Behaviour of the mother and the neonate in mammals : physiological factors of activation

Abstract

Raising young is an important step of reproductive success in Mammals. Postnatal survival depends on the presence of maternal behaviourand an adequate behaviour of the neonate. The determinants of maternal care differ between species, but some general rules doexist. In some species, the sensory cues provided by the neonates suffice to trigger immediate maternal care while in others, maternalendocrine and proprioceptive factors of parturition are also necessary. The aptitude of females to care for the young is improved generallyby maternal experience. In all species studied, parturition is a sensitive period of increased receptivity to the neonate, including inprimates and humans. The activating factors internal to the female can also differ between species. Nonetheless, estrogens, progesterone,expulsion of the foetus and its resulting intracerebral liberation of oxytocin are the most commonly encountered factors. The nervous targetstructures are mainly the medial-preoptic-area/bed-nucleus-of-the-stria-terminalis complex, the hypothalamic paraventricular nucleus,the olfactory bulbs and the amygdala. Also, in most species that have mature neonates, the mother learns to recognise her youngwithin a few hours, mainly by its smell and then rejects any alien young at the udder. This learning depends on the main olfactory systemand is facilitated by the expulsion process. It also involves the amygdala and other cortical structures. As for the neonate, its behaviour isguided by maternal sensory cues. The value of some of these cues can already be determined at birth (maternal pheromone in rabbits) oracquired through reinforcement by suckling (preference for the mother in lambs). The outcome leads to reciprocal interactions betweenthe mother and her young in which each member of the dyad becomes a factor of control of the other's behaviour.