LAY ABSTRACT IBN-9815478 Lactation and Weaning Effects on Autonomic Nervous System Function This application proposes preliminary studies of the effects of lactation on autonomic nervous system (ANS) function. Human and animal research suggests that during lactation, responses to stress are diminished. Specifically, hypothalamic-pituitary-adrenocortical and sympathetic-adrenal medullary responses to stressors are blunted under lactation. Human work from our laboratory indicate that lactational status affects sympathetic (SNS) and parasympathetic (PNS) nervous system measures during rest and in response to stress. Lactators showed a relatively high baseline SNS activity compared with Non-Lactators; however Non-Lactators showed more SNS responsivity to stressors. Weaning may alter ANS function as well. Lactators had a high coactivation of the SNS and PNS systems, with the latter predominating, while Weaning- Lactators showed coinhibition of the SNS and PNS systems. In addition, Weaning-Lactators showed relatively greater SNS responses to laboratory stressors. An investigation of these alterations in neuroendocrine regulation during lactation require procedures that are not possible in human mothers; therefore, it is necessary to develop an animal model to investigate the effects of lactation and weaning on cardiac autonomic function during baseline and in response to stressors. The hypotheses are that compared with lactating animals, weaning animals will have greater baseline heart rates and lower baseline heart period variability and will react to stressors with greater heart rate increases and greater decrements in heart rate variability. First and foremost, the proposed experiments will determine whether rats show ANS alterations as they do HPA changes in lactation and weaning. Secondly, the experiments will determine whether rats show ANS alterations similar to those found in human mothers, and therefore, whether rats are a suitab le model for normal function in health humans. Furthermore, procedural parameters must be investigated, e.g., at what day postpartum and postweaning are there maximal lactational effects on ANS. The proposed studies address these questions about feasibility and inform subsequent, more comprehensive studies of mechanisms underlying lactational effects on ANS function. If this rat model is suitable, future experiments proposals to NSF will address the underlying physiology of these effects using pharmacological blockade and surgical techniques to determine SNS and PNS contributions, hormonal assay and administration of agonists and antagonists to determine the role of oxytocin and prolactin in mediating the ANS effects of lactation, and bioenergetic issues.