Behavioral, physiological, and neuroendocrine circadian rhythms during lactation

Abstract

Lactation in mammals implies great challenges for the mothers, who must adapt their behavior and physiology to fulfill the costly demands of motherhood. Lactation is the main distinctive feature of mammals, and it is expressed in different modalities depending on the particular evolutionary characteristics of each species. Intense research, using mainly rodents and ungulates, is contributing to understand the complex physiological changes and their interaction with the nervous system during this period. Although this is a field of intense research, very little is known about the circadian rhythms of the mother during lactation. In the present chapter, we explore the importance of circadian rhythms during this period, focusing mainly in the rabbit as a model. There is a major reason for emphasizing attention on this species. The mother rabbit nurses her pups just once a day, for a period of less than 5 min. Although this behavior has long been known, only in recent years has it been firmly established that this event occurs around every 24 h, that is, with circadian periodicity. This is a unique characteristic among mammals, and perhaps for this reason the circadian control of lactation had been underestimated in considering that most of the research during lactation had been conducted in other groups of mammals. Then, in this chapter we present behavioral, physiological, and neuro-endocrine circadian rhythms during lactation in the rabbit, and whenever possible we include available literature in other mammal species, including humans.