Department of Psychology, University of Washington, Seattle, Washington, United States of America.
PLoS One. 2010 Dec 1;5(12):e15077. doi: 10.1371/journal.pone.0015077.
Social alarm calls alert animals to potential danger and thereby promote group survival. Adult laboratory rats in distress emit 22-kHz ultrasonic vocalization (USV) calls, but the question of whether these USV calls directly elicit defensive behavior in conspecifics is unresolved.
METHODOLOGY/PRINCIPAL FINDINGS: The present study investigated, in pair-housed male rats, whether and how the conditioned fear-induced 22-kHz USVs emitted by the 'sender' animal affect the behavior of its partner, the 'receiver' animal, when both are placed together in a novel chamber. The sender rats' conditioned fear responses evoked significant freezing (an overt evidence of fear) in receiver rats that had previously experienced an aversive event but not in naïve receiver rats. Permanent lesions and reversible inactivations of the medial geniculate nucleus (MGN) of the thalamus effectively blocked the receivers' freeezing response to the senders' conditioned fear responses, and this occurred in absence of lesions/inactivations impeding the receiver animals' ability to freeze and emit 22-kHz USVs to the aversive event per se.
CONCLUSIONS/SIGNIFICANCE: These results--that prior experience of fear and intact auditory system are required for receiver rats to respond to their conspecifics' conditioned fear responses--indicate that the 22-kHz USV is the main factor for social transmission of fear and that learning plays a crucial role in the development of social signaling of danger by USVs.
社会警报声提醒动物注意潜在的危险，从而促进群体生存。处于困境中的成年实验室大鼠会发出 22 千赫兹的超声波叫声（USV），但这些 USV 是否直接引起同类动物的防御行为，这一问题尚未得到解决。
方法/主要发现：本研究在成对饲养的雄性大鼠中，调查了“发送者”动物发出的条件恐惧诱导的 22 千赫兹 USV 是否以及如何影响其“接收者”动物的行为，当两者被放置在一个新的房间中时。发送者大鼠的条件恐惧反应在以前经历过厌恶事件的接收者大鼠中引起了显著的冻结（恐惧的明显证据），但在未接受过训练的接收者大鼠中没有引起这种反应。内侧膝状体核（MGN）的永久性损伤和可逆性失活有效地阻断了接收者对发送者条件恐惧反应的冻结反应，而且这种反应发生在不影响接收者动物对厌恶事件本身产生冻结和发出 22 千赫兹 USV 的能力的情况下。
结论/意义：这些结果表明，接收者大鼠需要有先前的恐惧经验和完整的听觉系统才能对其同类动物的条件恐惧反应做出反应，这表明 22 千赫兹 USV 是恐惧社会传递的主要因素，而学习在 USV 危险信号的社会信号发展中起着至关重要的作用。
