A new method for studying social eavesdropping using male golden hamsters.

Social eavesdropping is a special type of social learning and it is defined as the act of extracting information from social interactions between conspecifics. Social eavesdropping has advantages in information gathering and has attracted increasing attention. Emerging studies on social eavesdropping have been reported in several species, but the lack of suitable and manipulable laboratory rodent models remains a challenge to the study of the underlying mechanisms of social eavesdropping. The aim of this study was to take advantage of golden hamsters and their agonistic behaviors to develop a new laboratory method to study social eavesdropping. Male hamsters with or without a defeat experience were used as bystanders and were exposed to either a fighting interaction or a neutral encounter between two male demonstrators in a social learning chamber for a 3-day social learning. The behavioral responses of the bystanders toward observed demonstrators were tested in a U-shaped maze before and after the 3-day social learning. We found that (1) bystanders were attracted to the winning demonstrators in both short-term and long-term tests in experiment 1; (2) bystanders with a brief defeat experience displayed the opposite behavioral pattern and avoided approaching the winning demonstrator in experiment 2. It is evident that these hamsters acquired information about the relative qualities and dominance of the demonstrators and behaved differently toward different conspecifics afterward. Collectively, male hamsters are capable of social eavesdropping and prior experience of defeat has a significant impact on their consequent behaviors. Our newly developed behavioral method offers several advantages and it is useful for the study of social eavesdropping and its underlying mechanisms.

A biological validation procedure for the measurements of fecal outputs and fecal cortisol metabolites in male Syrian hamsters.

Monitoring fecal outputs and fecal cortisol metabolites (FCM), a noninvasive technique, has been used to investigate physiological responses to stress and relationships between hormones and behavior in an increasing number of species. The aim of this study was to investigate whether measurements of fecal outputs and FCM can be used as indexes to repeatedly and precisely monitor stress levels in male Syrian hamsters using a social defeat as a biological validation method. The feces voided by each animal were collected every 3 h for at least 1 day before and after experiencing a single fighting interaction, and the extracted FCM during the pre- and post-fight phases was quantified by enzyme immunoassays. During the pre-fight baseline phase, both the number of fecal pellets and the FCM levels fluctuated throughout the whole day. Although the number of fecal pellets did not differ between the dark and light cycles, the levels of FCM were significantly higher during the dark cycle than during the light cycle. During the post-fight phase, the experience of fighting did not result in a significant difference in the number of fecal pellets per hour between the winner and loser groups, but did considerably increase the total amount of fecal outputs in both groups. The level of FCM was significantly higher in the loser group than in the winner group during the 1st and 7th 3-h collection periods after the fight, which indicated that the experience of defect affected the behavioral and physiological responses of the losers. Our findings suggest that measurement of FCM is sensitive enough to distinguish the stress levels between winners and losers after experiencing a fight. The measurements of fecal outputs and FCM levels provide new opportunities to longitudinally and frequently monitor behavioral and hormonal responses to stress in hamsters and other small laboratory animals.

Characterization of behavioural responses in different test contexts after a single social defeat in male golden hamsters (Mesocricetus auratus).

The objective of the present study was to characterize behavioural responses of male hamsters in each of three test contexts after they had experienced either a single social defeat or a neutral encounter. In experiment 1, hamsters were observed in a familiar social context (i.e., their home cages), and defeated males displayed different amounts of time and submissive behaviours towards a known opponent than a novel intruder, whereas males in the neutral-encounter groups did not show such differences. In experiment 2, in an unfamiliar social context (i.e., a Y-maze), defeated males generated submissive behaviours and fear memory towards a known opponent that they re-encountered 5-min and 24-h after the defeat. The formation of long-term memory was interrupted by an injection of anisomycin (210 mg/kg). In experiment 3, in a non-social, anxiogenic context, hamsters that had previously had different social experiences did not demonstrate additional anxiety in an elevated plus-maze, with the exception of males that had previously experienced repeated social defeats. Our data suggested that hamsters' behavioural changes following defeat are context-dependent and stimulus-specific. The experience of a single social defeat is sufficient to regenerate submissive behaviours and fear memory when reencountering a known opponent.