Abstract
Rats are highly social animals known to communicate with ultrasonic vocalizations (USV) of different frequencies. Calls around 50 kHz are thought to represent a positive affective state, whereas calls around 22 kHz are believed to serve as alarm or distress calls. During playback of natural 50-kHz USV, rats show a reliable and strong social approach response toward the sound source. While this response has been studied in great detail in numerous publications, little is known about the emission of USV in response to natural 50-kHz USV playback. To close this gap, we capitalized on three data sets previously obtained and analyzed USV evoked by natural 50-kHz USV playback in male juvenile rats. We compared different rat stocks, namely Wistar (WI) and Sprague-Dawley (SD) and investigated the pharmacological treatment with the dopaminergic D2 receptor antagonist haloperidol. These response calls were found to vary broadly inter-individually in numbers, mean peak frequencies, durations and frequency modulations. Despite the large variability, the results showed no major differences between experimental conditions regarding call likelihood or call parameters, representing a robust phenomenon. However, most response calls had clearly lower frequencies and were longer than typical 50-kHz calls, i.e., around 30 kHz and lasting generally around 0.3 s. These calls resemble aversive 22-kHz USV of adult rats but were of higher frequencies and shorter durations. Moreover, blockade of dopamine D2 receptors did not substantially affect the emission of response calls suggesting that they are not dependent on the D2 receptor function. Taken together, this study provides a detailed analysis of response calls toward playback of 50-kHz USV in juvenile WI and SD rats. This includes calls representing 50-kHz USV, but mostly calls with lower frequencies that are not clearly categorizable within the so far known two main groups of USV in adult rats. We discuss the possible functions of these response calls addressing their communicative functions like contact or appeasing calls, and whether they may reflect a state of frustration. In future studies, response calls might also serve as a new read-out in rat models for neuropsychiatric disorders, where acoustic communication is impaired, such as autism spectrum disorder.
Highlights
Acoustic communication among conspecifics is an important aspect of the social life of many species and often essential for maintaining stable social structures
We showed, amongst others, that the social approach response toward 50-kHz calls is a stable phenomenon that occurs in Wistar (WI) and Sprague-Dawley (SD) rats and that it can be modulated by administration of the dopaminergic D2 receptor antagonist haloperidol (Halo; Berz et al, 2021)
We characterized response calls emitted by rats exposed to playback of appetitive 50-kHz ultrasonic vocalizations (USV), previously shown to function as social contact calls (Wöhr, 2018)
Summary
Acoustic communication among conspecifics is an important aspect of the social life of many species and often essential for maintaining stable social structures. Vocalizations with frequencies around 50 kHz are thought to represent a positive affective state usually emitted during appetitive situations like play or mating (Knutson et al, 1998; Panksepp, 2005). These appetitive calls are typically characterized by frequencies between 35 and 80 kHz and durations in a range of 10–150 ms (Burgdorf et al, 2008; Wöhr et al, 2008; Takahashi et al, 2010). They were repeatedly reported to occur during drug withdrawal (Ma et al, 2010; Simmons et al, 2018)
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