Electrostatically actuated encased cantilevers.

Background: Encased cantilevers are novel force sensors that overcome major limitations of liquid scanning probe microscopy. By trapping air inside an encasement around the cantilever, they provide low damping and maintain high resonance frequencies for exquisitely low tip-sample interaction forces even when immersed in a viscous fluid. Quantitative measurements of stiffness, energy dissipation and tip-sample interactions using dynamic force sensors remain challenging due to spurious resonances of the system. Results: We demonstrate for the first time electrostatic actuation with a built-in electrode. Solely actuating the cantilever results in a frequency response free of spurious peaks. We analyze static, harmonic, and sub-harmonic actuation modes. Sub-harmonic mode results in stable amplitudes unaffected by potential offsets or fluctuations of the electrical surface potential. We present a simple plate capacitor model to describe the electrostatic actuation. The predicted deflection and amplitudes match experimental results within a few percent. Consequently, target amplitudes can be set by the drive voltage without requiring calibration of optical lever sensitivity. Furthermore, the excitation bandwidth outperforms most other excitation methods. Conclusion: Compatible with any instrument using optical beam deflection detection electrostatic actuation in encased cantilevers combines ultra-low force noise with clean and stable excitation well-suited for quantitative measurements in liquid, compatible with air, or vacuum environments.

Phosphatase CD45 both positively and negatively regulates T cell receptor phosphorylation in reconstituted membrane protein clusters.

T cell receptor (TCR) phosphorylation requires the kinase Lck and phosphatase CD45. CD45 activates Lck by dephosphorylating an inhibitory tyrosine of Lck to relieve autoinhibition. However, CD45 also dephosphorylates the TCR, and the spatial exclusion of CD45 from TCR clustering in the plasma membrane appears to attenuate this negative effect of CD45. To further investigate the role of CD45 in signal initiation, we reconstituted membrane TCR clusters in vitro on supported lipid bilayers. Fluorescence microscopy of single clusters showed that incorporation of CD45 enhanced phosphorylation of TCR clusters, but only when Lck co-clustered with TCR. We found that clustered Lck autophosphorylated the inhibitory tyrosine and thus could be activated by CD45, whereas diffusive Lck molecules did not. In the TCR-Lck clusters and at low CD45 density, we speculate that the effect of Lck activation may overcome dephosphorylation of TCR, resulting in a net positive regulation. The CD45 density in physiological TCR clusters is also low because of the exclusion of CD45. Thus, we propose that the spatial organization of TCR/Lck/CD45 in T cell membranes is important not only for modulating the negative role of CD45 but also for creating conditions in which CD45 has a positive role in signal initiation.

El análisis de las prácticas instituidas como un modelo de producción de conocimiento / The analysis of the practices instituted as a model of knowledge production

El artículo refiere al proyecto de investigación "Dispositivos analizadores de la formación y práctica profesional del psicólogo", acreditado por PROINPSI. Se presentan resultados de una primera exploración cualitativa del objetivo general del proyecto: "Diseñar un dispositivo de intervención institucional en el ámbito de los trabajos prácticos, a fin de revisar críticamente los modos instituidos de aprender y enseñar en la formación del psicólogo y de posicionarse en el campo profesional." Se conceptualizan las características que toma el rol en el dispositivo propuesto describiendo las concepciones subyacentes y los instituidos de la formación. El avance realizado permite la descripción del modelo epistemológico que sostiene esta concepción de la Psicología Institucional que conjuga investigación-intervención y docencia.

This article refers to the Research Project "Analyzing Devices of psychologists' professional education and practice", authorized by PROINPSI. Results of a irst qualitative exploration of the project's general objective are the following: "To design an institutional intervention device on the area of classroom situation, in order to check in a critical way the established ways of learning and teaching in psychologists' education and the established positions in the professional field." The characteristics that the role takes in the proposed device are conceptualized. The underlying conceptions and the instituted practices in the formation are described. The description of the epistemological model that underlies this conception of Institutional Psychology is allowed by the research's progress. This model unifies intervention, research and teaching.

La construcción de la práctica docente como efecto de la intervención institucional en la formación del psicólogo / Building of the teaching practice as an effect of the institutional intervention in psychologists' education

El artículo refiere al proyecto de investigación "Dispositivos analizadores de la formación y práctica profesional del psicólogo", acreditado por PROINPSI. Trasmite el proceso de sistematización de la experiencia en el aula y de varios espacios de reflexión surgidos a partir de ella, de los docentes de la Cátedra I de Psicología Institucional. La Psicología Institucional es entendida como una perspectiva de conocimiento que interpela los imaginarios compartidos que sostienen las prácticas. El proceso de intervención sobre los saberes instituidos permite acompañar a otros en su revisión, a la vez que conocer los propios. Para hacerlo, se construyó en el espacio de trabajos prácticos un dispositivo de Análisis de las Prácticas. Además, esta investigación sistematiza la experiencia de docencia e intervención y provee herramientas para el Análisis de las Prácticas de los docentes, alumnos y profesionales.

The article attempts to convey the process experienced as lecturers of the Institutional Psychology I professorship that is embodied in the PROINPSI sanctioned research project, Education analyzing devices and the psychologist's professional practice, which aims to systematize the experience in the classroom and other spaces of reflection emerged from it. Institutional Psychology is a knowledge perspective that questions the shared imaginary that maintains the practices. The process of intervention allows to accompany in knowledge revision, at the same time as to know the own ones. In order to do it, a device of Analysis of the Practices was constructed. This research also systematize the teaching and intervention experience, and provides consumptions for the Practice Analysis of proffessors.

Inhibition of Ca(2+)-dependent glutamate release from cerebral cortex synaptosomes of rats with experimental autoimmune encephalomyelitis.

Several pathological studies have revealed a prominent involvement of the cerebral cortex in patients with multiple sclerosis (MS). In order to better understand the events that lead to the progressive neuronal dysfunction in MS, herein we explore the contribution of the glutamatergic release in cerebral cortex synaptosomes isolated from rats with experimental autoimmune encephalomyelitis, an animal model reproducing many features of MS. We found that the Ca(2+)-dependent but not the Ca(2+)-independent glutamate release induced by KCl and 4-aminopyridine was significantly decreased during the acute stage of the disease. This inhibited release coincides with the onset of the clinical signs and after 24 h tends to recover the level of the control animals. The results also showed an inhibition of the glutamate release stimulated by ionomycin. When the animals were totally recovered from clinical signs, the neurotransmitter release stimulated by the different inductors was similar to the controls. Examination of the cytosolic Ca(2+) using fura-2-acetoxymethyl ester revealed that the inhibition of glutamate release could not be attributed to a reduction in voltage-dependent Ca(2+) influx. However, this inhibition was concomitant with a lower phosphorylation of synapsin I at P-site1. Our results show that the inhibition observed on the Ca(2+)-dependent neurotransmitter release from cerebral cortex synaptosomes in experimental autoimmune encephalomyelitis is specific and correlates with the beginning of the clinical disease. Moreover, they suggest an alteration in the metabolism of proteins involved in the vesicular glutamate release more than a deregulation in the influx of cytosolic Ca(2+).