Vision and cellular communication in the retina: the role of mixed-input bipolar cells

Abstract

The sensitivity and adaptability of the visual system to the most varied light environments are impressive. Although a good part of our visual versatility lies in the existence of two types of photoreceptors with different light sensitivities in our retina, the rods and the cones, post-receptoral adaptive mechanisms are paramount to proper visual function, given the limited ability of rods to adapt to light. These post-receptoral gain control mechanisms are however poorly understood. Bipolar cells that receive input from both kinds of photoreceptors are key elements in the visual adaptation process, since they need to actively adjust their dynamic range in order to be able to transmit visual signals to the inner retina continuously under scotopic, mesopic and photopic levels. This project aims to clarify which mechanisms in these mixed-input bipolar cells allow such performance, by investigating the interactions between photoreceptor inputs at different adaptive states, their integration and gain control, the kind of filtering imposed by physiology and morphology of bipolar cells and their mechanisms of synaptic transmission. To answer these questions, we will perform experiments combining electrophysiological, morphological and pharmacological techniques, as well as mathematical modeling, in order to understand the coding strategies of mixed-input ON bipolar cells (mbON). These neurons receive substancial rod input and have, therefore, powerful gain control mechanisms. The results obtained in this study will not only increase our knowledge about retinal coding strategies, but may also have practical implications for the development of therapies for diseases that affect the first visual synapses, such as retinitis pigmentosa, retinoschisis and congenital stationary night blindness. (AU)