bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurotrophin‐3 promotes cerebellar granule cell exit from the EGL
Authors: Doughty Martin L. , Lohof Ann , Campana Aline , Delhaye‐Bouchaud Nicole , Mariani Jean
Published: December 2004

In the cerebellum, the mRNAs for neurotrophin‐3 (NT‐3) and its high‐affinity tyrosine kinase receptor trkC are expressed by both the differentiated granule cells of the internal granule cell layer (IGL) and their precursors in the external germinal layer (EGL). We have investigated the effects of chronic application of exogenous NT‐3 in vivo on cerebellar granule cell genesis and differentiation. NT‐3 was applied to the posterior surface of the rat cerebellum from P6 onwards using Elvax implants. At P10 the EGL of cerebellar lobules VII and VIII was significantly reduced in thickness in NT‐3 implanted rats when compared with controls. Immunocytochemical analysis of the EGL using antibodies to proliferating cell nuclear antigen (PCNA) revealed that the number of postmitotic, premigratory (PCNA‐immunonegative) granule cell precursors was preferentially reduced in the NT‐3 implanted rats. In situ DNA fragmentation labelling confirmed that this was not accompanied by increased cell death in the EGL. These results suggest that NT‐3 promotes the differentiation of postmitotic, premigratory granule cell precursors, accelerating cell exit from the EGL.
Calretinin expression as a critical component in the control of dentate gyrus long‐term potentiation induction in mice
Authors: Gurden Hirac , Schiffmann Serge N. , Lemaire Martine , Böhme Georg A. , Parmentier Marc , Schurmans Stéphane
Published: December 2004

We have recently reported that mice homozygous (Cr–/–) for a null mutation in the calretinin gene have impaired long‐term potentiation (LTP) induction in the dentate gyrus (S. Schurmans et al. (1997) Proc. Natl. Acad. Sci. USA, 94, 10415). Here, we investigated dentate LTP induction in mice heterozygous (Cr+/–) for the same mutation. Despite the presence of calretinin in neurons of these mice, although at reduced levels as compared with normal mice, LTP induction in dentate gyrus was totally impaired. Spatial memory and learning were found unaffected in Cr+/– mice, such as in Cr–/– mice. Altogether, our results suggest that calretinin is a critical component in the control of dentate synaptic plasticity in mice, and that levels of calretinin higher than those observed in Cr+/– mice are required to induce LTP in this area. The possible mechanisms leading to the absence of correlation between gene dosage and biological effects are discussed.
Contextual fear conditioning regulates the expression of brain‐specific small nucleolar RNAs in hippocampus
Authors: Rogelj Boris , Hartmann Christoph E. A. , Yeo Christopher H. , Hunt Stephen P. , Giese K. Peter
Published: December 2004

Some small nucleolar RNAs (snoRNAs) are exclusively expressed in the brain but they have no known role in higher brain function. We analysed the expression pattern of four brain‐specific snoRNAs: MBI‐36, MBII‐48, MBII‐52 and MBII‐85, in mouse brain using in situ hybridization. All of these genes were expressed in the hippocampus and, except for MBII‐85, their levels in ventral parts were higher than those in dorsal parts. Using quantitative real‐time polymer chain reaction we determined hippocampal expression changes after contextual fear conditioning in mice. Ninety minutes, but not 25 h, after conditioning, we observed significant downregulation of MBII‐48 and upregulation of MBII‐52. Our finding that the expression of MBII‐48 and MBII‐52 is regulated during learning suggests that these snoRNAs have an important role in higher brain function.
Glutamatergic modulation of synaptic plasticity at a PNS vertebrate cholinergic synapse
Authors: Pinard Audrée , Lévesque Sébastien , Vallée Joanne , Robitaille Richard
Published: December 2004

The presence and the functionality of a glutamatergic regulation was studied at the frog neuromuscular junction (NMJ), a singly innervated cholinergic synapse. Bath application of glutamate reduced transmitter release without affecting nerve‐evoked presynaptic Ca2+ entry and handling. (1S,3R)‐aminocyclopentanedicarboxylic acid (ACPD), a metabotropic glutamate receptor (mGluR) agonist, mimicked the effects of glutamate while (S)‐alpha‐methyl‐4‐carboxyphenylglycine (MCPG), a mGluR antagonist, blocked glutamate effects. MCPG had no effect on transmitter release evoked at low frequency (0.2 Hz) but significantly reduced synaptic depression (10 Hz, 80 s). This suggests that a frequency‐dependent endogenous glutamatergic modulation is present at the frog NMJ and is mediated through mGluRs. Immunohistochemical labelling revealed the presence of mGluRs at the end plate area, primarily on muscle fibers. Functional glutamate uptake machinery was also found at the NMJ as blockade of glutamate transport by the inhibitor dl‐threo‐β‐benzyloxyaspartate (DL‐TBOA) increased high frequency‐induced depression, suggesting that the transporters system is used to eliminate glutamate from the extracellular space. Moreover, immunohistochemical labelling revealed that glutamate‐aspartate transporters (GLASTs) are predominantly present on perisynaptic Schwann cells (PSCs). However, local application of glutamate on PSCs unreliability evoked small Ca2+ responses. Hence, these data suggest that functional glutamatergic interactions at a purely cholinergic synapse, shape synaptic efficacy and short‐term plasticity in a frequency‐dependent fashion.
Functional heterogeneity of the responses of histaminergic neuron subpopulations to various stress challenges
Authors: Miklós I. H. , Kovács K. J.
Published: December 2004

In rats, the cell bodies of the histaminergic neuronal system are clustered in five distinct cell groups (E1–E5) within the posterior hypothalamus. On the basis of tract tracing studies, these histaminergic subgroups have been regarded as one functional unit. In addition to its well‐characterized role in arousal, locomotor activity, metabolism, feeding, drinking and behaviour, as well as in coordination of autonomic functions, histamine has been implicated in regulation of the hypothalamo–pituitary–adrenocortical axis during stress. To address the capacity of different histaminergic subgroups to respond to various challenges, we revealed c‐Fos, the immediate early gene marker of activated neurons, in histamine synthesizing neurons by combining c‐Fos immunocytochemistry with in situ hybridization of histidine decarboxylase (HDC) mRNA. Compared to the negligible colocalization of these markers in control rats, restraint, insulin‐induced hypoglycaemia and foot shock resulted in specific activation of histamine synthesizing neurons of the E4 and E5 subgroup in the tuberomammillary region. Up to 36% of HDC mRNA‐expressing cells show c‐Fos immunoreactivity in the E5 region. In addition, some neurons of the E1, E2 and E3 histaminergic groups were activated after restraint stress. Many less c‐Fos‐positive histaminergic neurons were detected after immobilization and dehydration. Ether stress, acute hyperosmotic stimulus or injection of bacterial lipopolysaccharide did not activate hypothalamic HDC‐positive neurons. These results suggest, for the first time, the functional heterogeneity of histaminergic neuron population, the components of which are recruited in a stressor‐ and subgroup‐specific manner.
Structural and functional dichotomy of human midcingulate cortex
Authors: Vogt Brent A. , Berger Gail R. , Derbyshire Stuart W. G.
Published: December 2004

Anterior cingulate cortex is comprised of perigenual and midcingulate regions based on cytology, imaging and connections. Its anterior (aMCC) and posterior (pMCC) parts and transition to posterior area 23 were evaluated in six human cingulate gyri with Nissl staining and immunoreactions for neuron‐specific nuclear binding protein and intermediate neurofilament proteins (NFP), and their pain and emotion functions evaluated in standard coordinates. Morphological differences included a poorly differentiated layer III with few NFP‐expressing neurons in aMCC and a very dense layer Va with small and large pyramids intermingled in pMCC. The density of NFP‐positive, layer Vb neurons was higher in pMCC than in aMCC. The junction of pMCC with area 23 had a dysgranular area 23d with clumps of layer IV neurons and a very dense layer Va. Each case was co‐registered to standard coordinates and the regional borders identified and measured. Although both regions had overall equivalent activations during noxious cutaneous thermal stimulation, the posterior two‐thirds of pMCC was relatively inactive. About 60% of fear‐induced activity was in aMCC, sadness and happiness activated perigenual cortex, and neither were activated with non‐emotion tasks. Thus, pain activity is coupled to fear in aMCC, while other MCC processing is not related to affect. Beyond midcingulate duality, this is the first report of a very dense layer Va for areas p24′ and 23 and the features of transitional area 23d. The MCC dichotomy suggests that two circuits differentially regulate the two cingulate motor areas, and involvement of aMCC in pain and fear make it selectively vulnerable to chronic pain and stress syndromes.
Implication of corticosteroid receptors in the regulation of hippocampal structural plasticity
Authors: Montaron M. F. , Piazza P. V. , Aurousseau C. , Urani A. , Le Moal M. , Abrous D. N.
Published: December 2004

The dentate gyrus is one of the few areas of the adult brain that continues to produce neurons and to express the embryonic polysialylated isoforms of neuronal cell adhesion molecules (PSA‐NCAM). The stress hormone corticosterone exerts a complex modulation on neurogenesis and PSA‐NCAM, and previous studies have shown that mature granule cells require corticosterone for their survival. Thus, the aim of our work was to investigate the respective role of the different corticosteroid receptors on these three parameters in adrenalectomized rats. It was found that treatment with a low dose of the mineralocorticoid receptor agonist, aldosterone, prevents only the adrenalectomy‐induced increase in cell death. Treatment with a higher dose of aldosterone normalized cell proliferation whereas PSA‐NCAM expression was normalized only by treatment with the glucocorticoid receptor agonist, RU 28362. It is concluded that stimulation of the mineralocorticoid receptor is sufficient to mediate the effects of corticosterone on neurogenesis and to protect mature cells from cell death whereas stimulation of the glucocorticoid receptor is necessary to modulate PSA‐NCAM expression.
Light‐induced c‐fos in melanopsin retinal ganglion cells of young and aged rodless/coneless (rd/rd cl) mice
Authors: Semo Ma'ayan , Lupi Daniela , Peirson Stuart N. , Butler Jason N. , Foster Russell G.
Published: December 2004

Non‐rod, non‐cone ocular photoreceptors have been shown to mediate a range of irradiance detection tasks. The strongest candidates for these receptors are melanopsin‐positive retinal ganglion cells (RGCs). To provide a more complete understanding of these receptors in vivo, we have utilized a mouse that lacks rod and cone photoreceptors (rd/rd cl) and compared these animals to congenic wild‐types. Using real‐time polymerase chain reaction and immunohistochemistry, we address the following. (1) Is Fos expression within these RGCs driven by an input from the rods/cones or is it the product of the intrinsic photosensitivity of these neurons? We demonstrate that most Fos expression across the entire retina is due to the rods/cones, but in the absence of these photoreceptors, light will induce Fos within melanopsin RGCs. (2) Could the reported age‐related decline in circadian photosensitivity of rodents be linked to changes in the population of melanopsin RGCs? We show that old mice experience an ∼ 40% reduction in melanopsin RGCs. (3) Does the loss of inner retinal neurons affect the responses of melanopsin RGCs? Aged (∼ 700 days) rd/rd cl mice lose most of their inner retina but retain the retinal ganglion cell layer. In these mice, the proportion of melanopsin RGCs that express Fos in response to light is significantly reduced. Collectively, our data suggest that melanopsin RGCs form a heterogeneous population of neurons, and that most of the light‐induced c‐fos expression within these cells is associated with the endogenous photosensitivity of these neurons.
Developmental up‐regulation of KCC2 in the absence of GABAergic and glutamatergic transmission
Authors: Ludwig Anastasia , Li Hong , Saarma Mart , Kaila Kai , Rivera Claudio
Published: December 2004

Postsynaptic γ‐aminobutyric acid (GABA)A‐mediated responses switch from depolarizing to hyperpolarizing during postnatal development of the rodent hippocampus. This is attributable to a decrease in the concentration of intracellular chloride set by the expression of the neuron‐specific K+‐Cl− co‐transporter, KCC2. A recent in vitro study [Ganguly et al. (2001) Cell, 105, 521–532] showed that KCC2 expression may be under the trophic control of GABAA receptor‐mediated transmission. Here we have studied the developmental expression of KCC2 protein in mouse hippocampal dissociated cultures as well as organotypic cultures. A low somatic expression level was found in neurons prior to the formation of the first synapses, as detected by synaptophysin immunoreactivity. Thereafter, KCC2 expression was strongly up‐regulated during neuronal maturation. The developmental up‐regulation of KCC2 expression was not altered by a chronic application (throughout the culturing period; 2–15 days in vitro) of the action‐potential blocker TTX or the N‐methyl‐d‐aspartate (NMDA) and non‐NMDA antagonists APV and NBQX. Blockade of GABAA‐mediated transmission with picrotoxin did not affect the expression levels of KCC2 protein either. These data show that neither neuronal spiking nor ionotropic glutamatergic and GABAergic transmission are required for the developmental expression of KCC2 in mouse hippocampal neurons in vitro.
Central representation of bladder and colon revealed by dual transsynaptic tracing in the rat: substrates for pelvic visceral coordination
Authors: Rouzade‐Dominguez Marie‐Laure , Miselis Richard , Valentino Rita J.
Published: December 2004

The neurocircuitry underlying regulation of bladder and distal colon function by Barrington's nucleus (the pontine micturition centre) was investigated in rats by identifying neurons which were transsynaptically labelled from these viscera, with pseudorabies virus (PRV) or genetically modified forms of PRV [PRV–β‐galactosidase (PRV‐β‐Gal) and PRV–green fluorescent protein (PRV‐GFP)]. PRV injection into the bladder or the colon of separate rats suggested an overlap in the distribution of bladder‐ and colon‐related neurons in Barrington's nucleus, as well as a topographical arrangement whereby dorsal neurons were bladder‐related and ventral neurons were colon‐related. In rats injected with PRV‐β‐Gal into one viscera and PRV‐GFP into another, neurons in the major pelvic ganglion and lumbosacral spinal cord were primarily single‐labelled at relatively early survival times. With longer survival times many double‐labelled neurons (>70%) appeared in Barrington's nucleus, suggesting that individual Barrington's nucleus neurons are synaptically linked to preganglionic parasympathetic neurons which independently innervate the colon or the bladder. In addition to these dual‐labelled neurons, Barrington's nucleus neurons which were single‐labelled from either viscera were observed and these exhibited a viscerotopic organization consistent with the single‐labelling studies. Together, these findings suggest the existence of three neuronal populations in Barrington's nucleus, one which is synaptically linked to both the bladder and the colon and the other two populations which are specifically linked to either viscera. These anatomical substrates may underlie the central coordination of bladder and colon function and play a role in disorders characterized by a coexistence of bladder and colonic symptoms.
Disruption of prepulse inhibition in mice lacking mGluR1
Authors: Brody S. A. , Conquet F. , Geyer M. A.
Published: December 2004

Sensorimotor gating, measured by prepulse inhibition of the startle response (PPI), is a cross‐species form of information processing that is deficient in patients with schizophrenia and is widely used as a model to study the neurobiology of this disorder. The eight known metabotropic glutamate receptors (mGluRs) are divided into three groups on the basis of sequence homology and pharmacological properties. Group I consists of mGluR5 and mGluR1, both of which are coupled positively to phospholipase C. Mice lacking mGluR5 exhibit a deficit in PPI. Like mGluR5, mGluR1 is located in regions that are involved in the modulation of PPI. To test the hypothesis that mGluR1 is involved in the modulation of PPI we assessed PPI in mGluR1 knockout (KO) mice. Littermate mGluR1 wild‐type and KO mice were tested at multiple ages in a standard PPI paradigm containing a 65 dB background, 120 dB pulses and prepulses of 69, 73 and 77 dB. At all ages tested, mGluR1 KO mice exhibited a significant PPI deficit. The PPI deficit of the mGluR1 KO mice was not further exaggerated by administration of the N‐methyl‐d‐aspartate antagonist phencyclidine nor was it reversed by administration of the dopamine antagonist raclopride (3.0 mg/kg). The PPI deficit of the mGluR1 KO mice was, however, ameliorated by administration of the mood stabilizer lamotrigine (27 mg/kg base equivalent weight), though increases in PPI were also seen with lamotrigine in the wild‐type mice. Thus, both group I metabotropic glutamate receptors are involved in the regulation of PPI in mice.
The subcellular localization of GABAB receptor subunits in the rat substantia nigra
Authors: Boyes Justin , Bolam J. Paul
Published: December 2004

The inhibitory effects of GABA within the substantia nigra (SN) are mediated in part by metabotropic GABAB receptors. To better understand the mechanisms underlying these effects, we have examined the subcellular localization of the GABAB receptor subunits, GABAB1 and GABAB2, in SN neurons and afferents using pre‐embedding immunocytochemistry combined with anterograde or retrograde labelling. In both the SN pars compacta (SNc) and pars reticulata (SNr), GABAB1 and GABAB2 showed overlapping, but distinct, patterns of immunolabelling. GABAB1 was more strongly expressed by putative dopaminergic neurons in the SNc than by SNr projection neurons, whereas GABAB2 was mainly expressed in the neuropil of both regions. Immunogold labelling for GABAB1 and GABAB2 was localized in presynaptic and postsynaptic elements throughout the SN. The majority of labelling was intracellular or was associated with extrasynaptic sites on the plasma membrane. In addition, labelling for both subunits was found on the presynaptic and postsynaptic membranes at symmetric, putative GABAergic synapses, including those formed by anterogradely labelled striatonigral and pallidonigral terminals. Labelling was also observed on the presynaptic membrane and at the edge of the postsynaptic density at asymmetric, putative excitatory synapses. Double immunolabelling, using the vesicular glutamate transporter 2, revealed the glutamatergic nature of many of the immunogold‐labelled asymmetric synapses. The widespread distribution of GABAB subunits in the SNc and SNr suggests that GABAB‐mediated effects in these regions are likely to be more complex than previously described, involving presynaptic autoreceptors and heteroreceptors, and postsynaptic receptors on different populations of SN neurons.
Expression of an inwardly rectifying K+ channel, Kir5.1, in specific types of fibrocytes in the cochlear lateral wall suggests its functional importance in the establishment of endocochlear potential
Authors: Hibino Hiroshi , Higashi‐Shingai Kayoko , Fujita Akikazu , Iwai Kaori , Ishii Masaru , Kurachi Yoshihisa
Published: December 2004

Cochlear endolymph contains 150 mm K+ and has a highly positive potential of ≈ +80 mV. The specialized ionic composition and high potential in endolymph are essential for hearing and maintained by circulation of K+ from perilymph to endolymph through the cochlear lateral wall. Various types of K+ channel such as Kir4.1 and KCNQ1/KCNE1 are expressed in stria vascularis of the lateral wall and play essential roles in K+ circulation. In this study, we examined a distribution of another K+ channel, Kir5.1, and found it specifically expressed in the spiral ligament of the cochlear lateral wall. Specific immunoreactivity for Kir5.1 was detected in type II, IV and V fibrocytes of the ligament and spiral limbus, all of which are directly involved in K+ circulation. Kir5.1 was not found in either type I or III fibrocytes. Although Kir5.1 assembles with Kir4.1 to form a functional Kir channel in renal epithelia and retinal Müller cells, double‐immunolabelling revealed that they were expressed in distinct regions in the cochlea lateral wall, i.e. Kir4.1 only in stria vascularis vs. Kir5.1 in spiral ligament. During development, the expression of Kir5.1 subunits started significantly later than Kir4.1 and was correlated with the ‘rapid’ phase of the elevation of endocochlear potential (EP). Kir5.1 and Kir4.1 channel‐subunits may therefore play distinct functional roles in K+ circulation in the cochlear lateral wall.
Lesions of dorsolateral striatum preserve outcome expectancy but disrupt habit formation in instrumental learning
Authors: Yin Henry H. , Knowlton Barbara J. , Balleine Bernard W.
Published: December 2004

Habits are controlled by antecedent stimuli rather than by goal expectancy. Interval schedules of feedback have been shown to generate habits, as revealed by the insensitivity of behaviour acquired under this schedule to outcome devaluation treatments. Two experiments were conducted to assess the role of the dorsolateral striatum in habit learning. In Experiment 1, sham operated controls and rats with dorsolateral striatum lesions were trained to press a lever for sucrose under interval schedules. After training, the sucrose was devalued by inducing taste aversion to it using lithium chloride, whereas saline injections were given to the controls. Only rats given the devaluation treatment reduced their consumption of sucrose and this reduction was similar in both the sham and the lesioned groups. All rats were then returned to the instrumental chamber for an extinction test, in which the lever was extended but no sucrose was delivered. In contrast to sham operated controls, rats with dorsolateral striatum lesions refrained from pressing the lever if the outcome was devalued. To assess the specificity of the role of dorsolateral striatum in this effect a second experiment was conducted in which a group with lesions of dorsomedial striatum was added. In relation now to both the sham and the dorsomedial lesioned groups, only rats with lesions of dorsolateral striatum significantly reduced responding after outcome devaluation. In conclusion, this study provides direct evidence that the dorsolateral striatum is necessary for habit formation. Furthermore, it suggests that, when the habit system is disrupted, control over instrumental performance reverts to the system controlling the performance of goal‐directed instrumental actions.
Stimulus‐induced change in long‐range temporal correlations and scaling behaviour of sensorimotor oscillations
Authors: Linkenkaer‐Hansen Klaus , Nikulin Vadim V. , Palva J. Matias , Kaila Kai , Ilmoniemi Risto J.
Published: December 2004

The human brain spontaneously generates large‐scale network oscillations at around 10 and 20 Hz. The amplitude envelope of these oscillations fluctuates intermittently and was recently reported to exhibit power‐law decay of the autocorrelation for hundreds of seconds. This indicates that the underlying networks are in a dynamic state resembling the self‐organized critical state known to exist in many complex systems. Based on the mechanism of how correlations emerge in these systems, we hypothesized that the physiological basis of long‐range power‐law correlations is the buildup of a memory of past activity by a continuous modification of the network's functional connectivity by the ongoing oscillations. In this framework, exogenous perturbations of ongoing oscillations would degrade or abolish this dynamic network memory. We investigated the sensitivity of the temporal correlations in sensorimotor 10‐ and 20‐Hz oscillations to median nerve stimulation that is known to have immediate effects on ongoing oscillations. Our results show that the amplitude fluctuations of these oscillations were effectively modulated by the somatosensory stimuli but still exhibited long‐range temporal correlations and power‐law scaling behaviour. The magnitude of the temporal correlations was, however, attenuated and the power‐law exponents were decreased. This implies that the stimuli indeed degraded the network's memory of its past.
Cardiac arrest with cardiopulmonary resuscitation reduces dendritic spine density in CA1 pyramidal cells and selectively alters acquisition of spatial memory
Authors: Neigh Gretchen N. , Glasper Erica R. , Kofler Julia , Traystman Richard J. , Mervis Ronald F. , Bachstetter Adam , DeVries A. Courtney
Published: December 2004

The hippocampus is highly sensitive to ischemia and is one of the most extensively damaged regions of brain during cardiac arrest. Damage to hippocampus can subsequently lead to learning and memory deficits. The current study used the Morris water maze to characterize spatial learning and memory deficits elicited by 8 min of cardiac arrest with cardiopulmonary resuscitation (CA/CPR) in mice, which is associated with a 25–50% decrease in CA1 neurons. Mice were trained to navigate the water maze prior to CA/CPR or sham surgery (SHAM). They were retested in the water maze on days 7 and 8 postsurgery; both CA/CPR and SHAM groups were able to perform the task at presurgical levels. However, when the hidden platform was moved to a new location, the SHAM mice were able to adapt more quickly to the change and swam a shorter distance in search of the platform than did CA/CPR mice. Thus, CA/CPR did not affect the ability of mice to retain a previously learned platform location, but it did affect their ability to learn a new platform location. This behavioural impairment was correlated with dendritic spine density in the CA1 region of the hippocampus. Data presented here suggest that morphological changes, such as spine density, that occur in neurons that survive CA/CPR may be associated with cognitive impairments.
A meta‐analysis of biotic resistance to exotic plant invasions
Authors: Levine Jonathan M. , Adler Peter B. , Yelenik Stephanie G.
Published: December 2004

Biotic resistance describes the ability of resident species in a community to reduce the success of exotic invasions. Although resistance is a well‐accepted phenomenon, less clear are the processes that contribute most to it, and whether those processes are strong enough to completely repel invaders. Current perceptions of strong, competition‐driven biotic resistance stem from classic ecological theory, Elton's formulation of ecological resistance, and the general acceptance of the enemies‐release hypothesis. We conducted a meta‐analysis of the plant invasions literature to quantify the contribution of resident competitors, diversity, herbivores and soil fungal communities to biotic resistance. Results indicated large negative effects of all factors except fungal communities on invader establishment and performance. Contrary to predictions derived from the natural enemies hypothesis, resident herbivores reduced invasion success as effectively as resident competitors. Although biotic resistance significantly reduced the establishment of individual invaders, we found little evidence that species interactions completely repelled invasions. We conclude that ecological interactions rarely enable communities to resist invasion, but instead constrain the abundance of invasive species once they have successfully established.
Hazardous duty pay and the foraging cost of predation
Authors: Brown Joel S. , Kotler Burt P.
Published: December 2004

We review the concepts and research associated with measuring fear and its consequences for foraging. When foraging, animals should and do demand hazardous duty pay. They assess a foraging cost of predation to compensate for the risk of predation or the risk of catastrophic injury. Similarly, in weighing foraging options, animals tradeoff food and safety. The foraging cost of predation can be modelled, and it can be quantitatively and qualitatively measured using risk titrations. Giving‐up densities (GUDs) in depletable food patches and the distribution of foragers across safe and risky feeding opportunities are two frequent experimental tools for titrating food and safety. A growing body of literature shows that: (i) the cost of predation can be big and comprise the forager's largest foraging cost, (ii) seemingly small changes in habitat or microhabitat characteristics can lead to large changes in the cost of predation, and (iii) a forager's cost of predation rises with risk of mortality, the forager's energy state and a decrease in its marginal value of energy. In titrating for the cost of predation, researchers have investigated spatial and temporal variation in risk, scale‐dependent variation in risk, and the role of predation risk in a forager's ecology. A risk titration from a feeding animal often provides a more accurate behavioural indicator of predation risk than direct observations of predator‐inflicted mortality. Titrating for fear responses in foragers has some well‐established applications and holds promise for novel methodologies, concepts and applications. Future directions for expanding conceptual and empirical tools include: what are the consequences of foraging costs arising from interference behaviours and other sources of catastrophic loss? Are there alternative routes by which organisms can respond to tradeoffs of food and safety? What does an animal's landscape of fear look like as a spatially explicit map, and how do various environmental factors affect it? Behavioural titrations will help to illuminate these issues and more.
The σ54 regulon (sigmulon) of Pseudomonas putida
Authors: Cases Ildefonso , Ussery David W. , De Lorenzo Víctor
Published: December 2004

σ54 is unique among the bacterial sigma factors. Besides not being related in sequence with the rest of such factors, its mechanism of transcription initiation is completely different and requires the participation of a transcription activator. In addition, whereas the rest of the alternative sigma factors use to be involved in transcription of somehow related biological functions, this is not the case for σ54 and many different and unrelated genes have been shown to be transcribed from σ54‐dependent promoters, ranging from flagellation, to utilization of several different carbon and nitrogen sources, or alginate biosynthesis. These genes have been characterized in many different bacterial species and, only until recently with the arrival of complete genome sequences, we have been able to look at the σ54 functional role from a genomic perspective. Aided by computational methods, the σ54 regulon has been studied both in Escherichia coli, Salmonella typhimurium and several species of the Rhizobiaceae. Here we present the analysis of the σ54 regulon (sigmulon) in the complete genome of Pseudomonas putida KT2440. We have developed an improved method for the prediction of σ54‐dependent promoters which combines the scores of σ54‐RNAP target sequences and those of activator binding sites. In combination with other evidence obtained from the chromosomal context and the similarity with closely related bacteria, we have been able to predict more than 80% of the σ54‐dependent promoters of P. putida with high confidence. Our analysis has revealed new functions for σ54 and, by means of comparative analysis with the previous studies, we have drawn a potential mechanism for the evolution of this regulatory system.
Influence of maize mucilage on the diversity and activity of the denitrifying community
Authors: Mounier E. , Hallet S. , Chèneby D. , Benizri E. , Gruet Y. , Nguyen C. , Piutti S. , Robin C. , Slezack‐Deschaumes S. , Martin‐Laurent F. , Germon J.C. , Philippot L.
Published: December 2004

In order to understand the effect of the maize rhizosphere on denitrification, the diversity and the activity of the denitrifying community were studied in soil amended with maize mucilage. Diversity of the denitrifying community was investigated by polymerase chain reaction (PCR) amplification of total community DNA extracted from soils using gene fragments, encoding the nitrate reductase (narG) and the nitrous oxide reductase (nosZ), as molecular markers. To assess the underlying diversity, PCR products were cloned and 10 gene libraries were obtained for each targeted gene. Libraries containing 738 and 713 narG and nosZ clones, respectively, were screened by restriction fragment analysis, and grouped based on their RFLP (restriction fragment length polymorphism) patterns. In all, 117 and 171 different clone families have been identified for narG and nosZ and representatives of RFLP families containing at least two clones were sequenced. Rarefaction curves of both genes did not reach a clear saturation, indicating that analysis of an increasing number of clones would have revealed further diversity. Recovered NarG sequences were related to NarG from Actinomycetales and from Proteobacteria but most of them are not related to NarG from known bacteria. In contrast, most of the NosZ sequences were related to NosZ from α, β, and γProteobacteria. Denitrifying activity was monitored by incubating the control and amended soils anaerobically in presence of acetylene. The N2O production rates revealed denitrifying activity to be greater in amended soil than in control soil. Altogether, our results revealed that mucilage addition to the soil results in a strong impact on the activity of the denitrifying community and minor changes on its diversity.
Environmental regulation of the anaerobic oxidation of methane: a comparison of ANME‐I and ANME‐II communities
Authors: Nauhaus Katja , Treude Tina , Boetius Antje , Krüger Martin
Published: December 2004

The anaerobic oxidation of methane (AOM) is one of the major sinks for methane on earth and is known to be mediated by at least two phylogenetically different groups of anaerobic methanotrophic Archaea (ANME‐I and ANME‐II). We present the first comparative in vitro study of the environmental regulation and physiology of these two methane‐oxidizing communities, which occur naturally enriched in the anoxic Black Sea (ANME‐I) and at Hydrate Ridge (ANME‐II). Both types of methanotrophic communities are associated with sulfate‐reducing‐bacteria (SRB) and oxidize methane anaerobically in a 1:1 ratio to sulfate reduction (SR). They responded sensitively to elevated methane partial pressures with increased substrate turnover. The ANME‐II‐dominated community showed significantly higher cell‐specific AOM rates. Besides sulfate, no other electron acceptor was used for AOM. The processes of AOM and SR could not be uncoupled by feeding the SRB with electron donors such as acetate, formate or molecular hydrogen. AOM was completely inhibited by the addition of bromoethanesulfonate in both communities, indicating the participation of methanogenic enzymes in the process. Temperature influenced the intensity of AOM, with ANME‐II being more adapted to cold temperatures than ANME‐I. The variation of other environmental parameters, such as sulfate concentration, pH and salinity, did not influence the activity of both communities. In conclusion, the ecological niches of methanotrophic Archaea seem to be mainly defined by the availability of methane and sulfate, but it remains open which additional factors lead to the dominance of ANME‐I or ‐II in the environment.
Isolation and characterization of Tn‐Dha1, a transposon containing the tetrachloroethene reductive dehalogenase of Desulfitobacterium hafniense strain TCE1
Authors: Maillard Julien , Regeard Christophe , Holliger Christof
Published: December 2004

A new 9.9 kb catabolic transposon, Tn‐Dha1, containing the gene responsible for tetrachloroethene (PCE) reductive dechlorination activity, was isolated from Desulfitobacterium hafniense strain TCE1. Two fully identical copies of the insertion sequence ISDha1, a new member of the IS256 family, surround the gene cluster pceABCT, a truncated gene for another transposase and a short open reading frame with homology to a member of the twin‐arginine transport system (tatA). Evidence was obtained by Southern blot for an alternative form of the transposon element as a circular molecule containing only one copy of ISDha1. This latter structure most probably represents a dead‐end product of the transposition of Tn‐Dha1. Strong indications for the transposition activity of ISDha1 were given by polymerase chain reaction (PCR) amplification and sequencing of the intervening sequence located between both inverted repeats (IR) of ISDha1 (IR junction). A stable genomic ISDha1 tandem was excluded by quantitative real‐time PCR. Promoter mapping of the pceA gene, encoding the reductive dehalogenase, revealed the presence of a strong promoter partially encoded in the right inverted repeat of ISDha1. A sequence comparison with pce gene clusters from Desulfitobacterium sp. strains PCE‐S and Y51 and from Dehalobacter restrictus, all of which show 100% identity for the pceAB genes, indicated that both Desulfitobacterium strains seem to possess the same transposon structure, whereas only the pceABCT gene cluster is conserved in D. restrictus.
Diversity of functional genes of methanogens, methanotrophs and sulfate reducers in deep‐sea hydrothermal environments
Authors: Nercessian Olivier , Bienvenu Nadège , Moreira David , Prieur Daniel , Jeanthon Christian
Published: December 2004

To contribute to the identification of methanogens, methanotrophs and sulfate‐reducing bacteria (SRB) in microbial communities from the 13°N (East Pacific Rise) and Rainbow (Mid‐Atlantic Ridge) hydrothermal vent fields, we investigated the diversity of mcrA, pmoA and dsrAB genes sequences. Clone libraries were obtained using DNA isolated from fragments of diffuse vents, sediment and in situ samplers. The clones were categorized by restriction fragment length polymorphism, and representatives of each group were sequenced. Sequences were related to that of hyperthermophilic (order Methanopyrales and family Methanocaldococcaceae), thermophilic and mesophilic (family Methanococcaceae) methanogens, thermophilic (proposed genus ‘Methylothermus’) and mesophilic type I methanotrophs, and hyperthermophilic (order Archaeoglobales), thermophilic (order Thermodesulfobacteriales) and mesophilic (family Desulfobulbaceae) SRB. Several of the obtained sequences were distantly related to the genes of cultivated organisms, providing evidence of the existence of novel lineages in the three functional groups. This study provides for the first time an insight into the diversity of several functional genes of deep‐sea hydrothermal system microorganisms.
Modelling potential impacts of climate change on the bioclimatic envelope of species in Britain and Ireland
Authors: Berry P. M. , Dawson T. P. , Harrison P. A. , Pearson R. G.
Published: December 2004

Aim Climate change has the potential to have significant impacts on the distribution of species and on the composition of habitats. This paper identifies the potential changes in the future distribution of species under the UKCIP98 climate change scenarios, in order that such changes can be taken into account in conservation management.

Location The model was applied to Britain and Ireland.

Methods A model based on an artificial neural network was used to predict the changing bioclimate envelopes of species in Britain and Ireland. Fifty‐four species representing 15 habitats were modelled.

Results The modelled species could be placed into three categories: those losing suitable climate space, those gaining it, and those showing little or no change. When the species were associated with habitats it was found that Arctic–Alpine/montane heath communities were the most sensitive to climate change, followed by pine woodland and beech woodland in southern England. In lowland heath, wet heath, cereal field margins, coastal grazing marsh, drought‐prone acid grassland and calcareous grassland, the species either showed little change or an increase in suitable climate space. The other eight habitats showed a mixed response.

Conclusions The species show a variety of responses to climate change and thus their current habitat associations may alter. The uncertain future of some species and habitats is highlighted. Conservation policy and practice will need to be revised in the face of climate change.
Neural network ensembles: combining multiple models for enhanced performance using a multistage approach
Authors: Yang Shuang , Browne Antony
Published: December 2004

Abstract: Neural network ensembles (sometimes referred to as committees or classifier ensembles) are effective techniques to improve the generalization of a neural network system. Combining a set of neural network classifiers whose error distributions are diverse can generate better results than any single classifier. In this paper, some methods for creating ensembles are reviewed, including the following approaches: methods of selecting diverse training data from the original source data set, constructing different neural network models, selecting ensemble nets from ensemble candidates and combining ensemble members' results. In addition, new results on ensemble combination methods are reported.
Expression of human IL‐1α after intramarrow gene transfer into healthy non‐human primate by adenoviral vector
Authors: Bécard Nicolas , de Revel Thierry , Sorg Tania , Dormont Dominique , Le Grand Roger
Published: December 2004

Abstract:  Interleukin‐1α (IL‐1α) is a multifunctional cytokine that stimulates myelopoiesis in macaque. However, daily systemic injections of IL‐1α are associated with severe side effects. We therefore investigated the feasibility of a gene therapy strategy aimed at increasing the IL‐1α local production in bone marrow with limited release of the vector into the blood circulation. Intra‐medullar administration of adenoviral vector containing human IL‐1α (huIL‐1α) gene resulted in enhanced neutrophil, monocyte and platelet counts during the two first weeks after injection. The DNA vector, the transgene expression and the huIL‐1α production was detected in treated bone marrow without significant detection of huIL‐1α in the peripheral blood. Associated with huIL‐1α production, we observed concomitant plasma C reactive protein and IL‐1Ra peaks in the acellular fraction of treated bone marrow at days 3 and 7. No abnormal clinical side effects were observed in any of the animals following the adenoviral vector injection.
Effect of Promoter Region Mutations and
mgrA
Overexpression on Transcription of
norA
, Which Encodes a
Staphylococcus aureus
Multidrug Efflux Transporter
Authors: Kaatz Glenn W. , Thyagarajan Rama V. , Seo Susan M.
Published: December 2004

NorA is a
Staphylococcus aureus
multidrug transporter that confers resistance to structurally distinct compounds. The MgrA global regulatory protein is reported to augment
norA
expression when
mgrA
is overexpressed from an undefined plasmid-based promoter. Further details about
norA
regulatory mechanisms are scant. A chromosomal
norA
::
lacZ
transcriptional fusion was constructed in different
S. aureus
strains, and allele replacement was used to define the relevance of promoter region sequences to
norA
expression. The effect of
mgrA
overexpression in wild-type and mutant backgrounds was also determined. Contrary to existing data, overexpression of
mgrA
repressed
norA
transcription in all parent and selected
norA
promoter mutant strains in a dose-dependent fashion. Disruption of a near-perfect inverted repeat or other putative regulatory protein binding sites did not affect
norA
transcription, but the repressive effect of
mgrA
overexpression was blunted in these mutants. This result, and the conservation of all of these motifs in
S. aureus
, suggests that their presence is required for the full effect of MgrA, or other regulatory proteins, on
norA
expression. Mutations at the +5 nucleotide of
norA
mRNA (
flqB
mutations) had a major impact; all resulted in markedly increased
norA
expression that was significantly reversed by
mgrA
overexpression. The
flqB
position of
norA
mRNA is part of a conserved imperfect inverted repeat; it is feasible that this motif could be a binding site for a
norA
regulatory protein.
Molecular Cloning, Sequence Analysis, and Heterologous Expression of the Phosphinothricin Tripeptide Biosynthetic Gene Cluster from
Streptomyces viridochromogenes
DSM 40736
Authors: Blodgett Joshua A. V. , Zhang Jun Kai , Metcalf William W.
Published: December 2004

A fosmid library from genomic DNA of
Streptomyces viridochromogenes
DSM 40736 was constructed and screened for the presence of genes known to be involved in the biosynthesis of phosphinothricin tripeptide (PTT). Eight positives were identified, one of which was able to confer PTT biosynthetic capability upon
Streptomyces lividans
after integration of the fosmid into the chromosome of this heterologous host. Sequence analysis of the 40,241-bp fosmid insert revealed 29 complete open reading frames (ORFs). Deletion analysis demonstrated that a minimum set of 24 ORFs were required for PTT production in the heterologous host. Sequence analysis revealed that most of these PTT genes have been previously identified in either
S. viridochromogenes
or
S. hygroscopicus
(or both), although only 11 out of 24 of these ORFs have experimentally defined functions. Three previously unknown genes within the cluster were identified and are likely to have roles in the stepwise production of phosphonoformate from phosphonoacetaldehyde. This is the first report detailing the entire PTT gene cluster from any producing streptomycete.
bla
SHV
Genes in
Klebsiella pneumoniae
: Different Allele Distributions Are Associated with Different Promoters within Individual Isolates
Authors: Hammond David S. , Schooneveldt Jacqueline M. , Nimmo Graeme R. , Huygens Flavia , Giffard Philip M.
Published: December 2004

Extended-spectrum β-lactamases (ESBLs) emerge by point mutation from non-extended-spectrum precursors. The aims of this study were to reveal the basis for variations in resistance levels found in a collection of 21
Klebsiella pneumoniae
clinical isolates from Brisbane, Australia. Previous studies have shown that 20 of these isolates possess
bla
SHV-11
,
bla
SHV-2a
, and/or
bla
SHV-12
, and there is an association between the copy numbers of the ESBL-encoding genes and resistance levels. In this study, a real-time PCR method for interrogating the polymorphic sites at codons 238 and 240 was developed, and this confirmed the relationship between mutant gene copy numbers and resistance levels. The
bla
SHV
promoter region was cloned from one of the ESBL-expressing isolates, and this showed that
bla
SHV
genes exist downstream of two different promoters within this single isolate. These promoters have both been reported previously, and they differ by virtue of the presence or absence of an IS
26
insertion. The
bla
SHV
copy numbers in
cis
with the different promoters were measured, and the copy number of the IS
26
promoter was correlated with resistance levels. Cloning and analysis of PCR products showed that different
bla
SHV
variants existed in
cis
with individual promoters in individual isolates but that mutant genes were more abundant downstream of the IS
26
promoter. There were no ESBL-positive isolates without this promoter. It was concluded that
bla
SHV
in
cis
with the IS
26
promoter is located on an amplifiable replicon, and the presence of the IS
26
insertion may facilitate the acquisition of an ESBL-positive phenotype.