This proposal was designed to prepare the candidate for an independent career in neuroscience research. It includes training and research plans. The training plan combines formal mentorship and consultations, didactics, seminars, and meetings, all designed to provide: 1) expertise in the breeding, maintenance, and characterization of inducible transgenic mice;2) expertise in molecular and genetic approaches for tracing complex neural circuits from defined populations of neurons;3) a fund of knowledge in neurobiological issues that will enhance the candidate's ability to think creatively about animal models of psychiatric illness as they pertain to the regulation of neural circuits by stress and the environment;4) exposure to ethical issues in the responsible conduct of science;and 5) experience in effective laboratory management and mentoring trainees. The research plan entails an analysis of the role of adult-born neurons in hippocampal plasticity. Recent evidence implicates adult hippocampal neurogenesis in response to stress and antidepressant treatment. However, little is known about the contribution of adult-born neurons to the cellular composition of the dentate and to hippocampal projection circuits. In this research proposal, the investigator intends to determine the representation of adult-born neurons within the cellular structure of the dentate gyrus and within hippocampal projections over time. The effects of stress and antidepressant treatment on neuronal turnover and associated projections will also be assessed. Inducible transgenic mice will be used to restrict expression of reporter proteins to neuronal progenitor cells in adult animals. A series of viral and transgenic approaches will be used to restrict expression of trans-synaptic markers to neuronal progenitors. The outlined approaches will allow the investigator to assess how adult-born neurons are represented in the dentate gyrus and in hippocampal connections as a function of time and behavioral/pharmacologic manipulations. Completing the proposed research will define how adult-born neurons contribute to hippocampal plasticity. Completing the training and research plans will lead to establishing the candidate as an independent investigator with expertise in using molecular biological techniques to study how genes and experience modulate complex neural circuits.