–160 nm in diameter and containing a positive-stranded RNA genome. They possess prominent surface spikes and some species display a fringe of smaller surface projections believed to be the hemagglutinin (HE). Coronaviruses possess 3 to 4 structural proteins: the spike (S) glycoprotein (150–200 kDa), the integral membrane glycoprotein (M; 20–30 kDa) and the nucleocapsid phosphoprotein (N; 43–50 kDa). A subset of CV (BCV, HEV, turkey CV) possess a third glycoprotein on the virion surface, the HE (60–65 kDa). These proteins can be quantitated using pooled monoclonal antibodies (mAb) to distinct epitopes of each protein in ELISA. Most research has focused on the S protein as a candidate antigen for CV vaccines since it induces virus neutralizing (VN) antibodies. However the HE protein stimulates the production of VN and HE inhibiting antibodies and the M protein induces antibodies that neutralize virus in the presence of complement. Attempts to correlate in vitro VN antibody activity with in vivo protection have shown that the passive transfer of VN mAb to the S or HE protein conferred passive protection against CV challenge in some studies, but not others. Additional research has implicated a possible role for other CV proteins in immunity. Studies of mAb to the M protein of transmissible gastroenteritis (TGEV) have provided evidence for a direct role of the M protein in the induction of αIFN by porcine blood leukocytes. The potential significance of this phenomenon to immunity to TGEV is unclear. Similarly, studies of IBV have suggested that determinants recognized by T cells reside on the N protein and these determinants may be shared among heterologous strains of IBV, resulting in the induction of cross-protection. Thus epitopes on the N protein may be important for induction of cell mediated immunity (CMI). CMI may play an important role in protection of cats against FIPV, since induction of circulating antibodies to the S protein of FIPV contributes to disease pathogenesis by the induction of immune complexes and antibody dependent enhancement of the infectivity of FIPV for macrophages. An increased understanding of antibody and CMI responses following natural CV infections in animals is needed to identify the antigens and epitopes that induce protective immune responses. The expression of CV structural protein genes in various vectors will provide the recombinant proteins needed for future immunogenicity studies in the host species. Furthermore, live rDNA vectors that replicate in the gut and express coronavirus genes may provide a new generation of coronavirus vaccines.