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At least 1,045 records · Page 58Linked to original sources
PubMed1997

Single-channel kinetics, inactivation, and spatial distribution of inositol trisphosphate (IP3) receptors in Xenopus oocyte nucleus.

Single-channel properties of the Xenopus inositol trisphosphate receptor (IP3R) ion channel were examined by patch clamp electrophysiology of the outer nuclear membrane of isolated oocyte nuclei. With 140 mM K+ as the charge carrier (cytoplasmic [IP3] = 10 microM, free [Ca2+] = 200 nM), the IP3R exhibited four and possibly five conductance states. The conductance of the most-frequently observed state M was 113 pS around 0 mV and approximately 300 pS at 60 mV. The channel was frequently observed with high open probability (mean P(o) = 0.4 at 20 mV). Dwell time distribution analysis revealed at least two kinetic states of M with time constants tau < 5 ms and approximately 20 ms; and at least three closed states with tau approximately 1 ms, approximately 10 ms, and >1 s. Higher cytoplasmic potential increased the relative frequency and tau of the longest closed state. A novel "flicker" kinetic mode was observed, in which the channel alternated rapidly between two new conductance states: F1 and F2. The relative occupation probability of the flicker states exhibited voltage dependence described by a Boltzmann distribution corresponding to 1.33 electron charges moving across the entire electric field during F1 to F2 transitions. Channel run-down or inactivation (tau approximately 30 s) was consistently observed in the continuous presence of IP3 and the absence of change in [Ca2+]. Some (approximately 10%) channel disappearances could be reversed by an increase in voltage before irreversible inactivation. A model for voltage-dependent channel gating is proposed in which one mechanism controls channel opening in both the normal and flicker modes, whereas a separate independent mechanism generates flicker activity and voltage-reversible inactivation. Mapping of functional channels indicates that the IP3R tends to aggregate into microscopic (<1 microm) as well as macroscopic (approximately 10 microm) clusters. Ca2+-independent inactivation of IP3R and channel clustering may contribute to complex [Ca2+] signals in cells.

Animals↗
PubMed2006

Activation processes in a medical linear accelerator and spatial distribution of activation products.

Activation products have been identified by in situ gamma spectroscopy at the isocentre of a medical linear accelerator shortly after termination of a high energy photon beam irradiation with 15 x 15 cm field size. Spectra have been recorded either with an open or with a closed collimator. Whilst some activation products disappear from the spectrum with closed collimator or exhibit reduced count rates, others remain with identical intensity. The former isotopes are neutron-deficient and mostly decay by positron emission or electron capture; the latter have neutron excess and decay by beta(-) emission. This new finding is consistent with the assumption that photons in the primary beam produce activation products by (gamma, n) reactions in the treatment head and subsequently the neutrons created in these processes undergo (n, gamma) reactions creating activation products in a much larger area. These findings are expected to be generally applicable to all medical high energy linear accelerators.

Electrons↗
PubMed2006

Modeling the spatial distribution of mosquito vectors for West Nile virus in Connecticut, USA.

The risk of transmission of West Nile virus (WNV) to humans is associated with the density of infected vector mosquitoes in a given area. Current technology for estimating vector distribution and abundance is primarily based on Centers for Disease Control and Prevention (CDC) light trap collections, which provide only point data. In order to estimate mosquito abundance in areas not sampled by traps, we developed logistic regression models for five mosquito species implicated as the most likely vectors of WNV in Connecticut. Using data from 32 traps in Fairfield County from 2001 to 2003, the models were developed to predict high and low abundance for every 30 x 30 m pixel in the County. They were then tested with an independent dataset from 16 traps in adjacent New Haven County. Environmental predictors of abundance were extracted from remotely sensed data. The best predictive models included non-forested areas for Culex pipiens, surface water and distance to estuaries for Cx. salinarius, surface water and grasslands/agriculture for Aedes vexans and seasonal difference in the normalized difference vegetation index and distance to palustrine habitats for Culiseta melanura. No significant predictors were found for Cx. restuans. The sensitivity of the models ranged from 75% to 87.5% and the specificity from 75% to 93.8%. In New Haven County, the models correctly classified 81.3% of the traps for Cx. pipiens, 75.0% for Cx. salinarius, 62.5% for Ae. vexans, and 75.0% for Cs. melanura. Continuous surface maps of habitat suitability were generated for each species for both counties, which could contribute to future surveillance and intervention activities.

Aedes↗
PubMed2005

Spatial distribution and registry-based case-control analysis of Campylobacter infections in Denmark, 1991-2001.

Using data from an 11-year period (1991-2001), the authors analyzed available information on location of residence for all registered, laboratory-confirmed, domestically acquired cases of campylobacteriosis in Denmark. Patient data were merged with data from a national register on housing and addresses, and a population density index was constructed using the Danish population register. The study was performed as a register-based case-control study; 15 age-matched controls for each case were selected from the national population register. A total of 22,066 cases were compared with 318,958 controls in logistic regression analysis. Living in types of housing found in rural areas and living in areas with a low population density were both associated with an increased risk of infection. This relation concerned children in particular and explained one third of cases among children in the countryside. Furthermore, in some counties there was an association between infection and type of drinking-water company serving the home. This study indicated that contact with animals or the environment is the source of a substantial proportion of sporadic Campylobacter infections in the Danish countryside, particularly among children.

Adolescent↗
PubMed2006

The genetic diversity of two brazilian vellozia (velloziaceae) with different patterns of spatial distribution and pollination biology.

BACKGROUND AND AIMS: The genetic structure and variability of two species of Vellozia (Velloziaceae) with restricted distribution in high-altitude quartzitic fields in south-eastern Brazil were studied. Vellozia epidendroides is short, grows on pebbly or sandy soil, and is pollinated by bees. Vellozia leptopetala is arborescent, grows on rock outcrops, and is pollinated by bees and hummingbirds. Both are self-incompatible and have a short, massive flowering strategy. The study aimed to associate differences in their genetic diversity and structure with their microhabitat distribution and pollination ecology. METHODS: Leaves from 106 and 139 plants of V. epidendroides and V. leptopetala, respectively, were collected from five patches of each species and prepared for electrophoretic analyses. KEY RESULTS: Five enzyme systems could be reliably scored for both species. Vellozia epidendroides showed 100 % of the loci polymorphic for almost all patches. The average number of alleles per locus ranged between 2.2 and 2.4 among patches. The Wright's fixation index (F) for this species was 0.226. A significant (p) value indicates that there is a reasonable genetic divergence among patches. Vellozia leptopetala presented 47.5 % of polymorphic loci. All levels of P, A, A(p) and of heterozygosities were lower than those of V. epidendroides. Vellozia leptopetala showed high inbreeding within patches. CONCLUSIONS: The relatively high values of genetic diversity indices found for V. epidendroides may be associated with its large and widespread populations. On the other hand, the low values of genetic diversity found for V. leptopetala may be related to physical isolation on outcrops and intensive foraging by territorial hummingbirds, which may hinder gene flow among patches, aggravated by the very restricted seed dispersal characteristic of the genus, that facilitates sibling mating. It is important to stress the need to preserve the specific habitats of these species of Vellozia, in particular those of V. leptopetala that has lower genetic diversity and is restricted to rock outcrop environments.

Brazil↗
PubMed1998

The spatial distribution of visual attention in hemineglect and extinction patients.

We studied the visual field distribution of speed and accuracy of manual responses to small brief light flashes, in patients with left hemineglect or extinction resulting from right hemisphere vascular lesions and in brain-damaged and healthy control subjects. All patients with right hemisphere lesions showed a greater impairment in both the speed of response and the detection rate in the contralesional than in the ipsilesional hemifield. This interfield difference increased with the eccentricity of stimulus presentation and was especially pronounced in neglect patients who showed a paradoxical increase in speed of response and detection rate at increasingly larger eccentricities in the ipsilesional hemifield. We hypothesize that both the contralesional slowing down and the ipsilesional speeding up of the response depends upon an exaggerated gradient of attention towards the ipsilesional hemifield. To assess whether these abnormalities concern automatic or controlled attentional processes, in a second experiment, we manipulated the predictability of the side of the stimulus presentation by using blocked rather than randomized stimulus presentations. This resulted in a speeding up of responses in both hemifields thus showing that the patients were able to focus attention to the side of stimulus presentation voluntarily. However, there was no modification of the contra-ipsilesional differences which, therefore, are likely to be related to abnormal automatic processes rather than controlled attention.

Aged↗
PubMedDate not supplied

The spatial distribution of pulvinar neurons that project to two subregions of the inferior parietal lobule in the macaque.

The distribution of pulvinar neurons that project to the lateral intraparietal area (LIP) and area 7a, two subregions of the inferior parietal lobule in monkeys, was determined using small injections of retrogradely transported fluorescent dyes. Both LIP and 7a received the majority of their thalamic input from contiguous but distinct zones within the medial pulvinar nucleus. Thalamocortical cell bodies that projected to LIP were arranged in a dense, horizontally oriented cluster that was sandwiched between two similar clusters of neurons that projected to 7a. There was minimal overlap of the respective clusters. LIP also received an appreciable input from the dorsal half of the lateral pulvinar nucleus, but tracer placements in 7a resulted in only occasional labeled neurons in the lateral pulvinar.

Amidines↗
PubMed1999

Timing and spatial distribution of somatosensory responses recorded in the upper bank of the sylvian fissure (SII area) in humans.

We studied responses of the parieto-frontal opercular cortex to electric stimuli, as recorded by intra-cortical electrodes during stereotactic EEG presurgical assessment of patients with drug-resistant temporal lobe epilepsy. After electrical stimulation of the median nerve at the wrist, we consistently recorded a negative-positive biphasic response peaking at 60 ms (N60) and 90 ms (P90) post-stimulus in the upper bank of the sylvian fissure contralateral to stimulation. Talairach stereotactic coordinates of the electrode contacts recording these responses covered the pre- and post-rolandic part of the upper bank of the sylvian fissure (25<x<55 mm; -27<y<+13 mm; 0<z<21 mm), corresponding to the accepted localization of SII area in man. The sources of these responses were deeply situated in the cortex of the upper bank of the sylvian fissure at approximately 40 mm from the midline sagittal plane, so that some of them could be located in the insular cortex. Moreover this study suggests the existence of dipolar SII sources radial to the scalp surface, which are overlooked in magnetic recordings. Somatosensory evoked potentials (SEPs) recorded in SII are delayed by approximately 40 ms as compared with SEPs generated in the primary somatosensory cortex. This long delay between SI and SII responses is not fully explained though it is coherent with the timing of activation issued from MEG source modeling data.

Adult↗
PubMed2000

Nonrandom spatial distribution of synonymous substitutions in the GP63 gene from Leishmania.

In this work we analyze the variability in substitution rates in the GP63 gene from Leishmania. By using a sliding window to estimate substitution rates along the gene, we found that the rate of synonymous substitutions along the GP63 gene is highly correlated with both the rate of amino acid substitution and codon bias. Furthermore, we show that comparisons involving genes that represent independent phylogenetic lines yield very similar divergence/conservation patterns, thus suggesting that deterministic forces (i.e., nonstochastic forces such as selection) generated these patterns. We present evidence indicating that the variability in substitution rates is unambiguously related to functionally relevant features. In particular, there is a clear relationship between rates and the tertiary structure of the encoded protein since all divergent segments are located on the surface of the molecule and facing one side (almost parallel to the cell membrane) on the exposed surface of the organism. Remarkably, the protein segments encoded by these variable regions encircle the active site in a funnel-like distribution. These results strongly suggest that the pattern of nucleotide divergence and, notably, of synonymous divergence is affected by functional constraints.

Animals↗
PubMed1991

Seasonal movement and spatial distribution of the sheep ked (Diptera: Hippoboscidae) on Wyoming lambs.

When populations of adult sheep ked, Melophagus ovinus (L.), infesting unshorn lambs were monitored at the University of Wyoming Paradise Farm during 1986, we determined the body regions on which keds would be found at various times of the year and their seasonal population trends for optimal sampling. Results suggested that ked populations were consistently greater on the ribs than on any other area of the lamb. No significant differences were detected for ked populations between sides of a lamb. Distinct and similar ked population trends over time occurred only in the rib, thigh, shoulder, hind leg, belly, and hind flank areas of the lambs, suggesting that a significant seasonal migration did not occur. Analyses for seasonal population fluctuations indicated that ked populations increased in the winter and spring, decreased in summer and then increased again in the fall. Thus, sampling for keds in the rib area at shearing, which begins in March in Wyoming and runs through mid-April, would be an opportune time to detect keds. At other times of the year, the rib area should be inspected for presence of sheep ked.

Animals↗
PubMed1996

Spatial distribution of adult mosquitoes (Diptera:Culicidae) in habitats associated with the rice agroecosystem of northern California.

The objective of this study was to determine whether abundance, blood feeding rates, and sex ratios of adult Anopheles freeborni Aitken and Culex tarsalis Coquillett were associated significantly with either rice field, pasture, riparian, or mixed habitats found within the rice culture agroecosystem of northern California. Significantly higher numbers of adult An. freeborni occurred in riparian and mixed habitats compared with rice and pasture habitats. Such a pattern was not evident for Cx. tarsalis. Riparian and pasture habitats contained significantly higher proportions of blood fed An. freeborni females than did rice and mixed habitats; however, the proportions of blood fed Cx. tarsalis females did not vary significantly among habitat types. The proportions of blood fed An. freeborni and Cx. tarsalis females in riparian habitats decreased with increasing abundance. There was no correlation between blood feeding rates and abundance for An. freeborni and Cx. tarsalis females in the other habitat types. The sex ratio of An. freeborni in pasture and riparian habitats was significantly female biased, unlike the other habitats which did not differ significantly from unity (1:1). Overall, riparian and mixed habitats contained greater numbers of adults mosquitoes; therefore, surveillance and control efforts of these mosquito species should be focused on such habitats.

Agriculture↗
PubMed1997

Spatial distribution of Triatoma guasayana (Hemiptera:Reduviidae) in hardwood forest biotopes in Santiago del Estero, Argentina.

In the study area Triatoma guasayana Wygodzinsky & Abalos is the only wild triatomine found sympatric with Triatoma infestans (Klug) in peridomestic premises. The Trypanosoma cruzi Chagas wild cycle is centered around the same biotopes occupied by T. guasayana, which are also visited mainly by opossums with annual prevalences of 29-50%. Twelve hectares were sampled for 4 consecutive years during all seasons. During that time, 420 T. Guasayana individuals were collected in 11.3% of 1,188 biotopes of 4 types, which included quimiles (the cactus Opuntia quimilo), chaguares (several species of bromeliads), trees, and logs. Quimiles had the highest percentage of positive biotopes (31.5%) followed by chaguares (22.3%), whereas 5% of the logs were found infested. During all seasons, 9.6-15.2% of biotopes were found infested. Distance to artificial biotopes was not statistically significant when comparing the frequency of triatomine numbers per biotope in all biotope-season combinations. With the exception of quimiles in the fall, the mean number of triatomines was higher in chaguares during all seasons. Triatomine abundance by biotope and season strata showed a clumped distribution, except for the quimiles biotope during the summer. When pooling by seasons, the mean number of triatomines in chaguares and quimiles biotope was higher than in logs and trees, with all biotopes showing a strong clumped distribution. When pooling by biotopes, the mean number of T. guasayana was relatively similar for all seasons, with a strong clumped distribution. The strong contagious distribution of T. guasayana in the hardwood forest biotopes may explain the maintenance of the wild cycle of T. cruzi, despite the low number and the low prevalences of the insect vector.

Animals↗
PubMed2002

Spatial distribution of leaf nitrogen and photosynthetic capacity within the foliage of individual trees: disentangling the effects of local light quality, leaf irradiance, and transpiration.

There is presently no consensus about the factor(s) driving photosynthetic acclimation and the intra-canopy distribution of leaf characteristics under natural conditions. The impact was tested of local (i) light quality (red/far red ratio), (ii) leaf irradiance (PPFD(i)), and (iii) transpiration rate (E) on total non-structural carbohydrates per leaf area (TNC(a)), TNC-free leaf mass-to-area ratio (LMA), total leaf nitrogen per leaf area (N(a)), photosynthetic capacity (maximum carboxylation rate and light-saturated electron transport rate), and leaf N partitioning between carboxylation and bioenergetics within the foliage of young walnut trees grown outdoors. Light environment (quantity and quality) was controlled by placing individual branches under neutral or green screens during spring growth, and air vapour pressure deficit (VPD) was prescribed and leaf transpiration and photosynthesis measured at branch level by a branch bag technique. Under similar levels of leaf irradiance, low air vapour pressure deficit decreased transpiration rate but did not influence leaf characteristics. Close linear relationships were detected between leaf irradiance and leaf N(a), LMA or photosynthetic capacity, and low R/FR ratio decreased leaf N(a), LMA and photosynthetic capacity. Irradiance and R/FR also influenced the partitioning of leaf nitrogen into carboxylation and electron light transport. Thus, local light level and quality are the major factors driving photosynthetic acclimation and intra-canopy distribution of leaf characteristics, whereas local transpiration rate is of less importance.

Acclimatization↗