bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic theory of radiative transfer through generalized cloud fields
Authors: Lane‐Veron Dana E. , Somerville Richard C. J.
Published: September 2004

We present a coherent treatment, based on linear kinetic theory, of stochastic radiative transfer in an atmosphere containing clouds. A brief summary of statistical cloud radiation models is included. We explore the sensitivities inherent in the stochastic approach by using a well‐known plane‐parallel model developed by Fouquart and Bonnel together with our own stochastic model which generalizes earlier work of F. Malvagi, R. N. Byrne, G. C. Pomraning, and R. C. J. Somerville. In overcast conditions, in comparison to the plane parallel model, the stochastic model underestimates transmittance at small optical depths (<7) and overestimates transmittance at large optical depths. The stochastic model is strongly sensitive to cloud optical properties, including cloud water content and cloud droplet effective radius. The extension of the stochastic approach to an atmospheric general circulation model parameterization appears to be most appropriate for cloud fraction ranging from 25 to 70%. We conclude that stochastic theory holds substantial promise as a modeling approach for calculating shortwave radiative transfer through partially cloudy fields. Unlike cloud‐resolving models and Monte Carlo cloud models, stochastic cloud models do not depend on specific realizations of the cloud field. Instead, they calculate the transfer of radiation through a cloudy atmosphere whose properties are known statistically in the form of probability density functions characterizing cloud geometry and cloud optical properties. The advantage of the stochastic approach is its theoretical generality and its potential for representing a complex cloud field realistically at modest computational cost.
Annual CO2 exchange of a peat field growing spring barley or perennial forage grass
Authors: Lohila Annalea , Aurela Mika , Tuovinen Juha‐Pekka , Laurila Tuomas
Published: September 2004

We report on net ecosystem CO2 exchange (NEE) measurements conducted with the eddy covariance method over agricultural peat soil in the 2‐year period between October 2000 and October 2002. In 2001, spring barley and undersown grass were sown on the site. After the barley harvest, the perennial forage grass was left to grow, so that in 2002 the field was growing grass. A higher maximum net CO2 uptake was observed for barley than for grass during the height of the summer, peaking at about −1.0 and −0.75 mg CO2 m−2 s−1, respectively. The maximum nighttime total ecosystem respiration was measured in July and was similar for both crops, about 0.35 mg CO2 m−2s−1. During the growing season the field acted as a daily CO2 sink for only 40 days in barley versus 84 days in grass. In the winter the average carbon dioxide efflux varied from 15.6 to 16.5 μg CO2 m−2 s−1. The annual NEE of the agricultural peat soil growing barley and grass was 771 ± 104 and 290 ± 91 g CO2 m−2, respectively. The longer net CO2 uptake period was the main reason for the lower annual NEE for grass; however, owing to the higher amount of grass biomass produced the net ecosystem production (NEP), calculated as the sum of NEE and removed biomass, was slightly larger for grass (452 g C m−2) than for barley (336 g C m−2). These results show that the organic peat is still undergoing rapid decomposition after more than 100 years of cultivation activity. In addition, switching from an annual to a perennial crop did not turn the field into a CO2 sink, at least during a 1‐year period.
Terahertz emission from p-lnAs due to the instantaneous polarization
Authors: Adomavičius R. , Urbanowicz A. , Molis G. , Krotkus A. , Šatkovskis E.
Published: September 2004

Terahertz radiation from differently doped n- and p-type InAs crystal surfaces was investigated by time-resolved measurement. Large increase of the emitted terahertz power has been observed for p-InAs samples with the p-doping levels of approximately 1016–1017cm−3. This increase was explained by a large surface depletion layer and an electric-field-induced optical rectification effect in this layer.
A specific form of thioredoxin h occurs in plant mitochondria and regulates the alternative oxidase
Authors: Gelhaye Eric , Rouhier Nicolas , Gérard Joelle , Jolivet Yves , Gualberto José , Navrot Nicolas , Ohlsson Per-Ingvard , Wingsle Gunnar , Hirasawa Masakazu , Knaff David B. , Wang Hongmei , Dizengremel Pierre , Meyer Yves , Jacquot Jean-Pierre
Published: September 2004

The plant mitochondrial thioredoxin (Trx) system has been described as containing an NADPH-dependent Trx reductase and Trx
o
. In addition to the mitochondrial isoform, Trx
o
, plants are known to contain several chloroplastic Trx isoforms and the cytosolic Trx
h
isoforms. We report here the presence in plant mitochondria of a Trx isoform (PtTrx
h
2) belonging to the Trx
h
group. Western blot analyses with mitochondrial proteins isolated from both poplar and GFP fusion constructs indicate that PtTrx
h
2 is targeted to plant mitochondria. The recombinant protein, PtTrx
h
2, has been shown to be reduced efficiently by the mitochondrial Trx reductase AtNTRA. PtTrx
h
2 is also able to reduce alternative oxidase homodimers and to allow its activation by pyruvate. In contrast, neither PtTrx
h
2 nor AtTrx
o
1 exhibits activity with several poplar glutathione peroxidases and especially a putative mitochondrial isoform. Incubation of PtTrx
h
2 with glutathione disulfide led to the formation of glutathionylated Trx, identified by mass spectrometry. The formation of a glutathione adduct increases the redox potential of PtTrx
h
2 from -290 to -225 mV. In addition to Trx
o
, this study shows that Trx
h
could also be present in mitochondria. This previously unrecognized complexity is not unexpected, considering the multiple redox-regulated processes found in plant mitochondria.
Prohaptoglobin is proteolytically cleaved in the endoplasmic reticulum by the complement C1r-like protein
Authors: Wicher Krzysztof B. , Fries Erik
Published: September 2004

Many secretory proteins are synthesized as proforms that become biologically active through a proteolytic cleavage in the trans-Golgi complex or at a later stage in the secretory pathway. Haptoglobin (Hp) is unusual in that it is cleaved in the endoplasmic reticulum before it enters the Golgi. Here, we present evidence that the recently discovered complement C1r-like protein (C1r-LP) mediates this cleavage. C1r-LP has not previously been shown to possess proteolytic activity, despite its homology to trypsin-like Ser proteinases. We demonstrate that coexpression of the proform of Hp (proHp) and C1r-LP in COS-1 cells effected cleavage of proHp in the endoplasmic reticulum. This cleavage depended on proteolytic activity of C1r-LP because mutation of the putative active-site Ser residue abolished the reaction. Furthermore, incubation of affinity-purified C1r-LP and proHp led to the cleavage of the latter protein. ProHp appeared to be cleaved at the expected site because substitution of Gly for Arg-161 blocked the reaction. C1r-LP showed specificity for proHp, in that it did not cleave the proform of complement C1s, a protein similar to Hp particularly around the cleavage site. C1r-LP accounts for at least part of the endogenous proHp-cleavage activity because suppression of the C1r-LP expression by RNA interference reduced the cleavage of proHp by up to 45% in the cells of a human hepatoma cell line (HepG2).
New insights into allosteric mechanisms from trapping unstable protein conformations in silica gels
Authors: Viappiani Cristiano , Bettati Stefano , Bruno Stefano , Ronda Luca , Abbruzzetti Stefania , Mozzarelli Andrea , Eaton William A.
Published: September 2004

To understand why the classical two-state allosteric model of Monod, Wyman, and Changeux explains cooperative oxygen binding by hemoglobin but does not explain changes in oxygen affinity by allosteric inhibitors, we have investigated the kinetic properties of unstable conformations transiently trapped by encapsulation in silica gels. Conformational trapping reveals that after nanosecond photodissociation of carbon monoxide a large fraction of the subunits of theTquaternary structure has kinetic properties almost identical to those of subunits of theRquaternary structure. Addition of allosteric inhibitors reduces both the fraction ofR-like subunits and the oxygen affinity of theTquaternary structure. These kinetic and equilibrium results are readily explained by a recently proposed generalization of the Monod-Wyman-Changeux model in which a preequilibrium between two functionally different tertiary, rather than quaternary, conformations plays the central role.
Failure of a landmark to restrict spatial learning based on the shape of the environment
Authors: Hayward Andrew , Good Mark A. , Pearce John M.
Published: September 2004

Rats were required to find a submerged platform in the corner of a swimming pool with a distinctive shape. A landmark near the platform did not interfere with the control acquired by the pool's shape over searching for the platform. This outcome was observed with an overshadowing and a blocking design. A comparison of the ease with which the landmark and the pool's shape gained control over searching for the platform indicates that the failure of overshadowing and blocking was not a consequence of the landmark being less salient than the shape of the pool. The results are not readily explained by theories of associative learning, but they are consistent with the claim that learning about the shape of the environment takes place in a dedicated module, which excludes information about the significance of individual landmarks.
Asymmetry of generalization decrement in causal learning
Authors: Glautier Steven
Published: September 2004

Two experiments required volunteers to learn which of various “planes” caused high levels of pollution. Novel test items were then rated as causes of pollution. Items created by adding novel features were rated at the same level as that of the original training items but items created by removing features received reduced ratings. This asymmetry of generalization decrement was not predicted by a well-known configural model of stimulus representation (Pearce, 1987, 1994) but was predicted by a recently proposed model of stimulus representation, the replaced-elements model (Brandon, Vogel, & Wagner, 2000).
Retrospective revaluation effects in the conditioned suppression procedure
Authors: Shevill Ian , Hall Geoffrey
Published: September 2004

In four experiments using the conditioned suppression procedure, rats received initial reinforced training with two compound stimuli, AX and BY, each compound consisting of one auditory and one visual element. After a second phase of training consisting of nonreinforced presentations of A, the suppression governed by X and Y was tested. In Experiment 1 X evoked slightly less suppression than Y (a mediated extinction effect). This outcome was obtained when the auditory cues served as Xand Y(Experiment 1a), when the visual cues served as X and Y(Experiment 1b), and when the number of nonreinforced presentations of A was increased (Experiment 1c) from 18 to 216. In Experiment 2, however, in which the initial training was given with serial compounds (i.e., A → X and B → Y) X evoked more suppression than Y (a recovery-from-overshadowing effect). It was argued that extinction of A engages two learning processes, one increasing the effective associative strength of its associate (X) and one reducing it, and that the balance between these two depends on the specific conditions of training.
Backward blocking in honeybees
Authors: Blaser R. E. , Couvillon P. A. , Bitterman M. E.
Published: September 2004

Three experiments with foraging honeybees were designed to study the effect of experience with A on responding to B after AB+ training. In the first experiment, responding to B was the same whether the AB+ training was preceded or followed by A+ training. In the second experiment, responding to B after AB+ training was less in animals that also had A+ training than in control animals that were equally often reinforced in the absence of A; whether the A+ training preceded, was concurrent with, or followed the AB+ training made no difference. In the third experiment, responding to B after AB+ training was less when the AB+ training was followed by A+C– training than when it was followed by C+/A– training. These results, like those of some recent vertebrate experiments, take us beyond the traditional explanation of blocking in terms of impaired conditioning of B on AB+ trials and support the suggestion that the mechanism, still poorly understood, may nevertheless be a relatively simple one.
Outcome additivity, elemental processing and blocking in human causality judgements
Authors: Livesey Evan J. , Boakes Robert A.
Published: September 2004

Informing participants in a causal judgement task that outcomes are additive can increase blocking effects (Experiment 1). Outcome additivity information emphasizes the fact that the outcome following a compound is the sum of the effects of its elements. We suggest that the effect of providing outcome additivity information is to encourage elemental processing and thereby enhance blocking. Experiment 2 showed that blocking could be enhanced by factors encouraging elemental processing, and Experiment 3 demonstrated that blocking was reduced by manipulating the visual presentation of cues to encourage configural processing. While these experiments do not rule out the role of inference in causal judgement tasks, the results are most parsimoniously explained by associative accounts that allow flexibility in the encoding of compound cues.
Oxidative Stress ActivatesFUS1andRLM1Transcription in the YeastSaccharomyces cerevisiaein an Oxidant-dependent Manner
Authors: Staleva Liliana , Hall Andrea , Orlow Seth J.
Published: September 2004

Mating in haploid Saccharomyces cerevisiae occurs after activation of the pheromone response pathway. Biochemical components of this pathway are involved in other yeast signal transduction networks. To understand more about the coordination between signaling pathways, we used a “chemical genetic” approach, searching for compounds that would activate the pheromone-responsive gene FUS1 and RLM1, a reporter for the cell integrity pathway. We found that catecholamines (l-3,4-hydroxyphenylalanine [l-dopa], dopamine, adrenaline, and noradrenaline) elevate FUS1 and RLM1 transcription. N-Acetyl-cysteine, a powerful antioxidant in yeast, completely reversed this effect, suggesting that FUS1 and RLM1 activation in response to catecholamines is a result of oxidative stress. The oxidant hydrogen peroxide also was found to activate transcription of an RLM1 reporter. Further genetic analysis combined with immunoblotting revealed that Kss1, one of the mating mitogen-activated protein kinases (MAPKs), and Mpk1, an MAPK of the cell integrity pathway, participated in l-dopa-induced stimulation of FUS1 and RLM1 transcription. We also report that Mpk1 and Hog1, the high osmolarity MAPK, were phosphorylated upon induction by hydrogen peroxide. Together, our results demonstrate that cells respond to oxidative stress via different signal transduction machinery dependent upon the nature of the oxidant.
Inhibiting the Arp2/3 Complex Limits Infection of Both Intracellular Mature Vaccinia Virus and Primate Lentiviruses
Authors: Komano Jun , Miyauchi Kosuke , Matsuda Zene , Yamamoto Naoki
Published: September 2004

Characterizing cellular factors involved in the life cycle of human immunodeficiency virus type 1 (HIV-1) is an initial step toward controlling replication of HIV-1. Actin polymerization mediated by the Arp2/3 complex has been found to play a critical role in some pathogens' intracellular motility. We have asked whether this complex also contributes to the viral life cycles including that of HIV-1. We have used both the acidic domains from actin-related protein (Arp) 2/3 complex-binding proteins such as the Wiscott-Aldrich syndrome protein (N-WASP) or cortactin, and siRNA directing toward Arp2 to inhibit viral infection. HIV-1, simian immunodeficiency virus (SIV), and intracellular mature vaccinia virus (IMV) were sensitive to inhibition of the Arp2/3 complex, whereas MLV, HSV-1, and adenovirus were not. Interestingly, pseudotyping HIV-1 with vesicular stomatitis virus G protein (VSV-G) overcame this inhibition. Constitutive inhibition of the Arp2/3 complex in the T-cell line H9 also blocked replication of HIV-1. These data suggested the existence of an Arp2/3 complex-dependent event during the early phase of the life cycles of both primate lentiviruses and IMV. Inhibiting the HIV-1's ability to activate Arp2/3 complex could be a potential chemotherapeutic intervention for acquired immunodeficiency syndrome (AIDS).
Characterization of the TPX2 Domains Involved in Microtubule Nucleation and Spindle Assembly inXenopusEgg Extracts
Authors: Brunet Stéphane , Sardon Teresa , Zimmerman Timo , Wittmann Torsten , Pepperkok Rainer , Karsenti Eric , Vernos Isabelle
Published: September 2004

TPX2 has multiple functions during mitosis, including microtubule nucleation around the chromosomes and the targeting of Xklp2 and Aurora A to the spindle. We have performed a detailed domain functional analysis of TPX2 and found that a large N-terminal domain containing the Aurora A binding peptide interacts directly with and nucleates microtubules in pure tubulin solutions. However, it cannot substitute the endogenous TPX2 to support microtubule nucleation in response to Ran guanosine triphosphate (GTP) and spindle assembly in egg extracts. By contrast, a large C-terminal domain of TPX2 that does not bind directly to pure microtubules and does not bind Aurora A kinase rescues microtubule nucleation in response to RanGTP and spindle assembly in TPX2-depleted extract. These and previous results suggest that under physiological conditions, TPX2 is essential for microtubule nucleation around chromatin and functions in a network of other molecules, some of which also are regulated by RanGTP.
BIG2, A Guanine Nucleotide Exchange Factor for ADP-Ribosylation Factors: Its Localization to Recycling Endosomes and Implication in the Endosome Integrity
Authors: Shin Hye-Won , Morinaga Naoko , Noda Masatoshi , Nakayama Kazuhisa
Published: September 2004

Small GTPases of the ADP-ribosylation factor (ARF) family play a key role in membrane trafficking by regulating coated vesicle formation, and guanine nucleotide exchange is essential for the ARF function. Brefeldin A blocks the ARF-triggered coat assembly by inhibiting the guanine nucleotide exchange on ARFs and causes disintegration of the Golgi complex and tubulation of endosomal membranes. BIG2 is one of brefeldin A-inhibited guanine nucleotide exchange factors for the ARF GTPases and is associated mainly with the trans-Golgi network. In the present study, we have revealed that another population of BIG2 is associated with the recycling endosome and found that expression of a catalytically inactive BIG2 mutant, E738K, selectively induces membrane tubules from this compartment. We also have shown that BIG2 has an exchange activity toward class I ARFs (ARF1 and ARF3) in vivo and inactivation of either ARF exaggerates the BIG2(E738K)-induced tubulation of endosomal membranes. These observations together indicate that BIG2 is implicated in the structural integrity of the recycling endosome through activating class I ARFs.
mRNA Localization and ER-based Protein Sorting Mechanisms Dictate the Use of Transitional Endoplasmic Reticulum-Golgi Units Involved in Gurken Transport inDrosophilaOocytes
Authors: Herpers Bram , Rabouille Catherine
Published: September 2004

The anteroposterior and dorsoventral axes of the future embryo are specified within Drosophila oocytes by localizing gurken mRNA, which targets the secreted Gurken transforming growth factor-α synthesis and transport to the same site. A key question is whether gurken mRNA is targeted to a specialized exocytic pathway to achieve the polar deposition of the protein. Here, we show, by (immuno)electron microscopy that the exocytic pathway in stage 9–10 Drosophila oocytes comprises a thousand evenly distributed transitional endoplasmic reticulum (tER)-Golgi units. Using Drosophila mutants, we show that it is the localization of gurken mRNA coupled to efficient sorting of Gurken out of the ER that determines which of the numerous equivalent tER-Golgi units are used for the protein transport and processing. The choice of tER-Golgi units by mRNA localization makes them independent of each other and represents a nonconventional way, by which the oocyte implements polarized deposition of transmembrane/secreted proteins. We propose that this pretranslational mechanism could be a general way for targeted secretion in polarized cells, such as neurons.
Bipolarization and Poleward Flux Correlate duringXenopusExtract Spindle Assembly
Authors: Mitchison T.J. , Maddox P. , Groen A. , Cameron L. , Perlman Z. , Ohi R. , Desai A. , Salmon E.D. , Kapoor T.M.
Published: September 2004

We investigated the mechanism by which meiotic spindles become bipolar and the correlation between bipolarity and poleward flux, using Xenopus egg extracts. By speckle microscopy and computational alignment, we find that monopolar sperm asters do not show evidence for flux, partially contradicting previous work. We account for the discrepancy by describing spontaneous bipolarization of sperm asters that was missed previously. During spontaneous bipolarization, onset of flux correlated with onset of bipolarity, implying that antiparallel microtubule organization may be required for flux. Using a probe for TPX2 in addition to tubulin, we describe two pathways that lead to spontaneous bipolarization, new pole assembly near chromatin, and pole splitting. By inhibiting the Ran pathway with excess importin-alpha, we establish a role for chromatin-derived, antiparallel overlap bundles in generating the sliding force for flux, and we examine these bundles by electron microscopy. Our results highlight the importance of two processes, chromatin-initiated microtubule nucleation, and sliding forces generated between antiparallel microtubules, in self-organization of spindle bipolarity and poleward flux.
Maloriented Bivalents Have Metaphase Positions at the Spindle Equator with More Kinetochore Microtubules to One Pole than to the Other
Authors: LaFountain James R. , Oldenbourg Rudolf
Published: September 2004

To test the “traction fiber” model for metaphase positioning of bivalents during meiosis, kinetochore fibers of maloriented bivalents, induced during recovery from cold arrest, were analyzed with a liquid crystal polarizing microscope. The measured birefringence retardation of kinetochore fibers is proportional to the number of microtubules in a fiber. Five of the 11 maloriented bivalents analyzed exhibited bipolar malorientations that had at least four times more kinetochore microtubules to one pole than to the other pole, and two had microtubules directed to only one pole. Yet all maloriented bivalents had positions at or near the spindle equator. The traction fiber model predicts such maloriented bivalents should be positioned closer to the pole with more kinetochore microtubules. A metaphase position at the spindle equator, according to the model, requires equal numbers of kinetochore microtubules to both poles. Data from polarizing microscope images were not in accord with those predictions, leading to the conclusion that other factors, in addition to traction forces, must be involved in metaphase positioning in crane-fly spermatocytes. Although the identity of additional factors has not been established, one possibility is that polar ejection forces operate to exert away-from-the-pole forces that could counteract pole-directed traction forces. Another is that kinetochores are “smart,” meaning they embody a position-sensitive mechanism that controls their activity.
Requirements of Fission Yeast Septins for Complex Formation, Localization, and Function
Authors: An Hanbing , Morrell Jennifer L. , Jennings Jennifer L. , Link Andrew J. , Gould Kathleen L.
Published: September 2004

Septins are GTP binding proteins important for cytokinesis in many eukaryotes. The Schizosaccaromyces pombe genome sequence predicts orthologues of four of five Saccharomyces cerevisiae septins involved in cytokinesis and these are named Spns1-4p. That spns1-4 are not essential genes permitted the application of a combined genetic and proteomics approach to determine their functional relationships. Our findings indicate that Spns1-4p are present throughout interphase as a diffusely localized ∼8.5S complex containing two copies of each septin linked together as a chain in the order Spn3p-Spn4p-Spn1p-Spn2p. Septin recruitment to the medial region of the cell is genetically separable from ring formation, and whereas it is normally restricted to mitosis, it can be promoted without activation of the mitotic cell cycle machinery. Coalescence into ring structures requires Spn1p and Spn4p associate with at least one other septin subunit and the expression of Mid2p that is normally restricted to mitosis. This study establishes the functional requirements for septin complex organization in vivo.
Identification of Hemodynamic Compromise by Cerebrovascular Reserve and Oxygen Extraction Fraction in Occlusive Vascular Disease
Authors: Nemoto Edwin M. , Yonas Howard , Kuwabara Hiroto , Pindzola Ronda R. , Sashin Donald , Meltzer Carolyn C. , Price Julie C. , Chang Yuefang , Johnson David W.
Published: September 2004

Cerebrovascular reserve (CVR) and oxygen extraction fraction (OEF) are used to identify hemodynamic compromise in symptomatic patients with carotid occlusive vascular disease, but evidence suggests that they are not equivalent. The authors studied the relationship between CVR and OEF to evaluate their equivalence and stages of hemodynamic compromise. Symptomatic patients (N = 12) with carotid occlusion were studied by stable xenon–computed tomography CBF after intravenous acetazolamide administration for CVR, followed within 24 hours by positron emission tomography (PET) for OEF. Middle cerebral artery territories were analyzed by hemisphere and level. Hemispheric subcortical white matter infarctions were graded with magnetic resonance imaging. Both hemispheric and level analysis of CVR and OEF showed a significant ( P = 0.001), negative linear relationship [CVR (%) = −1.5 (OEF) + 83.4, ( r = −0.57, P = 0.001, n = 24]. However, 37.5% of the hemispheres showed compromised CVR but normal OEF and were associated ( P = 0.019) with subcortical white matter infarction. CMRO2 was elevated in stage II hemodynamic compromise (CVR < 10%, OEF > 50%). CVR and OEF showed a significant negative linear relationship in stage II hemodynamic compromise but revealed hemispheres in hemodynamic compromise by CVR but normal OEF that were associated with subcortical white matter infarction.
Modeling Cerebral Arteriovenous Lactate Kinetics after Intravenous Lactate Infusion in the Rat
Authors: Leegsma-Vogt Gea , van der Werf Siebren , Venema Kor , Korf Jakob
Published: September 2004

Venous-arterial lactate differences across the brain during lactate infusion in rats were studied, and the fate of lactate was described with a mathematical model that includes both cerebral and extracerebral kinetics. Ultrafiltration was used to sample continuously and simultaneously arterial and venous blood. Subsequent application of flow injection analysis and biosensors allowed the measurement of glucose and lactate concentrations every minute. Because of the high temporal resolution, arteriovenous lactate kinetics could be modeled in individual experiments. The existence of both a cerebral lactate sink and a lactate exchangeable compartment, representing approximately 24% of brain volume, was thus modeled.
Secondary Energy Failure after Cerebral Hypoxia–Ischemia in the Immature Rat
Authors: Vannucci Robert C. , Towfighi Javad , Vannucci Susan J.
Published: September 2004

A delayed or secondary energy failure occurs during recovery from perinatal cerebral hypoxia–ischemia. The question remains as to whether the energy failure causes or accentuates the ultimate brain damage or is a consequence of cell death. To resolve the issue, 7-day postnatal rats underwent unilateral common carotid artery occlusion followed thereafter by systemic hypoxia with 8% oxygen for 2.5 hours. During recovery, the brains were quick frozen and individually processed for histology and the measurements of 1) high-energy phosphate reserves and 2) neuronal (MAP-2, SNAP-25) and glial (GFAP) proteins. Phosphocreatine (PCr) and ATP, initially depleted during hypoxia–ischemia, were partially restored during the first 18 hours of recovery, with secondary depletions at 24 and 48 hours. During the initial recovery phase (6 to 18 hours), there was a significant correlation between PCr and the histology score (0 to 3), but not for ATP. During the late recovery phase, there was a highly significant correlation between all measured metabolites and the damage score. Significant correlation also exhibited between the neuronal protein markers, MAP-2 and SNAP-25, and PCr as well as the sum of PCr and Cr at both phases of recovery. No correlation existed between the high-energy reserves and the glial protein marker, GFAP. The close correspondence of PCr to histologic brain damage and the loss of MAP-2 and SNAP-25 during both the early and late recovery intervals suggest evolving cellular destruction as the primary event, which precedes and leads to the secondary energy failure.
The Chemokine Fractalkine in Patients with Severe Traumatic Brain Injury and a Mouse Model of Closed Head Injury
Authors: Rancan Mario , Bye Nicole , Otto Vivianne I. , Trentz Otmar , Kossmann Thomas , Frentzel Stefan , Morganti-Kossmann Maria Cristina
Published: September 2004

The potential role of the chemokine Fractalkine (CX3CL1) in the pathophysiology of traumatic brain injury (TBI) was investigated in patients with head trauma and in mice after experimental cortical contusion. In control individuals, soluble (s)Fractalkine was present at low concentrations in cerebrospinal fluid (CSF) (12.6 to 57.3 pg/mL) but at much higher levels in serum (21,288 to 74,548 pg/mL). Elevation of sFractalkine in CSF of TBI patients was observed during the whole study period (means: 29.92 to 535.33 pg/mL), whereas serum levels remained within normal ranges (means: 3,100 to 59,159 pg/mL). Based on these differences, a possible passage of sFractalkine from blood to CSF was supported by the strong correlation between blood–brain barrier dysfunction (according to the CSF-/serum-albumin quotient) and sFractalkine concentrations in CSF (R = 0.706; P < 0.01). In the brain of mice subjected to closed head injury, neither Fractalkine protein nor mRNA were found to be augmented; however, Fractalkine receptor (CX3CR1) mRNA steadily increased peaking at 1 week postinjury ( P < 0.05, one-way analysis of variance). This possibly implies the receptor to be the key factor determining the action of constitutively expressed Fractalkine. Altogether, these data suggest that the Fractalkine-CX3CR1 protein system may be involved in the inflammatory response to TBI, particularly for the accumulation of leukocytes in the injured parenchyma.
2,7-Bis-(4-Amidinobenzylidene)-Cycloheptan-1-One Dihydrochloride, tPA Stop, Prevents tPA-Enhanced Excitotoxicity Both In Vitro and In Vivo
Authors: Liot Géraldine , Benchenane Karim , Léveillé Frédéric , López-Atalaya José P. , Fernández-Monreal Mónica , Ruocco Antonio , MacKenzie Eric T. , Buisson Alain , Ali Carine , Vivien Denis
Published: September 2004

Tissue-type plasminogen activator (tPA) is available for the treatment of thromboembolic stroke in humans. However, adverse effects of tPA have been observed in animal models of ischemic brain injuries. In the present study, we have used a synthetic tPA inhibitor, named 2,7-bis-(4-amidinobenzylidene)-cycloheptan-1-one dihydrochloride (tPA stop), to investigate the role of endogenous tPA in the cerebral parenchyma. In mouse cortical cell cultures, we observed that although tPA stop reduced N-methyl-d-aspartic acid (NMDA)-mediated excitotoxic neuronal death, it failed to modulate α-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazole propanoic acid or kainate-mediated necrosis. In addition, we found that tPA stop could prevent the deleterious effects of both endogenous and exogenous tPA during NMDA exposure. At the functional level, tPA stop was found to prevent tPA-dependent potentiation of NMDA receptor-evoked calcium influx. The relevance of those findings was strengthened by the observation of a massive reduction of NMDA-induced excitotoxic lesion in rats when tPA stop was co-injected. Altogether, these data demonstrate that the blockade of the endogenous proteolytic activity of tPA in the cerebral parenchyma could be a powerful neuroprotective strategy raised against brain pathologies associated with excitotoxicity.
Increased Severity of Cerebral Ischemic Injury in Vascular Endothelial Growth Factor-B–Deficient Mice
Authors: Sun Yunjuan , Jin Kunlin , Childs Jocelyn T. , Xie Lin , Mao Xiao Ou , Greenberg David A.
Published: September 2004

Vascular endothelial growth factor-B (VegfB) is an angiogenic protein related to VegfA, although it acts on a different set of tyrosine kinase receptors. Like VegfA, VegfB is expressed in the brain and is induced at sites of brain injury. VegfA has neuroprotective and angiogenic effects, but VegfA-knockout mice die in utero, so the effect of endogenous VegfA signaling in neuropathologic states, such as cerebral ischemia, cannot be tested directly. In contrast, VegfB-knockout mice survive to adulthood with little abnormality in the absence of pathologic stresses. To determine if VegfB regulates the severity of cerebral ischemia, the middle cerebral artery was occluded in VegfB-knockout, heterozygous, and wild-type mice, and the volume of the resulting cerebral infarcts and associated impairment of neurologic function were measured. Infarct volume was increased by approximately 40% and neurologic impairment was more severe in VegfB-knockout mice, implying that endogenous VegfB acts to protect the brain from ischemic injury. VegfB also protected cultured cerebral cortical neurons from hypoxic injury, suggesting that its protective action is mediated at least in part through a direct effect on neurons.
Induction of Tolerance to Focal Ischemia in Rat Brain: Dissociation between Cortical Lesioning and Spreading Depression
Authors: Muramatsu Hiromi , Karikó Katalin , Welsh Frank A.
Published: September 2004

Cortical application of KCl has previously been shown to induce tolerance to a subsequent episode of cerebral ischemia. KCl triggers recurrent episodes of cortical spreading depression and produces a small lesion at the cortical application site. To determine whether a cortical lesion alone is sufficient to induce tolerance to ischemia, the authors used 5-mol/L NaCl to precondition rat brain 3 days before permanent occlusion of the middle cerebral artery. NaCl produced a small lesion at the application site without evoking cortical spreading depression. Preconditioning with 5-mol/L NaCl significantly attenuated the decrease in CBF after middle cerebral artery occlusion and reduced the volume of cortical infarction by 35%. The results show that a small cortical lesion, by itself, is sufficient to induce tolerance to ischemia.
Spontaneous Low-Frequency Oscillations Decline in the Aging Brain
Authors: Schroeter Matthias L. , Schmiedel Ole , von Cramon D. Yves
Published: September 2004

It is well known that aging leads to a degeneration of the vascular system. Hence, one may hypothesize that spontaneous oscillations decrease in the cerebral microvasculature with aging. Accordingly, the authors investigated the age dependency of spontaneous oscillations in the visual cortex during rest and functional activation. Functional near-infrared spectroscopy was used because it is particularly sensitive to the microvasculature. Visual stimulation led to an increase of oxyhemoglobin, total hemoglobin, and a decrease of deoxyhemoglobin, without any influence of age. Peaks of normalized power spectral density were detected for spontaneous low-frequency (0.07 to 0.11 Hz) and very-low-frequency (0.01 to 0.05 Hz) oscillations, with a higher amplitude for oxyhemoglobin than for deoxyhemoglobin. Spontaneous low-frequency oscillations of oxyhemoglobin and deoxyhemoglobin declined strongly with aging during both rest and visual stimulation. Reduction of spontaneous low-frequency oscillations might indicate a declining spontaneous activity in microvascular smooth muscle cells, in conjunction with an increased vessel stiffness with aging.
MMP-9 Deficiency Enhances Collagenase-Induced Intracerebral Hemorrhage and Brain Injury in Mutant Mice
Authors: Tang Jiping , Liu Jun , Zhou Changman , Alexander J. Steven , Nanda Anil , Granger D. Neil , Zhang John H.
Published: September 2004

Matrix metalloproteinase-9 (MMP-9) participates in the disregulation of blood–brain barrier during hemorrhagic transformation, and exacerbates brain injury after cerebral ischemia. However, the consequences of long-term inhibition or deficiency of MMP-9 activity (which might affect normal collagen or matrix homeostasis) remains to be determined. The authors investigated how MMP-9 gene deficiency enhances hemorrhage and increases mortality and neurologic deficits in a collagenase-induced intracerebral hemorrhage (ICH) model in MMP-9–knockout mice. MMP-9–knockout and corresponding wild-type mice at 20 to 35 weeks were used to model an aged population (because advanced age is a significant risk factor in human ICH). Collagenase VII-S (0.5 μL, 0.075 U) was injected into the right basal ganglia in mice and mortality, neurologic deficits, brain edema, and hemorrhage size measured. In addition, MMP-9 activity, brain collagen content, blood coagulation, cerebral arterial structure, and expressions of several MMPs were examined. Increased hemorrhage and brain edema that correlated with higher mortality and neurologic deficits were found in MMP-9–knockout mice. No apparent structural changes were observed in cerebral arteries, even though brain collagen content was reduced in MMP-9–knockout mice. MMP-9–knockout mice did exhibit an enhanced expression of MMP-2 and MMP-3 in response to ICH. The results indicate that a deficiency of MMP-9 gene in mutant mice increases collagenase-induced hemorrhage and the resulting brain injury. The intriguing relationship between MMP-9 deficiency and collagenase-induced ICH may reflect the reduction in collagen content and an enhanced expression of MMP-2 and MMP-3.
Effects of Combined Estrogen and Progesterone on Brain Infarction in Reproductively Senescent Female Rats
Authors: Toung Thomas J. , Chen Tsung-Ying , Littleton-Kearney Marguerite T. , Hurn Patricia D. , Murphy Stephanie J.
Published: September 2004

Recent data from the Women's Health Initiative have highlighted many fundamental issues about the utility and safety of long-term estrogen use in women. Current hormone replacement therapy for postmenopausal women incorporates progestin with estrogen, but it is uncertain if combined therapy provides major cerebrovascular risks or benefits to these women. No experimental animal stroke studies have examined combined hormone administration. The authors tested the hypothesis that combined hormone treatment reduces ischemic injury in middle-aged female rat brain. Reproductively senescent female rats underwent 2-hour middle cerebral artery occlusion (MCAO) followed by 22 hours reperfusion. Estrogen implants were placed subcutaneously at least 7 days before MCAO, and progesterone intraperitoneal injections were given 30 minutes before MCAO, at initiation, and at 6 hours of reperfusion. Rats received no hormone, a 25-μg estrogen implant, a 25-μg estrogen implant plus 5 mg/kg intraperitoneal progesterone, or 5 mg/kg intraperitoneal progesterone. Cortical, caudoputamen, and total infarct volumes were assessed by 2,3,5-triphenyltetrazolium chloride staining and digital image analysis at 22 hours reperfusion. Cortical and total infarct volumes, except in the acute progesterone-treated group, were significantly attenuated in all estrogen-alone and combined hormone-treated groups. There were no significant differences in caudoputamen infarct volumes in all hormone-treated groups as compared with untreated rats. These data have potential clinical implications relative to stroke for postmenopausal women taking combined hormone replacement therapy.
Pronounced Hypoperfusion during Spreading Depression in Mouse Cortex
Authors: Ayata Cenk , Shin Hwa Kyoung , Salomone Salvatore , Ozdemir-Gursoy Yasemin , Boas David A. , Dunn Andrew K. , Moskowitz Michael A.
Published: September 2004

We studied unique cerebral blood flow (CBF) responses to cortical spreading depression in mice using a novel two-dimensional CBF imaging technique, laser speckle flowmetry. Cortical spreading depression caused a triphasic CBF response in both rat and mouse cortex. In rats, mild initial hypoperfusion (approximately 75% of baseline) was followed by a transient hyperemia reaching approximately 220% of baseline. In mice, the initial hypoperfusion was pronounced (40–50% of baseline), and the anticipated hyperemic phase barely reached baseline. The duration of hypoperfusion significantly correlated with the duration of the DC shift. As a possible explanation for the pronounced hypoperfusion, mouse cerebral vessels showed enhanced resistance to relaxation by acetylcholine (3 μM) after K+-induced preconstriction (20, 40, and 80 mM) but dilated normally in response to acetylcholine after preconstriction with U46619, a synthetic thromboxane A2 analog. By contrast, rat vessels dilated readily to acetylcholine after preconstriction by K+. The transient normalization of CBF after hypoperfusion in the mouse was abolished by L-NA but not 7-NI. In summary, the CBF response to cortical spreading depression in mice contrasts with the rat in that the initial hypoperfusion is pronounced, and the hyperemic phase is markedly diminished. The differences in CBF response between species may be in part caused by an increased sensitivity of mouse cerebral vessels to elevated extracellular K+.
Caspase Inhibitor z-DEVD-fmk Attenuates Calpain and Necrotic Cell Death in Vitro and after Traumatic Brain Injury
Authors: Knoblach Susan M. , Alroy Daniel A. , Nikolaeva Maria , Cernak Ibolja , Stoica Bogdan A. , Faden Alan I.
Published: September 2004

In studies designed to evaluate the therapeutic window for treatment of traumatic brain injury, the caspase 3 inhibitor z-DEVD-fmk improved neurologic function and reduced lesion volumes when administered at 1 but not at 4, 8, or 24 hours after injury. Moreover, neither caspase 3 nor PARP, a caspase 3 substrate, were cleaved in injured, untreated cortex from 1 to 72 hours after injury. Few cortical neurons expressed active caspase 3 or were TUNEL positive from 6 to 24 hours after injury, and TUNEL staining was primarily Type I (necrotic). Nissl staining revealed extensive neuronal necrosis in the injured cortex from 6 to 24 hours after impact. Considered together, these data suggested that z-DEVD-fmk may reduce neuronal necrosis, so we used an in vitro model of necrotic cell death induced by maitotoxin to test this further and explore the potential mechanism(s) involved. Z-DEVD-fmk (1 nM-100 μM) significantly attenuated maitotoxin induced neuronal cell death and markedly reduced expression of the 145 kD calpain-mediated α-spectrin breakdown product after maitotoxin injury. Neither the 120 kD caspase-mediated α-spectrin cleavage product nor cathepsin B were expressed after maitotoxin injury. In a cell free assay, z-DEVD-fmk reduced hydrolysis of casein by purified calpain I. Finally, z-DEVD-fmk reduced expression of the 145 kD calpain-mediated α-spectrin cleavage fragment after traumatic brain injury in vivo. These data suggest that neuroprotection by z-DEVD-fmk may, in part, reflect inhibition of calpain-related necrotic cell death.
The AMPA Receptor Potentiator LY404187 Increases Cerebral Glucose Utilization and c-fos Expression in the Rat
Authors: Fowler Jill H. , Whalley Katherine , Murray Tracey , O'Neill Michael J. , McCulloch James
Published: September 2004

AMPA receptor potentiators enhance AMPA receptor-mediated glutamatergic neurotransmission and may have therapeutic potential as cognitive enhancers or antidepressants. The anatomical basis for the action of AMPA receptor potentiators is unknown. The aim of this study was to determine the effects of the biarylpropylsulfonamide AMPA receptor potentiator, LY404187 (0.05 to 5 mg/kg subcutaneously), upon cerebral glucose utilization and c-fos expression using 14C-2-deoxglucose autoradiography and c-fos immunocytochemistry. LY404187 (0.5 mg/kg) produced significant elevations in glucose utilization in 28 of the 52 anatomical regions analyzed, which included rostral neocortical areas and the hippocampus, as well the dorsal raphe nucleus, lateral habenula, and locus coeruleus. No significant decreases in glucose utilization were observed in any region after LY404187 administration. The increases in glucose utilization with LY404187 (0.5 mg/kg) were blocked by pretreatment with the AMPA receptor antagonist LY293558 (25 mg/kg), indicating that LY404187 acts through AMPA receptor-mediated mechanisms. LY404187 (0.5 mg/kg) also produced increases in c-fos immunoreactivity in the cortex, locus coeruleus, and the dorsal raphe nucleus. These studies demonstrate neuronal activation in key brain areas that are associated with memory processes and thus provide an anatomical basis for the cognitive enhancing effects of AMPA receptor potentiators.
Streptomyces africanus sp. nov., a novel streptomycete with blue aerial mycelium
Authors: Meyers Paul R. , Goodwin Candice M. , Bennett Jessica A. , Aken Bronwen L. , Price Claire E. , van Rooyen Jason M.
Published: September 2004

An actinomycete with blue aerial mycelium and yellow substrate mycelium was isolated from a suburban soil sample collected in Cape Town, South Africa and named strain CPJVR-HT. The colour of the substrate mycelium was not sensitive to changes in pH. The organism produced spiny spores in Spirales spore chains. Chemical taxonomy indicated that it is a member of the genus Streptomyces. Strain CPJVR-HT grew at 45 °C and did not produce melanin or any diffusible pigments. It exhibited weak antibacterial activity against a clinical isolate of Enterococcus faecium, but no antibacterial activity against Escherichia coli ATCC 25922 or Pseudomonas aeruginosa ATCC 27853. Analysis of its 16S rRNA gene sequence, DNA–DNA hybridization studies and the results of physiological tests showed that this strain represents a novel species of Streptomyces, for which the name Streptomyces africanus sp. nov. is proposed. The type strain is CPJVR-HT (=NRRL B-24143T=DSM 41829T).