bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and reproduction of three cladoceran species from a small wetland in the south‐eastern U.S.A.
Authors: Lemke A. M. , Benke A. C.
Published: July 2003

SUMMARY 1. Growth, reproduction and life‐history parameters were measured for three cladoceran species from a small south‐eastern wetland, U.S.A. Simocephalus serrulatus, Diaphanosoma brachyurum and Scapholeberis mucronata juveniles were reared at temperatures between 10 and 25 °C on natural food resources.

2. Growth rate increased with temperature and decreased with individual size for all three species. Maximum somatic growth rate was higher for Simocephalus (49–72% day−1) and Diaphanosoma (21–91% day−1) than for Scapholeberis (11–45% day−1). Multiple regression equations were developed which predict temperature‐ and mass‐specific growth rates for each species.

3. Scapholeberis egg production was positively related to temperature; however, maximum egg production occurred at intermediate temperatures for Simocephalus and Diaphanosoma. Mean cumulative egg production was higher for Scapholeberis (28–92 eggs per female) than for Simocephalus (18–25 eggs per female) and Diaphanosoma (1–41 eggs per female), and was related to differences in reproductive strategy and survival.

4. Survival was inversely related to temperature in most cases. For all three cladocerans, the intrinsic rate of increase (r) and net reproductive rate (R0) increased with temperature, whereas generation time (G) decreased. Greater egg production by Scapholeberis compared with the other two cladocerans was consistent with higher R0 values for Scapholeberis at any given temperature. Although r was very similar among species, G was typically longer for Scapholeberis than for Simocephalus and Diaphanosoma.

5. This analysis provides basic information about the population parameters of these coexisting wetland species, and the growth rate models can be applied to field data to determine production dynamics.
Spatio‐temporal heterogeneity in a planktonic Thiocystis minor population, studied by laser in situ particle analysis
Authors: Serra Teresa , Colomer Jordi , Soler Marianna , Vila Xavier
Published: July 2003

1. The development of a population of Thiocystis minor (formerly Chromatium minus) in the deepest, anoxic layers of Moncortès Lake (Lleida, Spain) was studied by means of an in situ, laser particle analyser. Particle size distribution was measured at hourly and monthly time intervals.

2. The population was located between the redoxcline (∼3 m below the mean population depth) and the oxycline (∼6 m above the mean population depth) with a seasonal vertical displacement (SVD) of up to 6 m (from April to October).

3. Diel vertical migration of the population was followed in three field campaigns, when the population was most abundant. The largest vertical displacement was 2.8 m (in 11.5 h) and the fastest vertical displacement was 0.6 m h−1. Sudden changes in the irradiance reaching the bacterial population were detected by the cells, which moved up or down, rapidly modifying the mean vertical position of the population.

4. There was positive phototaxis with an ascent during the morning and a descent during the afternoon/night. The whole population was active while migrating upwards (towards higher light intensity) or downwards (towards lower redox concentration).
Influences of habitat complexity on the diversity and abundance of epiphytic invertebrates on plants
Authors: Taniguchi Hiromi , Nakano Shigeru , Tokeshi Mutsunori
Published: July 2003

SUMMARY 1. The compound influence of habitat complexity and patch size on stream invertebrate assemblages associated with submerged macrophytes was investigated through field sampling of two natural macrophyte species with contrasting leaf morphologies (complex, Ranunculus yezoensis; simple, Sparganium emersum) and an experiment with two artificial plants with different levels of morphological complexity.

2. The artificial plant experiment was designed to separate the effects of habitat area (patch size) and habitat complexity, thus enabling a more rigorous assessment of complexity per se than in previous studies where only a single patch size was used. Simple and complex artificial plants were established with five different patch sizes corresponding to the range found in natural plants.

3. Invertebrates occurred on both complex and simple forms of natural and artificial plants at similar abundances with dipterans and ephemeropterans being predominant. Taxon richness was higher on structurally complex Ranunculus than on simple Sparganium and was similarly higher on the complex artificial plant than on the simple one, over the entire range of habitat patch sizes. Thus, architectural complexity affected the taxon richness of epiphytic invertebrates, independently of habitat scale.

4. On the natural plants there was no difference in the abundance (both number of individuals and biomass) of invertebrates between simple and complex forms, while on artificial plants more invertebrates occurred on complex than on simple forms. The amount of particulate organic matter, >225 μm (POM) and chlorophyll a showed mixed patterns on natural and artificial plants, suggesting that the availability of these resources is not an overriding proximate factor controlling invertebrate abundance on plants. The difficulty of extrapolating from experimental results involving use of artificial plants is discussed, especially when considering the relationship between habitat structure and the occurrence of epiphytic invertebrates on natural plants.
Changes in population biology of two succulent shrubs along a grazing gradient
Authors: Riginos Corinna , Hoffman M. Timm
Published: July 2003

Heavy livestock grazing in Namaqualand, South Africa, is threatening the region's unique diversity of succulent shrubs. This is especially true in the communally managed lands, where grazing is centred around fixed enclosures (stockposts) in which animals stay overnight. In this study we set out to determine the effects of a semi‐permanent stockpost on the composition of the surrounding vegetation and the mechanisms by which grazing limits the persistence of leaf‐succulent shrub populations.

We used the grazing gradient created by a stockpost to examine the impacts of grazing on vegetation composition and changes in mortality, reproductive output and seedling establishment for the leaf‐succulent species Ruschia robusta and Cheiridopsis denticulata.

Vegetation composition was found to change from a community dominated by the unpalatable shrub Galenia africana at high grazing intensities to a community dominated by the palatable leaf‐succulent shrub R. robusta at lower grazing intensities.

Mortality of the leaf‐succulents R. robusta and C. denticulata was high at the sites closest to the stockpost, while fruit production and seedling germination were substantially reduced over distances of 800 m and 2 km for the two species, respectively. Seedling establishment was not limited by either grazing or microsite availability. Thus reduction in reproductive output is the greatest impact of heavy grazing on these two species.

Synthesis and applications. This study demonstrates that marked zonation in vegetation composition and population biology can develop around a fixed stockpost and that the greatest impact of grazing on the two leaf‐succulent species studied is the suppression of flower and fruit production. Consistent suppression of reproductive output could have long‐term consequences for the persistence of succulent shrub populations in the heavily grazed communal lands of Namaqualand. We recommend that (i) herders should be encouraged to relocate their stockposts regularly to prevent the development of centres of degradation, and (ii) areas should be relieved periodically of all grazing pressure to allow for successful seed set of native shrubs.
Vertical structure and basal area development in second‐growthNothofagusstands in Chile
Authors: Lusk Christopher H. , Ortega Alicia
Published: July 2003

Some studies have shown that mixed forest stands can develop more biomass or basal area than pure stands when the component species occupy different strata. It has been predicted that such additive effects are most likely in moist habitat sites where size‐asymmetric competition controls stand development.

In south‐central Chile, secondary succession often gives rise to vertically stratified mixed forest stands, with aNothofagusoverstorey overtopping lower tiers dominated by more shade‐tolerant taxa. We examined the relationship between the degree of understorey development and total basal area accumulated by 83 second‐growthNothofagusstands aged 40–70 years. Basal area is defined as the cross‐sectional area at breast height of all trees in a stand, per unit land area.

When age, overstorey leaf habit and geographical location were controlled byancova, stands with a heavy understorey (> 6 m2 ha−1) yielded > 25% more total basal area on average than stands with little or no understorey. The average basal area of theNothofaguscomponent did not differ significantly between stand structure categories.

The total basal area of stands dominated by evergreenN. dombeyiwas nearly 50% higher on average than that of stands of similar age dominated by deciduousN. obliquaand/orN. nervosa, reflecting denser stockings in the former as a result of allometric differences. Although the percentage of total stand basal area contributed by the understorey was higher on deciduous‐dominant plots, mean absolute basal area of understorey associates was similar beneath evergreen and deciduousNothofagusoverstoreys.

Synthesis and applications. The results broaden the evidence for additive effects in mixtures of species with complementary light use, suggesting that no significant advantage to overstorey wood production will be gained by eliminating a woody understorey inNothofagussecond‐growth stands on mesic sites. Despite the minor contribution of the understorey to merchantable timber volume, other benefits and ecosystem services associated with subcanopy species in these stands can be regarded as additive to benefits obtained from theNothofagusoverstorey. Our findings are also consistent with the proposal that size‐asymmetric competition controls stand development after canopy closure on mesic sites.
Predicting spatial aspects of human–elephant conflict
Authors: Sitati N. W. , Walpole M. J. , Smith R. J. , Leader‐Williams N.
Published: July 2003

Human–elephant conflict (HEC) in Africa occurs wherever these two species coincide, and poses serious challenges to wildlife managers, local communities and elephants alike. Mitigation requires a detailed understanding of underlying patterns and processes. Although temporal patterns of HEC are relatively predictable, spatial variation has shown few universal trends, making it difficult to predict where conflict will take place. While this may be due to unpredictability in male elephant foraging behaviour (the male behaviour hypothesis) it may also be due to variations in the data resolution of earlier studies.

This study tested the male behaviour and data resolution hypotheses using HEC data from a 1000‐km2unprotected elephant range adjacent to the Masai Mara National Reserve in Kenya. HEC incidents were divided into crop raiding and human deaths or injuries. Crop raiding was further subdivided into incidents involving only male elephants or family groups. A relatively fine‐resolution, systematic, grid‐based method was used to assign the locations of conflict incidents, and spatial relations with underlying variables were explored using correlation analysis and logistic regression.

Crop raiding was clustered into distinct conflict zones. Both occurrence and intensity could be predicted on the basis of the area under cultivation and, for male elephant groups, proximity to major settlements. Conversely, incidents of elephant‐induced human injury and death were less predictable but were correlated with proximity to roads.

A grid‐based geographical information system (GIS) with a 25‐km2resolution utilizing cost‐effective data sources, combined with simple statistical tools, was capable of identifying spatial predictors of HEC. At finer resolutions spatial autocorrelation compromised the analyses.

Synthesis and applications. These results suggest that spatial correlates of HEC can be identified, regardless of the sex of the elephants involved. Moreover, the method described here is fully transferable to other sites for comparative analysis of HEC. Using these results to map vulnerability will enable the development and deployment of appropriate conflict mitigation strategies, such as guarding, early warning systems, barriers and deterrents. The utility of such methods and their strategic deployment should be assessed alongside alternative land‐use and livelihood strategies that limit cultivation within the elephant range.
Dispersal characteristics and management of a rare damselfly
Authors: Purse Bethan V. , Hopkins Graham W. , Day Kieron J. , Thompson David J.
Published: July 2003

Coenagrion mercurialeis a rare damselfly in Britain and mainland Europe and has been declining in the last 30 years. It has specialized habitat requirements and has been viewed, traditionally, as a poor disperser. Knowledge of its dispersal ability was considered in its Biodiversity Species Action Plan as essential for the formulation of appropriate conservation management strategies.

Mark–release–recapture (MRR) studies ofC.mercurialein two large UK heathland populations were undertaken. Mature adults had a low rate of movement within continuous areas of habitat (average < 25 m movement), low emigration rates (1·3–11·4%) and low colonization distances (maximum 1 km), all comparable to similarly sized coenagrionids.

Movements were more likely within than between patches of suitable habitat over short to medium distances (50–300 m). Between‐patch movements were more likely between patches that were close together. Scrub barriers reduced dispersal.

The probability of dispersal between two recaptures depended on the length of the time interval between them.Coenagrion mercurialeperformed considerable between‐patch movements within a small fraction (1–2 days) of its mean mature adult life span (7–8 days).

Qualitative comparison of field colonization distances measured here and distances between UK sites occupied byC.mercurialerevealed that empty sites within large clusters of sites would probably be recolonized rapidly and dispersal events would be frequent. However, such events would occur rarely within small isolated sites or clusters of sites, leaving local populations prone to extinction.

Synthesis and applications.These data show that management effort should be directed towards maximizing the likelihood ofC.mercurialerecolonizing sites naturally within 1–3 km of other populations (particularly within large clusters). Scrub boundaries should be removed between existing populations and empty, but suitable, sites to facilitate stepping‐stone dispersal movements.
An ecosystem‐based approach to management: using individual behaviour to predict the indirect effects of Antarctic krill fisheries on penguin foraging
Authors: Alonzo Suzanne H. , Switzer Paul V. , Mangel Marc
Published: July 2003

Changes in species’ abundance and distributions caused by human disturbances can have indirect effects on other species in a community. Although ecosystem approaches to management are becoming increasingly prevalent, they require a fuller understanding of how individual behaviour determines interactions within and between species.

Ecological interactions involving krill are of major importance to many species within the Antarctic. Despite extensive knowledge of the ecosystem that they occupy, there is still incomplete understanding of the links between species and the effect of environmental conditions on these interactions. In this study, we extended a behavioural model used previously to understand the interactions between penguins and krill to determine the indirect effect of krill fisheries on penguin foraging success and behaviour in adjacent breeding sites.

Increased fishing pressure offshore is predicted to reduce penguin food intake. Given the documented links between krill and penguins, this also leads to a prediction of decreased penguin survival and reproduction. Krill behaviour is predicted to cause stronger effects of krill fisheries than explained solely by the percentage of biomass removed. Environmental conditions that decrease krill growth rates or cause krill to spend time in deeper water are also predicted to increase the magnitude of the effect of fishing on penguin success. We show that changes in penguin foraging behaviour can be used to assess the impact of local fisheries on penguin reproductive success.

Synthesis and applications. These results demonstrate that an understanding of predator–prey interactions, indirect effects between species, and individual behaviour is imperative to our ability to manage populations. We describe a general method to use what is known about ecological and evolutionary processes with species‐specific information to predict the response of organisms to novel situations. We further show how individual behaviour can be used to assess the impact of human disturbance on ecosystems.
Dispersal of female southern elephant seals and their prey consumption during the austral summer: relevance to management and oceanographic zones
Authors: Hindell Mark A. , Bradshaw Corey J. A. , Sumner Michael D. , Michael Kelvin J. , Burton Harry R.
Published: July 2003

Numerical models that predict trophic structure require both accurate information on prey consumption rates and estimates of spatial and temporal variation. In the Southern Ocean little information exists on the spatial and temporal patterns of resource use by predators, so we attempted to examine these patterns for an important Antarctic predator, the southern elephant seal. We (i) defined the area of the ocean used by the adult female component of the elephant seal population at Macquarie Island; (ii) quantified the time these seals spent in the different regions of the Southern Ocean; and (iii) estimated the biomass of fish and squid prey consumed per fortnight and per region.

We used data from 42 post‐breeding females collected from 1992 to 2001. The data consisted of locations determined by geo‐location (based on light intensity) recorded using dataloggers. A randomized, incremental analysis of at‐sea locations indicated that a sample of 25 individuals was required to provide 95% coverage of the total area of ocean used.

The greatest amount of time (44·6%) was spent in the region between the Antarctic Polar Front (APF) and the Subantarctic Front (SAF). Up to 20% of time was spent south of the Antarctic Circle or within Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Statistical Subareas, indicating that seals from Macquarie Island are also important summer‐time predators in high Antarctic waters.

The adult female population was estimated to consume 122·73–125·81 × 106 MJ for the post‐lactation foraging trip (31 142–31 925 tonnes of prey). Of this, 47·2–53·4% was consumed within the CCAMLR Statistical Subareas and the Australian and New Zealand exclusive economic zones (EEZ).

Synthesis and applications. Our study emphasizes that (i) a large sample of individual seals (25) can estimate spatial trends in prey consumption; (ii) much of the estimated prey consumption occurs within fishery‐managed zones, therefore elephant seals should be included in models predicting trophic structure in the Southern Ocean; and (iii) recent commercial fishery catch within these zones is minimal relative to the prey consumed by elephant seals, but increases in fishing activity in these zones may result in competition for marine resources.
Simulating the distribution of southern Buller's albatross using an individual‐based population model
Authors: Broekhuizen N. , Stahl J. C. , Sagar P. M.
Published: July 2003

A spatially explicit, individual‐based population model (IBPM) for southern Buller's albatross Thalassarche bulleri bulleri was developed to simulate the species’ at‐sea distribution and interactions with fishing fleets.

Satellite tracking data for birds from colonies on Snares Islands and Solander Island (south of South Island, New Zealand) suggest that the feeding grounds utilized by a bird, and the duration of its foraging trips, are dependent upon colony, sex, pairing status and developmental stage of egg/chick. These dependencies were incorporated into the IBPM.

Simulated distributions were compared with independent shipboard observations by using the IBPM to make replicated ‘virtual counts’ corresponding to each shipboard count. Each shipboard count was assigned a score reflecting the likelihood that a count of this magnitude would have arisen if the true populations behave as described by the IBPM.

Randomization tests indicated that, for the months in which we had adequate telemetry data (March–July), predicted and observed distributions were very similar at scales down to 1 degree2. There was some evidence that bird densities around the south‐west corner of New Zealand's South Island were underpredicted in July, and at the scale of individual shipboard counts the ship data showed greater fine‐scale aggregation than the virtual data.

Comparison of observed and simulated distributions early in the breeding season (January and February, for which we had no telemetry data) suggested that the foraging behaviour of birds prior to egg laying differs from that exhibited by either breeding or pre‐breeding birds later in the season.

Synthesis and applications. In combination with reported by‐catch rates, our IBPM may enable us to derive fishing gear‐specific per‐capita capture rates for Buller's albatross. Our results also emphasize that it may be necessary to represent responses of individual birds encountering vessels at a finer spatiotemporal scale before it will be possible to make robust demographic predictions of the consequences of changes in fishing practices.
Modelling the emergence response of weed seeds to burial depth: interactions with seed density, weight and shape
Authors: Grundy A. C. , Mead A. , Burston S.
Published: July 2003

Weeds play an important role in arable and horticultural habitats, and models are being developed to improve our understanding of their population dynamics. The position of a weed seed in the soil profile influences the probability of a seed germinating, emerging successfully and its relative time of emergence. Identifying a relationship between the shape or weight of a seed and its ability to emerge from depth may allow the development of generic models. The aim of this study was to quantify seed response to burial depth, to improve the wider application of existing seedling emergence models.

A field experiment used weed seeds sown at different depths and densities in a standard substrate. In addition, two laboratory studies used pre‐germinated seeds of the same range of species, buried at a range of depths in optimum conditions using the same substrate. These studies explored the effects of seed size, shape and sowing density on seedling emergence and also enabled reserve‐dependent pre‐emergence mortality to be quantified.

The largest and heaviest of the seeds tested overall, Veronica hederifolia, emerged from the greatest depth (8 cm). In contrast, Tripleurospermum inodorum and Veronica arvensis, the two smallest species, showed a sharp decline when burial exceeded 1 cm. However, the link between seed shape or weight and the ability to emerge from depth suggests a complex relationship. Given optimum conditions, some species (Stellaria media and Chenopodium album) have the physical reserves to emerge from a wider range of burial depths than normally observed in the field, suggesting an ability to exploit opportunities when they occur.

For some species, emergence was reduced at high seed densities (e.g. Veronica arvensis). These responses may be associated with traits that have evolved to counteract sibling competition.

Synthesis and applications. Generic models identifying the maximum depths for seed germination and emergence have a number of practical applications. For example, they can be used to target cultivation to deplete the weed seed bank or to prescribe the optimum depth of mulches to favour certain species. Our model showed that, in general, larger‐seeded species emerged from deeper in the soil, but the relationship between seed size and shape and emergence was complex, possibly species specific. Our germination data may also assist our understanding of the relative importance of different causes of seed losses, particularly from different zones of the soil profile, such as the soil surface. Understanding the component processes of seed behaviour and germination is essential to developing sustainable weed management practices in agriculture and horticulture, and the work reported here contributes to a larger programme modelling weed seed bank population dynamics.
The effect of sapling density, heather height and season on browsing by mountain hares on birch
Authors: Rao S. J. , Iason G. R. , Hulbert I. A. R. , Elston D. A. , Racey P. A.
Published: July 2003

When mammalian herbivores are present at high densities their browsing activity can have a negative effect on establishment or regeneration of native woodlands. The impact on saplings of browsing by herbivores is known to vary in response to sapling density. Until now, experimental tests of the effect of sapling density have usually involved only one tree species and no alternative forages. In this study we used a planting experiment conducted in the field to test the effects of surrounding vegetation height, season and density of downy birch Betula pubescens on the extent of browsing damage by mountain hares Lepus timidus, in the presence of background vegetation that also represents an acceptable food source.

The experiment was conducted on heather Calluna vulgaris moorland between March 1998 and October 1999 in north‐east Scotland. Birch saplings (n = 6708) were planted in short and tall heather in arrays at low, medium and high sapling density within a 107‐ha area from which large herbivores were excluded. The number of saplings browsed was recorded monthly and individual sapling morphological measurements and characteristics of the ground vegetation were noted twice yearly, pre‐ and post‐winter.

More saplings were browsed in winter and spring than in summer, especially during the period immediately after planting. Saplings were browsed at a higher rate in short heather, which facilitated easier access by mountain hares. The proportion of saplings that were browsed decreased with planting density in all seasons except winter, when it increased.

At the individual sapling level, larger saplings were more likely to be attacked and to have more biomass removed than smaller saplings.

Synthesis and applications. This study demonstrates that mountain hares browse birch throughout the year, but browsing is at its most intense during winter and in short heather, and this may potentially suppress tree growth and tree regeneration. This result has important management implications for the uplands of Scotland, where downy birch is used to establish and regenerate native woodlands, often on moorland supporting high densities of mountain hares. Damage to trees by hares can be minimized by planting in tall vegetation where trees are less visible and accessible to hares. Tree planting can be synchronized with temporary hare control; however, effective reduction in hare numbers may be difficult to achieve. Finally, planting density should be low, as during winter, when browsing is most frequent, the rate of browsing increases with increasing tree density.
Neuronal activity and neurotrophic factors regulate GAD‐65/67 mRNA and protein expression in organotypic cultures of rat visual cortex
Authors: Patz Silke , Wirth Marcus J. , Gorba Thorsten , Klostermann Oliver , Wahle Petra
Published: July 2003

Environmental factors are known to regulate the molecular differentiation of neocortical interneurons. Their class‐defining transmitter synthetic enzymes are the glutamic acid decarboxylases (GAD); yet, fairly little is known about the developmental regulation of transcription and translation of the GAD‐65/67 isoforms. We have characterized the role of neuronal activity, neurotrophins and afferent systems for GAD‐65/67 expression in visual cortex in organotypic cultures (OTC) compared with in vivo in order to identify cortex‐intrinsic regulatory mechanisms. Spontaneously active OTC prepared at postnatal day 0 displayed from 10 days in vitro (DIV) onwards 12–14% GAD‐65/GAD‐67 neurons similar to in vivo. However, GAD‐65 mRNA was higher, whereas GAD‐67 protein was lower, than in vivo. During the first week neurotrophins increased whereas the Trk receptor inhibitor K252a and MEK inhibitors decreased both GAD mRNAs and proteins. After 10 DIV GAD expression no longer depended on neurotrophin signalling. Activity‐deprived OTC revealed only 6% GAD‐67 neurons and mRNA and protein were reduced by 50%. GAD‐65 mRNA was less reduced, but protein was reduced by half, suggesting translational regulation. Upon recovery of activity GAD mRNAs, cell numbers, and both proteins quickly returned to normal and these ‘adult’ levels were resistant to late‐onset deprivation. In 20 DIV activity‐deprived OTC, only neurotrophin 4 increased GAD‐65/67 mRNAs, rescued the percentage of GAD‐67 neurons and increased both proteins in a TrkB‐dependent manner. Activity deprivation had thus shifted the period of neurotrophin sensitivity to older ages. The results suggested neuronal activity as a major regulator differentially affecting transcription and translation of the GAD isoforms. The early presence of neuronal activity promoted the GAD expression in OTC to a neurotrophin‐independent state suggesting that neurotrophins play a context‐dependent role.
Hippocampal dopamine D2 receptors correlate with memory functions in Alzheimer's disease
Authors: Kemppainen N. , Laine M. , Laakso M. P. , Kaasinen V. , Någren K. , Vahlberg T. , Kurki T. , Rinne J. O.
Published: July 2003

Post mortem studies have revealed a loss of dopamine D2 receptors in the temporal lobes in Alzheimer's disease (AD). Moreover, the role of hippocampal D2 receptors on memory performance has been suggested in experimental studies. However, there are no previous in vivo studies on extrastriatal D2 receptors in AD. Our aim was to examine in vivo whether hippocampal or temporal cortical dopamine D2 receptors are affected in AD and whether D2 receptor availability is associated with the memory dysfunction seen in AD. Fourteen patients with probable AD and 11 age‐ and sex‐matched controls were studied with positron emission tomography using a dopamine D2/D3 receptor antagonist [11C]FLB 457. The D2 receptor binding potentials (BPs) were measured in extrastriatal brain regions and a neuropsychological investigation was performed on the patients with AD. In AD, the D2 receptor availability was reduced in the hippocampus: by 34% (P = 0.03) in the right hippocampus and by 14% (P = 0.78) in the left hippocampus as compared with controls. Multiple linear regression analysis showed that the BP in the right hippocampus had a significant positive association with verbal memory performance (Wechsler Memory Scale – Revised) (P = 0.001) and picture naming (the Boston Naming Test) (P = 0.002). Our findings suggest a role for temporal lobe D2 receptors in the memory and naming performance in AD, and suggest that studies to evaluate the efficiency of dopaminergic medication on patients with early AD might be warranted.
Role of protein kinase C family in the cerebellum‐dependent adaptive learning of horizontal optokinetic response eye movements in mice
Authors: Shutoh Fumihiro , Katoh Akira , Ohki Masafumi , Itohara Shigeyoshi , Tonegawa Susumu , Nagao Soichi
Published: July 2003

Among the subtypes of the Ca2+‐dependent protein kinase C (PKC), which play a crucial role in long‐term depression (LTD), both α and γ are expressed in the cerebellar floccular Purkinje cells. To reveal the functional differences of PKC subtypes, we examined the adaptability of ocular reflexes of PKCγ mutant mice, which show mild ataxia and normal LTD. In mutant mice, gains of the horizontal optokinetic eye response (HOKR) were reduced. Adaptation of the HOKR was not affected but its retinal slip dependency was altered in mutant mice. Sustained 1‐h sinusoidal screen oscillation, which induced a relatively large amount of retinal slips in both mutant and wild‐type mice, increased the HOKR gain in wild‐type mice but not in mutant mice. In contrast, exposure to 1 h of sustained slower screen oscillations, which induced relatively small retinal slips in mutant and wild‐type mice, increased the HOKR gain in both mutant and wild‐type mice. Adaptation of the HOKR of the mutant mice to slow screen oscillation and those of wild‐type mice to fast and slow screen oscillations were all abolished by local applications of a PKC inhibitor (chelerythrine) within the flocculi. Electrophysiological and anatomical studies showed no appreciable changes in the sources and magnitudes of climbing fibre inputs, which mediate retinal slip signals to the flocculus in the mutant mice. These results suggest that PKCγ has a modulatory role in determining retinal slip dependency, and other PKC subtypes, e.g. PKCα, may play a crucial role in the adaptation of the HOKR.
Calcium dynamics are altered in cortical neurons lacking the calmodulin‐binding protein RC3
Authors: Van Dalen Jacqueline J. W. , Gerendasy Dan D. , De Graan Pierre N. E. , Schrama Loes H. , Gruol Donna L.
Published: July 2003

RC3 is a neuronal calmodulin‐binding protein and protein kinase C substrate that is thought to play an important regulatory role in synaptic transmission and neuronal plasticity. Two molecules known to regulate synaptic transmission and neuronal plasticity are Ca2+ and calmodulin, and proposed mechanisms of RC3 action involve both molecules. However, physiological evidence for a role of RC3 in neuronal Ca2+ dynamics is limited. In the current study we utilized cultured cortical neurons obtained from RC3 knockout (RC3−/−) and wildtype mice (RC3+/+) and fura‐2‐based microscopic Ca2+ imaging to investigate a role for RC3 in neuronal Ca2+ dynamics. Immunocytochemical characterization showed that the RC3−/− cultures lack RC3 immunoreactivity, whereas cultures prepared from wildtype mice showed RC3 immunoreactivity at all ages studied. RC3+/+ and RC3−/− cultures were indistinguishable with respect to neuron density, neuronal morphology, the formation of extensive neuritic networks and the presence of glial fibrillary acidic protein (GFAP)‐positive astrocytes and γ‐aminobutyric acid (GABA)ergic neurons. However, the absence of RC3 in the RC3−/− neurons was found to alter neuronal Ca2+ dynamics including baseline Ca2+ levels measured under normal physiological conditions or after blockade of synaptic transmission, spontaneous intracellular Ca2+ oscillations generated by network synaptic activity, and Ca2+ responses elicited by exogenous application of N‐methyl‐d‐aspartate (NMDA) or class I metabotropic glutamate receptor agonists. Thus, significant changes in Ca2+ dynamics occur in cortical neurons when RC3 is absent and these changes do not involve changes in gross neuronal morphology or neuronal maturation. These data provide direct physiological evidence for a regulatory role of RC3 in neuronal Ca2+ dynamics.
Influence of object shape on responses of human tactile afferents under conditions characteristic of manipulation
Authors: Jenmalm Per , Birznieks Ingvars , Goodwin Antony W. , Johansson Roland S.
Published: July 2003

Most objects that we grasp, lift and further manipulate are curved, with curvatures of the same order of magnitude as those of the fingertips. Tactile information pertaining to such ‘gross’ geometrical features of objects are used in the automatic control of fingertip actions. We analyzed responses from 172 human tactile afferents distributed over the entire terminal phalanx when spherically shaped surfaces were applied to a standard site on the fingertip; the curvatures and force magnitudes and directions used were representative of everyday manipulations. Nearly all SA‐I, SA‐II and FA‐I afferents responded, and for more than 80% of these afferents the response intensity was correlated with curvature. The correlation was positive for approximately half the afferents and negative for the other half, resulting in a curvature contrast signal within the populations of tactile afferents; afferents terminating at the sides and end of the fingertip tended to show negative correlations. For nearly all afferents, curvature and force direction had interactive effects. Changing the direction of force affected an afferent's sensitivity to curvature and vice versa. We conclude that recognition of such shapes takes advantage of signals originating from tactile afferents distributed over the entire terminal phalanx, and that both the direction of fingertip forces and the curvatures of objects contacted during natural manipulations influence the afferents' responses. Consequently, if humans are able to perceive independently curvature and force direction from signals in tactile afferents, then the CNS must possess mechanisms that disentangle interactions between these and other parameters of stimuli on the fingertips.
Postdecentralization plasticity of voltage‐gated K+ currents in glandular sympathetic neurons in rats
Authors: Szulczyk Bartłomiej , Szulczyk Paweł
Published: July 2003

This paper presents the kinetic and pharmacological properties of voltage‐gated K+ currents in anatomically identified glandular postganglionic sympathetic neurons isolated from the superior cervical ganglia in rats. The neurons were labelled by injecting the fluorescent tracer Fast Blue into the submandibular gland. The first group of neurons remained intact, i.e. innervated by the preganglionic axons until the day of current recordings (control neurons). The second group of neurons was denervated by severing the superior cervical trunk 4–6 weeks prior to current recordings (decentralized neurons). In every control and decentralized neuron three categories of voltage‐dependent K+ currents were found. (i) The IAf K+ current, steady state, inactivated at hyperpolarized membrane potentials. This current was fast activated and fast time‐dependently inactivated, insensitive to TEA and partially depressed by 4‐AP. (ii) The IAs K+ current, which was steady‐state inactivated at less hyperpolarized membrane potentials than IAf. The current activation and time‐dependent inactivation kinetics were slower than those of IAf. IAs was blocked by TEA and partially inhibited by 4‐AP. (iii) The IK K+ current did not undergo steady‐state inactivation. In decentralized compared to control neurons the maximum IAf K+ current density (at +50 mV) increased from 116.9 ± 8.2 to 189.0 ± 11.5 pA/pF, the 10–90% current rise time decreased from 2.3 to 0.7 ms and the recovery from inactivation was faster. Similarly, in decentralized compared to control neurons the maximum IAs K+ current density (at +50 mV) increased from 49.9 ± 3.5 to 74.3 ± 5.0 pA/pF, the 10–90% current rise time shortened from 29 to 16 ms and the recovery from inactivation of the current was also faster. The maximum density (at +50 mV) of IK in decentralized compared to control neurons decreased from 76.6 ± 3.9 to 60.7 ± 6.3 pA/pF. We suggest that the upregulation of voltage‐gated time‐dependently‐inactivated K+ currents and their faster recovery from inactivation serve to restrain the activity of glandular sympathetic neurons after decentralization.
Firing regulation in dopaminergic cells: effect of the partial degeneration of nigrostriatal system in surviving neurons
Authors: Rodríguez Manuel , González Julián , Sabaté Magdalena , Obeso José , Pereda Ernesto
Published: July 2003

Two mechanisms for firing rate regulation were identified in dopaminergic nigrostriatal cells (DA cells), one of a renewal nature which prevents short and long interspike intervals (ISIs) and the other of a no‐renewal nature which compensates long ISIs with short ISIs and vice versa. Renewal regulation was found in 96% of DA cells and less frequently in nigrocollicular (63%), nigrothalamic (61%) and nigropeduncular (50%) nigral GABA cells. No‐renewal regulation was found in 77% of DA cells, and was only observed in 8% of GABA cells. Thus, most DA cells showed both regulatory mechanisms, which justifies the low variability in their firing rate and the low oscillation of extracellular striatal dopamine previously reported. DA cells surviving a partial degeneration of the nigrostriatal system did not show alterations in their firing rate and burst firing but presented a marked disturbance for no‐renewal regulation. Under these conditions, small fluctuations in firing rate are not compensated for in time, which could be one of the factors responsible for the motor fluctuations often observed in advanced Parkinson's disease.
Reduced anxiety and improved stress coping ability in mice lacking NPY‐Y2 receptors
Authors: Tschenett Alexandra , Singewald Nicolas , Carli Mirjana , Balducci Claudia , Salchner Peter , Vezzani Annamaria , Herzog Herbert , Sperk Günther
Published: July 2003

Neuropeptide Y (NPY) has been implicated in the pathophysiology of certain mood disorders, including depression and anxiety. It is, however, not known which of the five cloned NPY receptors mediate these functions. We investigated the effect of Y2 receptor deletion on anxiety and stress‐related behaviours. In the elevated plus maze, Y2 knock out (Y2−/−) mice showed a 2.7‐fold higher frequency of entering into, and spent 3.8 times more time within, the open arms compared to controls, while entries into the closed arms did not differ. Similarly Y2−/− mice entered the central area of the open field 1.7 times more frequently and also spent 1.8 times more time there. In the light/dark test Y2−/− mice had a 4.8‐fold lower latency to enter the lit area but stayed there 2.6 times longer than control mice. Y2−/− mice displayed 3.2‐fold less immobility in the forced swim test, indicating improved stress coping ability. Y2 receptors are predominantly located presynaptically where they mediate feedback inhibition of neurotransmitter release. Deletion of these receptors may result in enhanced release of NPY, GABA and/or glutamate in brain areas linked to the manifestation of anxiety, and stress‐related behaviour such as the amygdala. Taken together, deletion of the Y2 receptor has revealed an important role of Y2 receptors in the generation of anxiety‐related and stress‐related behaviours in mice.
The ablation of glial fibrillary acidic protein‐positive cells from the adult central nervous system results in the loss of forebrain neural stem cells but not retinal stem cells
Authors: Morshead Cindi M. , Garcia A. Denize , Sofroniew Michael V. , Van Der Kooy Derek
Published: July 2003

The adult mammalian forebrain subependyma contains neural stem cells (NSCs) capable of self‐renewal and multilineage differentiation. The in vivo identification of NSCs has not been definitively addressed using a loss of function approach. Using a transgenic mouse expressing herpes‐simplex virus thymidine kinase from the glial fibrillary acidic protein (GFAP) promotor, we have selectively killed dividing GFAP‐positive cells in the presence of ganciclovir (GCV) and shown a > 95% loss in the numbers of NSCs, as assayed by the formation of clonally derived neurospheres in vitro. This loss is seen following 3 days of GCV exposure in vivo or in vitro only and cannot be rescued by coculturing with pure astrocyte populations or control (green fluorescent protein‐expressing) subependymal cells. Exposure to GCV in vitro has no effect on adult retinal stem cells hence, we conclude that adult forebrain NSCs comprise a subpopulation of the GFAP‐positive cells within the subependyma.
Brain capillaries and cholinergic neurons persist in organotypic brain slices in the absence of blood flow
Authors: Moser Karma V. , Schmidt‐Kastner Rainald , Hinterhuber Hartmann , Humpel Christian
Published: July 2003

Angiogenesis plays an important role during development of the brain and under pathological conditions. The aim of the present study was to observe interaction of brain capillaries and cholinergic neurons in organotypic brain slices. Immunohistochemistry was used to visualize brain capillary‐like structures (RECA‐1 antigen) and cholinergic neurons (choline acetyltransferase). Under normal culture conditions, a very low number of brain capillaries was found in 2‐ and 4‐week‐old cortex brain slices. Treatment of slices with acidic medium (pH 6) or hyperthermia (42 °C) markedly enhanced the number of brain capillaries. Incubation with 10 ng/mL vascular endothelial growth factor only enhanced angiogenesis in more developed slices. Cholinergic neurons survived in slices of the basal nucleus of Meynert; however, hyperthermia but not acidosis markedly decreased their number. In coslices of the basal nucleus of Meynert and cortex (pretreated with acidic medium), a high number of RECA‐1‐positive capillaries and cholinergic neurons persisted and displayed strong nerve fibre growth of cholinergic fibres into the cortex. In conclusion, we have demonstrated that RECA‐1‐positive capillaries and cholinergic neurons can be studied in slice cultures in the absence of blood perfusion, and that this model could provide a system to study mechanisms involved in vascular dementia.
Regional differences in the circadian modulation of human sleep spindle characteristics
Authors: Knoblauch Vera , Martens Wim , Wirz‐Justice Anna , Kräuchi Kurt , Cajochen Christian
Published: July 2003

Electroencephalographic oscillations in the sleep spindle frequency range (11–16 Hz) are a key element of human nonrapid eye movement sleep. In the present study, sleep spindle characteristics along the anterior–posterior axis were analysed during and outside the circadian phase of melatonin secretion. Sleep electroencephalograms were recorded during naps distributed over the entire circadian cycle and analysed with two different methodological approaches, the classical fast Fourier transform in the frequency‐domain and a new method for instantaneous spectral analysis, the fast time frequency transform that yields high‐resolution parameters in the combined time‐frequency‐domain. During the phase of melatonin secretion, spindle density was generally increased and intraspindle frequency variation reduced. Furthermore, lower spindle frequencies were promoted: peak frequencies shifted towards the lower end of the spindle frequency range, and spindle amplitude was enhanced in the low‐frequency range (11–14.25 Hz) and reduced in the high‐frequency range (∼14.5–16 Hz). The circadian variation showed a clear dependence on brain topography such that it was maximal in the parietal and minimal in the frontal derivation. Our data provide evidence that the circadian pacemaker actively promotes low‐frequency sleep spindles during the biological night with a parietal predominance.