Fig. 2. Learning impairment of mutant mice during a place-avoidance.

a The learning ability of the mouse was experimentally tested with a place-avoidance task driven by an aversive stimulus. The mouse was free to explore an O-shaped maze, triggering an air puff each time it passed through a fixed location; after the mouse learned to avoid that position, the puff was moved to another location. The test is repeated with two groups of mice: a control group, and a group in which the astrocytic type 1 cannabinoid receptors had been knocked out (mutant). b Mutant mice showed slower learning with respect to control mice, only during reverse learning (Day 4). On each day, the mouse is free to explore the maze for a single session of 10 minutes, and the number of visits to the puff position is recorded. The box plots represent the statistics from 15 (control) and 17 (mutant) animals. There is no significant difference between the groups on Day 1, 2, and 3 (Day 1: 6.59 ± 0.73 vs. 6.13 ± 0.62, p = 0.62; Day 2: 1.41 ± 0.21 vs. 1.40 ± 0.34, p = 0.73; Day 3: 6.00 ± 1.50 vs. 7.27 ± 1.45, p = 0.45; two-sided Mann-Whitney U-test), while there is a very significant difference on Day 4 (Day 4: 3.65 ± 0.50 vs. 5.93 ± 0.61, p =  0.0066, two-sided Student’s t-test). The inset axis shows the same data for Day 4, binned into two 5-minute intervals. Each point is computed as the average over all the animals, and the error bar is the standard error. In the first 5 minutes, the mutant mice visited the puff position significantly more than the control mice, showing a learning deficit. In the last five minutes, the difference is no more observed. Figures adapted from ref. ³².