A conspecific attenuates prolactin responses to open-field exposure in rats

Acute exposure to a novel environment, such as an open field, generally res ults in a prolactin surge, while several days of exposure to the open field is often characterized by a decline in prolactin. As exposure to the open field is a psychological stressor, altering the animal's interpretation of the event should alter prolactin levels. In the present study, juvenile mal e and female rats were habituated to the open field for 1 or 5 days prior t o testing in the chamber alone or with a same-sex conspecific. Levels of pr olactin were measured across all rats, and play (pins) was recorded for ani mals tested with a conspecific. Five days of habituation to the chamber res ulted in lower levels of prolactin and more play than 1 day of habituation. Across both conditions of habituation, testing with a conspecific caused l ower levels of prolactin than testing alone. In addition, play and prolacti n were negatively correlated. The presence of a conspecific in a stressful situation may have reduced stress by altering the animal's negative interpr etation of the open field. Further, as the intensity of the social interact ion increased (more play), prolactin levels decreased. (C) 2000 Academic Pr ess.