Astrocyte dynamics revisited

A vast amount of experimental evidence hints that astrocytes could be active players in information processing of the brain. It remains unclear nevertheless how these cells could encode synaptic stimuli through variations of their intracellular Ca2+ levels as well as how they could influence the timing of neuronal activity. In this study, we adopt a dynamical system approach and use tools of bifurcation theory and statistics in order to address both these issues. We consider a Li-Rinzel description of astrocyte Ca2+ signalling and we show that thanks to specific choices of biophysical parameters, synaptic activity could be encoded by modulations of Ca2+ oscillations in amplitude (AM), in frequency (FM), or in both (AFM). Interestingly, AM- and FM-encoding pertain to different classes of Ca2+ excitability that are reminiscent of the analogous neuronal ones. In addition, any transition from AM to FM and viceversa is accomplished through a characteristic “Bautin-cusp" bifurcation sequence which could hint the conditions for the coexistence of both these encoding modes. Such a possibility is throughout investigated and eventually formalized in the “CPB rule", a heuristic criterion valid for any system of the Li-Rinzel type that allow us to determine several biophysical conditions under which AFM Ca2+ dynamics could occur in astrocytes. Successively, we demonstrate that different encoding modes could be accomplished not only on the basis of inherent heterogeneities of cellular properties but also thanks to the existence of different (opposite) Ca2+ feedbacks on IP3 production. In this regard we modify the Li-Rinzel system in order to include a third equation for IP3 metabolism which also considers Ca2+ activation of PLC (positive feedback) and Ca2+ activation of IP3 3-kinase (negative feedback). In agreement with experimental data and recent theoretical studies, our analysis hints that Ca2+-dependent activation of PLC could account for a much richer variety of oscillatory regimes and encoding modes with respect to the case of negative feedback. An inspection of the parameter space reveals that this is possible because positive Ca2+ feedback on IP3 production modifies the structure of the system towards the appearance of multistationarity which could also account for Ca2+ dynamics of bursting type. Moreover, we show that the lifetime of IP3 could be a critical limiting factor for the effects of both feedbacks. Meaningfully, IP3 turnover could influence the integrative properties of astrocytic Ca2+ signalling by affecting both the frequency band of Ca2+ oscillations and the threshold stimulus for their onset. In addition, IP3 turnover could regulate the expression of mGlu receptors on the astrocyte plasma membrane. In this regard, we show that the density of mGlu receptors could be proportional to the rate of IP3 turnover and accordingly we provide an estimation of this parameter which otherwise would remain experimentally unknown. In particular, on the basis of our bifurcation data, we estimate that AM-encoding astrocytes could express an average mGluR density between 1-50 receptors/um^2 that is of the same order of AMPA receptor density measured on Bergmann glia somas. We show however that FM-encoding astrocytes could be consistent with an overexpression of mGluRs by a factor of 8 or 10 with respect to AM-encoding cells. In the last part of our study, we finally consider the characterization of the possible integrative properties of astrocyte Ca2+ signalling and the effects of astrocytic Ca2+-dependent glutamate exocytosis on neuronal activity. For this purpose we develop a mathematical description of neuron-glial interactions at the level of a single astrocytic microdomain in which our modified Li-Rinzel model of astrocyte Ca2+/IP3 dynamics is coupled with an ensemble of Tsodyks-Uziel-Markram synapses on the soma a regular spiking Izhikevich neuron. We show that astrocytes of different classes of excitability could respond differently to stimuli of equal intensities and identical interspike-interval (ISI) statistics. On the other hand, stimuli at the same frequency but with different ISI statistics could trigger distinct Ca2+ responses in cells of the same type. All these possibilities are also dependent on the nature of the stimulatory pathway. Astrocyte Ca2+ signalling could therefore result from a complex integration of spatiotemporal features of synaptic stimuli which could represent a form of processing of neuronal activity. Perhaps even more intriguingly, Ca2+ signals could encode information on the past history of synaptic activity which in turn would be transferred back to neuron through Ca2+-dependent glutamate exocytosis with deep consequences on the informational content of postsynaptic neuronal activity. Computation of Fano Factors on simulated time series of postsynaptic action potentials reveal in fact that neuron-astrocyte interactions could substantially affect the rate of neuronal firing by adding long-range correlations to the timing of neuronal spikes. These results are consistent with the possibility that neuron-astrocyte bidirectional signalling could influence information processing of the brain by increasing the information-coding dimension of the neural code

Efeito de sistemas produtivos com soja e feijão caupi sobre a comunidade de crisomelideos

A família Crysomelidae contém diversas espécies consideradas pragas agrícolas. Entre elas Diabrotica speciosa, Colaspisspp e Cerotoma arcuatus, popularmente conhecidas como vaquinhas que quando larvas se alimentam de raízes enquanto que os adultos atacam o sistema foliar das plantas. Considerando que a espécie hospedeira pode influenciar nos parâmetros biológicos dos herbívoros, consequentemente na população da praga, instalou-se um ensaio de campo, durante dois anos, visando avaliar o efeito de sistemas produtivos e suas interações com plantas daninhas sobre a comunidade de insetos, sendo os tratamentos: Soja sucedida por soja (1), soja sucedida por pousio (2), soja sucedida por caupi (3) e caupi sucedido por caupi (4) em condições de controle total ou ausência de controle de plantas daninhas. Portanto, um experimento fatorial 4 x 2 (quatro sistemas produtivos x dois manejos de plantas daninhas) com quatro repetições. As coletas foram realizadas no momento de ?fechamento de ruas?, maturação fisiológica e 20 dias após a colheita. Para coletar os insetos, utilizou-se uma rede entomológica. Concomitantemente, as plantas daninhas foram coletadas manualmente pelo método do quadrado inventário (25 x 25cm). Apenas a população de C. arcuatus diferiu significativamente entre os sistemas produtivos, sendo sua maior presença nos tratamentos contendo a cultura do caupi exclusiva ou em sucessão a soja. Não houve interação entre sistemas produtivos e presença de plantas daninhas. Ao avaliar a quantidade de crisomelideos coletados ao longo do experimento, observa-se uma dominância de C. arcuatus(241 indivíduos), sendo sua população diferente significativamente de D. speciosa (136 indivíduos) e de Colaspis spp (53 indivíduos). Portanto, conclui-se que sistemas produtivos que contenham a cultura do caupi podem ter mais problemas com ataques de crisomelideo

Objects, actions, and images: a perspective on early number development

It is the purpose of this article to present a review of research evidence that indicates the existence of qualitatively different thinking in elementary number development. In doing so, the article summarizes empirical evidence obtained over a period of 10 years. This evidence first signaled qualitative differences in numerical processing, and was seminal in the development of the notion of procept. More recently, it examines the role of imagery in elementary number processing. Its conclusions indicate that in the abstraction of numerical concepts from numerical processes qualitatively different outcomes may arise because children concentrate on different objects or different aspects of the objects, which are components of numerical processing

Influence of psychopathologies on craniomandibular disorders

Psychopathologies play a role in the etiology and maintenance of craniomandibular disorders (CMD). In this study, the craniomandibular index was applied to valuate signs and symptoms of CMD in 60 dentate patients, who were assigned to 2 groups: symptomatic (n=35) and asymptomatic (n=25). An interview on psychopathologies was carried out with the aim to detect the presence of some mood disorders, such as depression, dysthymic and bipolar I disorders. Among these disturbances, depression was the most significant aspect to be reported (p<0.05) since it was present in most symptomatic patients. This important interaction was also significantly correlated (p<0.05) with the Palpation Index. These results suggest that psychopathological aspects could increase muscle tenderness and pain in addition to sleep dysfuntions and other physical complaints. Therefore, psychopathologies should be regarded as an important aspect in patients with orofacial pains.Os transtornos psíquicos podem desempenhar um importante papel na etiologia e manutenção das desordens craniomandibulares (DCM). Desta forma, neste estudo, foi aplicado o índice craniomandibular (ICM), o qual permite detectar a presença de sinais e sintomas de DCM em 60 pacientes totalmente dentados. Estes pacientes foram divididos em dois grupos: sintomáticos (n=35) e assintomáticos (n=25). Um teste psiquiátrico foi administrado para diagnosticar patologias psíquicas pertencentes ao DSM-IV, como a depressão e os transtornos distímico e bipolar I. Das patologias psíquicas relacionadas aos transtornos de humor, a depressão mostrou uma relação estatisticamente significante (p<0,05) com os pacientes sintomáticos para DCM. Ao analisar o índice de palpação separadamente, essa relação se manteve significante (p<0,05) numa escala crescente de valores, demonstrando a ação destes transtornos sobre a sintomatologia dolorosa muscular. Assim sendo, os transtornos mentais exerceriam uma influência considerável na etiologia da DCM, na medida em que potencializariam a dor. Isso ocorreria em função do aumento da tensão muscular, dos distúrbios do sono e de outras alterações fisiológicas advindas destes transtornos

Developing student spatial ability with 3D software applications

This paper reports on the design of a library of software applications for the teaching and learning of spatial geometry and visual thinking. The core objective of these applications is the development of a set of dynamic microworlds, which enables (i) students to construct, observe and manipulate configurations in space, (ii) students to study different solids and relates them to their corresponding nets, and (iii) students to promote their visualization skills through the process of constructing dynamic visual images. During the developmental process of software applications the key elements of spatial ability and visualization (mental images, external representations, processes, and abilities of visualization) are carefully taken into consideration