As a body ages, daily rhythms such as sleep patterns become less regular. Now, a study in mice has shown that these changes take place within the individual brain cells that make up the biological clock. Experts say the study, published in the September issue of Neuroscience, offers a unique perspective on a process usually studied in tissues. "We're not often able to measure aging at the single cell level," says neuroscientist Martha Gillette of the University of Illinois, Urbana-Champaign.
Older mice, like older people, often have sleep problems. When kept in the dark 24 hours a day, juveniles doze at regular intervals, but middle-aged mice exhibit irregular sleep. To see whether this disruption arises with individual neurons or results from their interaction, University of Virginia neuroscientist Gene Block and colleagues examined cells from the brain region in charge of daily timing, called the suprachiasmatic nucleus (SCN). They recorded the electrical activity of mouse SCN neurons cultured in such low concentrations that they were unlikely to communicate with one another.
Eight neurons from middle-aged mice beat irregularly for days in the dish, they found, while 12 cells from young adults keep strict rhythm. The research suggests that overall decline in SCN behavior is driven in large part by the deterioration of individual neurons, says neuroscientist Martha Harrington of Smith College in Northampton, Massachusetts.
Paradoxically, the researchers observed that aging appears to disrupt the rhythm of single cells more severely than it does the animals' overall behavior, as measured by their sleep patterns. That raises an interesting biological question, Block says: "How do you get reliability [despite] unreliable parts?"