bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Summary

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

Summary

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

Summary

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

Summary

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

AbstractEnvironmental 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

Abstract 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

AbstractAmong 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

AbstractRC3 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

AbstractMost 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

AbstractThis 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

AbstractTwo 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.