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The effects of reproductive experience on prefrontal cortex dependent learning and memory and pyramidal cell morphology in the rat dam Crozier, Tamara May

Abstract

Pregnancy, parturition, and motherhood, collectively known as reproductive experience, bring about profound and enduring changes in the hormonal, neural, and behavioral profile of the female rat. Much of the research to date investigating the effects of reproductive experience on learning and memory and cellular morphology in the rat dam has focused on the hippocampus. These studies revealed enhancements in spatial working and reference memory as well as alterations in pyramidal cell morphology following reproductive experience. Interestingly, it has long been established that other brain regions undergo persistent changes in response to reproductive experience including the prefrontal cortex, yet there remains a paucity of research investigating this area. Thus, the objective of the following experiments was to determine the effects of reproductive experience on prefrontal cortex-dependent learning and memory as well as pyramidal cell morphology in the prelimbic region in nulliparous, primiparous, and multiparous rats. For Experiment 1, age-matched nulli-, primi- and multiparous rats were tested for seventeen consecutive days using the delayed spatial win-shift task. This experiment revealed that multiparous rats committed fewer within-phase and omission errors than nulli- or primiparous rats on Blocks 2, 3, and 4 as well as committing fewer across-phase errors in Blocks 2 and 4 than either the nulli- or primiparous groups. Furthermore, the total number of within-phase errors significantly and negatively correlated with an increase in the total time engaged in nursing behaviors. Using Golgi impregnation, pyramidal cell morphology in Laminae 2/3 and 5 of the prelimbic region of the prefrontal cortex was examined in Experiment 2. The results of Experiment 2 revealed that multiparous rats have more total branch points in the apical region of Lamina 2/3. In addition, arched-back nursing was found to significantly positively correlate with the number of branch points in apical and basal regions of Lamina 5. Passive nursing significantly correlated with the number of basal branch points in Lamina 5 and apical length in Lamina 2/3. The findings from these studies suggest that multiparity may be necessary in realizing the effects of enhanced learning and memory and morphological changes associated with the prefrontal cortex in female rats.

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