"We know from previous studies that light can affect the development of other parts of the brain, for example the visual system. Our work shows that this is also true for the biological clock," said Ciarleglio.
The experiment was performed with a special strain of genetically engineered mice that it took McMahon two years to develop. The mice have an extra gene inserted in their genome that produces a naturally fluorescent green protein causing the biological clock neurons in their brains to glow green when they are active. This allows the scientists to directly monitor the activity of the master biological clock, which is located in the middle of the brain behind the eyes in a small area called the suprachiasmatic nucleus (SCN).
For the study, the researchers took three groups of six to eight newborn pups each and placed them (and their mothers) in environments with controlled day/night cycles. One group was placed in a "summer" cycle with 16 hours of light and eight hours of dark; another group was placed in a "winter" cycle with eight hours of light and 16 hours of dark; and a third group was placed in an equinox cycle with 12 hours of light and 12 hours of darkness. They were kept in these environments for three weeks until they were weaned.
"When they are born, the brains of mice are less developed than those of a human baby. As a result, their brains are still being wired during this period," McMahon said.
Once they were weaned, half of the summer-born mice were kept on the summer cycle and half were switched to the winter cycle for the following 28 days as they matured. The winter-born mice were given the same treatment. The equinox-born mice were split into three groups and put into summer, winter and equinox cycles.
After the mice matured, they were placed into an environment of continuous darkness.
|Contact: David F. Salisbury|