Armario, A., Ortiz, R., Balasch, J. 1983. Corticoadrenal and behavioral response to open field in pairs of male rats either familiar or non-familiar to each other. Experientia 39(11), 1316-1317.

The effect of the presence either of a familiar or non-familiar conspecific animal on serum corticosterone and some behavioral responses in the open field was studied in male Sprague-Dawley rats. Animals tested in presence of a familiar animal showed a higher corticosterone response and a higher defecation rate. It suggests that rats experienced more emotional reactivity in presence of a familiar animal than in presence of a non-familiar one. Time spent in social interaction was higher in non-familiar pairs; however, ambulation and rearing were lower, suggesting competition between social investigation and novel environment exploration.