The effects of pre-test social deprivation on a natural reward incentive test and concomitant 50 kHz ultrasonic vocalization production in adolescent and adult male Sprague-Dawley rats

In rats, ultrasonic vocalizations (USVs) are often used as a measure of affect, with 22 kHz USVs reflecting negative affect and 50 kHz USVs reflecting positive affect. This study used a modified reward approach task to assess behavioral approach and concomitant USV production toward either a food or social stimulus following varied amounts of pre-test social deprivation in both adolescent and adult rats. Adolescents spent significantly more time investigating the social stimulus than adults, although in the presence of the social stimulus isolate housed adults emitted more 50 kHz USVs than isolate housed adolescents. Isolate housed adults emitted more USVs to a social stimulus than adults that received less pre-test social isolation, a social deprivation effect not evident in the social approach data or any measure when animals were tested with a food stimulus. When tested with a food stimulus, adults emitted more 50 kHz USVs than adolescents, although they spent the same (or even less) time investigating that stimulus than did adolescents. Together, these data demonstrate that 50 kHz USV production and time spent investigating a rewarding stimulus are clearly dissociable and hence seemingly measure different states.

► There were no effects of social isolation on investigation of a food or social stimulus.
► Isolation increased 50 kHz USV production in to social but not food stimulus at either age.
► Adolescents investigated a social stimulus more than adults with no differences in USVs.
► Adults USV more to food than adolescents, no differences in investigation of food.
► There was a dissociation between investigation of a rewarding stimulus and USV production.