Jetting half way across the world, shift work and those crazy all-nighters are all things that can upset our body’s daily cycle, or circadian rhythm. Over the years, scientists have slowly been piecing together the components of our “biological clocks” that drive these rhythms, and we now have a pretty good understanding of how they are coordinated. Now, scientists have discovered what is effectively a “reset button” in mice, which could eventually help researchers develop novel treatments that correct mismatches between the environment and our internal body clocks.
Circadian rhythms are physiological, mental and behavioral changes that follow an approximately 24-hour cycle, which are primarily dictated by changes in light in the environment. These oscillations are driven by groups of interacting molecules in the body which are collectively known as biological clocks, and it is the job of a master pacemaker located in the brain to coordinate and regulate these clocks to make sure the body is in sync.
It’s been known for some time that this “master clock” is a bundle of neurons in a region called the suprachaismatic nucleus (SCN); however, scientists didn’t know whether altering the way that these cells fire could change how it operates. Now, researchers from Vanderbilt University have demonstrated that it is indeed possible to control the clock by selectively switching on and off this population of cells, which effectively mimics their daytime and nighttime activity.
In order to manipulate the activity of these neurons, the researchers used a sophisticated technique known as optogenetics. This involves inserting genes that code for light-sensitive proteins into distinct populations of cells, creating a bundle of neurons that now respond to light in a certain way. Then, after implanting an optical fiber into the brain, scientists can use lasers to either stimulate (switch on) or inhibit (switch off) these cells.
As described in Nature Neuroscience, the researchers found that by artificially stimulating the SCN neurons, they were able to manipulate the mouse’s sleep/wake rhythms, effectively resetting the master clock. This was particularly interesting because previous work suggested that the firing activity of these cells was only an output of the clock’s activity.
“Of course, this exact approach isn’t ready for human use yet,” said study author Michael Tackenberg. “But others are making progress toward eventually using optogenetics as therapy.” Tackenberg is now taking the work forward by examining whether mice suffering from seasonal affective disorder—a type of depression that has a seasonal pattern—respond to the stimulation.