Model of Low-pass Filtering of Local Field Potentials in Brain Tissue

Local field potentials (LFPs) are routinely measured experimentally in brain tissue, and exhibit strong low-pass frequency filtering properties, with high frequencies (such as action potentials) being visible only at very short distances ($\approx$10~$\mu m$) from the recording electrode. Understanding this filtering is crucial to relate LFP signals with neuronal activity, but not much is known about the exact mechanisms underlying this low-pass filtering. In this paper, we investigate a possible biophysical mechanism for the low-pass filtering properties of LFPs. We investigate the propagation of electric fields and its frequency dependence close to the current source, i.e. at length scales in the order of average interneuronal distance. We take into account the presence of a high density of cellular membranes around current sources, such as glial cells. By considering them as passive cells, we show that under the influence of the electric source field, they respond by polarisation, i.e., creation of an induced field. Because of the finite velocity of ionic charge movement, this polarization will not be instantaneous. Consequently, the induced electric field will be frequency-dependent, and much reduced for high frequencies. Our model establishes that with respect to frequency attenuation properties, this situation is analogous to an equivalent RC-circuit, or better a system of coupled RC-circuits. We present a number of numerical simulations of induced electric field for biologically realistic values of parameters, and show this frequency filtering effect as well as the attenuation of extracellular potentials with distance. We suggest that induced electric fields in passive cells surrounding neurons is the physical origin of frequency filtering properties of LFPs.Comment: 10 figs, revised tex file and revised fig

Role of transport performance on neuron cell morphology

The compartmental model is a basic tool for studying signal propagation in neurons, and, if the model parameters are adequately defined, it can also be of help in the study of electrical or fluid transport. Here we show that the input resistance, in different networks which simulate the passive properties of neurons, is the result of an interplay between the relevant conductances, morphology and size. These results suggest that neurons must grow in such a way that facilitates the current flow. We propose that power consumption is an important factor by which neurons attain their final morphological appearance.Comment: 9 pages with 3 figures, submitted to Neuroscience Letter

Beyond Hebb: Exclusive-OR and Biological Learning

A learning algorithm for multilayer neural networks based on biologically plausible mechanisms is studied. Motivated by findings in experimental neurobiology, we consider synaptic averaging in the induction of plasticity changes, which happen on a slower time scale than firing dynamics. This mechanism is shown to enable learning of the exclusive-OR (XOR) problem without the aid of error back-propagation, as well as to increase robustness of learning in the presence of noise.Comment: 4 pages RevTeX, 2 figures PostScript, revised versio

Neuroglia at the crossroads of homoeostasis, metabolism and signalling: evolution of the concept

Ever since Rudolf Virchow in 1858 publicly announced his apprehension of neuroglia being a true connective substance, this concept has been evolving to encompass a heterogeneous population of cells with various forms and functions. We briefly compare the 19th–20th century perspectives on neuroglia with the up-to-date view of these cells as an integral, and possibly integrating, component of brain metabolism and signalling in heath and disease. We conclude that the unifying property of otherwise diverse functions of various neuroglial cell sub-types is to maintain brain homoeostasis at different levels, from whole organ to molecular

Increased voltage-dependent K+ channel Kv1.3 and Kv1.5 expression correlates with leiomyosarcoma aggressiveness

Voltage-dependent K+ channels (Kv) are involved in the proliferation and differentiation of mammalian cells, since Kv antagonists impair cell cycle progression. Although myofibers are terminally differentiated, some myoblasts may re-enter the cell cycle and proliferate. Since Kv1.3 and Kv1.5 expression is remodeled during tumorigenesis and is involved in smooth muscle proliferation, the purpose of this study was to analyze the expression of Kv1.3 and Kv1.5 in smooth muscle neoplasms. In the present study, we examined human samples of smooth muscle tumors together with healthy speci­mens. Thus, leiomyoma (LM) and leiomyosarcoma (LMS) tumors were analyzed. Results showed that Kv1.3 was poorly expressed in the healthy muscle and indolent LM specimens, whereas aggressive LMS showed high levels of Kv1.3 expression. Kv1.5 staining was correlated with malignancy. The findings show a remodeling of Kv1.3 and Kv1.5 in human smooth muscle sarcoma. A correlation of Kv1.3 and Kv1.5 expression with tumor aggressiveness was observed. Thus, our results indicate Kv1.5 and Kv1.3 as potential tumorigenic targets for aggressive human LMS

Spiral arteries in second trimester of pregnancy : when is it possible to define expected physiological remodeling as abnormal?

Q2Q2After undergoing remodeling, uterine spiral arteries turn into wide, flexible tubes, with low resistance. If remodeling does not occur, spontaneous abortions, intrauterine growth restriction, and pregnancy-related hypertensive disorders can ensue. Arterial transformation begins at a very early gestational stage; however, second quarter pregnancy histopathological samples have yet to pinpoint the exact moment when abnormal remodeling transpires. We examined 100 samples, taken from consecutive abortions at 12–23 gestational weeks. Following Pijnenborg and Smith guidelines, blinded pathologists analyzed clinical data on remod eling stages. Lab results showed that arterial remodeling is not synchronic in all vessels; a single sample can include various remodeling stages; neither is remodeling homogenous in a single vessel: change may be occurring in one part of the vessel, but not in another. To our knowledge, no one has published this finding. In the examined age group, Smith stage IV predominates; around week 14, substantial muscle and endothelium loss takes place. After week 17, endovascular or fibrin trophoblast does not usually occur. Although scant consensus exists on what defines preeclampsia etiology, it is clear that it involves abnormal remodeling in decidua vessels. Improved understanding requires further knowledge on both the physiological and pathological aspects of the remodeling process. We observed that muscle and endothelial tissues disappear from weeks 14–17, after which time reendothelization predominates. We list the expected proportion of spiral artery changes for each gestational age which, to date, has not been available.https://orcid.org/0000-0002-7147-425XN/

Comparación entre las técnicas de cribado de patología cervical y las conizaciones de tres hospitales en españa

Objetivo: Analizar las características poblacionales y los métodos diagnósticos de patología cervical para la prevención del cáncer de cérvix de tres hospitales españoles para mejorar y unificar los programas de cribado y prevención. Material y métodos: Estudio retrospectivo de las características demográficas y clínicas de 408 mujeres con patología cervical uterina diagnosticadas en 3 hospitales españoles. Se comparan los factores de riesgo, el proceso diagnóstico y la indicación de tratamiento de dos grupos: las que requirieron conización cervical (n=222) y las que no precisaron tratamiento quirúrgico (n=186). También se analizan las recomendaciones vacunales y su grado de cumplimiento. Resultados: Las mujeres conizadas usaron más anticoncepción hormonal y tienen un mayor hábito tabáquico mientras que el número de compañeros sexuales es mayor en pacientes no conizadas. Más del 50% de pacientes con biopsia cervical positiva presentaron un resultado igual o más grave en la anatomía patológica de la pieza quirúrgica. Existen diferencias significativas en sensibilidad y valor predictivo positivo de la citología y de la determinación de HPV entre hospitales. La recomendación de vacunación en ambos grupos fue similar, el porcentaje de mujeres que no la cumplieron fue elevado y significativamente mayor entre pacientes conizadas. Conclusión: En nuestro medio las mujeres conizadas tienen características clínicas y epidemiológicas diferentes a las no conizadas, existen diferencias entre las técnicas diagnósticas de distintos hospitales y sin embargo la concordancia entre biopsia y resultado del cono es elevada. Sigue siendo necesaria una correcta educación sanitaria en relación con la vacunación en mujeres con patología cervical. Background: To analyse the characteristics of the population and diagnostic methods related to the cervical cancer prevention program in three different-level hospitals of a Spanish region in order to improve and unify the screening program. Methods: We retrospectively studied demographic and clinical characteristics of 408 women with cervical lesions diagnosed in three hospitals in Aragon (Spain). Correlation between risk factors, diagnosis process and conisation indication was analysed divided in two groups: conisation required (n=222) or non-conisation (n=186). We also assessed the number of vaccine recommendations made to the patients and the degree of compliance. Results: Conisaited women more frequently used a combined hormonal contraceptive method and are more smokers, while the sexual partners are more in women without conisation. More than 50% of women con positive biopsy was confirmed after surgical treatment. There are significant differences between sensibility and positive predictive value of pap-smear and HPV determination in different hospitals. The recombinant vaccine was recommended to both groups at a similar rate. The percentage of women who were recommended to receive the vaccine but chose not to do it, was high in both groups but significantly higher in the Conisation group. Conclusion: In our environment conisaited women have different clinical and epidemiological profiles, there are differences between diagnosis techniques in different hospitals, however, the concordance between biopsy and definitive result is high. A good sanitary education is necessary in relation with the vaccination of women with cervical pathology

Neuron-glia crosstalk in health and disease: fractalkine and CX3CR1 take centre stage

An essential aspect of normal brain function is the bidirectional interaction and communication between neurons and neighbouring glial cells. To this end, the brain has evolved ligand–receptor partnerships that facilitate crosstalk between different cell types. The chemokine, fractalkine (FKN), is expressed on neuronal cells, and its receptor, CX(3)CR1, is predominantly expressed on microglia. This review focuses on several important functional roles for FKN/CX(3)CR1 in both health and disease of the central nervous system. It has been posited that FKN is involved in microglial infiltration of the brain during development. Microglia, in turn, are implicated in the developmental synaptic pruning that occurs during brain maturation. The abundance of FKN on mature hippocampal neurons suggests a homeostatic non-inflammatory role in mechanisms of learning and memory. There is substantial evidence describing a role for FKN in hippocampal synaptic plasticity. FKN, on the one hand, appears to prevent excess microglial activation in the absence of injury while promoting activation of microglia and astrocytes during inflammatory episodes. Thus, FKN appears to be neuroprotective in some settings, whereas it contributes to neuronal damage in others. Many progressive neuroinflammatory disorders that are associated with increased microglial activation, such as Alzheimer's disease, show disruption of the FKN/CX(3)CR1 communication system. Thus, targeting CX(3)CR1 receptor hyperactivation with specific antagonists in such neuroinflammatory conditions may eventually lead to novel neurotherapeutics

The visual neural networks of Ramón y Cajal: comments on the facsimile of one of his handwritten drawings exhibited at the museum of the history of medicine of the National Academy of Medicine of Colombia

La obra de Santiago Ramón y Cajal ha sido ampliamente comentada en biografías y artículos científicos. El presente texto busca aportar información historiográfica sobre una ilustración facsimilar donada a la Academia Nacional de Medicina de Colombia, que se encuentra expuesta en su Museo de la Historia de la Medicina en Bogotá. Para el efecto, se recurrió a los archivos del Instituto Cajal en Madrid, España, en donde se conserva su legado original.The work of Santiago Ramón y Cajal has been widely commented in biographies and scientific articles. This text seeks to provide historiographical information on a facsimile illustration do-nated to the National Academy of Medicine of Colombia, currently on display in its permanent collections at the Museum of the History of Medicine in Bogotá. For this purpose, we accessed the archives of the Cajal Institute in Madrid, Spain, where his original legacy is preserved.https://orcid.org/0000-0002-5592-3844https://orcid.org/0000-0002-7147-425XRevista Nacional - IndexadaN