Effects of pregnancy on the maintenance of maternal behavior in the rat

Flexibility and adaptation of the neural substrate that supports maternal behavior in mammals

Maternal behavior is species-specific and expressed under different physiological conditions, and contexts. It is the result of neural processes that support different forms (e.g. postpartum, cycling sensitized and spontaneous maternal behavior) and modalities of mother-offspring interaction (e.g. maternal interaction with altricial/precocious young; selective/non-selective bond). To understand how the brain adapts to and regulates maternal behavior in different species, and physiological and social conditions we propose new neural models to explain different forms of maternal expression (e.g. sensitized and spontaneous maternal behavior) and the behavioral changes that occur across the postpartum period. We emphasize the changing role of the medial preoptic area in the neural circuitry that supports maternal behavior and the cortical regulation and adjustment of ongoing behavioral performance. Finally, we discuss how our accumulated knowledge about the psychobiology of mothering in animal models supports the validity of animal studies to guide our understanding of human mothering and to improve human welfare and health.

Transgene Insertion on Mouse Chromosome 6 Impairs Function of the Uterine Cervix and Causes Failure of Parturition1

The molecular mechanisms controlling the initiation of parturition remain largely undefined. We report a new animal model in which parturition does not occur. A line of mice expressing a human apolipoprotein B (APOB) gene fail to deliver their young if the transgene is present in homozygous (Tg/Tg), but not in heterozygous (Tg/Wt), form. Cloning and mapping of the transgene insertion locus indicate that 10 copies of the 80-kilobase APOB genomic fragment inserted into mouse chromosome 6 result in a small, 390-base pair deletion of mouse genomic DNA. Nine other lines expressing the transgene have normal labor, suggesting that transgene insertion in this mutant line disrupted a mouse gene crucial for successful parturition. The pathophysiology of parturition failure in these animals was defined using physiological, endocrinological, and morphological techniques. Results indicate that luteolysis occurs in Tg/Tg mice but is delayed by 1 day. Delivery did not occur in mutant mice at term after spontaneous luteolysis or even after removal of progesterone action by ovariectomy or antiprogestin treatment. Biomechanical and functional studies of the uterus and cervix revealed that the primary cause of failed parturition in Tg/Tg mice was not inadequate uterine contractions of labor but, rather, a rigid, inelastic cervix at term that was abnormally rich in neutrophils and tissue monocytes. Characterization of the transgene insertional mutant, Tg/Tg, indicates that progesterone withdrawal is insufficient to complete parturition in the presence of inadequate cervical ripening at term.