In humans, the suprachiasmatic nucleus (SCN) controls the body's circadian rhythms. Each day, sighted people have the opportunity to reset their internal clock based on the amount of ambient light entering their retinas. The retina contains a subset of retinal ganglion cells specialized in regulating the body's rhythms. These ganglion cells project to the SCN from both eyes via the retinohypothalamic pathway. But how do completely blind people synchronize with their environment? Non-photic cues may help blind people sense the passage of time, but they are not always enough to regulate the body's cycle of body temperature and hormones.
Keywords: Intrinsically photosensitive retinal ganglion cells (ipRGCs), retina, olivary pretectal nucleus (OPN)
[...] Doyle hypothesized that “early rod loss may cause reorganization of the developing retina in such a way that circadian responsivity is increased.” Doyle also hypothesized that melanopsin may function as a bistable opsin capable of switching back and forth between its conformations. More tests to discover the mechanism by which melanopsin is recycled showed that responses to light in ipRGCs also persist in the absence of a photoisomerase, a retinal G-protein coupled receptor. protein receptor systems work more slowly than direct enzymatic systems, which would explain why circadian photopigments respond to gradual changes in light intensity more than drastic changes (Doyle, et. [...]
[...] Fells, P. & Blakemore, C. (2001). Blindness. In The Oxford Companion to the Body (1st ed., Oxford). Oxford University Press. Freberg, L.A. (2006). Discovering biological psychology. Boston: Houghton Mifflin Company. pp. 314-319. Hattar, S., Liao, H.W., Takao, M., Berson, D.M., & Yau, K.W. (2002). Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science, 295(5557), pp. 1065-70. Hendrickson, A. E., Wagoner, N., & Cowan, W. M. (1972). An autoradiographic and electron microscopic study of retino-hypothalamic connections. Cell and [...]
[...] In the absence of information from the ipRGCs, blind people have difficulty readjusting their circadian rhythms to the environment. They often suffer from insomnia, and analysis of core body temperature and hormone levels reveal that their body is “free-running” or using a rhythm that never gets reset. Other blind people use non-photic cues, which do not involve light-sensitivity, to attempt to reset biological rhythms. Non-photic cues involve senses other than light and are never as successful as photic cues. Intrinsically photosensitive retinal ganglion cells (ipRGCs) in the retina provide the input to the system for resetting the biological clock in mammals. [...]
[...] In patients with cataracts, the lens of the eye becomes opaque, but ambient light levels are still detected. For patients with diabetic retinopathy, circadian photoentrainment is spared as well because the disease is caused by the growth of abnormal blood vessels and scarring from the breaking of blood vessels, not the degeneration of ipRGCs. Glaucoma can lead to problems with circadian photoreception because the peripheral retina is the first part of vision destroyed. In glaucoma, fluid builds up in the eye, causing pressure on the axons of ganglion cells, damaging them (Sommer, 2002). [...]
[...] (1999).Pituitary adenylyl cyclase-activating peptide: A pivotal modulator of glutaminergic regulation of the suprachiasmatic circadian clock. Proceedings of the National Academy of Sciences of the United States of America, 96(23), pp.13468-73. Czeisler, C. A., et al. (1995). Suppression of Melatonin Secretion in Some Blind Patients by Exposure to Bright Light. New England Journal of Medicine, 332(1), pp. 6-11. Doyle, S., et al. (2006). Nonvisual light responses in the Rpe65 knockout mouse: rod loss restores sensitivity to the melanopsin system. Proceedings of the National Academy of Sciences of the United States of America, 103(27), pp. [...]
using our reader.