Angst und Furcht in der Ratte - über den Einfluss situationsspezifischer und biologischer Faktoren auf das Spektrum der Ultraschallvokalisationen

Change-sensitive modeling of anxiety and fear in appropriate model organisms is essential for understanding pathological anxiety. In rats, the emission of ultrasonic vocalizations (USV) is commonly understood as an expression of emotional arousal coupled to situations of varying valence. Here, appetitive situations such as play behavior, mating, and the administration of addictive drugs are associated with vocalizations in a frequency range of around 50 kHz. Aversive conditions, such as the acute threat of predators or similarly threatening manipulations in the laboratory, on the other hand, are associated with vocalizations in a frequency range of around 22 kHz. The production of 50- and 22-kHz USV is thought to be mutually exclusive because they are controlled by fundamentally different, neural mechanisms, which has largely precluded consideration of 50-kHz USV in aversive contexts until now. However, a clear dichotomy of USV production cannot be maintained, as both inherently appetitive situations may well be accompanied by 22-kHz USV, whereas 50-kHz USV is equally emitted in non-explicitly rewarding or social contexts. Instead, it will be shown that USV emission occurs in a spectrum that makes the productions of 50- or of 22-kHz USV more likely depending on situation-specific and biological factors. Of particular interest in this context is the consideration of anxiety and fear as distinct phenomena that influence the spectrum of USV in different ways. Here, anxiety is understood as a response to uncertain and ambiguous situations, whereas fear is defined as a response to realistic, often imminent threat from specific stimuli with corresponding discrete behavioral responses. In the present studies, a variety of methods, apparatuses, and tests were used to allow investigation of situation-specific influences on USV emission. Standard procedures for measuring anxiety-like behavior (elevated plus-maze) and conditioned fear were supplemented by confrontation with predator odor and pharmacological manipulation of affective state in a neutral environment. In addition, the influence of biological factors - such as sex - and modified neuronal transmission via genetic manipulation of the serotonergic system, was investigated. Against the background of anxiety and fear, temporally stable characteristics (traits) were also considered in dependence on the biological factors. Fear was found to be associated in principle with a reduction in 50-kHz USV, whereas the production of 22-kHz USV occurred exclusively in association with concrete fear-inducing stimuli. Using the USV spectrum, a shift in USV emission as a function of sex and serotonergic transmission can be shown. Here, the prevalences for 50- and 22-kHz USV shift across different situations, as both females and genetically manipulated rats produce more 50-kHz USV in new, unfamiliar environments, maintain their emission longer as the aversiveness of the situation increases, and produce less 22-kHz USV in confrontation with acute threat, as it were. The sex-dependent shift in USV is accompanied by reduced anxiety across tests. However, the influence of serotonergic transmission on call production is opposite to locomotion-based measures of anxiety and fear. Accordingly, evaluation of USV emission using the presented spectrum can serve to specifically differentiate anxiety and fear, thus allowing locomotion-based behaviors to be better interpreted using finer nuances. In this context, situation-specific conditions lead to a anxiety-induced decrease in 50-kHz USV or a fear-induced increase in 22-kHz USV. Biological factors such as sex, altered serotonergic transmission, or general anxiety also moderate the situation-specific influence on the spectrum of USV.