Induction of maternal behavior in the virgin rat by lactating-rat brain extracts

Maternal behavior was induced in naive virgin rats by treatment with extracts of brain obtained from lactating mothers killed on day 16 of lactation. Neither blood nor kidney extracts from the same lactating rats were effective in initiating the maternal response. When the recipients were injected with extracts of brain prepared from virgin rats or from primiparous rats killed on postpartum day 1, none of the animals displayed maternal behavior during the 72 hr of trial. The results suggest the development, within the brain of the lactating mother, of a factor capable of inducing maternal behavior in a non-lactating rat. The “factor” appears to be located in the microsomal and soluble fraction of the brain homogenate.