A team of researchers at Ohio State is studying the brains of hamsters in hope of discovering why humans suffer from seasonal depression and other seasonal phenomena.
“We want to understand how internal seasonal clocks control the physiology of mammals,” said Dr. Brian Prendergast, a post-doctorate fellow in the Neurobiotechnology Center and author of the findings.
Specifically, the team aims to identify the genetic mechanism underlying the seasonal clocks, which help animals and humans distinguish between seasons to know, for example, whether to hibernate or mate, said Dr. Randy Nelson, professor of psychology and neuroscience and a member of the research team.
“Seasonal clocks, located in the central nervous system of animals, drive rhythmic changes in the reproduction cycles of hamsters,” Prendergast said.
Dwarf hamsters, chosen for the study because their seasonal clocks exhibit many traits similar to humans, cease reproduction in the winter because of inadequate food resources and low temperatures, Prendergast said.
In early September, hamsters’ sex organs actually begin to shrink in a process called gonadal regression. The hamster’s brain instructs the pineal gland to secrete the hormone melatonin, which measures the amount of light each day to reactivate reproduction, Prendergast said.
Shorter nights signal the onset of spring, which means a better environment for young offspring, he said. In early March, the hamsters re-grow their sex organs to ready themselves for breeding by mid-April.
Three genes in hamsters regulate the amount of thyroid hormones in a hamster’s brain, Prendergast said. The thyroid hormones may assist the brain in reacting to melatonin.
“Most of the genes and their functions are analogous in humans. If we understand the genes, we could extrapolate the findings into humans,” said Pappachan E. Kollattukudy, a member of the research team and faculty member of the University of Central Florida.
Through summer and autumn, gene expression in hamsters remains high, allowing the critters to follow the length of nights.
The genes aren’t expressed in late winter, so the research team has concluded the hamsters ignore light cues in order to begin re-growing their sex organs. As a result, the hamsters’ internal seasonal clocks ensure they’re ready to reproduce in the spring.
In humans, “cancer and many other diseases show a ‘seasonality’ to them,” Nelson said.
The research team hopes a better understanding of how mammalian seasonal clocks keep time will be “useful for interventions and therapies for people with seasonal disorders,” Prendergast said.
