Department of Medical Pharmacology, Rudolf Magnus Institute for Neurosciences, Utrecht University, Utrecht, The Netherlands
The social recognition paradigm is based on the observation that an adult male rat investigates a conspecific juvenile rat less during a second encounter, when the time interval between the encounters is relatively short. The diminished investigation is considered as recognition of the conspecific and is not present when a novel juvenile is encountered during the second exposure.
Social recognition can easilly be measured using a recently described protocol (Engelmann et al., Physiol. Behav. 58:315-321, 1995). During a 5-minute exposure period a juvenile rat is placed in the home cage of an adult rat. During this period the time spent by the adult male rat while investigating the juvenile is measured. This investigatory behaviour typically consists of following, sniffing, anogenital sniffing and grooming of the juvenile rat. After this first exposure the juvenile is removed from the home cage of the adult rat. Following a time interval the same juvenile and a novel juvenile are placed in the home cage of the adult rat for a second exposure period of 5 min. When the time interval between the first and second exposure is 30 min, the adult rat investigates the novel juvenile more than the same juvenile during the second exposure. This indicates that the adult rat recognizes the same juvenile. With a time interval of 2 h the adult rat investigates the same and novel juvenile equally, indicating that social recognition is not present anymore.
The social recognition paradigm can be employed to demonstrate effects of drugs or other experimental treatments on memory-related processes, which is demonstrated by an experiment with the vasopressin (VP) metabolite VP4-8. When VP4-8 was subcutaneously administered to the adult rat in a 1 ęg/kg dose 1 minute after the first exposure, social recognition was observed with an interexposure interval of 2 h. The same rats injected with saline did not show any social recognition using the same test procedure. These results suggest that the VP metabolite VP4-8 affects memory-related processes involved in social recognition in rats.