109 research outputs found
On the structure of cortical microcircuits inferred from small sample sizes
The structure in cortical microcircuits deviates from what would be expected in a purely random network, which has been seen as evidence of clustering. To address this issue, we sought to reproduce the nonrandom features of cortical circuits by considering several distinct classes of network topology, including clustered networks, networks with distance-dependent connectivity, and those with broad degree distributions. To our surprise, we found that all of these qualitatively distinct topologies could account equally well for all reported nonrandom features despite being easily distinguishable from one another at the network level. This apparent paradox was a consequence of estimating network properties given only small sample sizes. In other words, networks that differ markedly in their global structure can look quite similar locally. This makes inferring network structure from small sample sizes, a necessity given the technical difficulty inherent in simultaneous intracellular recordings, problematic. We found that a network statistic called the sample degree correlation (SDC) overcomes this difficulty. The SDC depends only on parameters that can be estimated reliably given small sample sizes and is an accurate fingerprint of every topological family. We applied the SDC criterion to data from rat visual and somatosensory cortex and discovered that the connectivity was not consistent with any of these main topological classes. However, we were able to fit the experimental data with a more general network class, of which all previous topologies were special cases. The resulting network topology could be interpreted as a combination of physical spatial dependence and nonspatial, hierarchical clustering.
SIGNIFICANCE STATEMENT The connectivity of cortical microcircuits exhibits features that are inconsistent with a simple random network. Here, we show that several classes of network models can account for this nonrandom structure despite qualitative differences in their global properties. This apparent paradox is a consequence of the small numbers of simultaneously recorded neurons in experiment: when inferred via small sample sizes, many networks may be indistinguishable despite being globally distinct. We develop a connectivity measure that successfully classifies networks even when estimated locally with a few neurons at a time. We show that data from rat cortex is consistent with a network in which the likelihood of a connection between neurons depends on spatial distance and on nonspatial, asymmetric clustering.Postprint (author's final draft
Emergent Dynamics in Neocortical Microcircuits
Interactions among neurons can take place in a wide variety of forms. It is the goal of this thesis to investigate the properties and implications of a number of these interactions that we believe are relevant for information processing in the brain. Neuroscience has progressed considerably in identifying the diverse neuronal cell-types and providing detailed information about their individual morphological, genetic and electrophysiological properties. It remains a great challenge to identify how this diversity of cells interacts at the microcircuit level. This task is made more complex by the fact that the forms of interaction are not always obvious or simple to observe, even with advanced scientific equipment. In order to achieve a better understanding and envision possible implications of the concerted activity of multiple neurons, experiments and models must often be used jointly and iteratively. In this thesis I first present the development of a computer-assisted system for multi-electrode patch-clamp that enabled new kinds of experiments, allowing qualitatively different information to be obtained concerning the interaction of multiple neurons. In the following chapters I describe the different questions addressed and approaches utilized in the investigation of neuronal interactions using multi-electrode patch-clamp experiments. The principles behind the clustered organization of synaptic connectivity in Layer V of the somatosensory cortex are the first experimental finding presented. I then quantify the ephaptic coupling between neurons and how apparently minute signals might help correlate the activity of many neurons. Next, the ubiquity of a neocortical microcircuit responsible for frequency-dependent disynaptic inhibition is demonstrated and the summation properties of this microcircuit are then analyzed. Finally a model to explain the interactions between gap junctions and synaptic transmission in the olfactory bulb is proposed
Computing the size and number of neuronal clusters in local circuits
The organization of connectivity in neuronal networks is fundamental to understanding the activity and function of neural networks and information processing in the brain. Recent studies show that the neocortex is not only organized in columns and layers but also, within these, into synaptically connected clusters of neurons (Ko et al., 2011; Perin et al., 2011). The recently discovered common neighbor rule, according to which the probability of any two neurons being synaptically connected grows with the number of their common neighbors, is an organizing principle for this local clustering. Here we investigated the theoretical constraints for how the spatial extent of neuronal axonal and dendritic arborization, heretofore described by morphological reach, the density of neurons and the size of the network determine cluster size and numbers within neural networks constructed according to the common neighbor rule. In the formulation we developed, morphological reach, cell density, and network size are sufficient to estimate how many neurons, on average, occur in a cluster and how many clusters exist in a given network. We find that cluster sizes do not grow indefinitely as network parameters increase, but tend to characteristic limiting values
Seletividade e eficácia de herbicidas aplicados à cultura do trigo
When not controlled efficiently, weeds in wheat crop stands may affect both the grain quality and yield production. This work aimed to assess the selectivity and efficacy of herbicides applied to control weeds in the wheat cultivar TBIO Sinuelo. Two experiments were set up to assess the selectivity and the efficacy of herbicides applied to wheat in randomized blocks design with four replications. Treatments tested were: iodosulfuron, pyroxsulam, metsulfuron-methyl, 2,4-D, clodinafop-propargyl, [bentazon + imazamox], saflufenacil, bentazon, carfentrazone-ethyl, imazamox, pendimethalin, [sulfentrazone + diuron], plus two control treatments, one weeded and the other infested. The greatest damages to wheat were caused by imazamox and the commercial mixture [bentazon + imazamox] with phytotoxicity of approximately 50%. On the other hand, applying the commercial mixture [sulfentrazone + diuron] allowed the highest wheat grain yield. The use of clodinafop-propargyl and pyroxsulam promoted the best control of Lolium multiflorum, with 100 and 98.25% at 21 days after treatment application, respectively. The control above 90% of Raphanus raphanistrum was reported with iodosulfuron, pyroxsulam, metsulfuron-methyl, 2,4-D, [bentazon + imazamox], saflufenacil, bentazon, and carfentrazone. Clodinafop-propargyl was the most efficient on ryegrass, and iodosulfuron, pyroxsulam, metsulfuron-methyl, 2,4-D, saflufenacil, and carfentrazone performed best on the turnip. Pyroxsulam was the treatment that showed, in both experiments, the best results for all-grain yield components, especially for grain yield.As plantas daninhas ocasionam efeitos negativos na produtividade e na qualidade dos grãos da cultura do trigo quando não controladas de modo eficiente. Assim sendo, objetivou-se com os trabalhos avaliar a seletividade e a eficácia de herbicidas aplicados para o manejo de plantas daninhas infestante da cultivar de trigo TBIO Sinuelo. Foram instalados dois experimentos, um para avaliar a seletividade e outro a eficácia de herbicidas aplicados em trigo, em blocos casualizados, com quatro repetições. Os tratamentos testados foram: iodosulfuron, pyroxsulam, metsulfuron-methyl, 2,4-D, clodinafope-propargil, [bentazon + imazamox], saflufenacil, bentazon, carfentrazone-ethyl, imazamox, pendimethalin, [sulfentrazone + diuron], mais duas testemunhas uma capinada e outra infestada. Os herbicidas que ocasionaram as maiores injúrias ao trigo foram o imazamox e a mistura comercial de [bentazon + imazamox] com fitotoxicidade próxima a 50%. A aplicação da mistura comercial de [sulfentrazone + diuron] demonstrou a maior produtividade de grãos do trigo. O uso de clodinafope-propargil e pyroxsulam apresentaram os melhores controles de Lolium multiflorum, com 100 e 98,25%, aos 21 dias após a aplicação dos tratamentos, respectivamente. Ocorreu controle acima de 90% de Raphanus raphanistrum com uso de iodosulfuron, pyroxsulam, metsulfuron-methyl, 2,4-D, [bentazon + imazamox], saflufenacil, bentazon e carfentrazone. O clodinafope-propargil demonstra o maior controle para o azevém e o iodosulfuron-ethyl, pyroxsulam, metsulfurom-metílico, 2,4-D, saflufenacil e carfentrazone para o nabo. O pyroxsulam foi o tratamento que demonstrou, nos dois experimentos, os melhores resultados para os componentes da produção, especialmente para a produtividade da cultura
A nanoemulsion of Rosmarinus officinalis L. essential oil with allelopathic effect against Lactuca sativa L. seeds / Uma nanoemulsão a partir do óleo essencial de Rosmarinus officinalis L com efeito alelopático em sementes de Lactuca sativa L
Plant's essential oils have a wide range of allelopathic effects with potential uses as bioherbicides. In addition, the application of oils through nanoemulsions represents a promising alternative for agriculture, as it offers better performance and lowers toxic waste generation. Therefore, this study aimed to evaluate the chemical constitution of Rosmarinus officinalis (rosemary) essential oil, as well as its effects on germination, initial growth, Catalase (CAT), Peroxidase (POX), and Superoxide-Dismutase (SOD) enzymes activity of Lactuca sativa seeds. Nanoemulsions were produced at 5% concentration and then diluted with distilled water to 5.0, 7.0, and 10.0 mg/mL. We compared data obtained using variance (ANOVA) analysis, followed by Tukey's test at 5% probability. Rosemary oil showed a wide variety of terpenoid compounds, mainly the 1,8-cineol monoterpene, which accounted for 46% of the sample. The oil showed a dose-dependent negative allelopathic influence on all variables analyzed, causing a drop in germination percentage (%G), germination speed index (GVI), mean germination time (MTG), and leaf and root length. There was no change in CAT and SOD activity. The POX activity showed a reduction starting at the concentration of 7.0 mg/mL. The results showed allelopathic effects of rosemary oil, with potential use as a natural bioherbicide
A Biophysically Detailed Model of Neocortical Local Field Potentials Predicts the Critical Role of Active Membrane Currents
Brain activity generates extracellular voltage fluctuations recorded as local field potentials (LFPs). It is known that the relevant microvariables, the ionic currents across membranes, jointly generate the macrovariables, the extracellular voltage, but neither the detailed biophysical knowledge nor the required computational power have been available to model these processes. We simulated the LFP in a model of the rodent neocortical column composed of >12,000 reconstructed, multicompartmental, and spiking cortical layer 4 and 5 pyramidal neurons and basket cells, including five million dendritic and somatic compartments with voltage- and ion-dependent currents, realistic connectivity, and probabilistic AMPA, NMDA, and GABA synapses. We found that, depending on a number of factors, the LFP reflects local and cross-layer processing. Active currents dominate the generation of LFPs, not synaptic ones. Spike-related currents impact the LFP not only at higher frequencies but below 50 Hz. This work calls for re-evaluating the genesis of LFPs
EPIDEMIOLOGIA E PERFIL DE SENSIBILIDADE DOS GERMES ISOLADOS DE HEMOCULTURAS DE PACIENTES HEMATOLÓGICOS COM NEUTROPENIA FEBRIL
Introdução: A neutropenia febril (NF) é uma complicação muito freqüente nos pacientes com neoplasias hematológicas submetidos à quimioterapia. O manejo da NF permanece muito problemático especialmente pela mudança constante do espectro dos germes e da sensibilidade aos antimicrobianos. Desta forma, torna-se imprescindível conhecer a epidemiologia local das infecções associadas à NF. Objetivo: Determinar a prevalência e a sensibilidade aos antimicrobianos dos germes isolados de hemoculturas (HMC) de pacientes hematológicos com NF internados no HCPA. Métodos: Foram analisadas, retrospectivamente, todas as HMC solicitadas para pacientes com NF (contagem total de neutrófilos 38,5oC ou duas medidas >38oC em 24 horas. Comparou-se o perfil de sensibilidade das infecções em pacientescom NF em relação às demais unidades de internação clínica do hospital.Resultados: Foram solicitadas no período em estudo 2389 hemoculturas para 178 pacientes. Destas, 719 (30,1%) foram positivas sendo que este percentual subiu para 38,7% quando consideradas apenas as hemoculturas coletas sem a vigência de antibiótico. A análise dos germes isolados revelou que a maioria das infecções foi causada por Bacilos Gram-negativos (53,8%) seguido pelos Cocos Gram-positivos (31,2%). Os microrganismos isolados com maior freqüência foram: E. coli (14,6%), S. aureus (13,8%), K. pneumoniae (12,2%), Streptococcus sp. (8,5%), Pseudomonas sp. (7,9%), Staphylococcus coagulase-negativo (7,3%). A sensibilidade dos Bacilos Gram-negativos aos diferentes antimicrobianos foi: Cefepime (63%), Amicacina (65%), Ciprofloxacin (63%), Piperacilina/Tazobactam (71%), Ceftazidima (63%),Meropenem (97%). A sensibilidade dos Cocos Gram-positivos foi: Oxacilina (30%), Levofloxacin (38%), Vancomicina (100%). Comparativamente ao perfil de sensibilidade das unidades de internação clínica adulta não-hematológicas constatou-se diferença estatisticamente significante (p<0,05) entre a sensibilidade dos Bacilos Gram-negativos ao Cefepime (63% x 82%) e a Ceftazidima (63% x 82%) e entre os Cocos Gram-positivos à Oxacilina (30% x 50%). Conclusões: A coleta constante de dados sobre a prevalência dos germes e sua sensibilidade aos antimicrobianos é indispensável para o estabelecimento de tratamentos empíricos para a NF. O perfil de sensibilidade diferenciado em relação às demais unidades de internação faz necessária a criação de protocolos específicos de tratamento da NF. Unitermos: Neutropenia febril; hemoculturas; epidemiologia; perfil de sensibilidadehematologia
Diagnóstico de comunidade de uma área geograficamente delimitada dentro do Distrito Sanitário de Porto Alegre : resultados finais
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