Figure 2: Social withdrawal in Lrfn2 KO mice.

(a) Postweaning body weight curve of male WT and Lrfn2 KO mice in-housed in groups (WT, n=10 mice; Lrfn2 KO, n=10 mice from two independent experiments; *P<0.05, **P<0.01, t-test) or singly after weaning at 3 weeks (WT, n=5 mice; Lrfn2 KO, n=7 mice). (b–d) Reciprocal social interaction test. The test was conducted on 3 consecutive days, each time with a different intruder mouse (10-week-old DBA2 male) that was new to resident mouse. (b) Snapshots of social behaviour in WT and Lrfn2 KO mice taken from representative experiments (Supplementary Movies 1 and 2). Arrowheads indicate the hiding mouse. (c) Time spent in each behaviour during 5 min total observation time. The inset shows the sum of time spent in avoidance behaviour, including escape, freezing and hiding (n=10 mice per genotype; *P<0.05, **P<0.01, t-test). (d) The number of contacts was significantly lower in the KO than in the WT (***P<0.001, two-way ANOVA). (e) Social interaction in a 3-chambered approach task. An empty cage or a cage with a stranger mouse (10-week-old DBA2) was placed in each side chamber. Left, time spent in each chamber during 5 min total observation time. Right, number of contacts with each cage (n=16 per genotype; *P<0.05, **P<0.01, one-way ANOVA). (f) Courtship vocalizations of adult male mice. USV were recorded from adult males exposed to a female mouse in oestrous. Number, duration, and peak frequency of the USV during the 5-min exposure were quantified (WT, n=13 mice; KO, n=12 for number; WT, n=12; KO, n=6 for duration and peak frequency. *P<0.05, U-test).