Abstract
Prolactin (PRL) is known to be one of the hormone involved in the induction of maternal behavior. Recent observation that PRL receptor (PRL-R)-knock-out (KO) mice show a deficiency in pup contact-induced maternal behavior indicates that PRL-R plays an essential role in the induction of the maternal behavior. However, PRL-KO mice exhibit no abnormality in the maternal behavior. This discrepancy in the maternal behavior between PRL-R- and PRL-KO mice suggests that actions of maternal PRL or placental lactogens (PLs) to the fetus and/or the pups are critical for the maternal behavior at adulthoods. In rat brain, the expression of mRNA for the long form PRL-R increases during maternal behavior in males and females, suggesting that PRL actions on the brain are important for maternal behavior. Expressions of rat PRL-R gene are known to be regulated in a tissue-specific manner by the promoters for multiple first exons. In addition to the three known first exons, E11, E12, and E13, we have recently identified two novel first exons, E14 and E15. E14 is expressed only in the brain with higher levels at pregnant and lactating periods compared to dioestrous period. The regulatory mechanisms for the expression of PRL-R gene in the brain associated with maternal behavior and molecular events responsive to the action of PRL on the brain to induce maternal behavior are discussed.
