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. 2022 Jun 15;5:589. doi: 10.1038/s42003-022-03446-1

Fig. 1. Mkln1 deletion impairs locomotor habituation and exploratory behavior in novel environments.

Fig. 1

a Assessment of activity in the open-field expressed as a function of 5-min bins revealed sustained locomotion in Mkln1–/– mice across four test days (genotype: F(1,26) = 15.67, P < 0.01). b An activity change ratio calculated to examine locomotor habituation shows impaired intersession habituation in Mkln1–/– mice (genotype: F(1,26) = 8.0, P < 0.01; genotype × days: F(3,78) = 3.50, P < 0.05). c Home cage recordings over three days indicated increased activity levels during the dark (active) phase (shaded area: ZT0-ZT12) and low activity during the light (sleeping) phase of the cycle (ZT13-ZT24) in both genotype groups. d Waveform cosine curves (solid lines) with 24 h periods fitted to estimate the circadian rhythm pattern show that Mkln1 knockout does not alter synchrony to light–dark cycles. Circles correspond to averaged activity at 1-h intervals over three days of recording. Dashed lines on the y axis depict an estimate of the central tendency of activity distribution (Midline Estimating Statistic of Rhythm (MESOR)) for each genotype group. e Scheme of a modified open-field test in which mice could escape into a dark enclosed compartment. f Mkln1–/– mice displayed pronounced locomotion across 2 test days (genotype: F(1,24) = 8.64, P < 0.01). g Scheme of the open-field experiment in which a novel object was introduced mid-way during the experiment. h Both genotype groups showed comparable activity levels during the 30-min (no Obj) session to an empty arena. However, Mkln1–/– mice displayed a heightened response to the novel object as reflected in significantly increased locomotor activity (genotype × session: F(1,17) = 6.21, P < 0.05 followed by Bonferroni post hoc test for pairwise comparisons (*P < 0.05)). i Time spent actively interacting with the object was significantly higher in Mkln1–/– mice (genotype: F(1,17) = 10.39, P < 0.01), indicating enhanced exploration. j In the three-chamber social interaction test, both genotypes demonstrate clear sociability by spending significantly more time interacting with a novel conspecific (S1) over an inanimate object (O) with no social valence (stimulus type: F(1,26) =  108.45, P < 0.0001). k Deficient preference for social novelty in Mkln1–/– mice during the recall session. Compared with Mkln1+/+ mice, Mkln1–/– mice spent significantly more time in contact with the now-familiar (S1) conspecific. Also, Mkln1–/– mice engaged with the S1 and S2 conspecifics equally (social stimulus × genotype: F(1,26) = 6.11, P < 0.05) followed by Bonferroni post hoc test for pairwise comparisons (*P < 0.05, **P < 0.01). l Representative heat map images depicting the animal’s nose-point cumulative location within each compartment during the novelty preference (recall) session. A high signal (occupancy) is detected around the active exploration area. m The discrimination index was negative and significantly lower in Mkln1–/– mice relative to Mkln1+/+ controls (genotype: F(1,26) = 8.25, P < 0.01), indicating impaired social memory. Only Mkln1+/+ controls show a preference for the novel conspecific that differs significantly from random exploration (one-sample t-test: ##P < 0.01). For data related to (a, b) (Mkln1+/+ (N = 15: M = 8, F = 7)); Mkln1–/– (N = 15: M = 8, F = 7); c, d (Mkln1+/+ (N = 22: M = 11, F = 11); Mkln1–/– (N = 18: M = 11, F = 7); e, f and j–m (Mkln1+/+ (N = 15: M = 8, F = 7); Mkln1–/– (N = 15: M = 8, F = 7); g–i Mkln1+/+ (N = 11: M = 5, F = 6); Mkln1–/– (N = 10: M = 5, F = 5). Data are presented as means ± SEM.