Estudio conductual y estructural del sistema visual de ratón RD10. Evaluación del efecto neuroprotector de la proinsulina

Abstract

The present work intends to look for some uninvestigated aspects of retinal degeneration in mice by means of morphological and behavioral studies. Also, this dissertation aims to look further into the possible neuroprotective effect of proinsulin, a molecule with a well known modulating effect in the mammalian nervous system. Since the dual theory of vision was proposed more than one century ago, it has been widely accepted that there are two photoreceptors in the vertebrate retina: rods and cones. Both systems are part of the visual pathway of the retina; this visual pathway projects to sub-cortical and cortical regions of the brain and carries out visual perception. Recently, a third type of retinal photoreceptor cell has been described, which projects mainly to the hypothalamus and does not seem to participate in visual perception. These cells have been named "intrinsically photosensitive retinal ganglion cells" (ipRGC), and they comprise a very reduced group of retinal ganglion cells that regulate the non-visual functions of the retina, like for instance circadian activity and pupil diameter. The work aims to study both, visual and non-visual, paths of the retina in mouse models of retinal degeneration. Also, and since it is such a new cell type, the Thesis intends to describe the morphological changes suffered by the ipRGC in different retinal degenerative stages. Lastly, the Thesis studies the possible neuroprotective effect of proinsulin in the retina of dystrophic mice. The morphological study of ipRGC was done by means of inmunohistochemistry staining which illustrates the structure of such cells, as well as their communication with other cells in the retina. On the other hand, the functional study of the paths of the retina was carried out by the use of animal behavioral tests in order to elucidate the ultimate repercussions that degenerative retinal diseases might have on animal conduct. Specifically, the optokinetic reflex was analyzed by means of the optomotor test, to study the visual path of the retina, and the circadian activity was examined by means of the activity wheel, to evaluate the non-visual path of the retina. The results show that photoreceptor degeneration in dystrophic mice is followed by changes in the structure of the inner retina, which affect its non-visual pathway. These changes involve alterations in the dendritic processes of the ipRGC. Furthermore, retinal degeneration goes hand in hand with a functional loss of the visual pathway that regulates the optokinetic reflex, and the temporal course of photoreceptor loss parallels the diminishing performance of dystrophic mice in the optomotor test. On the other hand, the optokinetic reflex studies show that dystrophic mice which express proinsulin are responsive to the optomotor test for a longer time compared to dystrophic mice that do not express proinsulin. In addition, photoreceptor degeneration in dystrophic mice does not seem to affect the intrinsic function of ipRGC related to the synchronization of the circadian activity with light conditions. However, the free running periods in dystrophic mice are significantly longer than the free running periods in control mice. Proinsulin, again, seems to have a neuroprotective effect in the retina, since proinsulin expressing dystrophic mice have a free running period similar to those in control mice. We conclude that this Thesis elucidates on the importance of the ipRGC in the visual conduct of mammals and confirms the neuroprotective effect of proinsulin in the mouse retina.