Social competition in rats: a test sensitive to acutely administered anxiolytics

Male Wistar rats were housed in groups of three (triads) and given brief sessions during which sweetened milk was available in a drinking bottle. The rats showed intense competition to obtain access to the milk and in many groups a stable rank order was formed of a dominant, an intermediate and a subordinate rat, when assessed as the amount of access to the drinking tube. When the subordinate rats were injected with the anxiolytic drugs chlordiazepoxide (1.25-20mg/kg), buspirone (0.3-5.0mg/kg) and alpidem (2.5-20mg/kg) and low doses of the hypnotic, zolpidem (0.125-2.0mg/kg) they increased their access to the milk. These increases were generally at the expense of the dominant rats whose access decreased. The effect of alpidem (5mg/kg) was antagonized by flumazenil (10mg/kg). Increases in access in subordinate rats were not seen after haloperidol (0.025-0.2mg/kg), imipramine (5, 10mg/kg) or morphine (2.5-10mg/kg). As the anxiolytic drugs were active at relatively low doses this test of social competition may provide a particularly sensitive and selective procedure for detecting and evaluating the actions of drugs from this class.