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Summer Mouse, Winter Mouse

Still at the height of summer, Columbus is enjoying some 15 hours of sunlight each day. In December it'll be down to just 9 hours and that change has a profound effect on human health, sleep patterns and mood. It may be obvious that people feel different in summer and winter but the extent of these seasonal changes and the biology behind them isn't so clear. One professor of psychology and neuroscience at Ohio State University studies the effects of day length on health, behavior and learning in rodents.

Randy Nelson has spent years asking mice, hamsters and lemmings what it's like to be exposed to more daylight or less. Their answers come in the form of behaviors that can be measured, changes in immune function, or differences in which genes are active. Although Nelson works with small mammals, he says he wants to understand humans.

"I think there's a lot of value in understanding how animals solve problems to be able to cope with the environment," he said. "I think this kind of work has a lot of immediate relevance."

Because many factors change seasonally right along with day length, it's hard to tell which of those factors affect human health and behavior. But unlike humans, rodents can be kept in controlled rooms that differ only in the hours of light they receive, with all other environmental factors kept constant. If the animals from the long-day room are consistently different from those in the short-day room, it must be because of the light.

Nelson checks the animals for differences in traits like mood, learning speed, or ability to resist disease. So how does he ask a hamster about its mood? Nelson measures depression in rodents using the anhedonia test which measures how much animals partake of their favorite activities.

"The favorite thing of many of these rodents is to eat sweet things, so we give them carnation condensed milk which is a delicious treat for them," Nelson said. "And when they're depressed, they'll eat less of the stuff, that's the anhedonia. And if you were to give them, say, Prozac, they would eat more of it."

Using anhedonia and other behavioral tests, Nelson finds out how day length affects the way his animals feel. Another test, for anxiety, is based on how much time animals spend exploring a new space or hiding. A test for learning measures how long it takes an animal to memorize a maze, and how fast it catches on when the maze changes.

If the animals' behavior changes with day length, it's likely that similar behaviors in humans do too. Aggression and depression are among the traits known to respond to light exposure. But Nelson doesn't stop at behavior alone.

"We're interested in looking to see how these seasonal changes influence physiology, behavior, and what are the genes underlying these changes," he said.

In Nelson's physiology lab, researchers can find out how certain genes turn on and off in response to day length, or how hormone levels and immune strength fluctuate. Body chemistry associated with the mellow summery day lengths could point the way toward drugs that mimic that healthier state.

The newest research in Nelson's lab examines the effects of what may be too MUCH light, at the wrong times. The bigger cities grow, the more they shed their light on humans and animals, all night long. The results aren't in yet but Nelson says it's a question of medical importance.

"We're very interested in the effects of light at night both in terms of human health and how that influences immune function and ultimately diseases like cancer, and for example, what light at night in a critical care medical facility might be doing to inflammatory responses that you want to obviously reduce in somebody who's just had a heart attack or a stroke," he said.

For now, though, it's time to go outside and take advantage of those long summer days while we can.