Figure 3. Horizontal and rearing activity per minute in an activity box open field test. (A) Activity in the first 5 minutes – the exploratory phase – decreased with aging for both males and females. The decline in horizontal (pM7-22=0.0065, pF7-22=0.0006; Student’s t-test) and rearing activities (pM7-22=0.0003, pF7-22=0.068; Mann-Whitney) indicated that exploratory behavior was highly affected by age. (B) Activity in 1-hour sessions of the same test. Horizontal activity was not altered from 7 to 22 months of age, whilst rearing activity declined for both female and male hybrids, thus illustrating an aging effect (pF7-22=0.043, pM7-22=0.043; Mann-Whitney). The decrease in horizontal activity observed in 15-month-old females was likely caused by different handling of this particular group due to technical reasons (see Methods). Values are mean ± SEM; nM7=7, nM15=10, nM22=10, nF7=10, nF15=12, nF22=7.