Infant rat separation is a sensitive test for novel anxiolytics.

1. Rat pups emit ultrasonic calls during brief episodes of social separation. These calls have been variously described as "distress" calls and may be related to the separation cries expressed by the young of many mammalian species. 2. Ultrasonic call of rat pups are modulated by environmental stimuli such as ambient temperature, olfactory and tactile stimuli associated with the nest. 3. Calls are also sensitive to a variety of purported anxiolytic and anxiogenic drugs, including the benzodiazepines, serotonin agonists, and ligands at the NMDA-glycine receptor complex. 4. In addition to providing a simple test for the anxiolytic properties of drugs, this model may also provide new insights about the development and neurobiology of anxiety.