22-kHz ultrasonic vocalization in rats as an index of anxiety but not fear: behavioral and pharmacological modulation of affective state.

Ultrasonic vocalization (USV) was found useful for differentiating fear and anxiety in rats. These affective states were established through a Pavlovian conditioning procedure. Danger stimulus, preceding unavoidable tail shock, elicited acute fear. Intertrial situational cues evoked anxiety. A safety signal (SS) indicating the omission of shock inhibited fear. Sustained 22-kHz USV characterized anxiety and was present between trials. A signal of danger resulted in immediate inhibition of vocalization, while a SS reversed this effect. These results are discussed in the context of three theories: Pavlovian, Bollesian and Konorskian. The anxiolytic drugs diazepam and buspirone (1 and 5 mg/kg) suppressed vocalization in the intertrial and SS periods. The reaction to the signal of danger remained complete inhibition of USV. Anxiogenic pentyletetrazole (1 and 5 mg/kg) enhanced intertrial vocalization, but did not affect its reoccurrence during the SS. Anxiogenic FG7142 (5 mg/kg) did not affect intertrial vocalization, but blocked its reappearance on the SS. It is suggested that the behavioral target of both anxiogenic drugs is different-pentyletetrazole supposedly exerts its anxiogenic effect by increasing situational anxiety, whereas FG7142 suppresses inhibition of fear.