Pattern of sucking in the infant rat during spontaneous milk ejection

Two methods are described for measuring the sucking of rat pups on the nipples of the mother. The first uses pressure recording of the cannulated teatduct; the second uses direct observation of sucking behavior. Using these methods, the sucking behavior of the pups during sequences of milk ejections was investigated. Pressure recordings of the sucking of individual pups on the nipple showed that between milk ejections the pups sucked intermittently in bursts. During milk ejection itself there was a longer period of vigorous and continuous sucking. Behavioral observations on the level of sucking in whole litters of pups showed that the background bursts of sucking from the litter as a whole were randomly distributed in relation to the inferred time of oxytocin release. These results indicate that once the pups are sucking on the nipples, variations in the sucking behavior of the litter have no role in the timing of milk ejections in the mother.