Three types of cells identified in the circadian rhythm cycle.

11 Dec Three types of cells identified in the circadian rhythm cycle.

Our circadian rhythm, that’s our body’s natural wake-to-sleep cycle, is important for proper daily functioning. There have been studies that showed disruptions to this cycle leading to diseases like cancer, heart disease, obesity, depressive disorders, and even type two diabetes in people who work night shift. Sunlight is a key factor to the circadian rhythm, when our bodies detect sunlight, our bodies begin to wake up. Same goes for when the sunlight starts to diminish, our body begins to go into rest mode. This can be difficult for those who work the night shift as they cannot rely on their own cycle to maintain their sleep schedule.

In recent research conducted by the Salk Institute, they looked at the eye and its ability to detect light and the subsequent alignment to the circadian rhythm. This is the first direct assessment of specific cells, these cells being the intrinsically photosensitive retinal ganglion cells (ipRGCs), in the eye, our ability to detect light, and our body’s response.

The study utilized healthy and functional retina samples from donors who had passed away and had them placed on an electrode grid to see how they react to different kinds of light. Researchers found that a small group of cells began firing after a 30 second pulse of light and once turned off, some cells took longer than others to turn off. The researchers also shined different coloured lights on the retina samples to gauge any different reactions.

Results showed that there were three distinct types of ipRCGs. Type one responded to light quickly but took longer to turn off. Type two took long to turn on and very long to turn off. Type three responded only when the light was very bright and switched on and off as soon as the light was present/gone. In terms of colour of the light, these cells were most sensitive to blue light, the light that appears in cool-white LED screens such as phones and laptop.

An interesting find in this study provides some insight to the phenomenon of blind people aligning their wake to sleep cycle with the sunlight and sleeping as a sighted person would indicating that these cells still communicate the presence of light to the brain even without the visual receptor cells of the rod and cones.

Using the results of this study, there could potentially be technology designed to mimic the natural sunrise-sunset rhythm to help induce sleep in those who otherwise cannot maintain their sleep themselves, specifically with night shift workers. Further research could look at varying intensities of these lights or shifting colours to mimic real life phenomenon like dusk to dawn settings.