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81.
Presynaptic Ca(V)2.1 channels, which conduct P/Q-type Ca(2+) currents, initiate synaptic transmission at most synapses in the central nervous system. Regulation of Ca(V)2.1 channels by CaM contributes significantly to short term facilitation and rapid depression of synaptic transmission. Short term synaptic plasticity is diverse in form and function at different synapses, yet CaM is ubiquitously expressed. Differential regulation of Ca(V)2.1 channels by CaM-like Ca(2+) sensor (CaS) proteins differentially affects short term synaptic facilitation and rapid synaptic depression in transfected sympathetic neuron synapses. Here, we define the molecular determinants for differential regulation of Ca(V)2.1 channels by the CaS protein calcium-binding protein-1 (CaBP1) by analysis of chimeras in which the unique structural domains of CaBP1 are inserted into CaM. Our results show that the N-terminal domain, including its myristoylation site, and the second EF-hand, which is inactive in Ca(2+) binding, are the key molecular determinants of differential regulation of Ca(V)2.1 channels by CaBP1. These findings give insight into the molecular code by which CaS proteins differentially regulate Ca(V)2.1 channel function and provide diversity of form and function of short term synaptic plasticity. 相似文献
82.
Distinct effects of D-serine on spinal nociceptive responses in normal and carrageenan-injected rats
Guo JD Wang H Zhang YQ Zhao ZQ 《Biochemical and biophysical research communications》2006,343(2):401-406
Single unit extracellular recordings from dorsal horn neurons were performed with glass micropipettes in pentobarbital-anesthetized rats. A total of 60 wide dynamic range (WDR) neurons were obtained from 34 rats. In normal rats (20/34), spinally administered D-serine (10 nmol), a putative endogenous agonist of glycine site of NMDA receptors, significantly enhanced the C- but not Abeta-, and Adelta-fiber responses of WDR neurons in the spinal dorsal horn. When 1 nmol of the glycine site antagonist 7-chlorokynurenic acid (7-CK) was co-administered with 10 nmol D-serine, the facilitation of D-serine on C-fiber response was completely blocked. 7-CK (1 nmol) alone failed to influence Abeta-, Adelta-, and C-fiber responses of WDR neurons. In contrast, in carrageenan-injected rats (14/34), 10 nmol D-serine had no effect on C-fiber response, while 1 nmol 7-CK per se markedly depressed C-fiber response of WDR neurons. These findings suggest that under physiological conditions, glycine sites in the spinal cord were available but became saturated following peripheral inflammation. Thus, increased endogenous d-serine or glycine may be involved in nociceptive transmission by modulating NMDA receptor activities. The glycine site of NMDA receptors may become a target for the prevention of inflammatory pain. 相似文献
83.
Our goal in these studies was to characterize some specific aspects of hypothalamic-pituitary-adrenal (HPA) activity in rats exposed to repeated social stress. We used a modification of the resident/intruder paradigm in which male intruder rats were subjected to defeat and then separated from the resident by an enclosure for a total of 30 min on Day 1. On Days 2-7, intruder rats were exposed to different resident rats every day through a wire mesh enclosure for 30 min in order to minimize injurious physical contact between the two rats. The intruder rats gained significantly less weight than controls over the 7-day period of stress though basal corticosterone levels and adrenal and thymus weights were not significantly different between the two groups. On Day 8, repeatedly stressed rats exhibited facilitation of HPA responses to novel restraint compared to controls but no differences in negative feedback sensitivity to dexamethasone (0.05 or 0.2 mg/kg) were observed. Thus, the HPA axis of socially stressed rats remains responsive to a stimulus that has never been encountered. Using this type of repeated presentation to an aggressive resident allows us to examine the neuroendocrine and behavioral consequences, and their underlying neural mechanisms, of exposure to a stressor that is social in nature and naturalistic for rodents. 相似文献
84.
Analysis of aerial photographs indicates that woody plant biomass has rapidly increased in Hluhluwe Game Reserve over the last 40 years. Open Acacia nilotica savanna is being replaced by broadleaf species, especially Euclea spp. We were interested in whether this secondary successional shift was due to high numbers of seedlings establishing and growing to maturity under acacias (facilitation) or due to the release of already established, but suppressed individuals (gullivers) of the resprouting broadleaf species. We examined the recruitment patterns and size-class distributions (height, basal diameter) of important species in this savanna.Densities of euclea seedlings (<0.6 cm basal diameter) under Acacia nilotica were low (median of 0 and mean of 0.06 m2) below adult canopies and effectively zero in adjacent interspaces. No differences in numbers of other broadleaf species were found between open sites and under Acacia nilotica sites. Few large eucleas or other broadleaf species occurred under Acacia nilotica. Few Acacia nilotica recruits were found either under adults or in the open whereas Acacia karroo recruits were more common.The overall size class distribution for eucleas was dominated by individuals in the intermediate size class, suggesting that recruitment is not the dominant demographic process. We propose that the escape of intermediate sized eucleas from the fire trap has caused the increase in woody plants.Analysis of a time sequence of aerial photographs shows that invasion occurred rapidly between 1954 and 1975. A common feature for sites where woody plant invasion has taken place, was the presence of barriers to fire (especially roads). We suggest that the recent and rapid increase in woody vegetation is due to a decrease in the frequency of intense fires, rather than the recent absence of megaherbivores which allowed Acacia nilotica establishment. Few intense fires allow suppressed tree or shrub individuals, ('gullivers'), to escape the grass/fire layer and thereby become tall and fire-resistant. This release may explain the rapid rate of invasion by inherently slow growing broad-leaf species. 相似文献
85.
Climate-driven interactions among rocky intertidal organisms caught between a rock and a hot place 总被引:6,自引:0,他引:6
To explore how climate may affect the structure of natural communities, we quantified the role of thermal stress in setting
the high intertidal borders of the acorn barnacle, Semibalanus balanoides. At sites north and south of Cape Cod, a major faunal and thermal boundary on the east coast of North America, we examined
the interacting effects of thermal stress and recruit density on individual survivorship. At hotter southern sites, particularly
in bays, high intertidal barnacle survivorship was enhanced by experimental shading or by neighbors which ameliorate heat
and desiccation stresses. In contrast, at cooler northern bay and coastal sites, neither shading nor group benefits increased
barnacle survival, and mortality patterns were driven primarily by predators with largely boreal distributions. Our field
results, like recent laboratory microcosm studies, suggest that predicting even simple community responses to climate change
may be more complex than is currently appreciated.
Received: 26 January 1999 / Accepted: 5 April 1999 相似文献
86.
Dickie IA Oleksyn J Reich PB Karolewski P Zytkowiak R Jagodzinski AM Turzanska E 《Mycorrhiza》2006,16(2):73-79
Established vegetation can facilitate the ectomycorrhizal infection of seedlings, but it is not known whether this interaction
is limited by the phylogenetic relatedness of trees and seedlings. We use a series of bioassay experiments to test whether
soil modification by different ectomycorrhizal tree species causes different levels of seedling infection, whether the extent
of seedling infection is a function of the relatedness of tree and seedling, and whether the effect of trees on seedlings
is mediated by biotic or abiotic soil factors. We found that soils from under different tree species do vary in their mycorrhizal
infectiveness. However, this variation is not related to the genetic relatedness of trees and seedlings but instead, appears
to be an attribute of the overstory species, irrespective of seedling species, mediated through a suite of humus- and base-cation-related
abiotic effects on soils. Modification of abiotic soil properties by overstory trees should be considered as an important
factor in the effect of different overstory trees on the extent of seedling mycorrhizal infection. 相似文献
87.
Sessile biota can compete with or facilitate each other, and the interaction of facilitation and competition at different
spatial scales is key to developing spatial patchiness and patterning. We examined density and scale dependence in a patterned,
soft sediment mussel bed. We followed mussel growth and density at two spatial scales separated by four orders of magnitude.
In summer, competition was important at both scales. In winter, there was net facilitation at the small scale with no evidence
of density dependence at the large scale. The mechanism for facilitation is probably density dependent protection from wave
dislodgement. Intraspecific interactions in soft sediment mussel beds thus vary both temporally and spatially. Our data support
the idea that pattern formation in ecological systems arises from competition at large scales and facilitation at smaller
scales, so far only shown in vegetation systems. The data, and a simple, heuristic model, also suggest that facilitative interactions
in sessile biota are mediated by physical stress, and that interactions change in strength and sign along a spatial or temporal
gradient of physical stress. 相似文献
88.
Knowledge about plant–plant interactions for pollinator service at the plant community level is still scarce, although such
interactions may be important to seed production and hence the population dynamics of individual plant species and the species
compositions of communities. An important step towards a better understanding of pollination interactions at the community
level is to assess if the variation in floral traits among plant species explain the variation in flower visitation frequency
among those species. We investigated the relative importance of various floral traits for the visitation frequency of all
insects, and bumblebees and flies separately, to plant species by measuring the visitation frequency to all insect-pollinated
species in a community during an entire flowering season. Visitation frequency was identified to be strongly positive related
to the visual display area and the date of peak flowering of plant species. Categorical variables, such as flower form and
symmetry, were important to the visitation frequency of flies only. We constructed floral similarity measures based on the
species’ floral traits and found that the floral similarity for all species’ traits combined and the continuous traits separately
were positively related to individual visitation frequency. On the other hand, plant species with similar categorical floral
traits did not have similar visitation frequencies. In conclusion, our results show that continuous traits, such as flower
size and/or density, are more important for the variation in visitation frequency among plant species than thought earlier.
Furthermore, differences in visitation frequency among pollinator groups give a poor support to the expectations derived from
the classical pollination syndromes. 相似文献
89.
Local modification of the soil environment by individual plants may affect the performance and composition of associated plant species. The aromatic plant Thymus vulgaris has the potential to modify the soil through leaching of water-soluble compounds from leaves and litter decomposition. In southern France, six different thyme chemotypes can be distinguished based on the dominant monoterpene in the essential oil, which is either phenolic or non-phenolic in structure. We examine how soils from within and away from thyme patches in sites dominated by either phenolic or non-phenolic chemotypes affect germination, growth and reproduction of the associated grass species Bromus erectus. To do so, we collected seeds of B. erectus from three phenolic and three non-phenolic sites. Seeds and seedlings were grown on soils from these sites in a reciprocal transplant type experiment in the glasshouse. Brome of non-phenolic origin performed significantly better on its home soil than on soil from a different non-phenolic or a phenolic site. This response to local chemotypes was only observed on soil collected directly underneath thyme plants and not on soil in the same site (<5 m away) but where no thyme plants were present. This is preliminary evidence that brome plants show an adaptive response to soil modifications mediated by the local thyme chemotypes. Reproductive effort was consistently higher in brome of phenolic origin than in brome of non-phenolic origin (on both thyme- and grass-soil), indicating that life-history variation may be related to environmental factors which also contribute to the spatial differentiation of thyme chemotypes. Moreover, we found that brome growing on thyme-soil in general was heavier than when growing on grass-soil, regardless of the origin of the brome plants. This is concordant with thyme-soil containing higher amounts of organic matter and nitrogen than grass-soil. Our results indicate that patterns of genetic differentiation and local adaptation may modify competitive interactions and possible facilitation effects in natural communities. 相似文献
90.
Indirect effects in a desert plant community: is competition among annuals more intense under shrub canopies? 总被引:6,自引:0,他引:6
An unresolved discussion in contemporary ecology deals with the relative importance of competition along environmental gradients. In deserts, local-scale differences in environmental productivity may be caused by the presence of shrubs, which represent a favorable habitat for annual populations within a nutrient-poor matrix. In this study, we attempted to test the hypothesis that facilitation of desert annuals by shrubs increase the intensity of competition among the annual plants. Such negative indirect effects have so far been ignored in studies about plant-plant interactions. We tested our hypothesis by measuring seedling survival and fecundity of four abundant annual plant species with and without neighbors in open areas and under shrub canopies in a sandy desert area. Our findings did not indicate indirect negative effects of shrubs on their understory annuals. Sensitivity to the presence of neighbors varied between species and surprisingly, the species with the smallest seeds was the only one which was not negatively affected by the presence of neighbors. In contrast to our hypothesis, there was no difference between the habitat types shrubs and openings in absolute and relative competition intensity. Our overall results suggest that negative indirect effects of shrubs are unimportant in determining demographic response of understory annual plants. 相似文献