Myoelectrical activity changes in the uterus and vagina during oviposition in the conscious domestic hen.

In the unrestrained domestic hen, myoelectrical activity of the uterus and vagina was recorded during the period from 10 min before to 10 min after oviposition. Recordings revealed significant changes in frequency and duration of bursts of spike potentials (BSP) between 3 min before and 2 min after the expulsion of the egg. These changes occurred successively, first in the uterus, then in the vagina. For the uterus, the frequency of BSP per minute increased. However, the duration decreased significantly during the same time period, remaining at the attained activity level throughout the 10-min postoviposition period. In the vagina, changes in BSP were transient. The duration of BSP was sharply augmented prior to oviposition, reflecting a nearly continuous discharge of spike potentials. The frequency reached minimal values after oviposition. The onset of changes in myoelectrical activity may reflect the moment the egg passes the registration electrodes. The increase in frequency of spike potentials may indicate augmented resistance to the passage of the egg in cranial direction (ovarium) so that it is propulsed towards the cloaca. The characteristic pattern of vaginal myoelectrical activity about oviposition argues for the active participation of this oviductal segment in the process.