Social experience: effects on auditory filtering through a serotonergic mechanism

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In addition to its well-known roles in regulating mood and appetite, the chemical serotonin plays an important role in the response of the brain to social interaction. Despite this, very little is known about its role in a crucial type of social behavior, communication. In their past work, the researchers have shown that serotonin modifies auditory responses to communication calls in mice, and that social partners trigger these increases in serotonin in the auditory system. In other regions of the brain, the serotonergic system itself is heavily influenced by past social experience. With this rationale, the researchers hypothesize that social experience changes the role of the serotonergic system in auditory processing. They will test this idea by measuring how housing mice individually or in social groups affects the way that the serotonergic system interacts with the auditory system. This work will explore a process fundamental to communication: how sensory systems adapt to features of the social environment like social history, with implications for how animals respond to their social partners. The work will also serve as a springboard for a local K-12 outreach program in which undergraduates present interactive lessons on themes of communication and sensory systems.The social experience hypothesis will be tested in male and female mice, which are increasingly studied models of vocal communication. Mice also demonstrate highly conserved serotonergic function in auditory regions compared with other vertebrates. The specific objectives of the proposed work are to examine the effect of group versus individual housing on three features of serotonin-auditory interactions in the inferior colliculus (IC), a mammalian auditory midbrain nucleus. 1) The first of these is the anatomy of the serotonergic system within the IC. This will be accomplished by measuring the density of immunohistochemically labeled serotonergic fibers. 2) A second feature is the transient serotonergic response to social interactions. This will be measured locally in the IC of behaving animals using carbon fiber voltammetry. 3) A final feature is the serotonergic regulation of the activation of the c-fos transcriptional pathway by social interaction, which will be explored by inducing systemic release or depletion of serotonin. These studies will provide a framework of how social experience creates plasticity in auditory-serotonin interactions at multiple levels of organization, generating testable hypotheses on the downstream consequences of such plasticity for neural encoding and perception.