Multiple Circadian Oscillators Regulate the Timing of Behavioral and Endocrine Rhythms in Female Golden Hamsters

A single daily "surge" in pituitary luteinizing hormone release was observed in ovariectomized-estrogen-treated hamsters expressing an intact circadian rhythm of locomotor activity. In contrast, two luteinizing hormone surges occurred within a single 24-hour period in hamsters whose activity rhythm had dissociated or "split" into two distinct components. These observations indicate that both behavioral and endocrine circadian rhythms are regulated by the same multioscillator system, which seems to be composed of at least two distinct circadian oscillators.