The Dynamics of Sustained Reentry in a Loop Model with Discrete Gap Junction Resistance

Dynamics of reentry are studied in a one dimensional loop of model cardiac cells with discrete intercellular gap junction resistance ($R$). Each cell is represented by a continuous cable with ionic current given by a modified Beeler-Reuter formulation. For $R$ below a limiting value, propagation is found to change from period-1 to quasi-periodic ($QP$) at a critical loop length ($L_{crit}$) that decreases with $R$. Quasi-periodic reentry exists from $L_{crit}$ to a minimum length ($L_{min}$) that is also shortening with $R$. The decrease of $L_{crit}(R)$ is not a simple scaling, but the bifurcation can still be predicted from the slope of the restitution curve giving the duration of the action potential as a function of the diastolic interval. However, the shape of the restitution curve changes with $R$.Comment: 6 pages, 7 figure

Composição e estrutura da ictiofauna demersal na Baía dos Pinheiros, Paraná

Between May of 2003 and April of 2004 the temporal changes were monitored in the structure of the demersal ichthyofauna of the Bay of Pinheiros (Paraná), through three bottom trawls accomplished monthly in each one of the four areas between the access bar and the most internal areas. In the 144 accomplished trawls 58 species belonging to 25 families were collected, totaling 18154 fishes. The families that presented larger wealth of species were Sciaenidae (15 species), Ariidae (5), Tetraodontidae (4), Engraulidae (4), Carangidae (4), Paralichthyidae (3) and Haemulidae (3). The species Stellifer rastrifer, Cathorops spixii, Chirocentrodon bleekerianus, Cynoscion leiarchus, Stellifer brasiliensis, Achirus lineatus and Micropogonias furnieri dominated in number of individuals, representing 91,4% of the total capture. Significantly, there was larger capture of number of fishes in April. Between the indexes of diversity of Shannon-Wiener and eveness of Pielou differences were not observed. Through the grouping analyses and ordination of the dominant species two groups were formed in the level of 70% of similarity. The first was composed by the dominant species S. rastrifer, C. spixii and C. leiarchus, and the second was formed by C. jamaicensis and P. harroweri, presents almost exclusively in the summer and autumn.Between May of 2003 and April of 2004 the temporal changes were monitored in the structure of the demersal ichthyofauna of the Bay of Pinheiros (Paraná), through three bottom trawls accomplished monthly in each one of the four areas between the access bar and the most internal areas. In the 144 accomplished trawls 58 species belonging to 25 families were collected, totaling 18154 fishes. The families that presented larger wealth of species were Sciaenidae (15 species), Ariidae (5), Tetraodontidae (4), Engraulidae (4), Carangidae (4), Paralichthyidae (3) and Haemulidae (3). The species Stellifer rastrifer, Cathorops spixii, Chirocentrodon bleekerianus, Cynoscion leiarchus, Stellifer brasiliensis, Achirus lineatus and Micropogonias furnieri dominated in number of individuals, representing 91,4% of the total capture. Significantly, there was larger capture of number of fishes in April. Between the indexes of diversity of Shannon-Wiener and eveness of Pielou differences were not observed. Through the grouping analyses and ordination of the dominant species two groups were formed in the level of 70% of similarity. The first was composed by the dominant species S. rastrifer, C. spixii and C. leiarchus, and the second was formed by C. jamaicensis and P. harroweri, presents almost exclusively in the summer and autumn

Vitamin D in the general population of young adults with autism in the Faroe Islands

Vitamin D deficiency has been proposed as a possible risk factor for developing autism spectrum disorder (ASD). 25-Hydroxyvitamin D3 (25(OH)D3) levels were examined in a cross-sectional population-based study in the Faroe Islands. The case group consisting of a total population cohort of 40 individuals with ASD (aged 15–24 years) had significantly lower 25(OH)D3 than their 62 typically-developing siblings and their 77 parents, and also significantly lower than 40 healthy age and gender matched comparisons. There was a trend for males having lower 25(OH)D3 than females. Effects of age, month/season of birth, IQ, various subcategories of ASD and Autism Diagnostic Observation Schedule score were also investigated, however, no association was found. The very low 25(OH)D3 in the ASD group suggests some underlying pathogenic mechanism

Growth and mortality estimates of Sardinella brasiliensis in the southeastern Brazilian Bight

Length frequency analisys were applied for sardine data collected from commercial catches throughout the southeastern Brazilian coast in 1977-1987. Age/length keys were obtained by otolith ring countings and utilized to transform length into age composition. Growth parameters were estimated by the von Bertalanffy growth equation using age and length data for each year and for all the period of investigation. The mean growth parameters for the entire period were estimated as L∞ = 271 mm and K= 0.59 year-1. Instantaneous total mortality (Z) coefficients per year were estimated using catch curves and methods based on the mean length of the fish caught. Total mortality rate for the entire period was obtained through the average of the annual values. Natural mortality (M) was estimated using the Paul/s empirical equation (1980a), and fishing mortality (F) by the difference between total and natural mortality values.The results were Z = 3.6 year-1; M = 0.96 year-1; and F= 2.6 year-1.Estudo sobre o crescimento e a mortalidade de Sardinella brasiliensis, da costa sudeste do Brasil, foi realizado para o período 1977 a 1987. As análises foram efetuadas a partir de dados existentes sobre distribuições de freqüência de comprimento de amostras da captura comercial. Chaves idade/comprimento, construidas a partir de leitura de anéis de crescimento em otólitos, dentro do Programa Integrado de Estudos Biológicos sobre a Sardinha - PIEBS, foram utilizadas para transformar as distribuiçes de comprimento em idade. Os parâmetros de crescimento da equação de von Bertalanffy foram estimados, anualmente e para o período como um todo, a partir de métodos que utilizam dados de idade e comprimento. Os parâmetros médios encontrados para o período foram: L∞ = 271 mm e K= 0,59 ano-1. Os coeficientes instantâneos de mortalidade total (Z) anuais foram calculados pelas curvas de captura e por métodos baseados no comprimento médio dos indivíduos nas capturas. A mortalidade total para todo o período foi obtida pela média dos valores anuais. O coeficiente instantâneo de mortalidade natural (M) foi estimado pela equação empírica de Pauly (1980a), usando um fator de correção de 0,8 para clupeoides, e o coeficiente instantâneo de mortalidade por pesca (F), pela diferença entre a mortalidade total e a natural. Os valores encontrados foram: Z= 3,6 ano-1, M = 0,96 ano-1 e F= 2,6 ano-1

Genetic Background Can Result in a Marked or Minimal Effect of Gene Knockout (GPR55 and CB2 Receptor) in Experimental Autoimmune Encephalomyelitis Models of Multiple Sclerosis

PMCID: PMC379391

Atrial Heterogeneity Generates Re-entrant Substrate during Atrial Fibrillation and Anti-arrhythmic Drug Action: Mechanistic Insights from Canine Atrial Models

Anti-arrhythmic drug therapy is a frontline treatment for atrial fibrillation (AF), but its success rates are highly variable. This is due to incomplete understanding of the mechanisms of action of specific drugs on the atrial substrate at different stages of AF progression. We aimed to elucidate the role of cellular, tissue and organ level atrial heterogeneities in the generation of a re-entrant substrate during AF progression, and their modulation by the acute action of selected anti-arrhythmic drugs. To explore the complex cell-to-organ mechanisms, a detailed biophysical models of the entire 3D canine atria was developed. The model incorporated atrial geometry and fibre orientation from high-resolution micro-computed tomography, region-specific atrial cell electrophysiology and the effects of progressive AF-induced remodelling. The actions of multi-channel class III anti-arrhythmic agents vernakalant and amiodarone were introduced in the model by inhibiting appropriate ionic channel currents according to experimentally reported concentration-response relationships. AF was initiated by applied ectopic pacing in the pulmonary veins, which led to the generation of localized sustained re-entrant waves (rotors), followed by progressive wave breakdown and rotor multiplication in both atria. The simulated AF scenarios were in agreement with observations in canine models and patients. The 3D atrial simulations revealed that a re-entrant substrate was typically provided by tissue regions of high heterogeneity of action potential duration (APD). Amiodarone increased atrial APD and reduced APD heterogeneity and was more effective in terminating AF than vernakalant, which increased both APD and APD dispersion. In summary, the initiation and sustenance of rotors in AF is linked to atrial APD heterogeneity and APD reduction due to progressive remodelling. Our results suggest that anti-arrhythmic strategies that increase atrial APD without increasing its dispersion are effective in terminating AF

Nycthemeral and Monthly Occupation of the Fish Assemblage on a Sheltered Beach of Baía Norte, Florianópolis, Santa Catarina State, Brazil

Interpreting fish community records is challenging for several reasons, including the lack of past ichthyofauna data, the cyclical temporal variations in the community, and the methodology employed, which usually underestimates fish assemblages. The objective of this study was to describe short-scale and meso-scale (nycthemeral period and months, respectively) temporal variations in the ichthyofauna composition and structure of a sheltered beach of Baía Norte (Florianópolis, Santa Catarina state, Brazil), using a capéchade net. Samples were collected monthly for a period of 48 hours. During the period from December 2010 to November 2011, a total of 19,302 individuals belonging to 89 species and 39 families were captured. The number of individuals that were sampled during the day and/or night was dependent on the sampling month. On average, the daytime assemblage was more abundant and different in structure and composition than the nighttime assemblage. Of the eight species that had the highest Index of Relative Importance (%IRI), five had higher variations (ANOVA F) between the day and night than between the months. This finding reinforced the need for sampling during both the day and night. The capéchade net effectively captured demersal and pelagic individuals in a broad range of sizes

Fish assemblages in a coastal bay adjacent to a network of marine protected areas in southern Brazil

Abstract Baía Norte (North Bay) in Santa Catarina State is considered a typical coastal bay and is surrounded by a network of Marine Protected Areas. The objectives of this study were to describe the composition of the demersal fish assemblage, identify seasonal and spatial structures on a fine scale and evaluate the role of habitat descriptors and abiotic variables affecting the fish assemblage structure. Seasonal samplings were conducted in 2005, using bottom trawls in six pre-established areas in Baía Norte in summer, fall, winter and spring. Simultaneously with each trawl, environmental data were collected with a multiparameter probe. Temporal and spatial differences in fish abundance were tested by a PERMANOVA. To illustratethe differences detected graphically we ran a canonical analysis of principal coordinates (CAP). The influence of environmental variables on the fish fauna was evaluated using a Distant Based Linear Model (DistLM) with Akaike's information criterion (AIC). A total of 9,888 specimens, distributed in 27 families and 62 species, were collected. Citharichthys spilopterus was the most abundant species. PERMANOVA detected differences for abundance between seasons, areas and interaction among all the factors. The DISTLM selected temperature and pH. The results highlight seasonality as an important factor in the structuring of fish fauna of the study place