We investigated whether positive daily peer-interactions counteract the effects of isolation in Octodon degus. Twenty-five-day-old degus were either isolated (ISO), socially housed (SOCIAL), or isolated and allowed 1-hr daily peer interaction (PARTIAL-ISO). The animals were observed over 4 weeks. Just prior to isolation and after 2 weeks of individual housing, the subjects were assessed for response to pleasant stimuli via a sucrose preference test and to fearful situations in open field and startle tests. Two weeks after the previous tests, the subjects were retested as above and observed in novelty and sociability tests. Only the ISO group showed significant alterations in sensitivity to reward and increased risk-taking behavior in fearful situations. The ISO group consumed more sucrose, spent less time freezing in the startle test and exhibited increased exploration in open field and novelty tests compared to PARTIAL-ISO and SOCIAL groups. In the sociability test, the SOCIAL group vocalized more than the other two groups during encounters with an unfamiliar degus. Our findings suggest that (i) chronic isolation induces alteration of hedonic, emotional and social profiles, with a maturational delay in fear-related responses; (ii) friendly interaction attenuates most behavioral changes induced by total social isolation. However, the positive effects of daily social interactions did not fully counteract deficits in social vocalizations. Our study represents one of the few available studies focused not only on the consequences of negative life events in this species, but also the protective role of relatively short periods of positive social activity on subsequent emotional development. (C) 2010 Wiley Periodicals, Inc. Dev Psychobiol 53: 280-290, 2011.
