"These studies individually demonstrate the genetic determinants of nerve cell number. Together, they show that different nerve cell types are modulated independent of one another," said Benjamin E. Reese, senior author and professor with the Neuroscience Research Institute and the Department of Psychological and Brain Sciences. he scientists used mice as a research model organism to show that the size of different populations of retinal neurons display wide-ranging variability among individuals.
In the PNAS article, they demonstrated a nearly two-fold variation in the number of interneurons called horizontal cells. In the IOVS article, they report a conspicuous variation in the number of cone photoreceptors.
The team explained that such natural variation in the ratio of nerve cells requires a degree of plasticity in the process of forming neural connectivity, to ensure that the entire visual field is served by neural circuits that mediate our visual abilities.
According to Resse, efforts to use genetic engineering and stem cell biology to repair diseased retinas depend upon a fuller appreciation of the developmental biology of the retina.
"These particular studies are just one contribution in an enormously complex process. Our fundamental interest is in the development the retina-how you 'build' this neural tissue that, when fully mature, will mediate our visual abilities." said Reese.
The studies are published in recent online versions of The Proceedings of the National Academy of Sciences (PNAS), and Investigative Ophthalmology and Visual Science (IOVS).