Date of Award


Document Type


Degree Name

Master of Arts




Hormonal fluctuations and maternal behavior associated with pregnancy and postpartum care of pups induce many changes in the female rat. Circulating hormonal surges during pregnancy modify the female brain in preparation for motherhood. Past studies identify the medial preoptic area, the hypothalamus and the basal forebrain as structures dense in hormonal receptors involved in controlling reproductive behavior. The hippocampus and amygdala possess many hormonal receptors. Neurons exposed to pregnancy hormones develop new synapses and increased spine density, changes reflected in behavioral preparations, such as nest building and increased foraging, for the new pups. Following the experience of birth, pup stimulation interacts with hormonal alterations to continue to change the brain and resultant behavior of the mother rat. Recently, behaviors not traditionally associated with maternal behavior, specifically learning and memory, have been found to be enriched following reproductive experience. Attenuation in stress responsiveness may be related to this observation.

This study examined stress responsiveness in primigravid, multigravida, primiparous, multiparous and nulliparous female rats exposed to a stressor (an open field) for thirty minutes, then processed for c-fos immunoreactivity of the amygdala and hippocampus (structures associated with stress perception and response). The nulliparous (control) group displayed the highest stress responsiveness on both behavioral and biocellular (c-fos expression) measures. Gravid animals exhibited the greatest stress attenuation on these measures. Parous groups displayed less stress attenuation than the gravid groups but more than nulliparous groups indicating these changes may persist beyond the reproductive experience.

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