The Oxytocin Clock

Mother Mouse and Baby
Originally uploaded by danedude.

Bora Zivkovic, who blogs as Coturnix at A Blog Around the Clock, has a very interesting and informative post about a study of the relationship between oxytocin and the timing of labor and birth in mice.

Coturnix ponders the implications of Oxytocin in the Circadian Timing of Birth by Jeffrey Roizen, Christina E. Luedke, Erik D. Herzog and Louis J. Muglia. In the study at Washington University School of Medicine, the researchers compared onset of labor and birth of young in normal (wild-type) mice and oxytocin-deficient mice. When they shifted the light cycle in the lab, the oxytocin-deficient mice gave birth at random times, while there was no change in when the normal mice gave birth.

Coturnix kindly explains:

In wildtype mice, those in which oxytocin is present, the births were clustered around a single time of day. However, the phase-shifting of the light cycle did not phase-shift the timing of birth! And it also did not shift the timing of oxytocin release either. This means that the circadian rhythm of oxytocin release is driven by a pacemaker that is separate and independent from the pacemaker governing the locomotor activity. The location of this pacemaker is yet to be elucidated, but it could be a subset of cell in the SCN, or a yet-unknown clock located in the paraventricular nucleus of the hypothalamus, or in the posterior pituitary itself. Anyway, the results support the hypothesis that oxytocin is in some way involved in the timing of birth.

Of course, in hospital births of humans, oxytocin is used very directly to shift the onset of labor and actual childbirth.