Recognition indices (RI; means+SEM) calculated from investigation durations during choice for the two experimental series.

<p><b>A</b> shows that In the first experimental series the RIs of all tested groups [129S1/SvImJ (129/S1), Hyb1, Hyb2, C57BL/6JOlaHsd (C57-Ola)] of both male (white bars) and female ES (black bars) were significantly higher than 50 (chance) indicating an intact long-term recognition memory. <b>B</b> illustrates that in the second experimental series genotypes 129S1/SvImJ (both sex), Hyb2 (both sex), C57BL/6JOlaHsd (both sex), and Hyb1 males showed a significantly higher RI than 50 indicating an intact recognition memory. Hyb1 = F1-hybrid line (♀129S1/SvImJ×♂C57BL/6JOlaHsd), Hyb2 = F1-hybrid line (♀C57BL/6JOlaHsd×♂129S1/SvImJ), C57-Ola = C57BL/6JOlaHsd, 129/S1 = 129S1/SvImJ; numbers in bars = animals/group. * p<0.05, ** P<0.01 and *** P<0.001, one sample t-test <i>versus</i> 50.