Figure 3.
Reference memory performance in the Morris water maze task. A–C, Data are illustrated as average latencies over testing days (A), average latency of days 5–7 across groups (B), and the free probe test (C). A, Control animals showed a decrease in latency time over the training days. A, B, Lesioning the cholinergic projection neurons in the NBM, MS/vDBB, or in both structures did not affect the learning capabilities of the rats. However, lesioning the dopaminergic neurons in the VTA resulted in disruption of the performance in these animals (A, filled symbols). B, Comparison of the performance between the groups on the average latency scores on days 5–7 when an asymptote was established in the control group showed that all VTA-lesioned groups took longer to find the platform to control animals. C, The free probe test confirmed that loss of dopaminergic neurons in the VTA resulted in a less-focused search for the platform, as shown by reduction in time spent in the target quadrant. Data are shown as mean latency values ±SEM. Difference compared with control group at *p < 0.05 (B: 1-way ANOVA, F (7,109) = 9.32, p < 0.0001, followed by post hoc Tukey HSD tests; C: 1-way ANOVA, F (7,109) = 7.48, p < 0.0001, followed by post hoc Tukey HSD tests). B, C, Groups are represented in the x-axis by presence (+) or absence (−) of a lesion in the given nucleus. Error bars indicate SEM.