Postpartum Luteinizing Hormone Release and Maternal Behavior in the Rat after Late-Gestational Depletion of Hypothalamic Norepinephrine

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Abstract
The effects of depletion of hypothalamic norepinephrine (NE) during late pregnancy on the postpartum ovulatory LH [luteinizing hormone] surge, the onset and maintenance of maternal behavior and lactation were examined in adult female rats. Bilateral transections of the ascending noradrenergic pathways (ANP) between days 14 and 17 of gestation resulted in a 70% depletion in hypothalamic NE content when assayed on day 6 postpartum. In spite of this depletion in hypothalamic NE content, a postpartum ovulatory surge of LH was observed in transected rats at 1800 h on either the day of parturition or 1 day later. The magnitude of the LH surge in experimental animals at this time appeared equal to that of controls. A 2nd group of transected and sham-transected rats was tested for maternal responsiveness postpartum and through day 6 postpartum. Primiparous transected females displayed normal maternal behavior during this period with only minor disruptions in nest-building behavior. The lactational performance of transected rats, however, was inferior to that of sham-transected animals. The hypothalamic content of NE in females that showed impairment of lactation was consistently below the NE content found in the controls. The importance of the noradrenergic system in the control of maternal behavior is discussed, and it is proposed that noradrenergic involvement in maternal behavior is modulatory rather than directly regulatory.

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