Our group uses modern neuroanatomical and molecular tools to investigate nervous system regulatory events that occur in animals when they respond and adapt to immune challenges, drug administration, psychosocial stress, or environmental enrichment. Behavior is characterized in validated tests for anxiety, depression, and social interactions. Responsive brain structures and cell types are identified and characterized by GFP-positive cell tracking in reporter animals, immunohistochemistry, in situ hybridization histochemistry, and cell sorting followed by phenotypic analyses. In addition to histochemical tools, we perform quantitative molecular assays for gene expression and protein levels as well as in vitro and ex vivo assays of isolated neurons, glia, and lymphocytes. We have examined the relationships among defeat-induced depressive states and environmental enrichment, the basis for stress resiliency or susceptibility, responsive brain circuits, and roles played by adult neurogenesis and adrenal hormones. Recent work on bi-directional communication between the brain and the immune system showed the ability of lymph node immune cells to be antidepressant agents. Our studies guide further work aimed at understanding the circuit, cellular, and molecular bases for altered emotionality.