Prolactin receptor gene expression in the forebrain of pregnant and lactating rats.

Prolactin plays a large role in the onset of maternal behavior at parturition. Knowledge of the change in expression of the prolactin receptor in the brain across pregnancy and lactation, however, is limited. Prolactin receptor gene expression was determined by in situ hybridization histochemistry during pregnancy and lactation in rats. Expression of the mRNA for the longform of the prolactin receptor (PRL-R-L) was measured in various forebrain structures in primigravid rats at different stages of pregnancy, in primiparous rats during early, mid-, and late lactation, and in age-matched, nulliparous females in diestrus. Hybridizations were performed using a [33P]-labeled riboprobe specific for the long form of the prolactin receptor mRNA complimentary to 290 bp of the prolactin receptor gene. The following areas of the forebrain were examined: medial preoptic area (MPOA), median preoptic nucleus both dorsal (MePOd) and ventral (MePOv) to the anterior commissure, ventral lateral septum (LSv), and the ventral and principal parts of the bed nucleus of the stria terminalis (BnSTv and BnSTpr, respectively). Overall, the number of cells expressing PRL-R-L mRNA was significantly higher at 2 h postpartum compared to diestrus in all areas examined except the LSv. In addition, there were lower numbers of PRL-R-L cells during all stages of lactation compared to pregnancy. The number of grains per cell in the MPOA and LSv did not change as dramatically as the number of cells expressing PRL-R-L mRNA in those brain regions. These data contribute to the growing body of evidence that the neural lactogenic system changes as a function of female reproductive state. Changes in PRL-R-L mRNA in terms of behavior and endocrine functions are discussed. Copyright 2002 Elsevier Science B.V.