Phase locking in integrate-and-fire models with refractory periods and modulation

It is known [8, 11, 16, 26] that phase locking can entrain frequency information when the leaky integrate-and-fire (IF) model of a neuron is forced by a periodic function. We show that this is still the case when the IF model is made more biologically realistic. We incorporate into our model spike dependent threshold modulation and refractory periods. Consecutive firing times from this model and their respective interspike intervals are related by an annulus map. We prove a general theorem concerning orientation reversing annulus twist homeomorphisms, which shows that our map admits a unique rotation number. This implies, in particular, that chaotic behaviour is not possible in our model and phase locking is predicted.This research was partially supported by NSF EIA-BITS grant 426411This research was partially supported by the Summer Undergraduate Research Program sponsored by IGERT grant NSF-DGE 9972824 and the Undergraduate Scholars Program at MSU-BozemanAcknowledgement The authors would like to thank Marcy Barge for discussions of prime ends and Sherry Heis for formatting the diagrams.     

Effect of hemodialysis on the antioxidative properties of serum

In patients with chronic renal failure undergoing regular hemodialysis (HD), oxidative stress is involved in the development of dialysis-related pathologies. The aim of the study was to measure the effect of HD treatment on the general antioxidative status of serum with special consideration of the specific oxidizability of lipids and proteins. Indicators for the oxidative/antioxidative status of plasma were monitored at the beginning and at the end of a dialysis session on the arterial and venous side of the dialyzer. A decrease in the antioxidant status was accompanied by an increased oxidizability of proteins as well as lipids during HD treatment. During the first passage of the dialyzer, the lag time of lipid oxidation decreased from 114.0+/-19.8 to 81.5+/-18.9 min, the lag time of protein oxidation decreased from 105.0+/-24.6 to 72.9+/-21.3 min and the total antioxidative status decreased from 518+/-24 to 252+/-124 microM trolox equivalents. The carbonyl content of serum proteins was high in patients with end stage renal disease (ESRD) (3.9+/-1.1 vs. 0.9+/-0.1 nmol/mg in controls) but did not change significantly during dialysis procedure. Our data demonstrate that the susceptibility of serum lipids and proteins to oxidative modification is severely increased by HD treatment.     

New Silurian cooksonias from dolostones of north-eastern North America

New specimens of Cooksonia and Hostinella are described from the Bertie Group of Ontario and New York State, which is dated by faunas as latest Silurian (Přídolí). The rare plant fossils are unusual in that they are preserved in fine-grained, slightly argillaceous dolostones ('waterlime') rather than clastic rocks. At least two species of Cooksonia are present, one with ± globular sporangial morphology close to C. hemisphaerica Lang. Those with ellipsoidal/discoidal sporangia are compared with C. pertoni Lang, C .  paranensis Gerrienne et al . and C. bohemica Schweitzer, the latter represented by a single specimen from the Přídolí of the Czech Republic. However, the paucity of specimens, which prevents assessment of taphonomic influences on shape, combined with the absence of any anatomical features and the gross morphological simplicity of the fossils, precludes specific assignment. Specimens of Hostinella include one in which apices and a lateral basal structure resembling a root are preserved. It is concluded that the Laurentian assemblage of Ontario and New York State is less diverse and disparate than coeval assemblages, which are also preserved in marine rocks. Its preservation in limestones may have been facilitated by the hypersalinity inferred from various sedimentary features, which would restrict the activity of many decomposers.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 399–413.     

Northern Goshawk Habitat: an Intersection of Science,Management, and Conservation

Abstract: We responded to the claim by Greenwald et al. (2005) that the management recommendations for the northern goshawk in the Southwestern United States (MRNG; Reynolds et al. 1992), a food web-based conservation plan that incorporated both northern goshawk (Accipiter gentilis) and multiple prey habitats, may be inadequate to protect goshawks. Greenwald et al. (2005) based this claim on their review of 12 telemetry studies of goshawk habitat selection and 5 nontelemetry studies of the effects of vegetation structure at the home range scale on goshawk nest occupancy and reproduction that appeared after the 1992 publication of the MRNG. Greenwald et al. (2005) summarized their review as showing that 1) goshawks were habitat specialists limited to forests with mature and old-growth structures including large trees, high canopy cover, multiple canopy layering, and abundant woody debris; 2) habitats were not selected on the basis of prey abundance and, therefore, managing for prey habitats diluted goshawk habitats; and 3) selection for openings, edges, and habitat diversity was inconclusive. Our review found that when the studies' respective authors pooled their radiotagged goshawks there were weak to strong selections for old forest structures. However, the studies also documented extensive variation in use of vegetation types and structures by individual goshawks; some avoided openings, edges, young forests, and old forests, whereas others selected for these characteristics. Additionally, by virtue of their wide geographic distribution, the studies showed that the focal populations themselves occurred in a variety of forest types, some with large structural differences. We found no evidence in Greenwald's et al. (2005) review that the MRNG are inadequate to protect goshawks. Rather, the studies reviewed by Greenwald et al. (2005), as well as many studies they missed, supported the MRNG. The suggestion of inadequacy by Greenwald et al. (2005) appeared rooted in misunderstandings of goshawk habitats described in the MRNG, a discounting of the extent of variation in vegetation structural and seral stages used by goshawks, a limited understanding of the extent to which prey limits goshawks, a failure to recognize the dynamic nature of forests, and an incomplete review of the literature. We believe the MRNG are adequate because they maximize the sustainable amount of mature and old forests in goshawk home ranges and specify the kinds and intermixtures of prey habitats within home ranges. Implementation of MRNG should reduce the likelihood that the availability of vegetation structures suited to goshawk nesting and foraging, as well as abundance and availability of prey, will limit goshawk nest occupancy and reproduction.     

Osmoregulation in Larvae of the Land-Crab, Cardisoma guanhumi Latreille

Daily studies were made of the osmoregulatory abilities of Cardisomaguanhumi from hatching to the end of larval development. Theseresults were compared to those of similar research on osmoregulationby larvae and megalopa of four species of estuarine, littoral,and sub-littoral crabs. The comparison shows that larvae ofC. guanhumi possess the same kinds of adaptations for waterintake at the time of molt that were found in Rhithropanopeusharrisii. Land-crab larvae hyperregulated in 10 p.p.t. sea waterand hyporegulated in water of 40 p.p.t. for experimental periodsfor 2 hr during the first one-third of their development. Duringthe remainder of larval life, they hyporegulated against 15p.p.t. in intermolt periods and became isosmotic with, or hyporegulatedagainst, 10 p.p.t. at the time of molting. From the time ofhatching, the osmoregulatory pattern of developing C. guanhumifits them for deep penetration of estuaries and for crossingsteep saline gradients. This pattern is evidence for a strongerand more enduring control of water balance, especially at thetime of molting, than we have found in non-terrestrial species.     

Prognostic value of the ABCD2 score beyond short-term follow-up after transient ischemic attack (TIA) - a cohort study

Background

In patients with Duchenne Muscular Dystrophy (DMD), the absent or diminished dystrophin leads to progressive skeletal muscle and heart failure. We evaluated the role of myocardial inflammation as a precipitating factor in the development of heart failure in DMD.

Methods

20 DMD patients (aged 15-18 yrs) and 20 age-matched healthy volunteers were studied and followed-up for 2 years. Evaluation of myocarditis with cardiovascular magnetic resonance imaging (CMR) was performed using STIR T2-weighted (T2W), T1-weighted (T1W) before and after contrast media and late enhanced images (LGE). Left ventricular volumes and ejection fraction were also calculated. Myocardial biopsy was performed in patients with positive CMR and immunohistologic and polymerase chain reaction (PCR) analysis was employed.

Results

In DMD patients, left ventricular end-diastolic volume (LVEDV) was not different compared to controls. Left ventricular end-systolic volume (LVESV) was higher (45.1 ± 6.6 vs. 37.3 ± 3.8 ml, p < 0.001) and left ventricular ejection fraction (LVEF) was lower (53.9 ± 2.1 vs. 63 ± 2.4%, p < 0.001). T2 heart/skeletal muscle ratio and early T1 ratio values in DMD patients presented no difference compared to controls. LGE areas were identified in six DMD patients. In four of them with CMR evidence of myocarditis, myocardial biopsy was performed. Active myocarditis was identified in one and healing myocarditis in three using immunohistology. All six patients with CMR evidence of myocarditis had a rapid deterioration of left ventricular function during the next year.

Conclusions

DMD patients with myocardial inflammation documented by CMR had a rigorous progression to heart failure.     

The Site Specificity of Two Species of Gregarina in Tenebrio molitor Larvae

The site specificity of the apicomplexans Gregarina cuneata and Gregarina sleini , in larval Tenebrio molitor was investigated. Gregarina cuneata was found to inhabit the anteriormost region of the larval midgut, while G. steini was restricted to the posterior portion of the intestine. The site specificity of the pair was conserved in single and concurrent infections. Interspecific interactions do not seem to be presently responsible for the resource partitioning by the 2 gregarine species. Key words. Gregarina, site specificity, Tenebrio molitor.     

Use of Shields stress to reconstruct and forecast changes in river metabolism

1. Discharge patterns of streams and rivers may be substantially affected by changes in water management, land use, or climate. Such hydrological alterations are likely to influence biotic processes, including overall ecosystem metabolism (photosynthesis and respiration). One regulator of aquatic ecosystem metabolism directly tied to hydrology is movement of bed sediments. 2. We propose that ecosystem metabolism can be reconstructed or predicted for any suite of hydrological conditions through the use of quantitative relationships between discharge, bed movement and metabolism. We tested this concept on a plains reach of the South Platte River in Colorado. 3. Movement of bed sediments was predicted from river discharge and the Shields stress, a ratio of velocity‐induced stress to sediment grain size. Quantitative relationships were established empirically between metabolic response to bed movement and recovery from bed movement, thus linking metabolism to hydrology. 4. The linkage of metabolism to hydrology allowed us to reconstruct daily photosynthesis and respiration over the 70‐year period for which discharge is known at our study site on the South Platte River. The reconstruction shows major ecological change caused by hydrological manipulation: the river has lost two‐thirds of its photosynthetic potential, and the ratio of photosynthesis to respiration is now much lower than it was prior to 1960. 5. The same approach could be used to anticipate ecological responses to proposed hydrological manipulations, to quantify benefits of hydrological restoration, or to illustrate potential effects of change in climate or land use on flowing‐water ecosystems.