Adult <i>En2</i>−/− exhibit absence of sociability and deficits in male-female social interactions.

<p>Social approach was tested in two separate cohorts using our automated three-chambered apparatus. Cohort 1: (<b>A</b>) <i>En2</i>+/+ and +/− displayed sociability, defined as spending more time in the chamber with the novel mouse than in the chamber with the novel object. <i>En2</i>−/− did not spend more time in the novel mouse chamber as compared to the novel object chamber, meeting the definition of lack of sociability for this task. (<b>B</b>) <i>En2</i>+/+ and +/− spent more time sniffing the novel mouse than the novel object. <i>En2</i>−/− did not spend more time sniffing the novel mouse than the novel object, meeting the definition of lack of sociability on this more sensitive parameter of social interaction, and confirming results from the chamber time parameter investigation. (<b>C</b>) No genotype differences were found for time spent in each chamber during the habituation phase. Cohort 2: (<b>D</b>) Similar lack of sociability was seen in <i>En2</i>−/− mice for time spent in the novel mouse chamber vs. the novel object chamber. (<b>E</b>) <i>En2</i>−/− mice again failed to spend more time sniffing the novel mouse vs. the novel object. (<b>F</b>) Time spent in each chamber during the habituation phase was not different between genotypes. Cohort 1: N = 16+/+, N = 16+/−, N = 15−/−; Cohort 2: N = 10+/+, N = 13+/−, N = 14−/−. *p<05 vs. novel object. Reciprocal social interactions and ultrasonic vocalizations (USVs) were measured in male <i>En2</i> mice during interaction with an unfamiliar estrus female mouse. (<b>G</b>) <i>En2</i>−/− males spent less time engaged in sniffing the body and anogenital regions of the female as compared to +/+ males. (<b>H</b>) The total number of USVs emitted during the test session did not differ between genotypes. (<b>I</b>) No genotype differences were found for bouts of test cage exploration during the 5-minute test session. N = 10+/+, N = 13+/−, N = 13−/−. *p<05 vs. +/+.