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  The Circadian Rhythm’s Role in Ovulation

Narrator: 
   This is Science Today. Researchers at the University of California, Berkeley are studying how the brain's internal clock affects hormone cycles in the body. In particular, Lance Kriegsfeld, a professor of psychology and neuroscience, is looking into how the body clock controls ovulation.

Kriegsfeld: 
   In humans, the ovulatory cycle is controlled by numerous factors; it's controlled by nutritional state, it can be altered due to stressful circumstances, but there is also evidence that there's a strong timing component if you look at women under controlled conditions. They will ovulate typically between midnight and morning time, so there seems to be a temporal component.

Narrator:
    Kriegsfeld recently found that the Circadian rhythm, or internal clock, may lift the brakes on a molecule that inhibits a substance released during ovulation called gonadotropin-releasing hormone, or GnRH.

Kriegsfeld:
    Everyone knew that there was a Circadian component to the cycle and they knew that there was a switch from this negative to positive feedback, but how that happened was a big mystery.

Narrator:    For Science Today, I'm Larissa Branin.