Maternal behaviors: evidence that they feed back to alter brain morphology and function.

We review evidence suggesting that the brain of maternally behaving rats is altered as a result of the behavior of the animal towards her pups. Morphological changes seen in the supraoptic nucleus, which contains oxytocinergic neurons important for lactation, are observed not only in parturient, lactating animals but also in virgin animals induced by the presence of rat pups to behave maternally. The supraoptic nuclei of lactating and maternally behaving virgin animals have a higher incidence of dendritic bundling relative to non-maternal virgin animals. Also, stimulation of the lateral olfactory tract in in vitro brain slices elevates electrotonic coupling among supraoptic neurons only in maternally behaving animals and not in male or non-maternal virgins. In general the evidence presented supports the idea that maternal behavior in lactating and non-lactating animals, can have profound effects on the morphology and physiological functioning of oxytocinergic neurons in the hypothalamus.