While evidence has linked growth factors such as BDNF to environmental complexity (EC), responsiveness to stress, and antidepressant action, few studies focused on the role of the FGF system in emotional reactivity. Recent data from our laboratory suggest that a single postnatal injection of FGF-2 significantly alters locomotor activity in response to a novel environment (Turner et al., SFN abstracts 2004). Since increased responsiveness to novelty is associated with decreased anxiety-like behavior, we propose that FGF-2 may be correlated with other indices of emotionality. We tested the hypothesis that changes in emotionality associated with EC may be related to FGF-2 gene expression in the hippocampus. Young adult male Sprague-Dawley rats were either exposed to a complex environment for 21 days or to standard cages. Following this treatment, rats were returned to standard cages for two weeks. Brains were then processed for neurogenesis by BrdU and Ki-67 immunohistochemistry. Another group of rats was tes...