Prepartum and postpartum regulation of maternal behaviour in the rat.

Maternal behaviour in the rat consists of four principal components: nursing or crouching over the young, retrieving pups to the nest, body and genital licking of pups, and nest-building. Normally the onset of maternal behaviour occurs at parturition but studies reveal that the true onset is somewhat earlier, around 24 hours pre partum. The onset of maternal behaviour is hormonally determined and it is most likely that the ovarian hormone oestradiol plays a major role under the specific conditions that exist pre partum. The onset of maternal behaviour requires the resolution of tendencies of fear-avoidance of pups, based on their olfactory characteristics, and attraction to them and response to the pup stimuli that elicit maternal behaviour. In most animals this resolution occurs almost immediately but in some animals several hours of contact with the pups is required for maternal behaviour to be firmly established. After parturition, maternal behaviour appears to be regulated chiefly by stimuli from the pups, and hormones do not play a role apart from their role in lactogenesis. Size of litter, age of pups, amount of externally induced stress and other factors can affect the mother-young interaction: there is a period of special vulnerability to disruption of the mother-young interrelationship shortly after parturition which corresponds, we believe, to the period of transition from hormonal to non-hormonal regulation of maternal behaviour. Weaning and the decline of maternal behaviour is a specific phase of maternal care. Maternal behaviours gradually decline as avoidance behaviours increase.