Dokument

Summary:
Rats are highly social animals. They have developed a variety of social behaviors including communication via so-called ultrasonic vocalizations (USV). Among these USV, two types can be distinguished in juvenile and adult rats. Appetitive 50-kHz USV are thought to represent a positive affective state, whereas aversive 22-kHz USV are supposed to depict a negative affective state. Playback of positive 50-kHz USV induces an approach behavior in rats as seen by their approach behavior to the sound source. Previous studies have shown that this behavior is only detectable during the first presentation, whereas a quick habituation towards 50-kHz USV results in the rats not approaching the 50-kHz USV playback a second time, even after several days. This habituation phenomenon seems to rely on learning and memory mechanisms. However, its underlying mechanisms have been studied scarcely so far. This dissertation revealed three factors influencing the habituation phenomenon. First, habituation was dependent on stocks. It was only present in Wistar but not Sprague-Dawley rats. Second, habituation could be prevented with treatment of the dopaminergic agonist d-amphetamine before the second 50-kHz USV playback. Third, habituation was state-dependent. It was shown that when the pharmacologically induced internal state changed between the two playbacks, no habituation occurred. Furthermore, the reciprocal nature of USV was investigated in this dissertation. Calls in response towards 50-kHz USV playback had been reported before, but this dissertation is the first to characterize response calls. We showed that response calls towards 50-kHz playback are around frequencies of 30 kHz, have a rather short duration of 0.3 s and hardly any frequency modulation. These parameters resemble aversive 22-kHz calls, which are unlikely to be found in an appetitive paradigm as the 50-kHz USV playback. Feasible functions of these response calls might be a frustrated state due to expectation violation after playback, appeasement calls to pacify the potential play partner indicated by the playback, or they might serve as social contact calls to establish proximity. Taken together, the findings of this dissertation shed light on the reciprocal nature of USV communication indicated by response calls towards 50-kHz USV playback and present possible mechanisms how to overcome the habituation phenomenon. This provides tools to further investigate neurodevelopmental disorders where communication and social behavior is impaired, such as autism spectrum disorder or the Angelman Syndrome, as well as affective disorders.

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