This mentored scientist development award proposes a program of research and training to extend the candidate's ethological perspective to incorporate molecular and neural aspects of behavioral regulation. This program will (1) strengthen and deepen the candidate's neuropharmacological and neuroanatomical skills gained at the Division of Developmental Psychobiology of Columbia University, (2) provide training in neuroendocrinological and molecular biological concepts and techniques in collaboration with specialized laboratories at Columbia University, Rockefeller University and CUNY, (3) apply these skills to investigate the development of behavioral regulation in the infant animal. The specific research aim of the proposed study is to investigate the molecular and neural substrates that underlies behavioral and endocrine stress responses, and the contribution of these substrates to developmental changes during early ontogeny in the rat. This will be done by (1) determining how different stressors that are ecologically relevant at different times during development induce defensive immobility and endocrine activation, (2) examining how early experience such as a different social environment modifies these stress responses, (3) assessing the role of corticotropin-releasing factor in limbic and brainstem areas in these stress responses and their developmental changes.