Lateral septal vasopressin in rats: Role in social and object recognition?

The capacity of male rats to remember familiar conspecifics is called social recognition. It is a form of short-term memory modulated by lateral septal (LS) vasopressin (VP). The specificity of this phenomenon was studied by examining whether recognition of previously investigated objects is also under control of lateral septal VP. For social recognition male Wistar rats were confronted with juveniles for 5 min. Re-exposure to the same juvenile took place after 30 or 120 min, or with a different juvenile after 30 min. This procedure was duplicated for object recognition using a plastic food cup or a 50 ml Erlenmeyer flask. After these initial tests osmotic minipumps and brain cannulae were implanted, infusing VP receptor antagonist into the LS (dPTyr(Et)AVP, 1 ng/0.5 mu 1/h, bilateral). Animals were re-tested for social and object recognition using 30 min re-test interval (same juvenile or object). We reproduced previous reports concerning social recognition; animals recognized juveniles after 30 min, not after 120 min and VP antagonist treatment blocked recognition. Testing for object recognition revealed a reduction in investigation time at the 30 min interval (same and different object), but not after 120 min. VP antagonist treatment was unable to block object recognition. The data suggest that, in contrast to social recognition, object recognition reflects a form of habituation, which is not under the control of lateral septal VP.