Development of the neural circuit that mediates maternal behavior in the rat

This thesis investigated the development of the neural circuit supporting maternal behavior in the rat. Juvenile (prepubertal) animals have fully functional neural circuits supporting maternal behavior and they express the behavior with very short latencies (1--3 days) after exposure to pups. This has been well studied and the evidence shows that the juveniles lack the initial adult aversive response to pups. Adults overcome this aversive response only at the end of pregnancy or after a long period (4--8 days) of exposure to pups. This less inhibited model of maternal behavior (juvenile model) helped to reveal how the different components of the neural circuit developed into an adult inhibited state and the mechanisms involved in the loss of that inhibition in the adult.;The first chapter of this thesis investigated whether the medial preoptic area (MPOA), critical for the performance of maternal behavior, was completely developed at puberty and whether the ovarian hormones were affecting its maturation during this period.;The second chapter investigated whether changes in the dopaminergic (DA) and serotonergic (5-HT) systems around puberty are involved in the maturation of the MPOA or other brain regions implicated in the inhibition (medial and cortical amygdala, MCA) or the facilitation (nucleus accumbens, NAC) of maternal behavior.;In the third chapter, I investigated whether the distribution of the DA and 5-HT fibers in the MPOA, MCA and NAC differ in adults and juveniles. No differences were found in the distribution of fibers for DA and 5-HT in these brain regions, suggesting that only the content but not the distribution of 5-HT and DA fibers undergo substantial changes around puberty.;Finally, in the fourth chapter I investigated whether the same brain regions engaged when maternal behavior is inhibited or stimulated in adults are also engaged when maternal behavior is inhibited or stimulated in juveniles.;I also investigated the areas of the brain engaged in the expression of pup-induced maternal behavior in adults and juveniles.;The results of these experiments support the hypothesis that important developmental changes occur around puberty that affect both brain regions commonly associated with the inhibition of maternal behavior (MCA, AH) and those involved in the facilitation of the behavior (MPOA/vBNST). (Abstract shortened by UMI.).