Distress vocalization in rat pups. A simple screening method for anxiolytic drugs.

A method is described for reproducible measurement of ultrasonic vocalization induced by tail-holding stress in rat pups. The anxiolytic benzodiazepines, chlordiazepoxide, diazepam, and CL 218872, reduced the ultrasounds at doses inducing little CNS depressant activity. Gross behavioral disruption such as sedation (muscimol, prazosin, and chlorpromazine), tremors (yohimbine), myoclonus (MK 212), and immobility (morphine) resulted in reduction of ultrasounds. Non-behaviourally active doses of these compound or any doses tested of mephenesin, amphetamine, amitriptyline, haloperidol, and naloxone did not affect the ultrasounds. Metergoline inhibited ultrasounds at doses producing little change in overt behavior. This method is proposed as a convenient model of anxiety which may also be influenced by central 5-hydroxytryptamine transmission.