- A new study calls into question a long-held “textbook concept” explaining how mammals’ retinas process light. For 30 years, scientists have believed that when a single particle of light is absorbed by rods in the retina, it starts a cascade of biochemical reactions involving around 500 G proteins. However, the new study from Johns Hopkins University School of Medicine, measuring the electrical signals triggered by a single G protein, has found that significantly fewer molecules are activated in the cascade – between 10 and 20, to be exact. “These pathways are a major target among pharmaceutical companies, because they control many diverse physiological processes, ranging from those that allow us to see images, to those tied to heart disease,” explained King-Wai Yau, Professor of Neuroscience and Ophthalmology at the university (1). His team hope the findings will help shape better treatments for visual malfunctions in the future.
- Could the complement system (a part of the innate immune system) play a protective role in degenerative eye diseases? Researchers at the National Eye Institute seem to think so. The team found that upregulation of complement expression and activation coincided with the onset of photoreceptor degeneration in a mouse model of retinitis pigmentosa. Interestingly, upregulation occurred in the exact location of the degeneration. By examining the role of C3 and CR3 – the central component of complement and its receptor – they discovered that absence of either component increased degeneration. These findings are a stark contrast to existing literature that suggests the complement system actually worsens retinal regeneration. While the study found that complement activation is helpful for clearing away dead cells and maintaining a state of homeostasis in the case of retinitis pigmentosa, it was found to have a harmful effect in AMD. “Appreciating this complexity is important for guiding the development of therapies that target the complement immune system to treat degenerative diseases of the retina,” said the study’s PI, Wai T Wong, chief the Neuron-Glia Interactions in Retinal Disease Section at NEI. (2)
- According to a report by Carnegie Mellon University, children with severe epilepsy are capable of retaining visual perception after brain surgery, even if they have lost tissue in the visual cortex. Researchers tested the perception of 20 children – 10 of whom had undergone surgery – and found that nearly all fell within the normal range for perception and memory, regardless of whether they had had surgery or not. To understand why, the researchers imaged each participant’s brain to map the regions required for individual tasks, such as facial recognition. They found that while most regions required for visual perception exist bilaterally, the areas responsible for facial recognition and visual word forming tend to be most dominant in the right hemisphere. Yet in the study, the children’s remaining hemisphere was able to compensate for missing regions, and in one participant – a child who had lost most of the visual cortex in their left hemisphere – this word-form area had remapped altogether to the right hemisphere. While the team are uncertain when compensation takes place, they theorize it may be a response to the damage that caused the epilepsy in the first place. (3)
References
- WWS Yue et al., “Elementary response triggered by transducin in retinal rods”, Proc Natl Acad Sci USA, 116, 5144 (2019). PMID: 30796193.
- SM Silverman, “C3- and CR3-dependent microglial clearance protects photoreceptors in retinitis pigmentosa”, J Exp Med (2019). PMID: 31209071.
- TT Liu, “Perceptual function and category selective neural organization in children with resections of visual cortex”, J Neurosci (2019). PMID: 31167940.
