Amygdala and Neurogenesis Figure 2. Effects of chronic treatment with fluoxetine on levels of cell proliferation and survival in the dentate gyrus of the hippocampus and depression-like behavior during the forced swimming test after neurochemical lesions of the basolateral complex of the amygdala (A,B,C) and according to anxiety (D,E,F). Error bars represent the standard error of the mean. [**p,0.01, *p,0.05 vs. corresponding vehicle group (ANOVA main effect); ++p,0.01, +p,0.05 vs. corresponding vehicle group (ANOVA simple main effect). doi:10.1371/journal.pone.0008618.g002 on indices of cell proliferation and survival and of depression-like behavior. Although ANOVAs performed respectively on Ki67- (see section D in Figure 2) and BrdU-IR (see section E in Figure 2) cell number indicated a lack of effect of anxiety on either of these indices of neurogenesis (all n.s.), a significant facilitating effect of fluoxetine treatment (all p,0.5) was observed. No significant interaction between these two factors was seen in either case. Analysis of the behavioral outcome (see section F in Figure 2) indicated that high anxiety was significantly associated with prolonged immobility in the forced-swim test (p,0.05). While there was no effect of fluoxetine (n.s.), there was a significant interaction between the two factors (p,0.05), and a simple effects analysis confirmed that fluoxetine decreased immobility time only in the HA group (p,0.01). Correlational analyses between indices of anxiety, cell proliferation and survival and depression-like behavior We then performed correlational analyses to address the following key questions: (i) whether differences in anxiety levels play a role in the studied effects, and (ii) whether there is a relationship between indices of neurogenesis and depression-like behavior. The analyses were performed on data from all animals in the study and then separately for each experimental group (see correlational matrix in the Table S2). Anxiety levels showed significant positive correlations with immobility in the forced-swim test both for the whole sample (r = 0.30, p,0.05) and for the BLA/Vh group (r = 0.79, p,0.01). Meanwhile negative correla- tions with Ki67-IR cell number were found in the same, BLA/Vh group (r = 20.77, p,0.01) and with BrdU-IR cells in the Sh/Vh group (r = 20.75, p,0.01). Exclusively for BLA/Vh animals was the immobility time in the forced-swim test negatively correlated with the levels of Ki67-IR cells (r = 20.67; p,0.01) and positively correlated with the levels of cell BrdU-IR cells (r = 0.75; p,0.05). For the other experimental groups, no significant correlations were observed. Structural equation modeling Construction of the models was guided by the results from the ANOVAs and the correlational matrix (see above) on the relationships between the six studied variables (fluoxetine treat- ment, BLA lesion, anxiety levels, Ki67, BrdU, and FST immobility). Details for total and indirect effects and path strength differences for the presented models are shown in Tables S3 to S9. In the text, below, only significant relationships (and occasionally nearly significant trends) are indicated. A general model (Figure 3) was generated in which a relational structure between the variables was proposed to test the direct or indirect impact of each of the 3 predictor variables (fluoxetine treatment, BLA lesion, anxiety levels) on the 3 output measures (Ki67, BrdU, and FST immobility) and in turn of the neurogenic PLoS ONE | www.plosone.org 5 January 2010 | Volume 5 | Issue 1 | e8618