Posted by Zubair Khan
Note by the Editor:Ahmadiyya Muslim Community Germany is blessed with lot many young male and female upcoming scientists. Each year large number is engaged in research and getting PhD degrees. It is clear proof that Muslim World is not void of talents. Effort will be made to introduce such scientists through the pages of MT.
The origin and mechanism of the spontaneous activity in the rd1 mouse retina and a proof of principle for the function of a chemical retinal implant.
An Abstract of thesis submitted By Wadood Mohammad Abdul Haq
Sight is the most valuable sense for humans to interact with their environment and essential for most of the vertebrates to survive at all. The loss of vision caused by injuries or genetic disorders has devastating impact on the lifestyle of the patients. The disease retinitis pigmentosa (RP) leads to blindness, due to a mutation (inherited or spontaneous) resulting in the degeneration of the light receptive cells of the retina, the photoreceptors (Bowes et al., 1990). Worldwide estimated 3 million humans are affected, but so far, no successful therapeutic agent is available to prevent or restore vision loss.
To improve and rescue vision at the initial phase of the retinal degeneration, when the photoreceptors are still present, strategies like photoreceptor transplantations (MacLaren et al., 2006) or gene replacement (Acland et al., 2001) have been suggested and are being currently investigated. In schemes to restore vision at the progressed stage of the RP, in the absence of the photoreceptors, preliminary successes have been reported with electrical implants in humans: patients equipped with a subretinal implant are able to distinguish basic geometric forms, read large letters, and even discriminate face expressions (Zrenner et al., 2011).
Technical limitations of the implants on the one hand and insufficient understanding of the RP disease at the other hand form barriers for the ultimate solution. During neuronal degenerative diseases, neurons degenerate and neuronal microcircuits undergo structural alterations leading to remodeling of synaptic connectivity. The functional consequences of synapse remodeling are mostly unknown. For instance, animal models for RD, e.g. the rd1 mouse, show beside the loss of photosensitivity of the retina also a remodeling process of the diseased retinal tissue (reviewed in Marc et al., 2003), which causes the emergence of aberrant light-independent spontaneous activity in the retina (Ye & Goo, 2007; Stasheff, 2008). Patients with retinal degenerative disorders, like RP or age-related macular degeneration, also report about the experience of light-independent bright flashes, known as photopsia (Bittner et al., 2009). It was proposed that the spontaneous activity observed in the rd1 mouse model reflects the photopsia in human patients (Borowska et al., 2011). In fact, photopsia in RD represents a severe problem, for the patients as well as for the development of therapeutic strategies, such as the retinal implants (Zrenner, 2012). The spontaneous activity of the diseased retina greatly degrades the efficiency of signal transmission in the retinal network; it masks the signals of the retinal implants (Hallum et al., 2006).