Fig. 1.

The ultrasonic vocalization apparatus and set-up are shown for Trial 2 (reintroduction across a barrier) and Trial 3 (physical interaction). A) In Trial 2 the cagemates were reintroduced across a perforated plastic grid that allowed sniffing and nose-touching but no other physical interactions. B) In Trial 3 the grid was removed from the apparatus and the cagemates were allowed to freely interact, and USVs recorded. Trial 3 was also videotaped and scored for activity, time interacting, and time engaged in anogenital investigation. During Trials 1 (habituation of each rat separately) and 4 (separation at the end of the test) the animals were alone in the apparati and recorded separately (images not shown).