Ultrasonic communication in rodents: genes, brain and behavior
Mice and rats emit distinct types of ultrasonic vocalizations (USVs), which serve as situation-dependent affective signals. Recently, it was demonstrated that aversive 22-kHz-USVs and appetitive 50-kHz-USVs induce call-specific behavioral responses in the receiver. While 22-kHz-USVs induce freezing behavior, indicating an alarm function, 50-kHz-USVs induce social approach behavior, supporting the notion that they serve as social contact calls. The opposite behavioral responses are paralleled by distinct patterns of brain activation. While 22-kHz-USVs induce activation in amygdala and periaqueductal gray, 50-kHz-USVs are followed by activation in the nucleus accumbens. Social approach behavior in response to 50-kHz-USVs is regulated by the endogenous opioid system. Enhanced social approach behavior was found in morphine treated rats, whereas naloxone treatment caused its reduction. Social approach in response to 50-kHz USVs further depends on social interactions during adolescence as no preference towards 50-kHz-USVs was found in rats exposed to long-term post-weaning social isolation, highlighting the importance of social experience during adolescence for affiliative behavior. Measuring USV production and behavioral responses to USVs provides therefore a unique tool to study rodent communication. This is particularly relevant for rodent models of autism as delayed language and poor communication skills are fundamental to the diagnosis of autism. Candidate genes for autism include the SHANK family of synaptic scaffolding proteins. When tested for isolation-induced USVs as pups, Shank1 null mutants emitted fewer USVs as compared to wildtype littermates; and as adults in response to female urine, the USV production by Shank1 null mutant males was characterized by an unusual time pattern and unresponsiveness to social experience. These data support the relevance of USVs for rodent models of neuropsychiatric disorders characterized by social and communication deficits.
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