Diazepam and gepirone selectively attenuate either 20-32 or 32-64 kHz ultrasonic vocalizations during aggressive encounters.

Abstract

Ultrasonic vocalizations (USV) in rats may communicate "affective" states, as they occur only in highly significant behavioral contexts such as during sex, aggression, exposure to painful or startling events. This proposal was evaluated in an experiment with adult male Long-Evans rats during agonistic encounters; specifically, the effects of diazepam, flumazenil and gepirone were studied on different types of USV emitted by intruder rats exposed to resident attacks and to "threat of attacks" (i.e., intruder protected within the home cage of the resident by a wire mesh cage). USV were readily emitted during agonistic encounters and consisted primarily of two distributions of pure tone whistles: 0.3- to 3-s, 20- to 32-kHz ("low") signals and 0.02- to 0.3-s, 32- to 64-kHz ("high") signals. A considerable repertoire of frequency modulated signals was observed and proved to be sensitive to the anxiolytic treatments. Diazepam (1-6 mg/kg) dose-dependently decreased high frequency USV during the threat of attack and decreased the mean pitch of the most predominant vocalizations but did not affect low frequency USV or the audible squeals (AS) in response to bites. Gepirone (0.3-6 mg/kg) dose-dependently decreased low frequency USV and did not affect high frequency USV or AS. Responses to thermal pain stimuli remained unaltered by all drugs, while walking duration was decreased and crouch postures were increased after diazepam but not after gepirone administration. Gepirone in the present dose range had minimal effects on submissive, exploratory and locomotor behaviors. The pattern of results is consistent with the proposal that low frequency USV reflect a heightened affective state which is ameliorated with 5HT1A but not benzodiazepine anxiolytics, and suggests that the suppression of high frequency USV in reaction to attacks or threats coincides with the sedative or muscle relaxant properties of these compounds.