A Computational Study on the Role of Gap Junctions and Rod Ih Conductance in the Enhancement of the Dynamic Range of the Retina

Recent works suggest that one of the roles of gap junctions in sensory systems is to enhance their dynamic range by avoiding early saturation in the first processing stages. In this work, we use a minimal conductance-based model of the ON rod pathways in the vertebrate retina to study the effects of electrical synaptic coupling via gap junctions among rods and among AII amacrine cells on the dynamic range of the retina. The model is also used to study the effects of the maximum conductance of rod hyperpolarization activated current Ih on the dynamic range of the retina, allowing a study of the interrelations between this intrinsic membrane parameter with those two retina connectivity characteristics. Our results show that for realistic values of Ih conductance the dynamic range is enhanced by rod-rod coupling, and that AII-AII coupling is less relevant to dynamic range amplification in comparison with receptor coupling. Furthermore, a plot of the retina output response versus input intensity for the optimal parameter configuration is well fitted by a power law with exponent . The results are consistent with predictions of more theoretical works and suggest that the earliest expression of gap junctions along the rod pathways, together with appropriate values of rod Ih conductance, has the highest impact on vertebrate retina dynamic range enhancement

Active dendrites enhance neuronal dynamic range

Since the first experimental evidences of active conductances in dendrites, most neurons have been shown to exhibit dendritic excitability through the expression of a variety of voltage-gated ion channels. However, despite experimental and theoretical efforts undertaken in the last decades, the role of this excitability for some kind of dendritic computation has remained elusive. Here we show that, owing to very general properties of excitable media, the average output of a model of active dendritic trees is a highly non-linear function of their afferent rate, attaining extremely large dynamic ranges (above 50 dB). Moreover, the model yields double-sigmoid response functions as experimentally observed in retinal ganglion cells. We claim that enhancement of dynamic range is the primary functional role of active dendritic conductances. We predict that neurons with larger dendritic trees should have larger dynamic range and that blocking of active conductances should lead to a decrease of dynamic range.Comment: 20 pages, 6 figure

A produção acadêmica sobre a Agência Nacional de Saúde Suplementar: um olhar a partir da Biblioteca Digital Brasileira de Teses e Dissertações

National Regulatory Agency for Private Health Insurance and Plans (ANS) is the regulatory agency linked to Ministry of Health, which is responsible for health insurance in Brazil. Although it was established in 2000, there is already a considerable number of production studies about the Agency, it is relevant to know what these researches cover. This literature review article aimed at analyzing academic production about the ANS, found on Brazilian Digital Library of Theses and Dissertations. It is a qualitative research that uses the technique of thematic content analysis. All studies in that library that address the ANS were examined. For bibliographic material selection, selecting a specific period was not needed. Only theses and dissertations that included “National Regulatory Agency for Private Health Insurance and Plans” expression in any of the search fields available were analyzed. It was possible to identify the main existing issues covered by these academic productions: economic regulation, political and legal aspects of regulation and health-related characteristics of regulation; similarities and differences of understanding such regulatory institution were also discussed. We concluded that the identified issues don’t exclude each other, on the contrary, they are complementary and indicate the different facets of the institution. Furthermore, analysis of academic production unearthed differences of understanding regarding the Agency, sometimes seen as conciliation proceedings, sometimes considered as a bureaucratic and slow institution, but also seen as an institution that encourages promotion practices to health, disease prevention and improved health quality.A Agência Nacional de Saúde Suplementar (ANS) é a agência reguladora vinculada ao Ministério da Saúde, e responsável pelo setor de planos de saúde no Brasil. Embora tenha sido criada no ano de 2000, já existe considerável produção de estudos sobre a Agência, sendo pertinente conhecer o que abordam essas pesquisas. Nesta perspectiva, este artigo de revisão bibliográfica buscou analisar a produção acadêmica sobre a ANS existente na Biblioteca Digital Brasileira de Teses e Dissertações. Trata-se de pesquisa qualitativa que utiliza a técnica análise de conteúdo temática. Todos os estudos presentes na Biblioteca que abordem a ANS foram examinados. Para a seleção do material bibliográfico não foi realizado recorte temporal. Foram incluídas as teses e dissertações que apresentaram a expressão “Agência Nacional de Saúde Suplementar” em quaisquer dos campos de busca disponíveis. Foi possível identificar os principais temas existentes nestas produções acadêmicas: aspectos econômicos da regulação, aspectos político-jurídicos da regulação e aspectos relacionados à saúde da regulação; também foram discutidas as semelhanças e as diferenças de compreensão em relação à referida instituição reguladora. Concluiu-se que os temas identificados não se excluem, ao contrário, são complementares, indicando as diferentes facetas da instituição estudada. Além disso, a análise da produção acadêmica permitiu revelar diferenças de compreensão em relação à Agência, ora vista como instância de conciliação, ora considerada órgão burocrático e lento, e também como instituição que incentiva práticas de promoção à saúde e prevenção de doenças e melhoria da qualidade em saúde